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Residual Vibration Suppression of an Under-water Fuel Transport System
Umer Hameed Shah,Mingxu Piao,Jae Young Jeon,Keum-Shik Hong 제어로봇시스템학회 2014 제어로봇시스템학회 국제학술대회 논문집 Vol.2014 No.10
This paper discusses the residual vibration suppression problem of a nuclear fuel transport system (FTS). The FTS is supposed to transport the fuel rods under-water to the desired locations within the plant in the minimum possible time. It has been observed that the rods oscillate at the end of such brisk maneuvers causing an undesirable delay in the operation, and affecting the system’s performance in terms both of productivity and of safety. In this case, input shaping can be used to generate shaped command profiles to transport the rods to the target position with minimum residual vibrations, however, due to the under-water maneuver the process becomes damped and input shaping becomes ineffective. Recently, a modified shaped command has been proposed based on the zero vibration (ZV) shaper, which effectively suppresses the rod’s residual vibrations in the presence of the hydrodynamic forces. In this paper, the said command is experimentally investigated with variations in its structure in order to get an insight into its capability of suppressing residual vibrations effectively.
Active Vibration Control of a Flexible Rod in Water
Umer Hameed Shah,Mingxu Piao,Gyoung-Hahn Kim,Keum-Shik Hong 제어로봇시스템학회 2017 제어로봇시스템학회 국제학술대회 논문집 Vol.2017 No.10
This paper addresses the vortex-induced vibration (VIV) suppression problem of nuclear fuel rods, which are transported by a refueling machine (RM) to given reactor locations in water. First, Hamilton’s principle is used to develop the equations of coupled motions of the RM and the fuel rod. The resulting equations of the hybrid (lumped-mass RM and distributed-parameter flexible rod) system are then utilized to investigate the VIVs of the fuel rod upon the movements of the RM. Then, a boundary control scheme is developed to suppress the VIVs of the rod in the course of its transportation in water. Furthermore, Lyapunov function-based stability analyses are performed to prove the uniform ultimate boundedness of the closed-loop system, considering the influence of the nonlinear hydrodynamic force acting on the fuel rod. Finally, simulations are performed to demonstrate the effectiveness of the proposed boundary control scheme.
High temperature ablation resistance of ZrN<sub>p</sub> reinforced W matrix composites
Umer, M.A.,Lee, D.,Ryu, H.J.,Hong, S.H. MPR Pub. Services 2014 INTERNATIONAL JOURNAL OF REFRACTORY METALS AND HAR Vol.42 No.-
For the purpose of improving the high temperature ablation resistance of tungsten-based materials, a new class of composites was fabricated using particulate ZrN as reinforcement. The high temperature ablation behavior of the composites was investigated using oxyacetylene torch. Three different volume contents (up to 30vol.%) of ZrN were added to tungsten. It was observed that the addition of ZrN particles significantly enhanced the ablation resistance of the tungsten composites. Higher volume fraction of ZrN particles resulted in lower ablation rates. It was observed that ZrN particles, when exposed to the flame, formed a stable oxidation layer of ZrO<SUB>2</SUB> on the surface of the sample. This layer prevents further damage to the tungsten matrix, thus resulting in lower ablation rates. The effect of ZrN reinforcement content on the thermal behavior of the tungsten-based composites was also investigated. Thermal conductivity of the composites was seen to decrease as a function of temperature and reinforcement content. Lower values of thermal conductivity are helpful in enhancing the elevated temperature performance of the composites.
Mining Pool Selection Strategy in Blockchain Networks: A Probabilistic Approach
Umer Majeed(우머 마지드),Kitae Kim(김기태),Choong Seon Hong(홍충선) 한국정보과학회 2020 정보과학회 컴퓨팅의 실제 논문지 Vol.26 No.6
풀 마이닝은 블록 체인 네트워크에 대한 솔로 마이닝에서 매우 다양한 보상에 대한 솔루션이며 풀 마이닝 에서 채굴자들은 마이닝 풀을 형성하고 꾸준한 보상 획득을 위하여 얻은 보상을 풀 정책에 따라 분배한다. 본 논문에서는 기존의 채굴 풀 중 하나와의 합동을 추구하는 새로운 마이닝 패러다임을 제안한다. 이러한 마이닝 풀 간 합병을 위하여 후보 마이닝 풀 중 가장 높은 승리 확률에 대한 기준을 설정하였으며 새로운 마이닝 엔터프라이즈와 통합하기 위한 마이닝 풀 선택에 대한 문제를 공식화하였다. 시나리오를 설정을 통한 시뮬레이션 결과 전파 지연 및 승리 확률에 대해 블록의 크기가 영향을 미치는 것을 확인하였으며 승리 확률과 경험적 분석을 기반으로 새로운 통합을 위한 최적의 마이닝 풀을 선택하였다. Pool mining is the solution to the highly variant reward incentive in solo-mining for blockchain networks. In pool mining, miners collaborate to form mining pools and distribute the earned rewards in accordance with pool policies to earn a steady income. In this paper, we considered a paradigm for a new mining enterprise seeking amalgamation with one of the existing mining pools. We set the criteria of the highest winning probability with respect to other mining pools for such a merger. We formulated our problem for the selection of a mining pool for consolidation with the new mining enterprise. The simulation for a case scenario shows the influence of block size on propagation delay and winning probability. Finally, we selected the optimal mining pool for consolidation with the new mining enterprise based on winning probability and empirical analysis.