Multi-physics design and optimization of flexible matrix composite driveshafts

Flexible matrix composites (FMCs) consist of low modulus elastomers such as polyurethanes which are reinforced with high-stiffness continuous fibers such as carbon. This fiber–resin system is more compliant compared to typical rigid matrix composites and hence allows for higher design flexibility. Continuous, single-piece FMC driveshafts can be used for helicopter applications. In the present investigation, an optimization tool using a genetic algorithm approach is developed to determine the best combination of stacking sequence, number of plies and number of in-span bearings for a minimum-weight, spinning, misaligned FMC helicopter driveshaft. In order to gain more insight into designing driveshafts, various loading scenarios are analyzed and the effect of misalignment of the shaft is investigated. This is the first time that a self-heating analysis of a driveshaft with frequency- and temperature-dependent material properties is incorporated within a design optimization model.     

基于声品质的直升机舱内典型降噪措施分析

直升机舱内噪声严重降低了乘员的乘坐舒适性,进行直升机舱内降噪设计研究十分必要。本文以声品质最优为目标,以直升机舱内噪声烦恼度评价结果为依据,通过多元线性回归方法构建舱内声品质模型,利用计算声学软件模拟直升机舱内添加不同种类降噪措施后的双耳可听声信号,从不同角度对典型降噪措施的效果进行测评及对比分析。结果表明:在舱内添加穿孔板(穿孔率13%,空腔厚0.5 m,前部填充0.1 m岩棉)后的声品质改善效果最好,添加毛毡乳胶粘合泡沫橡胶和5 mm厚针刺毡对声品质的改善效果最差。从吸声措施类型来看,吸声结构对声品质的改善效果最好,吸声材料次之,阻尼材料最差。     

A technique to measure optical properties of brownout clouds for modeling terahertz propagation

Brownout, the loss of visibility caused by dust resultant of helicopter downwash, is a factor in the large majority of military helicopter accidents. As terahertz radiation readily propagates through the associated dust aerosols and is attenuated by atmospheric water vapor within short distances, it can provide low-profile imaging that improves effective pilot visibility. In order to model this application of terahertz imaging, it is necessary to determine the optical properties of obscurants at these frequencies. We present here a method of empirical calculation and experimental measurement of the complex refractive index of the obscuring aerosols. Results derived from terahertz time-domain spectral measurements are incorporated into the AFIT CDE Laser Environmental Effects Definition and Reference (LEEDR) software.     

Battle damage repair of a helicopter composite frame-skin junction. Part 1: Depot repair

The Defence Science and Technology Organisation (DSTO), Australia, Delegation Generale Pour L’Armement (DGA), France and Eurocopter have carried out collaborative research in the area of battle damage repair techniques for military helicopter structures. Australian and French participants have focused on depot and field repairs, respectively. This paper summarises the research conducted at DSTO to develop battle damage repair methods for a helicopter composite frame-skin junction (FSJ) subjected to damage caused by a typical threat weapon. A generic BDR design approach was successfully applied, which involved use of a reverse engineering approach to determine the load requirements, application of a rapid repair design approach, and validation of the design using finite element analyses and experimental testing.     

Selection of a representative set of chemical accidents from a complex data matrix for the development of environment-accident index

Chemical accidents often lead to negative consequences for the environment. Preparedness and proper actions are, therefore, essential components in order to minimise environmental effects. To assist and facilitate this work, a proposed planning tool, the environment-accident index (EAI), was formulated by Scott [J. Hazard. Mater. 61 (1998) 305]. As a result of a first validation of the index, based on 21 chemical accidents, the database was complemented with 42 additional accidents covering a broader spectrum of chemicals. The additional accidents were collected by means of an inquiry and their environmental consequences are, so far, unknown. The collected data had an overrepresentation of accidents involving petroleum products (69%). Because of the overrepresentation of this group of chemicals in the material, the data was skewed with respect to chemical properties. Since the model should be valid for a variety of chemical accidents, a method was needed which enabled a proper and unbiased selection of a representative subset of accidents to be used in development and validation of the model. For this purpose, the possibility to use multivariate data analysis in combination with statistical design was investigated. The result showed the feasibility of this method in the selection of a representative subset from a complex and skewed large dataset. Within the new dataset, 53% were accidents involving petroleum products and 47% involved other chemicals. The selected accidents will be used in further work to evaluate the environmental consequences, for model development and model validation.     

Survey of fatigue failures in helicopter components and some lessons learnt

The paper presents a comprehensive review of the failure investigations carried out within AgustaWestland Limited (AWL) over the last 30 years. The results of this survey show that fatigue accounts for approximately 55% of all failures in helicopter components. Although fatigue failures can occur in a wide range of components the types of factors responsible for initiation differ depending on the application of the part. This paper identifies the most common fatigue prone areas in the helicopter, how design considerations and certain key factors such as fretting can influence fatigue life. The importance of aircraft maintenance and quality control in the supply chain will also be discussed. Based on the survey, the paper will also illustrate several instances where fatigue failures have been eliminated through the application of novel surface engineering techniques, improvements in material & processes and modifications to the original design.     

基于2mm微马达的微型直升机设计与研制

介绍了一种微型直升机的设计与研制过程,该直升机主要由两个直径仅2mm的电磁微马达组成,整体结构设计简单、将微马达作为机身的一个组成部分,分别驱动两个微型旋翼产生升力,使微直升机离地起飞。     

In-depth analysis of the causal factors of incidents reported in the Greek petrochemical industry

This paper presents a statistical analysis of all reported incidents in the Greek petrochemical industry from 1997 to 2003. A comprehensive database has been developed to include industrial accidents (fires, explosions and substance releases), occupational accidents, incidents without significant consequences and near misses. The study concentrates on identifying and analyzing the causal factors related to different consequences of incidents, in particular, injury, absence from work and material damage. Methods of analysis include logistic regression with one of these consequences as dependent variable. The causal factors that are considered cover four major categories related to organizational issues, equipment malfunctions, human errors (of commission or omission) and external causes. Further analyses aim to confirm the value of recording near misses by comparing their causal factors with those of more serious incidents. The statistical analysis highlights the connection between the human factor and the underlying causes of accidents or incidents.     

基于摄影测量法的头盔运动姿态测量技术

针对头盔瞄准具精度鉴定系统设计要求,需要精确测量头盔瞄准具活动范围、最大视场角以及相对瞄准线的方位、俯仰、滚转偏差等参数.本文利用加装在座舱内的两个摄像机,获取到两个不同视角的头盔运动影像.采用角锥体法、空间后方交会算法以及基于外方位元素分解的姿态解算算法,推导出了头盔姿态解算的数学模型,实现基于单视角影像的头盔运动姿...     

Fatigue Behavior,Strength, and Failure of Aluminum Foam

Foaming processes and the quality of the foamed material have improved considerably during the recent years. It now worth to evaluate the application of aluminum foams for helicopter components to reduce production costs and weight. Since the operating conditions of helicopters expose materials to repeated or fluctuating strains the fatigue behavior of foam materials is of crucial importance for their evaluation as potential materials for helicopter components.     

Empirical assessment of the impact of highway design exceptions on the frequency and severity of vehicle accidents

Compliance to standardized highway design criteria is considered essential to ensure roadway safety. However, for a variety of reasons, situations arise where exceptions to standard-design criteria are requested and accepted after review. This research explores the impact that such design exceptions have on the frequency and severity of highway accidents in Indiana. Data on accidents at carefully selected roadway sites with and without design exceptions are used to estimate appropriate statistical models of the frequency and severity of accidents at these sites using recent statistical advances with mixing distributions. The results of the modeling process show that presence of approved design exceptions has not had a statistically significant effect on the average frequency or severity of accidents - suggesting that current procedures for granting design exceptions have been sufficiently rigorous to avoid adverse safety impacts. However, the findings do suggest that the process that determines the frequency of accidents does vary between roadway sites with design exceptions and those without.     

A risk influence model applied to North Sea helicopter transport

Offshore helicopter transport represents a quite complex, socio-technical system. A number of factors affect the risk related to this activity, e.g. maintenance, design of helicopter/helideck, and the competence/training of the crew. The present paper presents an overall, holistic risk model, which aims at presenting the total risk picture and the risk influencing factors (RIFs) for helicopter transport. The main objective is to provide a tool for identifying the most effective risk reducing measures. The RIFs both for accident frequency and accident consequence are arranged hierarchically in a type of influence diagram, illustrating the effect of the various RIFs. Accident and incident statistics from North Sea helicopter transport are used in combination with expert judgements to assess the weight (importance) and the present status of the RIFs. The model is also used to provide numerical results.     

Application of Damage Tolerance principles to the design of helicopters

The design of helicopters against fatigue phenomena is a particularly important and complex problem, due to the peculiar load spectra, composed by a high number of low-amplitude cycles.The fatigue design methodology most commonly applied by the helicopter community was based on the Safe-Life philosophy, applied anyhow with a particular approach. Since 1989, the Airworthiness Regulations evolved towards the application of Damage Tolerance principles also to rotorcraft. This change has forced the helicopter industries to review their design methodologies, and to face new problems, linked with fracture mechanics applications to their typical structures. Flaws, accidental damages and manufacturing discrepancies must be accounted for, in addition to the retirement life based on Safe-Life.The paper reviews the current requirements and presents and discusses the methodologies that the helicopter industry adopts for demonstrating compliance with such regulatory requirements. In addition, recommendations are given on research and development activities required for refining the defined methodologies and for their better implementation.     

基于拓扑优化的直升机旋翼桨叶剖面设计

提出了一种基于拓扑优化的直升机旋翼桨叶剖面设计方法。采用了有限元方法计算直升机旋翼桨叶剖面刚度特性, 截面考虑了剪切和翘曲变形, 并消除了翘曲位移和刚体位移之间的耦合作用。基于SIMP拓扑优化算法, 以旋翼桨叶平均柔度或者剖面刚度为设计目标, 桨叶重量为约束函数, 建立了旋翼桨叶拓扑优化模型。提出的敏度求解算法具有较高的计算精度, 采用序列线性规划算法对旋翼桨叶剖面进行优化设计。结果表明在展长较小并且承受均布升力载荷情况下, Ⅱ型截面梁的柔度最小, 而当展长增大时, 工字梁截面具有最小的柔度。此外, 旋翼桨叶外载荷等对优化结果也有较大的影响。提出的拓扑优化方法适合于概念设计阶段的直升机旋翼桨叶剖面设计。     

Innovative Anti Crash Absorber for a Crashworthy Landing Gear

This paper defines an innovative concept to anti-crash absorber in composite material to be integrated on the landing gear as an energy-absorbing device in crash conditions to absorb the impact energy. A composite cylinder tube in carbon fiber material is installed coaxially to the shock absorber cylinder and, in an emergency landing gear condition, collapses in order to enhance the energy absorption performance of the landing system. This mechanism has been developed as an alternative solution to a high-pressure chamber installed on the Agusta A129 CBT helicopter, which can be considered dangerous when the helicopter operates in hard and/or crash landing. The characteristics of the anti-crash device are presented and the structural layout of a crashworthy landing gear adopting the developed additional energy absorbing stage is outlined. Experimental and numerical results relevant to the material characterization and the force peaks evaluation of the system development are reported. The anti-crash prototype was designed, analysed, optimized, made and finally the potential performances of a landing gear with the additional anti-crash absorber system are tested by drop test and then correlated with a similar test without the anti-crash system, showing that appreciable energy absorbing capabilities and efficiencies can be obtained in crash conditions.     

Strength design of composite beam using gradient and particle swarm optimization

This work addresses the optimum design of a composite box-beam structure subject to strength constraints. Such box-beams are used as the main load carrying members of helicopter rotor blades. A computationally efficient analytical model for box-beam is used. Optimal ply orientation angles are sought which maximize the failure margins with respect to the applied loading. The Tsai–Wu–Hahn failure criterion is used to calculate the reserve factor for each wall and ply and the minimum reserve factor is maximized. Ply angles are used as design variables and various cases of initial starting design and loadings are investigated. Both gradient-based and particle swarm optimization (PSO) methods are used. It is found that the optimization approach leads to the design of a box-beam with greatly improved reserve factors which can be useful for helicopter rotor structures. While the PSO yields globally best designs, the gradient-based method can also be used with appropriate starting designs to obtain useful designs efficiently.     

A concept to optimize quality and cost in thermoplastic composite components applied to the production of helicopter canopies

A concept for the optimization of manufacturing processes of composite material components with regard to product’s quality and cost is introduced and applied for the case of thermoplastic composite helicopter canopies produced by ‘Cold’ Diaphragm Forming (CDF) process. The proposed methodology relies on the consideration of the processes thermal cycle as decisive for the component’s quality and cost. Quality and cost sensitivity analyses were made to derive material dependent Quality Functions (QFs) and process dependent Cost Estimation Relationships (CERs). QFs and CERs are exploited to derive iteratively the optimal thermal cycle. The processes thermal cycle is numerically simulated to allow for its virtual application on the material. To perform the optimization procedure a new software tool is developed. CDF heating system configuration along with the optimal thermal cycle for producing helicopter canopies were obtained. The results of the study were successfully exploited by EUROCOPTER to produce 1:3 scale prototypes.     

Area-wide urban traffic calming schemes: a meta-analysis of safety effects

This paper presents a meta-analysis of 33 studies that have evaluated the effects on road safety of area-wide urban traffic calming schemes. Area-wide urban traffic calming schemes are typically implemented in residential areas in towns in order to reduce the environmental and safety problems caused by road traffic. A hierarchical road system is established and through traffic is removed from residential streets by means of, for example, street closures or one-way systems. Speed reducing devices are often installed in residential streets. Main roads are improved in order to carry a larger traffic volume without additional delays or more accidents. The meta-analysis shows that area-wide urban traffic calming schemes on the average reduce the number of injury accidents by about 15%. The largest reduction in the number of accidents is found for residential streets (about 25%), a somewhat smaller reduction is found for main roads (about 10%). Similar reductions are found in the number of property damage only accidents. The results of evaluation studies are robust with respect to study design. There is no evidence of publication bias in evaluation studies. Study findings are found to have high external validity.     

Particle swarm optimization approach for multi-objective composite box-beam design

This paper presents a multi-agent search technique to design an optimal composite box-beam helicopter rotor blade. The search technique is called particle swarm optimization (‘inspired by the choreography of a bird flock’). The continuous geometry parameters (cross-sectional dimensions) and discrete ply angles of the box-beams are considered as design variables. The objective of the design problem is to achieve (a) specified stiffness value and (b) maximum elastic coupling. The presence of maximum elastic coupling in the composite box-beam increases the aero-elastic stability of the helicopter rotor blade. The multi-objective design problem is formulated as a combinatorial optimization problem and solved collectively using particle swarm optimization technique. The optimal geometry and ply angles are obtained for a composite box-beam design with ply angle discretizations of 10°, 15° and 45°. The performance and computational efficiency of the proposed particle swarm optimization approach is compared with various genetic algorithm based design approaches. The simulation results clearly show that the particle swarm optimization algorithm provides better solutions in terms of performance and computational time than the genetic algorithm based approaches.     

基于AHP的建筑工程结构设计风险评价

为系统研究建筑工程结构设计风险,采用德而菲法和统计资料法,全面分析了建筑工程结构设计中因设计人员的疏忽或过失,以及因种种主、客观原因而出现的各种技术事故或问题．采用AHP法对建筑工程结构设计中会出现的各种技术事故或问题进行了综合评价,明确了结构设计中可能出现的各种技术事故或问题的重要性程度及其排序,对于有效地降低结构设计风险具有重要意义．