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扰动法在结构分枝失稳分析中的应用 被引量:4
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作者 李元齐 沈祖炎 《力学季刊》 CSCD 2000年第4期497-502,共6页
对结构进行平衡路径的跟踪分析,是全面了解该结构的受力性能所必须进行的一项工作。目前的结构非线性稳定分析技术一般仅对极值点失稳型问题较为有效,而对分枝点失稳型问题则困难较多。对于具有缺陷敏感性的结构,如拱结构、壳体等,在普... 对结构进行平衡路径的跟踪分析,是全面了解该结构的受力性能所必须进行的一项工作。目前的结构非线性稳定分析技术一般仅对极值点失稳型问题较为有效,而对分枝点失稳型问题则困难较多。对于具有缺陷敏感性的结构,如拱结构、壳体等,在普通荷载作用下,其失稳路径常包含分枝点。文献[1]提出并认为位移扰动法和力扰动法在分析结构分枝失稳时具有很好的效果。本文采用多个不同类型的算例,对扰动法在结构分枝失稳问题中的应用进行了分析比较,表明该方法具有较强的跟踪能力。最后,就扰动法在结构分枝失稳问题中的应用提出几点建议。 展开更多
关键词 分枝点失稳 单层网壳 位移扰动 力扰动法 结构
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Satellite remote sensing reveals overwhelming recovery of forest from disturbances in Asia
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作者 Yiying Zhu Hesong Wang Anzhi Zhang 《Atmospheric and Oceanic Science Letters》 2025年第1期46-51,共6页
Forest ecosystems play key roles in mitigating human-induced climate change through enhanced carbon uptake;however,frequently occurring climate extremes and human activities have considerably threatened the stability ... Forest ecosystems play key roles in mitigating human-induced climate change through enhanced carbon uptake;however,frequently occurring climate extremes and human activities have considerably threatened the stability of forests.At the same time,detailed accounts of disturbances and forest responses are not yet well quantified in Asia.This study employed the Breaks For Additive Seasonal and Trend method-an abrupt-change detection method-to analyze the Enhanced Vegetation Index time series in East Asia,South Asia,and Southeast Asia.This approach allowed us to detect forest disturbance and quantify the resilience after disturbance.Results showed that 20%of forests experienced disturbance with an increasing trend from 2000 to 2022,and Southeast Asian countries were more severely affected by disturbances.Specifically,95%of forests had robust resilience and could recover from disturbance within a few decades.The resilience of forests suffering from greater magnitude of disturbance tended to be stronger than forests with lower disturbance magnitude.In summary,this study investigated the resilience of forests across the low and middle latitudes of Asia over the past two decades.The authors found that most forests exhibited good resilience after disturbance and about two-thirds had recovered to a better state in 2022.The findings of this study underscore the complex relationship between disturbance and resilience,contributing to comprehension of forest resilience through satellite remote sensing. 展开更多
关键词 Forest ecosystem Enhanced vegetation index Breaks for additive seasonal and trend method DISTURBANCE RESILIENCE
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Approximate Solution for Mechanism of Thermally and Wind-driven Ocean Circulation 被引量:4
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作者 MO Jiaqi LIN Wantao LIN Yihua 《Chinese Geographical Science》 SCIE CSCD 2010年第5期383-388,共6页
The thermally and wind-driven ocean circulation is a complicated natural phenomenon in the atmospheric physics. Hence we need to reduce it using basic models and solve the models using approximate methods. A non-linea... The thermally and wind-driven ocean circulation is a complicated natural phenomenon in the atmospheric physics. Hence we need to reduce it using basic models and solve the models using approximate methods. A non-linear model of the thermally and wind-driven ocean circulation is used in this paper. The results show that the zero solution of the linear equation is a stable focus point, which is the path curve trend origin point as time (t) trend to infinity. By using the homotopic mapping perturbation method, the exact solution of the model is obtained. The homotopic mapping perturbation method is an analytic solving method, so the obtained solution can be used for analytic operating sequentially. And then we can also obtain the diversified qualitative and quantitative behaviors for corresponding physical quantities. 展开更多
关键词 global climate atmosphere-ocean oscillation homotopic mapping approximate solution
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Stress initialization methods for dynamic numerical simulation of rock mass with high in-situ stress 被引量:23
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作者 YANG Jia-cai LIU Ke-wei +1 位作者 LI Xu-dong LIU Zhi-xiang 《Journal of Central South University》 SCIE EI CAS CSCD 2020年第10期3149-3162,共14页
In the context of deep rock engineering,the in-situ stress state is of major importance as it plays an important role in rock dynamic response behavior.Thus,stress initialization becomes crucial and is the first step ... In the context of deep rock engineering,the in-situ stress state is of major importance as it plays an important role in rock dynamic response behavior.Thus,stress initialization becomes crucial and is the first step for the dynamic response simulation of rock mass in a high in-situ stress field.In this paper,stress initialization methods,including their principles and operating procedures for reproducing steady in-situ stress state in LS-DYNA,are first introduced.Then the most popular four methods,i.e.,explicit dynamic relaxation(DR)method,implicit-explicit sequence method,Dynain file method and quasi-static method,are exemplified through a case analysis by using the RHT and plastic hardening rock material models to simulate rock blasting under in-situ stress condition.Based on the simulations,it is concluded that the stress initialization results obtained by implicit-explicit sequence method and dynain file method are closely related to the rock material model,and the explicit DR method has an obvious advantage in solution time when compared to other methods.Besides that,it is recommended to adopt two separate analyses for the whole numerical simulation of rock mass under the combined action of in-situ stress and dynamic disturbance. 展开更多
关键词 in-situ stress stress initialization method dynamic disturbance numerical simulation rock mass
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On Efficiency of Simultaneous Perturbation Stochastic Approximation Method for Implementation of an Adaptive Filter
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作者 Hong Son Hoang Remy Baraille 《Computer Technology and Application》 2011年第12期948-962,共15页
In this paper, the simultaneous perturbation stochastic approximation (SPSA) algorithm is used for seeking optimal parameters in an adaptive filter developed for assimilating observations in the very high dimensiona... In this paper, the simultaneous perturbation stochastic approximation (SPSA) algorithm is used for seeking optimal parameters in an adaptive filter developed for assimilating observations in the very high dimensional dynamical systems. The main results show that the SPSA is capable of yielding the high filter performance similar to that produced by classical optimization algorithms, with better performance for non-linear filtering problems as more and more observations are assimilated. The advantage of the SPSA is that at each iteration it requires only two measurements of the objective function to approximate the gradient vector regardless of the dimension of the control vector (or maximally, three measurements if second-order optimization algorithms are used). The SPSA approach is thus free from the need to develop a discrete adjoint of tangent linear model as it is required up to now for solving optimization problems in very high dimensional systems. This technique offers promising perspectives on developing optimal assimilation systems encountered in the field of data assimilation in meteorology and oceanography. 展开更多
关键词 Stochastic approximation dominant Schur vectors minimum prediction error adaptive filter stability.
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INFLUENCE OF SLIP VELOCITY ON BLOOD FLOW THROUGH AN ARTERY WITH PERMEABLE WALL: A THEORETICAL STUDY
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作者 A. SINHA J. C. MISRA 《International Journal of Biomathematics》 2012年第5期147-166,共20页
A theoretical investigation concerning the influence of slip velocity on the flow of blood through an artery having its wall permeable has been carried out. Here blood is treated as a homogeneous Newtonian fluid. The ... A theoretical investigation concerning the influence of slip velocity on the flow of blood through an artery having its wall permeable has been carried out. Here blood is treated as a homogeneous Newtonian fluid. The flow is characterized by three parameters: /3 the ratio of radius to length of the arterial segment, Re the characteristic Reynolds number associated with the pressure outside the arterial segment and c the filtration coe^cient. The problem has been solved by the use of a perturbation technique, e is considered to be very small, ensuring the validity of the perturbation method. The computed numerical results are presented graphically to depict the variations in velocity, volumetric flow rate, wall shear stress and flow resistance. 展开更多
关键词 Slip velocity permeable artery newtonian fluid.
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Short-Time Linear Response with Reduced-Rank Tangent Map 被引量:1
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作者 Rafail V. ABRAMOV 《Chinese Annals of Mathematics,Series B》 SCIE CSCD 2009年第5期447-462,共16页
The recently developed short-time linear response algorithm,which predicts the response of a nonlinear chaotic forced-dissipative system to small external perturbation,yields high precision of the response prediction.... The recently developed short-time linear response algorithm,which predicts the response of a nonlinear chaotic forced-dissipative system to small external perturbation,yields high precision of the response prediction.However,the computation of the short-time linear response formula with the full rank tangent map can be expensive.Here,a numerical method to potentially overcome the increasing numerical complexity for large scale models with many variables by using the reduced-rank tangent map in the computation is proposed.The conditions for which the short-time linear response approximation with the reduced-rank tangent map is valid are established,and two practical situations are examined,where the response to small external perturbations is predicted for nonlinear chaotic forced-dissipative systems with different dynamical properties. 展开更多
关键词 Fluctuation-dissipation theorem Linear response
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