共查询到20条相似文献,搜索用时 203 毫秒
1.
本文把升阶谱技术应用于时间域,建立了一种高精度的逐步积分法。它能自由地升高阶次,以满足预定的精度要求。对于一些工程问题是一种很有效的方法。Wilson-θ法及孙焕纯的改进θ法都是本文方法的特例。 相似文献
2.
复合材料叠层结构剖面翘曲修正理论 总被引:3,自引:1,他引:3
首先假设复合材料叠层结构的面内位移沿厚度方向为直线分布,然后根据剪切变形进行连续修正,获得逐步升高的各阶翘曲位移分布函数。文中以叠层梁为例,应用最小势能原理导出其静力方程和力的边界条件。在长度方向则采用升阶谱位移函数,进行了数值计算。所得叠层梁的位移和应力分布的数值结果与精确解相比,表明本文方法有很好的收敛性。 相似文献
3.
利用复合材料叠层结构剖面翘曲修正理论和瑞利原理,导出了叠层梁的固有振动方程,然后利用升阶谱有限元法作数值计算,给出了叠层梁的动态特性及相应的动应力分布。与一阶剪切理论相比,指出一阶剪切理论在高频计算时有较大的误差 相似文献
4.
研究复合材料叠层结构在单轴拉伸状态下的边缘应力问题。在厚度方向 ,利用翘曲修正理论 ,推导出了叠层板三个方向的位移分布规律 ;在宽度方向 ,采用升阶谱位移模式 ;应用虚功原理 ,给出了叠层板边缘应力分析的特殊有限元模型。通过典型例题的计算表明 :边缘应力计算结果与精确弹性解符合很好 ,还进行了收敛性的研究。本文方法的自由度度少 ,方法简单 ,优于差分法、常规有限元法 ,适用于解决边缘效应问题 相似文献
5.
6.
7.
进口瞬时湍流脉动条件直接影响大涡模拟的精度。对比研究了更适合工程应用的合成涡和合成谱方法,并通过考虑进口速度时间相关和随机数的概率密度分布,对合成谱方法进行改进。对零压力梯度平板湍流模拟结果的对比表明:不同湍流合成方法得到的合成湍流均存在发展为真实湍流的过渡过程;考虑进口湍流脉动的时间相关有助于合成湍流更快地发展为真实湍流,需要的流向距离更短;合成谱方法采用正态分布系数优于均匀分布,改进的合成谱方法优于常规合成谱方法。 相似文献
8.
航空噪声的存在严重影响了机务人员和地勤人员的通信及健康,降低噪声是解决这一问题的有效途径。文章提出了一种新的改进谱减法,根据采集的真实航空噪声数据,将传统谱减法和改进的谱减法结果进行了比、较,计算结果表明,改进形式的谱减法可以有效降低航空噪声,提高语音的可懂度和信噪比。 相似文献
9.
10.
11.
A system for measuring the altitude-airspeed parameters of rotorcraft and very light flight vehicles
In this paper, a problem on measuring the altitude-airspeed parameters (AAPs) of rotorcraft and very light flight vehicles is considered. Some ways of improving systems used to measure the parameters of FV elements and units have been determined. Also suggested and substantiated are the principles and designs of the basic variants of these measuring systems as well as the algorithms of their operation. 相似文献
12.
大规格高强镁合金构件的研究开发对于推进镁合金的大规模应用意义重大,并引起国内外的广泛关注及高度重视。本文综述了常规高强镁合金、含稀土高强镁合金、新型塑性变形工艺及大规格镁合金的研究现状,指出了高强镁合金研究存在的问题及今后的研究方向。 相似文献
13.
For pt. I see ibid., vol. 32, no. 1, p. 1-15 (1996). Common buses are an extremely efficient structure for achieving area minimization so that the bus-oriented interconnection of registers and data operators plays an important role in data path synthesis. The overriding design goal is efficiently allocating the minimum number of buses and gating elements (i.e. multiplexers) for achieving communication between the data path elements. New efficient algorithms for the automated allocation of buses in data paths have been developed. The entire allocation process can be formulated as a graph partitioning problem. This formulation readily lends itself to the use of a varieties of heuristics for solving the allocation problem We present efficient algorithms which provide excellent solutions to this formulation of the allocation problem The operation of the algorithms is clearly demonstrated using detailed examples 相似文献
14.
口语分析与理解是实现自然语言人机接口的关键技术,其中省略问题的处理是不可回避的难点之一。本文将具体介绍一个用于自动仓库物流控制系统的(受限)自然语言人机接口中省略问题的一种解决方法。主要是针对汉语口语中经常出现的主语省略和宾语省略,谈谈识别和理解省略的一些具体的操作方法和设想。 相似文献
15.
J. Kovalevsky 《Space Science Reviews》1962,1(2):313-330
Summary The problem of the determination of the orbit of a celestial body is an old astronomical problem, of which solutions can be found in many classical books on elementary celestial mechanics. However, the introduction of new (radioelectric) means of observations for the artificial satellites have brought up new solutions of this old problem.The author reminds the definitions of the six elliptic elements of an orbit. The problem of their determination is usually divided into two separate steps: a preliminary orbit determination and the improvement of the preliminary elements. Two principal types of preliminary orbit determination exist: the Gaussian type, purely geometrical in which the positions of the body at two different times are determined, and the Laplacian type, of a more dynamical character, in which both position and velocity vectors are found for a given time. The improvement of the preliminary elements is usually obtained by a numerical solution of equations of variations of the elements, minimizing the sum of the squares of the angular distances between the computed and the observed points. The elements on which these variations are applied can be quite various. The coefficients of the equations are usually obtained numerically, although their analytical expressions can also be derived.Most of the modification proposed to the classical methods of orbit determination are more technical improvements in connection with the computation on electronic machines. The most interesting modifications are inspired by the fact that time measurements are less precise than the position (Batrakov, Iszak), the effects of this difference in errors are discussed in this paper. In some cases, using Laplace's method, no preliminary orbit is computed, and all the observations can be used at once (Barlier, Kovalevsky).The determination of orbits from radar measurements is discussed. The proposed methods are quite different in principle from the classical ones. They are actually improvements of a circular orbit whose determination is made by a method of undetermined coefficients (Baker). Some of the elements determined by these methods are quite unstable, and it is always wiser to use other informations together with radar measurements.The determination of orbits from Doppler data alone has been worked out by many investigators. It is the inverse problem of the main problem of all navigational systems. The method proposed by Patton is summarized. The principles of others are quite analogous. The results are improved when more than one receiver are used. The different types of corrections: refraction, perturbations, etc., should be introduced in later stages of the determination, and the whole frequency curve is to be used if a good determination of all elements is desired.Finally, the author quotes a method (Baker) using both Doppler and radar data, and the solution of a new problem: the determination of the orbit of a satellite of another planet from Doppler data alone (Deutsch). 相似文献
16.
17.
考虑库仑阻尼时叶盘系统振动响应的求解方法 总被引:3,自引:3,他引:0
本文研究了具有干摩擦阻尼的带冠叶盘系统振动响应的求解问题。解决了时频法中由于叠混和泄漏而使迭代发散的问题。最后用时频法获得了令人满意的响应计算结果。 相似文献
18.
专家系统在机翼结构布局优化中的应用研究 总被引:2,自引:0,他引:2
1.方法原理 一般结构优化仅将离散化后的有限元特征尺寸作为设计变量(例如板杆结构中的杆元横截面积和板元厚度),而其它布局参数(如板、杆元的数目、位置和材料等)在一次上机优化过程中是不变的。当然,可以将元件位置(用节点坐标表示)和元件材料包括进 相似文献
19.
Tobias C. Owen 《Space Science Reviews》2007,130(1-4):97-104
The predominance of nitrogen in highly volatile forms and of carbon in solids set the abundance ratios of these elements in
the inner planets, meteorites and comets. The absence of carbon compounds in an atmosphere then signals large deposits of
carbon-bearing compounds in surface and/or subsurface deposits. In contrast, the icy planetesimals that contributed heavy
elements to Jupiter must have had identical enrichments (relative to hydrogen) of both C and N, as well as other heavy elements
that have been measured, compared to solar values. Capture of N and Ar suggests that the icy planetesimals that carried these
elements must have formed at low temperatures, <40 K. New measurements of isotopes of nitrogen support this picture, but we
must have more measurements in more atmospheres to be certain of this scenario. 相似文献
20.
本文首先对Pfluger柱以简单的方式与工程上习惯的形式列出它的广义哈密尔顿变分泛函,遂使这一非保守问题广义保守化。据此变分原理进行了有限元离散尝试性试验、讨论了这种有限元离散的特点、以显式提供了一种单元模型全部对称的矩阵。在证实Pfluger柱以发散型失稳之后,指出采用通常的瑞利商迭代技术便可简单地获得临界载荷。算例印证了理论也显示了数值上的效力。对于类似的简支矩形板,文中指出可利用Pfluger柱的单元矩阵简单地获得板有限条模型的有关矩阵。 相似文献