A escola na transição para o digital: desafios para a incorporação de TIC e a contribuição da TVD

Pós-graduação em Televisão Digital: Informação e Conhecimento - FAAC

Telejornalismo na TVD: interatividade e mudanças na rotina da redação

Pós-graduação em Comunicação - FAAC

An Approximate Solution Of One-Dimensional Piston Problem

A new theory of shock dynamics has been developed in the form of a finite number of compatibility conditions along shock rays. It has been used to study the growth or decay of shock strength for accelerating or decelerating piston starting with a nonzero piston velocity. The results show good agreement with those obtained by Harten's high resolution TVD scheme.

Growth responses of sugarcane to mycorrhizal spore density and phosphorus rate

Arbuscular mycorrhizal (AM) fungi, commonly found in long-term cane-growing fields in northern Queensland, are linked with both negative and positive growth responses by sugarcane (Saccharum spp.), depending on P supply. A glasshouse trial was established to examine whether AM density might also have an important influence on these growth responses. Mycorrhizal spores (Glomus clarum), isolated from a long-term cane block in northern Queensland, were introduced into a pasteurised low-P cane soil at 5 densities (0, 0.06, 0.25, 1, 4 spores/g soil) and with 4 P treatments (0, 8.2, 25, and 47 mg/kg). At 83 days after planting, sugarcane tops responded positively to P fertilizer, although responses attributable to spore density were rarely observed. In one case, addition of 4 spores/g led to a 53% yield response over those without AM at 8 mgP/kg, or a relative benefit of 17 mg P/kg. Root colonisation was reduced for plants with nil or 74 mg P/kg. For those without AM, P concentration in the topmost visible dewlap (TVD) leaf increased significantly with fertiliser P (0.07 v. 0.15%). However, P concentration increased further with the presence of AM spores. Irrespective of AM, the critical P concentration in the TVD leaf was 0.18%. This study confirms earlier reports that sugarcane is poorly responsive to AM. Spore density, up to 4 spores/g soil, appears unable to influence this responsiveness, either positively or negatively. Attempts to gain P benefits by increasing AM density through rotation seem unlikely to lead to yield increases by sugarcane. Conversely, sugarcane grown in fields with high spore densities and high plant-available P, such as long-term cane-growing soils, is unlikely to suffer a yield reduction from mycorrhizal fungi.

Relaxation system based sub-grid scale modelling for large eddy simulation of Burgers' equation

An implicit sub-grid scale model for large eddy simulation is presented by utilising the concept of a relaxation system for one dimensional Burgers' equation in a novel way. The Burgers' equation is solved for three different unsteady flow situations by varying the ratio of relaxation parameter (epsilon) to time step. The coarse mesh results obtained with a relaxation scheme are compared with the filtered DNS solution of the same problem on a fine mesh using a fourth-order CWENO discretisation in space and third-order TVD Runge-Kutta discretisation in time. The numerical solutions obtained through the relaxation system have the same order of accuracy in space and time and they closely match with the filtered DNS solutions.

Chapman-Enskog analysis for finite-volume formulation of lattice Boltzmann equation

The classical Chapman-Enskog expansion is performed for the recently proposed finite-volume formulation of lattice Boltzmann equation (LBE) method D.V. Patil, K.N. Lakshmisha, Finite volume TVD formulation of lattice Boltzmann simulation on unstructured mesh, J. Comput. Phys. 228 (2009) 5262-5279]. First, a modified partial differential equation is derived from a numerical approximation of the discrete Boltzmann equation. Then, the multi-scale, small parameter expansion is followed to recover the continuity and the Navier-Stokes (NS) equations with additional error terms. The expression for apparent value of the kinematic viscosity is derived for finite-volume formulation under certain assumptions. The attenuation of a shear wave, Taylor-Green vortex flow and driven channel flow are studied to analyze the apparent viscosity relation.

LEVEL SET输运方程的求解方法及其对气-液两相流运动界面数值模拟的影响

用数值模拟方法来研究气-液两相流动与传热现象是当今多相流领域的一个热门课题.由于两相流固有的复杂性,气-液两相流界面迁移现象的数值模拟一直是两相流研究中的一大难点.本文介绍了捕捉气-液两相流相界面运动的水平集方法(Level Set)及其研究进展,介绍了求解Level Set输运方程的3种方法,即一般差分格式、Superbee-TVD格式和Runge-Kutta法-5阶WENO组合格式.结合主流场的求解,分别用这3种方法对4种典型相界面在5种流场中的迁移特性进行了模拟计算,并对计算结果进行了比较和分析.结果表明,Runge-Kutta法-5阶WENO组合格式求解Level Set输运方程的效果最好,在以后的计算中将主要采用这种组合格式来进行气-液相界面输运方程的求解.

High-Resolution Finite Compact Difference Schemes for Hyperbolic Conservation Laws

A finite compact (FC) difference scheme requiring only bi-diagonal matrix inversion is proposed by using the known high-resolution flux. Introducing TVD or ENO limiters in the numerical flux, several high-resolution FC-schemes of hyperbolic conservation law are developed, including the FC-TVD, third-order FC-ENO and fifth-order FC-ENO schemes. Boundary conditions formulated need only one unknown variable for third-order FC-ENO scheme and two unknown variables for fifth-order FC-ENO scheme. Numerical test results of the proposed FC-scheme were compared with traditional TVD, ENO and WENO schemes to demonstrate its high-order accuracy and high-resolution.

爆轰波平掠惰性气体界面及其解耦现象的数值研究

采用基元化学反应模型和迎风TVD格式,数值研究了爆轰波平掠惰性气体界面时的物理现象及其作用机制,并用点隐方法克服化学反应源项引起的计算刚性.数值结果显示,当爆轰波平掠过惰性气体界面时,形成了爆轰波、界面、透射激波以及稀疏波相互作用的现象.在高N2比例稀释的可燃混合气体情况下,当爆轰波平掠过特定惰性气体界面时,它与惰性气体界面相互作用产生的稀疏波可以导致爆轰波的解耦.

高超声速升力体气动力气动热数值计算

升力体气动布局，由于其良好的高超声速气动特性、有效的内部空间和有益的防热特性，越来越受到气动工作者的重视，该文应用张涵信院士的NND格式思想，用数值模拟的方法对类似于美国X-33的升力体外形进行了气动力、气动热研究。特别是在粘性项的离散和表面热流率的计算中应用了散度和梯度的积分定义，避免了数值计算的奇异性，保证了通量守恒，提高了计算效率。结果表明气动热计算结果与美国同类飞行器结果接近，驻点热流率与经典理论结果一致。

M_∞→1时圆球绕前体流场的数值模拟

本文根据来流马赫数Ｍ∞选取坐标变换函数，将Ｍ∞→１时的低超声速回球绕流前体流场变换到矩形的计算区域，忽略粘性影响，采用时间相关法，用ＴＶＤ有限差分格式求Ｅｕｌｅｒ方程的定常解，得到了Ｍ∞＝１．０５、１．０１和１．００５的流场分布。结果与弹道靶的实验吻合较好

Numerical-simulation of low supersonic-flow around a sphere

The controlled equations defined in a physical plane are changed into those in a computational plane with coordinate transformations suitable for different Mach number M(infinity). The computational area is limited in the body surface and in the vicinities of detached shock wave and sonic line. Thus the area can be greatly cut down when the shock wave moves away from the body surface as M(infinity) --> 1. Highly accurate, total variation diminishing (TVD) finite-difference schemes are used to calculate the low supersonic flowfield around a sphere. The stand-off distance, location of sonic line, etc. are well comparable with experimental data. The long pending problem concerning a flow passing a sphere at 1.3 greater-than-or-equal-to M(infinity) > 1 has been settled, and some new results on M(infinity) = 1.05 have been presented.

变截面流化床理论模型及数值模拟

基于双流体模型,在一定假设的条件下推导得到了用于描述变截面床流化过程的局部平衡模型。对于局部平衡模型,空间导数项的离散采用五阶精度的WENO有限差分格式,时间导数项的离散采用TVD Runge-Kutta型的离散格式,对流量突变后的瞬态过程进行了模拟,得到固相体积分数在整个变化过程中沿床高的分布以及床高变化规律和床层表面颗粒速度变化曲线。对于流量突增过程,在床内不同位置形成了一系列的连续波,当所有的连续波到达床面整个变化过程结束。而对于流量突然减小过程,将会有固相体积分数间断在分布板处形成,当所有间断到达床面时,塌落过程结束。

共用尾喷管多管脉冲爆震发动机数值模拟研究

采用基元反应模型和显式迎风TVD差分格式数值模拟方法，研究共用尾喷管多管脉冲爆震发动机（Pulse Detonation Engine，简称PDE）各爆震管之间相互影响。采用点隐算法解决化学反应引起的刚性问题，模拟了共用尾喷管内的流场，以及爆震波退化为激波遇到尾喷管收敛斜面反射及反射波向爆震管上游传播的过程。研究结果为多管PDE的共用尾喷管设计提供了理论基础。

再入飞行器湍流尾迹流场研究

再入飞行器湍流尾迹流场状况，直接系统到飞行器的雷达散射特性。对再入飞行器湍流尾迹等离子体场理论模型，试图通过湍流模式理论来表达，即使用k-ε-g模型方程来封闭平均化的全Navier-Stokes方程，从而准确获得流动平均场和脉动场住处。使用的N－S平均议程由质量加权平均过程产生，湍流模型方程也经过可压缩性能修正。真实气体效应重点考察空气处于局部热化学平衡状态。流动控制方程运用一个二阶TVD格式有限体积法求解。以一典型小钝锥体零攻角再入飞行为例，计算了在两高程（H = 40 km和H = 30 km）条件下的高超声速湍流尾迹流场。获得的尾迹流场参数与流动物理状况符合，并且湍流脉动参数与已有相应的实验结果定性一致，初步证实该方法合理。