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为探讨空爆冲击波对高速破片的绕流效应及影响因素,采用Ansys/Ls-dyna软件建立了端部贴有预制破片的柱状TNT空爆仿真模型,结合模型分析了冲击波对不同形状的高速破片绕流作用特点,对比讨论了破片形状因素对绕流冲击波的波形、强度等载荷特性的影响规律。结果表明:破片形状会影响绕流冲击波前端的波形和作用在结构上的载荷形式,对绕流冲击波的比冲量影响不大。当质量和厚度相同时,冲击波对三角形破片的扰流能力强于圆形和正方形破片;对于方形破片,破片越瘦长,冲击波对其绕流能力越强;当破片尺寸较小时,破片形状对绕流冲击波影响不明显。 相似文献
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为探讨空爆冲击波对高速破片的绕流效应及影响因素,采用Ansys/LS-DYNA软件建立了端部贴有预制破片的柱状TNT空爆仿真模型,结合实例分析冲击波对高速破片绕流作用特点,对比讨论破片间隙,破片尺寸和破片质量等因素对冲击波绕流的影响规律。结果表明:爆炸初期冲击波速度高于破片速度,在对破片加速的过程中,冲击波对高速破片存在绕流作用;破片间隙越大,单个破片尺寸越小,单个破片质量越大冲击波越容易对破片发生绕流;而在一定范围内破片之间间隙越小,破片尺寸越大,绕流过破片形成的冲击波强度越弱。所以爆炸初期在破片之前传播的冲击波为扰流过破片碰撞形成的冲击波,可为战斗部爆炸载荷传播特性和毁伤特性研究提供参考。 相似文献
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近自由面水下爆炸冲击波切断效应研究 总被引:3,自引:0,他引:3
近自由面水下爆炸形成的冲击波到达自由面时会反射稀疏波,并伴随着水面的上升、破碎和飞溅等复杂物理现象。文章基于无网格SPH方法建立了近自由面水下爆炸数值模型,开发了计算程序,模拟了冲击波和自由面反射的稀疏波的相互作用过程,分析了切断现象的特性、产生机理以及对冲击波参数的影响。研究发现,爆心正上方且距自由面较近处,稀疏波作用最强;近自由面爆炸冲击波冲量可衰减为无限水域爆炸的1/3左右。文中的研究旨在探索冲击波在自由面处的传播规律,并为近自由面水下爆炸载荷的确定提供参考。 相似文献
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水下爆炸试验过程中,实测冲击波压力信号很容易产生畸变,对试验结果评估造成困难。通过梳理过往实测试验数据发现,不同介质声学阻抗差异是影响近边界条件下冲击波传播的关键因素。在水面附近由于空气的声学阻抗小于水介质,冲击波曲线会突然下降,产生明显的水面截断效应;钢结构表面受压力波叠加影响,压力曲线会不同程度的提高;水底附近由于底质的复杂性,其声学阻抗差异较大,实测压力场会受入射波、反射波、前驱波、波后扰动等因素的影响,波形曲线呈现更加复杂的特性。 相似文献
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《中国舰船研究》2016,(2)
在舰船结构水下爆炸试验中,为了研究水下爆炸条件下水中自由场压力载荷的时频特征,针对某水下爆炸试验自由场压力测试试验数据,基于小波分析对信号进行时频特性分析,得到水中自由场压力信号的时频分布和能量分布状况。分析结果表明:针对水下爆炸自由场压力载荷,基于小波分析技术对其时频特征进行分析,可得到水下爆炸自由场压力载荷所包含的频率信息、强度信息以及不同频段下的载荷持续作用时间等信息;另外,可对冲击波、滞后流和二次压力波这3个不同信号阶段进行频段与能量统计分析;在不同频段上对冲南击信号的能量进行统计发现,冲击波阶段在8 k Hz以下频段集中了超过90%的能量,其中4 k Hz以下频段的能量最大,在滞后流和二次压力波阶段,需特别重视250 Hz以下的低频段对船体结构及设备的影响,该结果对舰船结构及设备的抗冲击防护具有借鉴意义。 相似文献
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WENO格式精度对舱室内爆炸载荷影响规律研究 总被引:1,自引:0,他引:1
舰船舱室内爆炸载荷主要包含瞬态多峰值冲击波和持续时间较长的准静态超压,为了研究WENO格式精度对舱室内爆炸载荷影响规律,基于Fortran平台,采用3阶、5阶、7阶WENO有限差分格式,开发了高精度舱室内爆炸载荷三维数值计算程序。采用Sod激波管、双爆轰波碰撞、激波与熵波相互作用等经典算例初步考察了各数值格式的计算性能。开展了封闭舱室、泄压舱室内爆炸载荷数值计算,探讨了WENO格式精度对舱室内爆炸载荷影响规律。研究表明:WENO格式精度对舱室内爆炸冲击波载荷影响较大,对舱室内爆炸准静态超压载荷影响较小。 相似文献
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The authors have already examined a method for evaluating the capsizing probability of a ship in the dead ship condition based
on a piecewise linear approximation of the restoring arm. Here, this method is extended to ships with trapped water on deck.
This is because the stability of ships having a relatively high bulwark, such as fishing vessels, could substantially deteriorate
due to trapped water on deck. First, the mean amount of water trapped on deck was estimated as a function of the significant
wave height and the mean wave period using a model experiment in irregular beam seas. Second, the restoring arm curve with
trapped water on deck was calculated hydrostatically and then approximated with a piecewise linear curve. Third, the roll
angle was estimated using a nonlinear and uncoupled equation of absolute roll angle under stochastic wave and wind exciting
moments. The short-term and long-term capsizing probabilities were calculated for a fishing vessel operating off Kyushu. Numerical
results quantitatively demonstrated that the effect on capsizing probability of trapped water on deck cannot be ignored when
accurately evaluating the stability of fishing vessels. 相似文献
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针对长甲板室纵向围壁端部与主船体露天甲板交界处的应力集中问题,采用结构有限元数值分析方法,探讨在空间布置受到限制的条件下,应力集中交界处圆弧型肘板臂长、圆弧半径等参数变化对应力分布和大小的影响,并得到降低应力集中系数的圆弧型肘板参数的最佳值。文中根据研究结果,对某艘实船的长甲板室纵向围壁端部与主船体露天甲板交界处圆弧型肘板进行优选设计,有效地降低了该处的应力集中水平。 相似文献
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In recent years, demands for car transportation by a ship have been increasing with favorable economic conditions in auto
sector, and the need of a pure car carrier (PCC) has grown quickly. A PCC needs huge parking space but smaller displacement
since a car is comparatively light for its volume. As a result, almost all PCCs have wide breadth, shallow draft and huge
structure above the water surface. These features cause some technical issues of a PCC, like lack of stability, effect of
strong winds on its resistance, difficulty of course keeping in rough seas, difficulty of berthing in strong winds, and so
on. To overcome these technical issues, one of the authors has proposed a new concept for a PCC. This is a trimaran PCC which
has very limited transverse bulkheads in the center hull by using two side hulls as fenders. In the present research, wind
forces acting on a scale model of the trimaran PCC were measured in the towing tank with a wind generator at Osaka Prefecture
University. Furthermore, in order to clarify the characteristics of wind pressure on the trimaran, height and width of tunnels
which are between a main hull and side hulls were changed. And then, in order to imitate a real ship, we used wind reduction
technology of corner-cut design for accommodation house of the ship. Moreover, the wind pressure acting on the trimaran was
compared with that on a mono-hull PCC. Using these experimental and theoretical results, an estimation method of wind pressure
acting on the trimaran PCC is deduced. 相似文献
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码头大管桩出现的不同类型缺陷,如混凝土脱落和钢筋锈蚀,会造成码头承载能力下降。基于完整桩-土体系的荷载传递理论,推导获得缺陷桩剩余极限承载力的计算公式。依托工程实践,考察混凝土剥落和钢筋锈蚀这两种缺陷类型对单桩极限承载力的影响,并得出相应结论:混凝土剥落位置对单桩竖向极限承载力和单桩抗拔极限承载力有影响,混凝土剥落位置位于土层内部会减小单桩竖向极限承载力和单桩抗拔极限承载力,单桩竖向极限承载力减小0.07%,单桩抗拔极限承载力减小1.72%;但对桩身竖向承载力却不同,混凝土缺损对桩身轴心受压承载力减小25.65%,钢筋损失对桩身竖向承载力减小20.95%。混凝土缺损比钢筋缺损对桩身各项承载力的影响要大得多。 相似文献
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Biological control of harmful algal blooms: A modelling study 总被引:1,自引:0,他引:1
A multispecies dynamic simulation model (ERSEM) was used to examine the influence of allelopathic and trophic interactions causing feeding avoidance by predators, on the formation of harmful algal blooms, under environmental scenarios typical of a Mediterranean harbour (Barcelona). The biological state variables of the model included four functional groups of phytoplankton (diatoms, toxic and non-toxic flagellates and picophytoplankton), heterotrophic flagellates, micro- and mesozooplankton and bacteria. The physical–chemical forcing (irradiance, temperature and major nutrient concentrations) was based on an actual series of measurements taken along a year cycle in the Barcelona harbour. In order to evaluate potential effects of advection, some runs were repeated after introducing a biomass loss term. Numerical simulations showed that allelopathic effects of a toxic alga on a non-toxic but otherwise similar competitor did not have appreciable influence on the dynamics of the system. However, induction of avoidance of the toxic alga by predators, which resulted on increased predation pressure on other algal groups had a significant effect on the development of algal and predator populations. The presence of advection overrided the effect of these interactions and only allowed organisms with sufficiently high potential growth rates to thrive. 相似文献
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D.E. Pitfield 《Research in Transportation Economics》2008,24(1):5-14
The phenomenon of the wide world growth in low-cost airlines has resulted in a focus on their pricing strategies, on issues of cost recovery and on their impact on the traffic and market shares of legacy carriers or other low-cost carriers when they are in competition, either directly or at adjacent airports.This paper provides a brief overview of the characteristics of these low-cost carriers as well as their history and geography. It goes on to outline ways in which these carriers compete and manage demand, ranging from price competition to advertising; some of these methods directly reflect their special characteristics. Some empirical evidence is presented which indicates a correlation in fare setting behaviour between competitors and insights are offered on cost recovery.The impact of the start-up of low-cost carriers is also analysed, focusing on their impacts on other low-cost carriers. The case of Ryanair competing with easyJet on London-Venice is examined along with Southwest and Frontier on Denver-Las Vegas. 相似文献