• The KSFM Journal of Fluid Machinery
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• v.15 no.6
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• pp.5-10
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• 2012

The effect of pressure-side opening length on three-dimensional flow fields and aerodynamic losses downstream of a cavity squealer tip has been investigated in a turbine rotor cascade for the squealer rim height-to-chord ratio and tip gap height-tochord ratio of $h_{st}/c$ = 5.05% and h/c = 2.0% respectively. The opening length-to-camber ratio is changed to be $OL/c_c$ = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.7 The results show that longer OL leads not only to weaker secondary flow but also to lower aerodynamic loss in the tip leakage vortex region, while it significantly widens the area with high aerodynamic loss in the passage vortex region. The aerodynamic loss coefficient mass-averaged all over the measurement plane is kept almost constant for $0.0{\leq}OL/c_c{\leq}0.3$, whereas it increases rapidly for $OL/c_c$ > 0.3 in proportion to $OL/c_c$. There is little deterioration in flow turning with increasing $OL/c_c$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.3
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• pp.356-365
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• 2001

Heat (mass) transfer characteristics have been investigated on the endwall of a large-scale linear turbine cascade. Its profile is based on the mid-span of the first-stage rotor blade in a industrial gas turbine. By using the naphthalene sublimation technique, local heat (mass) transfer coefficients are measured for two different free-stream turbulence intensities of 1.3% and 4.7%. The results show that local heat (mass) transfer Stanton number is widely varied on the endwall, and its distribution depends strongly on the three-dimensional vortical flows such as horseshoe vortices, passage vortex, and corner vortices. From this experiment, severe heat loads are found on the endwall near the blade suction side as well as near the leading and trailing edges of the blade. In addition, the effect of the free-stream turbulence on the heat (mass) transfer is also discussed in detail.

• Nuclear Engineering and Technology
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• v.50 no.6
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• pp.907-914
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• 2018

In this article, we conducted molecular dynamics simulations to investigate the effect of applied strain and temperature on irradiation-induced damage in alpha-zirconium. Cascade simulations were performed with primary knock-on atom energies ranging between 1 and 20 KeV, hydrostatic and uniaxial strain values ranging from -2% (compression) to 2% (tensile), and temperatures ranging from 100 to 1000 K. Results demonstrated that the number of defects increased when the displacement cascade proceeded under tensile uniaxial hydrostatic strain. In contrast, compressive strain states tended to decrease the defect production rate as compared with the reference no-strain condition. The proportions of vacancy and interstitial clustering increased by approximately 45% and 55% and 25% and 32% for 2% hydrostatic and uniaxial strain systems, respectively, as compared with the unstrained system, whereas both strain fields resulted in a 15-30% decrease in vacancy and interstitial clustering under compressive conditions. Tensile strains, specifically hydrostatic strain, tended to produce larger sized vacancy and interstitial clusters, whereas compressive strain systems did not significantly affect the size of defect clusters as compared with the reference no-strain condition. The influence of the strain system on radiation damage became more significant at lower temperatures because of less annealing than in higher temperature systems.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.1
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• pp.61-70
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• 2008

This paper investigates the modal acoustic power by a cascade of flat-plate airfoils interacting with homogeneous, isotropic turbulence. Basic formulation for the acoustic power upstream and downstream is based on the analytical theory of Smith and its generalization due to Cheong et al. The acoustic power spectrum has been expressed as the sum of cut-on acoustic modes, whose modal power is the product of three terms: a turbulence series, an upstream or downstream power factor and an upstream or downstream acoustic response function. The effect of these terms in the modal acoustic power has been examined. For isotropic turbulence gust, the turbulent series are only reducing factor of the modal acoustic power. The power factor tends to reduce the modal acoustic power in the upstream direction, although the power factor is liable to increase the modal acoustic power in the downstream direction. The modes close to cut-off are decreasing strongly, especially in the downstream direction. Therefore the modes close to cut-off don't contribute highly to the radiated acoustic power in the downstream direction, although the modal acoustic pressure is high for these modes.

• Journal of Advanced Information Technology and Convergence
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• v.10 no.2
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• pp.167-175
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• 2020

In this paper, we propose a traffic accident detection on vehicle-mounted camera. In the proposed method, the minimum bounding box coordinates the central coordinates on the bird's eye view and motion vectors of each vehicle object, and ego-motions of the vehicle equipped with dash-cam are extracted from the dash-cam video. By using extracted 4 kinds features as the input of Bi-LSTM (bidirectional LSTM), the accident probability (score) is predicted. To investigate the effect of each input feature on the probability of an accident, we analyze the performance of the detection the case of using a single feature input and the case of using a combination of features as input, respectively. And in these two cases, different detection models are defined and used. Bi-LSTM is used as a cascade, especially when a combination of the features is used as input. The proposed method shows 76.1% precision and 75.6% recall, which is superior to our previous work.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.853-858
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• 2000

The working fluid from the combustor to the turbine stage of a gas turbine makes various boundary layer thickness. Since the inlet boundary layer thickness is one of the important factors that affect the turbine efficiency. It is necessary to investigate secondary flow and loss with various boundary layer thickness conditions. In the present study, the effect of various inlet boundary layer thickness on secondary flow and loss and the proper height of the boundary layer fences for various boundary layer thickness were investigated. Measurements of secondary flow velocity and total pressure loss within and downstream of the passage were taken under 5 boundary layer thickness conditions, 16, 36, 52, 69, 110mm. It was found that total pressure loss and secondary flow areas were increased with increase of thickness but they were maintained almost at the same position. At the fellowing research about the boundary layer fences, 1/6, 1/3, 1/2 of each inlet boundary layer thickness and 12mm were used as the fence heights. As a result, it was observed that the proper height of the fences was generally constant since the passage vortex remained almost at the same position. Therefore once the geometry of a cascade is decided, the location of the Passage vortex and the proper fence height are appeared to be determined at the same time. When the inlet boundary layer thickness is relatively small, the loss caused by the proper fence becomes bigger than endwall loss so that it dominates secondary loss. In these cases the proper fence hight is decided not by the cascade geometry but by the inlet boundary layer thickness as previous investigations.

• The KSFM Journal of Fluid Machinery
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• v.14 no.1
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• pp.48-54
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• 2011

The effect of channel cutback on three-dimensional flow fields and aerodynamic losses downstream of a cavity squealer tip has been investigated in a turbine rotor cascade for the squealer rim height-to-chord ratio and tip gap height-to-chord ratio of $h_{st}/c$ = 5.51% and h/c = 2.0% respectively. The cutback length-to-camber ratio is changed to be $CB/c_c$ = 0.0, 0.1, 0.2 and 0.3. The results show that longer cutback delivers not only stronger secondary flow but also higher aerodynamic loss in the tip leakage vortex region, meanwhile it leads to lower aerodynamic loss in the passage vortex region. The discharge of cavity fluid through the cutback opening provides a beneficial effect in the reduction of aerodynamic loss, whereas there also exists a side effect of aerodynamic loss increase due to local wider tip gap near the trailing edge. With increasing $CB/c_c$ from 0.0 to 0.3, the aerodynamic loss coefficient mass-averaged all over the measurement plane tends to increase slightly.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.4
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• pp.506-519
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• 1999

An adaptive array antennal and a CCI canceller have been considered as techniques for cancelling Multi-User Interference(MUI) in Direct Sequence Code Division Multiple Access(DS-CDMA) system. These techniques have different problems respectively in the process of cancelling MUI as the number of users increases. For that reason, the scheme which can cancel MUI effectively by compensating for the problems of each of the techniques has been required. For the scheme, the technique to connect an adaptive array antenna and a CoChannel Interference(CCI) canceller in cascade form has been studied. In the existing study about the cascade connection method, the effect of cancelling MUI about two interference signals is analyzed, but the analysis for the quantitative BER(Bit Error Rate) improvement according to the number of users is not considered. Therefore, in this paper, we have analyzed the degree of BER performance improvement quantitatively according to the number of users by introducing the receiving system, which connects an adaptive array antenna and a CCI canceller to a DS-CDMA system in cascade form. For the method of analyzing the performance, we have performed the theoretical analysis and the simulation, considering the case of adopting only an adaptive array antenna and of cascade connection respectively, and having compared and analyzed the results. From the results, it is confirmed that in the case of adopting only an adaptive array antenna, the problems occur in the process of cancelling MUI according to the number of users and the receiving direction of interference signals, and can be compensated by the cascade connection method. In conclusion, we have known that MUI is cancelled effectively by using the cascade connection method, and the much better BER performance improvement is obtained.

• Proceedings of the IEEK Conference
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• 2001.06c
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• pp.185-188
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• 2001

In this paper, a cascade fuzzy control method is proposed, which presents a robustness of the effect of disturbances, and in which the number of rules of the controller increase linearly instead of exponentially with the number of input variables. The proposed fuzzy control method is composed of cascade structure. Each stage has a state and a change of state, and one consequent control variable, and previous consequent control variable is an input of next stage. Simulation of the proposed controller, which is applied to the linear and nonlinear system as SISO (single-input single-output) system, showed that the proposed control method has a good control performance and robustness of disturbances compared with a conventional fuzzy control method.

• Journal of computational fluids engineering
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• v.8 no.3
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• pp.1-6
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• 2003

Three-dimensional endwall flow within a linear cascade passage of high performance turbine blade is simulated with a 3-D Wavier-Stokes CFD code (MOSA3D), which is based on body-fitted coordinate system, pressure-correction and finite volume method. the endwall flow characteristics, including the development and generation of horseshoe vortex, passage vortex, etc. are clearly simulated, consistent with the generally known tendency The effects of both turbulence model and convective differencing scheme on the Prediction performance of endwall flow are systematically analyzed in the present paper. The convective scheme is found to have stronger effect than the turbulence modei on the prediction performance of endwall flow. The present simulation result also indicates that the suction leg of the horseshoe vortex continues on the suction side until it reaches the trailing edge.