3D激光快速成形技术研究

针对激光快速成形这一重要的3D打印技术,分析了技术原理、关键技术步骤和应用优势,综述了激光成形技术研究和应用现状,对其在直升机制造业中的应用前景进行了分析。     

Intelligent acoustic rotor speed estimation for an autonomous helicopter

Acoustic sensing to gather information about a machine can be highly beneficial, but processing the data can be difficult. In this work, a variety of methodologies have been studied to extract rotor speed information from the sound signature of an autonomous helicopter, with no a-priori knowledge of its underlying acoustic properties.     

武装直升机抗坠毁设计研究

介绍了武装直升机抗坠毁的概念设计原理 ,提出了抗坠毁设计中的一些关键问题 ,为武装直升机抗坠毁设计提供理论指导。     

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.     

直升机旋翼系统弹性轴承刚度特性试验方法研究

直升机旋翼系统是直升机的核心部件,弹性轴承将桨叶与桨毂相连,提供桨叶的挥舞、摆振和变距自由度,刚度特性是其主要的力学性能.通过采用松紧螺套驱动半圆形夹具转动来测试弹性轴承压缩、扭转和弯曲刚度特性,结果表明该试验方法新颖独特,具有一定的通用性,能准确判定弹性轴承是否合格,可为不同机型的弹性轴承提供装机前试验的方法.     

直升机复合材料桨叶的疲劳寿命计算

着重说明直升机复合材料桨叶安全寿命的计算方法。首先分析某型直升机的飞行任务剖面、桨叶载荷谱及材料的疲劳特性,然后利用迈勒线性累积损伤理论计算桨叶的安全疲劳寿命,并分析不同飞行状态及载荷变化对疲劳寿命的影响。计算结果证实直升机复合材料桨叶在正常飞行状态下的无限寿命设计理念。该方法可用于在直升机设计阶段对复合材料构件的疲劳寿命进行评估校核。     

直升机自动倾斜器竖向振动的神经网络识别

工程中的许多大型结构中的一些关键部件的振动无法直接测量，因而探索一种间接测量或识别的方法就显得尤为重要。由于直升机飞行状态的复杂性，不但测试困难，而且经典方法处理不理想。文中提出基于BP神经网络方法对直升机自动倾斜器竖向振动进行识别及评估。介绍了网络结构、训练学习过程、试验测试及数据处理过程和识别与估计方法。估计评价的准则主要考虑以估计第一阶谐和频率（6．4Hz)所对应的结果进行比较。由于神经网络方法考虑了不确定性因素，从而估计结果与真实结果相符得较好。最后分析了人工神经网络在用于动力学系统的识别与估计中的多方面问题。     

Application of the finite element method to predict the crashworthy response of a metallic helicopter under floor structure onto water

Helicopters are seen by the petroleum industry as the only viable way of transportation between on and offshore platforms. At present, there exists no certification requirement to ensure a high level of survivability in the event of a water impact. Within the literature, there exists a body of information related to the post crash analysis of accident data, which supports the finding that a conventional metallic under floor design performs poorly during a water impact, in relation to the transmission of water pressure and the absorption of energy.     

Crashworthiness of helicopter subfloor structures

To improve a helicopter design concept, which meets structural and crashworthiness requirements, a research program is undertaken to study the energy absorption capability of a subfloor structure. In particular, crash tests are performed on the subfloor structure and on the intersection elements, which are components of the structure and can create high deceleration peak loads at the cabin floor level causing dangerous inputs to the occupants. Then the structures are analysed by a commercial explicit finite element code, PAM-CRASH, using detailed geometrical models, suitable materials models and the appropriate definition of contact forces and rivets. The analysis shows that the load-shortening diagrams present a good correlation to the experimental data and that the structural collapse predictions correspond closely to the observed behaviour during the experimental tests. Consequently the finite element analysis can be used to aid the designers in evaluating the crashworthiness of different structural concepts and can therefore be an important mean of reducing development costs.     

Vortex Dissipation Due to Airfoil-Vortex Interaction

The influences due to several AVIs （airfoil-vortex interactions） are studied by using a two-dimensional CFD （computational fluid dynamics） method. The primary goal of this effort is to assess the variation of vortex center location and vortex circulation associated with sequential AVI toward an improvement of the hybrid method of CFD and prescribed wake model, which closely relates to predicting the BVI （blade-vortex interaction） noise radiated from a helicopter rotor. The representative of sequential AVI is performed by single vortex and two airfoils. Investigations with respect to vortex center location and vortex circulation after AVIs have been made by varying the miss-distance, which is the vertical distance between the airfoil leading edge and the vortex center. Correlations between miss-distance and vorticity field show that there exists complicated vortex wake flow with several vortices newly induced in 1st AVI. The pressure fluctuation amplitude clarifies that the intensity in 2nd AV1 is significantly low compared to the intensity in 1st AVI due to the influence of vortex dissipation. Simulations turned out to modify the vortex center location represented by the hybrid method using an offset value for a streamwise direction and to dissipate the vortex circulation for improving the accuracy of BVI noise prediction.