| Automobile seat greatly affects the ride comfort of drivers in a prolonged driving.Not only the layout parameters of automobile seats,such as seat height,cushion inclination angle,backrest inclination angle,etc,but also the surface of backrest related with lumbar support affects the seating comfort.In addition,humans face a multiplicity of vibrations in vehicles or at the workplace which may reduce the comfort of the occupants,or may lead to serious physical injuries.Low frequency vibration,especially in vertical direction,has more influence on dynamic response of human spine and body.For example,Low back pain and degenerative diseases of the spine occur more frequently among vehicle drivers exposed to vibration.Although it is difficult to measure directly the biodynamic properties of living human subjects,computational modeling of human body is frequently used in the study of biomechanics.On the one hand,invasive experiments on humans are limited by ethic concerns.On the other hand,results from questionnaires vary with the subjectivity of test persons and show a lack of reproducibility.Finite element analysis is a powerful tool routinely used to study complex biological systems.The traditional biodynamics studies of spine provided very useful information of biodynamics of human spine and modeling methods.However,the models of many studies included only partial or whole spine in vitro.Few literature studied effect of the factors(such as muscle and skin,Young's modulus of muscle,buttocks,viscera,arms,gravity,sitting postures,and boundary conditions)on the modal characteristics and biodynamic response of spine in vivo.In order to improve the seating comfort and reduce the injury of vibration on human spine under whole-body vibration,this paper studied the biomechanics of human body and the human body seat system on the basis of the finite element model of the human body and conducted vibration experiment research.The main researches are as follows:First,the three-dimensional finite element modeling method of the human body-seat system was investigated.The human body-seat system included the three-dimensional data of body based on anatomy and anthropometry,the three-dimensional data of seat and the adjustable assembly interaction between body and seat based on human body kinematics.Body height and driving posture were adjusted in POSER software.The skin,lumbar and pelvis of human body could be refined by using facet feature and could be restyled in software PRO/ENGINEER.3D CONVERTER software was applied to format the geometry file of human body.Then the finite element model of human skin,skeleton and muscle were created in ANSA software,and the integrated model of body-seat system was created in ABAQUS software for various analyzes.Five modeling methods of human body finite element model were presented according to different research purposes.This study used 50 percentile Chinese males' size to build different finite element models of human body in vertical or driving seating posture.Second,the static ride comfort of human body-seat system was studied by finite element analysis.The effects of different lumbar support on the pressure distribution of the backrest and the stress distribution of the lumbar intervertebral disc were studied.The adjustment of the lumbar support parameters was achieved by setting boundary condition of lumbar support region of seat.The geometry model of human body was verified by the major parameters of height and weight.The finite element model of human body-seat system was validated by comparison to available literature results.At last the finite element model was applied to analyze the effect of lumbar support parameters of seat on the interaction between body and seat under the action of gravity.The pressure value and distribution,contact area,total force of backrest and intervertebral disc stress were obtained.The analysis results showed that the optimal thickness of seat's lumbar support size for the seating comfort was 10 mm after comprehensive comparison and evaluation.The analysis results could provide a reference for the design of the lumbar support.Third,dynamic analyzes,including modal analysis,transient dynamics analysis and random response analysis,were performed for the finite element model of different lumbar spinal ligamentous motion segments,vertical seated human body and human body-seat system.The effect of skin and muscle soft tissue,viscera,buttocks,contact area of buttocks,lumped mass of upper body,moment of inertia of upper body,the position of lumped mass of upper body,sitting posture and gravity on biodynamics of human body and lumbar spine were investigated.The effect curves of position of lumped mass of upper body and Young's modulus of muscle soft tissue and viscera on first vertical resonant frequency of lumbar spine were obtained.The movement characteristics of different lumbar motion segments in the first order vertical resonance were obtained.The characteristics of the acceleration and stress distribution and the stress amplitude in the lumbar intervertebral disc were obtained by the transient dynamics analysis of seated human body in the forward,vertical and reclining postures.Random response analysis found that the response peak frequency in the vertical direction under the white noise excitation condition was the first order resonance frequency in the vertical direction.In addition,the effects of different sitting postures and different stiffness of seats on the dynamic response of human or body-seat systems were analyzed,and the response power spectral density of the human lumbar discs in two directions were obtained.The proposed FE model of biodynamics response analysis can be used to research on the responses of different schemes of human body-seat system to guide the design of seats and evaluate dynamic characteristics of newly designed seats.Forth,the effect of lumbar support on the state and vibration of lumbar muscle under the whole body vibration was studied by vibration test.Experiments were divided into three groups according to different magnitude of lumbar support d(d1=0mm,d2=20mm,d3=40mm).In the experiment,the subject sat on the seat with lumbar support device which was mounted on the vibration test device,and the vibration frequency of the vibration test device is 10 Hz and the amplitude is 0.42 m/s2 rms.In the thirty-minute vibration test,ten seconds' surface EMG signal and the acceleration signal of the lumbar muscle were recorded every three minutes.The results showed that lumbar support had influence on the activation level of the lumbar muscles and the vibration transmission ratio.In the d2 group,the lumbar muscle activation level and the vibration transmission ratio of the subjects were the smallest.In addition,it was found that the activation level and the vibration transmission ratio of the lumbar muscles were decreased with the prolongation of the vibration time in three groups of experiments,and this indicated that the lumbar muscle was fatigued with the extension of the vibration time. |
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