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1.
高阶数值流形方法的初应力公式   总被引:1,自引:0,他引:1  
高阶数值流形方法和高阶DDA方法可以显著提高结构变形的计算精度,但目前涉及几何非线性问题的研究成果大都计算精度差甚至不收敛,这是由高阶初应力公式的不准确或不正确引起的。本文介绍数值流形方法的大变形计算格式,基于平面三角形数学网格和多项式覆盖函数,提出高阶流形法的两种初应力处理方法,首次导出了高阶初应力的准确公式。该公式在分步计算的初应力累加中考虑了大变形结构的构形变化,并将初应力表示成多项式函数形式以满足单纯形积分的要求。文中给出的悬臂梁大变形数值算例与理论解的对比结果证明了方法的正确性。本文的方法和公式也适用于三维四面体数学网格,稍加修改后将可应用于高阶DDA方法和常规的有限元方法。  相似文献   

2.
针对用Hopkinson杆试验能否准确测量聚合物动态弹性模量以及其中主要影响因素的问题,本文基于重构试样初始加载阶段的应力波反射透射过程,分别计算了6个特征时间内的前三次反射波和透射波,得到试样的应力平衡度和试样的应力应变曲线。对于所研究的聚合物材料,通过比较重构的应力应变曲线的弹性模量与输入的材料弹性模量,发现在4个特征时间后,误差仅在3%左右。因此试样变形过程中的应力平衡与否不是材料在Hopkinson杆试验中弹性模量测不准的原因。通过环氧树脂试样试验发现,根据Hopkinson杆理论计算的应变结果要大于试样上应变片实测的结果,误差在11%左右。相应的数值模拟研究发现:试样和杆子端面接触状态直接决定着试样弹性模量测量的精度。关于惯性效应和压痕效应的研究也证实它们的影响是可以忽略的。  相似文献   

3.
921A钢纯剪切帽状试件在SHPB实验中的动态变形   总被引:1,自引:0,他引:1  
应用ANSYS/LS-DYNA软件,开展了一系列基于921A钢纯剪切帽状试件的SHPB数值模拟.结合SHPB系统应力波理论,研究不同加载速率v0(或应力脉冲I(t))下,特别是高应变率(约106 s-1)下的压杆轴向应变波形以及相应的试件动态变形特性,并对高速撞击下压杆中应变波形的适用性作了相关讨论.  相似文献   

4.
钟东海  郭鑫  熊雪梅  郑宇轩  宋力 《爆炸与冲击》2023,43(4):044101-1-044101-9

利用传统分离式霍普金森压杆(split Hopkinson pressure bar, SHPB)实验技术来实现试件在较低应变率下的大变形时,需要使用超长的压杆系统,杆件的加工和实验空间限制了该技术的推广应用。鉴于此,提出一种直撞式霍普金森压杆二次加载实验技术,利用透射杆中的应力波在其末端的准刚性壁反射实现对试件的二次加载,并分析了准刚性质量块尺寸对二次加载的影响规律;采用二点波分离方法对叠加的应力波进行了有效分离和计算,在总长4 m的压杆系统中实现了1.2 ms的长历时加载,并可以准确获得试件的加载应变率曲线和应力应变关系。建立了直撞式霍普金森压杆二次加载有限元模型,数值仿真结果表明,该实验技术能有效地实现试件的二次加载,与超长SHPB系统获得的仿真结果相比较,两者的试件应力应变关系完全一致。利用该技术对1100铝合金材料进行动态压缩实验,实现了其在102 s−1量级应变率下的大变形动态力学性能测试。

  相似文献   

5.
利用晶体细观力学模型,依据组元材料的单晶体变形性质,以Al-Al2Cu自生复合材料为模型材料,用数值法模拟其拉伸和循环拉伸变形过程,得到了与有关实验结果相符的应力-应变曲线,研究了增强相间距和循环加载过程对复合材料变形行为的影响,通过考虑变形过程中组元相及其界面的应力分布规律,分析研究了循环变形过程中基体Bauschinger效应对于复合材料微观变形与损伤机制的作用,结果表明,晶体细观力学模拟计算  相似文献   

6.
采用考虑横向惯性效应的Rayleigh-Love杆理论分析了一个弹性试件在分离式霍普金森压杆(SHPB)加载过程中的内部弹性波传播过程,运用Laplace变换和反变换方法,得到了试件内部各点的变形、速度、应变和应力解析解.通过数值计算,得到梯形入射波加载情况下,纵向应力在试件内部的连续变化过程,以及波传播所伴随的横向附加应力.计算表明:在试件/入射杆界面附近,初次加载所产生的横向附加应力最大,可达入射波平台的12%;在大部分试件区域,纵向应力波传播将造成入射波平台4%~6%的横向附加应力;材料的泊松比越大,或者杆/试件声阻抗比越小,所伴随的横向附加应力越大;梯形波的上升时间和试件长径比对横向附加应力影响不大.  相似文献   

7.
基于“增量变形力学”理论,研究了径向和轴向均匀初应力作用下单向复合材料圆柱板中周向波的传播特性,应用Legendre多项式方法求解了耦合波动方程。讨论了单向复合材料纤维方向分别为周向和轴向时,初应力对圆柱板中的周向类Lamb波和SH波的影响。数值分析结果表明初应力对周向类Lamb波和周向SH波的影响是非常不同的;轴向初应力对频散曲线、位移和应力分布的影响与径向初应力的影响也不相同。  相似文献   

8.
根据粘弹性蛋白质气泡有限变形的应力方程,利用Bingham流体的本构关系,得到Bingham流体中蛋白质气泡在内外压力差、弹性有限变形应力及粘性耗散产生的应力共同作用下内径的非线性振动方程.运用数值方法求解该方程,对蛋白质气泡有限变形的振动特性进行分析.研究了流体的静压力、Bingham流体的特性参数、蛋白质膜的粘弹性对蛋白质气泡振动特性的影响.结果表明,蛋白质气泡膜的振动具有非线性特性,降低气泡内外的压力差,振幅减小,振幅随时间衰减变慢,振动频率降低,平衡时气泡变形小,变形达到平衡时所需的时间也相对较短;增加Binghain流体的塑性粘度会使振幅衰减速度加快,频率降低,平衡时气泡变形小;增加蛋白质膜的粘弹性会抑制气泡的振动,增强气泡承受载荷的能力.  相似文献   

9.
动态拉伸试验中试样应变测试的有效性分析   总被引:3,自引:0,他引:3  
田宏伟  郭伟国 《实验力学》2008,23(5):403-410
为了评估将试样通过胶粘连接到加载杆的Hopkinson杆装置所获得试样应变的有效性,对四种强度刚度差异较大的纤维增强复合材料进行了动态拉伸试验。试验时,试样通过环氧胶和杆夹层粘接,试样的应变分别按照Hopkinson杆一维应力波理论计算和试样上应变计直接准确测量得到。结果证明:对小变形碳纤维复合材料,按一维应力波理论计算的应变与试样上直接所测应变值偏差超过100%;对较大变形的GFRP和KFRP层合板,两者偏差小于40%。说明采用Hopkinson杆一维应力波理论计算的试样应变不准确。为修正不准确性,一是通过大量数据分析建立按一维应力波理论计算值与直接测量应变之间的关系式,用此式可使此试验装置获得有效的试样应变;二是借助ABAQUS有限元模拟分析得出粘胶层以及试样过渡弧段的变形,用一维应力波理论计算的应变减去此变形,也可获得有效的试样应变。  相似文献   

10.
本文提出了有限条塑性系数增量初应力法,用于分析钢压杆的弹塑性稳定极限承载力,该法采用分级加载,用有限条法建立结构的增量平衡方程;在塑性范围,引入截面的塑性系数对弹性刚度进行折减得到结构的弹性刚度矩阵;用修正的Newto-Raphson方法迭代求解,数值结果表明,本法效率较高,与钢压杆试验结果吻合良好,可以考虑残余应力和载荷偏心的影响,可望实现大型超静定结构的极限载力分析。  相似文献   

11.
Numerical and experimental investigations on the influence of nonuniform initial temperature on the transient heat transfer measurements are presented in this paper. The case of film cooling is investigated. When the initial wall temperature is nonuniform, the results of heat transfer coefficient and film cooling effectiveness, which are calculated by the equations derived with constant initial temperature, could deviate from the true values badly, especially in the condition of short test duration. Using initial wall temperature which is higher than the real values causes the results of heat transfer coefficient and film cooling effectiveness lower than the true values. And lower initial wall temperature produces higher results of heat transfer coefficient and film cooling effectiveness. However, when the initial temperature distribution in the region where conduction plays more influence on the wall surface temperature than the convection is well fitted by the cubic polynomial, accurate results can be obtained by the new equation which is derived from 1-D unsteady conduction model with nonuniform initial wall temperature. Some suggestions are also introduced to reduce the influence of nonuniform initial temperature when the initial temperature distribution is difficult to obtain and the equation derived from constant initial temperature has to be employed.  相似文献   

12.
IntroductionThedynamicproblemofstructurestrengthisanoutstandingproblem.Afterconsultingsomepapers,wecanknowthatthissubjecthasbeenstudiedextensivelybyseveralauthors[1~7].Theirinvestigationsonlybasedoncalculatingvibrationinalayeredstructureandpresenting…  相似文献   

13.
徐强  张福祥 《实验力学》1999,14(4):505-508
介绍利用激光摩尔偏折仪和压阻式压力传感器对发动机喷流起始冲击波的基本形态进行的研究. 研究结果验证了在燃气流团前存在着起始冲击波及发展初期具有非球面的特性,并提出了喷口起始冲击波波阵面发展的新结构,对前人有关起始冲击波发展结构的研究结果进行了修正.  相似文献   

14.
The fractional viscoelastic equation (FVE), which is a second-order differential equation with fractional derivatives describing the dynamical behavior of a single-degree-of-freedom viscoelastic oscillator, is considered. Some viscoelastic damped mechanical systems may be described by FVEs. However, FVEs with conventional nonzero initial values cannot generally be solved. In this paper, the prehistories of the unknown functions before the initial times, referred to as the initial functions, are taken into account to solve FVEs. Mathematically, appropriate initial functions are essential for unique solutions of FVEs. Physically, the initial functions reflect the processes of giving the initial values. FVEs are solved for some initial functions both by analytical and numerical methods. The initial functions affect the solutions of FVEs. It is discussed how the solutions depend on the initial functions. Implication of the solutions to viscoelastic materials will be discussed.  相似文献   

15.
为了研究不同初始条件对甲烷-空气混合物爆炸极限的影响,利用容积为20 L的爆炸罐,在不同初始温度(25~200 ℃)和初始压力(0.1~1.0 MPa)条件下测定了甲烷-空气混合物的爆炸极限。实验结果表明,随着初始温度和初始压力的升高,爆炸上限升高,爆炸下限降低,爆炸极限范围扩大。在实验温度和压力范围内,常压/常温条件下,爆炸上限和下限与初始温度/初始压力呈线性相关。爆炸上限与初始温度的相关性受初始压力的影响,其与初始压力的相关性也与初始温度有关。然而,初始压力/初始温度对爆炸下限的影响与初始温度/初始压力的相关性并不显著。初始温度和初始压力对爆炸极限的耦合影响比单一因素对其的影响大,且相较而言,其对爆炸上限的影响更为显著。本文中绘制了影响曲面来描述初始温度和初始压力如何影响甲烷-空气混合物的爆炸极限。  相似文献   

16.
在单元的随动坐标系下,建立了初始弯曲对杆单元轴向刚度影响的计算公式,导出了考虑初始弯曲的非线性杆单元刚度矩阵;从经典的梁-柱理论出发,给出了考虑初始弯曲的非线性空间梁单元切线刚度矩阵推导过程。将建立的初始弯曲单元应用于弦支穹顶结构算例的非线性稳定承载力分析,研究了杆件初始弯曲对结构整体非线性稳定性能的影响,结果表明,杆件初始弯曲的存在会降低结构的整体刚度和极限承载力,而在不同的初始预应力状态下,极限荷载随初始弯曲增加都基本呈线性下降,并且其关系曲线基本平行。本文建立的基于初弯曲单元的非线性分析方法,可推广应用于各种类型空间网格结构的非线性分析,为结构设计方案的选择提供更为科学的依据。  相似文献   

17.
The fractional viscoelastic equation (FVE), which is a second-order differential equation with fractional derivatives describing the dynamical behavior of a single-degree-of-freedom viscoelastic oscillator, is considered. Some viscoelastic damped mechanical systems may be described by FVEs. However, FVEs with conventional nonzero initial values cannot generally be solved. In this paper, the prehistories of the unknown functions before the initial times, referred to as the initial functions, are taken into account to solve FVEs. Mathematically, appropriate initial functions are essential for unique solutions of FVEs. Physically, the initial functions reflect the processes of giving the initial values. FVEs are solved for some initial functions both by analytical and numerical methods. The initial functions affect the solutions of FVEs. It is discussed how the solutions depend on the initial functions. Implication of the solutions to viscoelastic materials will be discussed.  相似文献   

18.
Co-injection of water with CO2 is an effective scheme to control initial gas saturation in porous media. A fractional flow rate of water of approximately 5–10% is sufficient to reduce initial gas saturations. After water injection following the co-injection, most of the gas injected in the porous media is trapped by capillarity with a low fractional volume of migrating gas. In this study, we first derive an analytical model to predict the gas saturation levels for co-injection with water. The initial gas saturation is controlled by the fractional flow ratio in the co-injection process. Next, we experimentally investigate the effect of initial gas saturation on residual gas saturation at capillary trapping by co-injecting gas and water followed by pure water injection, using a water and nitrogen system at room temperature. Depending on relative permeability, initial gas saturation is reduced by co-injection of water. If the initial saturation in the Berea sandstone core is controlled at 20–40%, most of the gas is trapped by capillarity, and less than 20% of the gas with respect to the injected gas volume is migrated by water injection. In the packed bed of Toyoura standard sand, the initial gas saturation is approximately 20% for a wide range of gas with a fractional flow rate from 0.50 to 0.95. The residual gas saturation for these conditions is approximately 15%. Less than approximately 25% of the gas migrates by water injection. The amount of water required for co-injection systems is estimated on the basis of the analytical model and experimental results.  相似文献   

19.
The initial boundary value problem for the two-dimensional primitive equations of large scale oceanic motion in geophysics is considered.It is assumed that the depth of the ocean is a positive constant.Firstly,if the initial data are square integrable,then by Fadeo-Galerkin method,the existence of the global weak solutions for the problem is obtained.Secondly, if the initial data and their vertical derivatives axe all square integrable,then by Faedo-Galerkin method and anisotropic inequalities,the existerce and uniqueness of the giobal weakly strong solution for the above initial boundary problem axe obtained.  相似文献   

20.
The initial boundary value problem for the two-dimensional primitive equations of large scale oceanic motion in geophysics is considered. It is assumed that the depth of the ocean is a positive constant. Firstly, if the initial data are square integrable, then by Fadeo-Galerkin method, the existence of the global weak solutions for the problem is obtained. Secondly, if the initial data and their vertical derivatives are all square integrable, then by Faedo-Galerkin method and anisotropic inequalities, the existerce and uniqueness of the global weakly strong solution for the above initial boundary problem are obtained.  相似文献   

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