Papers by Author: Zhen Yue Ma

Abstract: A cohesive model (CM) was introduced in this paper. The constitutive response of cohesive behavior depends on a traction-separation description characterized by the initial stiffness, damage initiation threshold, and damage evolution properties.Through the aseismic analysis of a gravity dam, the displacement, stress and anti-sliding safety factor were discussed in the paper, the results were also compared between elastic model (EM) and plastic model (PM). The results shown that the displacement amplitude computed by PM and CM was nearly twice larger than that by EM, and the area of stress concentration became not so obvious. The cohesive model could efficiently simulate the discontinuous structure and the responses of seismic computed by PM and CM were more correspond to actual situation.

Abstract: The axial symmetric model has been widely used in the research and design of spiral case structure in hydraulic power station due to its convenience, however, instead of a continuous entity, the fixed guide vanes are discretely distributed around the vertical axis of the unit, and there are some different opinions on the simulation techniques for the fixed guide vane in the existing research. Commonly used processing methods for fixed guide vanes in the spiral case axial symmetry model are summarized and two new simulation techniques on the basis of existing research are proposed. Static analyses for a practical spiral case with cushion layer are conducted using 4 axial symmetry models and a 3-D FEM model. The influences of simulation techniques for fixed guide vanes on the stress and their distribution of steel liner, concrete and fixed guide vanes are investigated. The rationality and applicability of each simulation technique for fixed guide vanes are discussed.

Abstract: Basing on the theory of power flow, frequency response analysis was acted on in a hydropower house under dominant frequency with measured data of Three Gorges Station in spiral case and draft tube. Power flow in walls was calculated by APDL procedure and the properties were analyzed. The conclusion is that longitudinal wave is the main method in walls of the powerhouse, energy is reflected and stacked at the top of the walls. Displacement along the river changes and power flow in walls decays obviously. Intensity of vibration origin and distance between the vibration and the wall are both the influencing factors，increasing the stiffness of buttressed walls takes the role of limiting flexural wave and shear wave effect

Abstract: As the capacity and water head of large hydropower projects become higher and higher, the flow-induced structural vibration of powerhouse becomes a very important problem for the design and operation process. Especially as the water head and the running speed are much higher for the pump-turbine than the general turbine, the hydraulic exciting vibration is very remarkable. In this paper the simulation results of free-vibration characteristics of powerhouse structure for different types were concluded and the frequency behavior of the pressure fluctuation in spiral case and draft tube were discussed. The structural dynamic responses under hydraulic exciting were presented including the dynamic responses of displacement, velocity, acceleration and stresses. Based on the vibration criterion of the powerhouse structure, the vibration evaluation was made.

Abstract: The transient temperature field and thermal creep surrounding concrete are analyzed with a three-dimensional FEM model that simulates the construction process of spiral case, based on program development of ABAQUS. The effect of hydration and cooling pipes on temperature is studied. The comparison of temperature difference in schemes is performed, and then the reasonable construction scheme has been defined. The distribution of thermal creep stress with construction is given. It is concluded that the control measures is effective to temperature crack prevention.

Abstract: Based on applying nonlinear simulation with 3D FEM and elastic and plastic damage model of concrete, considering contact property between steel spiral case and peripheral reinforced concrete, calculating the stress levels of reinforced concrete and steel liner computed between directly-embedded spiral case (scheme I) and keeping constant internal pressure spiral case (scheme II), as well as examining the reinforced concrete crack and damage produced by water pressure, the result clearly indicated that scheme II was more excellent than scheme I in high head hydropower station on having the best performance of steel, limiting crack of the concrete, reducing the damage region and decreasing damage index of the concrete.

Abstract: This paper presents a new method to simultaneously search for the minimum reliability index and the critical probabilistic slip surface of earth slopes. By introducing the Hasofer-Lind reliability index, the probabilistic slope stability analysis problem is modeled as a constrained optimization problem. A recently proposed intelligent global optimization algorithm differential evolution with a penalty function is adopted to solve the constrained optimization problem. Numerical results on two slopes show that the propose technique is efficient and practical to reliability analysis of earth slopes.