A new method for calculating vehicle attitude using Cayley-Klein parameters

In this paper new matrices of the Cayley-Klein parameters are used to representcomposition of several consecutive finite rotations of rigid body.The generalcommutative rules of multiplication for these matrices is obtained.Furthermore,byusing these matrices it is convenient to prove the theorem on finite rotation of rigidbody.The result obtained in this paper is concise and easy to remember,and can beused to calculate vehicle attitude.     

一种基于数据库描述的电文参数通用解算方法

卫星导航电文参数解算通常采用硬编码方式实现,电文格式、参数编排、参数系数等信息均内嵌在程序代码中,代码可读性、可维护性和可扩充性差。为解决基于超帧、主帧和子帧的固定帧结构的电文参数通用解算问题,提出了一种采用数据库描述电文帧格式、电文参数编排方式以及电文参数结果定制的方法。设计了电文参数通用解算算法以及时间阈值判断算法,通过数据库配置实现不同格式导航电文参数的解算,参数结果根据数据库配置控制输出。采用实际接收的电文进行了测试,结果表明,所提出的方法具有良好的通用性,正确解算了GPS LNAV电文、北斗D1电文和北斗D2电文等3种导航电文参数,电文参数解算实现100%覆盖,参数结果组合输出100%可配置,电文参数增加、删除和修改等完全自适应,避免了电文帧丢失、电文参数更新造成的同一组参数不匹配问题。     

锥形长药柱水下爆炸冲击波参数计算方法

为了计算锥形长药柱水下爆炸冲击波压力,以及研究长脉宽冲击波的传输特性,基于叠加原理建立了冲击波压力-时间曲线的计算方法,通过实验验证了该方法的有效性,在此基础上分析了锥形长药柱不同方位冲击波压力的分布规律。研究结果表明:锥形长药柱产生的冲击波压力具有各向异性,在起爆端一侧形成的是具有厚波头特征的低幅值长脉宽冲击波,在装药径向形成的是接近指数衰减的高幅值冲击波,而在远离起爆端的冲击波压力幅值和脉宽则介于前两者之间。锥形长药柱与球形装药冲击波分布的差异是由于装药形状和起爆方式的改变所导致的,由于装药不同部位起爆的时间差,导致水下爆炸冲击波在不同位置的叠加效果存在明显差异,药柱周围流场中形成的冲击波压力具有方向性。利用提出的计算方法得到的计算结果与实验结果和数值模拟结果吻合较好,研究结果可为锥形长药柱水下爆炸冲击波威力场和毁伤评估提供参考和依据。     

离散单元法的计算参数和求解方法选择

本文对离散单元法的一些基本问题进行了研究,给出了刚度计算公式,提出了两种新的用于求解静态问题的自适应阻尼,并以自由落体运动为例,探讨了中心差分法、     

Approximate method for calculating the air parameters and the radiation intensity in a far wake

In the present paper an approximate method is proposed for solving wake problems that makes it possible to take into account the main features of a flow with complicated chemical kinetics. Analytic dependences are obtained for the distributions of the gas parameters and the radiation intensity, and also the determining dimensionless numbers. Satisfactory agreement is obtained between the theoretical and experimental results for all parameters that have been measured.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 165–175, November–December, 1980.We are very grateful to G. Yu. Stepanov, V. P. Shkadova, and K. S. Khoroshko for discussing the results of the work.     

一种求算结构可靠度指标的新方法

为解决结构功能函数在结构设计点附近非线性程度较高时,一次可靠度计算方法(如JC法)不收敛的问题,提出一种新的可靠度计算方法.该算法根据结构可靠指标的几何意义,先将迭代点靠近极限状态面,再通过在极限状态面上搜索下一迭代点,逐渐减小极限状态面上的点到标准正态空间中坐标原点的距离,从而达到收敛的目的.与其他方法相比,该方法不...     

求解截面主惯性矩的矩阵特征值法

提出求解截面形心主惯性矩的一种新算法,通过构造惯性矩阵,将主惯性矩和主惯性轴的计算归结为矩阵的特征值问题,算法简单,便于应用.     

Improving separated-flow predictions using an anisotropy-capturing subgrid-scale model

The major conclusion of this paper is that resolution requirements for large-eddy simulation (LES) of flow separation and reattachment can be significantly reduced using the anisotropy-capturing explicit algebraic subgrid-scale (SGS) stress model (EASSM) of Marstorp et al. (J. Fluid Mech., vol. 639, 2009, pp. 403–432), instead of the conventional isotropic dynamic eddy-viscosity model (DEVM). LES of flow separation in a channel with streamwise periodic hill-shaped constrictions and spanwise homogeneity is performed at coarse resolutions for which it is observed that flow separation cannot be predicted without a SGS model and cannot be correctly predicted by the DEVM, while reasonable predictions are obtained with the EASSM. It is shown that the lower resolution requirements by the EASSM, compared to the DEVM, is not only due its nonlinear formulation, but also due to the better formulation of its eddy-viscosity part. The improvements obtained with the EASSM have previously been demonstrated using higher-order numerical solvers for channel flows. In this study, it is observed that these improvements still remain using a low-order code with significant inherent numerical dissipation.     

A simple method for calculating thermal expansion of crystals

Summary A simple method based on the classical statistical mechanics is suggested for the calculation of thermal expansion of crystals. The adequacy of the procedure is tested for alkali halide crystals in conjunction with the interatomic potential of the modified Born-Mayer Type.     

频响函数计算的高精度级数展开法

把作者近期提出的用于频响函数计算的级数展开法进行了推广，使其计算精度进一步提高，并且能适用于自由－自由系统。数值示例表明，本文提出的方法是有效的。     

A numerical method for calculating unsteady two-dimensional laminar boundary layers

Summary A method for calculating unsteady two dimensional boundary layers in laminar incompressible flow has been developed and tested. No restrictive assumptions are made regarding the time-dependent terms in the boundary-layer equation. The differential equations are solved with an implicit difference scheme similar to that employed for steady two-dimensional boundary layers. At each step, here, known conditions at three stations are used to calculate the conditions at a new (fourth) station. The entire field is covered by a succession of these steps.

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Übersicht Es wird ein Verfahren zur Berechnung von zeitabhängigen zweidimensionalen Grenzschichten in laminarer inkompressibler Strömung entwickelt und auf seine Genauigkeit geprüft. Dabei werden keine einschränkenden Annahmen über die zeitabhängigen Glieder in der Grenzschichtgleichung gemacht. Die Differentialgleichungen werden durch ein implizites Differenzen-Verfahren gelöst, das dem gewöhnlich für stetige zweidimensionale Grenzschichten verwendeten ähnlich ist. Hier werden für jeden Schritt schon bekannte Werte an drei Stellen benutzt, um die Werte an einer neuen (vierten) Stelle zu berechnen. Das ganze Feld wird auf diese Weise schrittweise überdeckt.

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This work was done while the author was at The John Hopkins University, on leave from the Royal Aircraft Establishment, Farnborough. It was supported in part by a grant from the National Science Foundation (Geophysical Fluid Mechanics, GA-641X). British Crown Copyright, reproduced with the permission of the Controller, Her Britannic Majesty's Stationery Office.     

松弛方法在计算凝聚炸药爆轰问题中的应用

利用松弛近似,将非线性的凝聚炸药爆轰控制方程转化为线性的松弛方程组,并采用五阶WENO格式和五阶线性多步显隐格式对线性松弛方程组进行空间方向和时间方向的离散,由此建立具有高精度和高分辨率性质的计算凝聚炸药爆轰的松弛方法。建立的松弛方法可以避免求解Riemann问题及计算非线性通量的Jacobi矩阵,同时无需分裂处理反应源项。通过对凝聚炸药的平面一维定常爆轰波结构及球面一维聚心、散心爆轰起爆和传播过程的数值模拟,验证了所建立的松弛方法能够很好地计算凝聚炸药爆轰问题。     

A new method for calculating the Busemann head coefficients for radial impellers

Charts of the Busemann head coefficients which are widely used in the design of centrifugal pumps and compressors contain substantial errors. This paper presents a simplified method for evaluating these coefficients which is capable of giving results of high accuracy for impellers with two or more blades having blade angles from 10°–90°, covering most designs of practical interest. It is also shown that significant error may result from the conventional assumption that head coefficients are independent of radius ratio for values of the solidity greater than 1.0; a simple method of checking the magnitude of this error is given     

涡流检波器参数测试的时域方法研究

给出了基于沃尔什变换的涡流检波器参数测试的时域方法.计算机仿真和试验验证,该方法和频域方法相比,精度高,测试时间短,并具有良好的抗噪性.     

结点位移计算的一种简单方法

推导了一种结点位移计算的简单方法,在平面桁架结点位移的计算和静不定杆系结构的变形几何关系的确定中应用方便.     

Approximate method for calculating turbulent boundary layer with positive pressure gradient

A single-parameter integral method is proposed for calculating the turbulent boundary layer with positive pressure gradient which makes it possible to calculate the friction, thermal flux, and layer thickness both ahead of the separation point and in some region behind the separation point.Notation u velocity - density - ^* displacement thickness - ^** momentum thickness - energy thickness - M Mach number - r radius - dynamic viscosity - c_p specific heat at constant pressure - Reynolds number based on initial boundary layer thickness - P Prandtl number - p₁ static pressure at point of initial interaction - p₂ static pressure at pressureplateau - p₀ stagnation pressure - T₀ stagnation temperature - I enthalpy - T_e recovery temperature - T_w ⁰ temperature factor - H form parameter - r₁ recovery coefficient Indices 0 denotes initial section of boundary layer - 1 parameters taken at edge of boundary layer - w parameters taken at the wall temperature - * parameters referred to flow on a flat plate with =0     

Transient finite element method for calculating steady state three-dimensional free surfaces

In order to reduce the cost of large three-dimensional calculations of steady state free surfaces, we have combined a time-dependent approach, a decoupling algorithm and a conjugate gradient solver along the lines introduced earlier by Gresho and Chan. The free surface is calculated separately by applying the kinematic condition to a number of faces defined on the undeformed surface. For the pseudo-time-marching technique we show that it is economical to adopt different time steps for the free surface calculation and the other fields. The accuracy of the method is tested on the well-known circular die problem; the method is then used to reveal the effects of inertia and shear thinning on square and rectangular dies.