2012 Vol.25(3)
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2012, 26(3).
Abstract:
During shift, power flow is not interrupted in powertrains equipped with continuously variable transmission (CVT). When hard acceleration is commanded, engine speed will flare and corresponding torque will be consumed, which leads to a drop in vehicle drive torque and also the vehicle acceleration. This is the reason why CVT vehicles have poor drivability during hard acceleration maneuver. Conventional method such as torque compensation doesn’t always work due to the limited backup torque of engine. According to this, means to evaluate the drivability of CVT vehicles are studied, affect factors of drivability are analyzed in detail. Hard acceleration process of CVT vehicle is studied by theoretical analysis, based on which engine torque and ratio change rate of CVT are identified as two key control parameters that decide the drivability of CVT vehicles during hard acceleration maneuver. Therefore, a control strategy based on restricting the change rate of CVT ratio together with torque compensation is proposed, and two different algorithms to establish the limitation of ratio change rate are proposed. These two algorithms are simulated and compared with each other, results indicate that drop of vehicle acceleration is eliminated evidently by limit the change rate of CVT ratio, but small ratio change rate also results in a longer time to finish the accelerate process, an algorithm to decide a proper ratio change rate is needed in order to tune these different characteristics. In order to get better control effects, a new fuzzy logic based algorithm is proposed to decide a proper ratio change rate during kick down conditions, simulation and experiment results indicate that, the amount of vehicle acceleration decrease is reduced from about 1 ms2 to almost 0, in the mean time the accelerate process only delayed for about 0.3 s. The proposed control strategy and algorithm can effectively tune the characteristics of CVT equipped vehicle during kick down conditions.
During shift, power flow is not interrupted in powertrains equipped with continuously variable transmission (CVT). When hard acceleration is commanded, engine speed will flare and corresponding torque will be consumed, which leads to a drop in vehicle drive torque and also the vehicle acceleration. This is the reason why CVT vehicles have poor drivability during hard acceleration maneuver. Conventional method such as torque compensation doesn’t always work due to the limited backup torque of engine. According to this, means to evaluate the drivability of CVT vehicles are studied, affect factors of drivability are analyzed in detail. Hard acceleration process of CVT vehicle is studied by theoretical analysis, based on which engine torque and ratio change rate of CVT are identified as two key control parameters that decide the drivability of CVT vehicles during hard acceleration maneuver. Therefore, a control strategy based on restricting the change rate of CVT ratio together with torque compensation is proposed, and two different algorithms to establish the limitation of ratio change rate are proposed. These two algorithms are simulated and compared with each other, results indicate that drop of vehicle acceleration is eliminated evidently by limit the change rate of CVT ratio, but small ratio change rate also results in a longer time to finish the accelerate process, an algorithm to decide a proper ratio change rate is needed in order to tune these different characteristics. In order to get better control effects, a new fuzzy logic based algorithm is proposed to decide a proper ratio change rate during kick down conditions, simulation and experiment results indicate that, the amount of vehicle acceleration decrease is reduced from about 1 ms2 to almost 0, in the mean time the accelerate process only delayed for about 0.3 s. The proposed control strategy and algorithm can effectively tune the characteristics of CVT equipped vehicle during kick down conditions.
2012, 26(3).
Abstract:
Blade element moment (BEM) is a widely used technique for prediction of wind turbine aerodynamics performance, the reliability of airfoil data is an important factor to improve the prediction accuracy of aerodynamic loads and power using a BEM code. The method of determination of angle of attack on rotor blades developed by SHEN, et al is successfully used to extract airfoil data from experimental characteristics on the MEXICO (Model experiments in controlled conditions) rotor. Detailed surface pressure and particle image velocimetry (PIV) flow fields at different rotor azimuth positions are examined to determine the sectional airfoil data. The present technique uses simultaneously both PIV data and blade pressure data that include the actual flow conditions (for example, tunnel effects), therefore it is more advantageous than other techniques which only use the blade loading (pressure data). The extracted airfoil data are put into a BEM code, and the calculated axial and tangential forces are compared to both computations using BEM with Glauert’s and SHEN’s tip loss correction models and experimental data. The comparisons show that the present method of determination of angle of attack is correct, and the re-calculated forces have good agreements with the experiment.
Blade element moment (BEM) is a widely used technique for prediction of wind turbine aerodynamics performance, the reliability of airfoil data is an important factor to improve the prediction accuracy of aerodynamic loads and power using a BEM code. The method of determination of angle of attack on rotor blades developed by SHEN, et al is successfully used to extract airfoil data from experimental characteristics on the MEXICO (Model experiments in controlled conditions) rotor. Detailed surface pressure and particle image velocimetry (PIV) flow fields at different rotor azimuth positions are examined to determine the sectional airfoil data. The present technique uses simultaneously both PIV data and blade pressure data that include the actual flow conditions (for example, tunnel effects), therefore it is more advantageous than other techniques which only use the blade loading (pressure data). The extracted airfoil data are put into a BEM code, and the calculated axial and tangential forces are compared to both computations using BEM with Glauert’s and SHEN’s tip loss correction models and experimental data. The comparisons show that the present method of determination of angle of attack is correct, and the re-calculated forces have good agreements with the experiment.
2012, 26(3).
Abstract:
Limit loads are widely studied and several limit load solutions are proposed to some typical geometry of weldments. However, there are no limit load solutions exist for the single edge crack weldments in tension (SEC(T)), which is also a typical geometry in fracture analysis. The mis-matching limit load for thick plate with SEC(T) are investigated and the special limit load solutions are proposed based on the available mis-matching limit load solutions and systematic finite element analyses. The real weld configurations are simplified as a strip, and different weld strength mis-matching ratio M, crack depth/width ratio aW and weld width 2H are in consideration. As a result, it is found that there exists excellent agreement between the limit load solutions and the FE results for almost all the mis-matching ration M, aW and ligament-to-weld width ratio (Wa)H. Moreover, useful recommendations are given for evaluating the limit loads of the EBW structure with SEC(T). For the EBW joints with SEC(T), the mis-matching limit loads can be obtained assuming that the components are wholly made of base metal, when M changing from 1.6 to 0.6. When M decreasing to 0.4, the mis-matching limit loads can be obtained assuming that the components are wholly made of base metal only for large value of (Wa)H. The recommendations may be useful for evaluating the limit loads of the EBW structures with SEC(T). The engineering simplifications are given for assessing the limit loads of electron beam welded structure with SEC(T).
Limit loads are widely studied and several limit load solutions are proposed to some typical geometry of weldments. However, there are no limit load solutions exist for the single edge crack weldments in tension (SEC(T)), which is also a typical geometry in fracture analysis. The mis-matching limit load for thick plate with SEC(T) are investigated and the special limit load solutions are proposed based on the available mis-matching limit load solutions and systematic finite element analyses. The real weld configurations are simplified as a strip, and different weld strength mis-matching ratio M, crack depth/width ratio aW and weld width 2H are in consideration. As a result, it is found that there exists excellent agreement between the limit load solutions and the FE results for almost all the mis-matching ration M, aW and ligament-to-weld width ratio (Wa)H. Moreover, useful recommendations are given for evaluating the limit loads of the EBW structure with SEC(T). For the EBW joints with SEC(T), the mis-matching limit loads can be obtained assuming that the components are wholly made of base metal, when M changing from 1.6 to 0.6. When M decreasing to 0.4, the mis-matching limit loads can be obtained assuming that the components are wholly made of base metal only for large value of (Wa)H. The recommendations may be useful for evaluating the limit loads of the EBW structures with SEC(T). The engineering simplifications are given for assessing the limit loads of electron beam welded structure with SEC(T).
2012, 26(3).
Abstract:
The double blade pump is widely used in sewage treatment industry, however, the research on the internal flow characteristics of the double blade pump with particle image velocimetry (PIV) technology is very little at present. To reveal inner flow characteristics in double blade pump impeller under off-design and design conditions, inner flows in a double blade pump impeller, whose specific speed is 111, are measured under the five off-design conditions and design condition by using 3D PIV test technology. In order to ensure the accuracy of the 3D PIV test, the external trigger synchronization system which makes use of fiber optic and equivalent calibration method are applied. The 3D PIV relative velocity synthesis procedure is compiled by using Visual C++ 2005. Then absolute velocity distribution and relative velocity distribution in the double blade pump impeller are obtained. Test results show that vortex exists in each condition, but the location, size and velocity of vortex core are different. Average absolute velocity value of impeller outlet increases at first, then decreases, and then increases again with increase of flow rate. Again average relative velocity values under 0.4, 0.8, and 1.2 design condition are higher than that under 1.0 design condition, while under 0.6 and 1.4 design condition it is lower. Under low flow rate conditions, radial vectors of absolute velocities at impeller outlet and blade inlet near the pump shaft decrease with increase of flow rate, while that of relative velocities at the suction side near the pump shaft decreases. Radial vectors of absolute velocities and relative velocities change slightly under the two large flow rate conditions. The research results can be applied to instruct the hydraulic optimization design of double blade pumps.
The double blade pump is widely used in sewage treatment industry, however, the research on the internal flow characteristics of the double blade pump with particle image velocimetry (PIV) technology is very little at present. To reveal inner flow characteristics in double blade pump impeller under off-design and design conditions, inner flows in a double blade pump impeller, whose specific speed is 111, are measured under the five off-design conditions and design condition by using 3D PIV test technology. In order to ensure the accuracy of the 3D PIV test, the external trigger synchronization system which makes use of fiber optic and equivalent calibration method are applied. The 3D PIV relative velocity synthesis procedure is compiled by using Visual C++ 2005. Then absolute velocity distribution and relative velocity distribution in the double blade pump impeller are obtained. Test results show that vortex exists in each condition, but the location, size and velocity of vortex core are different. Average absolute velocity value of impeller outlet increases at first, then decreases, and then increases again with increase of flow rate. Again average relative velocity values under 0.4, 0.8, and 1.2 design condition are higher than that under 1.0 design condition, while under 0.6 and 1.4 design condition it is lower. Under low flow rate conditions, radial vectors of absolute velocities at impeller outlet and blade inlet near the pump shaft decrease with increase of flow rate, while that of relative velocities at the suction side near the pump shaft decreases. Radial vectors of absolute velocities and relative velocities change slightly under the two large flow rate conditions. The research results can be applied to instruct the hydraulic optimization design of double blade pumps.
2012, 26(3).
Abstract:
Vibration signals from diesel engine contain many different components mainly caused by combustion and mechanism operations, several blind source separation techniques are available for decomposing the signal into its components in the case of multichannel measurements, such as independent component analysis (ICA). However, the source separation of vibration signal from single-channel is impossible. In order to study the source separation from single-channel signal for the purpose of source extraction, the combination method of empirical mode decomposition (EMD) and ICA is proposed in diesel engine signal processing. The performance of the described methods of EMD-wavelet and EMD-ICA in vibration signal application is compared, and the results show that EMD-ICA method outperforms the other, and overcomes the drawback of ICA in the case of single-channel measurement. The independent source signal components can be separated and identified effectively from one-channel measurement by EMD-ICA. Hence, EMD-ICA improves the extraction and identification abilities of source signals from diesel engine vibration measurements.
Vibration signals from diesel engine contain many different components mainly caused by combustion and mechanism operations, several blind source separation techniques are available for decomposing the signal into its components in the case of multichannel measurements, such as independent component analysis (ICA). However, the source separation of vibration signal from single-channel is impossible. In order to study the source separation from single-channel signal for the purpose of source extraction, the combination method of empirical mode decomposition (EMD) and ICA is proposed in diesel engine signal processing. The performance of the described methods of EMD-wavelet and EMD-ICA in vibration signal application is compared, and the results show that EMD-ICA method outperforms the other, and overcomes the drawback of ICA in the case of single-channel measurement. The independent source signal components can be separated and identified effectively from one-channel measurement by EMD-ICA. Hence, EMD-ICA improves the extraction and identification abilities of source signals from diesel engine vibration measurements.
2012, 26(3).
Abstract:
Water-assisted injection molding (WAIM), a newly developed fluid-assisted injection molding technology has drawn more and more attentions for the energy saving, short cooling circle time and high quality of products. Existing research for the process of WAIM has shown that the pressure control of the injecting water is mostly important for the WAIM. However, the proportional pressure control for the WAIM system is quite complex due to the existence of nonlinearities in the water hydraulic system. In order to achieve better pressure control performance of the injecting water to meet the requirements of the WAIM, the proportional pressure control of the WAIM system is investigated both numerically and experimentally. A newly designed water hydraulic system for WAIM is first modeled in AMEsim environment, the load characteristics and the nonlinearities of water hydraulic system are both considered, then the main factors affecting the injecting pressure and load flow rate are extensively studied. Meanwhile, an open-loop model-based compensation control strategy is employed to regulate the water injection pressure and a feedback proportional integrator controller is further adopted to achieve better control performance. In order to verify the AMEsim simulation results WAIM experiment for particular Acrylonitrile Butadiene Styrene (ABS) parts is implemented and the measured experimental data including injecting pressure and flow rate results are compared with the simulation. The good coincidence between experiment and simulation shows that the AMEsim model is accurate, and the tracking performance of the load pressure indicates that the proposed control strategy is effective for the proportional pressure control of the nonlinear WAIM system. The proposed proportional pressure control strategy and the conclusions drawn from simulation and experiment contribute to the application of water hydraulic proportional control and WAIM technology.
Water-assisted injection molding (WAIM), a newly developed fluid-assisted injection molding technology has drawn more and more attentions for the energy saving, short cooling circle time and high quality of products. Existing research for the process of WAIM has shown that the pressure control of the injecting water is mostly important for the WAIM. However, the proportional pressure control for the WAIM system is quite complex due to the existence of nonlinearities in the water hydraulic system. In order to achieve better pressure control performance of the injecting water to meet the requirements of the WAIM, the proportional pressure control of the WAIM system is investigated both numerically and experimentally. A newly designed water hydraulic system for WAIM is first modeled in AMEsim environment, the load characteristics and the nonlinearities of water hydraulic system are both considered, then the main factors affecting the injecting pressure and load flow rate are extensively studied. Meanwhile, an open-loop model-based compensation control strategy is employed to regulate the water injection pressure and a feedback proportional integrator controller is further adopted to achieve better control performance. In order to verify the AMEsim simulation results WAIM experiment for particular Acrylonitrile Butadiene Styrene (ABS) parts is implemented and the measured experimental data including injecting pressure and flow rate results are compared with the simulation. The good coincidence between experiment and simulation shows that the AMEsim model is accurate, and the tracking performance of the load pressure indicates that the proposed control strategy is effective for the proportional pressure control of the nonlinear WAIM system. The proposed proportional pressure control strategy and the conclusions drawn from simulation and experiment contribute to the application of water hydraulic proportional control and WAIM technology.
Reliability Sensitivity-based Correlation Coefficient Calculation in Structural Reliability Analysis
2012, 26(3).
Abstract:
The correlation coefficients of random variables of mechanical structures are generally chosen with experience or even ignored, which cannot actually reflect the effects of parameter uncertainties on reliability. To discuss the selection problem of the correlation coefficients from the reliability-based sensitivity point of view, the theory principle of the problem is established based on the results of the reliability sensitivity, and the criterion of correlation among random variables is shown. The values of the correlation coefficients are obtained according to the proposed principle and the reliability sensitivity problem is discussed. Numerical studies have shown the following results: (1) If the sensitivity value of correlation coefficient is less than (at what magnitude 0.000 01), then the correlation could be ignored, which could simplify the procedure without introducing additional error. (2) However, as the difference between s, that is the most sensitive to the reliability, and R, that is with the smallest reliability, is less than 0.001, s is suggested to model the dependency of random variables. This could ensure the robust quality of system without the loss of safety requirement. (3) In the case of |Eabs|0.001 and also |Erel|0.001, R should be employed to quantify the correlation among random variables in order to ensure the accuracy of reliability analysis. Application of the proposed approach could provide a practical routine for mechanical design and manufactory to study the reliability and reliability-based sensitivity of basic design variables in mechanical reliability analysis and design.
The correlation coefficients of random variables of mechanical structures are generally chosen with experience or even ignored, which cannot actually reflect the effects of parameter uncertainties on reliability. To discuss the selection problem of the correlation coefficients from the reliability-based sensitivity point of view, the theory principle of the problem is established based on the results of the reliability sensitivity, and the criterion of correlation among random variables is shown. The values of the correlation coefficients are obtained according to the proposed principle and the reliability sensitivity problem is discussed. Numerical studies have shown the following results: (1) If the sensitivity value of correlation coefficient is less than (at what magnitude 0.000 01), then the correlation could be ignored, which could simplify the procedure without introducing additional error. (2) However, as the difference between s, that is the most sensitive to the reliability, and R, that is with the smallest reliability, is less than 0.001, s is suggested to model the dependency of random variables. This could ensure the robust quality of system without the loss of safety requirement. (3) In the case of |Eabs|0.001 and also |Erel|0.001, R should be employed to quantify the correlation among random variables in order to ensure the accuracy of reliability analysis. Application of the proposed approach could provide a practical routine for mechanical design and manufactory to study the reliability and reliability-based sensitivity of basic design variables in mechanical reliability analysis and design.
2012, 26(3).
Abstract:
PT fuel injector is one of the most important parts of modern diesel engine. To satisfy the requirements of the rapid and accurate test of PT fuel injector, the self-adaptive floating clamping mechanism was developed and used in the relevant bench. Its dynamic characteristics directly influence the test efficiency and accuracy. However, due to its special structure and complex oil pressure signal, related documents for evaluating dynamic characteristics of this mechanism are lack and some dynamic characteristics of this mechanism can’t be extracted and recognized effectively by traditional methods. Aiming at the problem above-mentioned, a new method based on Hilbert-Huang transform (HHT) is presented. Firstly, combining with the actual working process, the dynamic liquid pressure signal of the mechanism is acquired. By analyzing the pressure fluctuation during the whole working process in time domain, oil leakage and hydraulic shock in the clamping chamber are discovered. Secondly, owing to the nonlinearity and nonstationarity of pressure signal, empirical mode decomposition is used, and the signal is decomposed and reconstructed into forced vibration, free vibration and noise. By analyzing forced vibration in the time domain, machining error and installation error of cam are revealed. Finally, free vibration component is analyzed in time-frequency domain with HHT, the traits of free vibration in the time-frequency domain are revealed. Compared with traditional methods, Hilbert spectrum has higher time-frequency resolutions and higher credibility. The improved mechanism based on the above analyses can guarantee the test accuracy of injector injection. This new method based on the analyses of the pressure signal and combined with HHT can provide scientific basis for evaluation, design improvement of the mechanism, and give references for dynamic characteristics analysis of the hydraulic system in the interrelated fields.
PT fuel injector is one of the most important parts of modern diesel engine. To satisfy the requirements of the rapid and accurate test of PT fuel injector, the self-adaptive floating clamping mechanism was developed and used in the relevant bench. Its dynamic characteristics directly influence the test efficiency and accuracy. However, due to its special structure and complex oil pressure signal, related documents for evaluating dynamic characteristics of this mechanism are lack and some dynamic characteristics of this mechanism can’t be extracted and recognized effectively by traditional methods. Aiming at the problem above-mentioned, a new method based on Hilbert-Huang transform (HHT) is presented. Firstly, combining with the actual working process, the dynamic liquid pressure signal of the mechanism is acquired. By analyzing the pressure fluctuation during the whole working process in time domain, oil leakage and hydraulic shock in the clamping chamber are discovered. Secondly, owing to the nonlinearity and nonstationarity of pressure signal, empirical mode decomposition is used, and the signal is decomposed and reconstructed into forced vibration, free vibration and noise. By analyzing forced vibration in the time domain, machining error and installation error of cam are revealed. Finally, free vibration component is analyzed in time-frequency domain with HHT, the traits of free vibration in the time-frequency domain are revealed. Compared with traditional methods, Hilbert spectrum has higher time-frequency resolutions and higher credibility. The improved mechanism based on the above analyses can guarantee the test accuracy of injector injection. This new method based on the analyses of the pressure signal and combined with HHT can provide scientific basis for evaluation, design improvement of the mechanism, and give references for dynamic characteristics analysis of the hydraulic system in the interrelated fields.
2012, 26(3).
Abstract:
Typically, liquid pump and liquids mixer are two separate devices. The invention of piezoelectric pump makes it possible to integrate the two devices. Hower, the existing piezoelectric mixing-pumps are larger because the need the space outside the chamber, and another shortcome of them is that they cannot adjust the mixing ratio of two liquids. In this paper, a new piezoelectric pump being capable of integrating mixer and pump is presented, based on the theory of the piezoelectric pump with the unsymmetrical slopes element (USE). Besides the features of two inlets and one outlet, the piezoelectric pump has a rotatable unsymmetrical slopes element(RUSE). When the pump works, two fluids flow into the inlet channels respectively. Then the RUSE controls the ratio of the two flows by adjusting the flow resistances of the two inlet channels. The fluids form a net flow due to the USE principle, while they are mixed into a homogeneous solution due to strong turbulence flow field and complex vortices generated by RUSE in the chamber. And then the solution flows through the outlet. Firstly, the theoretical analysis on this pump is performed. Meanwhile, the flow field in the chamber is calculated and simulated. And then, the relationship between the flows of the two channels and the rotating angle of the RUSE is set up and analyzed. Finally, experiment with the proposed pump is carried out to verify the numerical results. A RUSE with 20° slope angle is used in the experiment. Four sets of data are tested with the RUSE at the rotating angles of 0°, 6°, 11°, and 16°, respectively, corresponding to the numerical models. The experimental results show that the empirical data and the theoretical data share the same trend. The maximum error between the theoretical flow and the experimental flow is 11.14%, and the maximum error between the theoretical flow ratio of the two inlets and the experimental one is 2.5%. The experiment verified the theoretical analysis. The proposed research provides a new idea for integration of micro liquids mixer and micro liquids pump.
Typically, liquid pump and liquids mixer are two separate devices. The invention of piezoelectric pump makes it possible to integrate the two devices. Hower, the existing piezoelectric mixing-pumps are larger because the need the space outside the chamber, and another shortcome of them is that they cannot adjust the mixing ratio of two liquids. In this paper, a new piezoelectric pump being capable of integrating mixer and pump is presented, based on the theory of the piezoelectric pump with the unsymmetrical slopes element (USE). Besides the features of two inlets and one outlet, the piezoelectric pump has a rotatable unsymmetrical slopes element(RUSE). When the pump works, two fluids flow into the inlet channels respectively. Then the RUSE controls the ratio of the two flows by adjusting the flow resistances of the two inlet channels. The fluids form a net flow due to the USE principle, while they are mixed into a homogeneous solution due to strong turbulence flow field and complex vortices generated by RUSE in the chamber. And then the solution flows through the outlet. Firstly, the theoretical analysis on this pump is performed. Meanwhile, the flow field in the chamber is calculated and simulated. And then, the relationship between the flows of the two channels and the rotating angle of the RUSE is set up and analyzed. Finally, experiment with the proposed pump is carried out to verify the numerical results. A RUSE with 20° slope angle is used in the experiment. Four sets of data are tested with the RUSE at the rotating angles of 0°, 6°, 11°, and 16°, respectively, corresponding to the numerical models. The experimental results show that the empirical data and the theoretical data share the same trend. The maximum error between the theoretical flow and the experimental flow is 11.14%, and the maximum error between the theoretical flow ratio of the two inlets and the experimental one is 2.5%. The experiment verified the theoretical analysis. The proposed research provides a new idea for integration of micro liquids mixer and micro liquids pump.
Experimental Investigation on the Flow-induced Noise under Variable Conditions for Centrifugal Pumps
2012, 26(3).
Abstract:
With extensively using of centrifugal pumps, noise generation in these pumps is increasingly receiving research attention in recent years. The noise sources in centrifugal pumps are mainly composed of mechanical noise and flow-induced noise. And the study of flow-induced noise has become a hotspot and important domain in the field. The flow-induced noise closely related to the inner pressure pulses and vibration of volute in pumps, therefore, it is necessary to research the interaction and mechanism among them. To investigate the relationships, a test system is designed which includes a test loop and a measurement system. The hydrophones and pressure sensors are installed on the outlet of the pump and vibration acceleration sensors are disposed on the pump body. Via these instruments, the signals of noise, pressure pulses and vibration are collected and analyzed. The results show that the level of flow-induced noise becomes smaller as the flow increment during low flow rate operations, and it is steadily close to the design point, then it increases with the growing of flow rate in high flow rate conditions. Furthermore, there are some similar peak points in the power spectrum charts of noise, pressure pulses and vibration. The broadband noise at low flow rate is mostly focused on the region of 0–40 times shaft frequency, which is mostly made by rotating stall and vortex; while the noise at high flow rate conditions is focused on the region of 60–100 times shaft frequency, which may be mostly made by cavitations. The proposed research is of practical and academic significance to the study of noise reduction for centrifugal pumps.
With extensively using of centrifugal pumps, noise generation in these pumps is increasingly receiving research attention in recent years. The noise sources in centrifugal pumps are mainly composed of mechanical noise and flow-induced noise. And the study of flow-induced noise has become a hotspot and important domain in the field. The flow-induced noise closely related to the inner pressure pulses and vibration of volute in pumps, therefore, it is necessary to research the interaction and mechanism among them. To investigate the relationships, a test system is designed which includes a test loop and a measurement system. The hydrophones and pressure sensors are installed on the outlet of the pump and vibration acceleration sensors are disposed on the pump body. Via these instruments, the signals of noise, pressure pulses and vibration are collected and analyzed. The results show that the level of flow-induced noise becomes smaller as the flow increment during low flow rate operations, and it is steadily close to the design point, then it increases with the growing of flow rate in high flow rate conditions. Furthermore, there are some similar peak points in the power spectrum charts of noise, pressure pulses and vibration. The broadband noise at low flow rate is mostly focused on the region of 0–40 times shaft frequency, which is mostly made by rotating stall and vortex; while the noise at high flow rate conditions is focused on the region of 60–100 times shaft frequency, which may be mostly made by cavitations. The proposed research is of practical and academic significance to the study of noise reduction for centrifugal pumps.
2012, 26(3).
Abstract:
The existing research of the integrated power and attitude control system (IPACS) in satellites mainly focuses on the IPACS concept, which aims at solving the coupled problem between the attitude control and power tracking. In the IPACS, the configuration design of IPACS is usually not considered, and the coupled problem between two flywheels during the attitude control and energy storage has not been resolved. In this paper, an integrated power and single axis attitude control system using two counter rotating magnetically suspended flywheels mounted to an air table is designed. The control method of power and attitude control using flywheel is investigated and the coupling problem between energy storage and attitude control is resolved. A computer simulation of an integrated power and single axis attitude control system with two flywheels is performed, which consists of two counter rotating magnetically suspended flywheels mounted to an air rotary table. Both DC bus and a single axis attitude are the regulation goals. An attitude & DC bus coordinator is put forward to separate DC bus regulation and attitude control problems. The simulation results of DC bus regulation and attitude control are presented respectively with a DC bus regulator and a simple PD attitude controller. The simulation results demonstrate that it is possible to integrate power and attitude control simultaneously for satellite using flywheels. The proposed research provides theory basis for design of the IPACS.
The existing research of the integrated power and attitude control system (IPACS) in satellites mainly focuses on the IPACS concept, which aims at solving the coupled problem between the attitude control and power tracking. In the IPACS, the configuration design of IPACS is usually not considered, and the coupled problem between two flywheels during the attitude control and energy storage has not been resolved. In this paper, an integrated power and single axis attitude control system using two counter rotating magnetically suspended flywheels mounted to an air table is designed. The control method of power and attitude control using flywheel is investigated and the coupling problem between energy storage and attitude control is resolved. A computer simulation of an integrated power and single axis attitude control system with two flywheels is performed, which consists of two counter rotating magnetically suspended flywheels mounted to an air rotary table. Both DC bus and a single axis attitude are the regulation goals. An attitude & DC bus coordinator is put forward to separate DC bus regulation and attitude control problems. The simulation results of DC bus regulation and attitude control are presented respectively with a DC bus regulator and a simple PD attitude controller. The simulation results demonstrate that it is possible to integrate power and attitude control simultaneously for satellite using flywheels. The proposed research provides theory basis for design of the IPACS.
2012, 26(3).
Abstract:
The minimum quantity of lubrication (MQL) technique is becoming increasingly more popular due to the safety of environment. Moreover, MQL technique not only leads to economical benefits by way of saving lubricant costs but also presents better machinability. However, the effect of MQL parameters on machining is still not clear, which needs to be overcome. In this paper, the effect of different modes of lubrication, i.e., conventional way using flushing, dry cutting and using the minimum quantity lubrication (MQL) technique on the machinability in end milling of a forged steel (50CrMnMo), is investigated. The influence of MQL parameters on tool wear and surface roughness is also discussed. MQL parameters include nozzle direction in relation to feed direction, nozzle elevation angle, distance from the nozzle tip to the cutting zone, lubricant flow rate and air pressure. The investigation results show that MQL technique lowers the tool wear and surface roughness values compared with that of conventional flood cutting fluid supply and dry cutting conditions. Based on the investigations of chip morphology and color, MQL technique reduces the cutting temperature to some extent. The relative nozzle-feed position at 120°, the angle elevation of 60° and distance from nozzle tip to cutting zone at 20 mm provide the prolonged tool life and reduced surface roughness values. This fact is due to the oil mists can penetrate in the inner zones of the tool edges in a very efficient way. Improvement in tool life and surface finish could be achieved utilizing higher oil flow rate and higher compressed air pressure. Moreover, oil flow rate increased from 43.8 mLh to 58.4 mLh leads to a small decrease of flank wear, but it is not very significant. The results obtained in this paper can be used to determine optimal conditions for milling of forged steel under MQL conditions.
The minimum quantity of lubrication (MQL) technique is becoming increasingly more popular due to the safety of environment. Moreover, MQL technique not only leads to economical benefits by way of saving lubricant costs but also presents better machinability. However, the effect of MQL parameters on machining is still not clear, which needs to be overcome. In this paper, the effect of different modes of lubrication, i.e., conventional way using flushing, dry cutting and using the minimum quantity lubrication (MQL) technique on the machinability in end milling of a forged steel (50CrMnMo), is investigated. The influence of MQL parameters on tool wear and surface roughness is also discussed. MQL parameters include nozzle direction in relation to feed direction, nozzle elevation angle, distance from the nozzle tip to the cutting zone, lubricant flow rate and air pressure. The investigation results show that MQL technique lowers the tool wear and surface roughness values compared with that of conventional flood cutting fluid supply and dry cutting conditions. Based on the investigations of chip morphology and color, MQL technique reduces the cutting temperature to some extent. The relative nozzle-feed position at 120°, the angle elevation of 60° and distance from nozzle tip to cutting zone at 20 mm provide the prolonged tool life and reduced surface roughness values. This fact is due to the oil mists can penetrate in the inner zones of the tool edges in a very efficient way. Improvement in tool life and surface finish could be achieved utilizing higher oil flow rate and higher compressed air pressure. Moreover, oil flow rate increased from 43.8 mLh to 58.4 mLh leads to a small decrease of flank wear, but it is not very significant. The results obtained in this paper can be used to determine optimal conditions for milling of forged steel under MQL conditions.
2012, 26(3).
Abstract:
In modern trains wheelset skidding leads to the deterioration of braking behavior, the degradation of comfort, as well as a boost in system hazards. Because of the nonlinearity and unknown characteristics of wheelset adhesion, simplifications are widely adopted in the modeling process of conventional antiskid controllers. Therefore, conventional antiskid controllers usually cannot perform satisfactorily. In this paper, systematic computer simulation and field tests for railway antiskid control system are introduced. The operating principal of antiskid control system is explained, which is fundamental to the simulation of antiskid brakes, and the simulation model is introduced, which incorporates both the adhesion creep curve and a pneumatic submodel of antiskid control system. In addition, the characteristics of adhesion curves and the simulation target are also provided. Using DHSplus, the pneumatic submodel is created to analyze the performance of the different control strategies of antiskid valves. Then the system simulation is realized by combining the kinematical characteristics of railway trains and the pneumatic submodel. The simulation is performed iteratively to obtain the optimized design of the antiskid control system. The design result is incorporated in the hardware design of the antiskid control system and is evaluated in the field tests in Shanghai Subway Line 1. Judging by the antiskid efficiency, the antiskid braking performance observed in the field tests shows the superiority of the optimized design. Therefore, the proposed simulation method, especially in view of its ease of application, appears to be a useful one for designing railway antiskid control systems.
In modern trains wheelset skidding leads to the deterioration of braking behavior, the degradation of comfort, as well as a boost in system hazards. Because of the nonlinearity and unknown characteristics of wheelset adhesion, simplifications are widely adopted in the modeling process of conventional antiskid controllers. Therefore, conventional antiskid controllers usually cannot perform satisfactorily. In this paper, systematic computer simulation and field tests for railway antiskid control system are introduced. The operating principal of antiskid control system is explained, which is fundamental to the simulation of antiskid brakes, and the simulation model is introduced, which incorporates both the adhesion creep curve and a pneumatic submodel of antiskid control system. In addition, the characteristics of adhesion curves and the simulation target are also provided. Using DHSplus, the pneumatic submodel is created to analyze the performance of the different control strategies of antiskid valves. Then the system simulation is realized by combining the kinematical characteristics of railway trains and the pneumatic submodel. The simulation is performed iteratively to obtain the optimized design of the antiskid control system. The design result is incorporated in the hardware design of the antiskid control system and is evaluated in the field tests in Shanghai Subway Line 1. Judging by the antiskid efficiency, the antiskid braking performance observed in the field tests shows the superiority of the optimized design. Therefore, the proposed simulation method, especially in view of its ease of application, appears to be a useful one for designing railway antiskid control systems.
2012, 26(3).
Abstract:
Autofrettage is an effective technique to improve load-bearing capacity and safety for pressure vessels. For autofrettaged cylinder, the depth of plastic zone, or overstrain is a key factor which affects load-bearing capacity and safety. The previous research on overstrain was not done in terms of the point of view of raising load-bearing capacity as far as possible and simultaneously avoiding compressive yield for cylinders experiencing autofrettage handling, and there were no analytic solutions of autofrettage in the above view point presented, the 3rd and 4th strength theories were not applied synthetically in the research to compare the results from these two theories. In this paper, with the aid of the analytic method, based on summing up the authors’ previous research, results from autofrettage of a cylinder based on the 3rd and 4th strength theories are studied and compared, and the laws contained in the results are looked into. Then, the essential cause and reason for the obtained laws are analyzed and the inherent and meaning relations between various parameters in autofrettage theory are revealed. It is shown that the maximum radius ratio for equivalent residual stress at inside surface never exceeds the yield strength even for a cylinder experiencing wholly yielded autofrettage, or the critical radius ratio is kc2.218 457 489 916 7…, irrespective of the 3rd or 4th strength theories. The equation relating the depth of plastic zone with the thickness of a cylinder is identical for the 3rd and 4th strength theories. In form, the optimum load-bearing capacity of an autofrettaged cylinder is two times the initial yield pressure of the unautofrettaged cylinder irrespective of the 3rd or 4th strength theory. The revealed inherent relations between various parameters and varying laws of the parameters as well as the forms of the relations under the 3rd and 4th strength theories not only have theoretical meanings but also have prospects in engineering application.
Autofrettage is an effective technique to improve load-bearing capacity and safety for pressure vessels. For autofrettaged cylinder, the depth of plastic zone, or overstrain is a key factor which affects load-bearing capacity and safety. The previous research on overstrain was not done in terms of the point of view of raising load-bearing capacity as far as possible and simultaneously avoiding compressive yield for cylinders experiencing autofrettage handling, and there were no analytic solutions of autofrettage in the above view point presented, the 3rd and 4th strength theories were not applied synthetically in the research to compare the results from these two theories. In this paper, with the aid of the analytic method, based on summing up the authors’ previous research, results from autofrettage of a cylinder based on the 3rd and 4th strength theories are studied and compared, and the laws contained in the results are looked into. Then, the essential cause and reason for the obtained laws are analyzed and the inherent and meaning relations between various parameters in autofrettage theory are revealed. It is shown that the maximum radius ratio for equivalent residual stress at inside surface never exceeds the yield strength even for a cylinder experiencing wholly yielded autofrettage, or the critical radius ratio is kc2.218 457 489 916 7…, irrespective of the 3rd or 4th strength theories. The equation relating the depth of plastic zone with the thickness of a cylinder is identical for the 3rd and 4th strength theories. In form, the optimum load-bearing capacity of an autofrettaged cylinder is two times the initial yield pressure of the unautofrettaged cylinder irrespective of the 3rd or 4th strength theory. The revealed inherent relations between various parameters and varying laws of the parameters as well as the forms of the relations under the 3rd and 4th strength theories not only have theoretical meanings but also have prospects in engineering application.
2012, 26(3).
Abstract:
The previous research of precision grinding optical glasses with electrolytic in process dressing (ELID) technology mainly concentrated on the action of ELID and machining parameters when grinding, which aim at generating very “smoothed” surfaces and reducing the subsurface damage. However, when grinding spectrosil 2000 and BK7 glass assisted with ELID technology, a deeply comparative study on material removal mechanism and the wheel wear behaviors have not been given yet. In this paper, the micronano indentation technique is initially applied for investigating the mechanical properties of optical glasses, whose results are then refereed to evaluate the machinability. In single grit diamond scratching on glasses, the scratching traces display four kinds of scratch characteristics according to different material removal modes. In normal grinding experiments, the result shows BK7 glass has a better machinability than that of spectrosil 2000, corresponding to what the micronano indentation vent revealed. Under the same grinding depth parameters, the smaller amplitude of acoustic emission (AE) raw signals, grinding force and grinding force ratio correspond to a better surface quality. While for these two kinds of glasses, with the increasing of grinding depth, the variation trends of the surface roughness, the force ratio, and the AE raw signals are contrary, which should be attributed to different material removal modes. Moreover, the SEM micrographs of used wheels surface indicate that diamond grains on the wheel surface after grinding BK7 glass are worn more severely than that of spectrosil 2000. The proposed research analyzes what happened in the grinding process with different material removal patterns, which can provide a basis for producing high-quality optical glasses and comprehensively evaluate the surface and subsurface integrity of optical glasses.
The previous research of precision grinding optical glasses with electrolytic in process dressing (ELID) technology mainly concentrated on the action of ELID and machining parameters when grinding, which aim at generating very “smoothed” surfaces and reducing the subsurface damage. However, when grinding spectrosil 2000 and BK7 glass assisted with ELID technology, a deeply comparative study on material removal mechanism and the wheel wear behaviors have not been given yet. In this paper, the micronano indentation technique is initially applied for investigating the mechanical properties of optical glasses, whose results are then refereed to evaluate the machinability. In single grit diamond scratching on glasses, the scratching traces display four kinds of scratch characteristics according to different material removal modes. In normal grinding experiments, the result shows BK7 glass has a better machinability than that of spectrosil 2000, corresponding to what the micronano indentation vent revealed. Under the same grinding depth parameters, the smaller amplitude of acoustic emission (AE) raw signals, grinding force and grinding force ratio correspond to a better surface quality. While for these two kinds of glasses, with the increasing of grinding depth, the variation trends of the surface roughness, the force ratio, and the AE raw signals are contrary, which should be attributed to different material removal modes. Moreover, the SEM micrographs of used wheels surface indicate that diamond grains on the wheel surface after grinding BK7 glass are worn more severely than that of spectrosil 2000. The proposed research analyzes what happened in the grinding process with different material removal patterns, which can provide a basis for producing high-quality optical glasses and comprehensively evaluate the surface and subsurface integrity of optical glasses.
2012, 26(3).
Abstract:
The Reynolds-averaged Navier-Stokes (RANS), such as the original k-ω two-equation closures, have been very popular in providing good prediction for a wide variety of flows with presently available computational resource. But for cavitating flows, the above equations noticeably over-predict turbulent production and hence effective viscosity. In this paper, the detached eddy simulation (DES) method for time-dependent turbulent cavitating flows is investigated. To assess the state-of-the-art of computational capabilities, different turbulence models including the widely used RANS model and DES model are conducted. Firstly, in order to investigate the grid dependency in computations, different grid sizes are adopted in the computation. Furthermore, the credibility of DES model is supported by the unsteady cavitating flows over a 2D hydrofoil. The results show that the DES model can effectively reduce the eddy viscosities. From the experimental validations regarding the force analysis, frequency and the unsteady cavity visualizations, more favorable agreement with experimental visualizations and measurements are obtained by DES model. DES model is better able to capture unsteady phenomena including cavity length and the resulting hydrodynamic characteristics, reproduces the time-averaged velocity quantitatively around the hydrofoil, and yields more acceptable and unsteady dynamics features. The DES model has shown to be effective in improving the overall predictive capability of unsteady cavitating flows
The Reynolds-averaged Navier-Stokes (RANS), such as the original k-ω two-equation closures, have been very popular in providing good prediction for a wide variety of flows with presently available computational resource. But for cavitating flows, the above equations noticeably over-predict turbulent production and hence effective viscosity. In this paper, the detached eddy simulation (DES) method for time-dependent turbulent cavitating flows is investigated. To assess the state-of-the-art of computational capabilities, different turbulence models including the widely used RANS model and DES model are conducted. Firstly, in order to investigate the grid dependency in computations, different grid sizes are adopted in the computation. Furthermore, the credibility of DES model is supported by the unsteady cavitating flows over a 2D hydrofoil. The results show that the DES model can effectively reduce the eddy viscosities. From the experimental validations regarding the force analysis, frequency and the unsteady cavity visualizations, more favorable agreement with experimental visualizations and measurements are obtained by DES model. DES model is better able to capture unsteady phenomena including cavity length and the resulting hydrodynamic characteristics, reproduces the time-averaged velocity quantitatively around the hydrofoil, and yields more acceptable and unsteady dynamics features. The DES model has shown to be effective in improving the overall predictive capability of unsteady cavitating flows
2012, 26(3).
Abstract:
With increasing recording density in computer hard disks, the flying height of the magnetic head becomes 10 nm or less. The numerical method of the control equations needs to be optimized consistently with the decrease of the flying height. The iterative process is usually divergent with traditional methods which cannot ensure the accuracy of the analysis results and the stability of numerical calculations. Firstly, a new scheme is presented to solve the ultra-thin lubricating control equations in this paper. The equilibrium equation is obtained by taking the Couette flow terms and time term as dominating terms in iterative process. Moreover, the weighting flow factor is introduced for the abrupt change of film thickness in order to reduce calculated deviation. Secondly, the rules for variation of flying pose of the magnetic head with time are obtained by the time domain analysis. The results show that the magnetic head can recover to the equilibrium position after being slightly influenced by outside disturbance. And the dynamic lubrication properties of the head suffer heavily from the vibrations in the height direction and fluctuation in the pitch direction. Finally, the analysis of the sine roughness-passing capacity of the head indicates that the head can surpass small sine waves and the equilibrium position can be retrieved after a period of decaying oscillation. The proposed research ensures the accuracy and stability of the numerical calculation of the control equations, and the dynamic characteristics and flying stability of a magnetic head is studied systematically. It can also be the theoretical basis for the analysis of the flight characteristics of the slider.
With increasing recording density in computer hard disks, the flying height of the magnetic head becomes 10 nm or less. The numerical method of the control equations needs to be optimized consistently with the decrease of the flying height. The iterative process is usually divergent with traditional methods which cannot ensure the accuracy of the analysis results and the stability of numerical calculations. Firstly, a new scheme is presented to solve the ultra-thin lubricating control equations in this paper. The equilibrium equation is obtained by taking the Couette flow terms and time term as dominating terms in iterative process. Moreover, the weighting flow factor is introduced for the abrupt change of film thickness in order to reduce calculated deviation. Secondly, the rules for variation of flying pose of the magnetic head with time are obtained by the time domain analysis. The results show that the magnetic head can recover to the equilibrium position after being slightly influenced by outside disturbance. And the dynamic lubrication properties of the head suffer heavily from the vibrations in the height direction and fluctuation in the pitch direction. Finally, the analysis of the sine roughness-passing capacity of the head indicates that the head can surpass small sine waves and the equilibrium position can be retrieved after a period of decaying oscillation. The proposed research ensures the accuracy and stability of the numerical calculation of the control equations, and the dynamic characteristics and flying stability of a magnetic head is studied systematically. It can also be the theoretical basis for the analysis of the flight characteristics of the slider.
2012, 26(3).
Abstract:
While introducing foreign advanced technology and cooperating with Chinese famous research institutes, the high-speed vehicles are designed and take the major task of passenger transport in China. In high-speed vehicle, the characteristic of shock absorber is an important parameter which determines overall behavior of the vehicle. The most existing researches neglect the influence of the series stiffness of the shock absorber on the vehicle dynamic behavior and have one-sided views on the equivalent conicity of wheel tread. In this paper, a high speed passenger vehicle in China is modeled to investigate the effect of the parameters taking series hydraulic shock absorber stiffness into consideration on Ruzicka model. Using the vehicle dynamic model, the effect of main suspension parameters on critical speed is studied. In order to verify the reasonableness of shock absorber parameter settings, vibration isolation characteristics are calculated and the relationship between suspension parameters and the vehicle critical hunting speed is studied. To study the influence of equivalent conicity on vehicle dynamic behavior, a series of wheel treads with different conicities are set and the vehicle critical hunting speeds with different wheel treads are calculated. The discipline between the equivalent conicity of wheel tread and critical speed are obtained in vehicle nonlinear system. The research results show that the critical speed of vehicle much depends on wheelset positioning stiffness and anti-hunting motion damper, and the series stiffness produces notable effect on the vehicle dynamic behavior. The critical speed has a peak value with the equivalent conicity increasing, which is different from the traditional opinion in which the critical speed will decrease with the conicity increasing. The relationship between critical speed and conicity of wheel tread is effected by the suspension parameters of the vehicle. The study results obtained offer a method and useful data to designing the parameters of the high speed vehicle and simulation study.
While introducing foreign advanced technology and cooperating with Chinese famous research institutes, the high-speed vehicles are designed and take the major task of passenger transport in China. In high-speed vehicle, the characteristic of shock absorber is an important parameter which determines overall behavior of the vehicle. The most existing researches neglect the influence of the series stiffness of the shock absorber on the vehicle dynamic behavior and have one-sided views on the equivalent conicity of wheel tread. In this paper, a high speed passenger vehicle in China is modeled to investigate the effect of the parameters taking series hydraulic shock absorber stiffness into consideration on Ruzicka model. Using the vehicle dynamic model, the effect of main suspension parameters on critical speed is studied. In order to verify the reasonableness of shock absorber parameter settings, vibration isolation characteristics are calculated and the relationship between suspension parameters and the vehicle critical hunting speed is studied. To study the influence of equivalent conicity on vehicle dynamic behavior, a series of wheel treads with different conicities are set and the vehicle critical hunting speeds with different wheel treads are calculated. The discipline between the equivalent conicity of wheel tread and critical speed are obtained in vehicle nonlinear system. The research results show that the critical speed of vehicle much depends on wheelset positioning stiffness and anti-hunting motion damper, and the series stiffness produces notable effect on the vehicle dynamic behavior. The critical speed has a peak value with the equivalent conicity increasing, which is different from the traditional opinion in which the critical speed will decrease with the conicity increasing. The relationship between critical speed and conicity of wheel tread is effected by the suspension parameters of the vehicle. The study results obtained offer a method and useful data to designing the parameters of the high speed vehicle and simulation study.
2012, 26(3).
Abstract:
Driving a hydraulic cylinder directly by a closed-loop hydraulic pump is currently a key research area in the field of electro-hydraulic control technology, and it is the most direct means to improve the energy efficiency of an electro-hydraulic control system. So far, this technology has been well applied to the pump-controlled symmetric hydraulic cylinder. However, for the differential cylinder that is widely used in hydraulic technology, satisfactory results have not yet been achieved, due to the asymmetric flow constraint. Therefore, based on the principle of the asymmetric valve controlled asymmetric cylinder in valve controlled cylinder technology, an innovative idea for an asymmetric pump controlled asymmetric cylinder is put forward to address this problem. The scheme proposes to transform the oil suction window of the existing axial piston pump into two series windows. When in use, one window is connected to the rod chamber of the hydraulic cylinder and the other is linked with a low-pressure oil tank. This allows the differential cylinders to be directly controlled by changing the displacement or rotation speed of the pumps. Compared with the loop principle of offsetting the area difference of the differential cylinder through hydraulic valve using existing technology, this method may simplify the circuits and increase the energy efficiency of the system. With the software SimulationX, a hydraulic pump simulation model is set up, which examines the movement characteristics of an individual piston and the compressibility of oil, as well as the flow distribution area as it changes with the rotation angle. The pump structure parameters, especially the size of the unloading groove of the valve plate, are determined through digital simulation. All of the components of the series arranged three distribution-window axial piston pump are designed, based on the simulation analysis of the flow pulse characteristics of the pump, and then the prototype pump is made. The basic characteristics, such as the pressure, flow and noise of the pumps under different rotation speeds, are measured on the test bench. The test results verify the correctness of the principle. The proposed research lays a theoretical foundation for the further development of a new pump-controlled cylinder system.
Driving a hydraulic cylinder directly by a closed-loop hydraulic pump is currently a key research area in the field of electro-hydraulic control technology, and it is the most direct means to improve the energy efficiency of an electro-hydraulic control system. So far, this technology has been well applied to the pump-controlled symmetric hydraulic cylinder. However, for the differential cylinder that is widely used in hydraulic technology, satisfactory results have not yet been achieved, due to the asymmetric flow constraint. Therefore, based on the principle of the asymmetric valve controlled asymmetric cylinder in valve controlled cylinder technology, an innovative idea for an asymmetric pump controlled asymmetric cylinder is put forward to address this problem. The scheme proposes to transform the oil suction window of the existing axial piston pump into two series windows. When in use, one window is connected to the rod chamber of the hydraulic cylinder and the other is linked with a low-pressure oil tank. This allows the differential cylinders to be directly controlled by changing the displacement or rotation speed of the pumps. Compared with the loop principle of offsetting the area difference of the differential cylinder through hydraulic valve using existing technology, this method may simplify the circuits and increase the energy efficiency of the system. With the software SimulationX, a hydraulic pump simulation model is set up, which examines the movement characteristics of an individual piston and the compressibility of oil, as well as the flow distribution area as it changes with the rotation angle. The pump structure parameters, especially the size of the unloading groove of the valve plate, are determined through digital simulation. All of the components of the series arranged three distribution-window axial piston pump are designed, based on the simulation analysis of the flow pulse characteristics of the pump, and then the prototype pump is made. The basic characteristics, such as the pressure, flow and noise of the pumps under different rotation speeds, are measured on the test bench. The test results verify the correctness of the principle. The proposed research lays a theoretical foundation for the further development of a new pump-controlled cylinder system.
2012, 26(3).
Abstract:
Much research effort has been devoted to economic design of & S control charts, however, there are some problems in usual methods. On the one hand, it is difficult to estimate the relationship between costs and other model parameters, so the economic design method is often not effective in producing charts that can quickly detect small shifts before substantial losses occur; on the other hand, in many cases, only one type of process shift or only one pair of process shifts are taken into consideration, which may not correctly reflect the actual process conditions. To improve the behavior of economic design of control chart, a cost & loss model with Taguchi’s loss function for the economic design of & S control charts is embellished, which is regarded as an optimization problem with multiple statistical constraints. The optimization design is also carried out based on a number of combinations of process shifts collected from the field operation of the conventional control charts, thus more hidden information about the shift combinations is mined and employed to the optimization design of control charts. At the same time, an improved particle swarm optimization (IPSO) is developed to solve such an optimization problem in design of & S control charts, IPSO is first tested for several benchmark problems from the literature and evaluated with standard performance metrics. Experimental results show that the proposed algorithm has significant advantages on obtaining the optimal design parameters of the charts. The proposed method can substantially reduce the total cost (or loss) of the control charts, and it will be a promising tool for economic design of control charts.
Much research effort has been devoted to economic design of & S control charts, however, there are some problems in usual methods. On the one hand, it is difficult to estimate the relationship between costs and other model parameters, so the economic design method is often not effective in producing charts that can quickly detect small shifts before substantial losses occur; on the other hand, in many cases, only one type of process shift or only one pair of process shifts are taken into consideration, which may not correctly reflect the actual process conditions. To improve the behavior of economic design of control chart, a cost & loss model with Taguchi’s loss function for the economic design of & S control charts is embellished, which is regarded as an optimization problem with multiple statistical constraints. The optimization design is also carried out based on a number of combinations of process shifts collected from the field operation of the conventional control charts, thus more hidden information about the shift combinations is mined and employed to the optimization design of control charts. At the same time, an improved particle swarm optimization (IPSO) is developed to solve such an optimization problem in design of & S control charts, IPSO is first tested for several benchmark problems from the literature and evaluated with standard performance metrics. Experimental results show that the proposed algorithm has significant advantages on obtaining the optimal design parameters of the charts. The proposed method can substantially reduce the total cost (or loss) of the control charts, and it will be a promising tool for economic design of control charts.
2012, 26(3).
Abstract:
Nanoscale adhesive contacts play a key role in micronano-electro-mechanical systems as the dimension of the components come to nanometer. Experimental studies on nanoscale adhesive contacts are limited by some uncertain factors and the cost of experiments is too high. Besides, nanoscale textured surfaces are difficult to process and nanoscale adhesive contacts of textured surfaces are still lack of investigation. By using multiscale method, which couples molecular dynamics simulation and finite element method, two-dimensional nanoscale adhesive contacts between a rigid cylindrical tip and an elastic substrate are investigated. For the contacts between the rigid cylindrical tip and smooth surface, Von Mises stress distributions, the maximum Von Mises stresses, and contact forces are compared for different radii to show the size effects and adhesive effects. The phenomena of hysteresis are observed and more obvious as the radii of the tip increase. The influences of indentation depth and indentation speed are also discussed. Then two series of textured surfaces are employed, and the influences of the texture asperity shape, asperity height, and asperity spacing on contact forces are studied. The contact forces comparisons show that textured surfaces can reduce contact forces effectively in the range of the two series. Contact forces of textured surfaces increase as the asperity heights increase, and textured surfaces with smaller asperity spacing will get higher contact forces. Contact forces may be controlled through textured surfaces in the future. The obtained results will help to improve contact condition and provide theory basis for texture design.
Nanoscale adhesive contacts play a key role in micronano-electro-mechanical systems as the dimension of the components come to nanometer. Experimental studies on nanoscale adhesive contacts are limited by some uncertain factors and the cost of experiments is too high. Besides, nanoscale textured surfaces are difficult to process and nanoscale adhesive contacts of textured surfaces are still lack of investigation. By using multiscale method, which couples molecular dynamics simulation and finite element method, two-dimensional nanoscale adhesive contacts between a rigid cylindrical tip and an elastic substrate are investigated. For the contacts between the rigid cylindrical tip and smooth surface, Von Mises stress distributions, the maximum Von Mises stresses, and contact forces are compared for different radii to show the size effects and adhesive effects. The phenomena of hysteresis are observed and more obvious as the radii of the tip increase. The influences of indentation depth and indentation speed are also discussed. Then two series of textured surfaces are employed, and the influences of the texture asperity shape, asperity height, and asperity spacing on contact forces are studied. The contact forces comparisons show that textured surfaces can reduce contact forces effectively in the range of the two series. Contact forces of textured surfaces increase as the asperity heights increase, and textured surfaces with smaller asperity spacing will get higher contact forces. Contact forces may be controlled through textured surfaces in the future. The obtained results will help to improve contact condition and provide theory basis for texture design.
2012, 26(3).
Abstract:
Automotive industry, as an important pillar of the national economy, has been rapidly developing in recent years. But proplems such as energy comsumption and environmental pollution are posed at the same time. Electro-mechanical variable transmission system is considered one of avilable workarounds. It is brought forward a kind of design methods of dual-mode electro-mechanical variable transmission system rotational speed characteristics and dual-mode drive diagrams. With the motor operating behavior of running in four quadrants and the speed characteristics of the simple internal and external meshing single planetary gear train, four kinds of dual-mode electro-mechanical transmission system scheme are designed. And the velocity, torque and power characteristics of one of the programs are analyzed. The magnitude of the electric split-flow power is an important factor which influences the system performance, so in the parameters matching design, it needs to reduce the power needs under the first mode of the motor. The motor, output rotational speed range and the position of the mode switching point have relationships with the characteristics design of the planetary gear set. The analysis method is to provide a reference for hybrid vehicles’ design. As the involved rotational speed and torque relationships are the natural contact of every part of transmission system, a theory basis of system program and performance analysis is provided.
Automotive industry, as an important pillar of the national economy, has been rapidly developing in recent years. But proplems such as energy comsumption and environmental pollution are posed at the same time. Electro-mechanical variable transmission system is considered one of avilable workarounds. It is brought forward a kind of design methods of dual-mode electro-mechanical variable transmission system rotational speed characteristics and dual-mode drive diagrams. With the motor operating behavior of running in four quadrants and the speed characteristics of the simple internal and external meshing single planetary gear train, four kinds of dual-mode electro-mechanical transmission system scheme are designed. And the velocity, torque and power characteristics of one of the programs are analyzed. The magnitude of the electric split-flow power is an important factor which influences the system performance, so in the parameters matching design, it needs to reduce the power needs under the first mode of the motor. The motor, output rotational speed range and the position of the mode switching point have relationships with the characteristics design of the planetary gear set. The analysis method is to provide a reference for hybrid vehicles’ design. As the involved rotational speed and torque relationships are the natural contact of every part of transmission system, a theory basis of system program and performance analysis is provided.
2012, 26(3).
Abstract:
The dynamics of turning system which is a nonlinear system normally has great impact on the transportation speed of the vehicle having heavy load and large size. The dynamics of turning system depends on control algorithm and its implementation, but the existing control algorithms which having high dynamics in the application of heavy transportation vehicle are complex for realization and high hardware requirement. So, the nonlinear turning system is analyzed for improving its dynamics by researching new efficient control algorithm. The models of electromagnetic valve, hydraulic cylinder and turning mechanical part are built individually to get the open-loop model of the turning system following characteristics analyzed. According to the model, a new control algorithm for heavy transportation vehicle which combined PID with Bang-Bang control is presented. Then the close-loop model of turning system is obtained under MatlabSimulink environment. By comparing the step response of different control algorithms in the same conditions, the new algorithm’s validity is verified. On the basis of the analysis results, the algorithm is adopted to implement the turning control system by using CAN field bus and PLC controllers. Furthermore, the turning control system has been applied in one type of heavy transportation vehicle. It reduces the response time of turning system from seconds level to 250 ms, and the speed of heavy transportation vehicle increases from 5 kmh to 30 kmh. The application result shows that the algorithm and turning control system have met all the turning requirements. This new type of turning control algorithm proposed is simple in implementation for fast response of nonlinear and large-scale turning system of heavy transportation vehicle.
The dynamics of turning system which is a nonlinear system normally has great impact on the transportation speed of the vehicle having heavy load and large size. The dynamics of turning system depends on control algorithm and its implementation, but the existing control algorithms which having high dynamics in the application of heavy transportation vehicle are complex for realization and high hardware requirement. So, the nonlinear turning system is analyzed for improving its dynamics by researching new efficient control algorithm. The models of electromagnetic valve, hydraulic cylinder and turning mechanical part are built individually to get the open-loop model of the turning system following characteristics analyzed. According to the model, a new control algorithm for heavy transportation vehicle which combined PID with Bang-Bang control is presented. Then the close-loop model of turning system is obtained under MatlabSimulink environment. By comparing the step response of different control algorithms in the same conditions, the new algorithm’s validity is verified. On the basis of the analysis results, the algorithm is adopted to implement the turning control system by using CAN field bus and PLC controllers. Furthermore, the turning control system has been applied in one type of heavy transportation vehicle. It reduces the response time of turning system from seconds level to 250 ms, and the speed of heavy transportation vehicle increases from 5 kmh to 30 kmh. The application result shows that the algorithm and turning control system have met all the turning requirements. This new type of turning control algorithm proposed is simple in implementation for fast response of nonlinear and large-scale turning system of heavy transportation vehicle.
2012, 26(3).
Abstract:
The work-class remotely-operated-underwater-vehicles (ROVs) are mainly driven by hydraulic propulsion system, and the effeciency of hydraulic propulsion system is an important performance index of ROVs. However, the efficiency of traditional hydraulic propulsion system controlled by throttle valves is too low. Therefore, in this paper, for small and medium ROVs, a novel propulsion system with higher efficiency based on high speed onoff valve control hydraulic propeller is proposed. To solve the conflict between large flow rate and high frequency response performance, a two-stage high speed onoff valve-motor unit with large flow rate and high response speed simultaneously is developed. Through theoretical analysis, an effective fluctuation control method and a novel pulse-width-pulse-frequency-modulation (PWPFM) are introduced to solve the conflict among inherently fluctuation, valve dynamic performance and system efficiency. A simulation model is established to evaluate the system performance. To prove the advantage of system in energy saving, and test the dynamic control performance of high speed onoff valve control propeller, a test setup is developed and a series of comparative experiments is completed. The smimulation and experiment results show that the two-stage high speed onoff valve has an excellent dynamic response performance, and can be used to realize high accuracy speed control. The experiment results prove that the new propulsion system has much more advantages than the traditional throttle speed regulation system in energy saving. The lowest efficiency is more than 40%. The application results on a ROV indicate that the high speed onoff valve control propeller system has good dynamic and steady-state control performances. Its transient time is only about 1 s–1.5 s, and steady-state error is less than 5%. Meanwhile, the speed fluctuation is small, and the smooth propeller speed control effect is obtained.On the premise of good propeller speed control performance, the proposed high speed onoff valve control propeller can improve the effeciency of ROV propulsion system significantly, and provides another attractive ROV propulsion system choice for engineers.
The work-class remotely-operated-underwater-vehicles (ROVs) are mainly driven by hydraulic propulsion system, and the effeciency of hydraulic propulsion system is an important performance index of ROVs. However, the efficiency of traditional hydraulic propulsion system controlled by throttle valves is too low. Therefore, in this paper, for small and medium ROVs, a novel propulsion system with higher efficiency based on high speed onoff valve control hydraulic propeller is proposed. To solve the conflict between large flow rate and high frequency response performance, a two-stage high speed onoff valve-motor unit with large flow rate and high response speed simultaneously is developed. Through theoretical analysis, an effective fluctuation control method and a novel pulse-width-pulse-frequency-modulation (PWPFM) are introduced to solve the conflict among inherently fluctuation, valve dynamic performance and system efficiency. A simulation model is established to evaluate the system performance. To prove the advantage of system in energy saving, and test the dynamic control performance of high speed onoff valve control propeller, a test setup is developed and a series of comparative experiments is completed. The smimulation and experiment results show that the two-stage high speed onoff valve has an excellent dynamic response performance, and can be used to realize high accuracy speed control. The experiment results prove that the new propulsion system has much more advantages than the traditional throttle speed regulation system in energy saving. The lowest efficiency is more than 40%. The application results on a ROV indicate that the high speed onoff valve control propeller system has good dynamic and steady-state control performances. Its transient time is only about 1 s–1.5 s, and steady-state error is less than 5%. Meanwhile, the speed fluctuation is small, and the smooth propeller speed control effect is obtained.On the premise of good propeller speed control performance, the proposed high speed onoff valve control propeller can improve the effeciency of ROV propulsion system significantly, and provides another attractive ROV propulsion system choice for engineers.
2012, 26(3).
Abstract:
Profile monitoring is used to check the stability of the quality of a product over time when the product quality is best represented by a function at each time point. However, most previous monitoring approaches have not considered that the argument values may vary from profile to profile, which is common in practice. A novel nonparametric control scheme based on profile error is proposed for monitoring nonlinear profiles with varied argument values. The proposed scheme uses the metrics of profile error as the statistics to construct the control charts. More details about the design of this nonparametric scheme are also discussed. The monitoring performance of the combined control scheme is compared with that of alternative nonparametric methods via simulation. Simulation studies show that the combined scheme is effective in detecting parameter error and is sensitive to small shifts in the process. In addition, due to the properties of the charting statistics, the out-of-control signal can provide diagnostic information for the users. Finally, the implementation steps of the proposed monitoring scheme are given and applied for monitoring the blade manufacturing process. With the application in blade manufacturing of aircraft engines, the proposed nonparametric control scheme is effective, interpretable, and easy to apply.
Profile monitoring is used to check the stability of the quality of a product over time when the product quality is best represented by a function at each time point. However, most previous monitoring approaches have not considered that the argument values may vary from profile to profile, which is common in practice. A novel nonparametric control scheme based on profile error is proposed for monitoring nonlinear profiles with varied argument values. The proposed scheme uses the metrics of profile error as the statistics to construct the control charts. More details about the design of this nonparametric scheme are also discussed. The monitoring performance of the combined control scheme is compared with that of alternative nonparametric methods via simulation. Simulation studies show that the combined scheme is effective in detecting parameter error and is sensitive to small shifts in the process. In addition, due to the properties of the charting statistics, the out-of-control signal can provide diagnostic information for the users. Finally, the implementation steps of the proposed monitoring scheme are given and applied for monitoring the blade manufacturing process. With the application in blade manufacturing of aircraft engines, the proposed nonparametric control scheme is effective, interpretable, and easy to apply.
2012, 26(3).
Abstract:
As the mesh models usually contain noise data, it is necessary to eliminate the noises and smooth the mesh. But existed methods always lose geometric features during the smoothing process. Hence, the noise is considered as a kind of random signal with high frequency, and then the mesh model smoothing is operated with signal processing theory. Local wave analysis is used to deal with geometric signal, and then a novel mesh smoothing method based on the local wave is proposed. The proposed method includes following steps: Firstly, analyze the principle of local wave decomposition for 1D signal, and expand it to 2D signal and 3D spherical surface signal processing; Secondly, map the mesh to the spherical surface with parameterization, resample the spherical mesh and decompose the spherical signals by local wave analysis; Thirdly, propose the coordinate smoothing and radical radius smoothing methods, the former filters the mesh points’ coordinates by local wave, and the latter filters the radical radius from their geometric center to mesh points by local wave; Finally, remove the high-frequency component of spherical signal, and obtain the smooth mesh model with inversely mapping from the spherical signal. Several mesh models with Gaussian noise are processed by local wave based method and other compared methods. The results show that local wave based method can obtain better smoothing performance, and reserve more original geometric features at the same time.
As the mesh models usually contain noise data, it is necessary to eliminate the noises and smooth the mesh. But existed methods always lose geometric features during the smoothing process. Hence, the noise is considered as a kind of random signal with high frequency, and then the mesh model smoothing is operated with signal processing theory. Local wave analysis is used to deal with geometric signal, and then a novel mesh smoothing method based on the local wave is proposed. The proposed method includes following steps: Firstly, analyze the principle of local wave decomposition for 1D signal, and expand it to 2D signal and 3D spherical surface signal processing; Secondly, map the mesh to the spherical surface with parameterization, resample the spherical mesh and decompose the spherical signals by local wave analysis; Thirdly, propose the coordinate smoothing and radical radius smoothing methods, the former filters the mesh points’ coordinates by local wave, and the latter filters the radical radius from their geometric center to mesh points by local wave; Finally, remove the high-frequency component of spherical signal, and obtain the smooth mesh model with inversely mapping from the spherical signal. Several mesh models with Gaussian noise are processed by local wave based method and other compared methods. The results show that local wave based method can obtain better smoothing performance, and reserve more original geometric features at the same time.
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