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1.
通过间解的分离,本文将径向多裂纹柱体的导曲函两个调和函数表示,使问题归为解一组混混合型积分方程。针对方程的特点,本文联合使用三次样条边界法与奇异积分方程的数值方法对所得方程建立了数值法,并对裂纹相交情形作了特殊处理。最后对工程中感兴趣的一些典型的多裂纹柱体的扭转作了例题计算,结果表明,本文方法具有收敛快,精度高的特点。 相似文献
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本文提出了一组应力函数,采用边界配置方法计算了含中心裂纹不同截面形状柱体扭转时的应力强度因子。有关椭圆截面柱体的算例表明,本文方法具有良好的精度。同时,文中给出了圆、椭圆和矩形等不同截面柱体的计算结果。 相似文献
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给出一个适合于带纵向裂纹柱体圣维南扭转的等参数元素,即在裂纹尖端具有r-1/2奇异性的“1/4”八结点等参数元素。利用这个尖端元素,配合以本文作者在参考文献[2]中引入的八结点等参数元素,对含有径向纵裂纹的圆柱体进行了扭转计算。 相似文献
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给出一个适合于带纵向裂纹柱体圣维南扭围的等参数元素,在即在裂纹法端具有r^-1/2奇异性的“1/4”八结点等参数元素,利用这个尖端元素,配合以本文作者在「2」中引入的八结点等参数元素,对含有径向纵裂的圆柱进行了扭转计算。 相似文献
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本文用复变函数方法讨论了带有单裂纹的任意形横截面柱体的 Saint-Venant 扭转问题,提出了解析求解这类问题的一般方法及相应的解析算式。 相似文献
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文[1]用Melin变换求解了带径向裂纹系圆柱体的扭转问题。本文改用Cauchy型积分的方法简洁地将其推广至带任意内曲线裂纹系园柱体的扭转问题。 设挠曲函数W=K_φ(x,y),K为扭转率。若选取圆心为坐标原点,则φ的定解问题 相似文献
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本文将拉氏变换-边界元法用于表面裂纹问题的瞬态响应分析。文中讨论了拉氏反演参数的选择和动态应力强度因子的计算方法。作为程序的考核和离散方案的选择,分别地计算了水平柱体一端固定、另一端受p(t)=poH(t)载荷时的位移响应和具有贯穿裂纹的厚板在两种离散方案时的动态应力强度因子响应。最后,还计算了若干载荷工况的半圆表面裂纹板应力强度因子的瞬态响应,获得了有效的数值结果。 相似文献
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方柱的涡脱落频率及端部影响的风洞实验 总被引:2,自引:0,他引:2
本文报告了用压力传感器测量方形柱体涡脱落的实验方法和结果。实验在大气边界层风洞进行。方柱的截面为正方形,高宽比为5。压力传感器在测试前经过严格的标定。测量结果表明,随着来源速度沿高度的变化,方柱的涡脱落频率也随高度而变,而且,在柱体端部附近,涡脱频率和St数发生明显的抑制。和二维柱体一样,在一定的Re数范围内,三维柱体的Ro数与Re数也存在一种线性关系。 相似文献
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This paper addresses the stabilizing control problem for nonlinear systems subject to unknown actuator saturation by using adaptive dynamic programming algorithm. The control strategy is composed of an online nominal optimal control and a neural network (NN)-based feed-forward saturation compensator. For nominal systems without actuator saturation, a critic NN is established to deal with the Hamilton–Jacobi–Bellman equation. Thus, the online approximate nominal optimal control policy can be obtained without action NN. Then, the unknown actuator saturation, which is considered as saturation nonlinearity by simple transformation, is compensated by employing a NN-based feed-forward control loop. The stability of the closed-loop nonlinear system is analyzed to be ultimately uniformly bounded via Lyapunov’s direct method. Finally, the effectiveness of the presented control method is demonstrated by two simulation examples. 相似文献
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M. H. Sadr S. Astaraki S. Salehi 《Archive of Applied Mechanics (Ingenieur Archiv)》2007,77(11):795-807
In developing a neural network technique for a finite element model updating, researchers have been shown that the number
of training samples and their quality, significantly affect the accuracy of the NN predication. In this study, based on the
genetic algorithm (GA) method, we reduce the number of analyses required to develop the training pairs and reduce the amount
of time for training the NN. In the other words, a uniform distribution of design points inside the design space will be obtained
by means of this approach. To validate the efficiency of GA sample selection, random generation (RG) method is used for comparison.
Two comparisons are made based on a numerical and experimental example. One is updated from 10 degrees of freedom lumped parameters
system and the other is updated from a free–free beam using test data. The results indicate that the GA sample selection can
reduce the number of training samples without affecting the accuracy of the NN predication. In our present study, also, the
advantages of using frequency response function (FRF) data as input to the NN are kept and the drawback of having too many
frequency points is overcome by the application of principal component analyses (PCA). 相似文献
13.
Jiawei Xiang Yongteng Zhong Xuefeng Chen Zhengjia He 《International Journal of Solids and Structures》2008,45(17):4782-4795
A new crack detection method is proposed for detecting crack location and depth in a shaft. Rotating Rayleigh-Euler and Rayleigh-Timoshenko beam elements of B-spline wavelet on the interval (BSWI) are constructed to discretize slender shaft and stiffness disc, respectively. According to linear fracture mechanics theory, the localized additional flexibility in crack vicinity can be represented by a lumped parameter element. The cracked shaft is modeled by wavelet-based elements to gain precise frequencies. The first three measured frequencies are used in crack detection process and the normalized crack location and depth are detected by means of genetic algorithm. To investigate the robustness and accuracy of the proposed method, some numerical examples and experimental cases of cracked shaft are conducted. It is found that the method is capable of detecting crack in a shaft. 相似文献
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An elliptical front crack has been found to be more accurate and realistic for modeling the transverse surface crack in rotating
machinery compared with the widely used straight front crack. When the shaft rotates, the elliptical crack opens and closes
alternatively, due to gravity, and thus, a “breathing effect” occurs. This variance in shaft stiffness is time-periodic, and
hence, a parametrically excited system is expected. Therefore, the dynamic instability and steady-state response of a rotating
shaft containing an elliptical front crack are studied in the paper. The local flexibility due to the crack is derived, and
the governing equations of the crack shaft system are established using the assumed modes method. Utilizing the Bolotin’s
method and harmonic balance method, the boundaries of two typical instability regions and maximum response amplitude of the
cracked shaft could be computed numerically. The elliptical crack parameters (depth, shape factor and position) and damping
are, respectively, considered and discussed for their effects on the dynamic behavior of the elliptical cracked shaft. Some
research results might be helpful for the crack detection in rotating machinery. 相似文献
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正交各向异性复合井壁应力变形分析与应用 总被引:1,自引:0,他引:1
推出了正交各向异性多层复合井壁的应力、位移计算公式,分析了双层混凝
土中间夹泡沫塑料板的复合井壁的应力、变形规律. 发现当井壁环向弹性模
量小于径向弹性模量时,内壁最大剪应力和径向位移会随着环向模量的减小
而显著增大,若仍按各向同性设计,将可能出现病态井壁. 通过工程应用和现场测
试综合分析验证了上述结论,并提出了多层复合井壁破裂的新依据. 相似文献
16.
Cracks in concrete are common defects that may enable rapid deterioration and failure of structures. Determination of a crack’s
depth using surface wave transmission measurement and the cut-off frequency in the transmission function (TRF) is difficult,
in part due to variability of the measurement data. In this study, use of complete TRF data as features for crack depth assessment
is proposed. A principal component analysis (PCA) is employed to generate a basis for the measured TRFs for various simulated
crack (notch) cases in concrete. The measured TRFs are represented by their projections onto the most significant PCs. Then
neural networks (NN), using the PCA-compressed TRFs, are applied to estimate the crack depth. An experimental study is carried
out for five different artificial crack (notch) cases to investigate the effectiveness of the proposed method. Results reveal
that the proposed method can effectively estimate the artificial crack depth in concrete structures, even with incomplete
NN training. 相似文献
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The paper is concerned with the problem of stability of a power transmitting thin-walled shaft made of the active laminate PFC (piezoelectric fiber composite). The shaft rotates with a given operational angular velocity, and is loaded by a static torque. Such a system is known to exhibit divergence or oscillating type of instability. On the one hand presence of internal friction in the material of the shaft leads to loss of stability at a certain critical rotation speed. The static torque can be responsible for spatial deformation of the shaft axis on the other. A method preventing the system from such behavior is discussed in the paper. The method is based on application of a composite material, which contains active piezoelectric fibers. The fibers produce bending moments, and this way affect the dynamics of the entire system. Two control strategies are investigated. Results of numerical simulations are presented graphically. 相似文献
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大型汽轮发电机组短路时轴系扭振动力响应计算与分析 总被引:2,自引:0,他引:2
大型汽轮发电机组在短路时的轴系扭振动力响应,对于机组的安全可靠运行甚为关键。本文以国产某200MW机组为例,建立了轴系的连续质量计算模型,利用传递矩阵法求得其扭振固有频率及主振型,用振型查加法计算轴系在两相短路情况下的动力响应,计算中考虑了叶片叶轮系统与轴系扭振的耦合作用。本文对计算结果进行了分析,讨论了该机组的轴系扭振安全性,为机组的安全运行提供了理论依据。 相似文献
19.
利用水平圆柱形激波管对激波驱动的可压缩性气固两相流进行了试验研究.
利用压电式压力传感器、电荷放大器、示波器及计算机组成的压力信号测试系统, 对激波
与颗粒作用前后的气相参数进行测量及分析. 试验中测得了激波在管中的传播速
度, 波后气流的压力, 反射激波、透射激波的压力和速度等. 分别考察颗粒、装载
比、驱动气源以及入射激波马赫数等因素的差异对气相参数的影响.
试验结果表明: 激波与颗粒群相互作用时, 会产生反射激波和透射激波,
其强度与驱动气源、颗粒大小、颗粒装载比等参数有关;
激波衰减率随着装载比、马赫数的增大而减小. 研究指出,
在颗粒群被激波加速的初始阶段, 颗粒间的弹性碰撞起着重要的作用. 相似文献
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弹性体非线性振动多重共振的能量法 总被引:10,自引:1,他引:10
本论文以非线性振动理论的平均法为基础和力学的能量概念结合起来,找到了求解弹性体系非线性振动多重共振的能量法。应用本方法研究了电机轴系的双重共振等问题,证明了它是一个简易适用的方法。揭示了双重共振的一些新现象,理论得到了实验验证。 相似文献