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G/T 500톤급 차도선 추진축계시스템의 비틀림진동 특성과 안전성 평가
송명호(Myeongho Song) 한국소음진동공학회 2019 한국소음진동공학회 논문집 Vol.29 No.6
In South Korea, which is surrounded by the sea on three sides, many passenger and car ferries operate around the coasts where there are many islands. Until recently, passenger and car ferries of the 200 gross tonnage (G/T) class were mainly built by small shipbuilding companies. In recent years, with the improvement of the berth facilities of islands, passenger and car ferries of the 500 G/T class have been built and operated to improve economic and operational efficiency. The propulsion shafting system applied to these ships requires a high speed of more than 1500 r/min and more than 1 MW of power for the main engine system, which consists of two engines and two shafts. In South Korea, D company manufactures and supplies high-speed engines of up to 800 kW depending on market demand, but domestic brand engines of greater power are still difficult to obtain. Therefore, main engines are mostly imported and propulsion shafting systems are designed and manufactured according to the sales policies and guides of various domestic dealers. Furthermore, due to the high prices of main engines, ship owners purchase them directly and supply them to shipyards. Consequently, the overall design of propulsion shafting systems considering torsional vibration is not being performed. As a result, accidents related to the main engine and shafting system occur frequently because the torsional vibration characteristics of the engine are not fully examined. This study evaluates the torsional vibration characteristics and safety of three engine models applied to the propulsion shafting system focusing on the recently increasing number of passenger and car ferries of the 500 G/T class.
프로펠러 가진에 의한 저속 디젤엔진을 갖는 추진축계의 종진동
송명호(Myeongho Song),이돈출(Donchool Lee) 한국소음진동공학회 2019 한국소음진동공학회 논문집 Vol.29 No.6
The axial vibration of propeller-induced excitation can be mostly seen in warships that have high-speed rotation propulsion shafting systems equipped with reduction gears. Coupled torsional and axial vibration is mainly focused on the excitation force that is induced by the cylinder’s gas pressure and the piston’s reciprocating mass in low-speed two-stroke diesel engines with seven or fewer cylinders; more complex vibration modes with one or more nodes can be seen in engines with eight or more cylinders. This thrust variation force caused by the axial vibration is the excitation force of the ship’s deckhouse in the longitudinal direction and has been researched extensively in the past. Recently, super-size containerships have been built that have more than 20 000 TEU. These ships have adopted low-speed diesel engines with 10 or more cylinders as their prime mover and the distance between the propeller and the main engine has increased significantly due to the streamlining of their hulls. As a result, there is the probability of resonance between the propeller’s axial excitation and the second node vibration. While this vibration frequency is rare, the possibility of resonance with the ship’s superstructure can create vibrations in the pipes and various accessories surrounding the main engine and stern tube. In addition, severe vibrations can occur if the natural frequency of these parts and that of the axial vibration are similar, which necessitates installing an additional damper on the intermediate shaft that resembles an axial vibration damper that is attached to the crankshaft free end. This paper intends to research the characteristics of axial vibration through theoretical analysis and measurement data with a focus on the 2nd order axial excitation of the propeller blade number in a propulsion shafting system with a 11G90ME engine as the research model.
송명호(Myeongho Song),이돈출(Donchool Lee) 한국소음진동공학회 2019 한국소음진동공학회 논문집 Vol.29 No.6
The axial vibration of the crankshaft was first introduced in 1940 and related studies were conducted in the 1960s. An axial vibration countermeasure of a de-tuner, similar to a thrust bearing, was applied at an early stage. After the first and second oil shocks in the 1970s, MAN Energy Solutions developed the fuel-saving long-stroke MC engine and they began to apply the axial vibration damper (AVD) in earnest. Around that time, WinGD also developed the RTA engine and started to apply AVD. They installed the AVD as a separate structure on the crankshaft end. Currently, a compact structure is applied to all two-stroke low-speed diesel engines for ships, regardless of the number of cylinders. However, hull vibration caused by thrust variation force resulting from axial vibration is occasionally a problem. There have been studies on the damping adjustment method of AVD to reduce the thrust variation force in specific operation areas. In this paper the AVD was modeled by various functions between a damper and de-tuner. The axial vibration characteristics of a propulsion shaft system using the research model 11G90ME engine were investigated through theoretical analysis and measurement data according to the AVD modeling method. The results indicated that the suitable modeling method of AVD was the combined function of damper and de-tuner.
송명호(Myeongho Song),김경연(Kyoungyoun Kim),손영준(Young-Jun Sohn),양태현(Tae-Hyun Yang) 한국추진공학회 2014 한국추진공학회 학술대회논문집 Vol.2014 No.12
연료전지 시스템 내의 스택의 냉각은 연료전지 성능에 많은 영향을 미친다. 스택 냉각이 원활히 이루어 지지 않으면, 스택내부의 온도분포의 불균형이 생기거나 과열로 인한 부품 손상 및 성능저하 문제가 발생한다. 본 연구에서는 고고도 무인기 연료전지 시스템 내의 스택 적정 온도를 얻기 위한 송풍기의 조건을 알아보기 위해 전산해석을 수행하였다. 속도의 크기, 냉각채널 단면 종횡비와 분리판의 종횡비에 따른 냉각 효과를 조사하였다. 냉각 채널의 유동 진행 방향을 줄이는 분리판 형상을 채택하고 냉각 채널의 단면 형상비를 증가시키면 냉각효과가 증가함을 확인하였다. Proper cooling of PEM fuel cell stack is essential for high performance operation of fuel cell system. Insufficient cooling of the stack can cause significant damage of components due to overheating and also can decrease cell performance by dehydration of the polymer electrolyte. In the present study, we performed a computational analysis to assess the condition of the cooling system to secure the proper temperature in fuel cell stack system for high altitude long endurance (HALE) unmanned aerial vehicle (UAV). Effects of flow velocity from the cooling fan and the cooling channel cross-sectional aspect ratio on the stack temperature and required power input were examined. The present numerical results showed that the cooling efficiency significantly increase with cooling channel cross-sectional aspect ratio. Futhermore, it was shown that replacement of the square bipolar plates to rectangular ones can also reduce the required input power by the cooling system.
Acoustic Emission Signal Monitoring Software for Marine Diesel Engine using MATLAB
Myeongho Song (송명호),QuangDao Vuong(벙광다오),Donchool Lee(이돈출) 한국소음진동공학회 2019 한국소음진동공학회 논문집 Vol.29 No.5
An engine/rotor vibration analysis and monitoring system (EVAMOS; brand name of Dynamic Lab. of Mokpo Maritime University) was developed to measure, monitor, store, and analyze vibration and noise data. It is highly reliable and user-friendly, therefore, it is recommended for hull and diesel engine vibration measurements based on ISO 20283-2, 20283-5, 8528-9, and class rules. To meet current trends, this software has been upgraded by using an acoustic emission sensor (AES) and the MATLAB language. The upgraded version, named EVAMOS AEM, has been developed for high-sampling rate measurements of up to 2 MS/s for each channel . This results in streams of huge amounts of data, which requires a special treatment method. Furthermore, a multithreaded programming algorithm and binary file format were applied. Experiments were conducted during the trial of a ship at sea to diagnose engine trouble concerning high frequency. The AES was installed on the cylinder bodies of the marine diesel engine to detect abnormal vibration signals. In this study, the AES characteristics were analyzed to distinguish two operating conditions of the main engine: engine top bracing (TB) on and engine TB off. In future, problems regarding the turbocharger or lubricating system, etc., can be diagnosed in advance to prevent failure.