A nonlinear magneto-thermo-elastic coupled hysteretic constitutive model for magnetostrictive alloys

This paper presents a general hysteretic constitutive law of nonlinear magneto-thermo-elastic coupling for magnetostrictive alloys. The model considered here is thermodynamically motivated and based on the Gibbs free energy function. A nonlinear part of the elastic strain arising from magnetic domain rotation induced by the pre-stress is taken into account. Furthermore, the movement of the domain walls is incorporated to describe hysteresis based on Jiles–Atherton's model. Then a set of closed and analytical expressions of the constitutive law for the magnetostrictive rods and films are obtained, and the parameters appearing in the model can be determined by those measurable experiments in mechanics and physics. Comparing this model with other existing models in this field, the quantitative results show that the relationships obtained here are more effective to describe the effects of the pre-stress or in-plane residual stress and ambient temperature on the magnetization or the magnetostriction hysteresis loops.     

一种耦合外部电路的脉冲感应推力器磁流体力学数值仿真模型

为了深入研究脉冲感应推力器的工作原理,预测其推进性能,建立了一种耦合外部电路的磁流体力学模型,实现了对加速通道内等离子体二维流场结构演化过程及驱动电路放电过程的同步耦合求解.模拟计算所得美国MK-1推力器加速通道内的等离子体瞬态参数分布及推力器比冲、效率等性能参数均与实验数据一致;计算结果成功复现了推力器的工作物理图景.借助这一新模型,实现了对电路-等离子体双向耦合作用的定量分析,分析结果表明:耦合等离子体导致驱动电路等效电阻增大,电感减小;激励线圈与等离子体之间的互感随等离子体整体远离线圈表面而逐渐减小.     

耦合的AKNS-Kaup-Newell孤子方程族的一类可积扩展模型

基于Lie圈代数?1的子代数建立了一个等谱问题，导出了耦合的AKNS- Kaup- Newell孤子方程族。另外，利用扩展相应Lie代数于?2的方法，建立了该方程族的可积扩展模型，即可积耦合。     

A multi-scale numerical simulation of the crystallisation and temperature field of glass

There is a big difference in the spatial scale between temperature field simulation and crystallisation simulation of the glass cooling process. The temperature field belongs to the macroscopic scale, while crystallisation is on the mesoscopic scale. In this paper, a coupled algorithm for the temperature field and crystallisation calculation is established in which the macroscopic temperature simulation is based on the finite element method while the mesoscopic crystallisation simulation is based on the Monte Carlo method using the Uhlmann model. In calculations, the temperature value is regarded as the input condition of the crystallisation calculation while the results of crystallisation in the form of latent heat are used as the input conditions for the temperature calculation. The pixel method is employed to deal with the collision process of crystal grain interfaces. A corresponding numerical simulation scheme has been developed and a multi-scale simulation of glass crystallisation and the cooling temperature field has been carried out. Finally, the presented model and developed simulation scheme have been shown to be very reasonable in comparison to both numerical predictions and with previous results from the literature.     

互耦相对论返波管等同锁相和功率放大的粒子模拟

推导了两个互耦高功率微波振荡系统等同锁相后的锁定频率公式,并利用粒子模拟软件对两个互耦相对论返波管进行了数值仿真实验。模拟时将相同结构的两个相对论返波管并排放置在一起,在它们的慢波结构的第１个波谷处,用一条饼状狭缝将它们并联起来,分别输入不同的加速电压,让它们工作于不同的状态。粒子模拟的结果表明:这两个并联的互耦相对论返波管之间进行了等同锁相,它们的频率都被锁定在同一个特定的频率点上,且其注波能量转换效率都提高了,总输出功率比单独工作时的总功率增加了约10%,同时耦合之后功率输出更平稳。     

互耦相对论返波管等同锁相和功率放大的粒子模拟

推导了两个互耦高功率微波振荡系统等同锁相后的锁定频率公式,并利用粒子模拟软件对两个互耦相对论返波管进行了数值仿真实验。模拟时将相同结构的两个相对论返波管并排放置在一起,在它们的慢波结构的第１个波谷处,用一条饼状狭缝将它们并联起来,分别输入不同的加速电压,让它们工作于不同的状态。粒子模拟的结果表明：这两个并联的互耦相对论返波管之间进行了等同锁相,它们的频率都被锁定在同一个特定的频率点上,且其注波能量转换效率都提高了,总输出功率比单独工作时的总功率增加了约10%,同时耦合之后功率输出更平稳。     

强流脉冲电子束表面改性的物理模型及数值模拟

 推导出了强流脉冲电子束处理过程的应力场方程，利用数值模拟，得到了温度场和应力场的分布曲线，分别给出了熔化深度、升降温的速率及温度梯度的大小，准静态应力和热应力波的幅值、应力波的传播及反射过程，利用数值模拟结果对实验中观察到的实验现象熔化深度、材料表层及次表层数微米范围内组织结构的变化及数百微米的硬度提高等给出了解释。     

强流脉冲电子束表面改性的物理模型及数值模拟

推导出了强流脉冲电子束处理过程的应力场方程,利用数值模拟,得到了温度场和应力场的分布曲线,分别给出了熔化深度、升降温的速率及温度梯度的大小,准静态应力和热应力波的幅值、应力波的传播及反射过程,利用数值模拟结果对实验中观察到的实验现象熔化深度、材料表层及次表层数微米范围内组织结构的变化及数百微米的硬度提高等给出了解释。     

94GHz缓变结构回旋管设计与数值模拟研究

通过分析广义传输线理论中的模式耦合系数,优化设计了一支94GHz光滑缓变结构回旋管,当电子注电压50kV,电流6A,横纵速度比1.4,工作磁场3.548 5T时,在频率94.099GHz处得到了41%互作用效率,约120kW的功率输出;与折变结构回旋管相比,缓变结构回旋管中的工作模式纯度提高约27dB,注波互作用效率提高约7%。基于自洽非线性理论计算的互作用效率与PIC模拟结果有较好的一致性。     

A general finite element model for numerical simulation of structure dynamics

A finite element model used to simulate the dynamics with continuum and discontinuum is presented. This new approach is conducted by constructing the general contact model. The conventional discrete element is treated as a standard finite element with one node in this new method. The one-node element has the same features as other finite elements, such as element stress and strain. Thus, a general finite element model that is consistent with the existed finite element model is set up. This new model is simple in mathematical concept and is straightforward to be combined into the existing standard finite element code. Numerical example demonstrates that this new approach is more effective to perform the dynamic process analysis in which the interactions among a large number of discrete bodies and continuum objects are included.     

A new fully nonisothermal coupled model for the simulation of ice sheet flow

A shallow ice thermocoupled model for the complex nonlinear polythermal ice sheet dynamics is proposed and solved by means of efficient numerical methods. A novelty is the obstacle problem formulation associated to a nonlinear integro-differential equation (with nonlocal temperature dependent coefficients) for the ice sheet profile. This formulation is motivated by the free boundary feature and the influence of the temperature on the profile (fully nonisothermal model). Concerning the temperature equation, a dynamically prescribed surface temperature, obtained from an Energy Balance model corrected by the altitude effect, is posed. As the profile and temperature equations are fully coupled, a nonlinear PDE system governing the upper ice sheet profile, the velocity field, the temperature and the basal stress is stated. In addition to the numerical difficulties associated to the new profile equation, several techniques have been considered for the numerical solution of the temperature, velocity and basal magnitudes. Discussions concerning the nonlinear dynamics of the different involved magnitudes and the improvement in their computed values with respect to previous works are also presented.     

A coupled ordinary differential equation lattice model for the simulation of epileptic seizures

A coupled ordinary differential equation lattice model for the CA3 region of the hippocampus (a common location of the epileptic focus) is developed. This model consists of a hexagonal lattice of nodes, each describing a subnetwork consisting of a group of prototypical excitatory pyramidal cells and a group of prototypical inhibitory interneurons connected via on/off excitatory and inhibitory synapses. The nodes communicate using simple rules to simulate the diffusion of extracellular potassium. Both the integration time over which a node's trajectory is integrated before the diffusional event is allowed to occur and the level of inhibition in each node were found to be important parameters. Shorter integration times lead to total synchronization of the lattice (similar to synchronous neural activity occurring during a seizure) whereas longer times cause more random spatiotemporal behavior. Moderately diminished levels of inhibition lead to simple nodal oscillatory behavior. It is postulated that both the lack of inhibition and an alteration in conduction time may be necessary for the development of a behaviorally manifest seizure. (c) 1999 American Institute of Physics.     

新型结构波导光栅耦合器的耦合特性分析和数值模拟

针对一种新型结构的波导光栅耦合器,通过求解波在直角坐标系下电场分量的亥姆霍兹方程获得了TE导模和TE辐射模的电场。运用模耦合理论分析了光束通过光栅被耦合到波导当中的情况。数值模拟了在不同的波导和光栅结构参数下耦合系数的变化情况。     

94 GHz缓变结构回旋管设计与数值模拟研究

通过分析广义传输线理论中的模式耦合系数,优化设计了一支94 GHz光滑缓变结构回旋管,当电子注电压50 kV,电流6 A,横纵速度比1.4,工作磁场3.548 5 T时,在频率94.099 GHz处得到了41%互作用效率,约120 kW的功率输出;与折变结构回旋管相比,缓变结构回旋管中的工作模式纯度提高约27 dB,注波互作用效率提高约7%。基于自洽非线性理论计算的互作用效率与PIC模拟结果有较好的一致性。     

考虑驾驶员预估效应的交通流格子模型与数值仿真

考虑驾驶员的预估效应对车流的影响,提出了一个改进的一维交通流格子模型.基于线性稳定性理论得到了该模型的线性稳定性判据;运用非线性分析方法导出了描述交通阻塞相变时的mKdV方程.应用数值仿真验证了mKdV方程的解,研究表明适当考虑车流中预估效应的作用能够增强交通流稳定性,从而能有效抑制交通阻塞的形成. 关键词： 预估效应 交通流 格子模型 数值仿真     

On the problem of constraints in minimally coupled relativistic wave equations for particles of unique mass

We study the problem of a possible change in the number of constraints in linear relativistic wave equations (-iβ _μ ∂ ^μ +m)ψ=0 for particles of unique mass, on introduction of minimal coupling to an external electromagnetic field. Complementing our earlier work in which we obtained conditions for non-loss of constraints in equations characterised by the minimalβ-algebraβ ₀ ⁵ =β ₀ ³ we derive here the conditions for such theories not to generate more constraints than in the free case. The results are illustrated by considering specific equations and a fallacy in certain conclusions of Kobayashi and Shamaly on this problem is pointed out.     

扇形腔旭日型磁控管结构的理论分析与数字模拟

利用场分析法推导了扇形腔旭日型磁控管的色散关系, 通过CST模拟软件验证了理论推导的正确性, 分析了扇形腔旭日型磁控管的各项结构参数对π 模截止频率和模式分隔度的影响. 研究表明: 色散关系的理论值与模拟值之间的最大相对误差不到3%, π 模截止频率的理论值与模拟值之间的最大相对误差不到1%; π 模截止频率f_πc与阴极半径R_c, 阳极半径R_a, 大腔张角2θ₁成正比关系, 与小腔半径R_d0, 大腔半径R_d1, 小腔张角2θ₀成反比关系, 这一定性结论与同腔型磁控管的定性结论并不完全一致; 在径向比较上, 结构参数对频率的影响由大到小依次为: 阳极半径, 大腔半径, 小腔半径和阴极半径; 在角向比较上, 大腔张角对频率的影响较大, 小腔张角对频率的影响较小; 另外, 模式分隔度γ 与大腔半径R_d1成正比关系, 与阴极半径R_c, 小腔半径R_d0, 小腔张角2θ₀成反比关系, 随阳极半径R_a或大腔张角2θ₁的增大先增大后减小. 关键词： 旭日型磁控管 扇形谐振腔 色散关系 场分析法     

A transport model and numerical simulation of the high-frequency dynamics of three-dimensional beam trusses

The theory of microlocal analysis shows that the energy density associated with the high-frequency vibrations of a three-dimensional Timoshenko beam satisfies a Liouville-type transport equation. In the present application, the material of the beam is assumed to be isotropic. Its parameters are allowed to vary along the beam axis at length scales much larger than the wavelength of the high-frequency waves traveling in it. Moreover, the curvature and torsion of the beam are accounted for. The first part of the paper focuses on the derivation of the transport model for a single three-dimensional beam. In order to extend this model to beam trusses, the reflection/transmission phenomena of the energy fluxes at junctions of beams are described by power flow reflection/transmission operators in a subsequent part. For numerical simulations, a discontinuous Galerkin finite element method is used on account of the discontinuities of the energy density field at the junctions. Thus, a complete mechanical-numerical modeling of the linear transient dynamics of beam trusses is proposed. It is illustrated by numerical examples highlighting some remarkable features of high-frequency vibrations: The onset of a diffusive regime characterized by energy equipartition rules at late times. Energy diffusion is prompted by the multiple reflection/transmission of waves at the junctions, with possible mode (polarization) conversions. This is the regime applicable to the statistical energy analysis of structural acoustics systems. The main purpose of this research is to develop an effective strategy to simulate and predict the transient response of beam trusses impacted by acoustic or mechanical shocks.     

The equilibrium limit of a constitutive model for two-phase granular mixtures and its numerical approximation

In this paper we analyze the equilibrium limit of the constitutive model for two-phase granular mixtures introduced in Papalexandris (2004) [13], and develop an algorithm for its numerical approximation. At, equilibrium, the constitutive model reduces to a strongly coupled, overdetermined system of quasilinear elliptic partial differential equations with respect to the pressure and the volume fraction of the solid granular phase. First we carry a perturbation analysis based on standard hydrostatic-type scaling arguments which reduces the complexity of the coupling of the equations. The perturbed system is then supplemented by an appropriate compatibility condition which arises from the properties of the gradient operator. Further, based on the Helmholtz decomposition and Ladyzhenskaya’s decomposition theorem, we develop a projection-type, Successive-Over-Relaxation numerical method. This method is general enough and can be applied to a variety of continuum models of complex mixtures and mixtures with micro-structure. We also prove that this method is both stable and consistent hence, under standard assumptions, convergent. The paper concludes with the presentation of representative numerical results.     

范德华力的广义参变本构模型及其在碳纳米管计算中的应用

提出了处理非成键原子间范德华力的广义参变本构模型以及基于此进行碳纳米管结构力学行为数值模拟的数学规划算法.纳米管中原子间短程力作用采用分子结构力学模型来模拟，而作为长程力的范德华力用杆单元来模拟，这类杆单元有着特殊的非线性本构关系.对于这种非线性问题的处理，建立了广义参变本构模型与参数二次规划求解算法.与一般的数值方法相比较，本方法不需要传统的冗长的、反复的迭代，并具有非常好的收敛性，因此为碳纳米管结构力学行为的有效预测提供了保障.数值结果证明了这种方法的正确性和有效性. 关键词： 广义参变本构模型 数学规划算法 分子结构力学 有限元法