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排序方式: 共有654条查询结果,搜索用时 15 毫秒
1.
M. Abdulkareem A. Ganiyu O. Nathaniel I. Mallum W. Dunu 《Materialwissenschaft und Werkstofftechnik》2021,52(10):1064-1072
Various damage detection methods have been proposed by several researchers in the past few decades. Amongst them, the efficiency of mode shapes in detecting damage has been demonstrated by many researchers when further processed. In most cases, the processing involves expansion or reduction of the mode shape data. However, vital information that are damage-prints are often lost during processing of the mode shape data. In addition, most of these processes involve long and complex computation, thus, leading to inaccurate damage identification. In this study, a simple and fast damage identification technique is proposed to identify damage in beam structures. Interval analysis is applied to the mode shapes of a beam structure in the damaged and undamaged states. The interval situations of each of the beam's segment via mode shape are derived to obtain the upper and lower bounds and the derived bounds are compared. To establish a relationship for identify the damaged point, a possibility of damage existence is defined for each segment of the beam structure. The mode shape increment is defined as the increase in the mode shape value. Furthermore, a damage measure index that provide enhance damage information is obtained as the product of the possibility of damage existence and mode shape increment. A numerical model of a simply supported steel beam is applied to demonstrate this method by imposing damage through thickness reduction of elements in segments. In addition, a parametric analysis is carried out to evaluate noise effect by considering varying damage severities and different noise levels. The results showed that this method is simple and provides considerable accurate results. 相似文献
2.
There are many coolants frequently used in the industry for controlling not only heat transfer, but also temperature distribution in a confined domain. However, little is known on the thermal properties of sodium droplets. The qualitative analysis of differential equations that model the thermal explosion, nonlinear dynamic of sodium droplet with variable thermophysical properties when thermal radiations are considered as suggested by Cogley et al, Sohrab et al, and P‐1 approximation Sazhin et al is deliberated upon in this study. The governing equations, first‐order nonlinear ordinary differential equations, are nondimensionalized using the appropriate similarity variables. The existence and uniqueness of the solutions, concavity, and convexity of the temperature distribution, and positivity nature of the solutions of the dimensionless governing equations are established. It is concluded that there exists a solution for a certain range of the admissible parameters and when the reduced activation energy is negative and temperature distribution fits concavity. More so, the major criteria to obtain a positive solution are outlined in this study. 相似文献
3.
世界范围内的土壤中广泛存在重金属污染,正确认识土壤中重金属的存在形式有利于采取适当的方式进行土壤修复。现有技术中,根据修复原理可分为物理、化学、生物、电气和热修复五种,具体方法为覆盖、封装、填埋、土壤冲洗、电动萃取、稳定化/固化、玻璃化、植物修复及微生物修复。这些技术具有相应的优缺点和适用性,覆盖、封装和填埋适用于污染严重面积小的区域;土壤冲洗工程量大,需要对螯合剂进行处理;电动萃取适用于浅层、低浓度污染场地,处理时间长;稳定化/固化应用广泛但不能从土壤中根除重金属;植物修复需提高效率。合适的修复技术对于重金属污染土壤再利用至关重要,需结合污染的类型和程度、修复目标、场地特征、成本效益、修复时间。 相似文献
4.
5.
Maia M. Svanadze 《热应力杂志》2018,41(8):1022-1041
In this article, the linear theory of binary thermoviscoelastic mixtures is considered and the basic boundary value problems (BVPs) of steady vibrations are investigated. Namely, the fundamental solution of the system of equations of steady vibrations is constructed explicitly and its basic properties are established. Green’s second and third identities are obtained and the uniqueness theorems for classical solutions of the internal and external basic BVPs of steady vibrations are proved. The surface and volume potentials are constructed and their basic properties are given. The determinants of symbolic matrices are calculated explicitly. The BVPs are reduced to the always solvable singular integral equations for which Fredholm’s theorems are valid. Finally, the existence theorems for classical solutions of the internal and external BVPs of steady vibrations are proved by the potential method and the theory of singular integral equations. 相似文献
6.
研究了一类有限非线性分数阶差分方程边值问题正解的存在性.首先利用分数阶差分方程及其边值条件给出了Green函数,并分析了其性质;然后利用Krasnosel’skii不动点定理,建立了这类分数阶差分方程边值问题正解的存在性定理. 相似文献
7.
在固气比[Gs/(ρg?Ug)]为2.13~47.95的范围内,对循环流化床变径组合提升管内团聚物持续时间进行了测量与分析,结果表明:单个团聚物持续时间为0.001 28~0.601 60 s,局部位置团聚物平均持续时间为0.014 32~0.160 64 s;在数量上,持续时间小于0.064 00 s的低浓度团聚物占87.69%,持续时间大于0.064 00 s 的高浓度团聚物占12.31%;在固气比较低时,主要由低浓度团聚物主导平均持续时间;在固气比较高时,临近边壁区域主要由高浓度团聚物主导平均持续时间。时间多尺度分析结果表明:低浓度团聚物中,在数量上主要以持续时间为0.001 28~0.038 40 s 的团聚物为主,在对平均持续时间的影响上主要以持续时间为0.012 80~0.038 40 s 的团聚物为主;高浓度团聚物中,在数量和对平均持续时间的影响上,均主要以持续时间为0.064 00~0.128 00 s 的团聚物为主。 相似文献
8.
Juntang Ding 《Computers & Mathematics with Applications》2013,65(11):1808-1822
In this paper we discuss the blow-up for classical solutions to the following class of parabolic equations with Robin boundary condition: where is a bounded domain of with smooth boundary . By constructing some appropriate auxiliary functions and using a first-order differential inequality technique, we derive conditions on the data which guarantee the blow-up or the global existence of the solution. For the blow-up solution, a lower bound on blow-up time is also obtained. Moreover, some examples are presented to illustrate the applications. 相似文献
9.
10.
研究机械加工过程中夹紧力的合理规划是保证加工质量的核心环节,对于实现加工过程的可靠性和精密化至关重要,为此构建了全区域夹紧力变向迭代规划算法。根据工件在装夹布局中的受力状态以及工件与装夹元件之间接触力的方向约束条件,分别依据夹紧力大小与夹紧点位置的未知和已知情况,结合线性规划技术建立了力的存在性和力的可行性分析方法。在夹紧力存在的条件下,通过离散夹紧表面为点集的方法,逐点地以一定步长正向从最小值开始选取夹紧力的大小,根据当前值与上一次取值之间可行性的差异,确定下一次取值的步长及其方向,若可行性相同则以相同步长继续正向取值,否则步长减半、反向取值,直至步长的绝对值在阈值范围之内,建立全区域内夹紧力的变向迭代规划算法。该算法将连续型的夹紧力设计问题转化为离散型,不仅适合于形状复杂的工件,而且还利于计算机实现夹紧力的自动化设计。 相似文献