A partition approach for underwater explosion based on smoothed particle method

As a Lagrangian particle method, smoothed particle hydrodynamics (SPH) has been applied into the problems of fluid-structure interaction (FSI) more and more. However, the transient fluid-structure interactions characterized by severe reactions and wide spreads are very expensive to be carried out with three-dimensional SPH method due to the approach of solid modeling, especially when the structure is subjected to the shock loads from mid-field or far-field, which is almost impossible to achieve. Therefore, based on the previous research, the coupled SPH-BEM method is put forward and applied to underwater explosion in this paper. The structure is modeled and solved with SPH method while the fluid boundary only required is coped with a boundary element method (BEM), the second-order doubly asymptotic approximations (DAA2). The FSI method will reduce the elements of structures and fluid greatly so as to solve the problems of fluid-structure interactions feasibly and efficiently. The mid-plane of a plate only discretized into a layer of particles is taken as the study object in the SPH shell element and the related physical quantities is integrated in the thickness direction to capture the dynamic response of structures; the fluid boundary only discretized into a piece of boundary elements is employed in the BEM method to solve fluid dynamics based on the retarded potential equation; treatments of the coupled fluid-structure interface are made to satisfy the compatibility conditions and the messages related to motions and loads are well delivered. Finally, two standard examples are carried out to test the above algorithm

Effect of Tensor Correlations on Gamow-Teller States in 90Zr and 208Pb

The tensor terms of the Skyrme effective interaction are included in the self-consistent Hartree-Fock plus Random Phase Approximation (HF+RPA) model. The Gamow-Teller (GT) strength function of 90Zr and 208Pb are calculated with and without the tensor terms. The main peaks are moved downwards by about 2 MeV when including the tensor contribution. About 10% of the non-energy weighted sum rule is shifted to the excitation energy region above 30 MeV by the RPA tensor correlations. The contribution of the tensor terms to the energy weighted sum rule is given analytically, and compared to the outcome of RPA.Comment: 13 pages, 2 figures,2 table

Statefinder diagnosis and the interacting ghost model of dark energy

A new model of dark energy namely "ghost dark energy model" has recently been suggested to interpret the positive acceleration of cosmic expansion. The energy density of ghost dark energy is proportional to the hubble parameter. In this paper we perform the statefinder diagnostic tool for this model both in flat and non-flat universe. We discuss the dependency of the evolutionary trajectories in $s-r$ and $q-r$ planes on the interaction parameter between dark matter and dark energy as well as the spatial curvature parameter of the universe. Eventually, in the light of SNe+BAO+OHD+CMB observational data, we plot the evolutionary trajectories in $s-r$ and $q-r$ planes for the best fit values of the cosmological parameters and compare the interacting ghost model with other dynamical dark energy models. We show that the evolutionary trajectory of ghost dark energy in statefinder diagram is similar to holographic dark energy model. It has been shown that the statefinder location of $\Lambda$CDM is in good agreement with observation and therefore the dark energy models whose current statefinder values are far from the $\Lambda$CDM point can be ruled out.Comment: 23 pages, 6 figure

Localization of interacting electrons in quantum dot arrays driven by an ac-field

We investigate the dynamics of two interacting electrons moving in a one-dimensional array of quantum dots under the influence of an ac-field. We show that the system exhibits two distinct regimes of behavior, depending on the ratio of the strength of the driving field to the inter-electron Coulomb repulsion. When the ac-field dominates, an effect termed coherent destruction of tunneling occurs at certain frequencies, in which transport along the array is suppressed. In the other, weak-driving, regime we find the surprising result that the two electrons can bind into a single composite particle -- despite the strong Coulomb repulsion between them -- which can then be controlled by the ac-field in an analogous way. We show how calculation of the Floquet quasienergies of the system explains these results, and thus how ac-fields can be used to control the localization of interacting electron systems.Comment: 7 pages, 6 eps figures V2. Minor changes, this version to be published in Phys. Rev.

Multi-phase SPH modelling of air effect on the dynamic flooding of a damaged cabin

The air flow may take effects on the responses of the damaged ship in the dynamic flooding process. It not only relates to the amount of inflow but also the stability of the ship. In order to accurately predict the responses of a damaged ship, it is essential to take the air into account. In this study, a multi-phase SPH model combined with a dummy boundary method is proposed. One of the advantages of the new SPH model in solving this nonlinear problem is that, it does not rely on other algorithms to track the interface of different phases but can easily deal with breaking, splashing and mixing. The stability and accuracy of the numerical model are verified by comparing with experimental and published numerical results. The air captured in the flooding process is further studied with focus on the exchange of air and water near the opening. Finally, the effects of the sizes and number of the deck openings on the air flow are analyzed. It is found that the air flow can reduce the kinematic energy of inflow water, leading to decreases in the dynamic moment formed by the flooding water and sinking rate of damaged cabin

QCD-scale modified-gravity universe

A possible gluon-condensate-induced modified-gravity model with f(R) \propto |R|^{1/2} has been suggested previously. Here, a simplified version is presented using the constant flat-spacetime equilibrium value of the QCD gluon condensate and a single pressureless matter component (cold dark matter, CDM). The resulting dynamical equations of a spatially-flat and homogeneous Robertson-Walker universe are solved numerically. This simple empirical model allows, in fact, for a careful treatment of the boundary conditions and does not require a further scaling analysis as the original model did. Reliable predictions are obtained for several observable quantities of the homogeneous model universe. In addition, the estimator E_{G}, proposed by Zhang et al. to search for deviations from standard Einstein gravity, is calculated for linear sub-horizon matter-density perturbations. The QCD-scale modified-gravity prediction for E_{G}(z) differs from that of the LambdaCDM model by about \pm 10 % depending on the redshift z.Comment: 24 pages; v7: published versio

Spin-isospin excitations as quantitative constraints for the tensor force

Gamow-Teller (GT) and charge-exchange spin-dipole (SD) excitation energies in 90Zr and 208Pb are systematically studied to determine the appropriate magnitude of the tensor terms of the Skyrme interactions. We have found that the centroid energies of GT and SD excitations are sensitive to the adopted strengths of the triplet-even and triplet-odd tensor interactions. Especially, the 1- SD state plays a crucial role in constraining the triplet-even part while the triplet-odd part is related rather to the GT peaks. Among the 36 TIJ parameter sets that include nonperturbatively the tensor terms, the four sets, T21, T32, T43, and T54, give reasonable results for the centroid energies in comparison with the experimental data. The sign and magnitude of the tensor terms are also discussed when these terms are added to the existing Skyrme interactions SGII and SLy5. The triplet-even strength can be constrained in a narrow range by using the available experimental data while further empirical data are needed to set a constraint on the triplet-odd term

Interacting Ghost Dark Energy in Non-Flat Universe

A new dark energy model called "ghost dark energy" was recently suggested to explain the observed accelerating expansion of the universe. This model originates from the Veneziano ghost of QCD. The dark energy density is proportional to Hubble parameter, $\rho_D=\alpha H$, where $\alpha$ is a constant of order $\Lambda_{\rm QCD}^3$ and $\Lambda_{\rm QCD}\sim 100 MeV$ is QCD mass scale. In this paper, we extend the ghost dark energy model to the universe with spatial curvature in the presence of interaction between dark matter and dark energy. We study cosmological implications of this model in detail. In the absence of interaction the equation of state parameter of ghost dark energy is always $w_D > -1$ and mimics a cosmological constant in the late time, while it is possible to have $w_D < -1$ provided the interaction is taken into account. When $k = 0$, all previous results of ghost dark energy in flat universe are recovered. To check the observational consistency, we use Supernova type Ia (SNIa) Gold sample, shift parameter of Cosmic Microwave Background radiation (CMB) and the Baryonic Acoustic Oscillation peak from Sloan Digital Sky Survey (SDSS). The best fit values of free parameter at $1\sigma$ confidence interval are: $\Omega_m^0= 0.35^{+0.02}_{-0.03}$, $\Omega_D^0=0.75_{-0.04}^{+0.01}$ and $b^2=0.08^{+0.03}_{-0.03}$. Consequently the total energy density of universe at present time in this model at 68% level equates to $\Omega_{\rm tot}^0=1.10^{+0.02}_{-0.05}$.Comment: 19 pages, 9 figures. V2: Added comments, observational consequences, references, figures and major corrections. Accepted for publication in General Relativity and Gravitatio