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A Study on Torsional Vibration Characteristics of a Direct Coupled Shaft Generating System on Low-speed Two Stroke Diesel Engine

Hoang Nam Truong

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Abstract Nowadays, developments in world economy have led to drastic changes in strategy operation of the shipping and shipbuilding industries. Because of the great economic benefits, fuel oil saving has been one of the most important goals being pursued. The application of power take-off configura...
Abstract Nowadays, developments in world economy have led to drastic changes in strategy operation of the shipping and shipbuilding industries. Because of the great economic benefits, fuel oil saving has been one of the most important goals being pursued. The application of power take-off configurations are seen to increase fuel economy and are suitable for power generation. In this thesis, the dynamic properties of a shaft generator coupled on a low-speed two stroke diesel engine of an 18,600TEU container vessel is presented. The torsional measurement was performed during official sea trial of the vessel in Mokpo by using modern equipment and EVAMOS program developed by Dynamics Laboratory of Mokpo National Maritime University (MMU) to examine torsional resonance on the propulsion shafting system. Despite of the advantages of increased maximum explosion pressure and mean effective pressure, the risk of several complicated vibration problems due to increased exciting torque and stresses must be concerned. Torsional vibration damper was attached at the free end of crankshaft to adjust natural frequency of the system and reduce torsional vibration as well as protect shafting system. The generator is placed on the intermediate shaft, where the vibration caused by explosion pressure is less than on the main engine. A strain gage was installed on the generator shaft, combine with telemetric system, which were used in order to determine the variation of the vibratory torque. Furthermore, gap sensor was installed on turning wheel to determine angular velocity fluctuation. All measured data was recorded and analyzed by EVAMOS program. Through actual measurement, calculated and measured results can be compared to ensure whether there is any danger or not for the propulsion shafting system when the engine work in both normal firing condition and misfiring condition. In addition, angular velocity fluctuation for each vibration order is proportional to voltage variation. At a certain engine speed, the angular velocity fluctuation of an order can be calculated and compared with the limit on Simons curve to evaluate the quality of electric power produced by the shaft generator and the possibility of connecting this power to the ship main electric network. The result of this study suggests a review on existing classification rules for generator design and the lowering of angular velocity variation limit.
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Table of content
Chapter 1. Introduction ................................................................................ 3
1.1 Literature review .................................................................................... 3
...
Table of content
Chapter 1. Introduction ................................................................................ 3
1.1 Literature review .................................................................................... 3
1.2. Thesis organization ............................................................................... 7
Chapter 2. Shaft generator classification ....................................................... 8
2.1. Shaft generators for low speed two-stroke diesel engines ............. ..... 8
a. Definitions and designations of shaft generators ................................. ... 8
b. PTO advantages ...................................................................................... 10
c. Characteristics of electric power from shaft generators ..................... 10
2.2. Shaft mounted generator ..................................................................... 13
Chapter 3. Torsional Vibration Review .......................................................... 16
3.1. Torsional Vibration Calculation ......................................................... 17
3.2. Equipment for measuring torsional vibration in Dynamics Laboratory ................................................................................................ 23
a. Gap sensor and magnetic sensor............................................................ 23
b. Encoder ................................................................................................ 24
c. A/D board ............................................................................................. 25
d. F/V converter ........................................................................................ 25
e. EVAMOS program ................................................................................. 27
Chapter 4. Case study ................................................................................ 30
4.1. Torsional vibration theoretical analysis ......................... .................... 30
4.2. Vibration measurement and results ............................ ....................... 39
Chapter 5. Conclusion ................................................................................ 49
References .................................................................................................. 51