| Ride comfort is an important indicator for vehicle performance evaluation,which has attracted more and more attention.Human bodies are frequently exposed to various whole-body vibrations when travelling in vehicles.The vibration is transmitted to the human body through a seat and changes the contact characteristics at the human-seat interface,which causes discomfort to the seated human body.Prolonged exposure to whole-body vibration may adversely affect the health of drivers and passengers,and increase the risk of low back pain.Therefore,it is important to study the human response to vibration and the body pressure distribution at the human-seat interface under vibration excitation for improving the riding comfort and body health of drivers and passengers.The study of biodynamic modelling can provide guidance for seat comfort design and help advance understanding of the mechanisms of how the human body responds to vibration.However,it is difficult to determine the biomechanical parameters of the human body during finite element modelling,which leads to a slow modelling process;There are some problems in the lumbar biomechanics modelling,such as over simplified and lack basis for lumbar posture adjustment,which make the model difficult to reflect the real dynamic response of the lumbar spine.In addition,body pressure distribution,as one of the important objective parameters for seated human comfort evaluation,has been fully reflected in the static comfort evaluation,while its application in the study of comfort under dynamic conditions is very limited.The thesis focuses on the comfort of the seated human body,determining the biomechanics parameters of the human body with the parameter identification method,and establishing a finite element model of the human body in sitting posture for biodynamic response prediction.Adjusting the posture of lumbar spine model according to the results of radiology research,and establishing a finite element model of the lumbar spine that conforms to the anatomical characteristics of human body for the dynamic response prediction of the lumbar spine.Analyzing the correlation between the body pressure distribution indicator and subjective comfort under vibration excitation,and applying the body pressure distribution indicator for vibration comfort evaluation of the seated human body.For solving the problem that the biomechanical parameters of human body are difficult to determine in the process of finite element modeling of human body under vertical vibration,the sensitivity analysis and multi-objective optimization idea are introduced into the process of finite element modeling of human body under vibration excitation.The parameters of human joints and soft tissues at the buttocks and thighs in the model are determined,and a finite element model of the seated human body is established,which can reflect the apparent mass of the human body,the transmissibility from the seat to the first thoracic spine and the modes of the human body.A finite element model of the seated human body with 175 cm in stature and 68.6 kg in weight,which consists of seven segments,six joints and soft tissue,was established to reflect apparent mass based on the Hybrid III dummy model.By comparing the body segment mass percentages with previous data,the rationality of mass distribution in this model was verified.In this study,the root-mean-square error between the calculated and the measured apparent mass was taken as objective function,and the effect of fifteen human parameters on the objective function was analyzed through sensitivity analysis.Then seven parameters with a considerable influence on the objective function were selected as design variables,and four approximate models were established for parameter optimization.Soft tissues and joint parameters of the model were determined by parameter identification,and the finite element model that can reflect vertical in-line and fore-and-aft cross-axis apparent mass of the human body without backrest was developed.The seated human model presented in this paper can also reflect the transmissibility from seat to the first thoracic spine and the main modes of the human body below 10 Hz,which is conducive to express the human response to vibration.For establishing a finite element model of lumbar spine to predict the dynamic response of lumbar spine under vibration excitation,a detailed lumbar geometry model is obtained from the database of human anatomy and anthropometry in Poser.The posture of the lumbar spine model is adjusted with reference to radiology research,and a finite element model of the human body including the lumbar spine model is established for the dynamic response prediction of the lumbar spine.The finite element model of the lumbar spine including the modelling of the vertebral body,nucleus pulposus,annulus fibrosis,endplates,collagen fibers,and ligaments,which was validated with intradiscal pressure,range of motion of the spine,and the first vertical resonance frequencies.The posture of the lumbar spine was adjusted according to radiological research and combined to establish a FE model of the seated human body,and validated by comparing the measured apparent mass and seat-to-lumbar spine transmissibility.The seated human model is used to calculate the biodynamic response of the lumbar spine with three inclined backrests(10°,20°,30°)under WBV,and the calculation results of disc compression force,intervertebral disc pressure,annulus stress and endplate stress under three backrest supports are obtained.For characterizing the subjective discomfort of the seated human body on a foam seat under vertical random vibration using dynamic body pressure distribution,the body pressure distribution indicator under vibration excitation is proposed based on the subjective evaluation and body pressure distribution test under vibration excitation,and the relationship between subjective and objective indicators is established.Firstly,the dynamic body pressure of twelve subjects seated on a foam seat exposed to vertical random excitation is measured at frequencies from 0.5 to 20 Hz with six magnitudes(0.2,0.4,0.6,0.8,1.0,and 1.2 m/s~2 r.m.s.).Meanwhile,the subjective discomfort rating of the foam seat is evaluated with the relative magnitude estimation method.Then,the influence of vibration magnitude on subjective discomfort ratings and dynamic body pressure indicators is investigated,and the relation between the subjective discomfort ratings and dynamic body pressure indicators is established using Stevens’power law.Finally,the proposed average pressure change rate root-mean-square and normal force change rate root-mean-square are applied to the vibration comfort evaluation of the vehicle seat.The applicability of body pressure distribution in the vibration comfort evaluation of vehicle seats is further demonstrated.Finally,twelve subjects are tested for the body pressure distribution of foam with three kinds of hardness and four kinds of thickness under vertical vibration.The influence of polyurethane foam thickness and hardness on body pressure distribution under vertical vibration excitation is analyzed with non-parametric statistical method,which provides a reference for the comfort design of vehicle seats. |
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