• The korean journal of orthodontics
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• v.34 no.1 s.102
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• pp.83-91
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• 2004

This study was performed to examine treatment efficiency and patient discomfort rate according to used handpiece speed in clean-up technique. Brackets were bonded to extracted human premolar(50 teeth). After debonding, 50 extracted human premolar were divided Into each two groups(low speed handpiece group with tungsten carbide bur and high speed handpiece group with ultra-fine diamond finishing bur) of 25 according to used handpiece speed in clean-up technique. In clean-up procedure, teeth vibration and pulp thermal changes were measured. After clean-up procedure, the enamel surfaces of randomly selected 10 teeth from each two groups were taken by SEM and evaluated. The findings of this study were as follows ; 1. During resin removal, tooth vibrations of various amplitude in low speed handpiece group were more than those of high speed handpiece. 2. The pulpal thermal changes of high speed handpiece group were significantly higher than those of low speed handpiece group, also the resin removal time in high speed handpiece group was almost as twice as in low speed handpiece group. 3. The figures of SEM to enamel surfaces after resin removal showed that notches and resin remnants in high speed handpiece group were more than those in low speed handpiece group.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.10
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• pp.985-993
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• 2015

Free-piston Stirling engines (FPSEs) have attracted much attention in the renewable energy field as a key device in the conversion from thermal to mechanical energy, and in the recycling of waste energy. Traditional Stirling engines consist of two pistons that are connected by a mechanical link, while FPSEs are formed as a vibration system by connecting each piston to a spring without a physical link. To ensure the correct design and control of operations, this requires elaborate dynamic-performance predictions. In this paper, we present the performance-prediction methodology using a linear and nonlinear dynamic analytical model considering the external load of FPSEs. We perform linear analyses to predict the operating point of the engine using the root locus technique. Using nonlinear analysis, we also predict the amplitude of pistons by performing numerical integration considering both the linear and nonlinear damping terms of the external load. We utilize the predicted dynamic behavior to predict the engine performance. In addition, we compare the experiment results and existing model predictions for RE-1000 to verify the reliability of the analytical model.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.5
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• pp.375-380
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• 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.

• Progress in Superconductivity
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• v.13 no.1
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• pp.58-63
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• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.6
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• pp.477-483
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• 2015

Investigations into cavity flows have been conducted for noise and vibration problems that arise in cavity systems. Cavity systems have been applied in engineering devices and have undergone rapid development in the aerospace industry. Meanwhile, to the author's best knowledge, the cavity on a curved wall has been seldom studied. The present work is conducted to study the flow physics of a cavity mounted on a curved wall. Numerical analysis is performed to investigate the cavity flow. Two variables of sub- and supersonic cavity flows were considered: the radius of curvature of the curved wall (L/R) and the inlet Mach number. The results show that the uniform vortex generated by the cavity flow on the curved wall stabilize the pressure fluctuation as time passes. As the inlet Mach number increases, the pressure fluctuation amplitude increases. The results obtained from the curved wall are compared with those from a straight wall using Rossiter's formula. The Strouhal number of the curved wall is lower than that of the straight wall. Lower Strouhal numbers have been obtained in the present computational fluid dynamics (CFD) results than in the theoretical results using Rossiter's formula.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.15 no.5
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• pp.95-107
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• 2016

The axle weight of a vehicle in motion can be measured with a low-speed or high-speed weigh-in-motion (WIM). However, the axial load dynamically change depending on the vehicle's characteristics-such as the chassis or axle structure-or the characteristics of the driving environment such as road flatness. The changes in dynamic load lead to differences between the vehicle's weight measured at rest and the vehicle's weight measured in motion. For this Study, an experiment was conducted with an instrumented vehicle to analyze the range of errors caused by uncontrollable environmental factors by identifying the characteristics of the dynamic load changes of a vehicle in motion, and determine the appropriate scale for the accuracy evaluation of a high-speed WIM, as a preparatory research for the introduction of unmanned overweight enforcement systems in the future. The key findings from the experiment are summarized as follows. First, The gross weight of the tested vehicle changed by approximately 1% at low velocities and approximately by 4% at high velocities, and the vehicle's axle weight changed by approximately 1-3%, at low velocities and by 2-9% at high velocities. A single axle showed larger weight changes than individual axles in a group. Secondly, The vehicle's gross weight and the axle weight on the impact section were up to eight times and three-to-twelve times higher, respectively, than its gross weight and the axle weight on the flat section. The vibration frequency of the vehicle's dynamic load was measured at between 2.4 and 5.8Hz, and found to return to the normal amplitude after moving approximately 30 meters.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.120-127
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• 2016

This study examined the dynamic characteristics of the gate to identify the optimal gate installation direction according to the installation direction. A 1:31 scale model was constructed for a 47.5m prototype gate using acrylic. The scaled weights were tuned by adding lead weights. The first step was to measure the natural frequencies of the model gates, and compare them with finite-element analysis of the prototypes as a calibration. The scaled model was tested in a 1.6 m wide concrete flume for two orientations to determine the effects of the gate orientation on structural vibrations. Vertical vibrations were measured under a range of operational conditions, including a range of bottom opening heights and different upstream and downstream water levels. For large bottom opening heights in the normal direction, relatively large vibrations were induced by vortices shed at the plate bottom that would strike the horizontal truss member. This phenomenon was avoided in the reverse direction. For small bottom opening heights in the normal direction, these vibrations were caused by a suction force that developed at the gate bottom. The gate model in the reverse direction was preferred because of its low overall vibrational response under general gate opening and flow level combinations.

• Journal of the Korean Geotechnical Society
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• v.38 no.12
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• pp.19-28
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• 2022

Cavities behind concrete walls can adversely affect the stability of structures. Thus study aims to detect cavities behind concrete structures using a microphone in a laboratory model test. A small-scale concrete wall is constructed in a chamber, which is composed of a reinforced concrete plate and dry soil. A plastic bowl is then placed between the plate and soil to simulate a cavity behind the concrete structure. Leaky surface acoustic waves are generated by impacting the concrete plate using a hammer and are measured using a microphone. The measured signals are analyzed using natural frequencies, and cavity-free sections are evaluated. The test results show that the first natural frequency decreases at the cavity section due to the flexural vibration behavior of the plate. In addition, the amplitude corresponding to the first natural frequency decreases as the measurement location becomes farther from the cavity center and significantly decreases at the measurement locations near the rebars. This study demonstrates that a microphone may be useful to detect cavities behind concrete walls.

• Korean Chemical Engineering Research
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• v.60 no.2
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• pp.249-254
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• 2022

With the rapid advance of the semiconductor and Information and communication technologies, remote environment monitoring technology, which can detect and analyze surrounding environmental conditions with various types of sensors and wireless communication technologies, is also drawing attention. However, since the conventional remote environmental monitoring systems require external power supplies, it causes time and space limitations on comfortable usage. In this study, we proposed the concept of the self-powered remote environmental monitoring system by supplying the power with the levitation-electromagnetic generator (L-EMG), which is rationally designed to effectively harvest biomechanical energy in consideration of the mechanical characteristics of biomechanical energy. In this regard, the proposed L-EMG is designed to effectively respond to the external vibration with the movable center magnet considering the mechanical characteristics of the biomechanical energy, such as relatively low-frequency and high amplitude of vibration. Hence the L-EMG based on the fragile force equilibrium can generate high-quality electrical energy to supply power. Additionally, the environmental detective sensor and wireless transmission module are composed of the micro control unit (MCU) to minimize the required power for electronic device operation by applying the sleep mode, resulting in the extension of operation time. Finally, in order to maximize user convenience, a mobile phone application was built to enable easy monitoring of the surrounding environment. Thus, the proposed concept not only verifies the possibility of establishing the self-powered remote environmental monitoring system using biomechanical energy but further suggests a design guideline.

• Proceedings of the KOR-BRONCHOESO Conference
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• 1983.05a
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• pp.11.2-11
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• 1983

Vocal nodules and polyps are much more frequent in singers, public speakers, teachers and actors. Voice trauma and voice misuse, at times associated with mild inflammatory reaction, appear to be important in their etiology. It is generally agreed that vocal cord nodules and polyps are inflammatory in nature and they arise in the subepithelial layer of loose connective tissue of the vocal cord. Since the junction of anterior and middle thirds of the membranous cord and has the greatest amplitude of vibration. This is the site of predilection for vocal cord nodules. The author performed laryngomicrosurgery for 70 cases of vocal nodules and polyps at Ewha Womans University Hospital during the period of 5 years. The result obtained were as follows ; 1) Surgical excision is not necessarily the best approach because vocal nodules in the early stages will resolve with the simplest voice therapy. 2) In children, surgery is rarely indicated because most nodules in children regress during adolescence. 3) For patients who use their voices professionally, voice therapy is indicated for three months. 4) If after three month of conservative treatment the cord lesion does not improve and the patient it still dissatisfied with his voice, laryngomicrosurgery can then be considered. 5) The small cuffed endotracheal tube in the interarytenoid space helps to keep the cords immobile and in an abducted position. 6) Removal of the nodule shoule be started by gentle retraction posteriorly and as soon as a tear appears anterior to the nodule. 7) On occasion it is preferable to start the dissection with a siccle knife while the nodule is held on the stretch. 8) Voice rest should be maintained for a week following which the free edges of the cords are usually healed.