Some fundamental concepts and problems in the research field of the structural topology optimization are introduced briefly. The essential characteristics of the truss-like and its discretization are analyzed. The classical analytical solutions as the benchmarks are listed in the references. The optimization strategies and the characteristics of various numerical methods for the structural topology optimization are reviewed. The numerical instabilities, such as the mesh-dependencies, the singular optima, the checkerboards and the local constraints, commonly in the structural topology optimization, are explained. The fundamental principles of the optimality criteria, the sequential programming and the heuristic methods are discussed.
The light-weighted sandwich structures are widely used in the field of energy absorption. The dynamic response of the spherical sandwich structure under inner blast loading is analyzed by means of numerical simulation. It is found that the inner wall of the spherical sandwich structure plays a key role in energy dissipation, which is different to that of the flat or curved sandwich plate. Compared with homogeneous spherical shell of the same mass, the core of spherical sandwich structure can effectively reduce the deformation and stress level of the outer wall. In addition, the influence of geometric size on energy absorption of spherical sandwich structure is obtained by theoretical analysis. Finally, it is pointed out that in the design of the explosive vessel, if the energy consumption of the inner wall of the spherical sandwich structure is fully utilized, the anti-explosive equivalent can be remarkably improved.
In this study, the dynamical characteristics of two-dimensional Janus particles in infinite electrolyte solution in the presence of an external electric field are considered. The equations for the electroosmotic flow in the electrolyte solution are established and decoupled on the basis of the order analysis. By introducing the finite computational domain to ensure the existence of the solution, the analytic solution of the electric field and the semi-analytical solution of the flow field around the circular particles are obtained. The relationship between the moments of the particle and the direction of the external electric field is obtained. The equilibrium attitude and the stability characteristics of the two-dimensional Janus particles are thus obtained.
In this paper, the inner flow of perforated liner ducts is studied numerically by the computational fluid dynamics method. The fractional resistance characteristics of the ducts are analyzed. In the simulation,it is assumed that the air flow will not go into or out of the sound absorbing material through the pinholes. It is found that the combination of the realizable k--" model with an enhanced wall function can be used for the simulation of this kind of duct flows, and the pressure drop deviation between the numerical simulation and the experimental measurement is less than 10%. In the flow resistance calculation for perforated liner ducts in the engineering design, the concept of equivalent roughness is proposed, which can be calculated by the Colebrook equation and the Darcy--Weisbach Formula based on the pressure drop data obtained by numerical simulations.The in fluence of the size of the pinholes and the perforation rate of the perforated plates on the equivalent roughness is examined. It is found that the equivalent roughness is proportional to the square of the perforation rate, and is linear to the size of the pinholes.
Based on the maximum principal stress criterion, the crack propagation of reinforced concrete three point bending beams are simulated with the XFEM (extended ˉnite element method). The accuracy and the effectiveness of the proposed method are veriˉed by comparing with the results of the existing model test. It is shown that the crack growth and the mechanical properties of the reinforced concrete members with cracks are not only affected by the size, the position, the inclination angle of the single crack, but also affected by the location of the cracks. The transverse and longitudinal distributions of cracks are the main factor that affects the crack growth path and the mechanical properties of the reinforced concrete beams with cracks.
The coiled tubing (CT) drilling technology is extensively employed in various operations of oil wells.The residual deformation of the CT caused by the winding on the reel has a magnificent effect on its extension length in horizontal wells. The friction curve fitting functions for various ratios of the diameter of the pipe to that of the tube and the residual deformation curve are obtained through similar experiments. The similarity of the model experiment and the actual coiled tubing operation is analyzed and the similarity constants are obtained, and then the friction between the coiled tubing and the casing wall is calculated. The final results show that the friction of a 2-inch CT with a residual deformation in the horizontal well is about 2.3 times of that of the CT without the residual deformation.
With the wide use of I-section short, deep beams and wide flange beams, the section nonlinear effect of shear deformation on the bending normal stress becomes an important issue, because enormous calculation errors will occur by using the traditional beam theory in the design. With the bar simulation method, formulas are derived in this paper for the calculation of the bending normal stress with consideration of the shear effect and results are compared with those obtained by various analytical methods and the finite element numerical simulation results. The results indicate that when § is small or ø is large, the bending deflection is affected greatly by the transverse shear. Besides, compared with the existing analytical methods, the proposed method offers more accurate results with an extended scope of application, which can be used for the structural design.
This paper proposes a discrete gradient method for the stress analysis for biological systems. A point-cloud is taken as the geometric input instead of the conventional CAD model. Before applying the discrete gradient method on the point-cloud model, the neighboring relationship is defined among points as well as the volume occupied by each point. The gradient interpolation vectors, which can approximate the gradient of a function, are defined for each point in the form of the generalized finite difference. The pointwise strain is calculated by using the discrete differentials involving the nodal displacements of a set of neighboring points. A mechanical solver using the discrete gradient method for finite strain elasticity is developed in weak form. It can be shown that this solver retains the similar accuracy and convergence rate of bilinear quadrilateral finite elements, with a locking-free behavior, and is more tolerant to the mesh distortion. An e±cient method is developed to extract the point-cloud model from medical images. Since a material constituent comprises pixels within a certain range of gray-scale values, the pixels within given thresholds are isolated and an initial point-cloud is formed. The physical coordinates are inferred from the image resolution. The Delaunay tessellation and the barycentric subdivision are utilized to provide the neighboring relation and the point volume. A static analysis of the abdominal aortic aneurysm inflation is carried out to demonstrate the usefulness of the method. Despite the use of the tessellation, the method is not element-based because the element-wise assumed solution is never constructed. A distinct feature of this method is that the entire process is completed with a minimal user interference or even fully automatically. This is significant for applications where a timely analysis is desired.
The change of the nasal structure can cause a change of the nasal aerodynamics, then cause a self-adaptation change of the inferior turbinate. A number of patients with nasal septum deviation are chosen to do the diorthosis, some of them with the movement of inferior turbinate bone. CT scanning is carried out for all patients both before and after the surgery, then a three-dimensional reconstruction is done for the nasal airway according to the CT data, to analyze the characteristics of the nasal aerodynamics with the method of the computational fluid dynamics. It is shown that the purpose of the corrective procedure for the nasal structure is not for the bilateral nasal symmetry of the volume,but with the nasal structure as an integral whole, to protect the nasal `green belt', in order to remodel the nasal cavity, and to recover the nasal physiologic function.