共查询到19条相似文献，搜索用时 296 毫秒
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根据一种修正的余能原理，建立了一类具有一个无外力圆弧边，且结点含转动自由度的4结点杂交应力膜元。该元内假定应力场满足以柱坐标表示的平衡方程，及圆弧边的无外力边界条件；边界位移与相邻元协调。数值算例表明，这类特殊杂交应力元，可有效地分析具有圆形槽孔及倒圆角槽孔板的应力分布。 相似文献
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应用假设应力杂交元的方法,导出了一个八节点的实体元。此元具有二个平行的表面及一个无外力自由的园柱表面。引用园柱坐标、以使所假设的应力场满足平衡方程及固柱边界面无外力的条件。当退化至平面应力状态时,此应力场也满足协调方程。一些算例证实这种特殊元在分析具有固孔实体时的优越性。 相似文献
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本文提出了在有限元中模拟铰接耳片的一种方法。利用不共用节点的两个三角板单元模拟耳片,在相同位置设有两个独立节点,采用MPC将两个节点连接,利用位移协调条件协调两个节点在耳片平面内的平动位移,释放两个单元在该位置的转动自由度及垂直耳片平面的自由度,从而使三角板单元只传递平行于耳片的剪力,而不再传递其它方向的力和力矩,更为准确地反映实际结构的传力特点。 相似文献
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根据杂交应力理性模式，基于一种修正的Hellinger－Reissuer原理，建立了具有一个无外力斜边的杂交应力元，其应力场由无边界面力在非协调位移上所作虚功之和为零的约束条件导出，将这种特殊元与具有一个无外力圆弧边的杂交应力元联合，可有效地分析具有倒圆角V型槽孔板的应力集中，并可提供远较一般假定位移及一般假定应力元准确的孔边应力分布。 相似文献
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基于修正的偶应力理论、Kelvin-Voigt模型,研究微观结构旋转影响下简支状态的双层粘弹性纳米板屈曲分析。首先,结合考虑修正的偶应力弹性理论和弛豫理论,将粘弹性微观结构、局部旋转和应力松弛分别纳入了经典粘弹性板理论中。通过分析粘弹性纳米板,得到了偶应力张量。基于达朗贝尔原理和Kirchhoff板理论,采用变分方法求出了粘弹性纳米板的尺寸相关微积分方程及其边界条件。该模型利用Boltzmann叠加原理,利用积分型本构关系对线性非老化材料的粘弹性行为进行了研究。利用Navier的方法 Laplace变换得出了简支的粘弹性双层板的屈曲荷载。根据解析解,分析发现介质的温克尔模量和剪切模量,极限弹性模量与初始弹性模量比值等因素对系统的屈曲荷载有一定的依赖关系。 相似文献
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根据Ｈｅｌｌｉｎｇｅｒ－Ｒｅｉｓｓｎｅｒ原理，建立了一种具有一个无外力圆形边界的特殊杂交应力元，其应力场准确满足弹性力学平衡方程、协调方程及无外力圆弧上的边界条件。根据修正的Ｈｅｌｌｉｎｇｅｒ－Ｒｅｉｓｓｎｅｒ原理，建立了另一种具有一个无外力直边界的特殊杂交应力元，其应力场在元上变分满足平衡方程，但准确满足无外力直边上的边界条件。数值算例表明：特殊假定应力元与一般假定位移元这两类元联合，能十分有效地进行纵向倒圆槽孔板的应力集中分析。 相似文献
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分析了风电机纽塔筒结构计算方法,着重对塔筒静强度分析的建模方法进行研究.实体单元建立塔筒有限元模型的位移计算结果偏差很小,而应力值偏差较大,这是由于实体单元的节点没有转动自由度,不能传递附加弯矩.且极限工况下,塔筒局部应力过大,可以通过增加壁厚的方法提高结构强度. 相似文献
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Couple-stress solutions are obtained near the hole boundary of an infinite elastic plane subjected to a radial concentrated force at x = b, y = 0,under the restriction of r/b<-0.2 and b/l?;-10. Here r and l are the distance from the center of the hole to the point of interest and a characteristic length (couple-stress constant). At r = a, θ = ±π2, the stress ratio of the couple-stress solution to the classical one for the current problem is slightly lower than one of the Mindlin problem (1) for some values of v, except for v = 0.5 where they are equal. The dimensionless stress σ̂θθ is found along the hole boundary. 相似文献
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《Journal of The Franklin Institute》2021,358(13):6897-6921
This paper presents a novel switching predefined-time parameter identification algorithm with a relaxed excitation condition based on the dynamic regressor extension and mixing (DREM) method. DREM often requires the persistent excitation (PE) of the extended square regressor's determinant to ensure exponential parameter convergence. Unlike the classical DREM method, a new parameter identification algorithm configured with a two-layer filter technique is proposed under a relaxed initial excitation (IE) condition, rather than strict PE. A key point in choosing IE instead of PE is the introduction of a smooth switching function that dominates the pure integral action and filter behavior of the extended square regressor. The proposed algorithm relies on the predefined-time stability theorem and the settling-time of the identification algorithm is set a priori as a system parameter. The contributions of this paper are a novel switching predefined-time parameter estimation algorithm that 1) relaxes the stringent PE condition, 2) achieves predefined-time convergence, and 3) guarantees the monotonicity of each element of the parameter error inherited from the classical DREM method. Comparative simulation results are presented to illustrate the effectiveness of the proposed algorithm. 相似文献
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《Journal of The Franklin Institute》2023,360(3):2116-2132
This paper studies the predefined-time practical consensus problem for multiple single-integrator systems through event-triggered control. A new kind of time-varying functions is firstly proposed. Then, new event-triggered control inputs as well as triggering conditions are designed on the basis of the time-varying function and the local broadcasted states. In particular, the control scheme is fully-distributed because no global information of the system and the communication topology is needed. Furthermore, the consensus analysis is presented based on a sufficient condition for predefined-time practical stability. It illustrates that practical consensus can be ensured with a completely pre-specified time. Besides, the exclusion of Zeno behavior at all the time instants is addressed. Numerical results verify the validity of the obtained control method. 相似文献
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Efficient lysis is critical when analyzing single cells in microfluidic droplets, but existing methods utilize detergents that can interfere with the assays to be performed. We demonstrate robust cell lysis without the use of detergents or other chemicals. In our method, cells are exposed to electric field immediately before encapsulation in droplets, resulting in cell lysis. We characterize lysis efficiency as a function of control parameters and demonstrate compatibility with enzymatic assays by measuring the catalysis of β-glucosidase, an important cellulase used in the conversion of biomass to biofuel. Our method enables assays in microfluidic droplets that are incompatible with detergents. 相似文献
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给出新型三类用理性杂交模式、根据一种修正的Ｈｅｌｌｉｎｇｅｒ－Ｒｅｉｓｓｎｅｒ原理、建立高精度非协调轴对称实体旋转有限元时，其单元刚度矩阵的准确计算式。 相似文献
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We conduct a numerical investigation and analytical analysis of the effect of slippage on the thermocapillary migration of a small liquid droplet on a horizontal solid surface. The finite element method is employed to solve the Navier-Stokes equations coupled with the energy equation. The effect of the slip behavior on the droplet migration is determined by using the Navier slip condition at the solid-liquid boundary. The results indicate that the dynamic contact angles and the contact angle hysteresis of the droplet are strictly correlated to the slip coefficient. The enhancement of the slip length leads to an increase in the droplet migration velocity due to the enhancement of the net momentum of thermocapillary convection vortices inside the droplet. A larger contact angle leads to an increase in the migration velocity which in turn enlarges the rate of the droplet migration velocity to the slip length. There is good agreement between the analytical and the numerical results when the dynamic contact angle utilizes in the analytical approach obtained from the results of the numerical computation, and the static contact angle is smaller than 50°. 相似文献
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Hong-Xiao Zhang Ping Hu Zhi-Wei Liu Li Ding 《Journal of The Franklin Institute》2017,354(14):6364-6380
In this article, a novel distributed event-triggered control protocol for the consensus of second-order multi-agent systems with undirected topology is studied. Based on the proposed control protocol, the event-triggered condition is evaluated only at every sampling instant. The control input for each agent will be updated with local information if and only if its condition is violated. Both ideal and quantized relative state measurements are considered under this framework. Some sufficient conditions for achieving consensus are derived using spectral properties of edge Laplacian matrix and the discrete-time Lyapunov function method. Finally, numerical examples are given to demonstrate the effectiveness of our theoretical results. 相似文献