A simple derivation of level spacing of quasinormal frequencies for a black hole with a deficit solid angle and quintessence-like matter

In this paper, we investigate analytically the level space of the imaginary part of quasinormal frequencies for a black hole with a deficit solid angle and quintessence-like matter by the Padmanabhan's method \cite{Padmanabhan}. Padmanabhan presented a method to study analytically the imaginary part of quasinormal frequencies for a class of spherically symmetric spacetimes including Schwarzschild-de Sitter black holes which has an evenly spaced structure. The results show that the level space of scalar and gravitational quasinormal frequencies for this kind of black holes only depend on the surface gravity of black-hole horizon in the range of -1 < w < -1/3, respectively . We also extend the range of $w$ to $w \leq -1$, the results of which are similar to that in -1 < w < -1/3 case. Particularly, a black hole with a deficit solid angle in accelerating universe will be a Schwarzschild-de Sitter black hole, fixing $w = -1$ and $\epsilon^2 = 0$. And a black hole with a deficit solid angle in the accelerating universe will be a Schwarzschild black hole,when $\rho_0 = 0$ and $\epsilon^2 = 0$. In this paper, $w$ is the parameter of state equation, $\epsilon^2$ is a parameter relating to a deficit solid angle and $\rho_0$ is the density of static spherically symmetrical quintessence-like matter at $r = 1$.Comment: 6 pages, Accepted for publication in Astrophysics & Space Scienc

Direct identification of continuous second - order plus dead-time model

Describes a direct identification of continuous second - order plus dead-time model

Global Monopole in Asymptotically dS/AdS Spacetime

In this paper, we investigate the global monopole in asymptotically dS/Ads spacetime and find that the mass of the monopole in the asymptotically dS spacetime could be positive if the cosmological constant is greater than a critical value. This shows that the gravitational field of the global monopole could be attractive or repulsive depending on the value of the cosmological constant.Comment: 5 pages, 1 figure, to appear in Phys. Rev.

Numerical simulation of focused wave impact on a 2-D floating structure

Freak (Extreme, rogue) waves are extremely large water waves in ocean and may occur all over the world sea area. Such a wave may lead to damage of coastal and offshore structures. Accurate prediction of extreme wave-induced forces and motions is of importance and necessaries for researchers and engineers for the purpose of structure design and disaster prevention. Due to the complexity of nonlinear wave-structure interactions related with distorted free surface and relatively large amplitude of structure response, a great deal of effort is required to investigate the physics. Here, a Computational Fluid Dynamics (CFD) model has been developed to study focused wave impact on a floating structure and validated by a newly designed experiment. Focused waves are generated based on the mechanism of wave focusing in a two-dimensional wave tank. In the experiment, a model of a box-shaped floating body with a small freeboard is adopted in order to easily obtain green water phenomena. The computations are performed by a Constrained Interpolation Profile (CIP)-based Cartesian grid method. The CIP algorithm is adopted as the base scheme to obtain a robust flow solver of the Navier-stokes equation with free surface boundary. An improved THINC scheme (THINC, tangent of hyperbola for interface capturing), the more accurate THINC/SW scheme (THINC with Slope Weighting), is applied as the free surface/ interface capturing method. Main attentions are paid to the three degrees of freedom (3-DOF) body motions, pressure domain around the structure and nonlinear phenomena, such as water on deck. The highly nonlinear wave-structure interactions, including significant body motion and water on deck, are modeled successfully in comparison with experimental measurements. It is concluded that the present model with the aid of the CIP technique can provide with acceptably accurate numerical results on the route to practical purposes

Attractor Solution of Phantom Field

In light of recent study on the dark energy models that manifest an equation of state $w<-1$, we investigate the cosmological evolution of phantom field in a specific potential, exponential potential in this paper. The phase plane analysis show that the there is a late time attractor solution in this model, which address the similar issues as that of fine tuning problems in conventional quintessence models. The equation of state $w$ is determined by the attractor solution which is dependent on the $\lambda$ parameter in the potential. We also show that this model is stable for our present observable universe.Comment: 9 pages, 3 ps figures; typos corrected, references updated, this is the final version to match the published versio

User friendly assessment of stress intensity factor in thermal shocked cracked structures with finite boundary restraint

AbstractEvaluation of thermal shock stress intensity factors is a problem of interest in many industries. Many structures experiencing thermal shock can be accurately idealised to comprise finite length elastically/thermo-elastically restrained plates and finite length elastically/thermo-elastically restrained hollow cylinders. This article describes how a ‘user-friendly‘ Compliance Adjusted Weight Function (CAWF) approach can be used to assess mode I stress intensity factor associated with the creep-free thermal shock of such structure with edge and semi-elliptical surface cracks. Based upon a mechanical weight function philosophy, the CAWF approach utilises a mechanical weight function analysis, available mechanical weight functions/geometry factors attributed to an equivalent semi-infinite cracked structure, a crack-free finite element analysis and an elastic Line-Spring analysis of compliance. The need for deriving different weight functions at each configuration of boundary restraint is therefore removed and the results of several verification exercises highlight that the CAWF approach is suitable for estimates within 5–10% of benchmark fracture mechanics finite element values. This suitability of the CAWF approach is valid for a wide range of cracked plate configurations, cracked hollow cylinder configurations and boundary restraint. An exception to this suitability is observed when examining semi-elliptical surface crack configurations and a free or near free boundary restraint condition. Adjustments to correction for this ‘free boundary effect’ are discussed elsewhere