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,Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,Copyright 2003-2011 by LIVERMORE SOFTWARE TECHNOLOGY CORPORATION Preload,1,Preload-Introduction,Sometimes it is important to induce a steady state preload before performing a transient dynamic analysis.,Rotating fan or turbine blades,rotating flywheels,Gravity,Pressure vessels or tires,Shrink-fit parts,Stresses induced by a torqued bolt,Preload-IntroductionSometime,Explicit Dynamic Relaxation(DR),Explicit DR is an,optional,transient analysis that takes place in pseudo-time(precedes regular transient analysis).,DR is typically used to preload a model before onset of transient loading.,Preload stresses are typically elastic and displacements are small.,In explicit DR,the computed nodal velocities are reduced each timestep by the dynamic relaxation factor(default=.995).Thus the solution undergoes a form of damping during DR.,The distortional kinetic energy is monitored.When this KE has been sufficiently reduced,i.e.,the“convergence factor”has become sufficiently small,the DR phase terminates and the solution automatically proceeds to the transient analysis phase.,Alternately,DR can be terminated at a preset termination time.,Explicit Dynamic Relaxation(D,Explicit Dynamic Relaxation,DR is typically invoked by setting parameter SIDR in a load curve(*DEFINE_CURVE)to 1 or 2.,Ramp the load during DR phase and then hold load constant until solution converges,Make sure convergence occurs,after,100%of preload is applied,Maintain the preload in subsequent transient analysis phase(use separate load curve without the ramp),DR,converges,SIDR=1(DR phase),SIDR=0(transient phase),Explicit Dynamic RelaxationDR,*CONTROL_DYNAMIC_RELAXATION,*CONTROL_DYNAMIC_RELAXATION parameters,Iterations between convergence check(default=250),Also affects output interval for“d3drlf”,Convergence tolerance(default 0.001),Ratio of distorsional KE at convergence to peak distorsional KE,Smaller value results in converged solution nearer to steady state but run will take longer to get there,Dynamic relaxation factor(default=0.995),Reduction factor for nodal velocities each time step,If value is too small,model never reach steady state due to overdamping,Optional termination time for DR(default=infinity),DR will stop if time reaches DRTERM even if convergence criterion not satisfied,Time step scale factor used during DR,Explicit Dynamic Relaxation,*CONTROL_DYNAMIC_RELAXATION*CO,*CONTROL_DYNAMIC_RELAXATION parameters,IDRFLG,Flag to activate DR(not required if DR is activated with*DEFINE_CURVE),Set to 2,will invoke a completely different and faster initialization approach,Initialization by Prescribed Geometry,.,Requires supplemental input file containing nodal displacements and rotations(“m=filename”on execution line).,Such a file,drdisp.sif,is written at conclusion of standard DR run.,If nodal rotations are not included in file,method is invalid for beams and shells.,LS-DYNA,runs a short transient analysis of 100 timesteps to preload the model by imposing the nodal displacements and rotations.,Solution then proceeds with regular transient analysis.,Set to 5,activates,implicit,method for solution of preloaded state,Must also set DRTERM to signal end of DR phase.,*CONTROL_IMPLICIT.provide controls on implicit phase.,*CONTROL_DYNAMIC_RELAXATION,Dynamic Relaxation,*CONTROL_DYNAMIC_RELAXATION pa,Output Related to Dynamic Relaxation,ASCII output files are NOT written during DR phase,e.g.,glstat,matsum,rcforc,etc.The binary,d3thdt,file can be used if IDRFLG=-1.,Binary database,d3drlf,is written by including command*DATABASE_BINARY_D3DRLF.Set output interval to 1.This will cause a state to be written each time convergence is checked during DR,Plotting time histories from,d3drlf,with LS-PrePost,allows user to confirm solution is near steady state,relax,file is automatically written and contains record of convergence history.Data can be plotted with LS-PrePost.,drdisp.sif,contains nodal displacements and rotations at conclusion of DR phase.,Dynamic Relaxation,Output Related to Dynamic Rela,Output Related to Explicit Dynamic Relaxation,Explicit Dynamic Relaxation,Dynamic Relaxation information is written,to the screen.The transient phase starts,when the convergence tolerance or a,Specified termination time is reached.,Convergence plot from,relax,file,Kinetic Energy plot from,relax,file,Output Related to Explicit Dyn,Typical Loads During Dynamic Relaxation,Gravity loads and centrifugal loads(spinning bodies)are imposed using*LOAD_BODY_option.,LCID and LCIDDR are separate curves for transient phase and DR phase,respectively.,Thermal stresses can be imposed using*LOAD_THERMAL_LOAD_CURVE.,Parts,e.g.,bolts,defined with a coefficient of thermal expansion will have thermal stresses imposed.,LCID and LCIDDR are separate curves for transient phase and DR phase,respectively.,Other load types or boundary conditions are applied during DR if SIDR in correspond
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