• Journal of Biomedical Engineering Research
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• v.13 no.3
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• pp.235-244
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• 1992

In this paper, fluttering behavior of mechanical monoleaflet tilting disc heart valve prostheses during the opening phase was analyzed taking into consideration the impact between the occluder and the guiding strut at the fully open position. The motion of the valve occluder was modeled as a rotating system, and equations were derived by employing the moment equilibrium principle. Forces due to lift, drag, gravity and buoyancy were considered as external forces acting on the occluder. The 4th order Runge-Kutta method was used to solve the governing equations. The results iimonstrated that the occludes reaches steady equilibrium position only after damped vibration. Fluttering frequency varies as a function of time after opening and is in the range of 8-84 Hz. Valve opening appears to be affected by the orientation of the valve relative to gravitational force. The opening velocities are in the range of 0.65-1.42m/sec and the dynamic loads by impact of the occludes and the strut are in the range of 90-190 N.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.3 s.246
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• pp.230-237
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• 2006

Flows in the cavity with pump out vane are calculated using the CFX-Tascflow CFD code. flow calculations are performed for different values of vane height, numbers, leakage flow rate, and rotational speed. The flow is very complex and three dimensional with strong vortex and leakage flow over the vane. The variations of pressure coefficient and K-factor with these parameters and resulting effects on the thrust and torque are studied. The present study contributes to showing the capability of flow simulation of back cavity with pump-out vane. The calculated results are good enough to be used back cavity design.

• Journal of the Korea Institute of Military Science and Technology
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• v.21 no.6
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• pp.790-798
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• 2018

Discrete noise signals from a small scale tactical unmanned aerial vehicle(UAV) propeller were predicted numerically using time domain approach. Two-bladed 29 inch propeller in diameter and 150 kgf in gross weight were used for main parameters of the UAV based on the actual size of the similar scale vehicle. Panel method and Farassat formula A1 were adopted for aerodynamic and aeroacoustic analysis respectively. Time domain signals of both thickness and loading noises were transformed into frequency domain to analyze the discrete noise characteristics. Directivity pattern in a plane perpendicular to the rotating disc plane and attenuation of noise intensity according to double distance were also presented.

• Membrane Journal
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• v.6 no.2
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• pp.86-95
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• 1996

Rotary disc ultrafiltration module(RDM) was developed for the separation of oil e$$\mu$sions. This module was devised to reduce the gel polarization phenomenon by decoupling the operation pressure and the surface velocity of solution in ultrafiltration(UF) processes. The rotary disc membrane consists of 3mm-thick ABS plate covered with UF membrane (UOP, U.S.A.). When the angular velocity($\omega$) was increased, the pure water flux was slightly decreased due to pressure drop caused by centrifugal force and slip flow at the surface of membrane. The pressure drop was proportional to the square of linear velocity(${\omega}r$). When the angular velocity was changed from 52.36rad/s to 2.62rad/s, the flux decline for 5% cutting oil in one-shaft RDM at $25^{\circ}C$ and 0.1MPa was 30.16%. In the lower concentrations, angular velocity tends to give less effect on the flux. Flux(J; $kg/m^{2} \cdot s$) in a rotating disc module is mainly a function of the bulk concentration($C_{B}$; %), the linear velocity(${\omega}r$; m/s) and the effective transmembrane pressure($\Delta P_{T}$ ; Pa). Using a modified resistance-in-series model, the flux data of cutting oil experiments were fitted to give the following equation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.4
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• pp.379-384
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• 2014

The most critical rotating parts of a gas turbine engine are turbine blades and disc, given that they must operate under severe conditions such as high turbine inlet temperature, high speeds, and high compression ratios. Owing to theses operating conditions and high rotational speed energy, some failures caused by turbine disks and blades are categorized into catastrophic and critical, respectively. To maximize the margin of structural integrity, we aim to optimize the vulnerable area of disc-blade interface region. Then, to check the robustness of the obtained optimized solution, we evaluated structural reliability under uncertainties such as dimensional tolerance and fatigue life variant. The results highlighted the necessity for and limitations of optimization which is one of deterministic methods, and pointed out the requirement for introducing reliability-based design optimization which is one of stochastic methods. Thermal-structural coupled-filed analysis and contact analysis are performed for them.

• Bulletin of the Korean Chemical Society
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• v.16 no.9
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• pp.819-823
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• 1995

Thin films of two kinds of Prussian Blue (PB)-modified, using iron(Ⅲ) complex instead of conventional FeCl3, were prepared on a gold substrate and these films were able to be electrochemically reduced in potassium nitrate solution. In case of PB-modified films prepared from Fe(Ⅲ)-ethylenediamine-N,N'-diacetic acid (FeEN3+)/K3Fe(CN)6 solution, the mid-peak potential was 0.156 V in 0.1 M KNO3 and it was found that potassium ion migrates into or out of the film during the electrolysis. These films were shown to be electrochromic. These films exhibited smaller peak separation than those formed from Fe(Ⅲ)-tartaric acid (FeTA3+)/K3Fe(CN)6 system. The diffusion coefficient of Fe(CN)63-/4- redox couple, evaluated using the fabricated Au rotating disc electrode(rde) previously reported, was in good agreement with the existing data. Two experimental procedures, including the voltammetry at relatively low scan rates and the rde study, have been used in order to characterize the electrode kinetics. The electrode kinetics of some redox couples (FeEN2+-FeEN3+ and FeTA2+-FeTA3+) on both PB-modified thin films and bare Au electrode were studied using a Au rde. In all cases the rate constants of electron transfer obtained with the PB-modified film electrodes were only slightly less than those obtained for the same reaction on bare Au disc electrodes. The conductivities, as determined from the slopes of the i-V curves for a ca. 1 mm sample for dried PB-modified potassium-rich and deficient bulk samples pressed between graphite electrodes, were 6.21 × 10-7 and 2.03 × 10-7(Ω·cm)-1, respectively.

• Journal of Aerospace System Engineering
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• v.13 no.3
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• pp.56-63
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• 2019

Performance analyses were performed on a propeller developed for use in a PAV (Personal Air Vehicle) under 600 kg Maximum Take-Off Weight (MTOW). The actuator disc theory and CFD analyses were used to estimate the hovering time with regards to MTOW variation for a given battery weight. The interference induced power factor kint was introduced to account for the effect of flow interference between the propellers and to estimate the performance of counter-rotating propellers. The Maximum Figure of Merit (FM) value of the propeller pitch was determined and the design RPM range for the required power inversely obtained from the CFD results. Previous research indicate that the flight time of large multi-copter is limited by the available battery energy density. Similarly, the propeller pitch settings and spacing are important factors in reducing the kint value.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.6_1
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• pp.881-888
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• 2020

A butterfly valve is a valve that adjusts flow rate by rotating a disc for about 90° with respect to the axis that is perpendicular to the flow path from the center of its body. This valve can be manufactured for low-temperature, high-temperature and high-pressure conditions because there are few restrictions on the used materials. However, the development of valves that can be used in a 600℃ environment is subject to many constraints. In this study, the butterfly valve's stability was evaluated by a fluid-structured interaction analysis, thermal-structure interaction analysis, and seismic analysis for the development of valves that can be used in high-temperature environments. When the reverse-pressure was applied to the valve in the structural analysis, the stress was low in the body and seat compared to the normal pressure. Compared with the allowable strength of the material for the parts of the valve system, the minimum safety factor was approximately 1.4, so the valve was stable. As a result of applying the design pressures of 0.5 MPa and 600℃ under the load conditions in the thermal-structural analysis, the safety factor in the valve body was about 3.4 when the normal pressure was applied and about 2.7 when the reverse pressure was applied. The stability of the fluid-structure interaction analysis was determined to be stable compared to the 600℃ yield strength of the material, and about 2.2 for the 40° open-angle disc for the valve body. In seismic analysis, the maximum value of the valve's stress value was about 9% to 11% when the seismic load was applied compared to the general structural analysis. Based on the results of this study, the structural stability and design feasibility of high-temperature valves that can be used in cogeneration plants and other power plants are presented.

• Structural Engineering and Mechanics
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• v.81 no.4
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• pp.411-428
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• 2022

This paper presents the Campbell diagram analysis of the rotordynamic system using the full order model (FOM) and the reduced order model (ROM) techniques to determine the critical speeds, identify the stability and reduce the computational time. Due to the spin-speed-dependent matrices (e.g., centrifugal stiffening matrix), several model order reduction (MOR) techniques may be considered, such as the modal superposition (MS) method and the Krylov subspace-based MOR techniques (e.g., Ritz vector (RV), quasi-static Ritz vector (QSRV), multifrequency quasi-static Ritz vector (MQSRV), multifrequency/ multi-spin-speed quasi-static Ritz vector (MMQSRV) and the combined Ritz vector & modal superposition (RV+MS) methods). The proposed MMQSRV method in this study is extended from the MQSRV method by incorporating the rotational-speed-dependent stiffness matrices into the Krylov subspace during the MOR process. Thus, the objective of this note is to respond to the question of whether to use the MS method or the Krylov subspace-based MOR technique in establishing the Campbell diagram of the shaft-disc-blade assembly systems in three-dimensional (3D) finite element analysis (FEA). The Campbell diagrams produced by the FOM and various MOR methods are presented and discussed thoroughly by computing the norm of relative errors (ER). It is found that the RV and the MS methods are dominant at low and high rotating speeds, respectively. More precisely, as the spinning velocity becomes large, the calculated ER produced by the RV method is significantly increased; in contrast, the ER produced by the MS method is smaller and more consistent. From a computational point of view, the MORs have substantially reduced the time computing considerably compared to the FOM. Additionally, the verification of the 3D FE rotordynamic model is also provided and found to be in close agreement with the existing solutions.

• Journal of the Korean Institute of Telematics and Electronics
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• v.11 no.1
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• pp.1-7
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• 1974

This paper discribes the reflector type ultrasonic concentrator which makes hghintencity of ultrasonic field. This was made by rotating parabolic surface which only using total reflection aria, that makes boundary by the critical angle of reflection of sound. I made two binds of concentrator acording to the type of ultrasonic transduser: one is internal surface reflector type concentrator, which is available for disc type transducer, and the other is external surface reflector type concentrator which is available cylinderical transduser. In the mony aspects the reflector tripe concentrator is supel'ier to the reflection type concentrator as plastics lens; It is more durable in high temperature and high intencity ultrasonicfield then refrector type concentrator because of it is made by glass or metal, and it has higher. efficiency because of it wasts made by only total reflection aria that is without absoption lose. I think this is useful ultrasonic concentrator in mony industrial field, in which high intencitr of ultrasonic energy was used.