This paper discusses some problems of nonlinear porous flows in low permeability porous media, the properties of the porous flow fluid, and the selectivity of fluids in passing through porous media. Based on these characters, a new porous flow model, which can better describe low permeability reservoirs, is established. This model can describe various patterns of porous flows, as Darcy's linear law. All parameters involved in the model, with definite physical meanings, can be obtained directly from experiments.
The strength is among the most important characteristics of a structural material. How to reasonably estimate the ultimate load carrying capacity of a fiber reinforced composite still remains a world-wide great challenge. Through years of studies by this author and his collaborators, the prediction of the ultimate strength of a laminated composite subjected to an arbitrary load based only on its constituent properties measured independently is no longer an unachievable goal. How to approach to this goal is briefly described in this paper. It is highly possible in a near future that, when a material database for all necessary properties of the candidate constituent fiber and matrix materials is established, the design and the development of any composite structure will not solely depend on experiments or can even be accomplished without any experiment on the composite itself. This will not only save a great amount of money for experiments, but also significantly shorten the development period of a new composite product, and promote more effective and wide usage of composite structures.
In this paper, a generalized actuator disk method combined with a three-dimensional Navier-Stokes equation solver is used to obtain the flow fields about wind turbines, in which the body forces are used in place of the blades of the wind turbine. The numerous meshes and the huge computational resource can be avoided in resolving the blade boundary layers, and more meshes and computational resources can be used to simulate the wind turbine wake flow field. Therefore, the generalized actuator disk method is suitable for the study of the wind turbine wake. Computational results for the wind turbine NH1500 obtained by the generalized actuator disk method and the common CFD (computational fluid dynamics) method are compared in the load distribution on the blade, validating the effectiveness and efficiency of the generalized actuator disk method. The generalized actuator disk method is then performed for two wind turbines in tandem to investigate the interaction of the wake created by the front wind turbine on the downstream wind turbine performance in various distances between the two wind turbines.
A vertical two dimensional coupling model of air-water-mud system is established to investigate the response of mud-water interface to surface waves, in which the mud is considered as a Newtonian fluid with high viscosity and turbulence is modeled by means of the SST (shear-stress transport). The VOF(volume of fluid) method is adopted to capture free surface, as well as mud-water interface. Different computational cases are considered according to five amplitudes and four periods of the surface wave to delineate the dependence of mud layer motion on the nonlinearity and the dispersivity of surface waves. The numerical results suggest that the mud-water interface undulates with the same wave length and period as the surface wave, albeit with a phase lead, which seems independent of the surface wave height and period. The wave height of the mud-water interface is almost proportional to that of the surface wave, and tends to increase with the period.
The dissociation of gas hydrate in seabed produces a lot of gas. If the seabed is permeable, the gas will escape, which will lead to the damage of the seabed, and to the decrease of the density of sea water and to threaten the safety of the structures above. In this paper, the movement and the expansion behavior of gas in the water are studied, then the damage of the seabed due to the gas escape is analyzed. The effects of gas pressure and thickness of soil layer are investigated. The expansion angle of gas in the water is obtained. The characteristics of the hole size induced by the gas escape under various gas pressure and soil thickness are also obtained. These results can be used in further research and practice.
Coalbed methane (CBM) is a kind of efficient and clean unconventional gas resources, and its producing process is mainly drawing down the formation pressure by draining water. CBM is primarily adsorbed in the coal rather than the most conventional gases stored in the pore space. CBM is desorbed from the coal when the coal bed pressure is lower than the critical desorption pressure, and is produced out with water. So, the fluids in coalbed are gas and water in different distributions. This paper introduced a set of transient well test model on the basis of desorption characteristic of CBM, the permeability relationships depended on gas and water distributions and the size of desorption area. The flow state of gas and water was described very well by using the separated areas in the CBM producing process. The model was solved by using finite volume method(FVM), and its type curves were obtained. The effects of the desorption coefficient, the desorption composite radius, the saturation distribution of gas and water, etc on type curves are analyzed. The research results of this study are of great guiding significance to develop CBM economically.
On the basis of the theory of thin plate of small deflection and the constitutive equation of KelvinVoigt, the governing equation of the viscoelastic annular plate is established. The natural frequencies and modes are calculated, respectively, in consideration of the boundary of the clamped inner edge and the free outer edge by employing the method of separation of variables. The results are compared with those obtained by the finite element method. The effects of the core ratio and the inner-outer radius ratio on the natural frequencies and the damping coefficient are discussed. Conclusions are as follows: the natural frequencies increase at first, then decrease with the increase of the core ratio,however,the damping coefficient increases with the increase of the core ratio. The natural frequencies and the damping coefficient also increase with the increase of the inner-outer radius ratio.
To study the delamination process of a laminated shell, the 8-node isoparametric element formulation for laminated shells based on the Hamilton canonical equation in the Cylindrical Coordinates is derived firstly. Then the separating-combining model and the weak-interface model are used to simulate the delamination between layers. The solution for whole shells is obtained. For the perfect interface and delamination situation, the two models are analyzed and the energy release rate of the delaminated shell is obtained finally. The results of numerical examples show that the energy release rate of a circumferential delamination is larger than that of an axial delamination, and the laminated thickness affects greatly the two models.
Based on the classical theories of stability of trusses, a computational method of buckling analysis of trusses is developed by using the eigenvalue theory and the critical buckling load of trusses is obtained by using both Euler's critical load theory and the static solution of removing buckling members. From the analysis of theories and corresponding examples, the computational method for identifying the buckling modes and the critical loads of trusses through the combination of the buckling eigenvalue theory and the Euler's critical load theory is demonstrated.
The interpolation of the plastic modulus between the real and imaginary stresses is used to determine the actual nonlinear deformation of the clay. The bounding surface model is suitable for the simulation of small nonlinear deformation of the clay. An anisotropic bounding surface model is developed based on Wheeler's elastoplastic model (S-CLAY1) and the bounding surface theory. The anisotropy of the natural clay can be captured by the model. Several problems on the theory of bounding surface model are discussed. The paper provides some guidance to understand and master the theory of the bounding surface model and to develop a new bounding surface model.
In this paper, the experimental and theoretical studies are presented of the contact electrification due to the ball-plate oblique impact, in which the ball and the plate have same chemical properties. Experimental results show that the ball can be electrified after impacting with a plate of the same chemical property as the ball, while the polarity of charge depends on the ball's material property. The magnitude of charge is related to the inclination angle of plate. With the increase of the inclination angle, the magnitude of charge first increases and then decreases. When the inclination angle reaches 50 degree, the magnitude of charge reaches its maximum value, which is 6-8 times of the magnitude of charge due to the direct impact. By a dynamic analysis of the ball-plate oblique impact, it is shown that the charge carried by the ball is highly related to the friction area between the ball and the plate in collision.
The similarities and differences between the proper orthogonal decomposition (POD) and the mode superposition method (MSM) are studied not only in principles but also in applications. According to the principles of POD and MSM, comparative studies are made theoretically. The similarities and differences are illustrated in their respective applications, with two random fields of the fluctuating wind loads and the corresponding fluctuating wind-induced responses of a hyperboloidal cooling tower as examples, obtained from wind tunnel tests and the dynamic calculations in the time-domain. Both POD and MSM are methods used for the decomposition and reconstruction of a random field by linear superpositions of the spatial modes and corresponding time coordinates. However, their application fields are quite different: the POD is always used for the analysis of known load fields but the MSM is for the calculation of unknown response fields. Furthermore, the extraction methods of the spatial modes and the corresponding time coordinates for the POD and the MSM are different, as well as their mathematical and physical meanings and their contributions to the original random fields. The spatial modes of the POD and the MSM are both orthotropic, but while the time coordinates of the POD are orthotropic, those of the MSM are not. Consequently, the sum of the POD eigenvalues reflects the whole energy of the original random field, but it is not the case for the MSM due to the coupling between different modes.