• Journal of the Society of Naval Architects of Korea
• /
• v.54 no.2
• /
• pp.161-169
• /
• 2017

Recently, ship owners have been requiring the assessment of the maneuverability of twin-screw ships under mechanical failures. Because this kind of assessment has not yet been conducted, it is necessary to study the types of machinery failures that can significantly affect the maneuverability of a ship, and to construct a procedure to simulate the maneuvering behavior under such failures. In this paper, the sole focus is the steering system failure from among the variety of failure types, and the maneuvering behavior of the ship under the single rudder failure is simulated for an investigation of the unique characteristics. First, the mathematical model for the twin-screw container ship is verified by comparing the simulated results for the $35^{\circ}$ turning test, $10^{\circ}/10^{\circ}$ zigzag test, and $20^{\circ}/20^{\circ}$ zigzag test under the normal operating condition with those obtained from free running model tests. After the IMO maneuvering tests are additionally simulated under the single rudder failure, the results are reviewed to investigate the maneuvering characteristics that are due to the failure. Further, the $35^{\circ}/35^{\circ}$ zigzag test and the $35^{\circ}$ turning test are simulated to additionally investigate the effects of the single rudder failure on the steering and turning abilities.

• The KSFM Journal of Fluid Machinery
• /
• v.8 no.6 s.33
• /
• pp.15-25
• /
• 2005

Check valves playa vital role in the operation and protection of nuclear power plants. Check valves failure in nuclear power plants often lead to a plant transient or trip. The analysis of historical failure data gives information on the populations of various types of check valves, the systems they are installed in, failure modes, effects, methods of detection, and the mechanisms of the failures. A majority of check valve failures are caused by improper application. The experimental apparatus is designed and installed to measure the disc positions with flow velocity, Vopen and Vmin for 3 inch and 6 inch swing check valves. The minimum flow velocity necessary to just open the disc at a full open position is referred to as Vopen, and Vmin is defined as the minimum velocity to fully open the disc and hold it without motion. In the experiments, Vmin is determined as the minimum flow velocity at which the back stop load begins to increase after the disc is fully opened or the oscillation level of disc is reduced below $1^{\circ}$. The results show that the Vmin velocities for 3 inch and 6 inch swing check valves are about 27.3% and 17.5% higher than the Vopen velocities, respectively.

• 유체기계공업학회:학술대회논문집
• /
• 2002.12a
• /
• pp.548-553
• /
• 2002

• International Journal of Fluid Machinery and Systems
• /
• v.6 no.2
• /
• pp.87-93
• /
• 2013

In order to study the effect of the fluid-structure interaction (FSI) on the simulation results, the external characteristics and internal flow features of a diffuser pump were analyzed with a two-way flow solid coupling method. And the static and dynamic structure analysis of the blade was also caculated with the FEA method. The steady flow field is based on Reynolds Averaged N-S equations with standard $k-{\varepsilon}$ turbulent model, the unsteady flow field is based on the large eddy simulation, and the structure response is based on elastic transient structural dynamic equation. The results showed that the effect of FSI on the head prediction based on CFD really exists. At the same radius, the van mises stress on the nodes closed shroud and hub was larger than other nodes. A large deformation region existed near inlet side at the middle of blades. The strength of impeller satisfied the strength requirement with static stress analysis based on the fourth strength theory. The dynamic stress varied periodically with the impeller rotating. It was also found that the fundamental frequency of the dynamic stress is the rotating frequency and its harmonic frequency. The frequency of maximum stress amplitude at node 1626 was 7 times of the rotating frequency. The frequency of maximum stress amplitude at node 2328 was 14 times of the rotating frequency. No matter strength failure or fatigue failure, the root of blades near shroud is the key region to analyse.

• 유체기계공업학회:학술대회논문집
• /
• 2005.12a
• /
• pp.607-612
• /
• 2005

Check valves playa vital role in the operation and protection of nuclear power plants. Check valves failure in nuclear power plants often lead to a plant transient or trip. An overview of the failure history of check valves needs to identify key area where resources can be best applied to further improve their reliability, and provide cost effective means for failure reduction. The analysis of historical failure data gives information on the populations of various types of check valves, the systems they are installed in, failure modes, effects, methods of detection, and the mechanisms of the failures. The results presented are based on information derived from operating records, nuclear industry reports, manufacturer supplied information. A majority of check valve failures are caused by improper application. Failure modes are identified for swing and lift check valves. Failures involving improper seating and valve disc stuck comprised the largest percentage of failures.

• Journal of Applied Reliability
• /
• v.13 no.3
• /
• pp.165-174
• /
• 2013

Thruster break for aerogenerator performs a role that is stopping the rotor in case of emergency such as strong wind, system abnormality or maintenance check. In this study, failure analysis and test evaluation on the thruster break for aerogenerator are proposed, and the entire process to improve reliability of the product through design improvement is presented. The typical failure case is fatigue and wear, and failure cause on these are identified and improvement plan is presented. Lastly, reliability improvement is established to analyse test results before after the life test.

• Geomechanics and Engineering
• /
• v.30 no.5
• /
• pp.401-411
• /
• 2022

To obtain the dynamic mechanical properties, fracture modes, energy and brittleness characteristics of Furong Baijiao coal rock, the dynamic impact compression tests under 0, 4, 8 and 12 MPa confining pressure were carried out using the split Hopkinson pressure bar. The results show that failure mode of coal rock in uniaxial state is axial splitting failure, while it is mainly compression-shear failure with tensile failure in triaxial state. With strain rate and confining pressure increasing, compressive strength and peak strain increase, average fragmentation increases and fractal dimension decreases. Based on energy dissipation theory, the dissipated energy density of coal rock increases gradually with growing confining pressure, but it has little correlation with strain rate. Considering progressive destruction process of coal rock, damage variable was defined as the ratio of dissipated energy density to total absorbed energy density. The maximum damage rate was obtained by deriving damage variable to reflect its maximum failure severity, then a brittleness index BD was established based on the maximum damage rate. BD value declined gradually as confining pressure and strain rate increase, indicating the decrease of brittleness and destruction degree. When confining pressure rises to 12 MPa, brittleness index and average fragmentation gradually stabilize, which shows confining pressure growing cannot cause continuous damage. Finally, integrating dynamic deformation and destruction process of coal rock and according to its final failure characteristics under different confining pressures, BD value is used to classify the brittleness into four grades.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
• /
• v.5B no.1
• /
• pp.78-83
• /
• 2005

Currently in Japan, the use of the small wind turbine is an upward trend. There are already many well established small wind turbine generators in use and their various failures have been reported. The most commonly sighted failure is blade damage. Thus the research purpose was set to develop a simple failure diagnostic system, where an Acoustic Emission (AE) signal was produced from the failure part of a blade which was measured by AE sensor. The failure diagnostic technique was thoroughly examined. Concurrently, the damage part of the blade was imitated, the AE signal was measured, and a FFT(Fast Fourier Transform) analysis was carried out, and was compared with the output characteristic. When one sheet of a blade was damaged 40mm or more, the level was computed at which failure could be diagnosed.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1992.10a
• /
• pp.325-329
• /
• 1992

The development of automatic production system have required intelligent diagnostic and monitoring function to repair system failure and reduce production loss by the failure. In order to perform accurate functions of intelligent system, inference about total system failure and fault analysis due to each mechanical component failures are required. Also the solution about repair and maintenance can be suggested from these analysis results. Generally, bearing is a essential mechanical component in the machinery. The bearing failure is caused by lubricant system failure, metallurgical defficiency, mechanical condition(vibration overloading misalignment), environmental effect. This study described roller bearing fault train due to stress variation and metallurgical defficiency from lubricant failure by using FTA.

• Tribology and Lubricants
• /
• v.25 no.5
• /
• pp.324-329
• /
• 2009

In this study a complex design fitness analysis of journal bearings is carried out for the LPLi rotary-vane fuel pump application, as an external and horizontal installation, in LPG vehicles. Bearings considered in the analyses are plain and 3-axial groove journal bearings. Upon reflecting the fact that the primary failure mode of bearings in the application is a premature friction and wear failure of bearing metal due to a very low viscosity of liquid fuel LPG as a bearing lubricant, the performance factors of bearings used in an evaluation process of design fitness are a load carrying capacity and vibration suppression ability relative to a rated speed. At this time the design variables of bearings are a radial clearance and length. Results show that, in terms of both of the load carrying capacity and vibration suppression ability, the plain journal bearings are superior to the 3-axial groove journal bearings and among the plain bearings the smaller the bearing clearance (5>10>$15\;{\mu}m$) is and the longer the bearing length (6<8<10<12<14 mm) is, the better the bearing performance is.