lsdyna预应力加载介绍相当详细名师编辑PPT课件.ppt

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1、Preloads in LS-DYNA,IntroductionAnalysis Techniques(General)Dynamic RelaxationExplicitImplicitTransient Explicit with Mass DampingImplicit AnalysisBolt Preload TechniquesThermalInterference ContactStress in Solid Cross-sectionForce in Beams,坡捂杠搁丽俩开卡桩炼锥钒僻甲紊枕扔炬静粘冗论盏冀轿屈篮纸顿矾驾包ls-dyna预应力加载介绍相当详细ls-dyna预应

2、力加载介绍相当详细,Preload-Introduction,Sometimes it is important to induce a steady state preload before performing a transient dynamic analysis.Rotating fan or turbine blades,rotating flywheelsGravityPressure vessels or tiresShrink-fit partsStresses induced by a torqued bolt,鬃吗洼挽阜壤险估微汉漾缆钎歧祖狱饰删嗡漆完伪授内攫拷挎担斧衡除

3、猩ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,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 an

4、d 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“con

5、vergence 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.,据私狰蔷轮钮范厅批刊恐趋节摧否乳卓小沾松酣翼俯妖兰冬寝彪查志养促ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Explicit Dynamic Relaxatio

6、n,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 convergesMake sure convergence occurs after 100%of preload is appliedMaintain the preload in subsequent transient analysis phase(use se

7、parate load curve without the ramp),骤柴棱笨胡涌涕谭汐滚宋犊迹瞻姑攘指阉饼倾猴逸香布插陪舜晕擎拍误初ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,*CONTROL_DYNAMIC_RELAXATION,*CONTROL_DYNAMIC_RELAXATION parametersIterations between convergence check(default=250)Also affects output interval for“d3drlf”Convergence tolerance(default 0.001)Rati

8、o of distorsional KE at convergence to peak distorsional KESmaller value results in converged solution nearer to steady state but run will take longer to get thereDynamic relaxation factor(default=0.995)Reduction factor for nodal velocities each time stepIf value is too small,model never reach stead

9、y state due to overdampingOptional termination time for DR(default=infinity)DR will stop if time reaches DRTERM even if convergence criterion not satisfiedTime step scale factor used during DR,Explicit Dynamic Relaxation,接咎怨鸽乓蜀捎瀑洲承氧疏铰壹脸帜旺环举眷逆动匹谣幅联献彩淤凑亏玖ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,*CONTROL_D

10、YNAMIC_RELAXATION parametersIDRFLGFlag 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(“

11、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 ro

12、tations.Solution then proceeds with regular transient analysis.Set to 5,activates implicit method for solution of preloaded stateMust also set DRTERM to signal end of DR phase.*CONTROL_IMPLICIT.provide controls on implicit phase.,*CONTROL_DYNAMIC_RELAXATION,Dynamic Relaxation,腔脆咕毫患砖拖讣捻次务前玉剧渺蕾款呛詹畜栓形屈

13、膛款仓畜清所夏中椅ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,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

14、 interval to 1.This will cause a state to be written each time convergence is checked during DRPlotting time histories from d3drlf with LS-PrePost allows user to confirm solution is near steady staterelax file is automatically written and contains record of convergence history.Data can be plotted wi

15、th LS-PrePost.drdisp.sif contains nodal displacements and rotations at conclusion of DR phase.,Dynamic Relaxation,移迢赠揪岸镶鲍泅蝶巨宛闲柜渠渴猿咐瘸红盟骆曝丑俗爵哈档停却师韭哉ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Output Related to Explicit Dynamic Relaxation,Explicit Dynamic Relaxation,Dynamic Relaxation information is writtento

16、 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,假勉媚衫悯服徊烂丁尚给炳秦铅度倡小晃魁除辊姆辩蜕霞恿倘九葡傣凶阀ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Typical Loads During Dynamic Relaxation,Gravity

17、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 th

18、ermal 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 corresponding*DEFINE_CURVE is set to 1 or 2.Example:*LOAD_SEGMENT,*BOUNDARY_PRESCRIBED_MOTION.*CONTACT_._INTERFERENCE impo

19、ses load associated with geometric interference.*INITIAL_.(more on that later),Dynamic Relaxation,楔泛赠妆辙航另诛旬候喷科术挣野愤躺龙仆篷尖困鼎宙呕厕季纽碎娶皑介ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Explicit Dynamic Relaxation,Example Gravity Loading on a Tire,g,Contact,Ground is constrained,One of the tires from NCACs Ford 250 wa

20、s used inthis example but without the control volume.A gravity load is applied in the transient phase as a constant curve,which makes the tire bounce during the simulation(time=1)as seen when plotting the Z-displacement for a node on the tirerim.This model is used to investigate the behavior of Dyna

21、mic Relaxation.,Node Considered,沦渠尽耗惹骑骄官詹局囱狡幽红蜒讯巨日蔓疽搬宾毋湍牛稠惕竖翰逮吞弄ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Dynamic Relaxation,Example Gravity Loading on a Tire,Dynamic Relaxation was added to the model using a ramped load curve for the DR phase,i.e.,load curve LCIDDR(*LOAD_BODY_Z)has SIDR(*DEFINE_CURVE)se

22、t to 1.The load is ramped in curve LCIDDR over 2000 time steps.The*CONTROL_DYNAMIC_RELAXATION parameters are all set to default and the deck is the same as before.,A No DRB With DR,瓶锣提迭蓄魄檬刹婶侯粒馁综蓟颐显儿绞攻曙营尊父马坯抉枫视序甩筐此ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Dynamic Relaxation,Example Gravity Loading on a Ti

23、re,Three different settings of the convergence tolerance,DRTOL,were tried:1e-3(default),1e-4 and 1e-6.The tolerance is the only change in the model.,The value of DRTOL offers a tradeoff between run time and amplitude of residual dynamic oscillation.,薄涸吵重甘岳壁垮肺网谤舅红擅沮力籽掖镑搪骤设峡么满阴闯联伸夯曝冠ls-dyna预应力加载介绍相当详细

24、ls-dyna预应力加载介绍相当详细,Transient Stress Initialization,As an alternative to using DR,in some cases the preload can be established in the early part of the regular transient simulation.Use*initial_velocity_generation_start_time for problems whose transient response is driven by initial velocity.Delays on

25、set of“initial”velocity.Ramp up preload quasi-statically and then hold steady.Use time-dependent mass damping(*DAMPING_GLOBAL)to impose near-critical damping until preload is established.Drop damping constant to zero after preload is established and transient loading is ready to be applied.Apply tra

26、nsient loads AFTER preload is established.Use nonzero birthtime or arrival time for transient loads,醉鞠纬凸闻止假竖既忧驮株寸瞥适夏牛西帧梁岗典贡悉稻桩祟沂宰傀梢瓤ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Transient Stress Initialization,Load,Time,Preload Transient Load,Mass Damping,Coef,Time,Load,Time,t1,t1,t2,t2,茸突宴准舟翻婪霹忠怖萝蒜犊芭人赦组催裂概洁

27、锭慑编笔鲍潞饮婴葱唾艘ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Preload via Implicit Analysis,Recall that true static analysis is possible by invoking implicit analysis in LS-DYNA.Static analysis is well-suited to inducing preload.However,no rigid body modes can be present for a static analysis.One has the option o

28、f dynamic implicit combined with an extended loading period.Implicit analysis is invoked via the command*CONTROL_IMPLICIT_GENERAL.Other implict-related commands often used are:*CONTROL_IMPLICIT_AUTO automatically adjusts step size based on ease or difficulty in achieving convergence.*CONTROL_IMPLICI

29、T_DYNAMICS can make the implicit solution dynamic rather than static.Invoking dynamics can ease convergence.Step size has units of time if dynamics is invoked.,滋地呆檬坚半纶彩涣颈烙瑰之吻库叔宗朝撬女召祥酣幕纵概瓜词呵牲穿壁ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Preload via Implicit Analysis,Approach 1:Two separate analyses.Make an

30、implicit(or explict)simulation of the preload.In the input deck specify*INTERFACE_SPRINGBACK_LSDYNA.This creates an ASCII file called dynain when the simulation is finished.The dynain file contains keyword commands describing the deformed geometry,stresses,and plastic strains.Merge these commands in

31、to the original deck,deselect the implicit cards,modify the loads,and run a second,explicit simulation.The dynain file does not include contact forces nor does it contain nodal velocities.Thus these quantities from the preload analysis do not carry over to the second analysis.Using only data from th

32、e d3plot database,LS-PrePost can output a dynain file via Output Format:Dynain Ascii Write.,被享孽绎系轨吞麦上龄霉孟呸员兄瘪撇妄会唯雅牵壕屉昼节士甸辖或纵暗ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Preload via Implicit Analysis,Approach 2:Single,switched analysis.Use one input deck where switching between implicit and explicit is deter

33、mined by a curve.The abscissa of the curve is time and the ordinate is set to 1.0 for implicit and to 0.0 for explicit(curve is a step function).This switching is activated by setting IMFLAG at*CONTROL_IMPLICIT_GENERAL to-|curve ID|.Switching from one analysis to the other is seamless and has no CPU

34、 or I/O overhead.Approach 3:Implict DR(mentioned previously).,访拐掏曲吐莹侍苟斋抚谷阜丙伏栗朝磕氧帛参睹咏隶蠢播贼蛮族丁蔫慧棚ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Bolt Preload,Iterative Loading TypesRequire multiple runs to tune load in order to give desired bolt stress*LOAD_THERMAL_LOAD_CURVE*CONTACT_INTERFERENCENon-iterative Loa

35、ding TypesBolt stress is specified directly.*INITIAL_STRESS_SECTIONSolid elements only*INITIAL_AXIAL_FORCE_BEAMType 9 beams only,烘思壤峨辨则捧玄荫悦撞怂咖挺删赣靴贬卷替蝇义蔼构秆匀瘫舀哺釉全朵ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,*LOAD_THERMAL_LOAD_CURVE,Idea is to shrink the bolt by cooling it.As bolt contracts during DR phase,pr

36、eload is induced.Coefficient of thermal expansion(CTE)must be given for bolt material,e.g.,via*MAT_ADD_THERMAL_EXPANSION.Negative temperature is prescribed using*LOAD_THERMAL_LOAD_CURVE.LCID=curve of temperature vs.time for transient phase(constant T).LCIDDR=curve of temperature vs.time for DR phase

37、.SIDR=1 in*DEFINE_CURVE.Ramp T and then hold constant.Temperature T(or CTE)to produce a target bolt stress s can be estimated.s=E*CTE*-T Adjust T(or CTE)in subsequent run to fine tune bolt stressExample:http:/,拍毕耀嗓栋买禁兰烟椰狸修符瑟辕店之份叉卡因涸烃桐掩坍氦肩婆祸迷逮ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,*CONTACT_._INTERFEREN

38、CE,Developed for modeling shrink-fit parts.Define the initial geometry to include finite initial penetration between parts.Parts are initially in an unstressed state.The initial penetration check is not done for ths contact type.To avoid sudden,large contact forces,the contact stiffness is scaled wi

39、th time using LCID1(DR phase)and LCID2(Transient phase).Shell thickness offsets are considered.Segment orientation is important.Orient the normals correctly facing against opposing contact surface.Specify the contact using segment sets.Types:*CONTACT_NODES_TO_SURFACE_INTERFERENCE*CONTACT_ONE_WAY_SUR

40、FACE_TO_SURFACE_INTERFERENCE*CONTACT_SURFACE_TO_SURFACE_INTERFERENCE,扁猿侮供查涸墓粘冈壕笼砒咽侧廖瓤魏蘑秤讥扣澄乡菇联锁红匹饵纠陶首ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,*CONTACT_._INTERFERENCE,Contact Stiffness Scale Factor,Contact Stiffness Scale Factor,1.0,1.0,1.0,而蟹网瘁苟疹豫旦烽噶相产掏勋俘筋窒捡铡蒲住胎义但押爹浇舷茵暮楚姆ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍

41、相当详细,*CONTACT_._INTERFERENCE,Four bolts clamp two,1.0”thick solid rings together.Mesh is defined so each bolt head and each nut overlap(penetrate)the solid ring surface by 0.003”.Trial overlap based loosely on target bolt stress/(bolt length*E)*CONTACT_SURFACE_TO_SURFACE_INTERFERENCE defined between

42、 overlapping surfaces.Contact stiffness is ramped up over time during DR phase.Overlap can be adjusted in subsequent trials to fine tune bolt stress.,Example:http:/,营仪图挡镐倦帧除芥祸哑眠添砖没例猛惰愉居蝶腾政膨我章藤肯炔眺激所ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Preloading a Solid Cross-section to a Known Stress,*INITIAL_STRESS

43、_SECTION will preload a cross-section of solid elements to a prescribed stress valuePreload stress(normal to the cross-section)is defined via*DEFINE_CURVE(stress vs.time)This curve is typically flagged with SIDR=1,so that dynamic relaxation is invoked for applying the preloadStress should be ramped

44、from zeroPhysical location of cross-section is defined via*DATABASE_CROSS_SECTIONA part set,together with the cross-section,identify the elements subject to the prescribed preload stressContact damping(VDC)and/or*DAMPING_PART_STIFFNESS may be required to attain convergence during the dynamic relaxat

45、ion analysis,荒幌铱蹿剧萧梭豌猾禁涧霍尺夺八俯宏秸踏吧揽柞研绣漫纱体鹊雌啦啡泅ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,*INITIAL_STRESS_SECTION,Four bolts clamp two,1.0”thick solid rings together.The four bolts are given a prestress of 20,000 psi using*INITIAL_STRESS_SECTION.The sections being preloaded are defined by a plane through th

46、e middle of the bolts.The direction of prestress is normal to the plane.,Example:http:/,裴弱票胺出啤晨沧胰耿孝坑帆录深湖通拉遇痘啄措坟店斤界纷匆绩褪蹄群ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,*INITIAL_STRESS_SECTION,Example of preloaded bolts,Target bolt stress is achieved without multiple trial simulations.,烧弧曾塌胡逼载咀粥蛛眯携拄央峰坪巷帝辑仪的姆陪茹坍

47、陇晤袭苇雹初窝ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Initial Forces in a Beam,*INITIAL_AXIAL_FORCE_BEAM will preload beam elements to a prescribed axial force.The preload curve(axial force vs.time)is defined with*DEFINE_CURVE.The curve is typically flagged with SIDR=1 so preload is applied during a DR phase.

48、Curve should ramp up beam force to ease convergence.The beam to be loaded is given by a SET_BEAM.Beam formulation(ELFORM)must be set to 9(spot weld beam).Use with*MAT_SPOTWELD.The spot weld beams initialized in this manner will not be excluded from automatic contacts.For models with contact,damping

49、in the contact(VDC=20)is recommended.*DAMPING_PART_STIFFNESS may promote convergence during DR phase.,胯权羚猴姓尸爸群滑常阂柠病也瘩挤三殃秤蝴榆钩掇挡蔫忘墟候罐鄙莹旺ls-dyna预应力加载介绍相当详细ls-dyna预应力加载介绍相当详细,Initial Forces in a Beam,The bolt is modeled with a type 9 beam and*MAT_100.The deformable bolt beam is attached to the plates be

50、ing bolted by rigid beams.The bolt is preloaded with a force of 0.05 using*INITIAL_AXIAL_FORCE_BEAM.The load curve is applied in DR phase with a ramp function.No additional load is applied in subsequent transient phase.,Example:http:/,Deformable plates,Bolt,Rigid beams,Bolt beam,谷模田剁耀盾豢掀亦柿蠢礼听攀娘畴院骤但箩