Applied Mechanics and Materials Vols. 170-173

Abstract: A robust reduced-order H∞ controller for the linear structures is investigated. This controller is with disturbance decoupling. First, a necessary and sufficient condition for the H∞ state feedback control problem is established. Second, based on the parametric design approach for generalized Sylvester matrix equations, we obtain a reduced-order H∞ controller for linear structures. Finally, numerical example is given to illustrate the validity of the results.

Abstract: A numerical case study is presented in this paper to demonstrate the feasibility of a finite element method with artificial boundary condition to simulate the wave in 3D ground soil. An unit centralized harmonic excitation at surface is adopted with four frequencies. The calculated vibration amplitudes are compared with the corresponding results by dynamic Green Function in frequency-wave number domain. The result shows a clear calculation error phenomena that the smaller mesh adopted, the smaller error is for a given frequency, and the lower frequency excited so the smaller error is for a given mesh size. A preliminary suggestion is presented as that the maximum mesh size of a 3D discrete grid must be no larger than 1/25 of the minimum wave length.

Abstract: Aiming at problem about real-time processing power is poorer as the cause of too many clutter plots in multisource information fusion conditions when traditional information algorithm is used, method of sensor clutter elimination based on statistical characteristics analysis is put forward. Firstly, statistical characteristics of clutter plots are extracted, calculated and analyzed. Secondly, in combination with the advantages of multi-sensor detection, the plots of real-target have been filtered according to certain threshold values and safeguarded. Finally, a specific simulation experiment is given. Experiment shows this method can achieve the real-time processing power effectively.

Abstract: To discuss the flow field of explosion in a hermitic cavity which is charged in center and the dynamic response of the shell structure, a FEA method is used. The overpressure-time curves of the gauges in the structure or on the wall and the deformation of the wall is shown in this paper, and some valuable conclusion is obtained.

Abstract: Engineering rock mass is a highly complex grey system, it is impossible to get all the parameters of rock mass by theoretical methods or field measurement approach. Underground engineering feedback analysis method is a reliable way to improve the design, optimization and construction. Based on the field data of underground cavern of a large-scale hydro-power station, the three-dimensional finite element model is established, and orthogonal experimental design and multi-objective optimization method are used for the rapid back analysis. This method could be used for obtaining the rock parameters by inversion calculating in the underground cavern construction of a large-scale hydro-power station. Meanwhile, the inversion parameters could also be applied in the excavation simulation for the next phase and the rock deformation and stability is predicted afterwards. The design and construction sectors are supposed to get its feedback in time, which effectively guarantees the stability of the surrounding rocks.

Abstract: Series of biaxial compression simulations are carried out to investigate the effects of boundary condition on the deformation of granular materials by using DEM. The parameters used in DEM are validated by the biaxial compression experiments on elliptical steel bars. The effects of boundary condition on the stress-strain relationship are analyzed. And special focus are put in the analysis of particle displacement, particle rotation, void distribution, particle long axis orientation and contact force with the development of deformation.

Abstract: We have investigated the optical properties of the Fm-3m-Mg2Si using the first-principles plane-wave pseudo-potential method. Some important optical parameters (reflectivity, refractive index, extinction coefficient, loss function and dielectric function) are calculated and investigated at high pressure. The calculated static dielectric constant ε(0) is 15.9. The computed plasma frequency is 12eV. Some interesting features in the optical parameters are found in the low frequency region. Nevertheless, the calculated result needs to be testified by experiments in the near future.

Abstract: The geometric shape of buildings in wind field is an important influencing factor of wind pressure distribution on the buildings. Along with the change of roof shape, wind pressure distributions vary obviously. In this paper, the numerical simulation of the wind pressure for four types of large-span roofs is carried out, using CFX12.0 as computing platform. The characteristics of wind pressure distribution are studied by considering some parameters, such as wind direction, rise-span ratio, and terrain roughness. Wind pressure distribution is greatly affected by wind direction, and the wind pressure on large-span roofs is dominated by suction; the vortex shedding produced by airflow separation is the main factor affecting the characteristics of wind load.

Abstract: The cohesive crack model and the crack band model are two convenient approaches in concrete fracture analysis. They can describe in full the fracture process by the different manner: The entire fracture process zone is lumped into the crack line and is characterized in the form of a stress-displacement law which exhibits softening; or the inelastic deformations in the fracture process zone are smeared over a band of a certain width, imagined to exist in front of the main crack. The correlation of the two models is developed based on a characteristic width of crack band. The analysis shows that they can yield about the same results if the crack opening displacement in the cohesive crack model is taken as the fracturing strain that is accumulated over the width of the crack band model. Some basic problems are also discussed in finite element analysis.

Abstract: we study the parameter identification of a class of non-autonomous chaotic system in this paper. Based on the stability theory, we implement accurate identification by suitable adaptive law are given to identify any uncertain parameters of a class of nonautonmous chaotic systems. Theory analysis and numerical simulations of Dufffing chaotic system is presented to verify that the adaptive control to identify the parameters are effective and feasible.