Papers by Author: Hong Li

Abstract: The technology of flywheel energy storage is already widely used in motorcar, electric power systems, spaceflight and martial fields. Decreasing the weight, increasing rotating speed and strength of the flywheel rotor and improving the energy storage efficiency of the flywheel are always attention-getting. In this paper, the flywheel energy storage wrapped with composite material by interference fit to hub is designed and finite element analysis is done to obtain the stress distribution of it before being produced. The maximum and variety of stress are studied and the influence of composite material wrapped on flywheel rotating at a high speed is discussed. Then the action of composite material preload to the flywheel is thought about. The results of this analysis can prepare a valuable guide for flywheel energy storage at design and manufacture stage.

Abstract: The technology of flywheel energy storage is already widely used in motorcar, electric power systems, spaceflight and martial fields. Decreasing the weight, increasing rotating speed and strength of the flywheel rotor and improving the energy storage efficiency of the flywheel are always attention-getting. In this paper, a flywheel energy storage is designed and finite element analysis is done to obtain the stress distribution of it before being produced. The maximum and variety of radial stress and circumferential stress are studied and the influence of composite material wrapped on flywheel rotating at high speed is discussed. Then the action of composite material to stress concentration around the small hole on the hub is thought about. The results of this analysis can prepare a valuable guide for flywheel energy storage at design and manufacture stage.

Abstract: Residual stresses and residual plastic strains of the welded structures are the products of nonlinear behaviors during welding. The residual stresses will cause errors during the assembly of the structure and injure the beauty of appearance of the structure. Based on an elastic-plastic-model, finite element numerical simulation of a representative tube sheet penetration assembly with loop welding line joined by multi-pass welding is carried out and the influence of welding conditions on residual stresses of the tube sheet welds is studied in this paper. Nonlinear three dimensional transient temperature fields and real-time dynamic stresses field are analyzed by FEM. The heat source is modeled as a moving heat flux following a double ellipsoid distribution and the temperature-dependent properties of materials are considered. The method of birth and death of element in finite element analysis is applied to simulate the gradual growth of weld pass metal. It is shown that welding sequence, size of groove welding and weld toes dressing will obviously change the magnitude of the residual stresses of tube sheet welds.

Abstract: Residual plastic strains of the shipboard are the product of nonlinear behaviors during welding. Deformations of a welded shipboard injure the beauty of appearance of the ship, cause errors during the assembly of the shipboard and reduce the strength of the ship. Residual welding deformations of shipboard of a container vessel are studied in this paper. Nonlinear three dimensional transient temperature fields are analyzed by FEM first. The heat source is modeled as a moving heat flux following a Gaussian distribution. Then, applying the equivalent loads induced by the inherent strain on the shipboard, the final in-plane shrinkage and out-of-plane deformations are calculated. Being compared with the experimental results of deformations, the simulated results show mostly conformity.

Abstract: A solving method with complex variable function which is fit for numerical calculation for stress concentration phenomena on an infinite plate where there are curvilinear holes is described in this paper. According to the method, the computer programs are made to study the stress concentration problems with curvilinear holes (hexagonal form and oblate form) that are often used in ship and other engineering structures. The maximum of the stresses at the edge of the holes and the distribution of the stresses under axial loading and pure bending moment are calculated respectively. Furthermore, the variations of factors of stress concentration with the different proportions of length and width for oblate holes are considered. The influence on factors of stress concentration due to the change of plate width is indicated. The solutions are consistent with the numerical results of boundary element method, finite element method and related articles.

Abstract: Due to high centralized instantaneous heat input in the process of the welding, a great deal of residual stresses and distortions should be brought in the welded structures, which can heavily influence the capability and reliability of the structure. Residual stresses and welding fatigue behaviors of stainless steel penetration assembly joined by multi-pass welding are studied in this paper. The distribution of transient temperature field and real-time dynamic stresses field in the welded region must be calculated first. Based on the residual stresses, the random wave load putting on the structure and fatigue factors, according to Miner fatigue damage law, some fatigue behaviors such as fatigue life and remaining life are obtained.

Abstract: Welding residual plastic strains and stresses cause errors during the assembly and reduce the strength of the structure. Based on an elastic-plastic-model, a three-dimensional finite element numerical simulation of multi-pass butt welding of a representative penetration assembly is carried out in this paper. The nonlinear transient temperature field and the real-time dynamic stresses field during multi-pass butt welding with girth welds are obtained. In the end, the residual stresses of the complicated stainless steel penetration structure are calculated by FEM software ANSYS.

Abstract: Welding residual plastic strains and residual stresses are the product of complicated nonlinear behaviors of the structures during welding. The residual strains and stresses for stiffened stainless steel structure and welding fatigue analysis are studied in this paper. The three-dimensional transient temperature field is analyzed by FEM first. Doing the welding experiment for fundamental model is to verify the numerical results, the infrared thermograph is used to follow and record the whole process. The results of FEM are supported by experimental data. Then, the elastic-plastic-model is established to analyze the residual strains and stresses. Based on the stresses, loading and fatigue factors, according to Miner fatigue damage law, some fatigue behaviors such as fatigue life and remaining life are obtained.

Abstract: In this study, the effect of combined environmental factors such as ultraviolet ray, high temperature and high moisture on mechanical and thermal analysis properties of glass fabric and phenolic composites are evaluated through a 2.5KW accelerated environmental aging tester. The environmental factors such as temperature, moisture and ultraviolet ray applied of specimens. A xenon-arc lamp is utilized for ultraviolet light and exposure time of up to 3000 hours are applied. Several types of specimens - tensile, bending, and shear specimens that are warp direction and fill direction are used to investigate the effects of environmental factors on mechanical properties of the composites. Mechanical degradations for tensile, bending and shear properties are evaluated through a Universal Testing Machine (UTM). Also, storage shear modulus, loss shear modulus and tan δ are measured as a function of exposure time through a Dynamic Mechanical Analyzer (DMA). From the experimental results, changes in material properties of glass fabric and phenolic composites are shown to be slightly degraded due to combined environmental effects.