No abstract

Recently, isogeometric analysis (IGA), which unifies the computer-aided design (CAD) model and the computer-aided engineering (CAE) model, has been adopted to develop the isogeometric topology optimization (ITO) framework. However, a critical study on the indispensability of IGA in topology optimization to take the place of the conventional finite element method (FEM) is still lacking. In the current work, two important problems are extensively discussed: (1) The lower numerical precision of the FEM resulting from the disunification between the CAD and CAE models damages the effectiveness of the topology optimization, which suggests the indispensability of IGA in the replacement of the FEM in optimization; (2) a material penalization model is required to ensure the generation of a full loading-transmission path during optimization in classic density-based methods, which causes a greater overestimation of structural stiffness and also suggests the necessity of an ersatz material model. The current paper describes a promising ITO method with point-wise design to gain smooth or binary symmetrical topologies, for which an extended density distribution function (DDF) was constructed to describe the structural topology. Two benchmarks of the stiffness-maximization problem and compliant mechanism are studied in the context of the above issues. Finally, several topologically optimized designs with symmetry are obtained using the ITO method.

This work explored the fluid–structure interaction (FSI) effect of crude oil and pipeline and the vibration characteristics of the pipe–crude oil structural system. A finite element computational analysis theory and corresponding simulation method were proposed for crude oil pipelines considering the FSI effect. Meanwhile, the spring model of the FSI interface between crude oil and pipeline was proposed. The experimental simulation and neural network were adopted to obtain the flow-excited pulsation pressure (FEPP), and the kinetic equations of the pipe–crude oil FSI were analyzed. The finite element computation (FEC) model for pipe–crude oil bi-directional FSI dynamics was established, which was composed of five support span lengths and four pipe liquid levels and can provide five different crude oil fluid velocities. One hundred orthogonal simulation test conditions were designed. In addition, the displacement response and acceleration response under FSI of the pipe wall were calculated, and the first six orders of inherent frequencies and main vibration patterns of the FEC model were analyzed. The results revealed that the dynamic effect of FSI between the crude oil transport medium and pipeline was complex and was influenced by the length of the pipeline crossing section, medium flow velocity, difference of liquid surface height, and displacement response. The acceleration response possessed prominent vibration decay characteristics, and the response peak in the same condition was about 8.2 times larger than that of the steady-flow state response. Therefore, the effect changed the inherent frequency and vibration pattern of the pipeline, to which the engineering design should pay sufficient attention.