• 수산해양교육연구
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• 제28권3호
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• pp.645-652
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• 2016

At the initial stage of propulsion shaft design, in line with shaft alignment, an intensified consideration of lateral vibration is needed to verify its operational safety. Recently the alignment problem affecting the lateral vibration has been becoming issues. However, the theoretical method of forced lateral vibration analysis is not cleary established so far and it is about to simply limited among the classification societies and international standards to avoid the blade natural frequency resonance cpm outside of ${\pm}20%$ of engine rpm at MCR. On the other hand, longer center distance between each support bearing shows an affirmative result normally in shaft alignment analysis whereas the blade order resonance speed may cause lowering near the limitation in the aspect of lateral vibration. Therefore, it is required careful attention to engineers as described above. As a method to solve the problem, it is mainly considered that remove forward stern tube bearing. In this paper, based on a medium size container ship case, theoretical study was carried out in the context of the forward stern tube bearing. The various effects and functions of forward stern tube bearing are reviewed and evaluated. Then an guidance note to lead the conclusion is proposed.

• Journal of Advanced Marine Engineering and Technology
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• 제22권5호
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• pp.626-634
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• 1998

Controllable pitch propeller(CPP) is usually adopted for easy and effective engine controls of a ship in a port. Unfortunately the torsional vibration may occur by a certain variation of engine torque and the major resonance peak may exist within the maximum continuous rating(MCR) In these cases an additional stress concentration on the oil passages such as longitudinal slots notches and circular holes of an oil distributor shaft(ODS) occurs by the torsional vibration of the CPP shaft. In this paper an analysis for the fatigue limit of an ODS system of the 5S70MC engine in a crude oil carrier is done by applying FEM and empirical formulas. Furthermore the additional stress on the ODS is investigated by analyzing the torsional vibration of the shaft system and a control method in which a tuning damper is adopted is introduced in the case of the additional stress exceeds the fatigue limit. The validity of analysis method is verified by comparing the results acquired by an actual measurement of the vibratory torque for the above ODS

• Journal of Advanced Marine Engineering and Technology
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• 제34권5호
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• pp.653-660
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• 2010

선미관 베어링은 프로펠러가 회전할 시 슬립을 방지하기 위하여 충분한 간섭량을 가지고 캐스팅에 강제 압입되어야 한다. 선미관 베어링을 캐스팅에 강제 압입 시에 필요한 힘을 계산할 때 사용되어지는 공식은 업체별로 각각 다르며, 계산 시 사용되어지는 요소들의 값도 상이하다. 이에 따라 조선소에서 선미관 베어링 강제 압입력을 계산할 때에는 업체별로 제시된 공식과 재질에 따라 고려되어지는 요소들의 값을 사용하지만 간섭량은 조선소의 경험에 기반한 값을 표준으로 사용하고 있다. 본 논문은 강제 압입법에 의한 시공시에 선미관 베어링에 사용되어지는 피팅관계식을 검토하여 선미관 베어링 업체별로 제시되어지는 값을 기반으로 한 결과를 실제 값과 비교하였다. 그 결과 업체별로 제시한 식이 두께가 두꺼운 실린더 이론을 이용하였음을 알 수 있었다. 특히 J사 및 B사의 경우에는 K사와는 달리 두께가 두꺼운 실린더 이론을 근간으로 하였지만, 두께가 얇은 실린더의 경우에도 사용할 수 있도록 변형하여 사용하고 있음을 알 수 있었다.

• Journal of Advanced Marine Engineering and Technology
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• 제32권1호
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• pp.33-41
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• 2008

Bearing damages by shaft misalignment have frequently been happened in marine ships. Specially. after stern tube bearing damage and failure for large crude oil carriers have been reported several times. However. the bearing reaction of the after stern tube bearing cannot be measured by jack-up test due to the hull structure condition. Therefore, when the jack-up test is used for the bearing reaction measurements, the bearing reaction for the after stern tube bearing obtained from the theoretical calculation method have to be used. In this paper, the shaft alignment on the large oil crude carrier is theoretically calculated and the differences between the calculated and actual installed bearing reaction values are compared. The bearing reactions for forward stern tube bearing and intermediate bearing are calculated by the simple formula using the strain gauge bending moments obtained from the measurements. Their reliability is confirmed by comparing the bearing reactions from jack-up test and the bearing reaction for after stern tube bearing is calculated by the same test. Also, the bearing reactions on the after stern tube bearing, forward stern tube bearing and intermediate shaft bearing under all operating conditions are calculated by using the bending moments obtained from the measurements and it is confirmed that the differences of the bearing reaction for all operating conditions are caused from hull deflection. The results of this study should prove useful for the future projects of the alignment calculation including the hull deflection effectiveness.

• Journal of Advanced Marine Engineering and Technology
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• 제6권2호
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• pp.69-91
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• 1982

The major factors which affect the crankshaft axial vibration are such items as the axial stiffness and mass of crankshaft, the thrust block stiffness, the propeller's entrained water and the exciting and damping forces of engine, propeller and shafting. Among above mentioned items, the axial stiffness and mass of crankshaft, thrust block stiffness and propeller's entrained water were treated in detail in part I, and so in this paper, the rest of above items will be studied. The exciting forces of crankshaft axial vibration are generated mainly from the gas explosion pressure of cylinder, the thrust fluctuation of propeller, and sometimes the torsional vibration of crankshaft induces the crankshaft axial vibration. As for the propeller thrust fluctuation, its harmonic components can be fairly exactly calculated from the experimental results of propeller in the towing tank, but as the calculation process is rather tedious and laborious, the empirical values are ordinarily used. On the other hand, the table of harmonic components of gas pressure has been already published by major slow speed diesel engine makers, but the axial thrust conversion factor of radial force is not unknown yet, and as its estimated value is unreliable, the axial vibration force of gas pressure is uncertain. As the calculation of damping force is very complicated and it includes some uncertain factors, the thoretically estimated amplitudes of axial vibration are much more incorrect in comparison with those of torsional vibrations. Authors have paid special attentions to deriving the theoretical calculation formula of axial conversion factor of radial force and damping force of crankshaft axial vibration and developed a computer program to calculate resonance amplitudes and additional stresses of crankshaft axial vibrations. Also, to check the reliability of the developed computer program, the axial vibrations of three ships' propulsion shaftings were analyzed and their results were compared with those of measured values and makers' results.

• 대한조선학회논문집
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• 제57권3호
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• pp.160-167
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• 2020

A two-stroke diesel engine and a propeller normally adopted in large merchant ships are regarded as major ship vibration sources. They are directly connected and generate various excitation components proportional to the rotating speed of diesel engine. Among the components, the magnitude of two excitation components with the same frequency generated by both engine and propeller can be compensated by the adjustment of their phase difference. It can be done by the optimization of propeller assembly angle but requires a number of burdensome trials to find the optimal angle. In this paper, the efficient estimation method to determine optimal propeller assembly angle is proposed. Its application requires the axial vibration measurement in sea trial and the numerical vibration analysis for propulsion shafting which can be substituted by additional vibration measurement after one-trial modification of propeller assembly angle. In order to verify the validity of the proposed method, the phase difference between two fifth order excitation components generated by both diesel engine and propeller of a real ship is calculated by the finite element analysis and its result is indirectly validated by the comparison of axial vibration responses at intermediate shaft obtained by the numerical analysis and the measurement in sea trial. Finally, it is numerically confirmed that axial vibration response at intermediate shaft at a resonant speed can be decreased more than 87 % if the optimal propeller assembly angle determined by the proposed method is applied.

• Journal of Advanced Marine Engineering and Technology
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• 제40권7호
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• pp.580-586
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• 2016

추진효율 향상을 위해 개발된 초장행정 엔진은 저속에서도 큰 출력을 낼 수 있는 장점이 있는 반면에 이전에 비해 비틀림진동의 기진력은 상당히 증가하였다. 따라서 이전에는 튜닝 휠 또는 플라이휠만으로도 제어가 가능하였던 선박들도 연료절약형 초장행정 엔진이 탑재되는 경우에는 비틀림진동 댐퍼를 적용해야만 제어가 가능하다. 본 논문에서는 비틀림진동 제어를 위해 적용된 점성-스프링 댐퍼의 동특성을 확인하고 해당 축계에 최적 동특성을 갖는 점성-스프링 댐퍼를 설계하여 비틀림진동 특성을 검토하였다. 또한, 일부 엔진증속 지연현상을 지닐 우려가 있는 선박의 경우에는 대상축계의 진동 특성을 고려하여 최적댐퍼 설계이론에 따라 선정된 파라미터를 적절히 조정함으로써 과도한 피로누적에 따른 축 절손현상을 방지할 수 있는 축계 비틀림진동 제어 방안을 제시하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제38권6호
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• pp.632-638
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• 2014

선박용 저속 2행정 디젤엔진의 선체 탑재 후 본체 진동제어를 위한 방법 중 하나로 마찰식 톱브레이싱과 유압식 톱브레이싱의 사용이 널리 이용되고 있으며 이들의 선택은 선주에게 일임되어져 왔다. 특히, 최근에 이르러 톱브레이싱 설치목적에 반하여 선체강성의 상대적 저하는 주 공진회전수를 상용회전수내에 존재하게 만들었고 마찰식 톱브레이싱이 장착된 선박에서 이와 관련된 사고 사례가 보고되었다. 이에 따른 효율적 해결방안으로 다양한 형태의 선박에 대하여 광범위한 진동측정이 제시되었다. 본 논문에서는 이를 바탕으로 톱브레이싱 형식에 따른 엔진 본체 진동의 특성을 확인하였고 엔진 본체 진동을 제어하기 위하여 보다 효율적인 방법에 대하여 고찰하였다.