Topology-optimized Structures Research Articles

Three-dimensional topology-optimized structures for enhanced low-temperature thermal energy storage

In this study, a three-dimensional topologically-optimized structure was developed to enhance the thermal energy storage performance of low-temperature phase change materials. The topology of the structure employed in the thermal energy storage device was developed using COMSOL Multiphysics by maximizing heat diffusion in a design domain with a constant temperature plate and adiabatic boundary conditions. The optimized thermal energy storage device was additively manufactured, and its thermal performance was experimentally characterized and compared against two conventional structures as baselines, viz., a plate fin and a pin fin structure. For the first time, this study seeks to determine the sole influence of fin topology on thermal energy storage performance by designing the fins with the same physical parameters, viz., surface area, volume, base plate size, and material. The fin structure volumes were set at approximately 5% of the simulated domain volume and were fabricated by Selective Laser Melting, a metal additive manufacturing technique. The fin structures were experimentally tested under three different constant plate temperatures (65 °C, 70 °C, and 75 °C) using two different phase change materials (RT35 and PEG1000). Their performances were evaluated by comparing the total charging time, melt fraction, and base plate temperature. Our results show that the topology of the optimized fin structure can reduce charging times by up to 9.1% when a constant plate temperature of 65 °C is applied. The topology of the optimized fins also achieved base plate temperatures that were up to 4 °C lower than conventional fins while having a more uniform distribution of heat to the phase change material within the housing. Additionally, by fixing the critical physical parameters of the fin structures, this work also shows that the fin topology plays a significant role in enhancing the melting performance of thermal storage devices.

Topology optimization with text-guided stylization

We propose an approach for the generation of topology-optimized structures with text-guided appearance stylization. This methodology aims to enrich the concurrent design of a structure’s physical functionality and aesthetic appearance. Users can effortlessly input descriptive text to govern the style of the structure. Our system employs a hash-encoded neural network as the implicit structure representation backbone, which serves as the foundation for the co-optimization of structural mechanical performance, style, and connectivity, to ensure full-color, high-quality 3D-printable solutions. We substantiate the effectiveness of our system through extensive comparisons, demonstrations, and a 3D-printing test.

Manipulating the phase and group delay of a unit cell in metasurface via impedance engineering

The emergence of metasurfaces that tailor the phase via carefully controlling each unit cell brings promising applications including wavefront manipulation, acoustic lenses and levitations. Although excellent phase engineering has been reported in the literature, most metasurface designs suffer from narrow operating bandwidth. To achieve consistent performance over a broad bandwidth, it is necessary to engineer the group delay, in addition to the phase delay, however, few studies have considered this. The majority of them realized specific group delay by true time delay via tuning the depth of a cavity or peculiar topology-optimized structures. No systematic method of unit cell design has been proposed which is a significant step to broadband design. In this work, we proposed a unit cell design process incorporated with transfer matrix method and equivalent LC-circuit fitting. The transfer matrix method is a semi-analytical model capable of predicting the phase response if parameter lists are given. The LC-fitting interprets targeted impedance profile of unit cell by the equivalent inductance and capacitance, assisting the parametric sweeps for geometry design. A numerical study presented showing the mapping of LC values with two physical parameters, leading to control of phase and group delay simultaneously.

Influence of the interfacial thermal resistance of a gadolinium/copper bimetal composite on solid-state magnetic refrigeration

The low heat transfer efficiency caused by a magnetocaloric material (MCM) with low thermal conductivity is the bottleneck that limits the performance of magnetic refrigeration (MR). Previous studies have shown that a bimetal composite of a high thermal conductivity material and an MCM is effective in improving the heat transfer rate. However, the bimetal composite structure causes extra interfacial thermal resistance (ITR). Therefore, this study investigates the processing of gadolinium/copper bimetal composites by fusion casting and experimentally determines the ITR. To evaluate the structural heat transfer capability, the equivalent thermal conductivity (keq) is proposed, which is calculated based on the ITR result and simulation. The influence of the ITR and keq on the cooling performance of a fully solid-state MR is carefully investigated using a validated simulation model. The results show that the smallest ITR of 3.74 × 10−5 m2 K W−1 is obtained with a copper pouring temperature of 1200 °C owing to the thinnest bonding interfacial layer. The topology-optimized structure, using the ITR obtained by fusion casting, has an keq of 159.8 W m−1K−1, with an increase of 39% compared to the structure assembled with thermal grease. As a result, the maximum specific cooling power (SCPmax) range and corresponding optimal operating range are significantly expanded to 45.6–209.3 W kg−1 and 0.23–0.61 rpm, respectively, with an average SCPmax increase of 35.5%. The combination of using topology optimization design to reduce the structural thermal resistance and using a suitable forming process to reduce the ITR can be more beneficial to the performance improvement of solid-state MR.

Topological Design of a Hinger Bracket Based on Additive Manufacturing.

Topology optimization technology is often used in the design of lightweight structures under the condition that mechanical performance should be guaranteed, but a topology-optimized structure is often complicated and difficult to process using traditional machining technology. In this study, the topology optimization method, with a volume constraint and the minimization of structural flexibility, is applied to the lightweight design of a hinge bracket for civil aircraft. A mechanical performance analysis is conducted using numerical simulations to obtain the stress and deformation of the hinge bracket before and after topology optimization. The numerical simulation results show that the topology-optimized hinge bracket has good mechanical properties, and its weight was reduced by 28% compared with the original design of the model. In addition, the hinge bracket samples before and after topology optimization are prepared with additive manufacturing technology and mechanical performance tests are conducted using a universal mechanical testing machine. The test results show that the topology-optimized hinge bracket can satisfy the mechanical performance requirements of a hinge bracket at a weight loss ratio of 28%.

Topology Optimization with Matlab: Geometrically Non-Linear Optimum Solid Structures at Random Force Strengths

This paper aims to investigate multiple large-strain topology-optimized structures, by interpreting their overlay as a probability density function. Such a strategy is suited to finding an optimum design of silicon electrodes subject to a random contact. Using this method, and prescribing a zero net-force constraint on the global system, the optimum structure is identified with a Schwarz P minimum-surface structure. Then, the optimum structure is subject to chemo-mechanically coupled cycling, in terms of an irreversible thermodynamic process, which shows the interplay between the mechanical and chemical fields. The Matlab-based optimization code is attached.

Maximum electromagnetic local density of states via material structuring

Abstract The electromagnetic local density of states (LDOS) is crucial to many aspects of photonics engineering, from enhancing emission of photon sources to radiative heat transfer and photovoltaics. We present a framework for evaluating upper bounds on the LDOS in structured media that can handle arbitrary bandwidths and accounts for critical wave scattering effects. The bounds are solely determined by the bandwidth, material susceptibility, and device footprint, with no assumptions on geometry. We derive an analytical expression for the maximum LDOS consistent with the conservation of energy across the entire design domain, which upon benchmarking with topology-optimized structures is shown to be nearly tight for large devices. Novel scaling laws for maximum LDOS enhancement are found: the bounds saturate to a finite value with increasing susceptibility and scale as the quartic root of the bandwidth for semi-infinite structures made of lossy materials, with direct implications on material selection and design applications.

Topology Optimization Design of Scramjet Structures With Forced Convective Heat Transfer on Unstructured Meshes

Abstract A topology optimization strategy with coupled fluid–solid interaction was proposed to maximize the cooling efficiency of a kind of structure applied for scramjets. The Galerkin finite element method (FEM) is used to solve the forced convective heat transfer, and the rational approximation of material properties (RAMP) method combined with the globally convergent method of moving asymptotes (GCMMA) method are used to solve the topological optimization models with different boundary conditions and objective functions. Examples are provided to demonstrate the validity and effectiveness of the optimization strategy. The optimal flow passages of scramjet structures are achieved successfully. Compared with a baseline structure with rectangular straight passages, the optimized flow passages significantly reduce the averaged bulk temperature and pressure loss, and the bulk temperature is more uniform to avoid the occurrence of concentrated high-temperature areas. With the Reynolds number changing from 1000 to 1750, the heat transfer performance of the three-dimensional topology-optimized structure increases by 16.79% to 20.82%.

Partitioning a topology-optimized structure into additively manufacturable parts using a feature-mapping approach: a novel decomposition optimization method

Partitioning a topology-optimized structure into additively manufacturable parts using a feature-mapping approach: a novel decomposition optimization method

A visualization of mechanical Kansei using the DNN approach

It is illustrated in general that the decision-making in conceptual design is highly dependent on the designer's aesthetic sense. However, even in a subjective phase, objective aspects such as mechanical rationality are implicitly or explicitly considered, and these two perspectives are inseparable. A concept of mechanical Kansei defined as “the capability to evaluate and judge impressions in terms of unconscious, intuitive, and integrative information in mechanics,” has been proposed to elucidate how this capability is utilized for design. In this article, we focus on the capability to unconsciously recall the force flow inside a structure; and take the topology-optimized structures as the representation of such force flow. Through learning the structural shapes with a variational autoencoder (VAE), dimensionality compression from the large design variable space to the lower dimensional latent variable space is performed. As a result, it was shown that the two-dimensional latent space reflected the geometric positions of randomly located supports on the design domain. The obtained mappings from the structural conditions to the representation of force flow in structure within the encoder and decoder of VAE can help to understand the mechanical Kansei.

Optimized One-Click Development for Topology-Optimized Structures

Topology optimization is a powerful digital engineering tool for the development of lightweight products. Nevertheless, the transition of obtained design proposals into manufacturable parts is still a challenging task. In this article, the development of a freeware framework is shown, which uses a hybrid topology optimization algorithm for stiffness and strength combined with manufacturing constraints based on finite spheres and a two-step smoothing algorithm to design manufacturable prototypes with “one click”. The presented workflow is shown in detail on a rocker, which is “one-click”-optimized and manufactured. These parts were experimentally tested using a universal testing machine. The objective of this article was to investigate the performance of “one-click”-optimized parts in comparison with manually redesigned optimized parts and the initial design space. The test results show that the design proposals created while applying the finite-spheres and two-step smoothing are equal to the manual redesigned parts based on the optimization results, proposing that the “one-click”-development can be used for the fast and direct development and fabrication of prototypes.

Topology-optimized lattice structures with simultaneously high stiffness and light weight fabricated by selective laser melting: Design, manufacturing and characterization

Abstract In this study, the level set-based topology optimization method was adopted to design novel lattice structures. The Ti-6Al-4V topology-optimized lattice structures with 30 % volume of solid materials were successfully fabricated by selective laser melting (SLM). The study on mechanical properties and energy absorption capability of the topology-optimized structures was also conducted through the quasi-static compressive testing. Results showed that as the unit cell number of lattice structures increases, the structural failure mechanism changes from the layer-by-layer fracture to the 45° inclined fracture. Topology-optimized lattice structures have a better relative elastic modulus of 0.037 than that of the majority of reported lattice structures, and the as-designed lattice structures possess relatively high energy absorption efficiency of 67.9 % at 0.15 strain. The findings illustrated that the proposed topology optimization method combined with SLM processing is an effective way to obtain novel lattice structures with high load-bearing and energy absorption capacities.

Exploration on Extracting Geometric Model by Topology Optimization Design

Topology optimization design is a way to achieve more efficient design with a minimal priori decision. However, due to the complexity of the solution obtained, topology optimization is usually limited to theoretical researches and can not be applied into actual manufacturing. As a new manufacturing method that is currently developing rapidly, additive manufacturing has made great progress in many fields. Additive manufacturing has fewer limitations on the shape and complexity of the design. And it is currently moving toward higher precision and larger dimensions. The combination of these two ways can solve the problem of topology optimization design well. However, the topology optimization design’s principle determines that it is difficult to transform into a 3D model that can be processed and manufactured pefectly. Based on the topology-optimized structure, this paper uses MATLAB to extract the geometric model and smooth it, which provides an effective method for extracting 3D models from topology optimization. Also, this paper puts forward an efficient method to optimize the structure and it gets a pretty good result in the simulation.

A lightweight bionic design for a scanner based on the 3D architecture of root system of pine trees

Lightweight design is usually a critical criterion in many engineering fields. In addition to the well-developed method topology optimization, structural bionics is also considered an effective approach to obtain innovative designs with lightweight. In nature, trees have evolved highly developed root systems to maximize the efficiency in anchorage. Inspired by the 3D branch structure of plant roots, this paper selects the root system of pine trees as a biological prototype for the optimization of a scanner which has a strict requirement for the flatness. First, a topology-optimized structure of the scanner is modeled and simulated for its mechanical behavior. Next, architectural and mechanical characteristics of the tap root system of pine trees are investigated through sensitivity analysis. Similarity analysis between the root system and the scanner is performed from three aspects. Then, by imitating the spatial configuration of pine tree roots, a bionic design for the scanner is proposed and modeled. Finally, finite element method (FEM) is carried out to evaluate the mechanical performance of the original model, the bionic model, and the topology-optimized model in terms of weight, dynamics response, and specific stiffness efficiency. Comparison results show that the proposed bionic model provides the best lightweight solution for the scanner, followed by the topology-optimized model. The proposed bionic model suggests a new solution to the design of the supporting system of “tower-like” structures and extends the application of branch-based bionics from planar systems to complex spatial systems.

Enhanced fatigue characteristics of a topology-optimized porous titanium structure produced by selective laser melting

The fatigue properties are critical considerations for porous structures, and most of the existing porous materials have unsatisfactory performances due to a lack of structural optimization. This work shows that a topology-optimized structure fabricated by selective laser melting using commercial-purity titanium (CP-Ti) exhibits excellent fatigue properties with an ultra-high normalized fatigue life of ∼0.65 at 106 cycles and at a low density of 1.3 g/cm3. The main factors affecting fatigue, i.e., material properties and a porous structure were studied. Both the factors can affect the fatigue crack initiation time, thereby affecting the fatigue life. Because of twinning that occurred during the fatigue process, the porous CP-Ti samples exhibit a high plasticity. In addition, the fatigue crack propagation rate is significantly reduced because of the high plasticity of the CP-Ti material and the occurrence of fatigue crack deflection.

Characterization of fracture in topology-optimized bioinspired networks.

Designing strong and robust bioinspired structures requires an understanding of how function arises from the architecture and geometry of materials found in nature. We draw from trabecular bone, a lightweight bone tissue that exhibits a complex, anisotropic microarchitecture, to generate networked structures using multiobjective topology optimization. Starting from an identical volume, we generate multiple different models by varying the objective weights for compliance, surface area, and stability. We examine the relative effects of these objectives on how resultant models respond to simulated mechanical loading and element failure. We adapt a network-based method developed initially in the context of modeling trabecular bone to describe the topology-optimized structures with a graph-theoretical framework, and we use community detection to characterize locations of fracture. This complementary combination of computational methods can provide valuable insights into the strength of bioinspired structures and mechanisms of fracture.

Microstructure design and degradation performance in vitro of three-dimensional printed bioscaffold for bone tissue engineering

In bone tissue engineering, three-dimensional printed biological scaffolds play an important role in the development of bone regeneration. The ideal scaffolds should have the ability to match the bone degradation rate and osteogenic ability. This article optimizes the unit cell model of the microstructure including spherical pore, gyroid, and topology to explore degradation performance of scaffolds. Boolean operation of array microstructure unit cells and selected part of a computer-aided design (CAD) femur model are adopted to create a reconstructed scaffold model. Polylactic acid/[Formula: see text]-tricalcium phosphate/hydroxyapatite scaffolds with spherical pore, gyroid, and topology-optimized structures are manufactured by three-dimensional printing utilizing the composition of bio-ink including polylactic acid, [Formula: see text]-tricalcium phosphate, and hydroxyapatite. After degradation of the scaffolds in vitro for several days, the mechanical properties are analyzed to study the effects of different microstructures on the degradation properties. The results show that the gyroid scaffolds with favorable degradability still maintain excellent mechanical properties after degradation. Mechanical properties of the scaffolds with topology-optimized structure and spherical pore microstructure scaffolds have a significant decrease after degradation.

New improvement opportunities through applying topology optimization combined with 3D printing to the construction of gearbox housings

The construction of gearbox housings is severely restricted by all the currently used machining processes. 3D metal printing opens up new possibilities in this area. However, a clear additional benefit compared to the standard cast housing must be given, in order to make additive manufacturing viable. The objective of the present project was to research both the potential and restrictions of additive manufacturing technologies regarding the design of gearbox housings. As a result of this investigation, a topology optimized lightweight gearbox housing with integrated oil channels and scraper was obtained. The topology optimization process of the new gearbox was carried out in two work steps. The first consisted of the determination and design of the primary load-bearing structure of the housing. Therefore, an iterative design process was needed in order to develop the final support structure, because the topology optimization only provides a design draft of the framework structure. Concerning the iteration, an FEM analysis was performed to check and improve the draft after each loop. During the evaluation, safety and weight were compared with the previous version. During the second step of the topology optimization, the structure of all the oil channels was developed, creating a morphological box. Finally, the new gearbox housing was generated by combining the topology optimization with the concepts from the morphological box. Selective Laser Melting (SLM) was chosen for manufacturing because it allows the printing of components of the desired dimension with the required accuracy. The developed gearbox prototype was printed using the aluminum alloy AlSi10Mg (A360). Due to the flexibility of the SLM technology, it was possible to fulfill all specific design criteria while also showing the typical topology-optimized structure too. Afterwards, the housing was machined to achieve precise dimensions and tolerances. Finally, the gearbox was assembled, and both its mechanical integrity and the functionality of the integrated oil systems were fully checked with short-term tests.

Numerical analysis of nonlinear dynamic structural behaviour of ice-loaded side-shell structures

This investigation examines how the nonlinear structural response of a ship side-shell structure that impacts with ice is affected by the layout/design of the structure, ice characteristics and ship speed operational conditions. The finite element (FE) method was used for nonlinear analysis and comparison of a reference side-shell structure with a topology-optimized structure. Nonlinear dynamic FE collision simulations were carried out, using the reference side-shell structure, to study how the impact with ice (having different values of damping coefficients), and the variation in ship speed operational conditions, affected the damage caused to the side-shell. In addition, the results from the comparison of the topology-optimized and reference side-shell structures showed slightly larger stresses locally in the former structure. It was concluded that it was possible to reduce the weight of the reference side-shell structure and that the objective function and optimization require more detailed investigation. The FE analyses with various damping coefficients of ice showed that, for the chosen values of the damping coefficients, there was only small influence on the dynamic nonlinear response of the reference side-shell structure. Finally, a limit value for the maximum allowed velocity in the normal direction towards a level ice belt of the reference side-shell structure was calculated to result in an elastic structural response of the side-shell. For a side-shell structure movement in the direction along a level ice, the influence of velocity on structural response was negligible due to low friction between the side-shell structure and the ice in the contact.

Imprinted silicon-based nanophotonics

We demonstrate and optically characterize silicon-on-insulator based nanophotonic devices fabricated by nanoimprint lithography. In our demonstration, we have realized ordinary and topology-optimized photonic crystal waveguide structures. The topology-optimized structures require lateral pattern definition on a sub 30-nm scale in combination with a deep vertical silicon etch of the order of ~300 nm. The nanoimprint method offers a cost-efficient parallel fabrication process with state-of-the-art replication fidelity, comparable to direct electron beam writing.