Transfer Path Contribution to Floor Vibration of Metro Vehicles Based on Operational Transfer Path Analysis Method

Operational transfer path analysis(OTPA)is an advanced vibration and noise transfer path identification and contribution evaluation method.However,the application of OTPA to rail transit vehicles considers only the excitation amplitude and ignores the influence of the excitation phase.This study considers the influence of the excitation amplitude and phase,and analyzes the contribution of the secondary suspension path to the floor vibration when the metro vehicle runs at 60 km/h,using an analysis based on the OTPA method.The results show that the vertical direction of the anti-rolling torsion bar area provides the maximum contribution to the floor vibration,with a contribution of 22.1%,followed by the longitudinal vibration of the air spring area,with a contribution of 17.1%.Based on the contribution analysis,a transfer path optimization scheme is proposed,which may provide a reference for the optimization of the transfer path of metro vehicles in the future.

Analysis of fluid vibration transfer path and parameter sensitivity of swash plate axial piston pump

Taking swash plate axial piston pump as the research object,the mechanism of fluid vibration and transfer rule are analyzed.The pump shell can be assumed as the ultimate recipient of vibration transmission,the path model and differential equations from the fluid to the shell are established.The parameters of the path model are determined by the simulation software,and the mathematical model is solved by the simulation software.And time/frequency domain analysis of vibration acceleration of shell is presented.Based on the different influence of various parameters in the transfer path model on transfer characteristics and vibrational recipients,the time-varying parameters are studied by using sensitivity analysis theory,and the influence of the structural parameters on the vibration characteristics of vibration subject is quantitatively analyzed.The research in the paper provides theoretical basis for vibration analysis and structure parameter optimization of axial piston pump.

An investigation into high-speed train interior noise with operational transfer path analysis method

Passengers’demands for riding comfort have been getting higher and higher as the high-speed railway develops.Scientific methods to analyze the interior noise of the high-speed train are needed and the operational transfer path analysis(OTPA)method provides a theoretical basis and guidance for the noise control of the train and overcomes the shortcomings of the traditional method,which has high test efficiency and can be carried out during the working state of the targeted machine.The OTPA model is established from the aspects of“path reference point-target point”and“sound source reference point-target point”.As for the mechanism of the noise transmission path,an assumption is made that the direct sound propagation is ignored,and the symmetric sound source and the symmetric path are merged.Using the operational test data and the OTPA method,combined with the results of spherical array sound source identification,the path contribution and sound source contribution of the interior noise are analyzed,respectively,from aspects of the total value and spectrum.The results show that the OTPA conforms to the calculation results of the spherical array sound source identification.At low speed,the contribution of the floor path and the contribution of the bogie sources are dominant.When the speed is greater than 300 km/h,the contribution of the roof path is dominant.Moreover,for the carriage with a pantograph,the lifted pantograph is an obvious source.The noise from the exterior sources of the train transfer into the interior mainly through the form of structural excitation,and the contribution of air excitation is non-significant.Certain analyses of train parts provide guides for the interior noise control.

Heat transfer enhancement in MOSFET mounted on different FR4 substrates by thermal transient measurement

Miniaturization of electronic package leads to high heat density and heat accumulation in electronics device, resulting in short life time and premature failure of the device. Junction temperature and thermal resistance are the critical parameters that determine the thermal management and reliability in electronics cooling. Metal oxide field effect transistor（MOSFET）is an important semiconductor device for light emitting diode-integrated circuit（LED IC） driver application, and thermal management in MOSFET is a major challenge. In this study, investigations on thermal performance of MOSFET are performed for evaluating the junction temperature and thermal resistance. Suitable modifications in FR4 substrates are proposed by introducing thermal vias and copper layer coating to improve the thermal performance of MOSFET. Experiments are conducted using thermal transient tester（T3ster） at 2.0 A input current and ambient temperature varying from25℃ to 75℃. The thermal parameters are measured for three proposed designs： FR4 with circular thermal vias, FR4 with single strip of copper layer and embedded vias, and FR4 with I-shaped copper layer, and compared with that of plain FR4 substrate. From the experimental results, FR4I-shaped shows promising results by 33.71% reduction in junction temperature and 54.19% reduction in thermal resistance. For elevated temperature, the relative increases in junction temperature and thermal resistance are lower for FR4I-shaped than those for other substrates considered. The introduction of thermal vias and copper layer plays a significant role in thermal performance.

Can hip abduction reduce the risk of femoral head necrosis deteriorated into osteoarthritis?A 3D finite element analysis

The purpose of this study was to investigate biomechanical behavior changes of femoral head necrosis(FHN)by increasing lower extremity abduction(LEA)angle,offering scientific basis on choosing the LEA procedure for the exact classifications.Methods:Thirty computational models were constructed and used to simulate six different abducent angles with five different progresses of FHN.The initial model was validated by the bony density distribution in X-rays images and the photograph of the cadaver bone in cross-section.The stress transfer path(STP)of each model was analyzed and the contact stresses were assessed.Results:During the midstance phase,STP of type A showed strong similarities with the healthy level;STP distribution was from the top of the femoral head to the calcar;the damage area of STP of type B was approximately 25%of the healthy.While STPs in both type C1 and C2 were broken off.As the increase of the abduction angle,STP of type B transformed into type A,STP of type C1 transformed into type B.STP of type C2 transformed into type C1.There was no significant difference in contact stress between the four settings of FHN and normal femoral head.Conclusions:We found computational biomechanical technique to be a sensitive and useful method for distinguishing the biomechanical difference of FHN during abduction gait.These results showed that LEA motion could effectively reduce collapse risk and interrupt the disease pathway of FHN deteriorated into osteoarthritis.Furthermore,our findings indicated that the LEA procedure was suitable for type A,B and C1,while type C2 of FHN involved surgical intervention might get a better clinical outcome.

Design and verification of a transfer path optimization method

This paper studies the transfer path planning problem for safe transfer of an aircraft on the aircraft carrier flight deck under a poor visibility condition or at night.First,we analyze the transfer path planning problem for carrier-based aircraft on the flight deck,and define the objective to be optimized and the constraints to be met.Second,to solve this problem,the mathematical support models for the flight deck,carrier aircraft entity,entity extension,entity posture,entity conflict detection,and path smoothing are established,as they provide the necessary basis for transfer path planning of the aircraft on the aircraft carrier.Third,to enable automatic transfer path planning,we design a multi-habitat parallel chaos algorithm(called KCMPSO),and use it as the optimization method for transfer path planning.Finally,we take the Kuznetsov aircraft carrier as a verification example,and conduct simulations.The simulation results show that compared with particle swarm optimization,this method can solve the transfer path planning problem for an aircraft on the aircraft carrier flight deck better.

Vibration Characteristics of Framed SUV Cab Based on Coupled Transfer Path Analysis

The vibration transmission paths in a sport-utility vehicle with a frame structure were used to evaluate the coupled vibra-tion of each vibration transmission link.This method was based on the transmission path of an“engine-powertrain mount system-frame-vehicle body suspension-body-driver seat rail,”and the research objective was to improve the vibration char-acteristics of the cab.This coupled transfer path analysis combined analysis and experiment to establish the vehicle vibration transmission path model and a finite element simulation model.With this method,the vibration level of the driver’s seat rail was reduced and engineering practice was effectively used to improve the vibration characteristics of the cab.This method was applied to a framed SUV cabin.

Gear fault diagnosis using gear meshing stiffness identified by gearbox housing vibration signals

Gearbox fault diagnosis based on vibration sensing has drawn much attention for a long time.For highly integrated complicated mechanical systems,the intercoupling of structure transfer paths results in a great reduction or even change of signal characteristics during the process of original vibration transmission.Therefore,using gearbox housing vibration signal to identify gear meshing excitation signal is of great significance to eliminate the influence of structure transfer paths,but accompanied by huge scientific challenges.This paper establishes an analytical mathematical description of the whole transfer process from gear meshing excitation to housing vibration.The gear meshing stiffness(GMS)identification approach is proposed by using housing vibration signals for two stages of inversion based on the mathematical description.Specifically,the linear system equations of transfer path analysis are first inverted to identify the bearing dynamic forces.Then the dynamic differential equations are inverted to identify the GMS.Numerical simulation and experimental results demonstrate the proposed method can realize gear fault diagnosis better than the original housing vibration signal and has the potential to be generalized to other speeds and loads.Some interesting properties are discovered in the identified GMS spectra,and the results also validate the rationality of using meshing stiffness to describe the actual gear meshing process.The identified GMS has a clear physical meaning and is thus very useful for fault diagnosis of the complicated equipment.