2010 Vol.23(5)
Display Mode： |
2010, 24(5).
Abstract:
Order analysis is one of the most important technique means of condition monitoring and fault diagnosis for rotary machinery. The traditional order analyses usually employ the Vold-Kalman filtering, however this method is confined to the expensive hardware equipments. This paper starts from Gabor transform and applies the Gabor time-frequency filtering to vibration signal. The order component’s time-frequency coefficients are extracted by mask operation. The order component is reconstructed from the obtained coefficients. The following four key technologies, such as smoothing rotary speed curve, defining filtering band width, constructing the mask operation matrix and reconstructing signal component, are also deeply discussed. Moreover, the technique to smooth the rotary speed curve based on polynomial approximation, the method to determine filtering band width, the arithmetic to constitute mask array and the iterative algorithm to reconstruct signal based on minimum mean square error are specifically analyzed. The 4th order component is successfully gained by using the methods that Gabor time-frequency filter, and the validity and feasibility of this method are approved. This method can solve the problem of order tracking filter technologies which used to depend on hardware and efficiently improve the accuracy of order analysis.
Order analysis is one of the most important technique means of condition monitoring and fault diagnosis for rotary machinery. The traditional order analyses usually employ the Vold-Kalman filtering, however this method is confined to the expensive hardware equipments. This paper starts from Gabor transform and applies the Gabor time-frequency filtering to vibration signal. The order component’s time-frequency coefficients are extracted by mask operation. The order component is reconstructed from the obtained coefficients. The following four key technologies, such as smoothing rotary speed curve, defining filtering band width, constructing the mask operation matrix and reconstructing signal component, are also deeply discussed. Moreover, the technique to smooth the rotary speed curve based on polynomial approximation, the method to determine filtering band width, the arithmetic to constitute mask array and the iterative algorithm to reconstruct signal based on minimum mean square error are specifically analyzed. The 4th order component is successfully gained by using the methods that Gabor time-frequency filter, and the validity and feasibility of this method are approved. This method can solve the problem of order tracking filter technologies which used to depend on hardware and efficiently improve the accuracy of order analysis.
2010, 24(5).
Abstract:
Conventional ball bearing reaction wheel used to control the attitude of spacecraft can’t absorb the centrifugal force caused by imbalance of the wheel rotor, and there will be a torque spike at zero speed, which seriously influences the accuracy and stability of spacecraft attitude control. Compared with traditional ball-bearing wheel, noncontact and no lubrication are the remarkable features of the magnetic bearing reaction wheel, and which can solve the high precision problems of wheel. In general, two radial magnetic bearings are needed in magnetic bearing wheel, and the design results in a relatively large axial dimension and smaller momentum-to-mass ratios. In this paper, a new type of magnetic bearing reaction wheel(MBRW) is introduced for satellite attitude control, and a novel integrated radial hybrid magnetic bearing(RHMB) with permanent magnet bias is designed to reduce the mass and minimize the size of the MBRW, etc. The equivalent magnetic circuit model for the RHMB is presented and a solution is found. The stiffness model is also presented, including current stiffness, position negative stiffness, as well as tilting current stiffness, tilting angular position negative stiffness, force and moment equilibrium equations. The design parameters of the RHMB are given according to the requirement of the MBRW with angular momentum of 30 N • m • s when the rotation speed of rotor reaches to 5 krmin. The nonlinearity of the RHMB is shown by using the characteristic curves of force–control current–position, current stiffness, position stiffness, moment–control current–angular displacement, tilting current stiffness and tilting angular position stiffness considering all the rotor position within the clearance space and the control current. The proposed research ensures the performance of the radial magnetic bearing with permanent magnet bias, and provides theory basis for design of the magnetic bearing wheel.
Conventional ball bearing reaction wheel used to control the attitude of spacecraft can’t absorb the centrifugal force caused by imbalance of the wheel rotor, and there will be a torque spike at zero speed, which seriously influences the accuracy and stability of spacecraft attitude control. Compared with traditional ball-bearing wheel, noncontact and no lubrication are the remarkable features of the magnetic bearing reaction wheel, and which can solve the high precision problems of wheel. In general, two radial magnetic bearings are needed in magnetic bearing wheel, and the design results in a relatively large axial dimension and smaller momentum-to-mass ratios. In this paper, a new type of magnetic bearing reaction wheel(MBRW) is introduced for satellite attitude control, and a novel integrated radial hybrid magnetic bearing(RHMB) with permanent magnet bias is designed to reduce the mass and minimize the size of the MBRW, etc. The equivalent magnetic circuit model for the RHMB is presented and a solution is found. The stiffness model is also presented, including current stiffness, position negative stiffness, as well as tilting current stiffness, tilting angular position negative stiffness, force and moment equilibrium equations. The design parameters of the RHMB are given according to the requirement of the MBRW with angular momentum of 30 N • m • s when the rotation speed of rotor reaches to 5 krmin. The nonlinearity of the RHMB is shown by using the characteristic curves of force–control current–position, current stiffness, position stiffness, moment–control current–angular displacement, tilting current stiffness and tilting angular position stiffness considering all the rotor position within the clearance space and the control current. The proposed research ensures the performance of the radial magnetic bearing with permanent magnet bias, and provides theory basis for design of the magnetic bearing wheel.
Optimum Design for Shrink-fit Multi-layer Vessels under Ultrahigh Pressure Using Different Materials
2010, 24(5).
Abstract:
Multi-layer pressure vessels are widely used in every field of high pressure technology. For the purpose of enhancing a vessels’ load bearing capacity, a beneficial process like shrink-fit is usually employed. However, few documents on optimum design for multi-layer shrink-fit vessels made of different strength materials can be found, available data are mainly on two-layer vessels. In this paper, an optimum design approach is developed for shrink-fit multi-layer vessels under ultrahigh pressure by using different materials. Maximum shear stress theory is applied as design criteria. The inner and outer radii of a multi-layer vessel, as well as the material of each layer, are assumed to be known. The optimization mathematical model is, thereby, built. Lagrange multipliers method is required to obtain the optimal design formula of wall ratio (ratio of outer to inner radii) of each layer, from which the optimum formulas of shrinkage pressure and radial interference are derived with the superposition principle employed. These formulas are applicable for the optimization design of all multi-layer vessels made of different materials, or same materials. The formulas of the limit working pressure and the contact pressure show that the optimum wall ratio of each layer and limit working pressure are only related to all selected material strength and unrelated to the position of the layer placement in the vessel. However, shrinkage pressure is related to the position of the layer placement in the vessel. Optimization design of an open ended shrink-fit three-layer vessel using different materials and comparisons proved that the optimized multi-layer vessels have outstanding characteristics of small radial interference and are easier for assembly. When the stress of each layer is distributed more evenly and appropriately, the load bearing capability and safety of vessels are enhanced. Therefore, this design is material-saving and cost-effective, and has prospect of engineering application.
Multi-layer pressure vessels are widely used in every field of high pressure technology. For the purpose of enhancing a vessels’ load bearing capacity, a beneficial process like shrink-fit is usually employed. However, few documents on optimum design for multi-layer shrink-fit vessels made of different strength materials can be found, available data are mainly on two-layer vessels. In this paper, an optimum design approach is developed for shrink-fit multi-layer vessels under ultrahigh pressure by using different materials. Maximum shear stress theory is applied as design criteria. The inner and outer radii of a multi-layer vessel, as well as the material of each layer, are assumed to be known. The optimization mathematical model is, thereby, built. Lagrange multipliers method is required to obtain the optimal design formula of wall ratio (ratio of outer to inner radii) of each layer, from which the optimum formulas of shrinkage pressure and radial interference are derived with the superposition principle employed. These formulas are applicable for the optimization design of all multi-layer vessels made of different materials, or same materials. The formulas of the limit working pressure and the contact pressure show that the optimum wall ratio of each layer and limit working pressure are only related to all selected material strength and unrelated to the position of the layer placement in the vessel. However, shrinkage pressure is related to the position of the layer placement in the vessel. Optimization design of an open ended shrink-fit three-layer vessel using different materials and comparisons proved that the optimized multi-layer vessels have outstanding characteristics of small radial interference and are easier for assembly. When the stress of each layer is distributed more evenly and appropriately, the load bearing capability and safety of vessels are enhanced. Therefore, this design is material-saving and cost-effective, and has prospect of engineering application.
2010, 24(5).
Abstract:
The existing research on shrinkage of the injection molded plastic part mainly focuses on various shrinkage ratios of the part dimensions, and the relevant experimental studies belong to mere dimension measurement after demoulding. Obviously, measuring after the plastic part is demoulded from the cavity can not offer shrinkage displacements of points on the plastic part. However, shrinkage displacements of points on an injection molded plastic part are essential for exposing the inner relation among shrinkage ratios of various dimensions of the part. So visualization of the in-mold plastic part which can indicate the location relationship between the part and the cavity is needed. In this paper, a visual injection mold was fabricated by adopting the half mold structure and light transmission manner. With the visual mold, in-mold shrinkage images of injection molded plastic parts were photographed after the plastic part stayed in the injection mold for 24 h. By means of digital image processing of the in-mold shrinkage images, the experimental data of shrinkage displacements of points on injection molded parts were researched. From the experimental data, it is found that shrinkage directions of points on an injection molded part are related with both positions of the gate and of the part centroid, and either the gate or the centroid will exert more influence on the shrinkage direction of some point which is closer. Furthermore, some point at the later filled area has more shrinkage distance than the point at the earlier filled area. Combination of shrinkage directions and shrinkage distances of points on an injection molded part determine shrinkage ratios for various dimensions of the part, and shrinkage directions are more influential to shrinkage ratios of dimensions. This experimental research of shrinkage displacements offers a unique approach to understand the shrinkage principles of injection molded parts.
The existing research on shrinkage of the injection molded plastic part mainly focuses on various shrinkage ratios of the part dimensions, and the relevant experimental studies belong to mere dimension measurement after demoulding. Obviously, measuring after the plastic part is demoulded from the cavity can not offer shrinkage displacements of points on the plastic part. However, shrinkage displacements of points on an injection molded plastic part are essential for exposing the inner relation among shrinkage ratios of various dimensions of the part. So visualization of the in-mold plastic part which can indicate the location relationship between the part and the cavity is needed. In this paper, a visual injection mold was fabricated by adopting the half mold structure and light transmission manner. With the visual mold, in-mold shrinkage images of injection molded plastic parts were photographed after the plastic part stayed in the injection mold for 24 h. By means of digital image processing of the in-mold shrinkage images, the experimental data of shrinkage displacements of points on injection molded parts were researched. From the experimental data, it is found that shrinkage directions of points on an injection molded part are related with both positions of the gate and of the part centroid, and either the gate or the centroid will exert more influence on the shrinkage direction of some point which is closer. Furthermore, some point at the later filled area has more shrinkage distance than the point at the earlier filled area. Combination of shrinkage directions and shrinkage distances of points on an injection molded part determine shrinkage ratios for various dimensions of the part, and shrinkage directions are more influential to shrinkage ratios of dimensions. This experimental research of shrinkage displacements offers a unique approach to understand the shrinkage principles of injection molded parts.
2010, 24(5).
Abstract:
Inlet recirculation is proved as an effective way for centrifugal compressor surge margin extension, and is successively used in some engineering applications. Unfortunately its working mechanism is still not being well understood, which leads to redesigning of inlet recirculation mostly by experience. Also, most study about inlet recirculation is steady to date. It is necessary to study surge margin extension mechanism about inlet recirculation. To expose the mechanism in detail, steady and unsteady numerical simulations were performed on a centrifugal compressor with and without inlet recirculation. The results showed that, with inlet recirculation, the inlet axial velocity is augmented, relative Mach number around blade tip leading edge area is significantly reduced and so is the flow angle. As the flow angle decreased, the incidence angle reduced which greatly improves the flow field inside the impeller. Moreover, inlet recirculation changes the blade loading around blade tip and restrains the flow separation on the blade suction side at the leading edge area. The unsteady results of static pressure around blade surface, entropy at inlet crossflow section and vorticity distributions at near tip span surface indicated that, at near stall condition, strong fluctuation exists in the vicinity of tip area due to the interaction between tip leakage flow and core flow. By inlet recirculation these strong flow fluctuations are eliminated so the flow stability is greatly enhanced. All these improvements mentioned above are the reason for inlet recirculation delays compressor stall. This research reveals the surge margin extension reason of inlet recirculation from an unsteady flow viewpoint and provides important reference for inlet recirculation structure design.
Inlet recirculation is proved as an effective way for centrifugal compressor surge margin extension, and is successively used in some engineering applications. Unfortunately its working mechanism is still not being well understood, which leads to redesigning of inlet recirculation mostly by experience. Also, most study about inlet recirculation is steady to date. It is necessary to study surge margin extension mechanism about inlet recirculation. To expose the mechanism in detail, steady and unsteady numerical simulations were performed on a centrifugal compressor with and without inlet recirculation. The results showed that, with inlet recirculation, the inlet axial velocity is augmented, relative Mach number around blade tip leading edge area is significantly reduced and so is the flow angle. As the flow angle decreased, the incidence angle reduced which greatly improves the flow field inside the impeller. Moreover, inlet recirculation changes the blade loading around blade tip and restrains the flow separation on the blade suction side at the leading edge area. The unsteady results of static pressure around blade surface, entropy at inlet crossflow section and vorticity distributions at near tip span surface indicated that, at near stall condition, strong fluctuation exists in the vicinity of tip area due to the interaction between tip leakage flow and core flow. By inlet recirculation these strong flow fluctuations are eliminated so the flow stability is greatly enhanced. All these improvements mentioned above are the reason for inlet recirculation delays compressor stall. This research reveals the surge margin extension reason of inlet recirculation from an unsteady flow viewpoint and provides important reference for inlet recirculation structure design.
2010, 24(5).
Abstract:
An intermittent connection is one of the major problems that affect the network reliability and communication quality. However, little attention has been paid to the detection, analysis and localization of the intermittent connections. Partially due to the limitations of the DeviceNet protocol, there is no effective online diagnostic tool available to identify the location of intermittent connection. On the basis of different DeviceNet fault scenarios induced by intermittent connections, a new graph-based diagnostic method is developed to analyze DeviceNet fault patterns, identify the corresponding fault scenarios, and infer the location of the intermittent connection problem by using passively captured network faults. A novel error source analysis tool, which integrates network data-link layer analysis and feature based network physical layer information, is developed to restore the snapshots of the network communication at each intermittent connection induced error. A graph based location identification method is developed to infer the location of the intermittent connections based on the restored error patterns. A 3-node laboratory test-bed, using master-slave polling communication method, is constructed to emulate the intermittent connection induced faults on the network drop cable by using digital switches, whose onoff states are controlled by a computer. During experiments, the network fault diagnosis is conducted by using information collected on trunk cable (backbone). Experimental study shows that the proposed method is effective to restore the snapshots of the network errors and locate the drop cable that experiences the intermittent connection problem.
An intermittent connection is one of the major problems that affect the network reliability and communication quality. However, little attention has been paid to the detection, analysis and localization of the intermittent connections. Partially due to the limitations of the DeviceNet protocol, there is no effective online diagnostic tool available to identify the location of intermittent connection. On the basis of different DeviceNet fault scenarios induced by intermittent connections, a new graph-based diagnostic method is developed to analyze DeviceNet fault patterns, identify the corresponding fault scenarios, and infer the location of the intermittent connection problem by using passively captured network faults. A novel error source analysis tool, which integrates network data-link layer analysis and feature based network physical layer information, is developed to restore the snapshots of the network communication at each intermittent connection induced error. A graph based location identification method is developed to infer the location of the intermittent connections based on the restored error patterns. A 3-node laboratory test-bed, using master-slave polling communication method, is constructed to emulate the intermittent connection induced faults on the network drop cable by using digital switches, whose onoff states are controlled by a computer. During experiments, the network fault diagnosis is conducted by using information collected on trunk cable (backbone). Experimental study shows that the proposed method is effective to restore the snapshots of the network errors and locate the drop cable that experiences the intermittent connection problem.
2010, 24(5).
Abstract:
Studying and understanding of the surface topography variation are the basis for analyzing tribological problems, and characterization of worn surface is necessary. Fractal geometry offers a more accurate description for surface roughness that topographic surfaces are statistically self-similar and can be quantitatively evaluated by fractal parameters. The change regularity of worn surface topography is one of the most important aspects of running-in study. However, the existing research normally adopts only one friction matching pair to explore the surface topography change, which interrupts the running-in wear process and makes the experimental result lack authenticity and objectivity. In this paper, to investigate the change regularity of surface topography during the real running-in process, a series of running-in tests by changing friction pairs under the same operating conditions are conducted on UMT-II Universal Multifunction Tester. The surface profile data are acquired by MiaoXAM2.5X-50X Ultrahigh Precision Surface 3D Profiler and analyzed using fractal dimension D, scale coefficient C and characteristic roughness based on root mean square(RMS) method. The characterization effects of the three parameters are discussed and compared. The results obtained show that there exists remarkable fractal feature of surface topography during running-in process, both D and increase gradually, while C decreases slowly as the wear-in process goes on, and all parameters tend to be stable when the wear process steps into the normal wear process. illustrates higher sensitivity for rough surface characterization compared with the other two parameters. In addition, the running-in test carried with a set of identical surface properties is more scientific and reasonable than the traditional one. The proposed research further indicates that the fractal method can quantitatively measure the rough surface, which also provides an evidence for running-in process identification and tribology design.
Studying and understanding of the surface topography variation are the basis for analyzing tribological problems, and characterization of worn surface is necessary. Fractal geometry offers a more accurate description for surface roughness that topographic surfaces are statistically self-similar and can be quantitatively evaluated by fractal parameters. The change regularity of worn surface topography is one of the most important aspects of running-in study. However, the existing research normally adopts only one friction matching pair to explore the surface topography change, which interrupts the running-in wear process and makes the experimental result lack authenticity and objectivity. In this paper, to investigate the change regularity of surface topography during the real running-in process, a series of running-in tests by changing friction pairs under the same operating conditions are conducted on UMT-II Universal Multifunction Tester. The surface profile data are acquired by MiaoXAM2.5X-50X Ultrahigh Precision Surface 3D Profiler and analyzed using fractal dimension D, scale coefficient C and characteristic roughness based on root mean square(RMS) method. The characterization effects of the three parameters are discussed and compared. The results obtained show that there exists remarkable fractal feature of surface topography during running-in process, both D and increase gradually, while C decreases slowly as the wear-in process goes on, and all parameters tend to be stable when the wear process steps into the normal wear process. illustrates higher sensitivity for rough surface characterization compared with the other two parameters. In addition, the running-in test carried with a set of identical surface properties is more scientific and reasonable than the traditional one. The proposed research further indicates that the fractal method can quantitatively measure the rough surface, which also provides an evidence for running-in process identification and tribology design.
2010, 24(5).
Abstract:
Accurate material constitutive model is considered highly necessary to perform finite element simulation and analysis. However, it is difficult to establish the material constitutive model because of uncertainty of mathematical relationship and constraint of existing experimental condition. At present, there exists considerable gap between finite element simulation result and actual cutting process. Particular emphases were put on investigating the correlation between “single factor” material constitutive model parameters and temperature for Ti6Al4V alloy, and also establishment of material constitutive model for this kind of material. Theoretical analyses based on dislocation theory and material functional relations showed that material model was deeply affected by variation temperature. By the least squares best fit to the available quasi-static and high-speed impact compression experiment data, material parameters at various temperatures were found. Experimental curves analyses and material parameters comparison showed that the “single factor” material constitutive model parameters were temperature dependent. Using the mathematical mapping between material parameters and temperature, “single factor” material constitutive model of Ti6Al4V alloy was established, which was proven to be right by comparing with experimental measurements. This work makes clear that the “single factor” material constitutive model parameters of Ti6Al4V alloy are temperature dependent. At the same time, an accurate material constitutive model is established, which helps to optimize cutting process and control machining distortion for Ti6Al4V alloy aerospace parts.
Accurate material constitutive model is considered highly necessary to perform finite element simulation and analysis. However, it is difficult to establish the material constitutive model because of uncertainty of mathematical relationship and constraint of existing experimental condition. At present, there exists considerable gap between finite element simulation result and actual cutting process. Particular emphases were put on investigating the correlation between “single factor” material constitutive model parameters and temperature for Ti6Al4V alloy, and also establishment of material constitutive model for this kind of material. Theoretical analyses based on dislocation theory and material functional relations showed that material model was deeply affected by variation temperature. By the least squares best fit to the available quasi-static and high-speed impact compression experiment data, material parameters at various temperatures were found. Experimental curves analyses and material parameters comparison showed that the “single factor” material constitutive model parameters were temperature dependent. Using the mathematical mapping between material parameters and temperature, “single factor” material constitutive model of Ti6Al4V alloy was established, which was proven to be right by comparing with experimental measurements. This work makes clear that the “single factor” material constitutive model parameters of Ti6Al4V alloy are temperature dependent. At the same time, an accurate material constitutive model is established, which helps to optimize cutting process and control machining distortion for Ti6Al4V alloy aerospace parts.
2010, 24(5).
Abstract:
As two independent problems, scheduling for parts fabrication line and sequencing for mixed-model assembly line have been addressed respectively by many researchers. However, these two problems should be considered simultaneously to improve the efficiency of the whole fabrication/assembly systems. By far, little research effort is devoted to sequencing problems for mixed-model fabrication/assembly systems. This paper is concerned about the sequencing problems in pull production systems which are composed of one mixed-model assembly line with limited intermediate buffers and two flexible parts fabrication flow lines with identical parallel machines and limited intermediate buffers. Two objectives are considered simultaneously: minimizing the total variation in parts consumption in the assembly line and minimizing the total makespan cost in the fabrication/assembly system. The integrated optimization framework, mathematical models and the method to construct the complete schedules for the fabrication lines according to the production sequences for the first stage in fabrication lines are presented. Since the above problems are non-deterministic polynomial-hard(NP-hard), a modified multi-objective genetic algorithm is proposed for solving the models, in which a method to generate the production sequences for the fabrication lines from the production sequences for the assembly line and a method to generate the initial population are put forward, new selection, crossover and mutation operators are designed, and Pareto ranking method and sharing function method are employed to evaluate the individuals’ fitness. The feasibility and efficiency of the multi-objective genetic algorithm is shown by computational comparison with a multi-objective simulated annealing algorithm. The sequencing problems for mixed-model production systems can be solved effectively by the proposed modified multi-objective genetic algorithm.
As two independent problems, scheduling for parts fabrication line and sequencing for mixed-model assembly line have been addressed respectively by many researchers. However, these two problems should be considered simultaneously to improve the efficiency of the whole fabrication/assembly systems. By far, little research effort is devoted to sequencing problems for mixed-model fabrication/assembly systems. This paper is concerned about the sequencing problems in pull production systems which are composed of one mixed-model assembly line with limited intermediate buffers and two flexible parts fabrication flow lines with identical parallel machines and limited intermediate buffers. Two objectives are considered simultaneously: minimizing the total variation in parts consumption in the assembly line and minimizing the total makespan cost in the fabrication/assembly system. The integrated optimization framework, mathematical models and the method to construct the complete schedules for the fabrication lines according to the production sequences for the first stage in fabrication lines are presented. Since the above problems are non-deterministic polynomial-hard(NP-hard), a modified multi-objective genetic algorithm is proposed for solving the models, in which a method to generate the production sequences for the fabrication lines from the production sequences for the assembly line and a method to generate the initial population are put forward, new selection, crossover and mutation operators are designed, and Pareto ranking method and sharing function method are employed to evaluate the individuals’ fitness. The feasibility and efficiency of the multi-objective genetic algorithm is shown by computational comparison with a multi-objective simulated annealing algorithm. The sequencing problems for mixed-model production systems can be solved effectively by the proposed modified multi-objective genetic algorithm.
2010, 24(5).
Abstract:
The condensation in pneumatic system is a complex physical phenomenon dependant upon status variation and phase transitions, which are related to the parameters of the compressed air, atmospheric conditions and the dimensions of the pneumatic components. Up to now, general research method for this problem is to calculate the status variation and movement quantity by numerical simulation and experiment directly. The comprehensive parameters composed of several different effect factors are rarely used to study the condensation. The composed components and the working conditions of each cylinder are different, a large number of experiments and complex calculations are necessary to determine the condensation. Additionally, the transferability of the determined results is poor. In this paper, the charging and discharging systems of serials cylinder with different structure parameters are studied. The condensation of the systems is observed and the effects of the structure parameters on condensation are analyzed. The changing trends of relative humidity, natural frequency and average speed against the structural parameters of the components during discharge of the pneumatic systems are analyzed. Three comprehensive parameters used to analyze and determine condensation composed by structure parameters of components are proposed, namely, the ratio of the effective area of the discharge tube and the container volume, the square root of the effective area of the discharge tube divided by the product of the container volume and the length of the discharge tube, and the discharge dimensionless tube-volume. The experimental results show that these comprehensive parameters can be used to quantitatively determine whether internal, external or zero condensation occurs in a pneumatic system, and can be also used to quantitatively analyze the experimental data of condensation in pneumatic systems directly. At the same time, the effect factors are too much and the effect relationships are very complex, which causes that the conclusions can’t be put forward by using single effect factor in experimental data processing individually. The three obtained comprehensive parameters can be used to resolve the above problem. The proposed parameters can also resolve the problem of poor transferability in determining the state of condensation in pneumatic systems, and provide a novel method for the further study of condensation theory.
The condensation in pneumatic system is a complex physical phenomenon dependant upon status variation and phase transitions, which are related to the parameters of the compressed air, atmospheric conditions and the dimensions of the pneumatic components. Up to now, general research method for this problem is to calculate the status variation and movement quantity by numerical simulation and experiment directly. The comprehensive parameters composed of several different effect factors are rarely used to study the condensation. The composed components and the working conditions of each cylinder are different, a large number of experiments and complex calculations are necessary to determine the condensation. Additionally, the transferability of the determined results is poor. In this paper, the charging and discharging systems of serials cylinder with different structure parameters are studied. The condensation of the systems is observed and the effects of the structure parameters on condensation are analyzed. The changing trends of relative humidity, natural frequency and average speed against the structural parameters of the components during discharge of the pneumatic systems are analyzed. Three comprehensive parameters used to analyze and determine condensation composed by structure parameters of components are proposed, namely, the ratio of the effective area of the discharge tube and the container volume, the square root of the effective area of the discharge tube divided by the product of the container volume and the length of the discharge tube, and the discharge dimensionless tube-volume. The experimental results show that these comprehensive parameters can be used to quantitatively determine whether internal, external or zero condensation occurs in a pneumatic system, and can be also used to quantitatively analyze the experimental data of condensation in pneumatic systems directly. At the same time, the effect factors are too much and the effect relationships are very complex, which causes that the conclusions can’t be put forward by using single effect factor in experimental data processing individually. The three obtained comprehensive parameters can be used to resolve the above problem. The proposed parameters can also resolve the problem of poor transferability in determining the state of condensation in pneumatic systems, and provide a novel method for the further study of condensation theory.
2010, 24(5).
Abstract:
With the development of analytical instrumentation to minimization, integration and automation, the microfluidic chips, which are more integrated, complex and diversified, have been applied widely on the manufacturing of analytical instrumentation. However, the present photolithography-based microfabrication technology, which is only able to pattern microchannels with simple inside structures, can not follow the rapid development of requirements. For solving the problem, a fabrication method based on the restricting effect of laminar flow is proposed for the micro etching on isotropic substrates. Experiments were conducted inside glass-based microchannels, in which certain etchant was used to form complicated microstructures. The flow parameters effects on the aspect ratio, side wall profile and etching rate were revealed by the experiments. The experimental results reveal that the topography of micro structures patterned with the restricted flow etching method is mainly determined by the flowrates of separator and etchant. The computational fluid dynamics(CFD) model on the interface between multiple streams was established for the etching process, and analysis on the causes of various micro topographies was conducted based on the CFD simulation results. The experimental data consisted with the simulation results very well. The investigation depicted in this paper indicate that the flow restricted etching method provides sufficient references for the research and understanding on the mass transport at the liquid-liquid surface in the microchannel and can be used to pattern complex micro structures with high aspect ratios, meantime, it greatly enriches the microfabrication technology for microfluidic chips.
With the development of analytical instrumentation to minimization, integration and automation, the microfluidic chips, which are more integrated, complex and diversified, have been applied widely on the manufacturing of analytical instrumentation. However, the present photolithography-based microfabrication technology, which is only able to pattern microchannels with simple inside structures, can not follow the rapid development of requirements. For solving the problem, a fabrication method based on the restricting effect of laminar flow is proposed for the micro etching on isotropic substrates. Experiments were conducted inside glass-based microchannels, in which certain etchant was used to form complicated microstructures. The flow parameters effects on the aspect ratio, side wall profile and etching rate were revealed by the experiments. The experimental results reveal that the topography of micro structures patterned with the restricted flow etching method is mainly determined by the flowrates of separator and etchant. The computational fluid dynamics(CFD) model on the interface between multiple streams was established for the etching process, and analysis on the causes of various micro topographies was conducted based on the CFD simulation results. The experimental data consisted with the simulation results very well. The investigation depicted in this paper indicate that the flow restricted etching method provides sufficient references for the research and understanding on the mass transport at the liquid-liquid surface in the microchannel and can be used to pattern complex micro structures with high aspect ratios, meantime, it greatly enriches the microfabrication technology for microfluidic chips.
2010, 24(5).
Abstract:
In dealing with abrasive waterjet machining(AWJM) simulation, most literatures apply finite element method(FEM) to build pure waterjet models or single abrasive particle erosion models. To overcome the mesh distortion caused by large deformation using FEM and to consider the effects of both water and abrasive, the smoothed particle hydrodynamics(SPH) coupled FEM modeling for AWJM simulation is presented, in which the abrasive waterjet is modeled by SPH particles and the target material is modeled by FEM. The two parts interact through contact algorithm. Utilizing this model, abrasive waterjet with high velocity penetrating the target materials is simulated and the mechanism of erosion is depicted. The relationships between the depth of penetration and jet parameters, including water pressure and traverse speed, etc, are analyzed based on the simulation. The simulation results agree well with the existed experimental data. The mixing multi-materials SPH particles, which contain abrasive and water, are adopted by means of the randomized algorithm and material model for the abrasive is presented. The study will not only provide a new powerful tool for the simulation of abrasive waterjet machining, but also be beneficial to understand its cutting mechanism and optimize the operating parameters.
In dealing with abrasive waterjet machining(AWJM) simulation, most literatures apply finite element method(FEM) to build pure waterjet models or single abrasive particle erosion models. To overcome the mesh distortion caused by large deformation using FEM and to consider the effects of both water and abrasive, the smoothed particle hydrodynamics(SPH) coupled FEM modeling for AWJM simulation is presented, in which the abrasive waterjet is modeled by SPH particles and the target material is modeled by FEM. The two parts interact through contact algorithm. Utilizing this model, abrasive waterjet with high velocity penetrating the target materials is simulated and the mechanism of erosion is depicted. The relationships between the depth of penetration and jet parameters, including water pressure and traverse speed, etc, are analyzed based on the simulation. The simulation results agree well with the existed experimental data. The mixing multi-materials SPH particles, which contain abrasive and water, are adopted by means of the randomized algorithm and material model for the abrasive is presented. The study will not only provide a new powerful tool for the simulation of abrasive waterjet machining, but also be beneficial to understand its cutting mechanism and optimize the operating parameters.
2010, 24(5).
Abstract:
Structural vibration control was an active research area for the past twenty years because of their potential applications in aerospace structures, civil structures, naval structures, etc. Semi-active vibration control methods based on piezoelectric actuators and synchronized switch damping on inductance(SSDI) techniques attract the attention of many researchers recently due to their advantages over passive and active methods. In the SSDI method, a switch shunt circuit is connected to the piezoelectric patch to shift the phase and amplify the magnitude of the voltage on the piezoelectric patch. The most important issue in SSDI method is to control the switching actions synchronously with the maximum vibration displacement or maximum strain. Hence, usually a displacement sensor is used to measure the vibration displacement or a collocated piezoelectric sensor is needed to measure the strain of the structure near the piezoelectric actuator. A self-sensing SSDI approach is proposed and applied to the vibration control of a composite beam, which avoids using a separate sensor. In the self-sensing technique, the same piezoelectric element functions as both a sensor and an actuator so that the total number of required piezoelectric elements can be reduced. One problem in the self-sensing actuator, which is the same as that in the traditional collocated piezoelectric sensors, is the noise generated in the sensor signal by the impact of voltage inversion, which may cause extra switching actions and deteriorate control performance. In order to prevent the shunt circuit from over-frequent on-and-off actions, a simple switch control algorithm is proposed. The results of control experiments show that the self-sensing SSDI approach combined with the improved switch control algorithm can effectively suppress over-frequent switching actions and gives good control performance by reducing the vibration amplitude by 45%, about 50% improvement from the traditional SSDI with a separate piezoelectric element and a classical switch.
Structural vibration control was an active research area for the past twenty years because of their potential applications in aerospace structures, civil structures, naval structures, etc. Semi-active vibration control methods based on piezoelectric actuators and synchronized switch damping on inductance(SSDI) techniques attract the attention of many researchers recently due to their advantages over passive and active methods. In the SSDI method, a switch shunt circuit is connected to the piezoelectric patch to shift the phase and amplify the magnitude of the voltage on the piezoelectric patch. The most important issue in SSDI method is to control the switching actions synchronously with the maximum vibration displacement or maximum strain. Hence, usually a displacement sensor is used to measure the vibration displacement or a collocated piezoelectric sensor is needed to measure the strain of the structure near the piezoelectric actuator. A self-sensing SSDI approach is proposed and applied to the vibration control of a composite beam, which avoids using a separate sensor. In the self-sensing technique, the same piezoelectric element functions as both a sensor and an actuator so that the total number of required piezoelectric elements can be reduced. One problem in the self-sensing actuator, which is the same as that in the traditional collocated piezoelectric sensors, is the noise generated in the sensor signal by the impact of voltage inversion, which may cause extra switching actions and deteriorate control performance. In order to prevent the shunt circuit from over-frequent on-and-off actions, a simple switch control algorithm is proposed. The results of control experiments show that the self-sensing SSDI approach combined with the improved switch control algorithm can effectively suppress over-frequent switching actions and gives good control performance by reducing the vibration amplitude by 45%, about 50% improvement from the traditional SSDI with a separate piezoelectric element and a classical switch.
2010, 24(5).
Abstract:
Finger seal is a new technology developed for gas path sealing in gas turbine engine. It has been paid attention to its good sealing performance and lower manufacture cost. The vibration behavior of finger seal is not be considered in performance analysis for the contact finger seal with compliant geometric configuration, then this will influence the reliability of the performance analysis and the parametric design of a finger seal. According to the dynamic character of finger seal, the harmonic vibration and free vibration models of a repetitive section of a two-layer finger seal that contains one high and one low finger seal are established separately. The dynamic behavior of finger seal in different working conditions is obtained based on the dynamic response analysis of finger’s vibrations. The dynamic low hysteresis and low wear terms based on the equivalent dynamic model of finger seal are put forward, which can be used to predict the dynamic behavior of finger seal. As an example, the dynamic behaviors of an 8-layer finger seal and a 10-layer finger seal were predicted, and the validity of the prediction was demonstrated by the leakage test results of these two finger seals. The work presented here not only could make the dynamic analysis of finger seal with complicated structure simple and easy especially for multi-layer finger seal system, but also suggest a useful method for designing the finger seal with good dynamic behavior by means of different seal layers assembly.
Finger seal is a new technology developed for gas path sealing in gas turbine engine. It has been paid attention to its good sealing performance and lower manufacture cost. The vibration behavior of finger seal is not be considered in performance analysis for the contact finger seal with compliant geometric configuration, then this will influence the reliability of the performance analysis and the parametric design of a finger seal. According to the dynamic character of finger seal, the harmonic vibration and free vibration models of a repetitive section of a two-layer finger seal that contains one high and one low finger seal are established separately. The dynamic behavior of finger seal in different working conditions is obtained based on the dynamic response analysis of finger’s vibrations. The dynamic low hysteresis and low wear terms based on the equivalent dynamic model of finger seal are put forward, which can be used to predict the dynamic behavior of finger seal. As an example, the dynamic behaviors of an 8-layer finger seal and a 10-layer finger seal were predicted, and the validity of the prediction was demonstrated by the leakage test results of these two finger seals. The work presented here not only could make the dynamic analysis of finger seal with complicated structure simple and easy especially for multi-layer finger seal system, but also suggest a useful method for designing the finger seal with good dynamic behavior by means of different seal layers assembly.
2010, 24(5).
Abstract:
Vacuum die casting is the optimal method to produce high quality aluminum alloy components. At present, there are still very few systematic studies on vacuum die casting theory and equipment design. On the basis of the existing theories of the vacuum die casting pumping and venting systems, a simplified model is established in this research. The model has an aggregate unit consisted of “vacuum pump buffer tank” and a cylindrical container (including the shot sleeve, cavity and exhaust channel). The theoretical analysis is carried out between the cavity pressure and the pumping time under different volume models. An auxiliary system for high vacuum die casting is designed based on the above analysis. This system is composed of a vacuum control machine and a new vacuum stop valve. The machine has a human-computer control mode with “programmable logic controller(PLC) touch screen” and a real-time monitoring function of vacuum degree for buffer tank and die cavity. The vacuum stop valve with the “compressed gas piston rod labyrinth groove” structure can realize the function of whole-process vacuum venting. The new system shows great advantages on vacuuming the cavity with a much faster speed by making tests on an existing die casting mold and a 250 t die casting machine. A die cavity pressure less than 10 kPa can be reached within 0.8 s in the experiment and the porosity of castings can be greatly decreased. The systematic studies on vacuum die casting theory and equipment have a great guiding significance for high vacuum die casting, and can also be applied to other high vacuum forming in related theoretical and practical research.
Vacuum die casting is the optimal method to produce high quality aluminum alloy components. At present, there are still very few systematic studies on vacuum die casting theory and equipment design. On the basis of the existing theories of the vacuum die casting pumping and venting systems, a simplified model is established in this research. The model has an aggregate unit consisted of “vacuum pump buffer tank” and a cylindrical container (including the shot sleeve, cavity and exhaust channel). The theoretical analysis is carried out between the cavity pressure and the pumping time under different volume models. An auxiliary system for high vacuum die casting is designed based on the above analysis. This system is composed of a vacuum control machine and a new vacuum stop valve. The machine has a human-computer control mode with “programmable logic controller(PLC) touch screen” and a real-time monitoring function of vacuum degree for buffer tank and die cavity. The vacuum stop valve with the “compressed gas piston rod labyrinth groove” structure can realize the function of whole-process vacuum venting. The new system shows great advantages on vacuuming the cavity with a much faster speed by making tests on an existing die casting mold and a 250 t die casting machine. A die cavity pressure less than 10 kPa can be reached within 0.8 s in the experiment and the porosity of castings can be greatly decreased. The systematic studies on vacuum die casting theory and equipment have a great guiding significance for high vacuum die casting, and can also be applied to other high vacuum forming in related theoretical and practical research.
2010, 24(5).
Abstract:
As the dynamic equations of space robots are highly nonlinear, strongly coupled and nonholonomic constrained, the efficiency of current dynamic modeling algorithms is difficult to meet the requirements of real-time simulation. This paper combines an efficient spatial operator algebra(SOA) algorithm for base fixed robots with the conservation of linear and angular momentum theory to establish dynamic equations for the free-floating space robot, and analyzes the influence to the base body’s position and posture when the manipulator is capturing a target. The recursive Newton-Euler kinematic equations on screw form for the space robot are derived, and the techniques of the sequential filtering and smoothing methods in optimal estimation theory are used to derive an innovation factorization and inverse of the generalized mass matrix which immediately achieve high computational efficiency. The high efficient SOA algorithm is spatially recursive and has a simple math expression and a clear physical understanding, and its computational complexity grows only linearly with the number of degrees of freedom. Finally, a space robot with three degrees of freedom manipulator is simulated in Matematica 6.0. Compared with ADAMS, the simulation reveals that the SOA algorithm is much more efficient to solve the forward and inverse dynamic problems. As a result, the requirements of real-time simulation for dynamics of free-floating space robot are solved and a new analytic modeling system is established for free-floating space robot.
As the dynamic equations of space robots are highly nonlinear, strongly coupled and nonholonomic constrained, the efficiency of current dynamic modeling algorithms is difficult to meet the requirements of real-time simulation. This paper combines an efficient spatial operator algebra(SOA) algorithm for base fixed robots with the conservation of linear and angular momentum theory to establish dynamic equations for the free-floating space robot, and analyzes the influence to the base body’s position and posture when the manipulator is capturing a target. The recursive Newton-Euler kinematic equations on screw form for the space robot are derived, and the techniques of the sequential filtering and smoothing methods in optimal estimation theory are used to derive an innovation factorization and inverse of the generalized mass matrix which immediately achieve high computational efficiency. The high efficient SOA algorithm is spatially recursive and has a simple math expression and a clear physical understanding, and its computational complexity grows only linearly with the number of degrees of freedom. Finally, a space robot with three degrees of freedom manipulator is simulated in Matematica 6.0. Compared with ADAMS, the simulation reveals that the SOA algorithm is much more efficient to solve the forward and inverse dynamic problems. As a result, the requirements of real-time simulation for dynamics of free-floating space robot are solved and a new analytic modeling system is established for free-floating space robot.
2010, 24(5).
Abstract:
For the constant distance spacing policy, the existing researches of the string stability focus on the single-predecessor information framework(SPIF) and predecessor-successor information framework(PSIF). The research results demonstrated that the string stability could not be guaranteed with the SPIF, and then the PSIF was proposed to resolve this string instability. But the issue, whether the string stability can be guaranteed when applying the PSIF, is still controversial. Meanwhile, most of the previous researches on the string stability were conducted without consideration of the parasitic time delays and lags. In this paper, the practical longitudinal vehicle dynamics model is built with consideration of the parasitic time delays and lags existing in the actuators, sensors or the communication systems. Secondly, the detailed theoretical analysis of string stability in frequency domain is conducted to demonstrate that the classical linear control laws can not ensure the string stability when applying both the symmetrical PSIF(SPSIF) and asymmetrical PSIF(APSIF). Thirdly, a control law, which adds the position and velocity information of the leading vehicle, is proposed to guarantee string stability for small/medium platoon, and the other control law, which adds the acceleration information of the controlled vehicle, is proposed to guarantee string stability for large platoon as well as small/medium platoon. Finally, the comparative simulation is conducted to confirm the conducted analysis and the proposed control laws. The conducted research completes the means to analyze the string stability in frequency domain, provides the parameters’ reference for the design and implementation of the practical automatic following controllers, and improves the reliability and stability of the platoon of automatic vehicles.
For the constant distance spacing policy, the existing researches of the string stability focus on the single-predecessor information framework(SPIF) and predecessor-successor information framework(PSIF). The research results demonstrated that the string stability could not be guaranteed with the SPIF, and then the PSIF was proposed to resolve this string instability. But the issue, whether the string stability can be guaranteed when applying the PSIF, is still controversial. Meanwhile, most of the previous researches on the string stability were conducted without consideration of the parasitic time delays and lags. In this paper, the practical longitudinal vehicle dynamics model is built with consideration of the parasitic time delays and lags existing in the actuators, sensors or the communication systems. Secondly, the detailed theoretical analysis of string stability in frequency domain is conducted to demonstrate that the classical linear control laws can not ensure the string stability when applying both the symmetrical PSIF(SPSIF) and asymmetrical PSIF(APSIF). Thirdly, a control law, which adds the position and velocity information of the leading vehicle, is proposed to guarantee string stability for small/medium platoon, and the other control law, which adds the acceleration information of the controlled vehicle, is proposed to guarantee string stability for large platoon as well as small/medium platoon. Finally, the comparative simulation is conducted to confirm the conducted analysis and the proposed control laws. The conducted research completes the means to analyze the string stability in frequency domain, provides the parameters’ reference for the design and implementation of the practical automatic following controllers, and improves the reliability and stability of the platoon of automatic vehicles.
2010, 24(5).
Abstract:
The performance of the vehicle dynamics stability control system(DSC) is dominated by the accurate estimation of tire forces in real-time. The characteristics of tire forces are determined by tire dynamic states and parameters, which vary in an obviously large scope along with different working conditions. Currently, there have been many methods based on the nonlinear observer to estimate the tire force and dynamic parameters, but they were only used in off-line analysis because of the computation complexity and the dynamics differences of four tires in the steering maneuver conditions were not considered properly. This paper develops a novel algorithm to observe tire parameters in real-time controller for DSC. The algorithm is based on the sensor-fusion technology with the signals of DSC sensors, and the tire parameters are estimated during a set of maneuver courses. The calibrated tire parameters in the control cycle are treated as the elementary states for vehicle dynamics observation, in which the errors between the calculated and the measured vehicle dynamics are used as the correcting factors for the tire parameter observing process. The test process with a given acceleration following a straight line is used to validate the estimation method of the longitudinal stiffness; while the test process with a given steering angle is used to validate the estimated value of the cornering stiffness. The ground test result shows that the proposed algorithm can estimate the tire stiffness accurately with an acceptable computation cost for real-time controller only using DSC sensor signal. The proposed algorithm can be an efficient algorithm for estimating the tire dynamic parameters in vehicle dynamics stability control system, and can be used to improve the robustness of the DSC controller.
The performance of the vehicle dynamics stability control system(DSC) is dominated by the accurate estimation of tire forces in real-time. The characteristics of tire forces are determined by tire dynamic states and parameters, which vary in an obviously large scope along with different working conditions. Currently, there have been many methods based on the nonlinear observer to estimate the tire force and dynamic parameters, but they were only used in off-line analysis because of the computation complexity and the dynamics differences of four tires in the steering maneuver conditions were not considered properly. This paper develops a novel algorithm to observe tire parameters in real-time controller for DSC. The algorithm is based on the sensor-fusion technology with the signals of DSC sensors, and the tire parameters are estimated during a set of maneuver courses. The calibrated tire parameters in the control cycle are treated as the elementary states for vehicle dynamics observation, in which the errors between the calculated and the measured vehicle dynamics are used as the correcting factors for the tire parameter observing process. The test process with a given acceleration following a straight line is used to validate the estimation method of the longitudinal stiffness; while the test process with a given steering angle is used to validate the estimated value of the cornering stiffness. The ground test result shows that the proposed algorithm can estimate the tire stiffness accurately with an acceptable computation cost for real-time controller only using DSC sensor signal. The proposed algorithm can be an efficient algorithm for estimating the tire dynamic parameters in vehicle dynamics stability control system, and can be used to improve the robustness of the DSC controller.
E-mail Alerts
