Characteristics of the 2011 Tohoku Tsunami and introduction of two level tsunamis for tsunami disaster mitigation

Characteristics of the 2011 Tohoku Tsunami have been revealed by collaborative tsunami surveys extensively performed under the coordination of the Joint Tsunami Survey Group. The complex behaviors of the mega-tsunami were characterized by the unprecedented scale and the low occurrence frequency. The limitation and the performance of tsunami countermeasures were described on the basis of tsunami surveys, laboratory experiments and numerical analyses. These findings contributed to the introduction of two-level tsunami hazards to establish a new strategy for tsunami disaster mitigation, combining structure-based flood protection designed by the Level-1 tsunami and non-structure-based damage reduction planned by the Level-2 tsunami.     

A numerical model of a line thermal: the influence of initial conditions

Summary It is shown that the flow generated by a discrete thermal with line symmetry will depend on the shape of the initial temperature perturbations. For the same original heat content a temperature excess with a large aspect ratio forms a thermal which rises faster than that developing from a long shallow perturbation. For initial conditions with the same aspect ratio, the rate of rise varies inversely with the size of the (initial) zero-temperature gradient near the axis. In all cases the thermals that form the smaller angle with the vertical axis rise faster. This observation is similar to that observed in laboratory models.

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Riassunto Si mostra che il flusso generato da una termica discreta con simmetria lineare dipende dalla forma delle perturbazioni iniziali di temperatura. Per lo stesso contenuto di calore originale un eccesso di temperatura con un grande allungamento forma una termica che sale più veloce di quello che si sviluppa da una perturbazione superficiale di lunga durata. Per condizioni iniziali con lo stesso allungamento, il valore di salita varia inversamente al valore del gradiente (iniziale) a temperatura nulla vicino all’asse. In tutti i casi, le termiche che formano l’angolo minore con l’asse verticale crescono più rapidamente. Questa osservazione è simile a quella di modelli di laboratorio.

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Резюме Показывается, что поток, образованный дискретным тепловым источником с линейной симметрией, будет зависетя от формы начальных температурных возмущений. Для одинаковой первоначальной площади нагрева избыток температуры с большим отношением образует восходящий поток, который поднимается быстрее, чем поток, развивающийся из длинного мелкого возмущения. Для начальных условий с одинаковым отношением скорость подъема изменяется в обратонй зависимости от величины градиента температуры вблизи оси. Во всех случаях восходящие потоки, которые образуют меньший угол с вертикальной осью, поднимаются быстрее. Этот результат аналогичен результату, обнаруженному в лабораторных моделях.

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To speed up publication, the author of this paper has agreed to not receive the proofs for correction.     

Method of finite-dimension particles in the cell for numerical modeling of high-velocity interaction of heterogeneous bodies

A method of finite-size particles for numerical simulation of high-velocity interaction of heterogeneous bodies was proposed. According to this method, a basic cell of a multicomponent material is identified with an Eulerian mixed cell. The main attention was paid to the adaptation of equations of state so as to make them usable in computational codes. An approximate method for correcting phenomenologically constructed caloric equations of state in the region of existence of liquid-vapor two-phase mixture with the help of the Maxwell rule is developed. The problem of describing the behavior of metastable states of the condensed phase at low temperatures is examined. An equilibrium model of the basic (mixed) cell with regard to phase transitions in its components (Lagrangian particles) is proposed. Calculation results on the high-velocity interaction of a lead cylinder with a heterogeneous glass-reinforced resin bar are given.     

Method for estimating the impact of atmospheric turbulence on 3D angular deformations measurement

The optical method is one of the most accurate methods for the 3D angular deformations measurement. However, the measured results fluctuate around a mean value as a result of the impact of the atmospheric turbulence, and the relationship between the fluctuation and the atmospheric turbulence is unclear. In this paper, we propose an optical 3D angular deformations measurement method to analyze the optical wave propagation, and study the impact of the atmospheric turbulence. The fluctuations of the three deformation angles are calculated in different atmospheric turbulences. It is found that this optical method is not suitable for high accuracy measurement with the refractive-index structure parameter larger than 10⁻¹⁴ m^−2/3. When the widths of the crosshairs fringes are different, the impacts of the atmospheric turbulence are nearly the same. It is also found that the impact of the atmospheric turbulence can be reduced by increasing the gray value of the image.     

Time domain numerical modeling of wave propagation in 2D heterogeneous porous media

This paper deals with the numerical modeling of wave propagation in porous media described by Biot’s theory. The viscous efforts between the fluid and the elastic skeleton are assumed to be a linear function of the relative velocity, which is valid in the low-frequency range. The coexistence of propagating fast compressional wave and shear wave, and of a diffusive slow compressional wave, makes numerical modeling tricky. To avoid restrictions on the time step, the Biot’s system is splitted into two parts: the propagative part is discretized by a fourth-order ADER scheme, while the diffusive part is solved analytically. Near the material interfaces, a space–time mesh refinement is implemented to capture the small spatial scales related to the slow compressional wave. The jump conditions along the interfaces are discretized by an immersed interface method. Numerical experiments and comparisons with exact solutions confirm the accuracy of the numerical modeling. The efficiency of the approach is illustrated by simulations of multiple scattering.     

Does inflation provide natural initial conditions for the universe

If our universe underwent inflation, its entropy during the inflationary phase was substantially lower than it is today. Because a low-entropy state is less likely to be chosen randomly than a high-entropy one, inflation is unlikely to arise through randomly-chosen initial conditions. To resolve this puzzle, we examine the notion of a natural state for the universe, and argue that it is a nearly-empty spacetime. If empty space has a small vacuum energy, however, inflation can begin spontaneously in this background. This scenario explains why a universe like ours is likely to have begun via a period of inflation, and also provides an origin for the cosmological arrow of time. This work was supported in part by the U.S. Dept. of Energy, the National Science Foundation, the NDSEG Fellowship, and the David and Lucile Packard Foundation. Second Award in the 2005 Essay Competition of the Gravity Research Foundation. - Ed.     

Symmetric waves are traveling waves for a shallow water equation modeling surface waves of moderate amplitude

Following a general principle introduced by Ehrnström, Holden and Raynaud in 2009, we prove that for an equation modeling the free surface evolution of moderate amplitude waves in shallow water, all symmetric waves are traveling waves.     

Second harmonic generation: the solution for an amplitude-modulated initial pulse

We address the initial value problem for one-dimensional second harmonic generation starting from a purely amplitude-modulated fundamental wave. A general method to solve the problem in terms of a Schrödinger equation is presented, in which the initial pulse-shape is taken as a potential. Several examples with the complete solution given in analytical form are discussed. A much broader class of solutions can be found with the help of a single numerical integration. In particular, solutions with incident pulses approximating a sech -shape have been obtained.     

ELM triggering conditions for the integrated modeling of H-mode plasmas

Recent advances in the integrated modeling of ELMy H-mode plasmas are presented. A new model for the H-mode pedestal and for the triggering of ELMs predicts the height, width, and shape of the H-mode pedestal and the frequency and width of ELMs. The model for the pedestal and ELMs is used in the ASTRA integrated transport code to follow the time evolution of tokamak discharges from L-mode through the transition from L-mode to H-mode, with the formation of the H-mode pedestal, and, subsequently, to the triggering of ELMs. Turbulence driven by the ion temperature gradient mode, resistive ballooning mode, trapped electron mode, and electron temperature gradient mode contributes to the anomalous thermal transport at the plasma edge in this model. Formation of the pedestal and the L-H transition is the direct result of flow shear suppression of anomalous transport. The periodic ELM crashes are triggered by MHD instabilities. Two mechanisms for triggering ELMs are considered: ELMs are triggered by ballooning modes if the pressure gradient exceeds the ballooning threshold or by peeling modes if the edge current density exceeds the peeling mode threshold. The BALOO, DCON, and ELITE ideal MHD stability codes are used to derive a new parametric expression for the peeling-ballooning threshold. The new dependence for the peeling-ballooning threshold is implemented in the ASTRA transport code. Results of integrated modeling of DIII-D like discharges are presented and compared with experimental observations. The results from the ideal MHD stability codes are compared with results from the resistive MHD stability code NIMROD.Presented at the Workshop Electric Fields Structures and Relaxation in Edge Plasmas, Nice, France, October 26–27, 2004.     

驻波法测超声波衰减系数

用驻波法测量超声波在空气中衰减系数的实验方法。与前人的方法进行比较。新的测量结果更符合实际。只有当换能器反射系数r〈0.619时,用简单波拟合得到的衰减系数才比较可信。同时讨论了该方法的实用意义。     

On co-evolution and the importance of initial conditions

We present a generic threshold model for the co-evolution of the structure of a network and the binary state of its nodes. We focus on regular directed networks and derive equations for the evolution of the system toward its absorbing state. It is shown that the system displays a transition from a connected phase to a fragmented phase, and that this transition is driven by the initial configuration of the system, as different initial conditions may lead to drastically different final configurations. Computer simulations are performed and confirm the theoretical predictions.     

A numerical modeling for eigenvibration analysis of honeycomb sandwich panels

The eigenvibration properties of honeycomb sandwich panels are investigated in this paper. A new numerical modeling for eigenvibration analysis of the honeycomb sandwich panels is proposed under the assumption that the orthotropic shell and two kinds of beam elements represent face materials, adhesive layers and honeycomb core, respectively. The shell element is also connected to the beam element through the thickness. The effects of geometry of honeycomb core and thickness of face material on the eigenfrequency are examined through the comparisons between finite element simulation and experimental results. It is shown as a result that the eigenvibration properties depend strongly on the face material rigidity and honeycomb core geometry. The implications of the findings for the design of eigenvibration of honeycomb sandwich panels are discussed from the point of view of overall flexural rigidity.     

Practical use of variational principles for modeling water waves

This paper describes a method for deriving approximate equations for irrotational water waves. The method is based on a ‘relaxed’ variational principle, i.e., on a Lagrangian involving as many variables as possible. This formulation is particularly suitable for the construction of approximate water wave models, since it allows more freedom while preserving a variational structure. The advantages of this relaxed formulation are illustrated with various examples in shallow and deep waters, as well as arbitrary depths. Using subordinate constraints (e.g., irrotationality or free surface impermeability) in various combinations, several model equations are derived, some being well-known, other being new. The models obtained are studied analytically and exact traveling wave solutions are constructed when possible.     

Considering azimuthal dependence in the numerical modeling of VCSELs

A method is proposed for the analysis of vertical cavity laser diodes where the cylinder symmetry has been perturbed. The full vectorial wave equation is used. The analysis is performed with the method of lines in cylindrical coordinates where the permittivity (r, ) and the fields are expanded in Fourier series in azimuthal direction. The discretization is done only in radial direction. As an example the original cylindrical geometry of a vertical cavity laser has been deformed and the influence on the wavelength of the lowest order cavity resonances and on the optical field is shown.     

Exact boundary conditions for the initial value problem of convex conservation laws

The initial value problem of convex conservation laws, which includes the famous Burgers’ (inviscid) equation, plays an important rule not only in theoretical analysis for conservation laws, but also in numerical computations for various numerical methods. For example, the initial value problem of the Burgers’ equation is one of the most popular benchmarks in testing various numerical methods. But in all the numerical tests the initial data have to be assumed that they are either periodic or having a compact support, so that periodic boundary conditions at the periodic boundaries or two constant boundary conditions at two far apart spatial artificial boundaries can be used in practical computations. In this paper for the initial value problem with any initial data we propose exact boundary conditions at two spatial artificial boundaries, which contain a finite computational domain, by using the Lax’s exact formulas for the convex conservation laws. The well-posedness of the initial-boundary problem is discussed and the finite difference schemes applied to the artificial boundary problems are described. Numerical tests with the proposed artificial boundary conditions are carried out by using the Lax–Friedrichs monotone difference schemes.     

弱电离等离子体对电磁波吸收的物理模型和数值求解

从物理基本方程、理论证明和数值分析三方面说明了在一维平板模型中，含时波动方程和亥 姆霍兹方程是等价的，即使电磁波波长小于等离子体的尺度，电磁波的全波解也具有简谐形 式. 对电磁波在弱电离强碰撞等离子体中的传播特性进行了数值研究，结果表明，弱电离强 碰撞等离子体对电磁波具有很强的吸收特性. 关键词： 电磁波 弱电离等离子体 过阻尼     

数值地震预测的关键物理问题*

数值地震预测是地震物理研究中的一个重要课题,具有基础性的科学意义和潜在的应用价值.文章介绍了数值地震预测的三个关键物理问题——地震发生率与应力变化的关系、地震断层的摩擦函数、地球中应力的传递问题,讨论了这些问题的意义、研究现状和发展趋势.