二维浅水波方程的数值激波不稳定性

研究二维浅水波方程的数值激波不稳定性问题.线性稳定性分析和数值实验表明,格式的临界稳定性与数值激波的不稳定现象有重要的联系.基于扰动量的增长矩阵分析,本文将高分辨率的数值格式和HLL格式进行特定的加权,设计一类新的混合型数值格式.其中可以调节非线性波速的HLLC与HLL的混合格式,数值试验展示了消除浅水波方程激波不稳定现象的有效性和鲁棒性.     

脉冲辐照热激波与压缩应力波

 扼要地阐述了X射线、电子束辐照材料时所产生的热激波与高速碰撞、炸药爆炸所产生的压缩波之间一些不同的现象特征，可为热激波的分析、研究以及模拟提供参考。     

膨胀石墨 3 mm波消光数值计算

为探讨膨胀石墨作为3 mm波干扰材料的消光、散射特性及其影响因素, 基于有限长度、有限电导率圆柱状导体的电磁散射, 利用矩量法建立了膨胀石墨的消光、散射、吸收及后向散射截面(雷达散射截面RCS)的计算式. 运用Mathematica编程计算并分析了膨胀石墨长度、半径、电导率、磁导率等因素与膨胀石墨消光、散射、吸收截面及RCS的关系. 结果表明: 当膨胀石墨的长度为1.5 mm、半径为0.05 mm时, 具有较好的消光、散射效果; 适当增大膨胀石墨的电导率、磁导率, 有利于提高其消光、散射能力. 本研究为探索增强膨胀石墨干扰3 mm波效果的技术途径提供了有价值的参考.关键词：膨胀石墨石墨层间化合物消光截面矩量法     

膨胀波火炮发射性能计算分析

 针对膨胀波火炮的发射性能及不同因素对发射性能的影响规律进行了研究分析。基于膨胀波火炮的发射机理,建立了膨胀波火炮两相流内弹道模型,给出了相应的数值求解方法。通过与同口径闭膛火炮内弹道过程的对比计算,分析了膨胀波火炮的发射性能,得到了装填条件、打开时机和后喷结构参数等因素对发射性能的影响规律。     

高压气体驱动激波管的数值模拟与参数影响分析

爆炸荷载作用下建筑构件的动态响应与损伤破坏的试验研究对于结构抗爆设计具有重要的参考价值。为了探究激波管参数对末端荷载峰值和持时的影响,首先,基于商用有限元分析软件ANSYS/LS-DYNA开展了典型激波管试验的数值模拟,通过对比膨胀段末端反射超压和测试构件的挠度时程,验证了激波管有限元模型、参数取值和数值分析方法的准确性;然后,设计了末端尺寸为3 m×3 m的激波管,开展了激波管几何参数和驱动段超压对末端反射超压的参数影响分析,结果表明：超压峰值和持时随驱动段长度、直径和超压的增大而增加,随膨胀段角度减小而增加;最后,给出了基于反射超压峰值和持时的激波管设计方法,并通过设计算例进行了验证。     

柱面Love波频散分析与SH波场的数值计算

对贴井壁环型剪切源在柱状双层弹性介质中激发的SH波场进行了理论求解,导出了柱面Love波频散方程,讨论了柱面Love波存在的条件及其区域.通过数值计算考察了柱面Love波的频散特性和激发强度,发现最低阶柱面Love波具有截止频率,这与平面半空间双层弹性介质模型下的Love波无截止频率的特征不同.渐近分析与数值考察都表明,井径r₁→∞时,柱面Love波频散方程趋向平面双层半空间的Love波方程,柱面Love波的截止频率趋于零.全波计算还显示用激发SH波来探测侵入带外原状地层的横波信息是一个十分简洁的途径..     

线性与非线性波的Chebyshev广义有限谱模拟

给出求解二维线性与非线性波的Chebyshev广义有限谱模拟方法.结合时间层次的高精度预报-校正方法，模拟了二维线性浅水驻波和波在浅滩的非线性变形.方法能够准确模拟水波的物理特征. 关键词： Chebyshev广义有限谱 线性波 非线性波     

变系数广义KdV方程新的类孤波解和精确解

用普通KdV方程作变换，构造变系数广义KdV方程的解，获得了变系数广义KdV方程新的Jacobi椭圆函数精确解、类孤波解、三角函数解和Weierstrass椭圆函数解. 关键词： KdV方程 变系数广义KdV方程 类孤波解 精确解     

二维平面激波折射的理论计算方法

围绕二维平面激波与物质界面作用,建立了流场波系结构的理论计算方法.首先分析了界面两侧激波独自沿界面传播过程,识别了两类正规折射和三类非正规折射;然后,根据两侧扰动沿界面传播的相对快慢,得到了三种不同的作用情形.与已有的Catherasoo方法相比,此方法:1)考虑了激波波后紧邻波阵面流场中扰动对界面附近折射的影响,区分了扰动的强弱及其是否可以追赶上激波阵面; 2)除了少数情形外,大都基于Euler方程精确解描述流场中波系相互作用.利用该方法对马赫数1.17的激波与空气/SF6界面作用进行计算,得到的波系结构与数值结果、已有实验数据基本一致,透射波阵面与水平方向夹角吻合程度优于Catherasoo结果;给出了反射波参数、界面偏折角度等,而Catherasoo方法不能计算这些参数.对于马赫数2.00的激波,通过比较不同介质密度比和界面倾角下的理论与数值结果,发现此方法对波系类型的识别比Catherasoo方法更为准确,且识别了波后强扰动追赶上激波形成三波结构的折射类型,后者无法识别此类型.上述结果表明,新方法具有良好的适用性,对波系类型的识别较已有方法的准确度更高,可获取更为丰富的波系结构...     

铁-铍介质界面上激波折射现象的数值研究

用数值方法研究铁-铍介质界面上的激波折射现象.运用激波极曲线理论分析不同强度的激波从正规折射过渡到非正规折射的临界角变化.运用一个具有二阶精度和波传播性质的激波捕捉法,数值求解激波折射运动的流体力学方程组.对正规折射,数值结果与激波极曲线理论一致;对非正规折射,不同强度的激波大都存在前驱的折射激波,并且入射激波的强度不同、入射角度不同,激波折射的图像也不同.     

On Ground-Traveling Waves for the Generalized Kadomtsev-Petviashvili Equations

As a continuation of our previous work, we improve some results on convergence of periodic KP traveling waves to solitary ones as the period goes to infinity. In addition, we present some qualitative properties of such waves, as well as nonexistence results, in the case of general nonlinearities. We suggest an approach which does not use any scaling argument. This revised version was published online in July 2006 with corrections to the Cover Date.     

Ion-Acoustic Shock Waves in Nonextensive Multi-Ion Plasmas

The nonlinear propagation of ion-acoustic (IA) shock waves (SHWs) in a nonextensive multi-ion plasma system (consisting of inertial positive light ions as well as negative heavy ions, noninertial nonextensive electrons and positrons) has been studied. The reductive perturbation technique has been employed to derive the Burgers equation. The basic properties (polarity, amplitude, width, etc.) of the IA SHWs are found to be significantly modified by the effects of nonextensivity of electrons and positrons, ion kinematic viscosity, temperature ratio of electrons and positrons, etc. It has been observed that SHWs with positive and negative potential are formed depending on the plasma parameters. The findings of our results obtained from this theoretical investigation may be useful in understanding the characteristics of IA SHWs both in laboratory and space plasmas.     

Electrostatic Nonplanar Positron-Acoustic Shock Waves in Superthermal Electron-Positron-Ion Plasmas

The basic properties of the nonlinear propagation of the nonplanar(cylindrical and spherical) positronacoustic(PA) shock waves(SHWs) in an unmagnetized electron-positron-ion(e-p-i) plasma containing immobile positive ions,mobile cold positrons,and superthermal(kappa distributed) hot positrons and electrons are investigated both analytically and numerically.The modified Burgers equation(mBE) is derived by using the reductive perturbation method.The basic features of PA SHWs are significantly modified by the cold positron kinematic viscosity(η),superthermal parameter of electrons(κ_e),superthermal parameter of hot positrons(κ_p),the ratio of the electron temperature to hot positron temperature(σ),the ratio of the electron number density to cold positron number density(μ_e),and the ratio of the hot positron number density to cold positron number density(μ_(ph)).This study could be useful to identify the basic properties of nonlinear electrostatic disturbances in dissipative space and laboratory plasmas.     

隔板深度对激波聚焦起爆影响的数值模拟研究

考虑几何结构参数对激波聚焦触发爆轰波的复杂影响,对H2/Air预混气的环形射流激波聚焦起爆现象开展了数值模拟研究,详细分析了不同隔板深度条件下的激波聚焦过程、流场演化特征以及爆轰波参数变化规律.研究结果表明,凹腔内激波聚焦诱导的局部爆炸以及隔板前缘处射流形成"卷吸涡"是引起爆轰波触发的两个重要机制,而隔板深度是影响环形...     

Cylindrical and Spherical Electron-Acoustic Shock Waves in Electron-Positron-Ion Plasmas with Nonextensive Electrons and Positrons

Electron-acoustic shock waves (EASWs) in an unmagnetized four-component plasma (containing hot electrons and positrons following the q-nonextensive distribution, cold mobile viscous electron fluid, and immobile positive ions) are studied in nonplanar (cylindrical and spherical) geometry. With the help of the reductive perturbation method, the modified Burgers equation is derived. Analytically, the effects of nonplanar geometry, nonextensivity, relative number density and temperature ratios, and cold electron kinematic viscosity on the basic properties (viz. amplitude, width, speed, etc.) of EASWs are discussed. It is examined that the EASWs in nonplanar geometry significantly differ from those in planar geometry. The results of this investigation can be helpful in understanding the nonlinear features of EASWs in various astrophysical plasmas.     

Planar and Nonplanar Shock Waves in a Degenerate Quantum Plasma

The nonlinear propagation of modified electron‐acoustic (mEA) shock waves in an unmagnetized, collisionless, relativistic, degenerate quantum plasma (containing non‐relativistic degenerate inertial cold electrons, both nonrelativistic and ultra‐relativistic degenerate hot electron and inertial positron fluids, and positively charged static ions) has been investigated theoretically. The well‐known Burgers type equation has been derived for both planar and nonplanar geometry by employing the reductive perturbation method. The shock wave solution has also been obtained and numerically analyzed. It has been observed that the mEA shock waves are significantly modified due to the effects of degenerate pressure and other plasma parameters arised in this investigation. The properties of planar Burgers shocks are quite different from those of nonplanar Burgers shocks. The basic features and the underlying physics of shock waves, which are relevant to some astrophysical compact objects (viz. non‐rotating white dwarfs, neutron stars, etc.), are briefly discussed. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

粘性物质中正激波稳定性分析

用线性稳定性理论,分析粘性物质中的正激波稳定性问题.粘性物质中任意强度的一维激波,其稳定性问题可归结为处理复数范围内的特征值问题,该特征值问题由两个一阶常微分方程及一个二阶常微分方程构成.这些常微分方程的系数依赖于流动的基本流场的物理量及其梯度.所获得的特征值问题由一个四阶精度的有限差分离散求解.分析考虑物质粘性的金属铝中的正激波稳定性,可以看出,正激波运动是稳定的,并且激波速度对波前和波后的小扰动量的衰减有相反的作用,而物质粘性有致稳的作用.     

并联铁电体冲击去极化输出电流实验和计算

 为分析不同数量铁电体的输出电流特征,进行了多片并联PZT95/5铁电体冲击去极化实验,测量了电阻负载下铁电体的输出电流;建立了并联铁电体输出电流的计算模型,计算了并联铁电体的输出电流。通过比较计算和实验结果,分析了铁电体数量和冲击波状态对铁电体输出电流的影响。结果表明：若进入铁电体的冲击波为平面波,铁电体输出电流的波形接近方波,电流峰值随铁电体并联数量的增加成比例增加,冲击波波形和侧向稀疏波对铁电体输出电流波形和去极化率有很大的影响。     

激波与火焰面相互作用数值模拟的GPU加速

为考察计算机图形处理器（GPU）在计算流体力学中的计算能力,采用基于CPU/GPU异构并行模式的方法对激波与火焰界面相互作用的典型可压缩反应流进行数值模拟,优化并行方案,考察不同网格精度对计算结果和计算加速性能的影响.结果表明,和传统的基于信息传递的MPI 8线程并行计算相比,GPU并行模拟结果与MPI并行模拟结果相同;两种计算方法的计算时间均随网格数量的增加呈线性增长趋势,但GPU的计算时间比MPI明显降低.当网格数量较小时（1.6×10⁴）,GPU计算得到的单个时间步长平均时间的加速比为8.6;随着网格数量的增加,GPU的加速比有所下降,但对较大规模的网格数量（4.2×10⁶）,GPU的加速比仍可达到5.9.基于GPU的异构并行加速算法为可压缩反应流的高分辨率大规模计算提供了较好的解决途径.     

Propagation of Electron Acoustic Soliton,Periodic and Shock Waves in Dissipative Plasma with a q-Nonextensive Electron Velocity Distribution

The nonlinear properties of small amplitude electron-acoustic (EA) solitary and shock waves in a homogeneous system of unmagnetized collisionless plasma with nonextensive distribution for hot electrons have been investigated. A reductive perturbation method used to obtain the Kadomstev-Petviashvili-Burgers equation. Bifurcation analysis has been discussed for non-dissipative system in the absence of Burgers term and reveals different classes of the traveling wave solutions. The obtained solutions are related to periodic and soliton waves and their behavior are shown graphically. In the presence of the Burgers term, the EXP-function method is used to solve the Kadomstev-Petviashvili-Burgers equation and the obtained solution is related to shock wave. The obtained results may be helpful in better conception of waves propagation in various space plasma environments as well as in inertial confinement fusion laboratory plasmas.