Giwoo Jeung

Reliability-Based Design Optimization of a Superconducting Magnetic Energy Storage System (SMES) Utilizing Reliability Index Approach

A reliability-based optimization method for electromagnetic design is presented to take uncertainties of design parameters into account. The method can provide an optimal design satisfying a specified confidence level in the presence of uncertain parameters. To achieve the goal, the reliability index approach based on the firstorder reliability method is adopted to deal with probabilistic constraint functions and a double-loop optimization algorithm is implemented to obtain an optimum. The proposed method is applied to the TEAM Workshop Problem 22 and its accuracy and efficiency is verified with reference of Monte Carlo simulation results.

Implementation of Material Sensitivity Analysis for Determining Unknown Remanent Magnetization of a Ferromagnetic Thin Shell

This paper deals with the numerical implementation of the material sensitivity analysis, which is used to efficiently determine an optimal magnetization distribution on a ship hull. A material sensitivity formula for the forward problem formulated in terms of the equivalent magnetic charge method is analytically derived. Then, the components of the adjoint system including the magnetic pseudo-source are thoroughly investigated in order to obtain the first-order gradient information of an objective function with respect to the magnetic charge. The formula facilitates applying the deterministic approach to searching for an optimal charge distribution and also it yields stable and reliable solutions to magnetostatic inverse problems in three dimensions. Finally, the proposed method has been successfully applied to a scale model ship and the predicted results on the underwater field disturbance due to the remanent magnetization of the hull have been compared to real measurements.

Efficient Methodology for Optimizing Degaussing Coil Currents in Ships Utilizing Magnetomotive Force Sensitivity Information

This paper presents an efficient methodology for optimizing degaussing coil currents in ships to minimize the anomaly of underwater magnetic fields due to the hull magnetization induced under the Earths magnetic field. To achieve this, first, the shielding effect of the hull on the underwater fields is thoroughly examined. Then, for a fast search of optimum degaussing currents, a sensitivity formula of an objective function with respect to the magnetomotive force is adopted. The feature of the proposed method is that it does not require any numerical field analyses to assess an objective function during optimization process providing experimental field data for each coil are given. The validity and effectiveness of the method has been tested with a model ship.

Reliability Assessment on Different Designs of a SMES System Based on the Reliability Index Approach

The current paper presents an effective methodology for assessing the reliability of electromagnetic designs when considering uncertainties of design variables. To achieve this goal, the reliability index approach based on the first-order reliability method is adopted to deal with probabilistic constraint functions, which are expressed in terms of random design variables. The proposed method is applied to three different designs of a superconducting magnetic energy storage system that corresponds to initial, deterministic, and roust designs. The validity and efficiency of the method is investigated with reference values obtained from Monte Carlo simulation.

Accurate prediction of unknown corrosion currents distributed on the hull of a naval ship utilizing material sensitivity analysis

This paper presents an efficient approach to determining the corrosion currents distributed on the hull of a naval ship, which offers useful information for the prediction of underwater electric fields and diagnosis of hull corrosion state. To achieve this goal, a material sensitivity formula containing the first-order gradient information of an objective function with respect to the corrosion current is analytically derived by exploiting the augmented Lagrangian method and the adjoint variable method. The validity of the proposed method has been proved through the comparison of the predicted and the measured fields for a test ship model.

Magnetic Dipole Modeling Combined With Material Sensitivity Analysis for Solving an Inverse Problem of Thin Ferromagnetic Sheet

This paper presents an efficient methodology for determining the underwater field anomaly due to the remanent magnetization of a ferromagnetic ship hull by utilizing a magnetic dipole modeling technique combined with material sensitivity analysis. The complicated 3D structure of the hull is replaced with an equivalent magnetic dipole array placed in a 2D plane, of which the optimal dipole moment values will be easily sought out with the aid of material sensitivity analysis. To achieve this, a material sensitivity formula, which contains the first-order gradient information of an objective function with respect to the magnetic dipoles, is analytically derived by exploiting the augmented objective function and adjoint variable method. The proposed method leads to easy numerical implementation and also dramatically reducing system unknowns of the 3D inverse problem considered. Finally, the validity of the method has been tested with real measurements of a scale model ship as well as numerical results of our previous work, which adopted the magnetic charge method in conjunction with material sensitivity analysis.

Optimization of Degaussing Coil Currents for Magnetic Silencing of a Ship Taking the Ferromagnetic Hull Effect Into Account

This paper presents an efficient methodology for optimizing degaussing coil currents in a ship with ferromagnetic hull to minimize magnetic field anomaly underwater. For fast search for an optimum, a magnetomotive force sensitivity formula is adopted. The feature of the method does not require any numerical field analyses to assess an objective function during optimization process providing experimental field data on each coil with respect to the reference magnetomotive force are given. Especially, the shielding effect of the hull on degaussing fields is thoroughly investigated. The validity of the proposed method has been tested with a model ship.

Design Optimization of Waveguide Filters Using Continuum Design Sensitivity Analysis

This paper presents a new methodology for design optimization of dielectric waveguide filters based on the continuum design sensitivity analysis in conjunction with standard electromagnetic analysis codes. To achieve this, first, an analytical sensitivity formula in the frequency domain is systematically derived by exploiting the augmented Lagrangian method, material derivative concept and adjoint variable method. Then unified program architecture integrating several engineering software packages into a design tool is proposed for optimum design of high-frequency devices. A 3-D dielectric resonator used in waveguide filters has been tested to prove the validity of the proposed method.

Indirect Fault Detection Method for an Onboard Degaussing Coil System Exploiting Underwater Magnetic Signals

This paper proposes an indirect fault detection method for an onboard degaussing coil system, installed to reduce the underwater magnetic field from the ferromagnetic hull. The method utilizes underwater field signals measured at specific magnetic treatment facilities instead of using time-consuming numerical field solutions in a three-dimensional space. An equivalent magnetic charge model combined with a material sensitivity formula is adopted to predict fault coil locations. The purpose of the proposed method is to yield reliable data on the location and type of a coil breakdown even without information on individual degaussing coils, such as dimension, location and number of turns. Under several fault conditions, the method is tested with a model ship equipped with 20 degaussing coils.

Efficient Methodology for Reliability Assessment of Electromagnetic Devices Utilizing Accurate Surrogate Models Based on Dynamic Kriging Method

This paper presents an efficient methodology for accurate reliability assessment of electromagnetic devices. To achieve the goal, elaborate surrogated models to approximate constraint functions of interest are generated based on the dynamic Kriging method and a hypercube local window. Then, the Monte Carlo simulation scheme is applied to the surrogate models. This leads to reducing computational cost dramatically without degrading accuracy of the reliability analysis. The validity of the proposed method is tested and examined with a mathematical example and a loudspeaker design.