In Gwun Jang

Development of the Optimization Framework for Low-Power Wireless Power Transfer Systems

Considering the high level of complexity inherent in wireless power transfer (WPT) systems, the foremost concern in the field is the development of an efficient and systematic design framework that can improve an objective function (e.g., transfer efficiency and system mass) while satisfying multiple constraint functions such as the electromagnetic fields, air-gap, and power capacity transferred. In this paper, an optimization framework for real-world WPT systems is developed through connecting commercial electromagnetic field analysis software and an optimization module using in-house codes. The developed design framework is validated with both unconstrained and constrained optimization cases and then applied to minimize the thickness of the secondary module in a wireless portable device charger. Using the proposed optimization framework, the thickness is successfully and efficiently reduced while the induced voltage and electric and magnetic fields are satisfied.

Traffic Signal Optimization for Oversaturated Urban Networks: Queue Growth Equalization

This paper develops a signal optimization algorithm that aims to equalize queue growth rates across links in oversaturated urban roadway networks and thus postpones queue spillbacks that form at the localized sections of networks. The performance of this algorithm is evaluated by simulating traffic conditions with optimized signal settings on an idealized 3 by 3 roadway network under various oversaturated demand scenarios. The simulation experiments show that the algorithm can delay queue spillbacks by distributing queues over upstream links that would otherwise be underused. The findings from the experiments also show that the signal settings optimized by the queue growth equalization (QGE) algorithm outperform those optimized using the conventional signal optimization software, TRANSYT-7F, for all the performance measures examined in this paper, i.e., compared with TRANSYT-7F, the QGE results in higher outflows, higher vehicle miles traveled, shorter delays, less sensitivity to various demand scenarios, and delayed queue spillbacks. In addition, the algorithm is computationally light to provide a promising groundwork for large-scale signal optimization.

Simulation-Based Feasibility Study on the Wireless Charging Railway System With a Ferriteless Primary Module

Wireless charging railway (WCR) systems have been recently introduced to solve the drawbacks of conventional electric locomotives such as noise, wear, arching, and sparking during wired power transfer. However, the high infrastructure cost of WCR systems weakens their competitiveness against conventional systems, thereby delaying commercialization. In this paper, a new concept of the WCR system that equips a ferriteless primary module is proposed to minimize the use of ferrite necessary for wireless charging and, therefore, to reduce the infrastructure cost. To effectively and efficiently investigate the feasibility of the proposed system with a high level of design complexity, a design optimization framework for high-power WCR systems is implemented to suppress the magnetic saturation and design abnormality during optimization. This framework successfully determines the optimal design that minimizes the mass of the secondary module with no use of the primary ferrite while satisfying various functional requirements of the WCR systems: electromagnetic field strength, magnetic saturation, and induced voltage. Compared with the ferrite-based WCR system, the proposed system can save up to 7.55 kg/m of primary ferrite, which is approximately

Homeostasis-based aging model for trabecular changes and its correlation with age-matched bone mineral densities and radiographs.

230.40/m for infrastructure costs. Thus, the feasibility of the proposed WCR system is proven through simulation-based design optimization, the results of which demonstrate the potential economic benefit for further commercialization.

Image resolution enhancement for healthy weight-bearing bones based on topology optimization

PURPOSE This paper aims (1) to propose a novel bone adaptation model for age-related trabecular changes by adopting two implicit parameters in optimization, (2) to compare the simulated bone volume fraction (BV/TV) with the reported bone mineral density (BMD), and (3) to review the simulated trabecular architectures with the age-matched radiographs. MATERIALS AND METHODS The proposed model simulated the trabecular changes for an age span of 32-80 years. Quantitative comparison was conducted in terms of BMD and other morphometric indices. Then, two radiologists scored the simulated trabecular architectures using the age-matched radiographs. This protocol was approved by the hospital institutional review board. RESULTS The simulated BV/TV was well correlated with BMD reported in the literature (R(2)=0.855; p<0.05). In comparison with age-matched radiographs, the consensus scores of agreement of the trabeculae were higher in age groups over the 50s, and the means of the Wards triangle areas were strongly correlated with those in the age-matched radiographs (R(2)=0.982; p<0.05). CONCLUSION The proposed model could reflect the targeted trabecular changes in proximal femur with age. With further follow-up measurements, this research would contribute to the development of patient-specific models that assist radiologists in predicting skeletal integrity with aging.

Layout optimization of the secondary coils for wireless power transfer systems

Although high-resolution skeletal images are essential for accurate bone strength assessment, the current high-resolution imaging modalities have critical problems that remain to be solved such as high radiation doses, low signal-to-noise ratios, and long scan times. Resolution enhancement techniques, which have recently received much attention, have also been difficult to obtain acceptable image resolutions. Inspired by the self-optimizing capabilities of bone (i.e. reorienting the trabecula for maximum mechanical efficiency with minimum bone mass), this paper proposes a novel resolution enhancement method that can reconstruct a high-resolution skeletal image from a low-resolution image. In order to achieve this, the proposed method conducts mesh refinement for resolution upscaling and then performs topology optimization with a constraint for the bone mineral density deviation in order to preserve the subject-specific bone distribution data. The numerical results show that the proposed method successfully reconstructs the enhanced images of trabecular architecture in terms of structure similarity and apparent elastic modulus, thereby demonstrating the feasibility of the proposed method for skeletal image resolution enhancement.

Optimization of the wireless power transfer system in an electric railway

Due to the complexity of wireless power transfer systems, little literature to date has addressed the development of systematic and efficient design framework for determining the optimal layout of coils. In this paper, introducing the concepts of fixed grid-based coil representation and effective turns, a novel layout optimization is proposed to determine the optimal layout of the secondary coils when the primary coils are given. Using the proposed method, the secondary-coil layouts are successfully determined to maximize the induced voltages while satisfying mass constraints. The optimized layouts are then validated through the experiments under the same conditions.

Computational study of estimating 3D trabecular bone microstructure for the volume of interest from CT scan data

Wireless power transfer (WPT) can be an effective way to solve the energy supply problems in electric railways (ER). In order to develop the desired system, design optimization can be a solution to optimize the objective function (e.g. mass of a system, transfer efficiency, and air-gap) while satisfying constraints such as electromagnetic field (EMF), magnetic saturation, and induced voltage. In this paper, the optimization framework for the railway-specific WPT systems was developed by connecting between an optimization module and the electromagnetic commercial software. The framework was then applied to minimize the mass of a WPT system of the Wireless Low Floor Tram (WTRAM) under the multiple constraints. As a result of optimization, the mass of the system could be successfully reduced by 64.3% while the performance-related constraints were being satisfied. The proposed framework would help us to reduce time and cost for the development of next-generation ER systems.

Precise Determination of the Optimal Coil for Wireless Power Transfer Systems Through Postprocessing in the Smooth Boundary Representation

Inspired by the self-optimizing capabilities of bone, a new concept of bone microstructure reconstruction has been recently introduced by using 2D synthetic skeletal images. As a preliminary clinical study, this paper proposes a topology optimization-based method that can estimate 3D trabecular bone microstructure for the volume of interest (VOI) from 3D computed tomography (CT) scan data with enhanced computational efficiency and phenomenological accuracy. For this purpose, a localized finite element (FE) model is constructed by segmenting a target bone from CT scan data and determining the physiological local loads for the VOI. Then, topology optimization is conducted with multiresolution bone mineral density (BMD) deviation constraints to preserve the patient-specific spatial bone distribution obtained from the CT scan data. For the first time, to our knowledge, this study has demonstrated that 60-μm resolution trabecular bone images can be reconstructed from 600-μm resolution CT scan data (a 62-year-old woman with no metabolic bone disorder) for the 4 VOIs in the proximal femur. The reconstructed trabecular bone includes the characteristic trabecular patterns and has morphometric indices that are in good agreement with the anatomical data in the literature. As for computational efficiency, the localization for the VOI reduces the number of FEs by 99%, compared with that of the full FE model. Compared with the previous single-resolution BMD deviation constraint, the proposed multiresolution BMD deviation constraints enable at least 65% and 47% reductions in the number of iterations and computing time, respectively. These results demonstrate the clinical feasibility and potential of the proposed method.

Layout Optimization of the Receiver Coils for Multitransmitter Wireless Power Transfer Systems

Recently, the layout optimization of the secondary coils for wireless power transfer systems has been developed using the fixed grid (FG) representation. Although this method can effectively and efficiently determine the optimized coil design under the given conditions, a distinct discrepancy exists between the evaluated coil mass (i.e., simulation data) and the physical coil mass (i.e., experiment data). In this paper, the FG-based coil layout optimization is revisited based on the smooth boundary (SB) representation in order to resolve the inherent drawbacks of the FG representation. Induced voltage, electromagnetic field strength, and coil mass, which have been previously derived in the FG representation, are reformulated in terms of design variables (i.e., a reference turn and relative turns in this paper) in the SB representation. Through the layout optimization, the optimized layouts of the secondary coil are determined in order to minimize the coil mass while satisfying the constraints for induced voltage and magnetic field strength; then, they are postprocessed in order to obtain a smooth, elaborate boundary. The experimental validation demonstrates that the proposed SB-based approach outperforms the previous FG-based method in terms of coil mass and boundary representation.