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This paper uses simulation-based portfolio optimization to mitigate the left tail risk of the portfolio. The contribution is twofold. (i) We propose the Markov regime-switching GARCH model with multivariate normal tempered stable innovation (MRS-MNTS-GARCH) to accommodate fat tails, volatility clustering and regime switch. The volatility of each asset independently follows the regime-switch GARCH model, while the correlation of joint innovation of the GARCH models follows the Hidden Markov Model. (ii) We use tail risk measures, namely conditional value-at-risk (CVaR) and conditional drawdown-at-risk (CDaR), in the portfolio optimization. The optimization is performed with the sample paths simulated by the MRS-MNTS-GARCH model. We conduct an empirical study on the performance of optimal portfolios. Out-of-sample tests show that the optimal portfolios with tail measures outperform the optimal portfolio with standard deviation measure and the equally weighted portfolio in various performance measures. The out-of-sample performance of the optimal portfolios is also more robust to suboptimality on the efficient frontier. [ABSTRACT FROM AUTHOR]

The properties of the material applied to the finite element (FE) simulation can be expressed by constitutive models, and simple constitutive and complex constitutive models can be used to show the actual phenomenon. The technology to improve the accuracy of the constitutive model applied to FE simulation is the inverse method. The inverse method is a method to curve fit the FE simulation result to the test data by utilizing finite element model updating (FEMU). Inverse methods are general approaches to update material properties. The inverse method can iteratively run many FE simulations for constitutive model optimization and consider metamodel-based simulation optimization (MBSO) to reduce this resource waste. With MBSO, one can obtain significant results with fewer resources. However, the MBSO algorithm has the problem in that the optimization performance deteriorates as the number of parameters increases. The typical process of the inverse method is to adjust these factor values individually. If there are many factors in the constitutive model, the optimization result may deteriorate owing to the performance limit of the MBSO when the structural method is used. This paper proposes a method of fitting a stress–strain constitutive model with a scaling factor to improve the efficiency of the inversion method using MBSO. For this purpose, a process was performed to determine the curve characteristics during the pretreatment stage. The results show that the proposed method significantly improved the prediction efficiency of the combination function. Thus, we conclude that initializing the combination function and setting the parameters of the inverse method by applying the proposed approach improves the efficiency of large deformation analyses. [ABSTRACT FROM AUTHOR]

A slurry pump is a device used to transport slurry, which is a mixture of solids and liquids. The slurry pump is subjected to physical erosion, generally resulting from erosion by friction between the solid and liquid particles. This study aimed to analyze the effects of process parameters on the erosion wear of a throat bush, which is the main component of a slurry pump. The erosion rate density (E) was analyzed based on the process parameters, that is, the slurry particle diameter, rotation speed of the impeller, and gap between the impeller and the throat bush. The discrete phase model (DPM) of the slurry pump was simulated using the process parameters. These parameters were optimized to minimize the erosion rate density. The optimization method using design of experiments (DOE) to derive a specific location with the greatest influence of the design variables through the one-way layout method and optimize the response value at that location is a method that efficiently analyzes a large number of cases. The optimization results confirmed that the erosion rate density was reduced in the optimization model compared with the earlier model. [ABSTRACT FROM AUTHOR]

A grommet is a representative component that fixes the position of a cable. It is made from hyper-elastic materials (rubber), such as ethylene propylene diene monomer (EPDM). The grommet and cable are conventionally fixed through bonding; however, this method has numerous disadvantages that can be improved through relevant research. To apply a fixing method using the elastic force of EPDM rubber, this paper presents an empirical equation for approximating the bonding force of EPDM grommet parts with a hollow shaft geometry. First, tensile tests and the inverse method were used to approximate the basic mechanical properties. The physical properties were derived through basic tests; furthermore, bonding force tests and the inverse method were used on a grommet with a hollow shaft structure. In addition, the Box–Behnken design of experiments was used to predict the amount of change in the bonding force according to the geometry variables. Finally, this study was validated by comparing the approximation results derived through the design of experiments with the analysis and bonding force test results. [ABSTRACT FROM AUTHOR]

Torsion springs, which transfer power through the twisting of their coil, provide advantages such as module simplification and efficient use of space. The design of a torsion spring has been formulated, but it is difficult to determine the local behaviors of torsion springs according to actual load conditions. This study proposes a torsion-spring design method through finite element analysis (FEA) using nonuniform-rational-basis-spline (NURBS) curves. Through experimentation, the angle and displacement values for the actual spring load were converted into useable data. Torsion-spring displacement values were obtained via experimentation and converted into coordinates that may be expressed using NURBS curves. The results of these experiments were then compared to those obtained via FEA, and the validity of this method was thereby verified. [ABSTRACT FROM AUTHOR]

The accidents caused by car collisions can be categorized into front collision, side collision, and rear-end collision, among which the fatal accident incidence rate of rear-end collisions is the highest. Because neck injury is the most common injury associated with rear-end collision, the car headrest should be redesigned to minimize such injuries. In this study, we investigated the neck injury indices in active and proactive headrests using a sled test. The predictability of injury indices was examined through the behavior analysis of the head and seat. The characteristics of the head–neck behavior and the structure of the headrest were studied. Furthermore, the neck injury indices corresponding to the two headrests were compared. The predictability of major neck injury indices was examined, which may be used as a reference for developing an active deployment system to complement the existing headrest deployment characteristics. [ABSTRACT FROM AUTHOR]

As automotive lamps are highly integrated, the heat generated from bulbs reduces the light quantity and lifespan of the bulbs. Numerous studies have been actively conducted worldwide on heat dissipation designs and material modifications for heat release. In this study, an analysis was carried out of the mechanical, thermal, and morphological characteristics of Polybutylene Terephthalate (PBT) and Polyamide (PA6) matrix composites containing alumina filler; further, their flowability and injection moldability were also studied. The PA6 matrix that was subjected to an addition of 60% alumina was selected as the sample. To compare the performances of the selected composites with that of the fog lamp reflector manufactured with conventional PBT, fog lamp reflectors were fabricated. When 60% alumina was added, the thermal conductivity was improved. Thus, the maximum temperature of the lamp reflector was reduced, and the heat was transferred to the surroundings; this was in contrast to the fog lamp reflector fabricated with conventional PBT. [ABSTRACT FROM AUTHOR]

Studying the characteristics of materials through a finite element analysis (FEA) has various benefits; hence, many studies have been conducted to improve the reliability of the analysis results. In general, the mechanical properties used in FEA for metals and metal composites are stress–strain data obtained through tensile tests, which are used for modeling from a macroscopic perspective. While many studies have been conducted on metal materials, there are limited studies on the analysis of polymer composite materials produced through injection and special processing. In this study, existing inverse methods were applied, and an FEA was conducted to reproduce the axial displacement of the tensile specimens comprising glass fiber-reinforced polymer (GFRP); further, errors were examined by comparing the test and analysis results. To reduce such errors, the experiment and the FEA results were analyzed through parameter optimization based on various empirical formulas. The accuracy of various inverse methods were examined and an inverse method suitable for GFRP was proposed. [ABSTRACT FROM AUTHOR]

A grommet, made of ethylene propylene diene methylene (EPDM) rubber, is an integral part used for fixing and protecting the wire inserted from the outside to the inside of vehicles. Rubber compounds exhibit various mechanical properties and vulcanization characteristics depending on the accelerator mixing ratio. These mechanical properties affect the insertion and detachment forces when the grommet is manufactured and fixed to the vehicle body. In this study, we experimentally analyzed the changes in the properties of EPDM rubber depending on the vulcanization accelerator to improve the mounting performance of the grommet, and subsequently derived the optimum accelerator mixing ratio. We implemented a mixture design strategy to derive the optimum mixing ratio for obtaining the desired mechanical properties and vulcanization characteristics. The insertion and separation forces of the existing grommet were compared with those of the grommet fabricated using the derived mixing ratio and we found that the mounting performance was improved compared to the existing grommet. [ABSTRACT FROM AUTHOR]

Among the various methods used for glass edge sealing, this study uses microwaves to seal glass edges. Through basic experiments, the main process conditions for edge sealing of glass were derived, and the experimental plan and analysis were carried out using the Box-Behnken method of response-surface analysis based on 3 factors and 3 levels. The step height which influences sealing was set as a response variable. If the step height becomes too large, the glass can be damaged, and if the step height is too small, the edge sealing will not be performed. Accordingly, process optimization that edge sealing is possible while minimizing the step height was carried out. A predictable regression equation was derived for the step height of edge sealing and the main-effect analysis was performed for the step height. Using the response-optimization tool, we derived the optimum process condition that minimized the step height of the edge sealing and verified that it matched the error value of 4.1% compared with the target value of the step height measurement result confirmed through the verification experiment. [ABSTRACT FROM AUTHOR]

Ethylene propylene diene monomer (EPDM) has superior mechanical properties, water resistance, heat resistance, and ozone resistance. It can be applied to various products owing to its low hardness and high slip resistance properties. A grommet is one of the various products made using EPDM rubber. It is a main component of automobiles, in which it protects wires throughout the inside and outside of a vehicle body. The grommet, made of EPDM, has different mounting performance depending on the process parameters and the shape of the grommet. This study conducted optimization to improve the mounting performance of a grommet using EPDM materials. The physical properties of the main molding materials were investigated according to process parameters. A grommet was fabricated according to the process parameters of fabrication. Insertion force and separation force were examined through experiments. Nonlinear material constants were determined through uniaxial and biaxial tensile tests. The nonlinear analysis of the grommet was conducted, and a compound design that incorporated the shape parameters for the minimum load of each part was derived. Then, additional nonlinear analysis was performed. This was followed by a comparative analysis of the actual model through experimental evaluation. [ABSTRACT FROM AUTHOR]

With the rapid development of ecofriendly cars, various inverters are also being developed depending on the performance of motors. The DC-link capacitor is used as an inverter component; however, there are several limitations on its size, such as the requirement for wide films. Film width is a major factor that affects the capacitor's equivalent series resistance (ESR) and is closely related to heat generation. When the temperature of the capacitor increases, the dielectric breakdown due to high voltage causes a reduction in capacitance, which leads to a decrease in inverter power and causes vehicle defects; this needs to be addressed to minimize the heat of the capacitor. Recently, genetic films that can be used at high temperatures have been developed. However, producing such films is difficult because of their 5 µm thickness; thus, the size increases when they are designed and they consequently cannot be used in practical applications. Based on a film width of 50 mm, this study analyzed the factors that can reduce ESR, set the level for each factor, and conducted experiments using the Box–Behnken design. The variables (thermal conductivity, film thickness, and capacitance) were set to three levels for each factor, and the ESR, thermal flux, and temperature characteristics were analyzed through finite element analysis. Based on the temperature results, optimized conditions for film thickness of 3.15 μm, capacitance of 390 μF, and thermal conductivity epoxy of 4.5 W/m·K were derived using Minitab, and samples were made for verification tests. A capacitor was installed in the chamber and was saturated for 2 h at 85 °C and current of 50 A rms was applied at 16 kHz frequency. The K Type sensor attached to the film surface was connected to a temperature recorder to measure the temperature change in the film over time after applying the current. The experimental results confirmed that the temperature of the genetic film with a 50 mm film width was similar to that with a 35 mm film width, and this confirmed that the set factors were similar to that of the genetic film with 35 mm film width. It was confirmed that increased film width can reduce ESR and minimize heat generation. [ABSTRACT FROM AUTHOR]

There has been a recent surge of interest in vacuum insulating glass (VIG) due to its excellent thermal insulation performance. Vacuum glazing is necessary for high-performance sealing solders and various applications in sealing technology. This paper describes experimental studies into heating and edge-sealing of flat glass using microwaves. Electric–thermal coupled analysis using ANSYS was employed and heating and edge-sealing experiments were conducted on flat glass. In order to ensure a uniform electric field distribution in the microwave chamber, the electric field and temperature distributions were analyzed according to waveguide patterns. In addition, the electric field and temperature distribution were analyzed with the inclusion of carbon susceptor plates. Based on the electric simulation results by waveguide pattern, a microwave heating chamber was fabricated, and a basic experiment was conducted on both heating and edge-sealing of the glass. The cross-section of the sealed glass confirmed that it was sealed without cracks or breakage. [ABSTRACT FROM AUTHOR]

Among the composite manufacturing methods, injection molding has higher time efficiency and improved processability. The production of composites via injection molding requires a pre-process to mix and pelletize the matrix polymer and reinforcement material. Herein, we studied the effect of extrusion process conditions for making pellets on the mechanical and thermal properties provided by injection molding. Polyamide 6 (PA6) was used as the base, and composites were produced by blending carbon fibers and Al2O3 as the filler. To determine the optimum blending ratio, the mechanical properties, thermal conductivity, and melt flow index (MI) were measured at various blending ratios. With this optimum blending ratio, pellets were produced by changing the temperature and RPM conditions, which are major process variables during compounding. Samples were fabricated by applying the same injection conditions, and the mechanical strength, MI values, and thermal properties were measured. The mechanical strength increased slightly as the temperature and RPM increased, and the MI and thermal conductivity also increased. The results of this study can be used as a basis for specifying the conditions of the mixing and compounding process such that the desired mechanical and thermal properties are obtained. [ABSTRACT FROM AUTHOR]