薄膜后屈曲振动行为分析

建立了矩形薄膜后屈曲动态特性的数值分析方法,分析了薄膜屈曲后的动态行为,分析表明:在小幅褶皱情况下,动态分析可以不考虑褶皱对薄膜动态特性的影响,而在大幅褶皱情况下,褶皱会对薄膜振动的固有频率及振动模态产生较大的影响,动态分析必须考虑褶皱的存在;褶皱薄膜的振动模态与褶皱构形具有一定的相关性.     

Analysis on membrane wrinkling using stress extremum method

A stress extremum method is developed based on Von Karman equations for analysis of membrane wrinkles in this paper.A mechanical model is also established for analyzing shear membrane wrinkles.Expressi...     

Method to analyze wrinkled membranes with zero shear modulus and equivalent stiffness

To solve the problems of divergence, low accuracy and project application of membrane wrinkling analysis, an analysis method of zero shear modulus and equivalent stiffness was proposed. This method is an improvement to the previous method (Method I) of local coordinate transposition and stiffness equivalence. The new method is derived and the feasibility is theoretically proved. A small-scale membrane structure is analyzed by the two methods, and the results show that the computational efficiency of the new method (Method II) is approximately 23 times that of Method I. When Method II is applied to a large-scale membrane stadium structure, it is found that this new method can quickly make the second principal stress of one way wrinkled elements zero, and make the two principal stresses of two-way wrinkled elements zero as well. It could attain the correct load responses right after the appearance of wrinkled elements, which indicates that Method II can be applied to wrinkling analysis of large-scale membrane structures.     

薄膜褶皱的纹理特征分析

用薄膜进行了褶皱实验,选取规则区域,利用灰度共生矩阵提取的纹理特征进行了褶皱的纹理分析.结果表明,利用灰度共生矩阵的纹理特征可以准确的判断褶皱的疏密程度和方向,实验结果与理论预测吻合.     

Wrinkling analysis of creased rectangular membrane

In this paper,the wrinkle-crease interaction behavior of a rectangular membrane under edge tension is simulated.The creased membrane is modeled by using a Modified Two-Parameter model.In this model,two crease parameters,i.e.the effective modulus of creased membrane and the residual stress from creasing,are computed by using MacNeal’s method that was firstly applied directly in a flat membrane with the local crease.We have proposed a method to solve the wrinkling computing issue of the creased membrane by using a Direct Perturb-Force technique in our previous work.Based on our method,the effects of crease location on the wrinkle-crease interaction behavior can be evaluated accurately.These results will be of great benefit to the analysis and the control of the wrinkles in the membrane structures.     

利用图像的统计分析方法评价织物免烫等级

利用计算机图像处理的统计分析方法对织物的抗皱恢复性能进行了系统地分析，提出以图像的均值，方差及直方图的均值，方差，扭曲度，峰度，熵等多项指标评价织物的免烫性能，比较了这些评价指标的准确程度。指出直方图统计指标具有较高的准确度，这为织物免烫等级评定提供了一种新的方法。     

Numerical simulation of wrinkle phenomenon during multi-point forming process of shallow rectangle cup

In this paper, the principle of multi-point forming (MPF) technique is presented. One of the most serious defects, wrinkling, during the multi-point forming process of a shallow rectangle cup is discussed by means of numerical simulation on the shallow rectangle cup forming process. The effects of thickness, material of sheet metal and the pressure of the blank holder are investigated. Based on the simulation results, the reasons and control methods of wrinkling are pointed out. Moreover, the experiment on the multi-point die forming of the shallow rectangle cup by the MPF machine is done to validate the efficiency of the numerical simulation,and the result oroves that the application of an elastic cushion in the forming can restrain wrinkling efficiently.     

Regulating wrinkling patterns by periodic surface stiffness in film-substrate structures

Surface wrinkling of materials holds promise for important applications in diverse fields such as multifunctional surfaces and biomedical engineering. For these applications, it is of interest to attain various surface wrinkles with tunable wavelengths and amplitudes. Through a combination of experiments and numerical simulations, we here propose a method to regulate the wrinkling patterns in a film-substrate system by introducing periodic surface stiffness, which is generated through sequential specified ultraviolet-ozone(UVO) treatments. Both experiments and numerical simulations demonstrate that the proposed technique can produce various patterns with wide, tunable geometrical features and anisotropy. The effects of surface stiffness distribution, the exposure durations of UVO-treatments, and the loading biaxiality are examined on the generated surface patterns.     

Wrinkling analysis of square space membrane structure under corner tension forces

An analytical approach based on the bifurcation theory is presented, in which the wrinkles are treated as the local buckling phenomena of the elastic thin plate with little bending stiffness. The average wrinkling wavelength was determined by incorporating the stress field and the out-of-plane force equilibrium condition of the wrinkled membrane. The wrinkling amplitude was then obtained by associating the characteristics of wrinkling texture with the obtained wrinkling wavelength. Results reveal that the wrinkled pattern exhibits a noticeable difference when the tension load is changed gradually, and two wrinkling styles are identified. The first style occurs for symmetric and moderately asymmetric loading, and it is characterized by small, radial corner wrinkles; the second style occurs for strongly asymmetric loading and is characterized by a deep, large diagonal wrinkle. The analytical predictions on the wrinkling characteristics and the developed rules are validated against wrinkling experimental observations.     

充气薄膜结构的SMS展开分析方法

为有效分析充气薄膜结构的展开,提出基于能量原理分析充气薄膜结构展开的SMS方法,即弹簧-质点系统方法.对卷曲折叠充气直管采用SMS方法进行数值模拟,并与实验结果进行对比分析,发现其结果吻合良好,验证了这种方法的正确性.运用SMS方法分析不同充气速率对卷曲折叠充气管展开过程的影响以及充气圆环管和充气膜面的展开过程及动力性能.与传统的有限元方法比较,SMS方法建模简单,思路清晰,数值稳定性好.     

拉伸作用下薄膜褶皱影响因素数值分析

薄膜因其轻质，折叠体积小以及良好的力学性能等优点，在航空航天领域扮演着很重要的角色。薄膜属于柔性材料，由于其厚度小，抗弯刚度小的特点，在外部载荷较大时极易出现局部屈曲现象，从而产生褶皱。褶皱是影响空间薄膜结构性能的重要因素之一，因此研究薄膜褶皱特性及其抑制对薄膜结构在空间等领域的应用至关重要。本文主要研究薄膜的结构参数以及边界条件对薄膜褶皱特性的影响。针对拉伸作用下的方形薄膜结构，采用显式动力法对该结构进行了褶皱仿真分析，并将其仿真结果与理论计算结果进行对比，验证了仿真模型和分析结果的正确性。为了探究拉力作用下褶皱特性的变化规律，以方形薄膜为研究对象，分析了薄膜长宽比、内角、夹持宽度等结构参数以及边索结构对褶皱特性以及变形的影响规律。结果表明，当薄膜长宽比由1.0增加至1.5时，薄膜的面外变形增大，且褶皱分布区域扩大。当薄膜中内角小于75°时，褶皱主要分布于薄膜两边夹角为锐角的角区域。此外，增大薄膜夹持宽度和增加边索结构均可有效抑制褶皱的发生。为了对分析结果进行进一步的验证，进行了不同夹持宽度下的褶皱测试，通过褶皱数量和幅值变化的趋势分析，及与仿真结果的对比，可以证明仿真模型的正确性，为薄膜结构的张拉分析提供了一定的理论依据。     

充气膜结构有限元找形的体积微分法

为确定充气膜结构找形分析时,在内压已知情况下膜面张力的大小,根据多元函数泰勒展开公式推导了该类结构充气膨胀的体积微分方程,并由基于U.L.格式的非线性有限单元法,建立了以节点位移和膜面初始张力为未知量的平衡方程,编制了在给定内部气压及膨胀体积情况下的找形分析程序。对球面及圆柱面充气膜结构进行了找形计算,得到的数值结果与由球面及圆柱面的矢高、内压、初始张力相互关系得到的理论解进行比较并得到了验证。计算结果表明,提出的基于有限元的体积微分法可有效的用于充气膜结构的找形分析。     

A simple analytical method for deflation prediction of inflatable structures

The static performance of inflatable structures has been well studied and the dynamic deployment simulation has received much attention. However, very few studies focus on its deflation behavior. Although there are several dynamic finite element algorithms that can be applied to the deflation simulation, their computation costs are expensive, especially for large scale structures. In this work, a simple method based on classic thermodynamics and the analytical relationship between air and membrane was proposed to efficiently analyze the air state variables under the condition of ventilation. Combined with failure analysis of static bearing capacity, a fast incremental analytical method was presented to predict both elastic and post wrinkling deflation process of inflatable structures. Comparisons between simplified analysis, dynamic finite element simulation, and a full-scale experimental test are presented and the suitability of this simple method for solving the air state and predicting the deflation behavior of inflatable structures is proved.     

张拉膜结构风致动力灾变研究进展

为明确膜结构的风致动力灾变机理,分别从现场实测、气弹模型风洞试验、流固耦合数值模拟等方面的研究进展,探讨了膜结构附加气动力和气弹失稳机理等问题.研究表明:受实测设备、气弹模型试验相似理论和流固耦合模拟方法等方面的限制,膜结构流固耦合现象的观测模拟方面,针对实际工程的研究仍比较少;流固耦合振动机理方面,普遍认为,气弹失稳与形成于结构表面附近的旋涡有关,表现为结构总阻尼比的大幅衰减;但已有研究成果多基于对简单膜结构在近似均匀流场中振动现象的观测得出,与实际工程相差比较大.建议以后从以下几方面进一步深入:气弹模型试验相似理论的相似偏差量化分析方法和误差修正技术;大型膜结构实际工程流固耦合数值模拟关键技术;基于现场实测、气弹模型风洞试验、数值模拟和解析等多种研究手段的膜结构气弹失稳机理研究;便于工程设计人员接受的考虑流固耦合的膜结构抗风设计方法.     

管件液压成形过程的有限元分析及实验研究

以圆管变形为管球相间零件为研究对象,对液压成形这种新工艺进行研究.采用计算机数值模拟与试验相结合的方法,分析了圆管液压成形过程.管件液压成形主要有褶皱和破裂两种失效形式,而成形控制中最主要的参数之一是压力,即管件内部压力和轴向压力.在对不同加载路径进行分析后,得出模拟结果与相同条件下的实验结果比较吻合的结论.研究表明了液压成形工艺中加载路径(内压力与轴向压力的配比关系)的重要性,同时也证实了用计算机模拟仿真液压成形过程具有一定的可靠性.     

Analysis on nonlinear wind-induced dynamic response of membrane roofs with aerodynamic effects

Based on the characteristics of membrane structures and the air influence factors, this paper presented a method to simulate the air aerodynamic force effects including the added air mass, the acoustic radiation damping and the pneumatic stiffness. The infinite air was modeled using the acoustic fluid element of commercial FE software and the finite element membrane roof models were coupled with fluid models. A comparison between the results obtained by FE computation and those obtained by the vibration experiment for a cable-membrane verified the validity of the method. Furthermore, applying the method to a flat membrane roof structure and using its wind tunnel test results, the analysis of nonlinear wind-induced dynamic responses for such geometrically nonlinear roofs, including the roof-air coupled model was performed. The result shows that the air has large influence on vibrating membrane roofs according to results of comparing the nodal time-history displacements, accelerations and stress of the two different cases. Meantime, numerical studies show that the method developed can successfully solve the nonlinear wind-induced dynamic response of the membrane roof with aerodynamic effects.     

剪力下起皱的有限元分析

针对剪力起皱的模拟试验模型，利用弹塑性有限元方法对试样变形区的受力进行了数值解析，得到了变形区的网格变化，应力等势线、起皱区边界的应力分布以及最初失稳点的近似纯剪应力状态，分析了最初失稳点的位移及剪应力在变形过程中的变化，发现它们的变化规律及起皱过程及其力的特征值完全相同，且分析结果与实验验证结果的误差很小。     

方盒形件多点成形缺陷的数值模拟

以方盒形件多点成形过程为例,从拉延形状、板厚、材质、压边力大小、变形程度等方面入手,利用逐级更新的Lagrange格式,采用满足Hill厚向异性屈服准则的弹塑性非线性材料模型,有效地模拟了盒形件多点成形过程中的压痕、起皱现象,并通过实验得到验证。同时得出利用弹性垫成形的新工艺可有效抑制压痕、起皱产生的结论。     

膜结构大变形分析的向量式有限元4节点膜单元

基于向量式有限元基本原理,首先推导了4节点膜单元的基本公式,详细阐述了通过逆向运动获得单元节点纯变形位移的过程,以及进一步通过变形坐标系获得单元节点内力的求解方法;同时对4节点膜单元的位置模式和内力计算的数值积分等问题提出了合理可行的处理方法。在此基础上编制了4节点膜单元的计算分析程序,通过算例分析验证了理论公式和所编制程序的正确性和有效性,进而将本文方法应用于气枕充气和布料悬垂等膜结构大变形大转动问题的计算分析。     

伞形膜结构在冰雹荷载作用下的非线性动力响应

对伞形张拉膜结构在自然灾害等外荷载冲击下的振动反应进行研究,为实际工程膜结构建筑受灾破坏分析提供依据。基于冯·卡门大挠度理论和薄板振动理论,建立伞形张拉膜结构在冰雹荷载作用下的非线性动力响应控制方程。采用贝塞尔函数及欧拉方程求得其振型函数,再运用KBM摄动法和迦辽金法对控制方程求解,得到其动力响应的近似解析解。利用Mathmatics软件对方程进行求解并对求解后的数据进行整理,通过Origin绘图软件画出膜面受迫振动后的时程位移图。采用ANSYS软件建立伞形张拉膜结构的有限元模型;再通过LS-DYNA显示动力学模块对冰雹冲击膜面的动力过程进行模拟,得到膜面动力响应的结果。同理,画出数值模拟结果的位移图,将整理后的理论与数值分析数据结果进行对比分析,结果表明,理论解析和数值分析结果吻合。