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In the present study, a topology optimization method of thermal-fluid-structural problems is researched to design the three-dimensional heat sink with load-carrying capability. The optimization is formulated as a mean temperature minimization problem controlled by Navier-Stokes (N-S) equations as well as energy balance and linear elasticity equations. In order to prevent an unrealistic and low load-carrying design, the power dissipation of the fluid device and the normal displacement on the load-carrying surface are taken as constraints. A parallel solver of multi-physics topology optimization problems is built-in Open Field Operation And Manipulation (OpenFOAM) software. The continuous adjoint method is adopted for the sensitivity analysis to make the best use of built-in solvers. With the developed tool, the three-dimensional (3D) thermal-fluid topology optimization is studied. It is found that the Darcy number, which is suitable for fluid design, may cause severe problems in thermal-fluid optimization. The structural features of 3D thermal-fluid-structural problems are also investigated. The “2D extruded designs” are helpful to improve the structural stiffness, and channels with a larger aspect ratio in high-temperature areas improve the cooling performance.

A topology optimization approach is developed to design the conformal cooling system for injection molding in this paper. During the design process, the cycle-averaged approach is used to simplify the analysis of the cooling process, and the boundary element method (BEM) is adopted to solve the governing equations and calculate the sensitivities. The optimization starts from the complicated network of channels, and the radius of each channel section and the location of each node are selected as the design variables. The topology of the cooling system can be modified by deleting excessively thin channel sections. We pick out two representative example models with areas that are hard to cool to test the effectiveness of the proposed optimization approach. The results show that our method can improve both efficiency and uniformity of the cooling process.

The liquid-cooled heat sink is an effective and robust cooling device and has been widely used in the industry. The fluid-thermal topology optimization approaches have been adopted for the heat sink design by many researchers. However, none of these works considered the optimization of heat source distribution. This work focuses on the synergic design of the cooling channels and the layout of heat sources with diverse intensities. A hybrid topology optimization approach is adopted, in which the channels are implicitly described with pseudo-density while the heat sources are considered as moving components. The maximum temperature of the system is taken as the objective and constrained by the fluid power dissipation. In order to avoid unrealistic designs such as suspended structures, the stiffness of the structure is considered as a constraint. Considering when heat sources have diverse intensities, the initial locations of the heat sources could significantly affect the optimal result. Aiming at this problem, a heuristic algorithm that can redistribute the heat sources efficiently during the optimization process by exchanging their locations is developed. The topology optimization is performed with a parallel solver developed in Open Field Operation And Manipulation (OpenFOAM) framework. The numerical tests show that the influence of the heat source distribution on the cooling performance could be even higher than the cooling channel design, and the synergic topology optimization method is an effective way to design high-performance heat sink.

This paper proposes an integrated two-step strategy for an optimal design of liquid-cooled channel layout based on the moving morphable component (MMC)-density approach. The proposed strategy intends to take the advantage of both the MMC approach for its high flexibility in searching a physically reasonable layout and the density approach for its better capacity of topology description. On the basis of the above-mentioned strategy, an intermediate layout is obtained through MMC approach and further optimized as initial solution of density approach step. Through density approach step, the final layout shows smoother boundary while retaining reasonable feature size. The original contributions of this paper are as follows: (i) An assembled quadratic Bézier curves component is proposed to describe the largely curved channel with limited numbers of optimization variables and computation order. (ii) Benefited from explicit geometric description, adaptive mesh refinement (AMR) is applied in MMC approach step for the first time. The application of AMR, from the numerical point of view, has two key ingredients to be highlighted: (i) the accuracy of solution in fluid–solid boundary region can be ensured with relatively limited computational cost. (ii) The contradiction that the difference step of MMC updating needs to be both as small as possible and integer multiple of the mesh size can be avoided. The performance of our methodology is demonstrated by numerical examples aiming for maximal heat exchange with power dissipation constraint. The main finding reveals that the proposed strategy can offer reasonable channel layout with better thermal performance, compared with conventional density approach. The whole numerical implementation relies on OpenFOAM and PETSc open-source software packages.

Microinjection-molded products with microfeatures are widely used in the biomedical field, microlens, etc. In this paper, a microinjection mold with venting design is fabricated for producing a polylactic acid (PLA) micropillar array product. The effect of injection velocity on the filling fraction is investigated. Results show that the farthest microcavity in the array to the sprue is readily filled with PLA melts at the given injection velocity conditions, while the nearest microcavity is the worst one in term of filling fraction, although increasing injection velocity can efficiently improve the entire filling fraction. By seriously analyzing the temperature and pressure from a simulation point of view, it reveals that the special geometrical structure of the product provides the condition which causes all the significant and interesting filling phenomena to appear in the experiment and simulation. This mechanism is beneficial to understand the filling behaviors of microfeatures and helps us to improve the replication of the product.

Binding affinity prediction of protein–ligand complexes has attracted widespread interest. In this study, a self-adaptive steered molecular dynamics (SMD) method is proposed to reveal the binding affinity of protein–ligand complexes. The SMD method is executed through adjusting pulling direction to find an optimum trajectory of ligand dissociation, which is realized by minimizing the stretching force automatically. The SMD method is then used to simulate the dissociations of 19 common protein–ligand complexes which are derived from two homology families, and the binding free energy values are gained through experimental techniques. Results show that the proposed SMD method follows a different dissociation pathway with lower a rupture force and energy barrier when compared with the conventional SMD method, and further analysis indicates the rupture forces of the complexes in the same protein family correlate well with their binding free energy, which reveals the possibility of using the proposed SMD method to identify the active ligand.

Background Although stents have great success of treating cardiovascular disease, it actually undermined by the in-stent restenosis and their long-term fatigue failure. The geometry of stent affects its service performance and ultimately affects its fatigue life. Besides, improper length of balloon leads to transient mechanical injury to the vessel wall and in-stent restenosis. Conventional optimization method of stent and its dilatation balloon by comparing several designs and choosing the best one as the optimal design cannot find the global optimal design in the design space. In this study, an adaptive optimization method based on Kriging surrogate model was proposed to optimize the structure of stent and the length of stent dilatation balloon so as to prolong stent service life and improve the performance of stent. Methods A finite element simulation based optimization method combing with Kriging surrogate model is proposed to optimize geometries of stent and length of stent dilatation balloon step by step. Kriging surrogate model coupled with design of experiment method is employed to construct the approximate functional relationship between optimization objectives and design variables. Modified rectangular grid is used to select initial training samples in the design space. Expected improvement function is used to balance the local and global searches to find the global optimal result. Finite element method is adopted to simulate the free expansion of balloon-expandable stent and the expansion of stent in stenotic artery. The well-known Goodman diagram was used for the fatigue life prediction of stent, while dogboning effect was used for stent expansion performance measurement. As the real design cases, diamond-shaped stent and sv-shaped stent were studied to demonstrate how the proposed method can be harnessed to design and refine stent fatigue life and expansion performance computationally. Results The fatigue life and expansion performance of both the diamond-shaped stent and sv-shaped stent are designed and refined, respectively. (a) diamond-shaped stent: The shortest distance from the data points to the failure line in the Goodman diagram was increased by 22.39%, which indicated a safer service performance of the optimal stent. The dogboning effect was almost completely eliminated, which implies more uniform expansion of stent along its length. Simultaneously, radial elastic recoil (RR) at the proximal and distal ends was reduced by 40.98 and 35% respectively and foreshortening (FS) was also decreased by 1.75%. (b) sv-shaped stent: The shortest distance from the data point to the failure line in the Goodman diagram was increased by 15.91%. The dogboning effect was also completely eliminated, RR at the proximal and distal ends was reduced by 82.70 and 97.13%, respectively, and the FS was decreased by 16.81%. Numerical results showed that the fatigue life of both stents was refined and the comprehensive expansion performance of them was improved. Conclusions This article presents an adaptive optimization method based on the Kriging surrogate model to optimize the structure of stents and the length of their dilatation balloon to prolong stents fatigue life and decreases the dogboning effect of stents during expansion process. Numerical results show that the adaptive optimization method based on Kriging surrogate model can effectively optimize the design of stents and the dilatation balloon. Further investigations containing more design goals and more effective multidisciplinary design optimization method are warranted.

Many injected engineering polymer structures have to suffer the external load conditions (thermal load, impact load, etc.). In this case, service-induced stress concerns safety of human and the plastic engineering structure. In this study, geometrical design factors are connected with the engineering service stress of the polycarbonate (PC) window which is in thermal and pressure load conditions for the first time. The mold is constructed by an injecting gate with six design parameters and a type of spherical spiral conformal cooling system. The thickness of the product cavity is characterized by a linear function. Molding defects (warpage and residual stress) are taken into consideration sufficiently. In order to reduce the service stress, kriging surrogate model is employed to interpolate the implicit service stress function with respect to 14 geometrical design parameters, expected improvement function optimization method is used to search the optimum result, and log-exponential smoothing function method is used to simplify the multi-constraints. The comparison shows that the service stress is affected by the mold construction greatly, and the optimized mold and product design scheme are preferred to improve the service quality of the PC window.

Background In stent design optimization, the functional relationship between design parameters and design goals is nonlinear, complex, and implicit and the multi-objective design of stents involves a number of potentially conflicting performance criteria. Therefore it is hard and time-consuming to find the optimal design of stent either by experiment or clinic test. Fortunately, computational methods have been developed to the point whereby optimization and simulation tools can be used to systematically design devices in a realistic time-scale. The aim of the present study is to propose an adaptive optimization method of stent design to improve its expansion performance. Methods Multi-objective optimization method based on Kriging surrogate model was proposed to decrease the dogboning effect and the radial elastic recoil of stents to improve stent expansion properties and thus reduce the risk of vascular in-stent restenosis injury. Integrating design of experiment methods and Kriging surrogate model were employed to construct the relationship between measures of stent dilation performance and geometric design parameters. Expected improvement, an infilling sampling criterion, was employed to balance local and global search with the aim of finding the global optimal design. A typical diamond-shaped coronary stent-balloon system was taken as an example to test the effectiveness of the optimization method. Finite element method was used to analyze the stent expansion of each design. Results 27 iterations were needed to obtain the optimal solution. The absolute values of the dogboning ratio at 32 and 42 ms were reduced by 94.21 and 89.43%, respectively. The dogboning effect was almost eliminated after optimization. The average of elastic recoil was reduced by 15.17%. Conclusion This article presents FEM based multi-objective optimization method combining with the Kriging surrogate model to decrease both the dogboning effect and radial elastic recoil of stents. The numerical results prove that the proposed optimization method effectively decreased both the dogboning effect and radial elastic recoil of stent. Further investigations containing more design goals and more effective multidisciplinary design optimization method are warranted.

This textbook includes eight chapters, and covers introduction, kinematic analysis of plane member systems, analysis of statically determinate structures,principle of virtual work and deflection calculation, force method, displacement method, influence lines of structures under moving loads, and matrix displacement method.