• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• v.7 no.3
• /
• pp.1-7
• /
• 2011

The analysis shows that the vibration is one of the main reasons of turbine failure. Especially, the problems caused by vibration occur right after retrofit of the turbine-generator and restarting the turbine. Through the case study of high vibration caused by after the turbine trip and restart, turbine vibration was identified to be influenced by startup condition. Turbine startup at high casing temperature right after unscheduled turbine trip cause radial expansion in rotor by contraction in axial direction, while casing continues to contract by steam flowing into casing. Consequently, gap between rotor and casing decrease until to metal contact to cause high vibration. Through the case study of high vibration of turbine-generator system after generator retrofit, it was identified that generator replacement could cause high vibration in turbine-generator system if the influence of generator replacement on entire system was not considered properly. To prevent startup delay caused by high vibration, it is important to keep the gaps at the design standard and start the turbine after thermal equilibrium.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2005.11a
• /
• pp.98-102
• /
• 2005

Most bearing casings are designed to focus on strength and weight of themselves because rotor speed passes through the critical speed when operation begins in large plants such as power plants. And It is treated importantly the relation between rotating frequency of the rotor and the natural frequency of casings to prevent resonance. But there is some cases that it is overlooked for harmonic components above rotating frequency. So we present experimentally a case that harmonic forces may make a resonance on casing fixing probes to measure vibration in a turbine-generator system and the vibration is generated when one component of harmonic forces excites the mode that the natural frequency of a certain bearing casing is close to one of harmonics of basic rotating frequency (1x).

• 한국지구물리탐사학회:학술대회논문집
• /
• 2005.09a
• /
• pp.43-54
• /
• 2005

Care should be taken when performing the P and S wave velocity loggings. Some of them are the effect of casing that is installed to prevent the borehole collapsing when the drilling is done on the loose ground such as soil and/or soft rock, and the discrepancy of the velocities of the same media according to the difference of the source wave frequency spectrum. To overcome these difficulties, the following suggestions are recommended; (1) try a careful drilling technique that can eliminate the necessity of the casing, and (2) apply the logging methods with the proper frequency spectrum that is appropriate to the object of the velocity logging.

• The Korean Journal of Mycology
• /
• v.9 no.1
• /
• pp.7-12
• /
• 1981

Attempts were made to investigate the effects of the temperature and carbon dioxide concentration in the growing room and soil moisture after casing on the mycelial growth, sporophore formation and mushroom yield of Agaricus bisporus (Lange) Sing. The growing room temperature influenced the mycelial growth in the casing layer after casing and the sporophore formation of Agaricus bisporus. The mycelial growth was the rapidest at $30^{\circ}C$ and gradually decreased with the temperature going down, while the sporophore formation and mushroom yield were the best at $25^{\circ}C$. The other factor which affected the mycelial growth and sporophore formation was the moisture content of casing soil. The mycelial growth was the best at 70 percent moisture, and the sporophore formation and mushroom yields were the highest at 60 percent moisture. The concentration of carbon dioxide in the growing room after casing had an important effect upon the mycelial growth in the casing layer and the sporophore formation. When the concentration of carbon dioxide was 0.16 percent, the mycelial growth and the sporophore formation were not inhibited. At 0.5 to 2.0 percent $CO_{2}$ the myceilal growth and the sporophore formation were severely decreased. The sporophore size of the mushroom was the maximum when the room temperature during the vegetative mycelium growth was $20^{\circ}C$ and the moisture content of casing soil was 70 percent.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.08a
• /
• pp.75.2-75.2
• /
• 2008

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.4 no.3
• /
• pp.207-216
• /
• 2002

Conventional Korean tunnel portals require a lot of overburden. For stability reasons, about 1.5 to 2.0 times the tunnel diameter is needed for the height in order to achieve a sufficient arching effect. Thus, considerable movement of earth and support constructions are required which lead to undesirably large changes of and damage to the environment. With a massively designed pipe roof, tunnels at low overburden can be built. To effectively construct pipe roof as an advanced safeguarding method, the following properties are indispensable: stability, insensitivity to settling and drilling accuracy. A new pipe roof method, AT-casing system, has been developed which on the one hand entirely combines the properties mentioned above, and which on the other hand permits the construction of safe, economical and environmentally friendly tunnels at low overburden heights of 3 to 5m.

• Journal of Mushroom
• /
• v.12 no.3
• /
• pp.220-225
• /
• 2014

This study was conducted to set the proper sterilization standards of casing soil for the stable production of button mushroom(Agaricus bisporus) from mushroom disease that occurs in infection of casing soil material. Changes of aerobic bacteria are increased as the longer grow-out period and sharply increased after second flushes. Fluorescence Psuedomonas showed high density at high sterilization temperature and $100^{\circ}C$ treatment has extremely high density at 30 min and 60 min in casing 22 days. Density of thermophilic actinomyces is sharply increase from casing with soil and the highest density at 22 days of casing and rapidly decrease after first flushes. Sterilizing temperature of casing soil affects quality and quantity of button mushroom. Treatment of 60 min, 90 min at $80^{\circ}C$ and 30 min at $100^{\circ}C$ produced the highest mushroom yields, especially mushrooms yields of A grads were the highest at treatment of 90 min at $80^{\circ}C$. Treatment of 60min at $100^{\circ}C$ products many yields, however, this treatment has low economic feasibility for its yields. Sterilizing temperature of casing soil has an effect on generating diseases and insect pests. Treatment of 60 min, 90 min at $80^{\circ}C$ and 30 min $100^{\circ}C$ showed lower incidence than the other treatment. Although treatment of 30 min at $100^{\circ}C$ causes low diseases and mushroom fly damage, it has low mushroom yields. Furthermore, although treatment of 60 min at $100^{\circ}C$ has high mushroom yields, it causes high diseases and mushroom fly damage. Therefore the best conditions for the sterilization of casing soils was 60 min and 90 min at $80^{\circ}C$.

• Geophysics and Geophysical Exploration
• /
• v.9 no.3
• /
• pp.185-192
• /
• 2006

Cares should be taken when performing the P and S wave velocity loggings in engineering and environmental fields. Some of them are the effect of casing, which is installed to prevent the borehole collapsing when the drilling is done on the loose ground such as soil and/or soft rock, and the discrepancy of the velocities of the same media according to the difference of the source wave frequency spectrum. The elastic moduli obtained from the P and S wave velocity logging have the dynamic characteristics. To overcome these difficulties, the following suggestions are recommended; (1) develop and apply a careful drilling technique that can keep the borehole wall without a casing, and (2) apply the logging methods with the suitable frequency bandwidth for the object of the velocity logging. It is important to make the aseismological engineers understand the difference between the dynamic elastic moduli and the static ones obtained from mechanical test, and to advise them to use the information properly.

• Proceedings of the KWS Conference
• /
• 2006.05a
• /
• pp.274-276
• /
• 2006

Weldability of high Cr ferritic steel for $620^{\circ}C$ grade turbin casing were investigated. The effect of carbon content on the cold and hot cracking susceptibility and HAZ softening was determined. The cast steel with higher carbon content showed higher HAZ hardness because of the dissolution of cabonitrides during welding thermal cycle. Moreover, it showed higher solidification cracking sensitivity because of the little S-ferrite formation in weld metal. Both steels showed HAZ softening at $900^{\circ}C$ peak temperature after PWHT.

• The KSFM Journal of Fluid Machinery
• /
• v.15 no.1
• /
• pp.36-40
• /
• 2012

The magnitude of the axial thrust acting on pump bearings has a great influence on the operational reliability and service life of a pump for turbopumps. In the present study, radial vanes are introduced to the pump casing to control the axial thrust by changing the cavity pressure between the impeller and the casing. To investigate the effect of the vanes on the axial thrust of the pump, experimental and computational studies were performed with and without the vanes. It is shown that the vanes reduce the cavity pressure by preventing the flow from rotating with the impeller. Experimental and computational results show similar trend for the axial thrust difference between two cases with and without the vanes. The results show that the cavity vanes are very effective in controlling the magnitude of the axial thrust.