• International Journal of Aeronautical and Space Sciences
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• 제16권4호
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• pp.571-580
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• 2015

In this paper, a computational study was conducted in order to investigate the rotor blade sweep effect on the aerodynamics of a small axial supersonic impulse turbine stage. For this purpose, three-dimensional unsteady RANS simulations have been performed with three different rotor blade sweep angles ($-15^{\circ}$, $0^{\circ}$, $+15^{\circ}$) and the results were compared with each other. Both NTG (No tip gap) and WTG (With tip gap) models were applied to examine the effect on tip leakage flow. As a result of the simulation, the positive sweep model ($+15^{\circ}$) showed better performance in relative flow angle, Mach number distribution, entropy rise, and tip leakage mass flow rate compared with no sweep model. With the blade static pressure distribution result, the positive sweep model showed that hub and tip loading was increased and midspan loading was reduced compared with no sweep model while the negative sweep model ($-15^{\circ}$) showed the opposite result. The positive sweep model also showed a good aerodynamic performance around the hub region compared with other models. Overall, the positive sweep angle enhanced the turbine efficiency.

• Journal of Electrical Engineering and Technology
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• 제7권6호
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• pp.1023-1033
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• 2012

An underwater planar covering problem is studied where the coverage region consists of polygonal cells, and line sweep motion is used for coverage. In many subsea applications, sidescan sonar has become a common tool, and the sidescan sonar data is meaningful only when the sonar is moving in a straight line. This work studies the optimal line sweep coverage where the sweep paths of the cells consist of straight lines and no turn is allowed inside the cell. An optimal line sweep coverage solution is presented when the line sweep path is parallel to an edge of the cell boundary. The total time to complete the coverage task is minimized. A unique contribution of this work is that the optimal sequence of cell visits is computed in addition to the optimal line sweep paths and the optimal cell decomposition.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 2000년도 International Symposium on Magnetics The 2000 Fall Conference
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• pp.230-238
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• 2000

We present the magnetisation reversal dynamics of epitaxial Fe thin films grown on GaAs(001) and InAs(001) studied as a function of field sweep rate in the range 0.01-160 kOe/s using magneto-optic Kerr effect (MOKE). For 55 and 250 ${\AA}$ Fe/GaAs(001), we find that the hysteresis loop area A follows the scaling relation A ∝ H$\^$${\alpha}$/ with ${\alpha}$=0.03∼0.05 at low sweep rates and 0.33-0.40 at high sweep rates. For the 150 ${\AA}$ Fe/InAs(001) film, ${\alpha}$ is found to be ∼0.02 at low sweep rates and ∼0.17 at high sweep rates. The differing values of ${\alpha}$ are attributed to a change of the magnetisation reversal process with increasing sweep rate. Domain wall motion dominates the magnetisation reversal at low sweep rates, but becomes less significant with increasing sweep rate. At high sweep rates, the variation of the dynamic coercivity H$\sub$c/ is attributed to domain nucleation dominating the reversal process. The results of magnetic relaxation studies for easy-axis reversal are consistent with the sweeping of one or more walls through the entire probed region (∼100 $\mu\textrm{m}$). Domain images obtained by scanning Kerr microscopy during the easy cubic axis reversal process reveal large area domains separated by zigzag walls.

• 한국유체기계학회 논문집
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• 제16권2호
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• pp.48-53
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• 2013

This paper presents a numerical investigation of the influence of the blade back sweep angle on the performance and flow characteristics in a centrifugal compressor with a vaneless diffuser. Five impellers with different back sweep angles were tested in the flow simulations. It was found that a low back sweep angle could improve the total-to-total pressure ratio and the work coefficient over whole operating ranges. However, the flow field in an impeller with a low back sweep angle produced a more non-uniform velocity distribution at the impeller exit because the wake region was significantly increased. As a consequence, the impeller with a low back sweep angle caused a low diffuser performance.

• 동력기계공학회지
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• 제13권4호
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• pp.31-37
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• 2009

The purpose of this numerical study was to investigate performance characteristics for cooling tower axial fans with sweep. Performance data for the fans with various sweep angles were obtained in terms of the setting angle at a constant flow rate. Viscous flow calculations were carried out to obtain Performance data of the total pressure rise and hydraulic efficiency. A solution of the Ffowcs Williams-Hawkings equations was used to calculate the sound pressure level at three times fan diameter away from the fan. The calculated performance data well represented performance characteristics of the cooling tower axial fan. The total pressure rise and hydraulic efficiency at the same setting angle decreased with sweep angle. Sound pressure level slightly decreased for the fan with a sweep angle of 10 degree. No significant effect of the sweep geometry was found on the sound pressure level.

• 한국유체기계학회 논문집
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• 제9권2호
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• pp.25-29
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• 2006

Computational and experimental studies on the forward-sweep inducer for the rocket-engine turbopump are presented in comparison with the conventional backward-sweep inducer. Computational results show that back flows at the inlet decrease in the case of forward-sweep inducers compared to the back-ward inducer. Moreover, the low pressure region at the back flow is decreased, which is presumed to improve the suction performance of the inducers. Experimental results show that the suction performance of the forward-sweep inducer is almost the same as that of the backward-sweep inducer although it has smaller inlet tip diameter and shorter length. The efficiency of the forward-type inducer is found better than that of the backward-sweep inducer due to the small size of back flows.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2005년도 연구개발 발표회 논문집
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• pp.650-654
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• 2005

Computational and experimental studies on the forward-sweep inducer for the rocket-engine turbopump are presented in comparison with the conventional backward-sweep inducer. It is shown that back flows at the inlet decreases for forward-sweep inducers. And the low pressure region at the back flow are also decreased, which is assumed to promote the suction performance of the inducers. The backward-sweep inducer shows almost the same suction performance as that of the backward-sweep inducers although it has small inlet tip diameter and shorter length. And the efficiency of the forward-type inducer shows better results than the backward-sweep inducer due to the small size of backflows.

• 한국정밀공학회지
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• 제18권2호
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• pp.102-110
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• 2001

In this paper, methods to analyze wire sweep and paddle shift during the semiconductor ship-encapsulation process have been studied. The analysis of wire sweep includes flow-field analysis in a complicated geometry, drag-force calculation for given flow of fluid, and wire-deformation calculation for given loads. The paddle-shift analysis is used to analyze the deformation of the paddle due to the pressure difference in two cavities. the analysis is done using either analytical solutions or numerical simulation. The analytical solution is used for rough but fast calculation of wire sweep. The numerical solution is used for more accurate calculation of wire-sweep. The numerical results of wire sweep show good agreements with the experimental ones.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권3호
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• pp.1026-1039
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• 2014

We present a new method for generating sweep surfaces using bivariate B-spline motion. The sweep surface is defined as the trace of a single point under bivariate B-spline motion. Direct manipulation of the sweep surface is achieved by controlling its motion components while producing various editing effects. We demonstrate the effectiveness of our technique by modeling and deforming various three-dimensional shapes.

• Advances in aircraft and spacecraft science
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• 제5권2호
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• pp.187-204
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• 2018

The sine sweep base excitation test campaign is a major milestone in the process of mechanical qualification of space structures. The objectives of these vibration tests are to qualify the specimen with respect to the dynamic environment induced by the launcher and to demonstrate that the spacecraft FE model is sufficiently well correlated with the test specimen. Dynamic qualification constraints lead to performing base excitation sine tests using a sine sweep over a prescribed frequency range such that at each frequency the response levels at all accelerometers, load cells and strain gages is the same as the steady state response. However, in practice steady state conditions are not always satisfied. If the sweep rate is too high the response levels will be affected by the presence of transients which in turn will have a direct effect on the estimation of modal parameters. A study funded by ESA and AIRBUS D&S was recently carried out in order to investigate the influence of sine sweep rates in actual test conditions. This paper presents the results of this study along with recommendations concerning the choice of methods.