• Tribology and Lubricants
• /
• 제40권5호
• /
• pp.151-156
• /
• 2024

Gas foil thrust bearings (GFTBs) support axial loads in oil-free, high speed rotating machinery using gas as a lubricant. However, under low-speed and high-load conditions, such a bearing experiences friction, leading to wear and a reduced lifespan. Therefore, a pressurized GFTB (PGFTB) that combines hydrostatic and hydrodynamic lubrication by supplying pressurized gas through the supply hole of the top foil has been developed, and various studies have been conducted. In this study, we develop mathematical models of PGFTBs with sloped and stepped recesses and predict its load support performance. The PGFTB maintains a minimum film thickness of approximately 20 ㎛ at rest (0 rpm), regardless of the type of recess, indicating a sufficient hydrostatic pressure to lift the runner at a low rotor speed. Furthermore, the minimum film thickness increases slightly as the numbers of feed holes in the in- and outward radial directions relative to the centerline of the PGFTB pad increase. These findings highlight the importance of supply hole placement in enhancing load support performance. As the rotor speed increases, the minimum film thickness increases rapidly, regardless of the number of supply holes, and without pressurization, sufficient hydrodynamic pressure is generated to lift the runner upon exceeding a certain rotor speed. When comparing the sloped and stepped recesses, the PGFTB with the sloped groove exhibits a superior overall load support performance.

• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• 제6권2호
• /
• pp.1-8
• /
• 2010

Nuclear steam generator tubes have experienced wear degradation at tube support structure. Morphology of wear scar was analyzed by using eddy current signal. A burst test facility for steam generator tubes was established and tubes with 3 types of defects were tested. The burst test results show that the depth of wear scar is the main factor influencing the burst pressure of tubes, meanwhile, both the longitudinal length and the angle also have effect on the burst pressure. Based on test results, the burst pressure equation for wear degradation was proposed.

• Tunnel and Underground Space
• /
• 제19권3호
• /
• pp.181-189
• /
• 2009

This study is to evaluate an effect of supports with respect to these supports after comparing the characteristic of support between rock bolt of a widely used type and spiral bolt of a new type. For these purposes, we performed pull-out test in laboratory about rock and spiral bolts in the case of cement-mortar grout curing periods, 7 and 28 days, then calculated pull-out load, displacement, external pressure, inner pressure and shear stress using data obtained from the results of pull-out test, respectively. In relation between pull-out load and displacement, displacement of spiral bolt is larger than one of rock bolt. It is considered that mechanical property of rock bolt is due to larger than one of spiral bolt. In addition, displacement of supports shows nearly same or decreasing with curing periods. We found that because adhesive force between supports and cement-mortar grout is increasing with compressive strength of grout according to curing periods. The inner pressure of spiral bolt is represented larger than one of rock bolt at a step of same pull-out load. It is suggested that spiral bolt is more stable than rock bolt, maintaining stability of ground or rock mass, when supports are installed in a ground or rock mass under the same condition. Putting together with above results, we can consider that spiral bolt as a new support on an aspect of pull-out load and inner pressure is larger than rock bolt in a ground or rock mass under the same condition. Moreover, spiral bolt is more effective support than rock bolt, considering an economical and constructive aspects of supports, as well as ground or rock stability before or after installing supports.

• Journal of Korean Physical Therapy Science
• /
• 제11권4호
• /
• pp.29-37
• /
• 2004

Measurements of plantar pressure provide an indication of foot and ankle function during gait and other functional activities because the foot and ankle provide necessary support and flexibility for weight bearing and weight shifting while people are performing these activities. Plantar pressure is being increasingly used in both research and clinical practice to measure the effects of various footwear and physical therapy intervention. The influence of walking speed and ground inclination on plantar pressure parameters However has not been evaluated in detail. So, in this study to determine the effect of changes in walking speed and ground inclination on plantar pressure treadmills with different walking speeds and inclination were used. Plantar pressure parameters were measured with the Parotec system using the walking and running in 20 healthy participants(10 male, 10 female) aged $20{\sim}28$(mean 22.22, S.D.2.26 years) when slow walking and running. The result of this study with increased die walking speed, the peak pressure of 1st, 5th metatarsal head and total contact time and impulse total at the forefoot was affected by walking speed; however, die peak pressure, contact time and impulse total at the forefoot was not affected by ground inclination.

• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• 제7권1호
• /
• pp.17-26
• /
• 2011

CANDU reactor core is composed a few hundreds pressure tubes, which support and locate the nuclear fuels in the reactor. Each pressure tube provides pressure boundary and flow path of primary heat transport system in the core region. In order to guarantee the structural integrity of pressure tube flaws which can be found by in-service inspection, crack growth and fracture initiation assessment have to be performed. Stress intensity factors are important and basic information for structural integrity assessment of planar and laminar flaws (e. g. crack). This paper reviews and confirms the stress intensity factor of axial crack, proposed in CSA N285.8-05, which is an fitness-for-service evaluation code for pressure tubes in CANDU nuclear reactors. The stress intensity factors in CSA N285.8-05 were compared with stress intensity factors calculated by three methods (finite element results, API 579-1/ASME FFS-1 2007 Fitness-For-Service and ASME Boiler and Pressure Vessel Code Section XI). The effects of Poisson's ratio and anisotropic elastic modulus on stress intensity factors were also discussed.

• Journal of Surface Science and Engineering
• /
• 제37권5호
• /
• pp.289-295
• /
• 2004

A dense palladium-nikel (Pd-Ni) alloy composite membrane has been fabricated on microporous nickel support mixed with submicron/micron nickel powder instead of mesoporous stainless steel support. Plasma treatment process is introduced as pre-treatment process instead of HCI activation. Pd-Ni alloy composite membrane prepared by electro plating was fairly a uniform and dense surface morphology. The membrane was characterized by permeation experiments with hydrogen and nitrogen gases at temperature 773 K and pressure 2.2 psi. The results showed that hydrogen ($H_2$) permeance was 27 ml/$\textrm{cm}^2$ㆍatmㆍmin and hydrogen/ nitrogen ($_H2$$N_2$) selectivity was 8 at 773 K.

• Journal of Information Technology Services
• /
• 제10권1호
• /
• pp.135-149
• /
• 2011

In this paper, we propose the high-risk group detection model for patients with high blood pressure using case-based reasoning. The proposed model can be applied for public health maintenance organizations to effectively manage knowledge related to high blood pressure and efficiently allocate limited health care resources. Especially, the focus is on the development of the model that can handle constraints such as managing large volume of data, enabling the automatic learning to adapt to external environmental changes and operating the system on a real-time basis. Using real data collected from local public health centers, the optimal high-risk group detection model was derived incorporating optimal parameter sets. The results of the performance test for the model using test data show that the prediction accuracy of the proposed model is two times better than the natural risk of high blood pressure.

• Proceedings of the KIEE Conference
• /
• 대한전기학회 2007년도 제38회 하계학술대회
• /
• pp.150-151
• /
• 2007

In hydraulic oil pump system, pressure has a linear relationship with output torque of motor. Torque control of pump drive can easily output stable pressure, and it can retain required pressure at minimum speed to save power consumption. Switched reluctance motor(SRM) has many advantages such as low cost and low inertia. It can generate high torque at low speed. But inherent high torque ripple of SRM influences performance of pressure control in hydraulic oil system. This paper presents direct instantaneous torque control(DITC) of hydraulic oil pump system. DITC method can reduce inherent torque ripple of SRM, and output smoothing torque to load. So the proposed hydraulic oil pump system can support smooth pressure and fast dynamic power supply to the hydraulic pump system. At last the proposed hydraulic oil pump system is verified by computer simulation and experimental results.

• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• 제12권2호
• /
• pp.25-33
• /
• 2016

The thermal stratification phenomenon in the nuclear power plant can cause abnormal deformation of the piping, contact with the support, damage to the support system. Repetition of the thermal stratification phenomenon or variation of the thermal boundary layer can cause thermal fatigue. Thermal stratification phenomenon in nuclear power plants is still an ongoing issue and active research has been carried out. In this paper, the current situation in Korean nuclear power plants is described, followed by the status of research and the future problems on the thermal stratification phenomenon in Korea.

• International Commerce and Information Review
• /
• 제6권3호
• /
• pp.123-136
• /
• 2004

In recent years, although far behind, the "e-Trade (B to G)" is propelled vigorously in Japan. But the diffusion of the "e-Trade" among companies (B to B) represented by bolero.net does not meet expectation. This paper carried out the questionnaire survey to the enterprises, which adopt bolero.net and examined why the diffusion is stagnated to the measures for its future spread. As a result, the top 3 adoption factors are: (1) Transaction climate, (2) Top management support, and (3) Operational improvement. In other words, it depends that top management has the will, which adopts e-trade positively among the reliable business partners and the operational performances can improve efficiently by carrying e-trade. We would like to clarify what will be crucial to spur the diffusion in the future. Based on the findings from the result, the concrete key points to promote the spread are to be indicated as follows: (1) Improve the scores of "Cost" and "Competitive pressure" (2) Improve the institutional factor.