Research On Methodology Of Seat Forward Design Based On Body Pressure Distribution

Pressure distribution has great significance for evaluating and improving seats and cabin design.Seat comfort can be evaluated by comparing the contact pressure with ideal one.Therefore,an appropriate pressure distribution must be obtained when designing a seat,in order to meet the comfort requirement.However,it is uneasy for seat manufacturers to determine the perfect shape and dimensions of the foam,which is liable to cause design iterations.In this thesis,the ideal body pressure distribution which met the comfort requirements of human body,were adopted to match the shape and hardness of the seat foam.By using simulative way,the methodology of the seat forward design was studied,so as to ensure the perfect seating posture and the reasonable body pressure as much as possible,which would ensure good comfort.The design process presented in this thesis is described as follows.Three human body finite elements(FE)models were constructed based on the multi-dimensional body dimension joint distribution of target group and packaging parameters.The ideal pressure was imposed on the human body surface,and then human body contours could be obtained from the numerical simulation,which was also the position of foam deformation.The polyurethane foam and its thickness of different contact regions between the seat and the driver were accordingly determined to meet the design requirement of the comfort degree,and the deformation of polyurethane foam could be calculated according to the mathematical model among pressure,thickness,and deformation of polyurethane foam.The foam deformation was compensated with the position of foam deformation,and then the seat surface could be obtained.Theoretically,the seat surface obtained with the ideal pressure distribution could meet the comfort demand of different drivers.Furthermore,the constitutive model of hyper-elastic material was introduced.The material model which is suitable for the simulation of the human body tissue and polyurethane foam was selected.The effect of the modeling parameters on the material mechanical properties was investigated.Then the mathematical model between the pressure,the thickness and the deformation of polyurethane foam was established.Three drivers were selected based on the anthropometry attribute extraction and multi-dimensional body dimension joint distribution.The selected driver size was calculated according to the prediction model,after which the parameterized geometry model of the driver body was established.The geometric model of driver was adjusted through the driving posture prediction model,after that,the material properties were assigned to establish the finite element model of the human body.At the same time,the distance between the human hip point and H point was calculated.The pressure distribution simulation was carried out in order to detect the influence of the driver size and the polyurethane foam hardness on pressure distribution.The geometry model and the FE model of the seat were established based on a simplified driver’s seat model;and then the resultant pressure distribution between human body and seat was analyzed varying with human body dimensions.Simulation results showed that stress concentration was always encountered in the central thigh and front area of the thigh,meanwhile,with the increase of the driver stature which led to a higher contact area between the driver and the seat,the average pressure decreased gradually.Finally,the influence of different polyurethane foam materials on the pressure distribution was analyzed.It was suggested that the softer polyurethane foam could reduce the human tissue stress as well as the pressure on the contact area between the seat and the driver,consequently,the comfort condition of the seat would be improved.Finally,the forward design method of the multi-hardness seat was investigated.Firstly,the ideal pressure distribution was constructed;then,the contact area between the seat and the driver was divided into eight regions;the deformation of the three drivers were simulated by put ideal pressure on each region,Thus,the surface contours of the driver were obtained by surface fitting of these eight area.Secondly,the hardness and thickness of the polyurethane foam of different contact area between the seat and the driver were determined.Then,the ideal pressure was mapped on each point coordinate on the body surface;simultaneously,the deformation need to be compensated could be calculated according to the mathematical model of the polyurethane foam.Thirdly,the seat surface under ideal pressure distribution could be obtained by surface fitting.Finally,the comfort of designed seat was verified through the simulation of pressure distribution,and the results showed a good consistency with the ideal pressure distribution,sequentially validating the feasibility of this method.