运用气阻模型解决循环冷却水回水不畅初探

针对生产中出现的回水不畅问题,运用气阻模型,在管道最高点安装排气装置,消除了复杂管道的气阻现象。

3种空气阻力模型及其运动规律研究

在把物体视为质点及假定空气密度均匀和物体运动轨迹为直线的条件下 ,给出了物体以不同速度运动时的空气阻力模型 ,求出了物体在相应模型下的运动规律 ,最后讨论了物体的速度变化情况 ,并给出了速度变化曲线。

空气阻力模型与运动方程的关系研究

以质点作直线运动为研究对象从理论上讨论并分析了三种空气阻力模型下的物体运动规律，对三种空气阻力模型的运动情形进行了比较，并说明了建立正确的阻力模型对研究物体运动的重要性。

自由场景下烟雾动态追踪的实时仿真

针对烟雾在自由场景下跟随物体的运动形态刻画困难的问题,本文提出一种动态追踪方法。首先,针对追踪烟雾因空气阻力产生运动态势变化问题,建立空气阻力模型,实现自然逼真的烟雾运动;其次,构建自适应网格场,引入边界盒子覆盖网格区域,实时捕捉物体中心与自适应网格场中心在可接受偏差内转换,实现烟雾的位置追踪;再次,采用旋转矢量法,通过影响热浮力方向向量有效解决烟雾方向偏转;然后,利用有限差分法快速求解N-S方程,对流项采用Mac Cormack方法实现无插值,减少数值耗散,提高实时性;最后,架设多种烟雾动态追踪实例。实验表明,本文方法能够真实实时模拟出烟雾动态追踪运动物体的自然逼真效果。

耙吸船艏喷喷距计算及泥浆运动轨迹分析

针对喷距制约耙吸船艏喷驻船位和施工船布置问题,通过分析艏喷喷距影响参数,推导理想状态下喷距的计算模型;通过引入空气阻力公式,建立考虑空气阻力的喷距计算模型,经实船测试和验证,考虑空气阻力的喷距模型计算精度明显高于理想模型。在此基础上分析空气阻力系数、泥浆密度及喷射角度等参数对泥浆运动轨迹的影响,这有利于耙吸船艏喷施工获得最佳的艏喷控制点和驻船位。

基于阻尼力的二维桥式吊车模糊PID控制器设计

针对桥式吊车系统防摆定位问题,本文建立了一种阻尼力作用下的二维桥式吊车系统模型.考虑复杂工作环境下存在的空气阻力及吊车与轨道间的摩擦力影响,引入一种新颖的空气阻力模型以及摩擦力模型,建立了更为精确的阻尼力作用下可变绳长二维桥式吊车模型;设计合适的模糊规则,在此基础上构造模糊自适应PID控制器,实现桥式吊车的防摆定位控制;仿真结果表明,对比多滑模控制器,本文设计的控制器取得了较好的控制效果,并具有强鲁棒性.

Eulerian–Lagrangian simulation of bubble coalescence in bubbly flow using the spring-dashpot model

The Eulerian–Lagrangian simulation of bubbly flow has the advantage of tracking the motion of bubbles in continuous fluid, and hence the position and velocity of each bubble could be accurately acquired. Previous simulation usually used the hard-sphere model for bubble–bubble interactions, assuming that bubbles are rigid spheres and the collisions between bubbles are instantaneous. The bubble contact time during collision processes is not directly taken into account in the collision model. However, the contact time is physically a prerequisite for bubbles to coalesce, and should be long enough for liquid film drainage. In this work we applied the spring-dashpot model to model the bubble collisions and the bubble contact time, and then integrated the spring-dashpot model with the film drainage model for coalescence and a bubble breakage model. The bubble contact time is therefore accurately recorded during the collisions. We investigated the performance of the spring-dashpot model and the effect of the normal stiffness coefficient on bubble coalescence in the simulation.The results indicate that the spring-dashpot model together with the bubble coalescence and breakage model could reasonably reproduce the two-phase flow field, bubble coalescence and bubble size distribution. The influence of normal stiffness coefficient on simulation is also discussed.

Micro-bubble Drag Reduction on a High Speed Vessel Model

Ship hull form of the underwater area strongly influences the resistance of the ship. The major factor in ship resistance is skin friction resistance. Bulbous bows, polymer paint, water repellent paint （highly water-repellent wall）, air injection, and specific roughness have been used by researchers as an attempt to obtain the resistance reduction and operation efficiency of ships. Micro-bubble injection is a promising technique for lowering frictional resistance. The injected air bubbles are supposed to somehow modify the energy inside the turbulent boundary layer and thereby lower the skin friction. The purpose of this study was to identify the effect of injected micro bubbles on a navy fast patrol boat （FPB） 57 m type model with the following main dimensions： L=2 450 ram, B=400 mm, and T=190 mm. The influence of the location of micro bubble injection and bubble velocity was also investigated. The ship model was pulled by an electric motor whose speed could be varied and adjusted. The ship model resistance was precisely measured by a load cell transducer. Comparison of ship resistance with and without micro-bubble injection was shown on a graph as a function of the drag coefficient and Froude number. It was shown that micro bubble injection behind the mid-ship is the best location to achieve the most effective drag reduction, and the drag reduction caused by the micro-bubbles can reach 6%-9%.

消防水炮无风状态射流轨迹的预测方法

该文在室内无风状态下,开展了两种小模型消防水炮在不同仰角,不同工作压力下的射流轨迹测量试验。基于单水滴空气中飞行的轨迹计算,采用指数增长形式的空气阻力模型,提出仅含1个待定系数b的射流轨迹预测方法,计算了各个工况下几种系数b取值的射流轨迹。以各个测量点的射流轨迹高度与计算轨迹的高度之差,其算术平均值越小,标准偏差?越小为约束条件,获得预测模型中待定系数b的合适取值,并将该合适b值下计算的射程、射高与实验值对比。结果表明直流式消防水炮b值取0.01,导流式水炮b值取0.08能获得很好的预测精度,试验值与计算值对比,直流式水炮的测点高差算术平均值小于0.25 m,射程预测误差小于1.3%,水射流的射高预测误差小于1.2%,导流式水炮测点高差算术平均值小于0.3 m,射程误差小于2.98%,射高误差小于4.7%。该文的方法可用于开展远射程消防水炮的射程预估。