Jin-Hyeong Kim

Broad-band Multi-layered Radar Absorbing Material Design for Radar Cross Section Reduction of Complex Targets Consisting of Multiple Reflection Structures

An optimum design process of the broad-band multi-layered radar absorbing material, using genetic algorithm, is established for the radar cross section reduction of a complex target, which consists of multiple reflection structures, such as surface warships. It follows the successive process of radar cross section analysis, scattering center analysis, radar absorbing material design, and reanalysis of radar cross section after applying the radar absorbing material. It is demonstrated that it is very effective even in the optimum design of the multi-layer radar absorbing material. This results from the fact that the three factors, i.e.. the incident angle range, broad-band frequencies, and maximum thickness can be simultaneously taken into account by adopting the genetic algorithm.

A Study on the Effective Scattering Center Analysis for Radar Cross Section Reduction of Complex Structures

Scattering center extraction schemes for radar cross section reduction of large complex targets, like warships, was developed, which are an 1-D radar image method(range profile), and a direct analysis based on an object precision method. The analysis result of partial dihedral model shows that the presented direct analysis method is more efficient than the 1-D radar image method for scattering center extraction of interested targets, in terms of radar cross section reduction design, not signal processing. In order to verify the accuracy of the direct analysis method, a scattering center analysis of an naval weapon system was carried out, and the result was coincident with that of another well-known RCS analysis program. Finally, an analysis result of RCS and its scattering center of an 120m class warship-like model presented that the direct analysis method can be an efficient and powerful tools for radar cross section reduction of large complex targets.

Propulsion Shafting Alignment Analysis Considering the Interaction between Shaft Deflection and Oil Film Pressure of Sterntube Journal Bearing

선박 추진축계 정렬은 선체 변형 및 프로펠러에 작용하는 편 심 추력 등을 고려한 축계 구성요소의 최적 설계와 배치로 축계 가 이상적인 베어링 반력으로 지지되어 마찰 또는 과부하로 인한 축 지지 베어링 손상이 발생하지 않도록 하는 것이다. 이를 위해 서는 설계 단계에서의 축 지지 베어링의 종류와 배치는 물론 다 양한 하중조건별 선체 변형과 베어링 반력을 고려한 지지 베어링 의 오프셋(offset) 최적화가 필요하다. 한편, 1990년대 초반부터 선박의 대형화, 구조 설계 최적화 및 고장력강 사용의 증가 등으 로 인해 선체 변형은 상대적으로 커진 반면, 추진시스템의 단위 축 처짐과 선미관 저널 베어링 유막 압력의 상호작용을 고려한 추진축계 정렬 해석 조대승 .장흥규1 .진병무2 .김국현3 .김성찬4 .김진형5 부산대학교 조선해양공학과 (주)디섹 구조기본/상세설계부 동명대학교 조선해양공학과 인하공업전문대학 조선해양과 (주)크리에이텍 기술연구소

Instantaneous Environmental Noise Simulation of High-speed Train by Quasi-stationary Analysis

An instantaneous environmental noise simulation method emitted by a moving high-speed train by quasi-stationary analysis is proposed in this study. In the method, the propagation attenuations from stationary point sources on segmented railways to a receiver are calculated using a general purpose environmental noise prediction program ENPro based on the ISO 9613-2 method. Then, the instantaneous environmental noise at a receiver due to a moving high-speed train considering convection effect is evaluated with the information on the propagation attenuations from the instantaneous train location to the receiver and the sound power levels and directivity of stationary point sources evaluated by German Schall 03 (2006). To demonstrate the validity of proposed method, simulated and measured time history of instantaneous noise for KTX-I and KTX-II on running are compared and the results show that the method can be utilized for the train noise source identification as well as the simulation of instantaneous environmental noise emitted by a high-speed train.

Development of a Framework for Improving Efficiency of Ship Vibration Analysis

ABSTRACT Free and forced vibration analysis of the global ship structure using the 3-dimensional finite ele-ment(FE) method requires not only the specialized knowledge such as ship structure interacted with fluid, damping and various excitations due to propulsion system but also time-consuming manual tasks in FE modeling, analysis and response evaluation. As a result, the quality of the vibration analysis highly depends on engineers expertise and experience. In this study, a framework system to improve the efficiency of global ship vibration analysis is introduced. The system promising the uti-lization of MSC/Patran and MSC/Nastran consists of various modules to support data management, FE modeling of ship structure and loading, input deck generation for free and forced vibration analy-sis, data extraction and evaluation of analysis results, and databases for FE models of marine diesel engines and vibration criteria. The system may be useful for pursuing standardization of uncertain analysis factors as well as reducing time, cost and human dependency in ship vibration analysis.

Numerical Analysis on the Effect of Long-crested Wave to the RCS of Marine Target

RCS effects of long-crested wave surfaces to marine targets are numerically analyzed using a 4-path model and a direct analysis method, developed based on physical optics and a combined method of physical optics/geometric optics, respectively. Reflectivity of long-crested wave surfaces is described with `Fresnel reflection coefficients` The MPM(modified Pierson-Moskowitz) ocean spectrum is adopted to simulate long-crested waves in the direct analysis method. A numerical analysis of a benchmark model assures the validity of both methods. The direct analysis method is applied to the RCS calculation of electromagnetically large marine targets, which are vertically oriented or slanted to the long crested wave surfaces randomly generated with various significant wave heights. The long-crested wave surface much highly increases the RCS of the marine target, but those effects are decreased as the significant wave height grows up. At low elevation angle, the vertical model has entirely high RCS comparing slanted model, and the RCS of vertical flat plate is the highest on the calm sea surface, while those of slanted flat plates are the lowest on the calm sea surface. The RCS of marine targets on continuously-varying sea surface is more coherent at lower elevation angles, as well.