• Wind and Structures
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• v.29 no.1
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• pp.15-32
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• 2019

Much advancement has been made in wind power due to modern technological developments. The wind energy technology is the world's fastest-growing energy option. More power can be generated from wind energy by the use of new design and techniques of wind energy machines. The geographical areas with suitable wind speed are more favorable and preferred for wind power deployment over other sources of energy generation. Today's wind turbines are mainly the horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs). HAWTs are commercially available in various sizes starting from a few kilowatts to multi-megawatts and are suitable for almost all applications, including both onshore and offshore deployment. On the other hand, VAWTs finds their places in small and residential wind applications. The objective of the present work is to review the technological development, available sizes, efficiencies, structural types, and structural stability of VAWTs. Structural stability and efficiencies of the VAWTS are found to be dependent on the structural shape and size.

• Journal of the Semiconductor & Display Technology
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• v.22 no.1
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• pp.33-38
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• 2023

As the demand for large flexible displays such as tablet computers continues to rise, there is an increasing need for cost-efficient colorless and optically transparent polyimide film that can meet the desired performance, particularly optical transmittance. In this study, we investigated a detailed procedure for achieving optimal optical transmittance using two different combinations of monomers: 6FDA+BAPB and 6FDA+BPA+TFDB. We employed a design of experiment method to systematically synthesize polymers, allowing for the optimization of optical transmittance. In addition, we were able to achieve uniform thickness in the films by using a doctor blade. By comparing the price and optical transmittance of four different monomer combinations, we obtained fundamental data on the production of polyimide films that can be customized to meet the specific price and performance requirements of manufacturers. This approach enables users to select the most suitable polyimide film based on their desired price and performance parameters while achieving optimal optical transmittance.

• Structural Engineering and Mechanics
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• v.37 no.4
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• pp.427-442
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• 2011

In fatigue life design of mechanical components, uncertainties arising from materials and manufacturing processes should be taken into account for ensuring reliability. A common practice is to apply a safety factor in conjunction with a physics model for evaluating the lifecycle, which most likely relies on the designer's experience. Due to conservative design, predictions are often in disagreement with field observations, which makes it difficult to schedule maintenance. In this paper, the Bayesian technique, which incorporates the field failure data into prior knowledge, is used to obtain a more dependable prediction of fatigue life. The effects of prior knowledge, noise in data, and bias in measurements on the distribution of fatigue life are discussed in detail. By assuming a distribution type of fatigue life, its parameters are identified first, followed by estimating the distribution of fatigue life, which represents the degree of belief of the fatigue life conditional to the observed data. As more data are provided, the values will be updated to reduce the credible interval. The results can be used in various needs such as a risk analysis, reliability based design optimization, maintenance scheduling, or validation of reliability analysis codes. In order to obtain the posterior distribution, the Markov Chain Monte Carlo technique is employed, which is a modern statistical computational method which effectively draws the samples of the given distribution. Field data of turbine components are exploited to illustrate our approach, which counts as a regular inspection of the number of failed blades in a turbine disk.

• 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.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.2
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• pp.175-181
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• 2011

The purpose of this study is to secure the design data for the optimization of the radial turbine and heat cycle system, by using the CFD analysis technique and the design of 100kW class radial turbine applicable to waste heat recovery generation system for ship. Radial turbine was comprised of scroll casing, vane nozzle with 18 blades and rotor with 13 blades, and analysis grid was used to about 2.3 million. Mass flow rate and rotational speed was 0.5kg/s, 75,0000rpm, respectively. Eight kinds of inlet pressure was set between 195 and 620kPa. As the flow accelerated through the nozzle passage to the throat, the pressure level at the pressure and suction sides becomed similar to about Mach number of 0.35. When the inlet temperature and pressure was $250^{\circ}C$, 352kPa respectively, the isentropic efficiency and mechanical power showed the analysis results of 74% and 108kW.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.7
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• pp.20-28
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• 2002

In this paper, the aerodynamic performance prediction of a 30kW counter-rotating (C/R) wind turbine system has been made by using the momentum theory as well as the two-dimensional quasi-steady strip theory with special care on the wake and the post-stall effects. In order to take into account the wake effects in the performance analysis, the wind tunnel test data obtained for a scaled blade are used. Both the axial and rotational inductions behind the auxiliary rotors are determined through the wake model. In addition, the optimum chord and twist distributions along the blades are obtained from the Glauert's optimum actuator disk model considering the Prandtl's tip loss effect. The performance results of the counter-rotating wind turbine system are compared with those of the conventional single rotor system and demonstrated the effectiveness of the counter-rotating wind turbine system.

• Journal of the Korean Society of Industry Convergence
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• v.4 no.3
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• pp.243-251
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• 2001

The effects of various operating parameters(agitation speed, impeller type, antiform agents, impeller spacing etc.) on air-liquid mass transfer was characterized by volumetric mass transfer coefficient($k_La$). Also, the dual-impeller agitated systems are compared with single-impeller agitated systems with a special focus on its applications for bioreactors, $k_La$ was take over a range of 200~450 rpm of agitation speed, and 0.5~2.5 vvm of air flow rates, for four single impeller and impeller combinations consisting of four impeller types, namely rushton, pitched blade, scaba, intermig were tested. The rushton impeller showed the best $k_La$ as compared with other single impellers. The dual impeller system are found to be superior as compared to single impeller in all aspects, The best combination of the dual impeller was a intermig of axial flow type as an upper impeller and a rushton of radial flow type as a lower part. Also, the control of the DO level with the variation of agitation speed was more efficient than that with an increase in air flow rate. The addition of antiform dropped the $k_La$ very large up to 1g/L regardless the type. PPG was less effect on $k_La$ than other antiforms. The impeller spacing and presence of solute are found very effective on $k_La$. When the $NaNO_3$is presented as solute, the $k_La$ increased approximately 50% then control.

• The Journal of the Acoustical Society of Korea
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• v.42 no.6
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• pp.519-528
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• 2023

The aim of this study was to enhance the flow rate and noise performance of a centrifugal pump in dishwashers by designing an optimized impeller shape through numerical and experimental investigations. To evaluate the performance of the target centrifugal pump, experiment was conducted using a pump performance tester and noise experiment was carried out in a semi-anechoic chamber with microphones and a reflecting wall behind the dishwasher. Through the use of advanced computational fluid dynamics techniques, numerical simulations were performed to analyze the flow and aeroacoustics performance of our target centrifugal pump impeller. To achieve this, numerical simulations were carried out using the Reynolds-Average Navier-Stokes equations and Ffowcs-Willliams and Hawkings equations as governing equations. In order to ensure the validity of numerical methods, a thorough comparison of numerical results with experimental results. After having confirmed the reliability of the current numerical method of this study, the optimization of the target centrifugal pump impeller was conducted. An improvement in flow rate was confirmed numerically, and a manufactured proto-type of the optimized model was used for experimental investigation. Furthermore, it was observed that by applying the fan law, we could effectively reduce noise levels without reducing the flow rate.

• KEPCO Journal on Electric Power and Energy
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• v.6 no.2
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• pp.137-143
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• 2020

The CM247LC, a Ni-based superalloy material used for gas turbine hot gas path parts, is casted using directionally solidified technology to analyze the mechanical properties and microstructures through HIP (Hot Isostatic Pressing) and post-heat treatment, and to derive optimal HIP treatment conditions. The CM247LC material is being researched in various ways as an alternative material for prototyping gas turbine blades. In particular, the blade rotating part is exposed and operated in a high temperature and high-pressure environment, and when damaged, it may cause huge economic losses. Therefore, in order to use the CM247LC material as prototyping materials for gas turbine blades, the reliability of the microstructure and mechanical properties must be verified. In this study, after casting rod test specimens using CM247LC material by directionally solidified technology, after that the specimens were performed by HIP treatment and post-heat treatment to test two HIP conditions designed by KEPCO to derive the possibility of prototyping of CM247LC material and optimization of HIP treatment conditions. Additionally, the properties of CM247LC material were compared to the GTD111DS material using for 1,300℃ class gas turbine blades.