RDE: 1600 Dummy Settling
Quasistatic loading analysis on a dummy, settling on a seat before crash analysis, using Altair Radioss explicit or Radioss implicit solvers.
Options and Keywords Used
 /SHELL,/BRICK, and /BEAM elements
 Quasistatic analysis by explicit, kinetic and dynamic relaxation (/KEREL, /DYREL and /ADYREL), and Rayleigh damping (/DAMP)
 Contact interface (/INTER/TYPE7)
 Hyperfoam material (/MAT/LAW62 (VISC_HYP))
 Linear elastic material (/MAT/LAW1 (ELAST))
 General solid property set (/PROP/TYPE14 (SOLID)) and shell property (/PROP/TYPE1 (SHELL))
 Void material (/MAT/LAW0 (VOID)) and void property (/PROP/TYPE0 (VOID))
 Added mass (/ADMAS)
 Boundary conditions (/BCS)
 Gravity (/GRAV)
 Rigid body (/RBODY)
Input Files
 Explicit
 RDE1601_Explicit.zip
 Implicit
 RDE1602_Implicit.zip
Model Description
Model Method
 a dummy with only the external surface is defined as a rigid body
 a seat is comprised of six parts:
 foam seat back
 foam seat cushion
 seat back brace
 seat bottom brace
 seat legs
 the floor
The seat structure and the floor are defined in a rigid body. Only the seat cushion parts are deformable during simulation.
The main node coordinates, and skew are extracted from the pelvis part of the dummy rigid body.
The main node of the seat and floor rigid body is clamped.
Material Properties
 Material Properties
 Value
 Young's modulus
 210000 $\left[\mathrm{MPa}\right]$
 Poisson's ratio
 0.3
 Density
 7.8E^{9} ton/mm^{3}
 Material Properties
 Value
 Ground shear modulus
 (0.02,2), (0.01,2)
 Poisson's ratio (foam behavior)
 0
 Density
 7.8 x 10^{9} ton/mm^{3}
 Material Properties
 Value
 Young's modulus
 2070 $\left[\mathrm{MPa}\right]$
 Poisson's ratio
 0.28
 Density
 5E^{11} ton/mm^{3}
Element Properties
 I_{solid}
 24 (HEPH)
 I_{cpre}, I_{frame} and I_{smstr}
 Set to 1 (Recommended value)
The other parameters are set to default (0).
 Seat back thickness
 2 mm
 Floor thickness
 1 mm
Shell properties used are default value for all parameters (0).
 Area
 2580 mm^{2}
 Inertia

 IXX
 554975 mm^{4}
 IYY
 554975 mm^{4}
 IZZ
 937908 mm^{4}
 Dummy thickness
 1 mm
Contact Interfaces
 Seat foams define the Main surface, Dummy parts define the Secondary nodes
 Dummy parts define the Main surface, Seat foams define the Secondary nodes (symmetrical contact)
 The floor defines the Main surface, dummy feet define the Secondary nodes
 Contact gap
 5 mm
 Coulomb friction
 0.3
 Stiffness
 4 (minimum stiffness between main and secondary)
 Minimum stiffness
 1000 N/mm (usually value for automotive crash analysis)
 Friction formulation
 2 (stiffness)
Refer to the Radioss Theory Manual and Starter Input for further information about the definition of the TYPE7 interface.
Resolution Methods
 Explicit solver:
A quasistatic simulation using a dynamic resolution method needs to minimize the dynamic effects to converge towards static equilibrium. This usually describes the preloading case prior to dynamic analysis. Thus, the quasistatic solution of gravity loading on the model is the steadystate part of the transient response.
A first analysis is done to view the dynamic effect due to gravity loading and compare the results with the different methods to reduce the dynamic effect.
To reduce the dynamic effect, the following options are available in the Engine file: Kinetic energy relaxation (/KEREL)
All velocities are set to zero each time the kinetic energy reaches a maximum value (no additional input parameters are required).
 Dynamic relaxation (/DYREL)
 Dynamic relaxation with a userdefined damping factor and period to damp.
 The model without dynamic relaxation is computed to identify the period to damp and defined the parameters for the /DYREL card.
 Dynamic relaxation (/ADYREL)
 Dynamic relaxation with autodefined adaptive damping.
 Radioss solver automatically defines the period to damp. There is no parameter to set.
 Rayleigh damping (/DAMP)
 Rayleigh mass and stiffness damping coefficients applied to a set of nodes for any nodal DOF either in local or global coordinate system.
 For this application, the mass needs to be damped to reduce the kinetic energy.
 The parameter, $\alpha $ is defined as a damping percentage divided by the computation time step.
Detailed information about the different formulations are available in the Radioss Theory Manual.
 Kinetic energy relaxation (/KEREL)
 Implicit solver:
However, the implicit algorithm uses a global resolution which requires convergence for each time step and has low robustness in comparison to the explicit (null pivots, divergence for high nonlinearities, and so on).
The implicit methods result in solving a linear system for each time step, which is relatively expensive but enables a large time step: so there are few expensive calculations. The explicit method treats linear or nonlinear systems depending on the problem. It is less expensive and faster for each step, but requires short time steps to ensure stability of the scheme that has many inexpensive cycles.
For this example, the following implicit solution and solver is used: Nonlinear solver
 Modified Newton method with relative residual in force (/IMPL/NONLIN/1)
 Linear solver
 Direct solver MUMPS (/IMPL/SOLVER/2)
 Quasistatic solution
 Considers the mass and inertia with a scale factor (/IMPL/QSTAT/DTSCAL)
 Time step
 Arclength method is used to accelerate and to control the convergence (/IMPL/DT/2)
 Time step control
 Initial (/IMPL/DTINI), minimum and maximum time step (/IMPL/DT/STOP)
Detailed information about the different formulations are available in the Radioss Theory Manual.
Results
Curve and Animation
The results are similar for all methods used; except for the model without relaxation or damping (as is to be expected).
 Model
 Convergence time
 Explicit without damping
 Can not converge to static equilibrium
 Explicit ADYREL
 0.4
 Explicit DYREL
 1.5
 Explicit KEREL
 0.2
 Explicit RAYLEIGH
 1.5
 Implicit Nonlinear
 > 1.5
Conclusion
The model with dynamic relaxation (/DYREL), automatic dynamic relaxation (/ADYREL), and Rayleigh damping (/DAMP) converges to the same results. Automatic dynamic relaxation converges faster.
The results can be slightly different between the methods mainly because of the contact treatment, how the contact starts and how it evolves according to the elastic vibrations.