Showing papers in "Chinese Journal of Mechanical Engineering in 2012"

Experimental study of the pressure fluctuations in a pump turbine at large partial flow conditions

Abstract: Frequent shifts of output and operating mode require a pump turbine with excellent stability. Current researches show that large partial flow conditions in pump mode experience positive-slope phenomena with a large head drop. The pressure fluctuation at the positive slope is crucial to the pump turbine unit safety. The operating instabilities at large partial flow conditions for a pump turbine are analyzed. The hydraulic performance of a model pump turbine is tested with the pressure fluctuations measured at unstable operating points near a positive slope in the performance curve. The hydraulic performance tests show that there are two separated positive-slope regions for the pump turbine, with the flow discharge for the first positive slope from 0.85 to 0.91 times that at the maximum efficiency point. The amplitudes of the pressure fluctuations at these unstable large partial flow conditions near the first positive slope are much larger than those at stable operating condtions. A dominant frequency is measured at 0.2 times the impeller rotational frequency in the flow passage near the impeller exit, which is believed to be induced by the rotating stall in the flow passage of the wicket gates. The test results also show hysteresis with pressure fluctuations when the pump turbine is operated near the first positive slope. The hysteresis creates different pressure fluctuations for those operation points even though their flow rates and heads are similar respectively. The pressure fluctuation characteristics at large partial flow conditions obtained by the present study will be helpful for the safe operation of pumped storage units.

Development of a hand exoskeleton system for index finger rehabilitation

Abstract: In order to overcome the drawbacks of traditional rehabilitation method, the robot-aided rehabilitation has been widely investigated for the recent years. And the hand rehabilitation robot, as one of the hot research fields, remains many challenging issues to be investigated. This paper presents a new hand exoskeleton system with some novel characteristics. Firstly, both active and passive rehabilitative motions are realized. Secondly, the device is elaborately designed and brings advantages in many aspects. For example, joint motion is accomplished by a parallelogram mechanism and high level motion control is therefore made very simple without the need of complicated kinematics. The adjustable joint limit design ensures that the actual joint angles don’t exceed the joint range of motion (ROM) and thus the patient safety is guaranteed. This design can fit to the different patients with different joint ROM as well as to the dynamically changing ROM for individual patient. The device can also accommodate to some extent variety of hand sizes. Thirdly, the proposed control strategy simultaneously realizes the position control and force control with the motor driver which only works in force control mode. Meanwhile, the system resistance compensation is preliminary realized and the resisting force is effectively reduced. Some experiments were conducted to verify the proposed system. Experimentally collected data show that the achieved ROM is close to that of a healthy hand and the range of phalange length (ROPL) covers the size of a typical hand, satisfying the size need of regular hand rehabilitation. In order to evaluate the performance when it works as a haptic device in active mode, the equivalent moment of inertia (MOI) of the device was calculated. The results prove that the device has low inertia which is critical in order to obtain good backdrivability. The experiments also show that in the active mode the virtual interactive force is successfully feedback to the finger and the resistance is reduced by one-third; for the passive control mode, the desired trajectory is realized satisfactorily.

Influence of minimum quantity lubrication parameters on tool wear and surface roughness in milling of forged steel

Abstract: The minimum quantity of lubrication (MQL) technique is becoming increasingly more popular due to the safety of environment. Moreover, MQL technique not only leads to economical benefits by way of saving lubricant costs but also presents better machinability. However, the effect of MQL parameters on machining is still not clear, which needs to be overcome. In this paper, the effect of different modes of lubrication, i.e., conventional way using flushing, dry cutting and using the minimum quantity lubrication (MQL) technique on the machinability in end milling of a forged steel (50CrMnMo), is investigated. The influence of MQL parameters on tool wear and surface roughness is also discussed. MQL parameters include nozzle direction in relation to feed direction, nozzle elevation angle, distance from the nozzle tip to the cutting zone, lubricant flow rate and air pressure. The investigation results show that MQL technique lowers the tool wear and surface roughness values compared with that of conventional flood cutting fluid supply and dry cutting conditions. Based on the investigations of chip morphology and color, MQL technique reduces the cutting temperature to some extent. The relative nozzle-feed position at 120°, the angle elevation of 60° and distance from nozzle tip to cutting zone at 20 mm provide the prolonged tool life and reduced surface roughness values. This fact is due to the oil mists can penetrate in the inner zones of the tool edges in a very efficient way. Improvement in tool life and surface finish could be achieved utilizing higher oil flow rate and higher compressed air pressure. Moreover, oil flow rate increased from 43.8 mL/h to 58.4 mL/h leads to a small decrease of flank wear, but it is not very significant. The results obtained in this paper can be used to determine optimal conditions for milling of forged steel under MQL conditions.

Hydraulic accumulator-motor-generator energy regeneration system for a hybrid hydraulic excavator

Abstract: Though the traditional energy regeneration system(ERS) which used a hydraulic motor and a generator in hybrid excavators can regenerate part of the energy, the power of the motor and the generator should be larger and the time for regenerating energy is so short. At first, the structure of new ERS that combines the advantages of an electric and hydraulic accumulator is analyzed. The energy can be converted into both the electric energy and the hydraulic energy at the lowering of the boom and the generator can still works when the boom stops going down. Then, a method how to set the working pressure of the hydraulic accumulator is proposed. To avoid the excess loss, extra noise and shock pressure, a two-level pressure threshold method that the generator starts to work at the rising edge of the high pressure threshold and stops working at the falling edge of the low pressure threshold is presented to characterize the working mode of the generator. The control strategies on how to control the boom velocity at the lowering of the boom and how to improve the recovery efficiency when the boom stops going down are presented. The test bench of hybrid excavator with ERS is constructed, with which the studies on the influences of ERS on energy conversion efficiency and control performance are carried out. Experimental results show that the proposed ERS features better speed control performance of the boom than traditional ERS. It is also observed that an estimated 45% of the total potential energy could be regenerated at the lowering of the boom in the proposed ERS, and the power level of the generator and the hydraulic motor could be reduced by 60%. Hence, the proposed ERS has obvious advantages over the traditional ERS on the improvement of energy regeneration time, energy efficiency, control performance and economy.

Multi-objective stability control algorithm of heavy tractor semi-trailer based on differential braking

Abstract: Rollover and jack-knifing of tractor semi-trailer are serious threats for vehicle safety, and accordingly active safety technologies have been widely used to reduce or prevent the occurrence of such accidents. However, currently tractor semi-trailer stability control is generally only a single hazardous condition (rollover or jack-knifing) control, it is difficult to ensure the vehicle comprehensive stability of various dangerous conditions. The main objective of this study is to introduce a multi-objective stability control algorithm which can improve the vehicle stability of a tractor semi-trailer by using differential braking. A vehicle controller is designed to minimize the likelihood of rollover and jack-knifing. First a linear vehicle model of tractor semi-trailer is constructed. Then an optimal yaw control for tractor using differential braking is applied to minimize the yaw rate and lateral acceleration deviation of tractor, as well as the hitch articulation angle of tractor semi-trailer, so as to improve the vehicle stability. Second a braking scheme and variable structure control with sliding mode control are introduced in order to achieve the best braking effect. Last Fishhook maneuver is introduced to the active safety simulation and the active control system effect verification. The simulation results show that multi-objective stability control algorithm of semi-trailer could improve the vehicle stability significantly during the transient maneuvers. The proposed multi-objective stability control algorithm is effective to prevent the vehicle rollover and jackknifing.

Influence of weave structures on the tribological properties of hybrid Kevlar/PTFE fabric composites

Abstract: The existing research of the woven fabric self-lubricating liner mainly focus on the tribological performance improvements and the service life raised by changing different fiber type combinations, adding additive modification, and performing fiber surface modification. As fabric composites, the weave structures play an important role in the mechanical and tribological performances of the liners. However, hardly any literature is available on the friction and wear behavior of such composites with different weave structures. In this paper, three weave structures (plain, twill 1/3 and satin 8/5) of hybrid Kevlar/PTFE fabric composites are selected and pin-on-flat linear reciprocating wear studies are done on a CETR tester under different pressures and different frequencies. The relationship between the tensile strength and the wear performance are studied. The morphologies of the worn surfaces under the typical test conditions are analyzed by means of scanning electron microscopy (SEM). The analysis results show that at 10 MPa, satin 8/5 performs the best in friction-reduction and antiwear performance, and plain is the worst. At 30 MPa, however, the antiwear performance is reversed and satin 8/5 does not even complete the 2 h wear test at 16 Hz. There is no clear evidence proving that the tensile strength has an influence on the wear performance. So the different tribological performance of the three weave structures of fabric composites may be attributed to the different PTFE proportions in the fabric surface and the different wear mechanisms. The fabric composites are divided into three regions: the lubrication region, the reinforced region and the bonding region. The major mechanisms are fatigue wear and the shear effects of the friction force in the lubrication region. In the reinforced region fiber-matrix de-bonding and fiber breakage are involved. The proposed research proposes a regional wear model and further indicates the wear process and the wear mechanism of fabric composites.

Needle steering for robot-assisted insertion into soft tissue: A survey

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.

Numerical robust stability estimation in milling process

Abstract: The conventional prediction of milling stability has been extensively studied based on the assumptions that the milling process dynamics is time invariant. However, nominal cutting parameters cannot guarantee the stability of milling process at the shop floor level since there exists many uncertain factors in a practical manufacturing environment. This paper proposes a novel numerical method to estimate the upper and lower bounds of Lobe diagram, which is used to predict the milling stability in a robust way by taking into account the uncertain parameters of milling system. Time finite element method, a milling stability theory is adopted as the conventional deterministic model. The uncertain dynamics parameters are dealt with by the non-probabilistic model in which the parameters with uncertainties are assumed to be bounded and there is no need for probabilistic distribution densities functions. By doing so, interval instead of deterministic stability Lobe is obtained, which guarantees the stability of milling process in an uncertain milling environment. In the simulations, the upper and lower bounds of Lobe diagram obtained by the changes of modal parameters of spindle-tool system and cutting coefficients are given, respectively. The simulation results show that the proposed method is effective and can obtain satisfying bounds of Lobe diagrams. The proposed method is helpful for researchers at shop floor to making decision on machining parameters selection.

Power-balancing instantaneous optimization energy management for a novel series-parallel hybrid electric bus

Abstract: Energy management(EM) is a core technique of hybrid electric bus(HEB) in order to advance fuel economy performance optimization and is unique for the corresponding configuration. There are existing algorithms of control strategy seldom take battery power management into account with international combustion engine power management. In this paper, a type of power-balancing instantaneous optimization(PBIO) energy management control strategy is proposed for a novel series-parallel hybrid electric bus. According to the characteristic of the novel series-parallel architecture, the switching boundary condition between series and parallel mode as well as the control rules of the power-balancing strategy are developed. The equivalent fuel model of battery is implemented and combined with the fuel of engine to constitute the objective function which is to minimize the fuel consumption at each sampled time and to coordinate the power distribution in real-time between the engine and battery. To validate the proposed strategy effective and reasonable, a forward model is built based on Matlab/Simulink for the simulation and the dSPACE autobox is applied to act as a controller for hardware in-the-loop integrated with bench test. Both the results of simulation and hardware-in-the-loop demonstrate that the proposed strategy not only enable to sustain the battery SOC within its operational range and keep the engine operation point locating the peak efficiency region, but also the fuel economy of series-parallel hybrid electric bus(SPHEB) dramatically advanced up to 30.73% via comparing with the prototype bus and a similar improvement for PBIO strategy relative to rule-based strategy, the reduction of fuel consumption is up to 12.38%. The proposed research ensures the algorithm of PBIO is real-time applicability, improves the efficiency of SPHEB system, as well as suite to complicated configuration perfectly.

Flow behaviour analysis and experimental investigation for emitter micro-channels

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 labyrinthchannel 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.

Enhanced detection of rolling element bearing fault based on stochastic resonance

Abstract: Early bearing faults can generate a series of weak impacts. All the influence factors in measurement may degrade the vibration signal. Currently, bearing fault enhanced detection method based on stochastic resonance(SR) is implemented by expensive computation and demands high sampling rate, which requires high quality software and hardware for fault diagnosis. In order to extract bearing characteristic frequencies component, SR normalized scale transform procedures are presented and a circuit module is designed based on parameter-tuning bistable SR. In the simulation test, discrete and analog sinusoidal signals under heavy noise are enhanced by SR normalized scale transform and circuit module respectively. Two bearing fault enhanced detection strategies are proposed. One is realized by pure computation with normalized scale transform for sampled vibration signal, and the other is carried out by designed SR hardware with circuit module for analog vibration signal directly. The first strategy is flexible for discrete signal processing, and the second strategy demands much lower sampling frequency and less computational cost. The application results of the two strategies on bearing inner race fault detection of a test rig show that the local signal to noise ratio of the characteristic components obtained by the proposed methods are enhanced by about 50% compared with the band pass envelope analysis for the bearing with weaker fault. In addition, helicopter transmission bearing fault detection validates the effectiveness of the enhanced detection strategy with hardware. The combination of SR normalized scale transform and circuit module can meet the need of different application fields or conditions, thus providing a practical scheme for enhanced detection of bearing fault.

Quality control on crimping of large diameter welding pipe

Abstract: Crimping is used in production of large diameter submerged-arc welding pipes. Many researches are focused on crimping in certain manufacturing mode of welding pipe. The application scopes of research achievements become limited due to lack of uniformity in theoretical analysis. In order to propose a crimping prediction method in order to control forming quality, the theory model of crimping based on elastic-plastic mechanics is established. The main technical parameters are determined by theoretical analysis, including length of crimping, base radius of punch, terminal angle of punch, base radius of die, terminal angle of die and horizontal distance between punch and die. In addition, a method used to evaluate the forming quality is presented, which investigates the bending angle after springback, forming force, straight edge length and equivalent radius of curvature. In order to investigate the effects of technical parameters on forming quality, a two-dimensional finite element model is established by finite element software ABAQUS. The finite element model is verified in that its shapes error is less than 5% by comparable experiments, which shows that their geometric precision meets demand. The crimping characteristics is obtained, such as the distribution of stress and strain and the changes of forming force, and the relation curves of technical parameters on forming quality are given by simulation analysis. The sensitivity analysis indicates that the effects of length of crimping, technical parameters of punch on forming quality are significant. In particular, the data from simulation analysis are regressed by response surface method (RSM) to establish prediction model. The feasible technical parameters are obtained from the prediction model. This method presented provides a new thought used to design technical parameters of crimping forming and makes a basis for improving crimping forming quality.

Precision balance method for cupped wave gyro based on cup-bottom trimming

Abstract: The mechanical balance process is the key process to eliminate the quadrature error and improve the performance of the cupped wave gyro. The conventional mechanical balance method for cupped wave gyro based on cup-wall trimming requires high control accuracy of trimming quantity, which increases the production cost and decreases the fabrication efficiency in large extent. However, it is hard to reach the high balance accuracy with the natural frequency split of mHz grade by using the conventional method. In this paper, the lumped mass dynamic model of the cupped wave gyro is built by discretization method, and the effects of different position trimming on the natural frequency are analyzed. It is pointed out that trimming off a tiny quantity of material from cup-wall causes large variation of the natural frequency is the main reason for the low accuracy of the conventional mechanical balance method. Then, a precision balance method for cupped wave gyro based on cup-bottom trimming is presented and the entire procedures of this method are given. The static balance process and dynamic balance process of the precision balance method are simulated by the finite element software. The simulation result shows that the precision balance method based on cup-bottom trimming brings less additional natural frequency split in the static balance process, minimizes the natural frequency split to mHz grade and rectify the angle of mode offset to 0.1° grade in the dynamic balance process, furthermore, the method decreases the requirement for control accuracy of trimming quantity evidently. The research work provides references for structure optimization design and balance process plan of the cupped wave gyro.

Detached-eddy Simulation for Time-dependent Turbulent Cavitating Flows

Abstract: The Reynolds-averaged Navier-Stokes (RANS), such as the original k-ω two-equation closures, have been very popular in providing good prediction for a wide variety of flows with presently available computational resource. But for cavitating flows, the above equations noticeably over-predict turbulent production and hence effective viscosity. In this paper, the detached eddy simulation (DES) method for time-dependent turbulent cavitating flows is investigated. To assess the state-of-the-art of computational capabilities, different turbulence models including the widely used RANS model and DES model are conducted. Firstly, in order to investigate the grid dependency in computations, different grid sizes are adopted in the computation. Furthermore, the credibility of DES model is supported by the unsteady cavitating flows over a 2D hydrofoil. The results show that the DES model can effectively reduce the eddy viscosities. From the experimental validations regarding the force analysis, frequency and the unsteady cavity visualizations, more favorable agreement with experimental visualizations and measurements are obtained by DES model. DES model is better able to capture unsteady phenomena including cavity length and the resulting hydrodynamic characteristics, reproduces the time-averaged velocity quantitatively around the hydrofoil, and yields more acceptable and unsteady dynamics features. The DES model has shown to be effective in improving the overall predictive capability of unsteady cavitating flows.

Effect of oxygenates blending with gasoline to improve fuel properties

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.

Excavator energy-saving efficiency based on diesel engine cylinder deactivation technology

Abstract: The hydraulic excavator energy-saving research mainly embodies the following three measures: to improve the performance of diesel engine and hydraulic component, to improve the hydraulic system, and to improve the power matching of diesel-hydraulic system-actuator. Although the above measures have certain energy-saving effect, but because the hydraulic excavator load changes frequently and fluctuates dramatically, so the diesel engine often works in high-speed and light load condition, and the fuel consumption is higher. Therefore, in order to improve the economy of diesel engine in light load, and reduce the fuel consumption of hydraulic excavator, energy management concept is proposed based on diesel engine cylinder deactivation technology. By comparing the universal characteristic under diesel normal and deactivated cylinder condition, the mechanism that fuel consumption can be reduced significantly by adopting cylinder deactivation technology under part of loads condition can be clarified. The simulation models for hydraulic system and diesel engine are established by using AMESim software, and fuel combustion consumption by using cylinder-deactivation-technology is studied through digital simulation approach. In this way, the zone of cylinder deactivation is specified. The testing system for the excavator with this technology is set up based on simulated results, and the results show that the diesel engine can still work at high efficiency with part of loads after adopting this technology; fuel consumption is dropped down to 11% and 13% under economic and heavy-load mode respectively under the condition of driving requirements. The research provides references to the energy-saving study of the hydraulic excavators.

Geometry Design and Tooth Contact Analysis of Crossed Beveloid Gears for Marine Transmissions

Abstract: Beveloid gears, also known as conical gears, gain more and more importance in industry practice due to their abilities for power transmission between parallel, intersected and crossed axis. However, this type of gearing with crossed axes has no common plane of action which results in a point contact and low tooth durability. Therefore, a geometry design approach assuming line contact is developed to analyze the tooth engagement process of crossed beveloid gears with small shaft angle for marine transmission applications. The loaded gear tooth contact behavior is simulated by applying a quasi-static analysis to study the effects of gearing parameters on mesh characteristics. Using the proposed method, a series of sensitivity analyses to examine the effects of critical gearing parameters such as shaft angle, cone angle, helix angle and profile-shift coefficient on the theoretical gear mesh is performed. The parametric analysis of pitch cone design shows that the dominant design parameters represented by the angle between the first principle directions (FPD) and normal angular factor are more sensitive to the shaft and cone angles than they are to the helix angle. The theoretical contact path is highly sensitive to the profile-shift coefficient, which is determined from the theoretical tooth contact analysis. The FPD angle is found to change the distribution of contact pattern, contact pressure and root stress as well as the translational transmission error and the variation of the mesh stiffness significantly. The contact pattern is clearly different between the drive and coast sides due to different designed FPD angles. Finally, a practical experimental setup for marine transmission is performed and tooth bearing test is conducted to demonstrate the proposed design procedure. The experimental result compared well with the simulation. Results of this study yield a better understanding of the geometry design and loaded gear mesh characteristics for crossed beveloid gears used in marine transmission.

Metadynamic recrystallization of the as-cast 42CrMo steel after normalizing and tempering during hot compression

Abstract: The existing researches of hot ring rolling process are mainly based on forged billet. Compared with the existing process, the new ring casting-rolling compound forming process has significant advantages in saving materials and energy, reducing emission and reducing the production cost. The microstructure evolution of the casting materials during hot deformation is the basis of the research of the new process. However, the researches on the casting materials are rare. The metadynamic recrystallization of the as-cast 42CrMo steel after normalizing and tempering during the hot compression is investigated. The tests are performed on the Gleeble-1500 thermal-mechanical simulator. The influence rule of the deformation parameters on the metadynamic recrystallization is obtained by analyzing the experimental data. The kinetic model of the metadynamic recrystallization is deduced. The analysis results show that the metadynamic recrystallization fraction increases with the increase of the deformation temperature and the strain rate. The metallographic experiments are used to investigate the influence rule of the deformation parameters on the grain size of the metadynamic recrystallization. The experimental results show that the grain of the metadynamic recrystallization could be refined with the increase of the strain rate and the decrease of the deformation temperature during hot compression. The occurrence of the metadynamic recrystallization during the hot deformation is more difficult in as-cast 42CrMo steel than in forged 42CrMo steel. The research can provide the foundation for the further research of the hot deformation behaviors of the as-cast structure and theoretical support for the new ring casting-rolling compound process.

Tool Wear and Its Effect on Surface Roughness in Diamond Cutting of Glass Soda-lime

Abstract: For the technology of diamond cutting of optical glass, the high tool wear rate is a main reason for hindering the practical application of this technology. Many researches on diamond tool wear in glass cutting rest on wear phenomenon describing simply without analyzing the genesis of wear phenomenon and interpreting the formation process of tool wear in mechanics. For in depth understanding of the tool wear and its effect on surface roughness in diamond cutting of glass, experiments of diamond turning with cutting distance increasing gradually are carried out on soda-lime glass. The wear morphology of rake face and flank face, the corresponding surface features of workpiece and the surface roughness, and the material compositions of flank wear area are detected. Experimental results indicate that the flank wear is predominant in diamond cutting glass and the flank wear land is characterized by micro-grooves, some smooth crater on the rake face is also seen. The surface roughness begins to increase rapidly, when the cutting mode changes from ductile to brittle for the aggravation of tool wear with the cutting distance over 150 m. The main mechanisms of inducing tool wear in diamond cutting of glass are diffusion, mechanical friction, thermo-chemical action and abrasive wear. The proposed research makes analysis and research from wear mechanism on the tool wear and its effect on surface roughness in diamond cutting of glass, and provides theoretical basis for minimizing the tool wear in diamond cutting brittle materials, such as optical glass.

Dynamics and wheel's slip ratio of a wheel-legged robot in wheeled motion considering the change of height

Abstract: The existing research on dynamics and slip ratio of wheeled mobile robot (WMR) are derived without considering the effect of height, and the existing models can not be used to analyze the dynamics performance of the robot with variable height while moving such as NOROS-II. The existing method of dynamics modeling is improved by adding the constraint equation between perpendicular displacement of body and horizontal displacement of wheel into the constraint conditions. The dynamic model of NOROS-II in wheel motion is built by the Lagrange method under nonholonomic constraints. The inverse dynamics is calculated in three different paths based on this model, and the results demonstrate that torques of hip pitching joints are inversely proportional to the height of robot. The relative error of calculated torques is less than 2% compared with that of ADAMS simulation, by which the validity of dynamic model is verified. Moreover, the relative horizontal motion between fore/hind wheels and body is produced when the height is changed, and thus the accurate slip ratio can not be obtained by the traditional equation. The improved slip ratio equations with the parameter of the vertical velocity of body are introduced for fore wheels and hind wheels respectively. Numerical simulations of slip ratios are conducted to reveal the effect of varied height on slip ratios of different wheels. The result shows that the slip ratios of fore/hind wheels become larger/smaller respectively as the height increases, and as the height is reduced, the reverse applies. The proposed research of dynamic model and slip ratio based on the robot height provides the effective method to analyze the dynamics of WMRs with varying height.

Global optimization method using SLE and adaptive RBF based on fuzzy clustering

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.

Type design for heavy-payload forging manipulators

Abstract: Heavy-payload forging manipulators are mainly characterized by large load output and large capacitive-load input. The relationship between outputs and inputs, which will greatly influence the control and the reliability, is the key issue in type design for heavy-payload forging manipulators. In this paper, a type design method by considering the incidence relationship between output characteristics and actuator inputs is presented and used to design the mechanism for forging manipulators. The concept of modeling method based on the outputs tasks is defined and investigated. The principle of type design from the viewpoints of the relationship between output characteristics and actuator inputs is discussed. An idea of establishing the incidence relationship between output characteristics and actuator inputs is proposed. The incidence relationship matrix between outputs and inputs is also given. The design flow is obtained, and the incidence relationship between outputs and inputs for heavy-payload forging manipulators is divided into three parts after detailed understanding of the functional properties. Four types of mechanisms for heavy-payload forging manipulators are given, and the corresponding spatial mechanical sketches are also drawn, some new designed mechanisms have been adopted by company or used as prototype. These novel forging manipulators which satisfy certain functional requirements provide an effective help for the design of forging manipulators and patent application.

Evaluation of subgrid-scale models in large-eddy simulations of turbulent flow in a centrifugal pump impeller

Abstract: The current research of large eddy simulation (LES) of turbulent flow in pumps mainly concentrates in applying conventional subgrid-scale (SGS) model to simulate turbulent flow, which aims at obtaining the flow field in pump. The selection of SGS model is usually not considered seriously, so the accuracy and efficiency of the simulation cannot be ensured. Three SGS models including Smagorinsky-Lilly model, dynamic Smagorinsky model and dynamic mixed model are comparably studied by using the commercial CFD code Fluent combined with its user define function. The simulations are performed for the turbulent flow in a centrifugal pump impeller. The simulation results indicate that the mean flows predicted by the three SGS models agree well with the experimental data obtained from the test that detailed measurements of the flow inside the rotating passages of a six-bladed shrouded centrifugal pump impeller performed using particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). The comparable results show that dynamic mixed model gives the most accurate results for mean flow in the centrifugal pump impeller. The SGS stress of dynamic mixed model is decompose into the scale similar part and the eddy viscous part. The scale similar part of SGS stress plays a significant role in high curvature regions, such as the leading edge and training edge of pump blade. It is also found that the dynamic mixed model is more adaptive to compute turbulence in the pump impeller. The research results presented is useful to improve the computational accuracy and efficiency of LES for centrifugal pumps, and provide important reference for carrying out simulation in similar fluid machineries.

Numerical simulation and experimental research on the influence of solid-phase characteristics on centrifugal pump performance

Abstract: The law governing the movement of particles in the centrifugal pump channel is complicated; thus, it is difficult to examine the solid-liquid two-phase turbulent flow in the pump. Consequently, the solid-liquid two-phase pump is designed based only on the unary theory. However, the obvious variety of centrifugal-pump internal flow appears because of the existence of solid phase, thus changing pump performance. Therefore, it is necessary to establish the flow characteristics of the solid-liquid two-phase pump. In the current paper, two-phase numerical simulation and centrifugal pump performance tests are carried out using different solid-particle diameters and two-phase mixture concentration conditions. Inner flow features are revealed by comparing the simulated and experimental results. The comparing results indicate that the influence of the solid-phase characteristics on centrifugal-pump performance is small when the flow rate is low, specifically when it is less than 2 m3/h. The maximum efficiency declines, and the best efficiency point tends toward the low flow-rate direction along with increasing solid-particle diameter and volume fraction, leading to reduced pump steady efficient range. The variation tendency of the pump head is basically consistent with that of the efficiency. The efficiency and head values of the two-phase mixture transportation are even larger than those of pure-water transportation under smaller particle diameter and volume fraction conditions at the low-flow-rate region. The change of the particle volume fraction has a greater effect on the pump performance than the change in the particle diameter. The experimental values are totally smaller than the simulated values. This research provides the theoretical foundation for the optimal design of centrifugal pump.

Geometric approach for kinematic analysis of a class of 2-DOF rotational parallel manipulators

Abstract: Euler angles are commonly used as the orientation representation of most two degrees of freedom (2-DOF) rotational parallel mechanisms (RPMs), as a result, the coupling of two angle parameters leads to complexity of kinematic model of this family of mechanisms While a simple analytical kinematic model with respect to those parameters representing the geometrical characteristics of the mechanism, is very helpful to improve the performance of RPMs In this paper, a new geometric kinematic modeling approach based on the concept of instantaneous single-rotation-angle is proposed and used for the 2-DOF RPMs with symmetry in a homo-kinetic plane To authors’ knowledge, this is a new contribution to parallel mechanisms By means of this method, the forwards kinematics of 2-DOF RPMs is derived in a simple way, and three cases ie 4-4R mechanism (Omni-wrist III), spherical five-bar one, and 3-RSR&1-SS one demonstrate the validity of the proposed geometric method In addition, a novel 2-DOF RPM architecture with virtual center-of-motion is presented by aid of the same method The result provides a useful tool for simplifying the model and extending the application of the RPMs

Non-linear torsional vibration characteristics of an internal combustion engine crankshaft assembly

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.

Effects of laser shock processing on mechanical properties of laser welded ANSI 304 stainless steel joint

Abstract: With the rapid development of engineering component with integration, high-speed and multi-parameter, traditional techniques haven’t met practical needs in extreme service environment. Laser welding, a new welding technology, has been widely used. However, it would generate the drop of mechanical properties for laser welded joint due to its thermal effect. Laser shock processing (LSP) is one of the most effective methods to improve the mechanical properties of laser welded ANSI 304 stainless steel joint. In this paper, the effects of LSP on the mechanical properties of laser welded ANSI 304 stainless steel joint have been investigated. The welded joint on the front of the tensile samples is treated by LSP impacts, and the overlapping rate of the laser spot is 50%. The tensile test of the laser welded joint with and without LSP impacts is carried out, and the fracture morphology of the tensile samples is analyzed by scanning electron microscope (SEM). Compared with the yield strength of 11.70 kN, the tensile strength of 37.66 kN, the yield-to-tensile strength ratio of 0.310 7, the elongation of 25.20%, the area reduction of 32.68% and the elastic modulus of 13 063.876 MPa, the corresponding values after LSP impacts are 14.25 kN, 38.74 kN, 0.367 8, 26.58%, 42.29% and 14 754.394 MPa, respectively. Through LSP impacts, the increasing ratio of the yield strength and tensile strength are 121.79% and 102.87%, respectively; the elongation and area reduction are improved by 5.48% and 29.38%, respectively. By comparing with coarse fracture surface of the welded joint, the delamination splitting with some cracks in the sharp corner of the welded joint and asymmetric dimples, LSP can cause brighter fracture surface, and finer and more uniform dimples. Finally, the schematic illustration of dimple formation with LSP is clearly described. The proposed research ensures that the LSP technology can clearly improve the yield strength, tensile strength, yield-to-tensile strength ratio, elongation, area reduction and elastic modulus of the welded joint. The enhancement mechanism of LSP on laser welded ANSI 304 stainless steel joint is mainly due to the fact that the refined and uniform dimples effectively delay the fracture of laser welded joints.

Quasi-static Analysis of Thrust-loaded Angular Contact Ball Bearings Part I: Theoretical Formulation

Abstract: Ball bearings play an important role in various rotating machineries, but the complicated kinematic and tribological features of ball bearings make many aspects of their operating behaviors still inconclusive. Most theoretical analyses of ball bearings up to date are based on either the hypothesis of race control or other empirical models to determine the ball motion of ball bearings, but none of these strategies can reveal and consequently employ the intrinsic coupling mechanism between the spin and the tangential traction of contacting bodies rolling upon one another. To remedy the deficiency of current analytical models for ball bearing analysis, the rolling contact theory is employed to establish an explicit link between motions and interactions within ball bearings. A differential slip model is established to precisely define the slip component due to the significant curvature of the common contact patches between the ball and inner/outer raceways. The creepage and the spin ratio are formulated to accurately define the relative rigid motion between the ball and the inner/outer raceway. Then a quasi-static analytical model is established that can accurately determine the motions of the balls and races of the ball bearing. It can also give a vivid description of the slip and traction distributions within the contact area. The analytical model can be effectively used to analyze the operational conditions and tribological features of solid-lubricated ball bearings. It can also be used optimize the construction of ball bearings for specific applications.

Online learning control for hybrid electric vehicle

Abstract: Improvements in hybrid electric vehicle (HEV) fuel economy and emissions heavily depend on an efficient energy management strategy (EMS). However, the uncertainty of future driving conditions generally cannot be easily tackled in EMS design. Most existing EMSs act upon fixed parameters and cannot adapt to varying driving conditions. Therefore, they usually fail to fully explore the potential of these advanced vehicles. In this paper, a novel EMS design procedure based on neural dynamic programming (NDP) is proposed. The NDP is a generic online learning algorithm, which combines stochastic dynamic programming (SDP) and the temporal difference (TD) method. Instead of computing the utility function and optimal control actions through Bellman equations, the NDP algorithm uses two neural networks to approximate them. The weights of these neural networks are updated online by the TD method. It avoids the high computational cost that SDP suffers from and is suitable for real-time implementation. The main advantages of NDP EMS is that it does not rely on prior information related to future driving conditions, and can self-tune with a wide variance in operating conditions. The NDP EMS has been applied to “Qianghua-I”, a prototype of a parallel HEV, using a revolving drum test bench for verification. Experiment results illustrate the potential of the proposed EMS in terms of fuel economy and in keeping state of charge (SOC) deviations at a low level. The proposed research ensures the optimality of NDP EMS, as well as real-time applicability.

Design and dynamic modeling of a 2-DOF decoupled flexure-based mechanism

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.