• Tribology and Lubricants
• /
• 제40권2호
• /
• pp.39-46
• /
• 2024

The Morton effect (ME) is an instability phenomenon occurring in rotating machineries supported by fluid film bearings and is induced by the thermal deformation of the overhung mass, which is a part of the rotating shaft. Herein, we describe the ME during the high-speed balancing test of a 20 MW class steam turbine. Additionally, to predict the rotating speed at which the ME occurs, we apply the sensitivity vector theory for the steam turbine. During the operation of the steam turbine, we observe a continuous increase in vibration and hysteresis near the rated speed, which is typical of the ME. Increasing the temperature of the lubricating oil supplied to the bearings from 40 to 60℃ suppresses the occurrence of the ME. The rotordynamic analysis for the steam turbine suggests the existence of a mode in which the overhung mass undergoes significant deformation near the rated speed, and we presume that such a mode will increase the occurrence of the ME. The predicted rotating speed of ME occurrence, obtained through the sensitivity vector method, correlates with the test results. Moreover, increasing the temperature of the supplied lubricating oil mitigates the occurrence of ME by reducing the sensitivity between the temperature deviation vector and unbalance mass vector.

• Journal of Korea Foresty Energy
• /
• 제17권1호
• /
• pp.47-55
• /
• 1998

In the search for broadband damping composites, it is desirable to have polymers with a broad and high loss region, covering the entire temperature and frequency range of interest. Interpenetrating polymer networks, IPN's, are materials composed of two or more crosslinked polymers intimately and irrevocably interwinded. The resulting distribution of microenviron-ments can result in a materials with a high mechanical loss broad end over that of either polymer component alone. In this study, several series of copolymer, crosslinked copolymer and copolymer/copolymer IPN's were synthesized for possible use as broadband damping materials. Then their dynamic tensile properties were measured and compared with the damping properties of sandwich composites. Dynamic mechanical analysis showed that the temperature of loss peak may be varied over a wide temperature range with formulation. The compatibility of IPN`s was depended on the compatibility of A and B polymers as well as crosslink density. The damping factor(tan ${\delta}_c$) of composites became greater when a polymer of approximate storage module(E`) range of 5X10$^7$ to 10$^9$ dyne/cm$^2$ and large tan ${\delta}$ at the same time was used. The damping properities of poly (2-EHA80-co-St20)/poly(2-EHA20-co-St80) IPN`s crosslinked with 3%-DEGDM were relatively better over a broad temperature range.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• 제18권9호
• /
• pp.418-424
• /
• 2017

Magnesium has a higher specific strength than other metals and is widely used industry wide due to its excellent vibration absorption ability and electromagnetic wave shielding property.For example, it is used for automobile parts such as car seat frames and cylinder heads, and is widely used in electronic products such as notebook cases and mobile phone cases. In addition, it is in the spotlight as a bone-implant material used to assist in the treatment of damaged bones when the bones are cracked or broken. Currently, Ti alloy, stainless steel and Co-Cr-Mo alloy are used as the implant material, and the Mg alloy remains in research stage. The current problem with bone implant implants is that the patients must undergo reoperation to remove the implants after joint surgery. Magnesium, however, can achieve sufficient strength compared to current materials. In addition, since it is self-decomposed after the recovery, reoperation is not necessary. In this paper, Mg alloys were designed by adding harmless Ca and Zn to the human body. In order to improve the strength and corrosion resistance, the final alloy was designed by adding a small amount of Sr as a grain refiner. The radioactive elements of Sr are harmful to the human body, but other naturally occurring Sr elements are harmless. Microstructure analysis of the alloys was performed by optical microscopy and scanning electron microscopy. The mechanical properties and corrosion characteristics were evaluated by tensile test, potentiodynamic test and immersion test.

• 대한공업교육학회지
• /
• 제34권2호
• /
• pp.331-345
• /
• 2009

In this research Sagnac interferometer three different types of mandrel are suggested and this fiber optic sensor is using in monitoring of electric transformer. Vibration characteristics of those mandrels were analyzed and finally more sensitivity mandrel are suggested. Three different mandrels using in fiber optic sensor are hollow cylinder with outer bump, pure hollow cylinder, hollow cylinder with inner bump. Natural frequencies and mode shapes are investigated using finite element method. Mode shape are considered at the frequency range from 2 kHz to 20 kHz. Fundamental dimensions of the hollow cylinder type's mandrel are 30 mm in outer diameter, 50 mm in length, 1 mm in cylinder thickness, $2mm{\times}2mm$ in bump size. Based on the finite element results, when the outer acoustic frequency is near 11 kHz outer bump type and hollow cylinder can get higher sensitivity. Near 17 kHz outer bump and inner bump mandrel can get higher sensitivity. Near 20 kHz hollow cylinder and inner bump mandrel is useful. This results can be applied to design of fiber optic sensor using in monitoring the electrical transformer. Several MHz of outer acoustic frequency can be easily detected using more sensitive mandrel in pursuing expand this technique.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• 제19권5호
• /
• pp.82-88
• /
• 2018

This study investigated the structure of an 8-pole 8-slot linear generator, which acts as an electromagnetic damper by combining the structure of an electromagnetic suspension device capable of generating electrical energy through energy harvesting by absorbing the vibration energy from the road surface while driving. To compare the energy harvesting effect of the electromagnetic suspension according to the actual road surface, a driving road test was simulated for two actual road conditions, an asphalt road surface and unpacked road surface condition, using a civilian combined vehicle model in conjunction with a vehicle simulation program, Carsim and Simulink. As a result, the relative displacements of the suspensions on the asphalt road surface and the unpaved road were 8 mm and 13 mm, respectively. By applying the suspension displacement value derived by modeling the linear generator coupled to the electromagnetic suspension, the simulation was then performed for an analysis time of 0.3s by applying the same analytical conditions using the commercial electromagnetic analysis program, ANSYS MAXWELL, The average power generation on the unpacked roads and asphalt roads was 198.6W and 98.7W respectively, which was 103.7% higher for unpackaged roads. Finally, to compare the sensitivity of the road surface frequency and the suspension input displacement to the power generation output, the sensitivity of the two variables was 1.725 and 1.283, respectively, and the road surface frequency had a 34.5% higher effect on the average power generation.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• 제41권5호
• /
• pp.375-380
• /
• 2017

This paper reports the results of an acceleration test to predict the contact-induced failure that could occur at the cylinder-to-hole joint for the fuel rod of a sodium-cooled fast reactor (SFR). To incorporate the fuel life of the SFR currently under development at KAERI (around 35,000 h), the acceleration test method of reliability engineering was adopted in this work. A finite element method was used to evaluate the flow-induced vibration frequency and amplitude for the test parameter values. Five specimens were tested. The failure criterion during the life of the SFR fuel was applied. The S-N curve of the HT-9, the material of concern, was used to obtain the acceleration factor. As a result, a test time of 16.5 h was obtained for each specimen. It was concluded that the $B_{0.004}$ life would be guaranteed for the SFR fuel rods with 99％ confidence if no failure was observed at any of the contact surfaces of the five specimens.

• The Bulletin of The Korean Astronomical Society
• /
• 제35권1호
• /
• pp.40.1-40.1
• /
• 2010

The Main payload of the STSAT-3 (Korea Science & Technology Satellite-3), MIRIS (Multipurpose Infra-Red Imaging System) has been developed for last 3 years by KASI, and its Flight Model (FM) is now being developed as the final stage. All optical lenses and the opto-mechanical components of the FM have been completely fabricated with slight modifications that have been made to some components based on the Engineering Qualification Model (EQM) performances. The components of the telescope have been assembled and the test results show its optical performances are acceptable for required specifications in visual wavelength (@633 nm) at room temperature. The ensuing focal plane integration and focus test will be made soon using the vacuum chamber. The MIRIS mechanical structure of the EQM has been modified to develop FM according to the performance and environment test results. The filter-wheel module in the cryostat was newly designed with Finite Element Analysis (FEM) in order to compensate for the vibration stress in the launching conditions. Surface finishing of all components were also modified to implement the thermal model for the passive cooling technique. The FM electronics design has been completed for final fabrication process. Some minor modifications of the electronics boards were made based on EQM test performances. The ground calibration tests of MIRIS FM will be made with the science grade Teledyne PICNIC IR-array.

• Progress in Superconductivity
• /
• 제13권1호
• /
• pp.58-63
• /
• 2011

Recently, superconductor flywheel energy storage systems (SFESs) have been developed for application to a regenerative power of train, a power quality improvement, the storage of distributed power sources such as solar and wind power, and a load leveling. As the high temperature superconductor (HTS) bearings offer dynamic stability without the use of active control, accurate analysis of the HTS bearing is very important for application to SFESs. Mechanical property of a HTS bearing is the main index for evaluating the capacity of an HTS bearing and is determined by the interaction between the HTS bulks and the permanent magnet (PM) rotor. HTS bearing rotor consists of PM and iron collector and the proper dimension design of them is very important to determine a supporting characteristics. In this study, we have optimized a rotor magnet array, which depends on the limited bulk size and performed various dimension layouts for thickness of the pole pitch and iron collector. HTS bearing rotor was installed into a single axis universal test machine for a stiffness test. A hydraulic pump was used to control the amplitude and frequency of the rotor vibration. As a result, the stiffness result showed a large difference more than 30 % according to the thickness of permanent magnet and iron collector. This is closely related to the bulk stiffness controlled by flux pining area, which is limited by the total bulk dimension. Finally, the optimized HTS bearing rotor was installed into a flywheel system for a dynamic stability test. We discussed the dynamic properties of the superconductor bearing rotor and these results can be used for the optimal design of HTS bearings of the 10kWh SFESs.

• Journal of KSNVE
• /
• 제10권6호
• /
• pp.1059-1066
• /
• 2000

In this paper. a new indirect feedback active noise control (ANC) scheme barred on the fundamental frequency estimation is proposed for systems with a harmonic noise. When reference signals necessary for feedforward ANC configuration are difficult to obtain, the conventional ANC algorithms for multi-tonal noise do not measure the reference signals but generate them with the estimated frequencies.$^{(4)}$ However, the beating phenomena, in which certain frequency components of the noise vanish intermittently, may make the adaptive frequency estimation difficult. The confusion in the estimated frequencies due to the beating phenomena makes the generated reference signals worthless. The proposed algorithm consists of two parts. The first part is a reference generator using the fundamental frequency estimation and the second one is the conventional feedforward control. We propose the fundamental frequency estimation algorithm using decision rules. which is insensitive to the beating phenomena. In addition, the proposed fundamental frequency estimation algorithm has good tracking capability and lower variance of frequency estimation error than that of the conventional cascade ANF method.$^{(4)}$ We are also able to control all interested modes of the noise, even which cannot be estimated by the conventional frequency estimation method because of the poor S/N ratio. We verify the performance of the proposed ANC method through simulations for the measured cabin noise of a passenger ship and the measured time-varying engine booming noise of a passenger vehicle.

• Journal of the Korean Applied Science and Technology
• /
• 제33권4호
• /
• pp.802-812
• /
• 2016

Silicone foam is very useful as flame resistant material for many industrial areas such as high performance gasketing, thermal shielding, vibration mounts, and press pads. A silicone foam was prepared through simultaneous crosslinking and foaming by hydrogen condensation reaction of a vinyl-containing polysiloxane (V-silicone) and a hydroxyl-containing polysiloxane (OH-silicone) with hydride containing polysiloxane (H-silicone) in the presence of platinum catalyst and imorganic filler at room temperature. This is more convenient process for silicone foam manufacturing than the conventional separated crosslinking and foaming systems. Funtionalized silicones we used in this experiment were consisted with a V-silicone containing 1,0 meq/g of vinyl groups and a viscosity of 20 Pa-s, an OH-silicone with 0.4 meq/g of hydroxyl groups and a viscosity from 50 Pa-s, and an H-silicone containing 7.5 meq/g of hydride groups and a viscosity of 0.06 Pa.s. The effects of compositions of functionalized silicones and additives, such as catalyst and filler on the structure and mechanical properties of silicone foam were studied. 0.5 wt% of Pt catalyst was enough to accelerate the foaming rate of silicone resins. The addition of OH-silicone with lower viscosity accelerates the initial foaming rate and decreases the foam density, but the addition of V-silicone with lower viscosity reduces the tensile strength as well as the elongation. The final foam density, tensile strength, and elogation of silicone foam prepared under the SF-3 condition increase maximum to $0.58g/cm^3$, $3,51kg_f/cm^2$, and 176 %, repectively. We found out the filler alumina also played an important role to improve the mechanical properties of silicone foams in our foaming system.