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A topology-optimization-based design method for a flow-reversing chamber muffler is suggested to maximize the transmission loss value at a target frequency considering flow power dissipation. Rigid partitions for high noise reduction should be carefully placed inside the muffler to avoid extreme flow power dissipation due to a 180° change in flow direction from an inlet to an outlet. The optimal flow path for minimum flow power dissipation is well known to change depending on the Reynolds number, which is a function of the inlet flow velocity. To optimize the partition layout with an optimal flow path in an expansion chamber at a given Reynolds number, a flow-reversing chamber muffler design problem is formulated by topology optimization. The formulated topology optimization problem is implemented using the finite element method with a gradient-based optimization algorithm and is solved for various design conditions such as the target frequencies, rigid partition volumes, Reynolds numbers, non-design domain settings, and allowed amounts of flow power dissipation. The effectiveness of our suggested approach is verified by comparing the optimized partition layouts obtained by the suggested method and previous methods.

This study presents a structural analysis and optimization for the lightweight design of a buoyant rotor-type permanent magnet (BRPM) generator, which was first presented in Bang (2010), and compares its structural performance to that of a conventional generator with a spoke arm-type rotor and stator. The main benefit of a BRPM generator is that it can be constructed as a bearingless drive system, free from the mechanical failure of rotor bearings, by using a buoyant rotor. Additionally, the deformation of the generator by blade vibration can be effectively suppressed using joint couplings between the blades and the rotor. For design optimization, the objective is set as the mass of the rotor and the stator, and the maximum deformation of the airgap clearance between the rotor and the stator by external forces is constrained below 10% of the gap width. The commercial software OptiStruct is used for the analysis and optimization. In this investigation, the analysis and optimization are conducted for a 10 MW wind turbine generator. However, the proposed methods can be extended to larger generator designs without requiring considerable modification. The mass of the optimized 10 MW BRPM generator is 160.7 tons (19.3 tons for the rotor and 141.4 tons for the stator), while that of an optimized conventional spoke arm-type generator is 325.6 tons.

This investigation presents a topology optimization method for the design of lightweight serial robots for industrial applications such as welding robots and painting robots. It might be numerically efficient to perform topology optimization of a robot structure by dividing the problem into part-level optimization problems. However, the robot structure whose parts are separately optimized is not necessarily the optimized structure in the system level. For example, a robot whose parts are separately designed to have maximum stiffness-to-mass ratio cannot have the maximum stiffness in the system level. This is because it is impossible to know in the stage of the problem formulation how the total mass should be divided into each part to have maximized system stiffness. To deal with this, a metamodel relating the stiffness and the mass usage is constructed in each part-level optimization problem. The proper division of a mass in the part level is determined by solving the system-level optimization problem which is formulated by using the part-level metamodels. Optimized robot structures obtained by the proposed approach are shown to have performances close to system-level optimized ones in test problems with two- and three-dimensional static and dynamic cases. Based on the proposed idea, topology optimization of a painting robot is performed; a base frame, a lower frame and an upper frame of the robot are optimized to lower the maximum system strain energy during the motion.

A novel optimization-based approach for automated synthesis of linkage mechanisms is introduced. The method involves using moving morphable links (MMLs) as design components in topology optimization. These links float in the design space, connecting to create a linkage mechanism with a target output path for a given input motion. The design change of each link is represented by four design variables, corresponding to the positions of its endpoints. This results in a significant decrease in the number of design variables when compared to a model employing spring-connected rigid blocks (SBM), which is one of the most effective design models for topology optimization of linkage mechanisms. Additionally, the use of MML allows for the synthesis of mechanism layouts with cross-links, which cannot be achieved using the SBM. The proposed approach’s efficiency is further enhanced due to the use of global optimizers to solve the optimization problem. For this investigation, the Bayesian optimization method is employed. To improve the effectiveness of the global optimizer by finding optimal hyperparameter settings, the study of the design space’s nonlinearity is conducted. The proposed method’s validity is demonstrated by successfully solving synthesis problems involving four-bar mechanisms and six-bar mechanisms including cross-link layouts.

The use of the finite element method (FEM) for buckling topology optimization of a beam cross section requires large numerical cost due to the discretization in the length direction of the beam. This investigation employs the finite prism method (FPM) as a tool for linear buckling analysis, reducing degrees of freedom of three-dimensional nodes of FEM to those of two-dimensional nodes with the help of harmonic basis functions in the length direction. The optimization problem is defined as the maximization problem of the lowest eigenvalue, for which a bound variable is introduced and set as the design objective to treat mode switching phenomena of multiple eigenvalues. The use of the bound formulation also helps the proposed optimization to treat beams having local plate buckling modes as the fundamental modes as well as beams having global buckling modes. The axial stress is calculated according to the distribution of material modulus which is interpolated using the SIMP approach. Optimization problems finding cross-section layouts from rectangular, L-shaped and generally-shaped design domains are solved for various beam lengths to ascertain the effectiveness of the proposed method.

A layout optimization method for a two-dimensional acoustic lens system used in underwater imaging is presented. To this end, a shape and topology optimization is formulated for the design problem of a lens system for the first time. The layout of a lens system to be optimized includes the number of lenses, shape of lens surfaces, distances between lenses, and lens materials. A phase field function is employed to implicitly parameterize the boundaries of the lenses, which move according to design sensitivities during optimization. Multiple lenses with different materials are optimized using a single phase field function. Because the ratio of the acoustic wavelength with respect to lens dimensions is large, diffraction effects should be taken into account. Accordingly, the performance of a lens system should be analyzed using wave acoustics and not the ray tracing method. The optimization problem is formulated to remove the aberrations of coma and field curvature. The validity of the proposed optimization method is demonstrated by solving benchmark design problems including a lens system with a large field of view.

When a higher-order or generalized beam theory is used for the buckling analysis of thin-walled beams, the analysis accuracy critically depends on the number and shapes of the cross-sectional modes associated with warping and distortion. In the study, we propose to use the hierarchically-derived cross-sectional modes consistent with the higher-order beam theory for the analysis of pre-buckling stress and buckling load. The proposed formulation is applicable to any box beams subjected to arbitrary loads and general boundary conditions. We demonstrate the effectiveness of the proposed method by performing buckling analyses for axial, bending, torsional, and general loadings. Length-to-height ratios of the beams are also varied from 1 to 100. If up to fifty cross-sectional and rigid-body modes are employed, the calculated buckling loads are found to match favorably those predicted by the shell finite element analysis. In that a unified buckling analysis under general loads is developed for box beams, the present study is expected to contribute towards new possibilities for the efficient buckling analysis of more general box beam structures involving several joints.

This research presents a beam model-based fast optimization for the design of a lightweight car body frame at a concept design stage. Because the stiffness of a thin-walled beam frame is significantly affected by the stiffness of joints, the optimization is focused on the reinforcement of joint regions. To overcome the limitations of beam elements in accurately predicting the stiffness of a thin-walled beam frame, especially at joints, a higher-order beam theory (HOBT) is employed for beam modeling. The optimization problems are formulated as mean compliance minimization problems by employing two types of design components: joint springs and diaphragms. Instead of using the geometric parameters of joints as design variables, the directional stiffnesses of joint springs are employed as design variables. Joint reinforcement used for optimization is defined as a virtual part that has stiffness only against bending and torsional deformation, with zero stiffness against higher-order deformations such as warping or distortion. This approach facilitates the calculation of mass increase due to joint springs during optimization. The optimized results of joint springs are inversely designed to sectional shapes of reinforcement through topology optimization. The use of a diaphragm at a joint effectively suppresses the sectional distortion of thin-walled beams and significantly increases their stiffness. The locations of diaphragms are determined through optimization using a 0–1 formulation. The validity of the proposed optimization method is shown by solving subframe and car body frame problems. Joint reinforcement optimization of a car body frame with a 2.5% mass increase and the addition of 6 diaphragms reduced compliance by 13.88% and increased natural frequencies by up to 7.64%.

Level set–based optimization for two-dimensional structural configurations with thin members is presented. A structural domain with thin thickness is defined as a narrow band region on the zero-level contour of the level set function. No additional constraints or penalty functional is required to enforce semi-uniformity in member thickness. Design velocity is calculated on the zero level set, not on domain boundaries, and extended to level set grids in the narrow band. For complicated structural layouts, multiple level set functions are employed. The effectiveness of the proposed method is verified by solving optimization problems of bar configurations. Since no thickness constraints are employed, structurally unfavorable distorted joints seen in other literature do not appear in the results.

An alternative lightweight flatbed trailer design is achieved through a multi-stage optimization procedure. Topology optimization is used to obtain the optimal layout of flatbed trailer frame beams that provide minimum compliance when subjected to bending loads and exhibits maximum torsional natural frequency. The ground structure approach is used to define the trailer frame layout by generating numerous beams connected to predefined points in the trailer. Topology optimization is formulated as a multi-objective problem subject to a mass constraint. Responses and sensitivities are evaluated using ANSYS, and the optimization problem is solved using the moving asymptotes method. The thicknesses, widths, and heights of the C-channel beams are optimized for further weight reduction while at least maintaining the structural performances of the original design. Size and shape optimizations are performed using OptiStruct. The new optimal design is approximately 13% (275 kg) lighter than and as stiff as the original design for bending loads. However, the former has 3.5 times higher torsional natural frequency than the latter. Moreover, the new optimal design has positive manufacturability because the channel beams will be made out of commercially available sheet metals. The same fabrication technology as for a conventional flatbed trailer is possibly to be used.