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This paper presents a multi-material topology optimisation (MMTO) process for the lightweight design of an electric bus roof structure including the self-weight. The usage of electric buses is increasing owing to environmental issues. However, it is challenging to design a lightweight structure, because the heavy battery pack mounted on the roof increases the deformation and reduces the safety. In a design including the self-weight, the appropriate distribution of multiple materials improves the performance more than that of a single material. The MMTO method has been applied to identify the optimal distribution of multiple materials. However, in the real-engineering problem, only a simple objective function such as compliance and a single constraint function such as the volume of material have been considered, whereas the mass reduction is the most important factor. In this paper, an MMTO process is proposed for the lightweight design of the bus roof structure to consider multiple displacement constraints including the self-weight. To control the complexity of the distribution of multiple materials for improving the manufacturability, the welding surface function is proposed. An optimisation process was constructed that can handle the complex finite-element model and multiple load cases, and it was validated according to the well-known compliance minimisation problem. Mass reduction was achieved via the lightweight optimisation, and the interfacial area between the different materials was reduced by employing the welding surface function. [ABSTRACT FROM AUTHOR]

This paper investigates material interpolation schemes in multi-material topology optimization (MMTO) for magnetic device design. Different interpolations of material properties lead to a non-unique layout and differences in performance, thereby affecting the initial design dependence. However, there is a lack of research on material interpolation in MMTO for the magnetic design problem. In this research, two types of material interpolation schemes are compared: recursive multiphase (RM) and discrete material optimization (DMO). To compare only the effects of material interpolations, the non-convex feasible set of material constraints in RM interpolation schemes were transformed into the convex feasible set by a linear form. The performance profile was employed to obtain the global performance of each interpolation scheme. Examples of the C-core actuator and the permanent magnet actuator (PMA) were applied for performance comparison, and the performance profile indicated that the DMO interpolation scheme is robust to initial material distributions and different material constraints compared to the RM interpolation scheme. [ABSTRACT FROM AUTHOR]

We report the thermal transition and concomitant morphology change of polyimide films, investigated through dynamic mechanical analyses, thermo-mechanical analyses, and X-ray diffraction spectroscopy. For this study, highly transparent polyimide films composed of 3,4,3′,4′-biphenyltetracarboxylic dianhydride and fluorinated diamines, 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl, are prepared through a solvent-casting method. The films are annealed at different temperatures, and two kinds of reaction solvents (n-methyl-2-pyrrolidone and N,N-dimethylacetamide) for the polyimide precursors are compared. The mechanical analyses during thermal transition along with spectroscopic measurements reveal unusual transition behaviors and morphology differences between the polyimide films at various annealing temperatures. The results can be applied to the quantitative analysis of the imidization ratio in highly imidized polyimides when the films are imidized thermally at temperatures above 300 °C. [ABSTRACT FROM AUTHOR]

The submerged helium injection process results in the heat and mass transfer between the helium bubble and the cryogenic liquid. The objective of this paper is to analyze the dynamics of the heat and mass transfer process. It is observed that during the helium injection process the dynamics of mass transfer is dominant and the transient heat transfer is negligible. The helium bubble shape and rising patterns are observed with a visualization device that helps to discern the dominant process between heat transfer and mass transfer. The clustering patterns such as coalescence of helium bubbles are observed with the visualization device. The visualization results indicate that, it is very difficult to determine the representative size of bubbles due to the irregular shape of the helium bubbles. The shape and size of the helium bubbles are important parameters for evaluating the overall mass transfer coefficient ( k G A ) which is the essential parameter for calculating the evaporation rate of the bulk liquid into the helium bubbles. In this paper, the simplified lumped model is considered to fairly approximate the evaporation rate of the cryogenic liquid into the bubbles and the cooling rate of helium injection. The empirical correlation for the average concentration ( C ‾ A ) of evaporated cryogenic liquid into the helium bubbles is presented and the overall mass transfer coefficients ( k G A ) are calculated as the result of the lumped model. The proposed model and empirical correlations are compared with the experimental results, and the comparison result shows good agreement with differences that are less than ±0.4 K. [ABSTRACT FROM AUTHOR]

Highlights: [•] Thermal expansion for rigid and planar polyimides depends on film thickness. [•] Charge transfer complex is formed more favorably at thinner films. [•] Variable thermal expansion originates from complex morphological effects. [•] Variable thermal expansion provides optimum film thickness for display substrates. [Copyright &y& Elsevier]

In this paper, a new method is presented to concurrently determine the structural layout and joint interface during the multi-material topology optimization (MMTO) process. Although the development of additive manufacturing techniques allows the fabrication of multi-material structures for soft materials with graded properties, joint materials for joining metals or composites are still needed. This paper proposes a novel material interpolation scheme for defining the joint area between dissimilar materials using a two-step filtering process. The general MMTO process is performed in the first filtering step. Furthermore, the filtered variables generate the joint area, and the filter radius controls the thickness of the area in the second filtering step. A modified discrete material optimization (DMO) approach is developed to control the different materials independently and to expand the applicability of the method to cases with more than two design materials. To demonstrate the performance of the proposed method, a compliance minimization problem is formulated for various volume constraints, joint thicknesses, material properties, mesh types, and number of materials. To show the scalability, 3-D design and compliant mechanism design examples are adopted. Based on numerical examples, it was confirmed that the proposed method performs well in various cases; moreover, the results demonstrate that the concurrent designing of the structural layout and joint interface leads to better performance than when joint stiffness is not considered. • A new multi-material topology optimization for considering joint stiffness between dissimilar materials is proposed. • A modified discrete material optimization (DMO) approach for defining joint area is developed. • The two-step filtering process for controlling the structural feature size and the joint thickness are adopted. • Via numerical examples with various cases: joint thickness, material property, and mesh type, the proposed method is validated. [ABSTRACT FROM AUTHOR]

In this paper, we propose the use of deep learning-based image super-resolution to accelerate structural topology optimization. Topology optimization suffers from iterative computation and a time cost that increases with the number of elements. Recently, there have been attempts to accelerate topology optimization using deep learning-based models, but they often do not address a wide range of physical conditions or require extensive training data. This highlights the need for an approach that can effectively solve different problem conditions with less training data. Our approach first starts topology optimization at a low resolution to quickly obtain an optimized structure. It is converted to the structure at a higher resolution by using an image super-resolution model. Then, the final structure is obtained by performing topology optimization at this high resolution by using the converted structure as the starting configuration. The super-resolution model learns how to transform low-resolution structural features into high-resolution ones regardless of optimization conditions. As a result, it can be applied to any problems different from the problem used to generate the data for training the model. The proposed approach's excellent acceleration and generalization performance is demonstrated for three representative problems in structural topology optimization with a small number of training datasets. Furthermore, it has been shown to be effective in the deck arch bridge problem and the natural frequency maximization problem. Finally, the proposed approach is also found to be effective on the three-dimensional cantilever beam problem. [ABSTRACT FROM AUTHOR]

In this paper, we propose the use of deep learning-based image super-resolution to accelerate structural topology optimization. Topology optimization suffers from iterative computation and a time cost that increases with the number of elements. Recently, there have been attempts to accelerate topology optimization using deep learning-based models, but they often do not address a wide range of physical conditions or require extensive training data. This highlights the need for an approach that can effectively solve different problem conditions with less training data. Our approach first starts topology optimization at a low resolution to quickly obtain an optimized structure. It is converted to the structure at a higher resolution by using an image super-resolution model. Then, the final structure is obtained by performing topology optimization at this high resolution by using the converted structure as the starting configuration. The super-resolution model learns how to transform low-resolution structural features into high-resolution ones regardless of optimization conditions. As a result, it can be applied to any problems different from the problem used to generate the data for training the model. The proposed approach's excellent acceleration and generalization performance is demonstrated for three representative problems in structural topology optimization with a small number of training datasets. Furthermore, it has been shown to be effective in the deck arch bridge problem and the natural frequency maximization problem. Finally, the proposed approach is also found to be effective on the three-dimensional cantilever beam problem. [ABSTRACT FROM AUTHOR]

The impact of microplastics (MPs) on the metabolic functions of the liver is currently unclear and not completely understood. To investigate the effects of the administration of MPs on the hepatic metabolism of normal and obese mice, alterations in the lipid, glucose (Glu), and amino acid regulation pathways were analyzed in the liver and adipose tissues of C57BL/6Korl (wild type, WT) or C57BL/6-Lepem1hwl/Korl mice (leptin knockout, Lep KO) orally administered polystyrene (PS) MPs for 9 weeks. Significant alterations in the lipid accumulation, adipogenesis, lipogenesis, and lipolysis pathways were detected in the liver tissue of MP-treated WT and Lep KO mice compared to the vehicle-treated group. These alterations in their liver tissues were accompanied by an upregulation of the serum lipid profile, as well as alterations in the adipogenesis, lipogenesis, and lipolysis pathways in the adipose tissues of MP-treated WT and Lep KO mice. Specifically, the level of leptin was increased in the adipose tissues of MP-treated WT mice without any change in their food intake. Also, MP-induced disruptions in the glycogenolysis, Glu transporter type 4 (GLUT4)-5′ AMP-activated protein kinase (AMPK) signaling pathway, levels of lipid intermediates, and the insulin resistance of the liver tissues of WT and Lep KO mice were observed. Furthermore, the levels of seven endogenous metabolites were remarkably changed in the serum of WT and Lep KO mice after MP administrations. Finally, the impact of the MP administration observed in both types of mice was further verified in differentiated 3T3-L1 adipocytes and HepG2 cells. Thus, these results suggest that the oral administration of MPs for 9 weeks may be associated with the disruption of lipid, Glu, and amino acid metabolism in the liver tissue of obese WT and Lep KO mice. [ABSTRACT FROM AUTHOR]

• Cryogenic natural circulation loop analyzed experimentally and mathematically. • The circulation flow-rate calculated by the two-phase flow model: HEM and TEDFM. • The TEDFM estimated the circulation flow rate with 5% error. • The two-phase flow pattern of cryogenic liquid verified with flow visualization. This paper presents the application of cryogenic natural circulation loop for engine cooling of launch vehicles, and the experimental measurements of the natural circulation system. The experimental results indicate that the circulation flow rate increases with an increase in heat input and a decrease in system pressure, on varying them. The study includes the temperature and pressure profiles of the natural circulation loop. The steady-state flow rate calculation was developed with two-phase models: the homogeneous equilibrium model (HEM) and thermal equilibrium drift-flux model (TEDFM). The TEDFM revealed a 5% error in the experimental circulation flow rate, and it is agreeable with the experimental results. The small-scale experimental setup verified the two-phase flow pattern in the cryogenic natural circulation loop. A fully liquid flow was observed in the downward section. The horizontal section had a bubbly flow, where the speed of the gas and liquid were similar. The slug and churn flows were present in the vertically upward section, where gas velocities were faster than liquid. Both HEM and TEDFM can be applied in the horizontal heated section. However, it is more appropriate to apply TEDFM in the vertically upward section during the pressure drop calculation for the cryogenic natural circulation loop. [ABSTRACT FROM AUTHOR]

This paper proposes a multi-objective optimization method using an adaptive weight determination scheme and tunneling method. To find the optimum designs that are evenly distributed on the Pareto front, the weights of different objective functions are adaptively determined by using the concept of a hyperplane so that new solutions can be gradually found in the objective space. In addition, to avoid locally optimized solutions that are dominated by other Pareto optimum designs, a tunneling method is employed in the optimization process. To confirm the effectiveness of the proposed method, topology optimization of the magnetic actuator is performed. The magnetic force and volume of the actuator are considered as two conflicting objective functions in the optimization problem, and Pareto optimum solutions that are evenly distributed in the objective space could be obtained. [ABSTRACT FROM AUTHOR]

The authors elucidate an origin and probable mechanism of adhesion strength change at an interface of fluorinated poly(amic acid) and stainless steel. Fluorination provides favorable delamination with release strength weaker than 0.08 N/mm from a metal surface, once the amount of residual solvent becomes less than 35 wt. %. However, the release strength critically depends on film drying temperature. Characterization on stainless steel surfaces and thermodynamic analyses on wet films reveal a drying temperature of 80 °C fosters interaction between the metal oxides at stainless steel surface and the free electron donating groups in poly(amic acid). [ABSTRACT FROM AUTHOR]

• Cryogenic propellant is pressurized with hot helium in typical launch vehicle. • Depressurization of ullage was observed with cold helium input to the LN 2 tank. • Cryogenic liquid droplet propagation observed during the pressurization. • The ullage temperature and pressure decreased due to the ullage cooling effect. • The ullage depressurization is possible during the helium gas with liquid droplets. In liquid propellant propulsion systems, helium pressurization is required to transfer liquid propellant from the tank to the engine. When a cryogenic liquid propellant is used, the tank becomes pressurized by relatively high temperature helium. Typically, the ullage pressure increases with the helium inflow. However, in one particular case, the ullage pressure reduced while cold helium was supplied through direct gas injection. High-velocity gaseous helium strikes the cryogenic liquid surface that generates the liquid splash in the ullage. The cryogenic liquid splash in the ullage then transfers heat between the gas and the liquid. Therefore, the ullage pressure decreases because of the decrease in the ullage temperature. The pressure behavior of the cryogenic tank during the gas inflow is experimentally examined, and the depressurization during the pressurization process is analyzed. The results indicate that the gas–liquid interface disturbance decreases the ullage pressure. The observed gas–liquid interface disturbance effect can be employed in pressure decrease applications in cryogenic liquid storage tanks. [ABSTRACT FROM AUTHOR]

Toughness and high elastic elongation are important requirements for polyimide films used as substrates in flexible displays. However, these properties can be altered by imidization during the thermal treatment. In the present study, we investigated a probable mechanism to enhance the toughness by shrinking fluorinated polyimide films containing benzidine moieties. A higher degree of fluorination leads to weaker intermolecular charge transfer and optically clearer films, but it also degrades the mechanical properties. Moreover, β -transition originating from the molecular rotation around benzidines makes the film dependent on the elongation conditions during solvent drying. According to frequency-sweeping measurements and simulations based on density functional theory and molecular dynamics, the β -transition temperature increases and the phase lag in elastic energy loss decreases with increasing shrinkage. Both experimental and theoretical findings suggest that the change in frequency dependence can be attributed to the variation in elasticity retardation, which possibly originates from the chain-entanglement density. [ABSTRACT FROM AUTHOR]