2012 Vol.25(4)

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Global Optimization Method Using SLE and Adaptive RBF Based on Fuzzy Clustering
2012, 26(4).
[Abstract](2510) [PDF 482KB](117)
Abstract:
High fidelity analysis models, which are beneficial to improving the design quality, have been more and more widely utilized in the modern engineering design optimization problems. However, the high fidelity analysis models are so computationally expensive that the time required in design optimization is usually unacceptable. In order to improve the efficiency of optimization involving high fidelity analysis models, the optimization efficiency can be upgraded through applying surrogates to approximate the computationally expensive models, which can greately reduce the computation time. An efficient heuristic global optimization method using adaptive radial basis function (RBF) based on fuzzy clustering (ARFC) is proposed. In this method, a novel algorithm of maximin Latin hypercube design using successive local enumeration (SLE) is employed to obtain sample points with good performance in both space-filling and projective uniformity properties, which does a great deal of good to metamodels accuracy. RBF method is adopted for constructing the metamodels, and with the increasing the number of sample points the approximation accuracy of RBF is gradually enhanced. The fuzzy c-means clustering method is applied to identify the reduced attractive regions in the original design space. The numerical benchmark examples are used for validating the performance of ARFC. The results demonstrates that for most application examples the global optima are effectively obtained and comparison with adaptive response surface method (ARSM) proves that the proposed method can intuitively capture promising design regions and can efficiently identify the global or near-global design optimum. This method improves the efficiency and global convergence of the optimization problems, and gives a new optimization strategy for engineering design optimization problems involving computationally expensive models.
Reconstruction of Emission Coefficients for a Non-axisymmetric Coupling Arc Based on MALDONADOs Method
2012, 26(4).
[Abstract](2481) [PDF 497KB](135)
Abstract:
The reconstruction of emission coefficient is a key factor for the calculation of temperature field. However, most of the researches for determining arc plasmas are based on axisymmetric sources, little has been done to study non-axisymmetric arc plasmas. In order to reveal temperatures of a non-axisymmetric coupling arc, the distribution of emission coefficients must be reconstructed in advance. In this paper, the argon atomic line intensities of the coupling arc are obtained by using the imaging system that involves a high speed camera in conjunction with a neutral and a narrow-band filter. The converted programme between emission coefficients and emitted intensities is programmed based on MALDONADO’s method. A displaced Gaussian model is used for evaluating the validity of the converted programme. Then, the emission coefficients of a free burning arc are reconstructed by MALDONADO’s method and an Abel inversion, respectively, and good agreement is obtained. Finally, the emission coefficient profiles of the coupling arc are achieved. The results show that the distribution of emission coefficient for the coupling arc is non-axisymmetric. The emission coefficient profile is similar to an ellipse, and the short axis of the ellipse is in the direction that the two electrodes are arranged along. The peak temperature of the coupling arc is in the middle of both electrodes. There is a strong interaction between both arcs within the coupling arc. The proposed research solves difficulties for determining asymmetric arcs and enlarges the application scope of spectroscopic techniques.
Non-linear Torsional Vibration Characteristics of an Internal Combustion Engine Crankshaft Assembly
2012, 26(4).
[Abstract](2234) [PDF 1052KB](150)
Abstract:
Crankshaft assembly failure is one of the main factors that affects the reliability and service life of engines. The linear lumped mass method, which has been universally applied to the dynamic modeling of engine crankshaft assembly, reveals obvious simulation errors. The nonlinear dynamic characteristics of a crankshaft assembly are instructionally significant to the improvement of modeling correctness. In this paper, a general expression for the non-constant inertia of a crankshaft assembly is derived based on the instantaneous kinetic energy equivalence method. The nonlinear dynamic equations of a multi-cylinder crankshaft assembly are established using the Lagrange rule considering nonlinear factors such as the non-constant inertia of reciprocating components and the structural damping of shaft segments. The natural frequency and mode shapes of a crankshaft assembly are investigated employing the eigenvector method. The forced vibration response of a diesel engine crankshaft assembly taking into account the non-constant inertia is studied using the numerical integral method. The simulation results are compared with a lumped mass model and a detailed model using the system matrix method. Results of non-linear torsional vibration analysis indicate that the additional excitation torque created by non-constant inertia activates the 2nd order rolling vibration, and the additional damping torque resulting from the non-constant inertia is the main nonlinear factor. The increased torsional angular displacement evoked by the high order excitation torque relates to the non-constant inertia. This research project is aimed at improving nonlinear dynamics theory, and the confirmed nonlinear parameters can be used for the structure design of a crankshaft assembly.
Tool Wear in Turning of Titanium Alloy after Thermohydrogen Treatment
2012, 26(4).
[Abstract](2248) [PDF 467KB](290)
Abstract:
The influence of hydrogen contents on the tool wear has been mainly focused on the flank wear of the common tool, and the influence of hydrogen contents on the rake crater wear (main wear type) of the tool, particularly for the fine granular material tool, has been less investigated comprehensively. In this paper, for the purpose of researching the influence of hydrogen contents on tool wear, the titanium alloy Ti-6Al-4V is hydrogenated at 800 ℃ by thermohydrogen treatment technology and the turning experiments are carried out by applying uncoated WC-Co cemented carbide tool. The three-dimensional video microscope is used to take photos and measure tool wear. The results show that both of crater wear depth (KT) and average flank wear width (VB) firstly decreases and then increases with the increasing of hydrogen content. The maximum reducing amplitude of KT and VB is about 50% and 55%, respectively. Under the given conditions, the optimum hydrogen content is 0.26%. It is considered that the reduction of cutting temperature is an important factor for improving tool wear after the Ti-6Al-4V alloy is properly hydrogenated. Furthermore, the reasons of hydrogen effect on the tool wear are chiefly attributed to comprehensive effect of hydrogen contents on microstructure, physical properties and dynamic mechanical properties of the Ti-6Al-4V alloy. The proposed research provides the basic data for evaluating the machinability of hydrogenation Ti-6Al-4V alloy, and promotes practical application of thermohydrogen treatment technology in titanium alloys.
Flow Behaviour Analysis and Experimental Investigation for Emitter Micro-channels
2012, 26(4).
[Abstract](2274) [PDF 924KB](271)
Abstract:
The existing research of the flow behavior in emitter micro-channels mainly focuses on the single-phase flow behavior. And the recent micro-particle image velocimetry (PIV) experimental research on the flow characteristics in various micro-channels mainly focuses on the single-phase fluid flow. However, using an original-size emitter prototype to perform the experiments on the two-phase flow characteristics of the labyrinth channels is seldom reported. In this paper, the practical flow of water, mixed with sand escaped from filtering, in the labyrinth channel, is investigated. And some research work on the clogging mechanism of the labyrinth channel’s structure is conducted. Computational fluid dynamics(CFD) analysis has been performed on liquid-solid two-phase flow in labyrinth- channel emitters. Based on flow visualization technology—micro-PIV, the flow in labyrinth channel has been photographed and recorded. The path line graph and velocity vector graph are obtained through the post-treatment of experimental results. The graphs agree well with CFD analysis results, so CFD analysis can be used in optimal design of labyrinth-channel emitters. And the optimized anti-clogging structures of the rectangular channel and zigzag channel have been designed here. The CFD numerical simulation and the micro-PIV experiments analysis on labyrinth-channel emitter, make the “black box” of the flow behavior in the emitter channel broken. Furthermore, the proposed research promotes an advanced method to evaluate the emitter’s performance and can be used to conducting the optimal design of the labyrinth-channel emitters.
Influence of Deposition Temperature and Pressure on Microstructure and Tribological Properties of Arc Ion Plated Ag Films
2012, 26(4).
[Abstract](2279) [PDF 579KB](90)
Abstract:
The films deposited at low temperature (LT-films) have increasingly attracted theoretical and technical interests since such films exhibit obvious difference in structure and performances compared to those deposited at room temperature. Studies on the tribological properties of LT-films are rarely reported in available literatures. In this paper, the structure, morphology and tribological properties of Ag films, deposited at LT (166 K) under various Ar pressures on AISI 440C steel substrates by arc ion plating (AIP), are studied by X-ray diffraction (XRD), atomic force microscopy (AFM) and a vacuum ball-on-disk tribometer, and compared with the Ag films deposited at RT (300 K). XRD results show that (200) preferred orientation of the films is promoted at LT and low Ar pressure. The Crystallite sizes are 70 nm–80 nm for LT-Ag films deposited at 0.2 Pa and 0.8 Pa and larger than 100 nm for LT-Ag films deposited at 0.4 Pa and 0.6 Pa, while they are 55 nm–60 nm for RT-Ag films deposited at 0.2 Pa–0.6 Pa and 37 nm for RT-Ag films deposited at 0.8 Pa. The surfaces of LT-Ag films are fibre-like at 0.6 Pa and 0.8 Pa, terrace-like at 0.4 Pa, and sphere-like at 0.2 Pa, while the surfaces of RT-Ag films are composed of sphere-like grains separated by voids. Wear tests reveal that, due to the compact microstructure LT-Ag films have better wear resistances than RT-Ag film. These results indicate that the microstructure and wear resistance of Ag films deposited by AIP can be improved by low temperature deposition.
Psychoacoustic Study on Contribution of Fan Noise to Engine Noise
2012, 26(4).
[Abstract](2238) [PDF 452KB](101)
Abstract:
There are more researches on engine fan noise control focusing on reducing fan noise level through optimizing fan structure, and a lot of research achievements have been obtained. However, researches on the effect of fan noise to engine noise quality are lacking. The influences of the effects of fan structure optimization on the engine noise quality are unclear. Thus, there will be a decline in fan noise level, but the deterioration of engine noise quality. Aiming at the above problems, in consideration of fan structure design and engine noise quality, an innovative method to analyze the contribution of fan noise to engine noise quality using psychoacoustic theory is proposed. The noises of diesel engine installing different cooling fans are measured by using the acoustic pressure method. The experiment results are regarded as analysis samples. The model of sensory pleasantness is used to analyze the sound quality of a diesel engine with different cooling fans. Results show that after installing 10-blade fan in medium diameter the sensory pleasantness at each test point is increased, and the increase is 13.53% on average, which indicate the improvement of the engine noise quality. In order to verify the psychoacoustical analysis, the subjective assessment is carried out. The test result shows the noise quality of engine installed10-blade fan in medium diameter is most superior. 13 octave frequency spectrum analysis is used to study the reason of the improvement of engine noise quality. It is found that after installing proper cooling fan the sound pressure level below 400 Hz are obviously increased, the frequency assignment and spectral envelope are more reasonable and a proper cooling fan can optimize the spectrum structure of the engine noise. The psychoacoustic study is applied in the contribution of fan noise to engine noise, and the idea of engine sound quality improvement through the structure optimization is proposed.
Exact Solutions for Piezoelectric Materials with an Elliptic Hole or a Crack under Uniform Internal Pressure
2012, 26(4).
[Abstract](2286) [PDF 457KB](167)
Abstract:
The existing investigations on piezoelectric materials containing an elliptic hole or a crack mainly focus on remote uniform tensile loads. In order to have a better understanding for the fracture behavior of piezoelectric materials under different loading conditions, theoretical and numerical solutions are presented for an elliptic hole or a crack in transversely isotropic piezoelectric materials subjected to uniform internal pressure and remote electro-mechanical loads. On the basis of the complex variable approach, analytical solutions of the elastic and electric fields inside and outside the defect are derived by satisfying permeable electric boundary condition at the surface of the elliptical hole. As an example of PZT-4 ceramics, numerical results of electro-elastic fields inside and outside the crack under various electric boundary conditions and electro-mechanical loads are given, and graphs of the electro-elastic fields in the vicinity of the crack tip are presented. The non-singular term is compared to the asymptotic one in the figures. It is shown that the dielectric constant of the air in the crack has no effect on the electric displacement component perpendicular to the crack, and the stresses in the piezoelectric material depend on the material properties and the mechanical loads on the crack surface and at infinity, but not on the electric loads at infinity. The figures obtained are strikingly similar to the available results. Unlike the existing work, the existence of electric fields inside an elliptic hole or a crack is considered, and the piezoelectric solid is subjected to complicated electro-mechanical loads.
Design and Dynamic Modeling of a 2-DOF Decoupled Flexure-Based Mechanism
2012, 26(4).
[Abstract](2272) [PDF 684KB](254)
Abstract:
Flexure mechanisms with decoupled characteristics have been widely utilized in precision positioning applications. However, these mechanisms suffer from either slow response or low load capability. Furthermore, asymmetric design always leads to thermal error. In order to solve these issues, a novel 2-DOF decoupled mechanism is developed by monolithically manufacturing sets of statically indeterminate symmetric (SIS) flexure structures in parallel. Symmetric design helps to eliminate the thermal error and Finite Element Analysis (FEA) results show that the maximum coupling ratio between X and Y axes is below 0.25% when a maximum pretension force of 200 N is applied. By ignoring the mass effect, all the SIS flexure structures are simplified to “spring-damper” components, from which the static and dynamics model are derived. The relation between the first resonant frequency of the mechanism and the load is investigated by incorporating the load mass into the proposed dynamics model. Analytical results show that even with a load of 0.5 kg, the first resonant frequency is still higher than 300 Hz, indicating a high load capability. The mechanism’s static and dynamic performances are experimentally examined. The linear stiffnesses of the mechanism at the working platform and at the driving point are measured to be 3.563 0 N•μm–1 and 3.362 1 N•μm–1, respectively. The corresponding estimation values from analytical models are 3.405 7 N•μm–1 and 3.381 7 N•μm–1, which correspond to estimation errors of –4.41% and 0.6%, respectively. With an additional load of 0.16 kg, the measured and estimated first resonant frequencies are 362 Hz and 365 Hz, respectively. The estimation error is only 0.55%. The analytical and experimental results show that the developed mechanism has good performances in both decoupling ability and load capability; its static and dynamic performance can be precisely estimated from corresponding analytical models. The proposed mechanism has wide potentials in precision positioning applications.
Reciprocal Screw Theory Based Singularity Analysis of a Novel 3-DOF Parallel Manipulator
2012, 26(4).
[Abstract](2283) [PDF 521KB](158)
Abstract:
Singularity analysis is an essential issue for the development and application of parallel manipulators. Most of the existing researches focus on the singularity of parallel manipulators are carried out based on the study of Jacobian matrices. A 3-DOF parallel manipulator with symmetrical structure is presented. The novel parallel manipulator employs only revolute joints and consists of four closed-loop subchains connecting to both base and platform via revolute joints. The closed-loop subchain in each chain-leg is a spherical 6R linkage. The motion characteristics of the output link in the spherical 6R linkage with symmetrical structure are analyzed based on the interrelationships between screw systems. The constraints that are exerted on the platform by each chain-leg are investigated applying the concept of generalized kinematic pair in terms of equivalent screw system. Considering the geometric characteristics of the parallel manipulator, the singularity criteria of the parallel manipulator corresponding to different configurations are revealed based on the dependency of screw system and line geometry. The existing conditions of certain configuration that a singularity must occur are determined. This paper presents a new way of singularity analysis based on disposition of constraint forces on the geometrically identified constraint plane and the proposed approach is capable of avoiding the complexity in solving the Jacobian matrices.
Effect of Oxygenates Blending with Gasoline to Improve Fuel Properties
2012, 26(4).
[Abstract](2276) [PDF 425KB](230)
Abstract:
The purpose of this paper is to study the effect of oxygenate additives into gasoline for the improvement of physicochemical properties of blends. Methyl Tertiary Butyl Ether (MTBE), Methanol, Tertiary butyl alcohol (TBA), and Tertiary amyl alcohol (TAA) blend into unleaded gasoline with various blended rates of 2.5%, 5%, 7.5%, 10%, 15%, and 20%. Physicochemical properties of blends are analyzed by the standard American Society of Testing and Materials (ASTM) methods. Methanol, TBA, and TAA increase density of the mixtures, but MTBE decreases density. The addition of oxygenates lead to a distortion of the base gasoline’s distillation curves. The Reid vapor pressure (RVP) of gasoline is found to increase with the addition of the oxygenated compounds. All oxygenates improve both motor and research octane numbers. Among these four additives, TBA shows the best fuel properties.
Performances of a Balanced Hydraulic Motor with Planetary Gear Train
2012, 26(4).
[Abstract](2256) [PDF 536KB](92)
Abstract:
The current research of a balanced hydraulic motor focuses on the characteristics of the motor with three planet gears. References of a balanced hydraulic motor with more than three planet gears are hardly found. In order to study the characteristics of a balanced hydraulic motor with planetary gear train that includes more than three planet gears, on the basis of analysis of the structure and working principle of a balanced hydraulic motor with planetary gear train, formulas are deduced for calculating the hydraulic motor’s primary performance indexes such as displacement, unit volume displacement, flowrate fluctuation ratio, etc. Influences of the gears’ tooth number on displacement and flowrate characteristics are analyzed. In order to guarantee the reliability of sealing capability, the necessary conditions that tooth number of the sun gear and the planet gears should satisfy are discussed. Selecting large unit volume displacement and small displacement fluctuation ratio as designing objectives, a balanced hydraulic motor with three planet gears and a common gear motor are designed under the conditions of same displacement, tooth addendum coefficien and clearance coefficient. By comparing the unit volume displacement and fluctuation ratio of the two motors, it can be seen that the balanced hydraulic motor with planetary gear train has the advantages of smaller fluctuation ratio and larger unit volume displacement. The results provide theoretical basis for choosing gear tooth-number of this kind of hydraulic motor.
Single-phase Computational Fluid Dynamics Applicability for the Study of Three-dimensional Flow in 5 5 Rod Bundles with Spacer Grids
2012, 26(4).
[Abstract](2244) [PDF 900KB](98)
Abstract:
Spacer grids play an important role in pressurized water reactor (PWR) fuel assembly in that they have significant influence on the thermal-hydraulic characteristics of the reactor core. But so far, the numerical studies are performed without regarding dimple and spring of spacer grids, just considering mixing vane. Moreover, these studies use k–ε turbulence model without considering the suitability of the other turbulence models upon the different spacer grids flow. A study is carried out to understand the 3-D single-phase flow in AFA-2G 5×5 rod bundles with spacer grids based on numerical method. In order to investigate the suitability of different turbulence models, k–ε model and k–ω model, the influence of different parts of spacer grid on the fluid flow is also predicted. By using second-order upwind scheme, hybrid grids technique, and improved SIMPLEC algorithm, the Reynolds averaged mass conservation and momentum conservation equations are solved, and the pressure and velocity field of flow are obtained. The numerical simulation results are compared with experiment results and the agreement is satisfactory. The simulation results show the influences of the spring, dimple and mixing vane, and the different characteristics of the k–ε model and k–ω model. Comparing with the experiment results, the simulation results suggest that the k–ω model is suitable for the simulation of the rod bundle flow with spacer grids; the spring and dimple are the main causes of the pressure loss in the spacer grid channel. The friction coefficient of the channel with spring and dimple is 1.5 times the coefficient of the channel with the vane. These results are beneficial to enhance the simulation ability of spacer grids flow and optimization design ability of spaces grid.
Calculation and Analysis of Velocity and Viscous Drag in an Artery with a Periodic Pressure Gradient
2012, 26(4).
[Abstract](2288) [PDF 507KB](8)
Abstract:
Blood as a fluid that human and other living creatures are dependent on has been always considered by scientists and researchers. Any changes in blood pressure and its normal velocity can be a sign of a disease. Whatever significant in blood fluids mechanics is Constitutive equations and finding some relations for analysis and description of drag, velocity and periodic blood pressure in vessels. In this paper, by considering available experimental quantities, for blood pressure and velocity in periodic time of a thigh artery of a living dog, at first it is written into Fourier series, then by solving Navier-Stokes equations, a relation for curve drawing of vessel blood pressure with rigid wall is obtained. Likewise in another part of this paper, vessel wall is taken in to consideration that vessel wall is elastic and its pressure and velocity are written into complex Fourier series. In this case, by solving Navier-Stokes equations, some relations for blood velocity, viscous drag on vessel wall and blood pressure are obtained. In this study by noting that vessel diameter is almost is large (3.7 mm), and blood is considered as a Newtonian fluid. Finally, available experimental quantities of pressure with obtained curve of solving Navier-Stokes equations are compared. In blood analysis in rigid vessel, existence of 48% variance in pressure curve systole peak caused vessel blood flow analysis with elastic wall, results in new relations for blood flow description. The Resultant curve is obtained from new relations holding 10% variance in systole peak
Motion Error Compensation of Multi-legged Walking Robots
2012, 26(4).
[Abstract](2268) [PDF 667KB](70)
Abstract:
Existing errors in the structure and kinematic parameters of multi-legged walking robots, the motion trajectory of robot will diverge from the ideal sports requirements in movement. Since the existing error compensation is usually used for control compensation of manipulator arm, the error compensation of multi-legged robots has seldom been explored. In order to reduce the kinematic error of robots, a motion error compensation method based on the feedforward for multi-legged mobile robots is proposed to improve motion precision of a mobile robot. The locus error of a robot body is measured, when robot moves along a given track. Error of driven joint variables is obtained by error calculation model in terms of the locus error of robot body. Error value is used to compensate driven joint variables and modify control model of robot, which can drive the robots following control model modified. The model of the relation between robot’s locus errors and kinematic variables errors is set up to achieve the kinematic error compensation. On the basis of the inverse kinematics of a multi-legged walking robot, the relation between error of the motion trajectory and driven joint variables of robots is discussed. Moreover, the equation set is obtained, which expresses relation among error of driven joint variables, structure parameters and error of robot’s locus. Take MiniQuad as an example, when the robot MiniQuad moves following beeline tread, motion error compensation is studied. The actual locus errors of the robot body are measured before and after compensation in the test. According to the test, variations of the actual coordinate value of the robot centroid in x-direction and z-direction are reduced more than one time. The kinematic errors of robot body are reduced effectively by the use of the motion error compensation method based on the feedforward.
Needle Steering for Robot-Assisted Insertion into Soft Tissue: A Survey
2012, 26(4).
[Abstract](2356) [PDF 767KB](134)
Abstract:
Needle insertion is a common surgical procedure used in diagnosis and treatment. The needle steering technologies make continuous developments in theoretical and practical aspects along with the in-depth research on needle insertion. It is necessary to summarize and analyze the existing results to promote the future development of theories and applications of needle insertion. Thus, a survey of the state of the art of research is presented on algorithms of needle steering techniques, the surgical robots and devices. Based on the analysis of the needle insertion procedure, the concept of needle steering is defined as a kinematics problem, which is to place the needle at the target and avoid the obstacles. The needle steering techniques, including the artificial potential field method and the nonholonomic model, are introduced to control the needles for improving the accuracy. Based on the quasi-static thinking, the virtual spring model and the cantilever-beam model are developed to calculate the amount of needle deflection and generate the needle path. The phantoms instead of the real tissue are used to verify the models mentioned in most of the experimentations. For the desired needle trajectories, the image-guided robotic devices and some novel needles are presented to achieve the needle steering. Finally, the challenges are provided involving the controllability of the long flexible needle and the properties of soft tissue. The results and investigations can be used for further study on the precision and accuracy of needle insertion.
Coaxial Twin-shaft Magnetic Fluid Seals Applied in Vacuum Wafer-Handling Robot
2012, 26(4).
[Abstract](2341) [PDF 696KB](103)
Abstract:
Compared with traditional mechanical seals, magnetic fluid seals have unique characters of high airtightness, minimal friction torque requirements, pollution-free and long life-span, widely used in vacuum robots. With the rapid development of Integrate Circuit (IC), there is a stringent requirement for sealing wafer-handling robots when working in a vacuum environment. The parameters of magnetic fluid seals structure is very important in the vacuum robot design. This paper gives a magnetic fluid seal device for the robot. Firstly, the seal differential pressure formulas of magnetic fluid seal are deduced according to the theory of ferrohydrodynamics, which indicate that the magnetic field gradient in the sealing gap determines the seal capacity of magnetic fluid seal. Secondly, the magnetic analysis model of twin-shaft magnetic fluid seals structure is established. By analyzing the magnetic field distribution of dual magnetic fluid seal, the optimal value ranges of important parameters, including parameters of the permanent magnetic ring, the magnetic pole tooth, the outer shaft, the outer shaft sleeve and the axial relative position of two permanent magnetic rings, which affect the seal differential pressure, are obtained. A wafer-handling robot equipped with coaxial twin-shaft magnetic fluid rotary seals and bellows seal is devised and an optimized twin-shaft magnetic fluid seals experimental platform is built. Test result shows that when the speed of the two rotational shafts ranges from 0–500 rmin, the maximum burst pressure is about 0.24 MPa. Magnetic fluid rotary seals can provide satisfactory performance in the application of wafer-handling robot. The proposed coaxial twin-shaft magnetic fluid rotary seal provides the instruction to design high-speed vacuum robot.
Rarefaction and Temperature Gradient Effect on the Performance of the Knudsen Pump
2012, 26(4).
[Abstract](2324) [PDF 531KB](98)
Abstract:
The prediction of the multiscale flow in the Knudsen pump is important for understanding its pumping mechanism. However, there is little research on such interesting multiscale phenomenon in the Knudsen pumps. In this paper, a novel numerical analysis method combining the direct simulation Monte Carlo (DSMC) method with the smoothed particle hydrodynamics (SPH) method is presented for simulating the multiscale flow, which is often encountered in the application of the Knudsen pumps. Validity and accuracy of the new method are given by comparing its results with that of the previous research. Using the coupled multiscale approach, the rarefaction and the temperature drive are studied, which are two main factors on the performance of the Knudsen pumps. To investigate the effect of rarefaction on the performance of the Knudsen pump, various pump operation pressures are compared. The flow characteristics and pumping ability at different rarefaction are analyzed, and the phenomenon of the multiscale flow is also discussed. Several cases with different linear or nonlinear temperature gradients are set to investigate the effect of temperature gradient on the performance of the Knudsen pump. The flow characteristics of the Knudsen pump such as the velocity, pressure increase, and the mass flowrate are presented. A unique phenomenon, the reverse transpiration effect caused by the nonlinear temperature gradient is studied, and the reason of the significant pressure increase in the pump channel is also analyzed. Since the multiscale gas flow is widely encountered in the microflow systems, the above method and its results can also be greatly beneficial and provide significant insights for the design of the MEMS devices.
Selection of Machining Datum and Allocation of Tolerance through Tolerance Charting Technique
2012, 26(4).
[Abstract](2326) [PDF 701KB](86)
Abstract:
Tolerance charting is an effective tool to determine the optimal allocation of working dimensions and working tolerances such that the blueprint dimensions and tolerances can be achieved to accomplish the cost objectives. The selection of machining datum and allocation of tolerances are critical in any machining process planning as they directly affect any setup methods/machine tools selection and machining time. This paper mainly focuses on the selection of optimum machining datums and machining tolerances simultaneously in process planning. A dynamic tolerance charting constraint scheme is developed and implemented in the optimization procedure. An optimization model is formulated for selecting machining datum and tolerances and implemented with an algorithm namely Elitist Non-Dominated Sorting Genetic Algorithm (NSGA-II).The computational results indicate that the proposed methodology is capable and robust in finding the optimal machining datum set and tolerances.
Pinion Tooth Surface Generation Strategy of Spiral Bevel Gears
2012, 26(4).
[Abstract](2295) [PDF 615KB](89)
Abstract:
Aviation spiral bevel gears are often generated by spiral generated modified (SGM) roll method. In this style, pinion tooth surface modified generation strategy has an important influence on the meshing and contact performances. For the optimal contact pattern and transmission error function, local synthesis is applied to obtain the machine-tool settings of pinion. For digitized machine, four tooth surface generation styles of pinion are proposed. For every style, tooth contact analysis (TCA) is applied to obtain contact pattern and transmission error function. For the difference between TCA transmission error function and design objective curve, the degree of symmetry and agreement are defined and the corresponding sub-objective functions are established. Linear weighted combination method is applied to get an equivalent objective function to evaluate the shape of transmission error function. The computer programs for the process above are developed to analyze the meshing performances of the four pinion tooth surface generation styles for a pair of aviation spiral bevel gears with 38/43 teeth numbers. The four analytical results are compared with each other and show that the incomplete modified roll is optimal for this gear pair. This study is an expansion to generation strategy of spiral bevel gears, and offers new alternatives to computer numerical control (CNC) manufacture of spiral bevel gears.
Physical Characteristics of Welding Arc Ignition Process
2012, 26(4).
[Abstract](2290) [PDF 514KB](129)
Abstract:
The existing research of welding arc mainly focuses on the stable combustion state and the research on the mechanism of welding arc ignition process is quite lack. The tungsten inert gas(TIG) touch arc ignition process is observed via a high speed camera and the high time resolution spectral diagnosis system. The changing phenomenon of main ionized element provided the electrons in the arc ignition is found. The metallic element is the main contributor to provide the electrons at the beginning of the discharging, and then the excitated shielding gas element replaces the function of the metallic element. The electron density during the period of the arc ignition is calculated by the Stark-broadened lines of Hα. Through the discussion with the repeatability in relaxation phenomenon, the statistical regularity in the arc ignition process is analyzed. The similar rules as above are observed through the comparison with the laser-assisted arc ignition experiments and the metal inert gas(MIG) arc ignition experiments. This research is helpful to further understanding on the generation mechanism of welding arc ignition and also has a certain academic and practical significance on enriching the welding physical theoretical foundation and improving the precise monitoring on automatic arc welding process.
Novel Gas-tight Multi-sampler for Discrete Deep-sea Water
2012, 26(4).
[Abstract](2323) [PDF 885KB](174)
Abstract:
The issues of how to quickly collect seawater samples and of how to make sure that those samples truly reflect the in-situ information on gas composition and concentration have therefore become a hot but difficult topic in the field of ocean technology. Most conventional seawater samplers only focus on collecting seawater itself, but take little consideration on gas preservation. A set of new oceanographic tools are presented for ocean resource exploration such as hydrothermal sulfide and gas hydrate, and for investigations on the processes and mechanisms of marine physical, chemical and biological evolutions. A gas-tight deep-sea water sampling system (GTWSS) is designed for the collection of deep-sea geochemical samples. This set of tools mainly consists of a conductivity temperature depth profiler (CTD), release devices and gas-tight deep-sea water samplers (GTWS). The GTWS is able to hold the gases in deep-sea water samples tightly, providing in-situ information on gas contents in the seawater samples and can be deployed on a routine wire-deployed CTD sampler for multi-layer discrete sampling of gas-tight seawater. Sea trials are performed successfully in 2008 and 2009, on a research vessel named HaiYang Si Hao in South China Sea, with the deepest trial depth 3 930 m. GTWSS is capable of quickly sampling 12 discrete gas-tight seawater samples (8.3 L per sample) during its single deployment. The head space method is employed to separate the gases from the seawater samples immediately after recovery of the seawater samples on the vessel. Field geochemical analysis is carried out by gaseous hydrocarbon sensors and an infrared gas analyzer. Results show that the concentrations of CH4 and CO2 in the seawater sampled by GTWSS are higher than those sampled by general non-gas-tight water samplers, thus confirming the gas tightness of GTWSS. Seawater samples can be collected quickly by using GTWSS, and GTWSS can keep the samples integrity quite well.
Improved Reliability Analysis Method Based on the Failure Assessment Diagram
2012, 26(4).
[Abstract](2338) [PDF 469KB](211)
Abstract:
With the uncertainties related to operating conditions, in-service non-destructive testing (NDT) measurements and material properties considered in the structural integrity assessment, probabilistic analysis based on the failure assessment diagram (FAD) approach has recently become an important concern. However, the point density revealing the probabilistic distribution characteristics of the assessment points is usually ignored. To obtain more detailed and direct knowledge from the reliability analysis, an improved probabilistic fracture mechanics (PFM) assessment method is proposed. By integrating 2D kernel density estimation (KDE) technology into the traditional probabilistic assessment, the probabilistic density of the randomly distributed assessment points is visualized in the assessment diagram. Moreover, a modified interval sensitivity analysis is implemented and compared with probabilistic sensitivity analysis. The improved reliability analysis method is applied to the assessment of a high pressure pipe containing an axial internal semi-elliptical surface crack. The results indicate that these two methods can give consistent sensitivities of input parameters, but the interval sensitivity analysis is computationally more efficient. Meanwhile, the point density distribution and its contour are plotted in the FAD, thereby better revealing the characteristics of PFM assessment. This study provides a powerful tool for the reliability analysis of critical structures.
Adaptive Walking of a Quadrupedal Robot Based on Layered Biological Reflexes
2012, 26(4).
[Abstract](2304) [PDF 904KB](81)
Abstract:
A multiple-legged robot is traditionally controlled by using its dynamic model. But the dynamic-model-based approach fails to acquire satisfactory performances when the robot faces rough terrains and unknown environments. Referring animals’ neural control mechanisms, a control model is built for a quadruped robot walking adaptively. The basic rhythmic motion of the robot is controlled by a well-designed rhythmic motion controller(RMC) comprising a central pattern generator(CPG) for hip joints and a rhythmic coupler (RC) for knee joints. CPG and RC have relationships of motion-mapping and rhythmic couple. Multiple sensory-motor models, abstracted from the neural reflexes of a cat, are employed. These reflex models are organized and thus interact with the CPG in three layers, to meet different requirements of complexity and response time to the tasks. On the basis of the RMC and layered biological reflexes, a quadruped robot is constructed, which can clear obstacles and walk uphill and downhill autonomously, and make a turn voluntarily in uncertain environments, interacting with the environment in a way similar to that of an animal. The paper provides a biologically inspired architecture, with which a robot can walk adaptively in uncertain environments in a simple and effective way, and achieve better performances.
Modeling of Fatigue Crack Growth Closure Considering the Integrative Effect of Cyclic Stress Ratio, Specimen Thickness and Poisson’s Ratio
2012, 26(4).
[Abstract](2341) [PDF 753KB](89)
Abstract:
Key components of large structures in aeronautics industry are required to be made light and have long enough fatigue lives. It is of vital importance to estimate the fatigue life of these structures accurately. Since the FCG process is affected by various factors, no universal model exists due to the complexity of the mechanisms. Most of the existing models are obtained by fitting the experimental data and could hardly describe the integrative effect of most existing factors simultaneously. In order to account for the integrative effect of specimen parameters, material property and loading conditions on FCG process, a new model named integrative influence factor model (IIF) is proposed based on the plasticity-induced crack closure theory. Accordingly to the predictions of crack opening ratio (γ) and effective stress intensity factor range ratio (U) with different material under various loading conditions, predictions of γ and U by the IIF model are completely identical to the theoretical results from the plane stress state to the plane strain state when Poisson’s ratio equals 1/3. When Poisson’s ratio equals 0.3, predictions of γ and U by the IIF model are larger than the predictions by the existing model, and more close to the theoretical results. In addition, it describes the influence of R ratios on γ and U effectively in the whole region from –1.0 to 1.0. Moreover, several sets of test data of FCG rates in 5 kinds of aluminum alloys with various specimen thicknesses under different loading conditions are used to validate the IIF model, most of the test data are situated on the predicted curves or between the two curves that represent the specimen with different thicknesses under the same stress ratio. Some of the test data slightly departure from the predictions by the IIF model due to the surface roughness and errors in measurement. Besides, based on the analysis of the physical rule of crack opening ratios, a relative thickness of specimen is defined to describe the influence of material property, specimen thickness and so forth on FCG characteristics conveniently. In conclusion, the relative thickness of specimen simplifies the expression of FCG characteristic and provides a general parameter to analyze the fatigue characteristics of different materials with various thicknesses under different loading conditions. The IIF model describes the integrative effect of existing influence factors explicitly and quantitatively, and provides a helpful tool for fatigue property estimation of practical component and experiment design.
Design Schemes and Comparison Research of the End-effector of Large Space Manipulator
2012, 26(4).
[Abstract](2268) [PDF 1039KB](302)
Abstract:
The end-effector of the large space manipulator is employed to assist the manipulator in handling and manipulating large payloads on orbit. Currently, there are few researches about the end-effector, and the existing end-effectors have some disadvantages, such as poor misalignment tolerance capability and complex mechanical components. According to the end positioning errors and the residual vibration characters of the large space manipulators, two basic performance requirements of the end-effector which include the capabilities of misalignment tolerance and soft capture are proposed. And the end-effector should accommodate the following misalignments of the mechanical interface. The translation misalignments in axial and radial directions and the angular misalignments in roll, pitch and yaw are 100 mm, 100 mm, 10°, 15°, 15°, respectively. Seven end-effector schemes are presented and the capabilities of misalignment tolerance and soft capture are analyzed elementarily. The three fingers-three petals end-effector and the steel cable-snared end-effector are the most feasible schemes among the seven schemes, and they are designed in detail. The capabilities of misalignment tolerance and soft capture are validated and evaluated, through the experiment on the micro-gravity simulating device and the dynamic analysis in ADAMS software. The results show that the misalignment tolerance capabilities of these two schemes could satisfy the requirement. And the translation misalignment tolerances in axial and radial directions and the angular misalignment tolerances in roll, pitch and yaw of the steel cable-snared end-effector are 30mm, 15mm, 6°, 3° and 3° larger than those of the three fingers-three petals end-effector, respectively. And the contact force of the steel cable-snared end-effector is smaller and smoother than that of the three fingers-three petals end-effector. The end-effector schemes and research methods are beneficial to the developments of the large space manipulator end-effctor and the space docking mechanism.
Quadratic Programming-based Approach for Autonomous Vehicle Path Planning in Space
2012, 26(4).
[Abstract](2425) [PDF 787KB](104)
Abstract:
Path planning for space vehicles is still a challenging problem although considerable progress has been made over the past decades. The major difficulties are that most of existing methods only adapt to static environment instead of dynamic one, and also can not solve the inherent constraints arising from the robot body and the exterior environment. To address these difficulties, this research aims to provide a feasible trajectory based on quadratic programming(QP) for path planning in three-dimensional space where an autonomous vehicle is requested to pursue a target while avoiding static or dynamic obstacles. First, the objective function is derived from the pursuit task which is defined in terms of the relative distance to the target, as well as the angle between the velocity and the position in the relative velocity coordinates(RVCs). The optimization is in quadratic polynomial form according to QP formulation. Then, the avoidance task is modeled with linear constraints in RVCs. Some other constraints, such as kinematics, dynamics, and sensor range, are included. Last, simulations with typical multiple obstacles are carried out, including in static and dynamic environments and one of human-in-the-loop. The results indicate that the optimal trajectories of the autonomous robot in three-dimensional space satisfy the required performances. Therefore, the QP model proposed in this paper not only adapts to dynamic environment with uncertainty, but also can satisfy all kinds of constraints, and it provides an efficient approach to solve the problems of path planning in three-dimensional space.
Characterizing the Spheroidization Grade and Strength of 15CrMo Steel through Determining Fractal Dimension
2012, 26(4).
[Abstract](2257) [PDF 742KB](149)
Abstract:
The fractal dimension (FD) of surfaces has been widely used to characterize the properties of materials. However, most of the previous researches were concentrated on the correlation between the FD of surfaces and mechanical properties of materials, such as impact energy and fracture toughness, etc. The aim of this paper is to characterize the spheroidization grade and strength of 15CrMo steel through determination of FD of cementite phase on the basis of two-dimension microstructural image. Two methods, namely slit-island method (SIM) and box-counting method (BCM), are used to determine the value of FD. It is found that the FD value evaluated by using BCM is generally higher than that evaluated by SIM. This phenomenon may be due to the difference in the principles used in different methods. Whether SIM or BCM is used, the spheroidization grade in 15CrMo steel linearly increases with decreasing the value of FD. The relationship between the FD value, D, and spheroidization grade, Sg, can be approximately expressed as D≌–0.11Sg+A, where A is a constant value which is depended on the evaluation method. Both the ultimate strength and the yielding strength of 15CrMo steel increase with increasing FD of cementite phase. There may be a common relationship between the FD of cementite phase and strength of 15CrMo steel. When the FD of cementite phase in 15CrMo steel is determined, the strength of this steel can be evaluated. The present paper can provide a novel method to evaluate the strength and spheroidization grade of carbon steel through determination of fractal dimension (FD) of cementite phase.