Life-cycle reliability-based optimization of civil and aerospace structures

Today, it is widely recognized that optimization methodologies should account for the stochastic nature of engineering systems and that concepts and methods of life-cycle engineering should be used to obtain a cost-effective design during a specified time horizon. The recent developments in life-cycle engineering of civil and aerospace structures based on system reliability, time-dependent reliability, life-cycle maintenance, life-cycle cost and optimization constitute an important progress. The objective of this study is to present a brief review of the life-cycle reliability-based optimization field with emphasis on civil and aerospace structures.     

A course in computer-aided aerospace design

This paper describes a new sophomore course being offered at Purdue University in the area of aerospace design. While the course and the examples used in this presentation deal with aerospace engineering, the overall structure is presented as being applicable in other engineering areas as well. The basic idea is that, with time, more of the design processes will involve the use of a computer and this necessarily will force the design process towards a higher degree of organization. The course is a simple illustrative example within this viewpoint. The basic modules of aerospace engineering of flight mechanics, aerodynamics, structures, propulsion, weights, air transportation, stability and control, and performance are used to formulate a set of constraints, which, in the particular example, are positive static stability, trim, structural integrity, and range. A (paper) aircraft is defined as an element of the set of feasible values of design parameters (geometry, altitude, speed). Then, given the subset of aircraft which satisfies all the constraints, the aircraft, with the optimum index of performance, is defined to be the best aircraft.     

Topology Optimization in Aircraft and Aerospace Structures Design

Topology optimization has become an effective tool for least-weight and performance design, especially in aeronautics and aerospace engineering. The purpose of this paper is to survey recent advances of topology optimization techniques applied in aircraft and aerospace structures design. This paper firstly reviews several existing applications: (1) standard material layout design for airframe structures, (2) layout design of stiffener ribs for aircraft panels, (3) multi-component layout design for aerospace structural systems, (4) multi-fasteners design for assembled aircraft structures. Secondly, potential applications of topology optimization in dynamic responses design, shape preserving design, smart structures design, structural features design and additive manufacturing are introduced to provide a forward-looking perspective.     

航天嵌入式软件整数溢出的形式化验证方法

整数溢出引起的软件系统安全性问题屡见不鲜,已有的模型检测技术由于存在状态空间爆炸、不能有效支持中断驱动型程序检测等缺点而少有工程应用.结合真实案例,对航天嵌入式软件整数溢出问题的分布和特征进行了系统性的分析.在有界模型检测技术的基础上,结合整数溢出特征,提出了基于整数溢出变量依赖的程序模型约简技术;同时,针对中断驱动型程序,结合中断函数特征抽象,提出了基于干扰变量的中断驱动程序顺序化方法.经过基准测试程序和真实航天嵌入式软件实验,结果表明：该方法在保证整数溢出问题检出率的前提下,不仅能够提高分析效率,还使得已有的模型检测技术能够适用于中断驱动型程序整数溢出检测.     

An integrated modeling method for assessment of quality systems applied to aerospace manufacturing supply chains

In highly regulated industries such as aerospace, the introduction of new quality standard can provide the framework for developing and formulating innovative novel business models which become the foundation to build a competitive, customer-centric enterprise. A number of enterprise modeling methods have been developed in recent years mainly to offer support for enterprise design and help specify systems requirements and solutions. However, those methods are inefficient in providing sufficient support for quality systems links and assessment. The implementation parts of the processes linked to the standards remain unclear and ambiguous for the practitioners as a result of new standards introduction. This paper proposed to integrate new revision of AS/EN9100 aerospace quality elements through systematic integration approach which can help the enterprises in business re-engineering process. The assessment capability model is also presented to identify impacts on the existing system as a result of introducing new standards.     

Problems of automatic control education in developing countries

The problem of automatic control education in developing countries is an integral part of related difficulties in the education of engineering and applied sciences in such regions. Some of the basic problems are lack of technical manpower, shortage of related industries, insufficient technical programs, and deficiency in competent and qualified faculty members. Other problems, which depend on the particular region, country or circumstance are historical traditions, economic conditions, population size, financial budgets, educational tools, media of instructions, curriculum structures and non-uniformity of the educational programs. Most of these problems are closely related and cannot be separately discussed nor can a unique solution for them be proposed. For example, the shortage of ‘technical manpower’ is commonly due to the lack of development of ‘technical training programs’, which are, in turn, a mere reflection of the very nature of their underdeveloped or developing ‘economies’ and ‘industries’.In this paper, an attempt is made to bring up some of the problems and difficulties of the education of automatic control in developing countries. The problems of control education are divided into primary and secondary classes. After the exposition of the problems and their nature in each category, a proposal is made to help as a guideline for better understanding of the difficulties and to provide likely clues for their solution.     

Mixed-integer second-order cone programming for global optimization of compliance of frame structure with discrete design variables

Frame structures are extensively used in mechanical, civil, and aerospace engineering. Besides generating reasonable designs of frame structures themselves, frame topology optimization may serve as a tool providing us with conceptual designs of diverse engineering structures. Due to its nonconvexity, however, most of existing approaches to frame topology optimization are local optimization methods based on nonlinear programming with continuous design variables or (meta)heuristics allowing some discrete design variables. Presented in this paper is a new global optimization approach to the frame topology optimization with discrete design variables. It is shown that the compliance minimization problem with predetermined candidate cross-sections can be formulated as a mixed-integer second-order cone programming problem. The global optimal solution is then computed with an existing solver based on a branch-and-cut algorithm. Numerical experiments are performed to examine computational efficiency of the proposed approach.     

Numerical solution of time-fractional fourth-order partial differential equations

A quintic B-spline collocation technique is employed for the numerical solution of time-fractional fourth-order partial differential equations. These equations occur in many applications in real-life problems such as modelling of plates and thin beams, strain gradient elasticity and phase separation in binary mixtures, which are basic elements in engineering structures and are of great practical significance to civil, mechanical and aerospace engineering. The time-fractional derivative is described in the Caputo sense. Backward Euler scheme is used for time discretization and the quintic B-spline-based numerical method is used for space discretization. The stability and convergence properties related to the time discretization are discussed and theoretically proven. The given problem is solved with three different boundary conditions, including clamped-type condition, simply supported-type condition, and a transversely supported-type condition. Numerical results are considered to investigate the accuracy and efficiency of the proposed method.     

测控天线健康管理与支援保障系统研究及设计

针对航天测控网内天线设备在监测、设备健康管理及维护保障方面的需求,参考目前设备状态维修的相关标准和预测及健康管理(PHM)功能框架,面向航天地面测控设备,提出了测控天线健康管理与支援保障系统的建设思路。针对测站、用户中心和厂所在设备管理与保障中的不同功能定位,设计了测站、中心的分级分层管理和远程支援的总体架构,明确了系统内各节点的功能设计要点及系统工作流程、运行模式和关键技术要点。并以测控设备的天线系统作为健康管理对象,通过建立测站管理终端和测控设备健康管理中心应用平台,对系统主要功能、节点间信息交互、运行模式和关键技术在工程中进行了实践和验证,系统架构合理可行,对工程应用具有积极的指导和借鉴意义。     

Type safety for feature-oriented product lines

A feature-oriented product line is a family of programs that share a common set of features. A feature implements a stakeholder’s requirement and represents a design decision or configuration option. When added to a program, a feature involves the introduction of new structures, such as classes and methods, and the refinement of existing ones, such as extending methods. A feature-oriented decomposition enables a generator to create an executable program by composing feature code solely on the basis of the feature selection of a user—no other information needed. A key challenge of product line engineering is to guarantee that only well-typed programs are generated. As the number of valid feature combinations grows combinatorially with the number of features, it is not feasible to type check all programs individually. The only feasible approach is to have a type system check the entire code base of the feature-oriented product line. We have developed such a type system on the basis of a formal model of a feature-oriented Java-like language. The type system guaranties type safety for feature-oriented product lines. That is, it ensures that every valid program of a well-typed product line is well-typed. Our formal model including type system is sound and complete.     

Integrated modeling, finite-element analysis, and engineering design for thin-shell structures using subdivision

Many engineering design applications require geometric modeling and mechanical simulation of thin flexible structures, such as those found in the automotive and aerospace industries. Traditionally, geometric modeling, mechanical simulation, and engineering design are treated as separate modules requiring different methods and representations. Due to the incompatibility of the involved representations the transition from geometric modeling to mechanical simulation, as well as in the opposite direction, requires substantial effort. However, for engineering design purposes efficient transition between geometric modeling and mechanical simulation is essential. We propose the use of subdivision surfaces as a common foundation for modeling, simulation, and design in a unified framework. Subdivision surfaces provide a flexible and efficient tool for arbitrary topology free-form surface modeling, avoiding many of the problems inherent in traditional spline patch based approaches. The underlying basis functions are also ideally suited for a finite-element treatment of the so-called thin-shell equations, which describe the mechanical behavior of the modeled structures. The resulting solvers are highly scalable, providing an efficient computational foundation for design exploration and optimization. We demonstrate our claims with several design examples, showing the versatility and high accuracy of the proposed method.     

外流作用下管道流固耦合非线性动力学研究进展

管道广泛应用于海洋、核电以及航空航天等重大工程中,是采油平台、蒸汽发生器等重要工程装备的关键结构之一.当有外部流体经过时,管道会发生流固耦合振动行为,是导致重大装备振动破坏和失效的重要原因之一,已成为重大工程设计必须解决的关键问题.本文针对外流作用下柔性管道流固耦合非线性动力学机理这一科学问题,梳理了国内外学者的重要研究成果,重点分析了柔性管道分别在横向外流和轴向外流作用下的流固耦合非线性振动行为.从实验研究、仿真分析和理论建模等方面进行了深入地探讨,揭示了外部流体对管道动力学行为的影响机制.最后,对当前国内外研究现状进行了简要的总结,并给出了这一研究仍存在的难点与挑战.     

Realistic and efficient reliability estimation for aerospace structures

In this paper an efficient procedure for calculating non-exceedance probabilities of the structural response is presented, with emphasis on structures modeled by large finite element systems with many uncertain parameters. This is a problem which receives considerable attention in numerous applications of engineering mechanics, such as space and aerospace engineering. For this purpose, a novel sampling procedure is introduced, which allows a significant reduction of the variance of the estimator of the probability of failure when compared to that of direct Monte Carlo simulation. This improvement in the computational efficiency is most important, as the computational efforts are much higher when uncertainties are considered.The only prerequisite for the application of this sampling procedure is an estimate of the gradient of the performance function of the structure. The calculation of the gradient is carried out efficiently, by exploiting the correlation between a randomly chosen input and the corresponding output of the system. The proposed concept is especially suited for high-dimensional problems in reliability engineering, e.g. for a rather large number n of random variables, say n > 100.To demonstrate the practical value of the methodology a reliability analysis of the INTEGRAL-satellite of the European Space Agency (ESA) has been performed. The results show that both for the frequency response analysis and the structural reliability analysis a substantial number of parameters of the finite element model play an important role.     

INTEGRATED ACCESS TO INFORMATION SYSTEMS

The French Scientific and Technical Center for Building (CSTB) is involved in a very large number of programs, covering a wide range of scopes in the area of building, including technical, legal, social, and economic topics. The actions carried out encompass scientific research or technical missions, engineering, writing regulations, or state-of-the-art documents, such as unified codes of practice or assessment of the social impact of new technologies, and the need to facilitate access to this huge amount of data has become a considerable challenge. Information in such a case is a very generic term covering a vague understanding in that it can include basic data representing a primary corpus or, at the other end of the scale, sophisticated services offered by experts able to solve complex problems. Customers for such information have very different needs but agree on the necessity to facilitate access to the relevant data and to various high-value services accounted for by computer systems. As the semantic level of the services differs considerably, the need became apparent to merge different tools within an integrated software environment to satisfy the previous objective. The main components to be assembled are retrieval systems to locate the relevant data, object-oriented databases to offer a reusable storage model, hypertext and hyperobject systems to browse the content of hypermedia entities, and multifunctional expert systems to provide sophisticated computer systems with an adaptable entry and behavior.     

Commercially available structural engineering computer programs

The computer programs which are the subject of this paper are those which have been developed by private organizations and for usage of which a fee has to be paid.These programs as well as all engineering programs may be classified into three types: Artisan, Academic and Engineering. Artisan type programs are those which consist of computarization of old manual methods. Academic type programs are those which consist of computerization of advanced theoretical methods for a refined analysis, or for an exact optimization, or for an interactive design. Engineering type programs are those which consist of a combination of some features of the two previous types in order to design the lightest structures capable of supporting the governing combination of loading conditions and satisfying the pertinent Building Code criteria.The paper discusses each of these three program types and describes in some detail a few cases of application of engineering type programs.     

Dependability issues in visual–haptic interfaces

Dependability of a system is commonly referred to its reliability, its availability and its maintenability (RAM), but when this concept is applied to user interfaces there is no common agreement on what aspects of user–system interaction are related to a satisfactory RAM level for the whole system. In particular, when dealing with haptic systems, interface dependability may become a crucial issue in medical and in military domains when life-critical systems are to be manipulated or where costly remote control operations are to be performed, like in industrial processes control or in aerospace/automotive engineering and manufacturing. This paper discusses the role of dependability in haptic user interfaces, aiming to the definition of a framework for the assessment of the usability and dependability properties of haptic systems and their possible correlations. The research is based on the analysis of a visual–haptic-based simulator targeted to maintenance activity training for aerospace industry which is taken as a case study. As a result, we propose a novel framework able to collect and then process relevant interaction data during the execution of haptic tasks, enabling to analyze dependability vs. usability correlations.     

Efficient binary transfer of pointer structures

This paper presents a pair of algorithms for output and input of pointer structures in binary format. Both algorithms operate in linear space and time. They have been inspired by copying garbage collection algorithms, and make similar assumptions about the representations of pointer structures. In real programs, the transfer of entire pointer structures is often inappropriate. The algorithms are extended to transfer partitions of a pointer structure lazily: the receiver requests partitions when it needs them. A remote procedure call mechanism is presented that uses the binary transfer algorithms for communicating arguments and results. A use of this as an enabling mechanism in the implementation of a software engineering environment is discussed.