Simcenter Madymo Simcenter Madymo - Generic Multi-Body seat model

The MB seat model consists of an assembly of kinematic joints, rigid bodies and MB surfaces. Some of the surfaces are only used for visual purposes and the other ones used in contact definitions. For the kinematic joints, all of the setting joints (sitting height, seat track position, seatback angle and headrest position) remain locked during the simulation whereas the deformation joints (seat pan and seatback) are set to free as default; for these two latter ones, joint restraints are used to control the deformation. If no deformation for these two joints is desired for the analysis, the user can easily set them to locked status using the parameter SEAT_deformation (FREE or LOCK).

The entire seat model is defined in a single SYSTEM.MODEL and referred as an include file which makes it easy to copy and paste in any other applications. A set of DEFINE variables are also made available to the user. They are divided in 3 categories; positioning, design and setting parameters. The available parameters are listed below.

Fig. 1 - Available DEFINE variables

The positioning parameters are used to position the seat in the environment, for example the vehicle's body at a certain position and orientation (the reference position of the seat is defined as the mid point of the four mounting bolts). The design parameters allow the user to define the seat track length (distance from rearmost to foremost), the position of the kinematic joints such as the position of the seat pan rotation joint (JOINT.REVO) in X- and Z-directions, the seatback pivot joint (JOINT.REVO) in X- and Z-positions and the headrest height adjuster joint (JOINT.TRAN) in X- and Z-directions, and the orientation around Y-axis of the sliding mechanism. Two stiffness parameters (SEAT_seatcushionstiffness and SEAT_seatbackstiffness) are also defined to adjust the seat pan and seatback deformation capability if necessary. The rest of the seat geometry (ellipsoids and planes) was not parametrized due to the complexity of each individual seat design.

The setting parameters are used to set the seat in the desired position. These are:

• SEAT_trackpos: longitudinal adjustment of the seat track (unidirectional, JOINT.TRAN)
• SEAT_heightoffsetZ/SEAT_heightoffsetX: sitting height adjuster; two parameters are used here because the seat does not only move vertically but also forward when the seat is moved up because of the seat height adjuster mechanism (parallelogram). Therefore a planar joint is used in this case.

Fig. 2 - Seat travel path

• SEAT_seatcushionangle: inclination of the seat cushion (0° means horizontal in the vehicle's coordinate system) 
• SEAT_seatbackangle: inclination of the seatback (0° means horizontal in the vehicle's coordinate system) 
• SEAT_headrestheight: height of the headrest
• SEAT_headrestori: orientation of the headrest around Y-axis

The seat is shown below as example at SRP (rearmost and lowest position) and at foremost/uppermost positions.

Fig. 3 - Different seat settings

For the contact definitions with the dummy and the environment, 5 contact groups are pre-defined:

• Seatcushion_gmb; refers to a plane for the seat cushion and to ellipsoids for the seat cushion bolsters - mainly used in contact with the pelvis and the upper legs.
• SeatcushionFront_gmb: refers to ellipsoids only - mainly used in contact with the lower legs in the rebound phase
• SeatbackHeadrest_gmb; refers to a plane for the seatback and to ellipsoids for the seatback bolsters - mainly used in contact with the pelvis, head, neck, lumbar spine and upper torso (or jacket) of the dummy. 
• ASM_gmb (Anti Sub-Marining plate): refers to a cylinder. Mainly used in contact with the upper legs and the pelvis.
• SeatbackBackside_gmb: refers to ellipsoids - mainly used in contact with second/third row occupants or with airbags if the seat is not facing the driving direction.

Fig. 4 - Pre-defined contact MB groups

Contact characteristics are pre-defined for all surfaces and using generic loading and unloading functions with scaling factors for all foam components (seat cushion, seatback, bolsters etc.). For the anti-submaring (ASM) plate, a specific contact characteristic and function are defined. The user is obviously free to update the functions and characteristics with data from component testing.

Fig. 5 - Pre-defined contact characteristics

For the seat pan and seatback deformations, characteristics related to the joint restrains (SeatPanDeformation_rst and SeatbackDefo_jrs) are also pre-defined. The user is free to update the functions and characteristics with data from component testing.

Fig. 6 - Pre-defined deformation characteristics for the seat pan and the seatback

Please contact your local Simcenter Madymo support organization for further questions/details on this topic.