Applied Mechanics and Materials Vols. 444-445

Abstract: Pumps as turbines (PAT) is an attractive alternative for recovering the pressure-energy. Establishing an external characteristic correlation between pumps and turbines is essential in selecting the proper machine. In this study, a theoretical method was presented to predict the performance of PAT at best efficiency point based on pump’s characteristics (geometric and hydraulic). In order to verify the theoretical results, the pumps with specific speed 55, 86,128,180,200 were simulated in direct and reverse modes by FLUENT12.0. Using theoretical and numerical results, the characteristic correlation curves of pumps in direct and reverse modes were obtained. Deviations of theoretical results s in higher flow rate and head than pump mode, the best efficiency of PAT was 2%~6% lower than pump mode.

Abstract: The structure of cavity flow field with high mach number is very complex, in which pressure and velocity pulsate seriously, leading a seriously noise about almost 170dB. The noise poses a great threaten to the safety of the missile in the cavity and the structure of the cavity. The active control method (jet flow) by applying the CFD technology based on Scale-Adaptive Simulation (SAS) model developed from two-equation SST turbulent model is used to simulate the changing of the dynamic noise in the standard cavity M219(the ratio of the length to the depth is 5), and studied the flow character, flow field structure and noise mechanism. First, the accuracy of the noise prediction method is validated. Base on above-mentioned method, the suppression effect on the noise in the cavity of jet flow is analyzed and the conclusion is that jet flow has a great influence on the aerodynamic noise suppression in the cavity.

Abstract: In the work of medium-term inspection evaluation about master degree thesis in colleges and universities, its only grade but no superior difference. In response to this situation, this paper uses bounded closed interval numbers geometric mean sorting method make pros and cons sorting to be in the same professional degree thesis, which can break out the bound of grade and make the work of medium-term inspection of master degree thesis become more perfect, fair and justice.

Abstract: LASSO is a very useful variable selection method for high-dimensional data , But it does not possess oracle property [Fan and Li, 200 and group effect [Zou and Hastie, 200. In this paper, we firstly review four improved LASSO-type methods which satisfy oracle property and (or) group effect, and then give another two new ones called WFEN and WFAEN. The performance on both the simulation and real data sets shows that WFEN and WFAEN are competitive with other LASSO-type methods.

Abstract: In this paper, an equivalent representation for strictly-diagonally dominant matrices according to circuit is given by using the theory of diagonally dominant matrices. As its application, some criteria for nonsingular H-matrices are obtained.

Abstract: New integration schemes are presented for integrands with singularity of 1/r. We partition the element with a singular center into several triangles sharing the center. Then, a transformation between a standard square and each of the triangles is conducted. We prove such a transformation itself brings about the Jacobian with the factor r, leading to no need to introduce any other transformation. Both two-dimensional and three-dimensional cases are considered. Compared to the Duffy transformation, the proposed methods enjoy more excellent numerical properties. Numerical examples in elastic fracture are also presented to illustrate the performance of the new integration techniques.

Abstract: This paper studies the construction problems of five order nonnegative matrices from spectrum data. Let be a list of complex numbers with . Necessary and sufficient conditions for the existence of an entry-wise nonnegative 5×5 matrix with spectrum are presented.

Abstract: In this paper we present a special kind of real symmetric matrices: the real symmetric doubly arrow matrices. That is, matrices which look like two arrow matrices, forward and backward, with heads against each other at the station, . We study a kind of inverse eigenvalue problem and give a necessary and sufficient condition for the existence of such matrices.

Abstract: This paper presents a 3D numerical simulation of water droplets merging under a given shock wave. We couple interpolation method to RGFM (Real Ghost Fluid Method) to improve the numerical accuracy of RGFM. The flow states of air-water interface are calculated by ARPS (approximate Riemann problem solver). Flow field is solved by Euler equation with fifth-order WENO spatial discretization and fourth-order R-K (Runge-Kutta) time discretization. We also employ fifth-order HJ-WENO to discretize level set equation to keep track of gas-liquid interface. Numerical results demonstrate that droplets shape has little change before merging and the merged droplet gradually becomes umbrella-shaped under the given shock wave. We verify that combination of RGFM with interpolation method has the property of reducing numerical error by comparing to the results without employment of interpolation method.

Abstract: To preserve the symplecticity property, it is natural to require numerical integration of Hamiltonian systems to be symplectic. As a famous numerical integration, it is known that the 2-stage RadauIA method is not symplectic. With the help of symplectic conditions of Runge-Kutta method and partitioned Runge-Kutta method, a symplectic partitioned Runge-Kutta method and a symplectic Runge-Kutta method are constructed on the basis of 2-stage RadauIA method in this paper.