• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.05a
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• pp.32-36
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• 2003

This paper deals with a theoretical method for the design of a biased asymmetric preswirl stator propulsion system which has been used to increase efficiency by the recovery of a propeller slipstream rotational energy by the counter rotating flow of a stator. In the case of full slow-speed ship, the upward flow is generated at the propeller plane by the after body hull form. The generated upward flow cancells the rotating flow of the propeller at the starboard part while it increases at port part. A biased asymmetric preswirl stator propulsion system consists of three blades at the port and one blade at the starboard which can recover the biased rotating flow effectively. This paper provides the design concept which gives more simple and a high degree of efficiency. The model tests for the designed compound propulsion system will be carried out later.

• Wind and Structures
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• v.39 no.4
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• pp.243-258
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• 2024

In this paper, the aerodynamic performance of the Basalt Fiber Reinforced Polymer (BFRP) bionic plate wind turbine blade with different pitch angles, incoming wind speeds and rotational speeds was investigated. The influence of the tower shadow effect on the wake velocity, aerodynamic load, displacement and stress of BFRP bionic plate wind turbine blade under the rated condition was obtained by establishing the whole machine model including tower tube, and the error analysis of the simplified calculation formula of aerodynamic load was carried out. Results show that the incoming wind speed has a great influence on the stress and wind speed backflow and the tower shadow effect has a great influence on the horizontal thrust and torque of BFRP bionic plate wind turbine blade. The simplified calculation formula of aerodynamic load can accurately simulate the displacement and stress trend of BFRP bionic plate wind turbine blade and the recommended values of the pitch angle, incoming wind speed and the rotational speed of BFRP bionic plate wind turbine blade were given. The research results can provide the dynamic parameter reference for the engineering design of BFRP bionic plate wind turbine blade.

• International Journal of Fluid Machinery and Systems
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• v.6 no.2
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• pp.105-112
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• 2013

The application of contra-rotating rotors for higher specific speed pump has been proposed in our studies, which is in principle effective for reducing the rotational speed and/or the pump size under the same specification of conventional axial flow pump. In the previous experiments of our prototype, the cavitation inception at the tip region of the rear rotor rather than that of the front rotor and the strong potential interaction from the suction surface of the rear rotor blade to the pressure surface of the front one were observed, indicating the possibility to further improve the pump performance by optimizing rotational speed combination between the two rotors. The present research aims at the design of rear rotor with lower rotational speed. Considering the fact that the incoming flow velocity defects at the tip region of the rear rotor, an integrated inflow model of 'forced vortex' and 'free vortex' is employed. The variation of maximum camber location from hub to tip as well as other related considerations are also taken into account for further performance improvement. The ideas cited above are separately or comprehensively applied in the design of three types of rear rotor, which are subsequently simulated in ANSYS CFX to evaluate the related pump performance and therefore the whole low speed design idea. Finally, the experimental validation is carried out on one type to offer further proofs for the availability of the whole design method.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.5
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• pp.545-565
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• 2018

A numerical code is developed based on potential flow theory to investigate nonlinear sloshing in rectangular Liquefied Natural Gas (LNG) tanks under forced excitation. Using this code, internal free-surface elevation and sloshing loads on liquid tanks can be obtained both in time domain and frequency domain. In the mathematical model, acceleration potential is solved in the calculation of pressure on tanks and the artificial damping model is adopted to account for energy dissipation during sloshing. The Boundary Element Method (BEM) is used to solve boundary value problems of both velocity potential and acceleration potential. Numerical calculation results are compared with published results to determine the efficiency and accuracy of the numerical code. Sloshing properties in partially filled rectangular and membrane tank under translational and rotational excitations are investigated. It is found that sloshing under horizontal and rotational excitations share similar properties. The first resonant mode and excitation frequency are the dominant response frequencies. Resonant sloshing will be excited when vertical excitation lies in the instability region. For liquid tank under rotational excitation, sloshing responses including amplitude and phase are sensitive to the location of the center of rotation. Moreover, experimental tests were conducted to analyze viscous effects on sloshing and to validate the feasibility of artificial damping models. The results show that the artificial damping model with modifying wall boundary conditions has better applicability in simulating sloshing under different fill levels and excitations.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.6
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• pp.521-526
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• 2016

This paper suggests a new design that makes use of rotary inertia that can allow autonomous movement of an autonomous colonoscope robot in the colon of a patient as a locomotive mechanism. As commercial colonoscopy causes a lengthy time of pain and discomfort to the patients when colonoscopy patients are reluctant to receive surgery, there is a tendency to avoid the test in the early diagnosis of colorectal cancer. To solve this problem, research has been conducted on the next generation of robotic colonoscopes that can reduce the discomfort and pain by moving autonomously within the colon of the patients. In the driving mechanism utilizing the rotational inertia, a flywheel is driven by a motor to store energy and produce rotational inertia. By the energy stored and released by the flywheel, the stick phenomenon that occurs when the robot is running in the intestine can be overcome effectively. To do this, a controller that can control the velocity of the flywheel and is robust to high frequency noise was designed and implemented. The driving mechanism using the rotational inertia presented here showed that the structure is also effective and the experiment can be run easily compared to another mechanism.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.8 s.239
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• pp.895-902
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• 2005

Lock-on characteristics of flow around a circular cylinder oscillating rotationally with a relatively high forcing frequency have been investigated experimentally. Dominant governing parameters are Reynolds number (Re), angular amplitude of oscillation (${\theta}_A$), and frequency ratio $F_R=f_f/f_n,\;where\;f_f$ is a forcing frequency and $f_n$ is a natural frequency of vortex shedding. Experiments were carried out under the conditions of $Re=4.14{\times}10^3,\;{\pi}/90{\leq}{\theta_A}{\leq}{\pi}/3,\;and\;F_R=1.0$. The effect of this active flow control technique on the lock-on flow characteristics of the cylinder wake was evaluated with wake velocity measurements and spectral analysis of hot-wire signals. The rotational oscillation modifies the flow structure of near wake significantly. The lock-on phenomenon always occurs at $F_R=1.0$, regardless of the angular amplitude ${\theta}_A$. In addition, when the angular amplitude is less than a certain value, the lock-on characteristics appear only at $F_R=1.0$,. The range of lock-on phenomena expands and vortex formation length is decreased, as the angular amplitude increases. The rotational oscillation create a small-scale vortex structure in the region just near the cylinder surface. At ${\theta}_A=60^{\circ}$, the drag coefficient was reduced about $43.7\%$ at maximum.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.5
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• pp.357-365
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• 2013

In this study, forces and moments were measured on a projectile which consisted of a missile configuration body(shell) and a head installed control fins. The shell and the head were separated each other and the shell was rotated by an electric motor. The head rotated reversely against the rotational direction of the shell. The rotational force on the head was obtained from a couple of fixed fins of which angular displacement were set to the rotational direction equally. The air velocity was 40m/s on the experiment and the Reynolds number based on the diameter of head was $1.3{\times}10^5$. The other couple of fins were used to control the position and direction of the projectile by changing the angular displacement. From this experiment, the variation of force and moment were measured on the rotating projectile, and the effective amplitude and frequency were obtained through the FFT analysis.

• Advances in Energy Research
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• v.7 no.1
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• pp.1-19
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• 2020

Energy consumption of air-conditioning and refrigeration systems is responsible for about 25 to 30% of the energy demand especially in hot seasons. This equipment is mostly electricity dependent and their use in principle affects negatively the environment. Enhancing the energy efficiency of the existing equipment is important as one of the measures to reduce environment impacts. This paper reports the results of an experimental study to evaluate the impacts of the use electronic expansion valve and variable velocity compressor on the performance of vapor compression refrigeration system. The experimental rig is composed of two independent circuits one for the vapor compression system and the other is the secondary fluid system. The vapor compression system is composed of a forced air condenser unit, evaporator, hermetic compressor and expansion elements, while the secondary system has a pump for circulating the secondary fluid, and an air conditioning heat exchanger. The manufacturer's data was used to determine the optimal points of operation of the system and consequently tests were done to evaluate the influence of variation of the compressor velocity and the opening of the expansion device on the performance of the refrigeration system. A fuzzy logic model was developed to control the rotational velocity of the compressor and the thermal load. Fuzzy control model was made in LabVIEW software with the objective of improving the system performance, stability and energy saving. The results showed that the use of fuzzy logic as a form of control strategy resulted in a better energy efficiency.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.193-196
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• 2008

The vortical structures in a turbulent boundary layer (TBL) developed over a flat plate have been investigated experimentally. The flow conditions tested in this study were Re$_{\theta}$ = 3700, Re$_{\delta}$ = 11${\times}$105 and the shape factor H = 1.3. Instantaneous velocity fields in the streamwise-wall-normal planes were measured by using a dynamic PIV system. A trip-wire and sandpapers were placed behind the leading edge to promote the turbulent transition. 1000 velocity fields were obtained consecutively with a time interval of 1 millisecond. Streamwise u-velocity components were temporally averaged in the measuring plane. In addition, 2000 velocity fields were obtained randomly and ensemble-averaged to get the fully-developed turbulent characteristics. Profiles of the normalized u-component, turbulent intensities and Reynolds shear stress were evaluated. The structures of spanwise vortices were extracted from the instantaneous velocity fields by determining the swirling strength, ${\lambda}_{ci}$. The wall-normalized locations of vortices were temporally averaged in the measuring plane with respect to their rotational direction. The correlations between the temporally averaged u and the temporally averaged $y^+$ of vortices were evaluated. For the case of positive vortices, the correlation is not significant. However, the negative vortices show a strong negative correlation. The y-location of negative vortices tends to increase, as the averaged u decreases and vice versa. These findings indicate that the number of negative vortices in the outer layer increases during the outward bursting events.

• Aerospace Engineering and Technology
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• v.9 no.2
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• pp.185-192
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• 2010

Design of velocity-compounded turbine for 75ton class LRE turbopump application and pressure compounded turbine for 30ton class LRE turbopump has been performed. 1D calculation and CFD analysis were conducted in determining blade and flow passage shape of velocity compounded turbine iteratively. Finally, 23.1% improved specific power and 5% reduced weight turbine to the original design was developed. In case of pressure-compounded supersonic turbine design, rotational speed was increased by 50% and the effect of carryover ratio, 2nd nozzle installation angle, leakage flow of 2nd nozzle, and work sharing factor was studied. Final 1D design resulted 36% increased specific power and 51% reduced weight comparing to the original single-row impulse turbine. It is anticipated that nozzle flow path design will be very important for the accomplishment of expected performance of pressure-compounded turbine and nozzle shape optimization will be conducted through the CFD analysis.