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941.
In this paper, the substructuring technique is extended for the dynamics simulation of flexible beams with large deformation. The dynamics equation of a spatial straight beam undergoing large displacement and small deformation is deduced by using the Jourdain variation principle and the model synthesis method. The longitudinal shortening effect due to the transversal deformation is taken into consideration in the dynamics equation. In this way, the geometric stiffening effect, which is also called stress stiffening effect, is accounted for in the dynamics equation. The transfer equation of the flexible beam is obtained by assembling the dynamics equation and the kinematic relationship between the two connection points of the flexible beam. Treating a flexible beam with small deformation as a substructure, one can solve the dynamics of a flexible beam with large deformation by using the substructuring technique and the transfer matrix method. The dynamics simulation of a flexible beam with large deformation is carried out by using the proposed approach and the results are verified by comparing with those obtained from Abaqus software. 相似文献
942.
Minimum resistance ship hull uncertainty optimization design based on simulation-based design method
In the ship hull optimization design based on simulation-based design (SBD) technology, low precision of the approximate model leads to an uncertainty form of optimization model. In order to enable the approximate model with finite precision to maximize the effectiveness, uncertainty optimization method is introduced here. Wave resistance coefficient approximation model, built by back propagation (BP) neural network, is represented as a form of interval. Afterwards, a minimum resistance optimization model is established with the design space constituted by principal dimensions and ship form coefficients. Double-level nested optimization architecture is proposed: for outer layer, improved particle swarm optimization (IPSO) algorithm with learning factor improvement strategy is used to generate design variables, and for inner layer, modified very fast simulated annealing (MVFSA) algorithm is used to solve the objective function interval with uncertainty region. Cases calculation proves the effectiveness and superiority of uncertainty optimization method for ship hull SBD optimization design, thus providing a good way for finding optimal designs. 相似文献
943.
SHUAI Chang-geng HE Lin and LU Zhi-qiang Inst. of Vibration & Noise Naval Uni. of Engineering Wu Han China 《船舶与海洋工程学报》2003,2(2):61-66
The flexible pipe bend can not only reduce the structural vibration and fluid noise in pipeline, but also realize the flexible connection of a horizontal line and a vertical line and compensate the displacement of three dimensions produced by the shock or vibration of pipeline in the special situations. Up to now, little attention has been paid to study the flexible pipe bend applied in the pipeline of medium or high pressure, because no appropriate framework materials can be used to reinforce it which must endure the burst pressure higher than 10 MPa. The investigation shows that it is possible to produce the flexible pipe bend of medium or high pressure if such fibers with high performance as Kevlar fibers are used to be its reinforced materials. However, its structural designing theory, manufacturing technology and measuring techniques aren‘t yet perfect and systematic, which leads to the instability of the performance of products. Furthermore, few references about its research can be seen. Therefore, it is necessary to systematically and thoroughly develop the structural designing theory, manufacture technology and measuring techniques of flexible pipe bend. 相似文献
944.
从城市生态角度探讨了交通对城市生态的负面影响及其主要对策.主要例举了不良城市交通对城市自然生态系统构成的八大影响,和针对这八大影响可以采取的主要对策,包括宏观方面的对策和微观方面的对策.最后,就宏观对策和微观对策中存在的主要问题,以及对"先污染,再治理"的发展道路对现代城市病的影响,进一步的作出一些探讨和思考. 相似文献
945.
946.
947.
This paper introduces a new means to predict consolidation deformation of soil from its microstructure. Based on a kind of
pore-size distribution density function, a fractal model for soil consolidation is established. Through this model, the relation
between macroscopic deformation and microcosmic pore property of soil is founded. In order to justify this proposed model
for soil consolidation, consolidation experiments of soft clay are performed. Afterward, the microstructure of soft clay unconsolidated
and consolidated under every pressure is studied by a scanning electron microscope (SEM). The results show that the proposed
model for soil consolidation is valid in predicting consolidation deformation. 相似文献
948.
The non-destructive testing (NDT) of debonding in stainless steel composites plate (SSCP) is performed by infrared thermography,
finite element analysis (FEA) software ANSYS is taken as the simulative tool, and 2D simulative model has been set up to investigate
effect of the thickness of coating and/or substrate on the detectibility of debonging in SSCPs. Two parameters, namely the
maximum defect temperature difference and defect appearing index, are defined to evaluate the detectivity of defects, and
their computational methods and formulas are given respectively. The preliminary changing tendency of the maximum defect temperature
difference and defect appearing index with the thickness of coating and/or substrate is found by numerical simulation. 相似文献
949.
Urban travel demand, consisting of thousands or millions of origin–destination trips, can be viewed as a large-scale weighted directed graph. The paper applies a complex network-motivated approach to understand and characterize urban travel demand patterns through analysis of statistical properties of origin–destination demand networks. We compare selected network characteristics of travel demand patterns in two cities, presenting a comparative network-theoretic analysis of Chicago and Melbourne. The proposed approach develops an interdisciplinary and quantitative framework to understand mobility characteristics in urban areas. The paper explores statistical properties of the complex weighted network of urban trips of the selected cities. We show that travel demand networks exhibit similar properties despite their differences in topography and urban structure. Results provide a quantitative characterization of the network structure of origin–destination demand in cities, suggesting that the underlying dynamical processes in travel demand networks are similar and evolved by the distribution of activities and interaction between places in cities. 相似文献
950.
Lingqian Hu 《Transportation》2017,44(6):1421-1443
Improving job accessibility can increase the probability for individual persons to be employed and reduce their commutes. Empirical research suggests that the relationship between job accessibility and employment outcomes differ across income groups, but no research has investigated the difference or explored which income groups benefit the most from job accessibility improvements. This research fills the gap by examining six income groups in the Los Angeles metropolitan area. Results show that job accessibility affects the employment status of medium-to-low income groups (household income between US$25,000 and US$75,000). For the lowest-income group (household income lower than US$25,000), owning a car significantly improves their chances to be employed, but job accessibility has no effect. On the other hand, higher job accessibility is associated with shorter commuting distance for the other five income groups, but not for the lowest-income group. These results suggest that transportation and land use policies need to address the specific needs of distinct population groups and underscore the importance of spatial access for the middle-class, which tends to be overlooked in the literature on transportation equity. 相似文献