半穿甲弹丸对加筋靶板侵彻的终点弹道的实验和理论研究

以舰船典型筋板结构为目标,设计了带加强筋的结构靶,并用模拟实验弹体,对单层带加强筋的结构靶进行了斜侵彻实验,通过天幕靶和高速运动分析系统的测量,得到了两种倾斜着靶条件下不同着靶位置的靶前、靶后弹道参数;通过对靶板破坏结果的分析,得到实验弹靶条件下加强筋结构靶的破坏模式。在现有弹丸侵彻均质靶板理论的基础上和一定假设条件下,得到弹丸对加筋结构靶侵彻的终点弹道理论计算模型,弹丸过靶后剩余速度的理论计算结果与实验结果基本一致。     

转管炮弹丸运动的研究

弹丸的起始扰动是造成旋转弹丸散布主要因素之一.本文建立了不对称弹丸在旋转挠性线膛炮管内和后效期内运动的动力学模型;导出了弹丸在各期间内的统一的运动微分方程;求得弹丸在各期间内运动的解析公式;从而研究了弹丸的起始扰动;其公式对某弹炮系统的计算结果与实验吻合较好.     

锥形端部弹体在岩石(混凝土)介质层中侵彻实用计算方法

采用刚塑性不可压缩的介质模型 ,用极限分析理论的上限方法 ,通过建立动力学许可速度场得到介质对弹体侵彻的静阻力分量 ,通过破碎介质动量守恒条件得到弹体侵彻的动阻力分量 ,在模型中还考虑了介质的尺度关系和弹体的弹头形状两种影响因素。侵彻过程中的速度、加速度、阻力和经历时间通过弹体的运动方程增量计算得到。通过与几种常用经验公式比较说明了本文方法的实用和可靠性。     

重力扰动对极区下高精度惯导系统的影响分析及补偿

考虑载体极区航行下导航能力需求,研究了重力扰动对高精度惯导系统的影响和重力扰动补偿方法。首先,推导了重力扰动矢量在横地理坐标系投影;进一步,分别将水平重力扰动分量假设为确定性常值以及马尔科夫随机量,分析其对横坐标系捷联惯导系统的影响;在此基础上,基于EIGEN-6C4重力场球谐模型获取极区重力扰动数据,并利用三次样条插值法对其进行插值处理,从而对横坐标系下惯导系统进行重力扰动补偿。理论分析及仿真实验结果表明：在横坐标下,确定性常值水平重力扰动分量将导致惯导系统产生振荡性误差以及常值性偏差,随机水平重力扰动分量将导致系统位置误差呈线性振荡增长,且位置误差漂移率与重力扰动方差成正比,并且同时受载体航行速度及马尔科夫模型阶数影响,与常规坐标系下引起的误差一致。基于2190阶EIGEN-6C4重力场球谐模型对横坐标系捷联惯导系统进行重力扰动补偿后,水平姿态精度提高68%,定位精度提高2.5%。     

考虑两相流内弹道的自行火炮发射动力学计算

为了更加准确地计算火炮弹丸的起始扰动,将两相流内弹道应用于发射动力学研究。建立了完整的自行火炮系统发射动力学方程组,包括火炮系统的体动力学方程组、弹丸在膛内运动的动力学方程以及两相流内弹道方程。编制了计算程序,实现了对某自行火炮发射过程的数值模拟,在准确计算内弹道过程的同时,获得了火炮的动力响应、弹丸膛内运动和起始扰动。部分模拟结果与实验实测结果吻合较好。计算表明,采用两相流内弹道模型将提高发射动力学计算精度。     

面元法求解有限水深船舶兴波及水底压力变化

应用势流理论中的格林函数方法计算了船舶定常运动的水动力参数,将有限水深Kelvin移动兴波源格林函数分解成三部分:简单Rankine源集合、局部扰动项和波函数项。在亚临界和超临界航速时,采用不同的积分顺序来消除被积函数的奇异性。利用面元法在船体表面上分布Kelvin源,计算了有限水深下船体表面的源强、压力分布及表面兴波,比较了有限与无限水深结果的区别和联系,进一步求解了船舶航行时引起的水底压力变化,计算结果与实验测量结果吻合良好。     

高精度惯导系统重力扰动的阻尼抑制方法

重力扰动已经成为高精度长航时惯导系统的主要误差源之一。针对船用高精度惯导系统的重力扰动抑制问题,从舰船INS误差模型出发,推导了重力扰动在惯导系统中的传播特性。仿真结果表明垂线偏差将引起系统较大的舒拉振荡误差。为抑制重力扰动对系统的影响,引入常速度误差反馈阻尼网络和相位超前串联阻尼网络。分析了重力扰动在水平阻尼网络中的传递特性,实现了相应滤波器的设计。在此基础上完成了实验验证,海上试验结果表明,所引入的两种阻尼网络都能够阻尼掉重力扰动引起的舒拉振荡型导航误差,其中,相位超前串联阻尼网络效果更优,抑制率达到70%以上。     

倾转旋翼过渡状态的尾迹及气动力特性计算与分析

建立了倾转旋翼机倾转过渡状态旋翼尾迹和气动力的计算方法.该方法中,桨叶的气动模型采用Weissinger-L升力面理论模拟,尾迹的控制方程考虑了旋翼倾转运动对速度分量的影响,并采用时间步进方法求解旋翼自由尾迹,为提高计算精度,使用了4阶Adams-Moulton预测-校正数值算法.同时,该方法中还推导了能适用于倾转过渡状态的旋翼桨叶挥舞运动方程,并结合了旋翼配平模型.利用所建立的方法,首先计算了悬停和前飞状态时的旋翼自由尾迹几何形状,并通过与可得到的实验结果对比,验证了计算方法的有效性.然后,计算和分析了旋翼在不同倾转状态下的尾迹滞后及弯曲特征,以及倾转旋翼的拉力、俯仰和滚转力矩随时间的变化,在此基础上,得出了一些有意义的结论.     

入口扰动频率对矩形射流影响的大涡模拟

为研究入口扰动对矩形射流的影响,对不同扰动频率下的三维矩形射流进行了大涡模拟,用分布投影法求解动量方程,对压力泊松方程采用FACR直接解法.计算结果预报的速度在横向的单峰分布和速度半宽沿流向的近似线性增长与实验结果吻合良好.计算结果表明扰动频率为射流的本征频率fe=0.22时射流的卷吸作用最强,而高频扰动则抑制卷吸作用;激励频率接近本征频率时射流提前出现速度在展向的马鞍型双峰分布,更早趋于圆射流形态.进一步的流场二维和三维瞬态涡结构图谱表明:上述现象与f=0.1和f=0.22时射流近场更频繁卷起、更丰富的大涡结构存在密切关系,正是这些大涡运动不断地在横向卷吸入外界流体,实现射流在横向的迅速扩展.     

多自由度参激系统稳定性的数值分析

提出多自由度周期参激系统稳定性的数值直接法。通过将扰动方程表示成状态方程形式,再根据Flo-quet理论将扰动解表示成指数特征分量与周期分量之积,并将其周期分量与系统周期系数展成Fourier级数,导出一系列代数方程,建立矩阵特征值问题,从而由数值求解特征值可直接确定参激系统的稳定性。该方法可用于一般周期参激阻尼系统,特征值矩阵不含逆子阵。应用于斜拉索在支座周期运动激励下的参激振动不稳定性分析,数值结果表明该方法的有效性。     

Collision of water drop on water

A series of experiments are performed to study the collision of a water drop with various impact velocities, ranged from 0 to 600 cm/s, onto a water surface. Three kinds of phenomena have been recorded. Two of them named “penetration” and “cleavage”, were observed for low impact velocity (up to 100 cm/s). Their common characteristics are that no obvious disturbances on the surface were observed during the colliding process. Namely no splashing jets nor obvious crater were observed. By penetration we mean that a drop fallen into water becomes a ring, which penetrates the water smoothly with a velocity of several centimeters per second. During the penetrating process no obvious change of its configuration was observed. The falling height corresponding to penetration is proportional to volume of the original drop. Some periodicity of the falling heights (corresponding to penetration) was revealed. The phenomenon named “cleavage” occurs when the impact velocity is other than that corresponding to penetration, then the drop cleaves into an “inverted cauliflower” after falling below the surface of water. It almost does not decend. By diffusing and slowly expanding it vanishes in the vessel water several minutes after. These two kinds of phenomena, as we know, have not been reported before. As the impact velocity approaches or exceeds 100 cm/s, the third kind of phenomena, the splash, appears. The diameter and depth of the crater occuring in the case of splash, together with the time for the crater to reach its maximum size, and the time for the rebounding column to begin to rise are given as functions of the falling height of the drop.     

Collision of water drops with a plane water surface

The dependence of the outcome of the collision of uncharged water drops with a plane water surface on the impact angle , the velocity v₁ and the radius r₁ of the drops has been investigated experimentally. The impact parameters were varied over the intervals: v₁=0.40–1.05 m/sec, r₁=75–150m, and =16-85°. The method employed made it possible to avoid having to monitor the individual high-speed impact process. A stream of drops, produced in a vibrating reed type monodisperse droplet generator, was directed at the target. The impact parameters were measured by means of pulsed illumination. The results are expressed in the form of the dependence of the rebound probability and the coalescence coefficient E_S on the impact parameters. The existence of alternating conditional rebound-coalescence-rebound zones for different impact angles is established, together with a decrease in E_S with increase in r₁ and v₁. The data obtained generalize the results of previous experiments.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 165–168, May–June, 1990.     

Dynamic-inlet water jet

Summary Jet propulsion is becoming increasingly popular in the field of fast navigation, and is steadily tending towards the «dynamic-inlet» pattern in the range of higher powers. Indeed, the choice of a «slanting-inlet» nozzle (fig. 1), placed on the boat bottom without any protrusion (which might increase draft), meets the particular requirements of small seaside craft. However, the more suitable solution in general is certainly the straight one (figs. 2 and 3), which allows the best recovery of the energy resulting from forward motion. On the other hand, not only sport boating, but also coastal navigation for civilian and military duties show an increasing tendency to high speed, especially in connection with the present success of hydrofoil ships (fig. 3).This report outlines the main points in the design of a «dynamic-inlet» water jet propulsion unit through a generalized adimensional analysis. A specific-thrust optimization method is given, so that the choice of size and shape is merely reduced to considerations of the necessary compromise between efficiency and overall dimensions. Moreover, a procedure is reported in order to estimate working conditions different from the nominal ones, and to optimize the relative characteristic curves. Finally, the results of an experimental investigation carried out on a low power unit are reported. This investigation used a special mobile bench, equipped with a straingauge load cell to provide direct evaluation of the instantaneous thrust at several speeds.

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Sommario La propulsione a getto trova applicazione sempre più diffusa nella navigazione veloce.Il campo delle potenze più elevate (particolarmente connesso al rapido sviluppo degli aliscafi) per impieghi costieri ed intercostieri, presume l'adozione dell'imbocco «dinamico» (cfr. fig. 2 e 3) quale soluzione più efficace quandanche non obbligata, in alternativa all'adozione dell'imbocco «obliquo» (cfr. fig. 1), che soddisfa solo parziali e contingenti esigenze di piccoli battelli per il turismo balneare.Questo studio giustifica e configura le linee principali di progettazione dell'idrogetto ad imbocco «dinamico» tramite una analisi adimensionale generalizzata.Viene instaurato un processo di ottimizzazione della spinta specifica, che riduce il dimensionamento ad una semplice alternativa di compromesso fra rendimento ed ingombro. Quindi viene esposto un procedimento per la previsione delle prestazioni transitorie e per la scelta più conveniente delle relative curve «caratteristiche».Infine vengono riferiti i risultati di una verifica sperimentale condotta su di una unità di piccola potenza.

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Biofouling in water systems

The paper describes the mechanisms in the development of biofouling layers (initial surface conditioning, microbial transport and attachment, mass transfer of nutrients to the biofilm surface and through the microbial layer, cell metabolism, and detachment of cells and of larger parts of the biofilm) and summarizes the effects of several factors on the buildup and stability of biofilms (nutrient availability, fluid velocity and turbulence, temperature, surface condition, and nonliving particles). Mass transfer within biofilms is treated in more detail. A biofouling model applied to the development of biofilms in heat exchangers is presented. Finally, references are made to biofouling control methods (biocide and the proper design and operation of heat exchangers) and to future research needs in this area.     

Scattering of water waves by inclined thin plate submerged in finite-depth water

Summary  The problem of water wave scattering by an inclined thin plate submerged in water of uniform finite depth is investigated here under the assumption of irrotational motion and linear theory. A hypersingular integral equation formulation of the problem is obtained by an appropriate use of Green's integral theorem followed by utilization of the boundary condition on the plate. This hypersingular integral equation involves the discontinuity in the potential function across the plate, which is approximated by a finite series involving Chebyshev polynomials. The coefficients of this finite series are obtained numerically by collocation method. The quantities of physical interest, namely the reflection and transmission coefficients, force and moment acting on the plate per unit width, are then obtained numerically for different values of various parameters, and are depicted graphically against the wavenumber. Effects of finite-depth water, angle of inclination of the plate with the vertical over the deep water and vertical plate results for these quantities are shown. It is observed that the deep-water results effectively hold good if the depth of the mid-point of the submerged plate below the free surface is of the order of one-tenth of the depth of the bottom. Received 30 November 2000; accepted for publication 26 June 2001     

Non-linear shallow water theory

The equations controlling the three dimensional motion of a viscous, incompressible fluid in shallow water, are derived for use in any orthogonal coordinate system. Simplified equations for two dimensional motion are also developed. The equations are developed in terms of special coordinate dependent functions.