AN ADAPTIVE ITERATION METHOD FOR STRUCTURAL STATIC REANALYSIS of TOPOLOGICAL MODIFICATIONS

基于guyAn缩减和EPSIlOn算法,提出了结构拓扑修改静态重分析的自适应迭代方法。首先将新增加的自由度通过guyAn缩减方法凝聚到原结构自由度上,形成缩减方程。其次,根据刚度矩阵增量,利用nEuMAnn级数建立基向量,采用向量EPSIlOn算法对基向量部分和系列进行迭代加速,并给出了控制迭代收敛精度的误差计算方法,可以根据结构改变的大小自适应选择迭代次数,从而快速求出原结构自由度的位移。新增加自由度的位移可从缩减方程恢复得到。给出了一个数值算例,将该方法与组合近似法(CA)进行比较。数值计算结果表明,该方法可以根据精度要求自动选择迭代次数,且计算效率比CA方法高。Based on the Guyan reduction and epsilon algorithm, an adaptive iteration method for structural static reanalysis of topological modification is presented.In this process, the equations of the newly added degree of freedoms(DofS)(if any) are condensed to the original structure by means of Guyan reduction.And then, the basis vector is formed using Neumann serial according to the increment of the stiffness matrix, and the epsilon algorithm is used to accelerate the convergence of the partial sum of the basis vectors.An error evaluation method is introduced to control the accuracy of the iteration adaptively.A numerical example is given to compare the computational cost and approximation accuracy between the combined approximation and the presented method, the numerical results show that the present method is effective and easy to integrate into a general optimization approach.国家自然科学基金项目(50905033);中国博士后科学基金项目(20070420761);广东省自然科学基金项目(8451009001001414);广州市科技计划项目(2006Z2-D9061);广东省科技计划项目(2009B010900032);粤港招标项目(20070103-1

Adaptiver Suchansatz zur multidisziplinären Optimierung von Leichtbaustrukturen unter Verwendung hybrider Metaheuristik

Within the last few years environmental regulations, safety requirements and market competitions forced the automotive industry to open up a wide range of new technologies. Lightweight design is considered as one of the most innovative concepts to fulfil environmental, safety and many other objectives at competitive prices. Choosing the best design and production process in the development period is the most significant link in the automobile production chain. A wide range of design and process parameters needs to be evaluated to achieve numerous goals of production. These goals often stand in conflict with each other. In addition to the variation of the concepts and following the objectives, some limitations such as manufacturing restrictions, financial limits, and deadlines influence the choice of the best combination of variables. This study introduces a structural optimization tool for assemblies made of sheet metal, e.g. the automobile body, based on parametrization and evaluation of concepts in CAD and CAE. This methodology focuses on those concepts, which leads to the use of the right amount of light and strong material in the right place, instead of substituting the whole structure with the new material. An adaptive hybrid metaheuristic algorithm is designed to eliminate all factors that would lead to a local minimum instead of global optimum. Finding the global optimum is granted by using some explorative and exploitative search heuristics, which are intelligently organized by a central controller. Reliability, accuracy and the speed of the proposed algorithm are validated via a comparative study with similar algorithms for an academic optimization problem, which shows valuable results. Since structures might be subject to a wide range of load cases, e.g. static, cyclic, dynamic, temperature-dependent etc., these requirements need to be addressed by a multidisciplinary optimization algorithm. To handle the nonlinear response of objectives and to tackle the time-consuming FEM analyses in crash situations, a surrogate model is implemented in the optimization tool. The ability of such tool to present the optimum results in multi-objective problems is improved by using some user-selected fitness functions. Finally, an exemplary sub-assembly made of sheet metal parts from a car body is optimized to enhance both, static load case and crashworthiness.Die Automobilindustrie hat in den letzten Jahren unter dem Druck von Umweltvorschriften, Sicherheitsanforderungen und wettbewerbsfähigem Markt neue Wege auf dem Gebiet der Technologien eröffnet. Leichtbau gilt als eine der innovativsten und offenkundigsten Lösungen, um Umwelt- und Sicherheitsziele zu wettbewerbsfähigen Preisen zu erreichen. Die Wahl des besten Designs und Verfahrens für Produktionen in der Entwicklungsphase ist der wichtigste Ring der Automobilproduktionskette. Um unzählige Produktionsziele zu erreichen, müssen zahlreiche Design- und Prozessparameter bewertet werden. Die Anzahl und Variation der Lösungen und Ziele sowie einige Einschränkungen wie Fertigungsbeschränkungen, finanzielle Grenzen und Fristen beeinflussen die Auswahl einer guten Kombination von Variablen. In dieser Studie werden strukturelle Optimierungswerkzeuge für aus Blech gefertigte Baugruppen, z. Karosserie, basierend auf Parametrisierung und Bewertung von Lösungen in CAD bzw. CAE. Diese Methodik konzentriert sich auf die Lösungen, die dazu führen, dass die richtige Menge an leichtem / festem Material an der richtigen Stelle der Struktur verwendet wird, anstatt vollständig ersetzt zu werden. Eine adaptive Hybrid-Metaheuristik soll verhindern, dass alle Faktoren, die Bedrohungsoptimierungstools in einem lokalen Minimum konvergieren, anstelle eines globalen Optimums. Das Auffinden des globalen Optimums wird durch einige explorative und ausbeuterische Such Heuristiken gewährleistet. Die Zuverlässigkeit, Genauigkeit und Geschwindigkeit des vorgeschlagenen Algorithmus wird mit ähnlichen Algorithmen in akademischen Optimierungsproblemen validiert und führt zu respektablen Ergebnissen. Da Strukturen möglicherweise einem weiten Bereich von Lastfällen unterliegen, z. statische, zyklische, dynamische, Temperatur usw. Möglichkeit der multidisziplinären Optimierung wurde in Optimierungswerkzeugen bereitgestellt. Um die nichtlineare Reaktion von Zielen zu überwinden und um den hohen Zeitverbrauch von FEM-Analysen in Absturzereignissen zu bewältigen, könnte ein Ersatzmodell vom Benutzer verwendet werden. Die Fähigkeit von Optimierungswerkzeugen, optimale Ergebnisse bei Problemen mit mehreren Zielsetzungen zu präsentieren, wird durch die Verwendung einiger vom Benutzer ausgewählten Fitnessfunktionen verbessert. Eine Unterbaugruppe aus Blechteilen, die zur Automobilkarosserie gehören, ist optimiert, um beide zu verbessern; statischer Lastfall und Crashsicherheit

Aeronautical engineering: A continuing bibliography with indexes (supplement 289)

This bibliography lists 792 reports, articles, and other documents introduced into the NASA scientific and technical information system in Mar. 1993. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment, and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Modelado de Multifractura Discreta en Materiales Quasi-Frágiles Monografía

In this work, a new modal reanalysis algorithm based on AMLS method is proposed for local, nontop ological,high rank modifications. Instead of using some perturbation technique[44, 85] or using the Kirsch Combined method[223, 226], the proposed reanalysis procedure uses AMLS method to perform the reanalysisexp lo itin g the concept of substructure. The modification affects a particular path on the hierarchical partitiontree, which traces back from the modified nodes to the root node. In our proposed modal reanalysis algorithmonly the modified substructures and affected substructures due to the propagation need to be recalculated. This algorithm can significantly improve the efficiency compared to the full recalculation. Some of the advantages are: 1. Larger substructure size increases moderately the accurate of the AMLS method. For medium substructure size, the efficiency of AMLS method can be improved using a sparse linear solver and sparse eigen solver. 2. If the modified substructures are recalculated using exact method, the reanalysis does not affect the precision of the final results by AMLS method. The eigen-values computed are accurate as the precision of AMLS method is. 3. The amplitude of modification is not limited to small modification change, as being required by approximate method. 4. It is only required to identify the corresponding modified and affected sub-structures for performing the recalculation and save the data of the non-modified sub-structures. In the worst case, the computational cost is no more than the fresh AMLS-solution. 5. It is more suitable for large-scale eigen value problem with local high-rank modifications. &nbsp

HPCCP/CAS Workshop Proceedings 1998

This publication is a collection of extended abstracts of presentations given at the HPCCP/CAS (High Performance Computing and Communications Program/Computational Aerosciences Project) Workshop held on August 24-26, 1998, at NASA Ames Research Center, Moffett Field, California. The objective of the Workshop was to bring together the aerospace high performance computing community, consisting of airframe and propulsion companies, independent software vendors, university researchers, and government scientists and engineers. The Workshop was sponsored by the HPCCP Office at NASA Ames Research Center. The Workshop consisted of over 40 presentations, including an overview of NASA's High Performance Computing and Communications Program and the Computational Aerosciences Project; ten sessions of papers representative of the high performance computing research conducted within the Program by the aerospace industry, academia, NASA, and other government laboratories; two panel sessions; and a special presentation by Mr. James Bailey

Aeronautical engineering: A continuing bibliography with indexes (supplement 211)

A continuing bibliography (NASA SP-7037) lists 519 reports, journal articles and other documents originally announced in February 1987 in Scientific and Technical Aerospace Reports (STAR) or in the International Aerospace Abstracts (IAA). The coverage includes documents on the engineering and theoretical aspect of design, construction, evaluation, testing, operation, and performance of aircraft (including aircraft engines) and associated components, equipment, and systems. It also includes research and development in aerodynamics, aeronautics, and ground support equipment for aeronautical vehicles. Each entry in the bibliography consists of a standard bibliographic citation accompanied in most cases by an abstract. The listing of the entries is arranged by the first nine STAR specific categories and the remaining STAR major categories. The arrangement offers the user the most advantageous breakdown for individual objectives. The citations include the original accession numbers from the respective announcement journals. The IAA items will precede the STAR items within each category. Seven indexes entitled subject, personal author, corporate source, foreign technology, contract number, report number, and accession number are included

Analysis and integration of regional scale temperature datasets into a seasonal crop monitoring system.

Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Populations in excess of 20 million people in southern Africa annually face food insecurity. This number increases appreciably when detrimental seasonal climate conditions lead to widespread reductions in crop harvests. This situation has led to the development of regionalscale crop monitoring systems that incorporate crop-specific water balance (CSWB) models for early detection and warning of impending weather-related crop production shortfalls. Early warning of anticipated reductions in crop harvests facilitates early action in responding to potential crises. One such system, used by the Famine Early Warning Systems Network (FEWS NET) in southern Africa for crop monitoring, calculates the water requirements satisfaction index (WRSI) using a CSWB model. Operationally, CSWB models for calculating WRSI have used a static length of growing period (LGP) to bracket the period over which rainfall and evapotranspiration variations can affect crop yields. In the long term, concerns have been raised by some studies on the impact of rising air temperatures on crop production. There is therefore a need to incorporate the impacts of air temperature on crops directly into food security monitoring systems, in order to improve the accuracy of these monitoring systems in identifying and locating weather-related crop production shortfalls. This study sought to assess the potential improvements that can be introduced to the crop monitoring system in general and the WRSI in particular, by incorporating air temperature data into the CSWB model. To address this objective, daily maximum and minimum air temperature grids derived from a general circulation model reanalysis were used to generate thermal time estimates, expressed as growing degree day (GDD) grids for a maize crop. The GDDs were used to estimate the LGP of maize for each pixel of each summer season (which typically runs between around October and March) from 1982/1983 to 2016/2017 in southern Africa. The variable, temperature-driven LGP estimates compared favourably with LGP values obtained from literature for a few sample locations. The variable LGP was used to calculate the WRSI for 35 seasons, and the resultant WRSI showed improved correlation with historical yield estimates compared to the static-LGP WRSI, particularly after the farming practice of planting on multiple dates was taken into consideration. Various expressions of WRSI were considered in the analysis, including WRSI calculated assuming planting at the onset of rains, WRSI aggregated from varying number of separate planting dates, including three and six planting dates as test examples, and WRSI calculated using a modified soil water holding capacity to better capture local soil management practices. Historical maize yields for sub-national administrative units from seven southern African countries were correlated with the various WRSI expressions. Gridded GDD data that reflect the accumulated severity of extreme warm temperatures experienced during the crop growth period, referred to as extreme growing degree days, or eGDD, were also noted to have significant correlations with historical maize yields in several southern African countries. A number of variants of the eGDDs were tested, including eGDDs accumulated throughout the crop’s growth period, eGDDs that only occurred simultaneously with periods of crop water deficit, eGDDs that occurred during the crop flowering stage, and eGDDs scaled by the severity of crop water deficit. In several areas, the various eGDD expressions indicated higher correlations with yield than any of the WRSI variants indicated. The eGDD parameter showed strong correlations with WRSI, suggesting that the accumulated high temperatures were a reflection of the influence of low rainfall and low soil moisture during episodes of high temperature. More work is required to calibrate and refine the temperature-based monitoring parameters that were developed in this study, at local, sub-national scales. In particular, assumptions of the linearity of maize yield response for the various parameters should be tested. Potential improvements of the combined eGDD-water deficit parameter through the incorporation of prediction coefficients and constants should also be tested. A secondary aim of the study was to explore how readily available temperature-related datasets can be utilized to derive air-temperature metrics. To this end, satellite-derived thermal infrared (TIR) brightness temperature data were analysed, and a method was developed for identifying cloud cover, while simultaneously estimating cloud-free diurnal brightness temperature curves, using a single TIR satellite channel. The diurnal brightness temperature curves were developed using a sinusoidal and exponential model for daytime and nighttime respectively, utilizing modifications that enabled the curves to be estimated from two known temperatures at any two given times with cloud-free brightness temperature scenes. Comparison of the cloud mask developed in this study with an existing operational cloud mask based on a methodology developed by the EUMETSAT Satellite Applications Facility for Nowcasting gave an accuracy of 85.4%, when the operational method was considered as truth in a confusion matrix analysis. Situations were identified in which the different cloud detection methods showed superior performance, and could therefore complement each other. A statistical method was also developed for calibrating the cloud-free brightness temperatures to station-observed 2-m air temperatures using relationships between the means and diurnal temperature ranges of the two datasets. This enabled the identification of periods of occurrence of extreme warm air temperatures with a coefficient of determination of 0.91, and demonstrated the potential for the usage of TIR data for generating estimates of useful air temperature metrics. The efficiency of the algorithms that were used for simultaneous cloud masking and generation of cloud-free brightness temperature should be improved, in order to enable the methodology to be scaled up to a regional or global gridded level of analysis. Further work for improving operational gridded air temperature datasets by combining station-observed temperature data, modelled data from global circulation models, satellite-derived modelled cloud-free brightness temperature data and cloud masks is recommended

The Third Air Force/NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization

The third Air Force/NASA Symposium on Recent Advances in Multidisciplinary Analysis and Optimization was held on 24-26 Sept. 1990. Sessions were on the following topics: dynamics and controls; multilevel optimization; sensitivity analysis; aerodynamic design software systems; optimization theory; analysis and design; shape optimization; vehicle components; structural optimization; aeroelasticity; artificial intelligence; multidisciplinary optimization; and composites

Bibliography of Lewis Research Center technical publications announced in 1993

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1993. All the publications were announced in the 1993 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses