• Journal of The Korean Association For Science Education
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• v.17 no.4
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• pp.373-381
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• 1997

To investigate the preconceptions on the reference frame and relativity of motion, 251 of grade 7 pupils were selected. The questionnaire has 15 questions consisted of four test domains made by the researchers: object looks rest or moving in the rest frame, object looks rest or moving in the moving frame. The result shows that pupils took the observations in the moving frame for those in the rest frame, or vice versa. In addition, their answers varied according as the context of the observation differed.

• 유체기계공업학회:학술대회논문집
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• 2001.11a
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• pp.454-459
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• 2001

The present study is concerned with the flow patterns induced by other impellers in a rectangular tank Impellers are FBT(Flat blade turbine), PBT(Pitched blade turbine), Shroud turbine, Rushton Turbine, and Helical ribbon turbine. The solution of flows in moving reference frames requires the use of 'moving' cell zone. The moving zone approaches are MRF(Multiple reference frame), which is a steady-state approximation and Sliding method, which is a unsteady-state approximation. Numerical results using two moving zone approaches are compared with experiments by Ranade & Joshi, which have done extensive LDA measurements of the flow generated by a standard six-bladed Rushton turbine in a cylindrical baffled vessel. In this paper we simulated the flow patterns with above mentioned moving zone approaches and impellers. Turbulence model is RNG k-$\epsilon$ model.

• Nuclear Engineering and Technology
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• v.54 no.3
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• pp.888-895
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• 2022

Lately, ocean nuclear power plants have attracted attention as one of diverse uses of nuclear power plants. Because ocean nuclear power plants are movable or transportable, it is necessary to analyze the thermal hydraulics in a moving frame of reference, and computer codes have been developed to predict thermal hydraulics in large moving systems. The purpose of this study is to incorporate a three dimensional dynamic motion model into the SPACE code (Safety and Performance Analysis CodE) so that the code is able to analyze thermal hydraulics in an ocean nuclear power plant. A rotation system that describes three-dimensional rotations about an arbitrary axis was implemented, and modifications were made to the one-dimensional momentum equations to reflect the rectilinear and rotational acceleration effects. To demonstrate the code's ability to solve a problem utilizing a rotational frame of reference, code calculations were conducted on various conceptual problems in the two-dimensional and three-dimensional pipeline loops. In particular, the code results for the three-dimensional pipeline loop with a tilted rotation axis agreed well with the multi-dimensional CFD results.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.49 no.4
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• pp.62-70
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• 2012

In this paper, we propose the gunnery detection method based on reference frame modeling and frame difference method. The frame difference method is basic method in target detection, and it's applicable to the detection of moving targets. The goal of proposed method is the detection of gunnery target which has huge variation of energy and size in the time domain. So, proposed method is based on frame difference, and it guarantee real-time processing and high detection performance. In the method of frame difference, it's important to generate reference frame. In the proposed method, reference frame is modeled and updated in real time processing using statistical values for each pixels. We performed the simulation on 73 IR video data that has gunnery targets, and the experimental results showed that the proposed method has 95.7% detection ratio under condition that false alarm is 1 per hour.

• Journal of the Optical Society of Korea
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• v.13 no.2
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• pp.245-250
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• 2009

We propose a digital holographic interference analysis method based on a 2-frame phase-shifting technique for measuring an optical mirror surface. The technique using 2-frame phase-shifting digital interferometry is more efficient than multi-frame phase-shifting techniques because the 2-frame method has the advantage of a reduced number of interferograms, and then takes less time to acquire the wanted topography information from interferograms. In this measurement system, 2-frame phase-shifting digital interferograms are acquired by moving the reference flat mirror surface, which is attached to a piezoelectric transducer, with phase step of 0 or $\pi$/2 in the reference beam path. The measurements are recorded on a CCD detector. The optical interferometry is designed on the basis of polarization characteristics of a polarizing beam splitter. Therefore the noise from outside turbulence can be decreased. The proposed 2-frame algorithm uses the relative phase difference of the neighbor pixels. The experiment has been carried out on an optical mirror which flatness is less than $\lambda$/4. The measurement of the optical mirror surface topography using 2-frame phase-shifting interferometry shows that the peak-to-peak value is calculated to be about $0.1779{\mu}m$, the root-mean-square value is about $0.034{\mu}m$. Thus, the proposed method is expected to be used in nondestructive testing of optical components.

• The KSFM Journal of Fluid Machinery
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• v.5 no.2 s.15
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• pp.29-35
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• 2002

The present study is concerned with the flow patterns induced by various impellers in a rectangular tank. Impellers are FBT (Flat blade turbine), PBT (Pitched blade turbine), Shroud turbine, Rushton turbine, and Helical ribbon turbine types. The solutions of flows in moving reference frames require the use of 'moving' cell zone. The moving zone approaches are based on MRF (Multiple reference frame), which is a steady-state approximation and sliding method, which is an unsteady-state approximation. Numerical results using two moving zone approaches we compared with experiments by Ranade & Joshi, which have done extensive LDA measurements of the flow generated by a standard six-bladed Rushton turbine in a cylindrical baffled vessel. In this paper, we simulated the flow patterns with above-mentioned moving zone approaches and impellers. Turbulence model used is RNG $k-{\epsilon}$ model. Sliding-mesh method is more effective than MRF for simulating the rectangular tank with inlet and outlet. RNG $k-{\epsilon}$ model strongly underestimates the velocity of experimental data and velocity by Chen & Kim's model, but it seems to be correctly predicted in overall distribution.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.4
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• pp.337-344
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• 2014

While implicit integration methods such as Newton's method have excellent stability for the analysis of stiff and constrained mechanical systems, they have the drawback that the evaluation and LU-factorization of the system Jacobian matrix required at every time step are time-consuming. This paper proposes a Jacobian update-free Newton's method in order to overcome these defects. Because the motions of all bodies in a vehicle model are limited with respect to the chassis body, the equations are formulated with respect to the moving chassis-body reference frame instead of the fixed inertial reference frame. This makes the system Jacobian remain nearly constant, and thus allows the Newton's method to be free from the Jacobian update. Consequently, the proposed method significantly decreases the computational cost of the vehicle dynamic simulation. This paper provides detailed generalized formulation procedures for the equations of motion, constraint equations, and generalized forces of the proposed method.

• Journal of computational fluids engineering
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• v.20 no.2
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• pp.81-87
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• 2015

For Underwater vehicles, Unwanted roll excursions are inevitable as they are caused by induced propeller torque, disturbances, and banking motion during turns. To estimate the manoeuvring performance of underwater vehicle, it is necessary to obtain the roll coefficient of body. This paper was covered estimation of roll coefficient of underwater vehicle using STAR-CCM+, commercial CFD(Computational Fluid Dynamics) code. The RANS equations for incompressible fluid flows was solved numerically by using a finite volume method. An MRF(Moving Reference Frame) Method was Also adopted for rotations of body. For the validation, the flow around a DARPA SUBOFF bare hull model was simulated and good agreement with experiments was obtained. And Pure roll coefficients were calculated and campared with the experimental data which were presented by Seoul National University. Finally, an underwater vehicle model with propeller was simulated and analyzed for estimation of roll coefficient variation caused by induced propeller torque.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.30 no.2
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• pp.92-99
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• 2018

A numerical analysis of a compressor dehumidifier has been conducted focusing on the air side heat transfer, which is a part of a series research on the dehumidifier. The moving reference frame was applied to the fan modeling, and the porous model was used for the evaporator and condenser modeling. Curve fitting obtained the inertial and viscous resistances parameters to the results of the physical model of the unit cell with actual shape of a fin tube. The porous model was validated within a reasonable computation time for the range of practical inlet velocity of a dehumidifier. A parametric study has been conducted for fin number, fan speed (i.e., air flow rate), and evaporator/condenser tube arrangement. ANOVA analysis showed the dependency of each parameter on the velocity and temperature uniformity, which are desirable for high performance of the dehumidifier.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.7
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• pp.587-594
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• 2005

In this paper, a robust correlation-based video tracking is proposed to track a moving object in correlated image sequences. A correlation-based video tracking algorithm seeks to align the incoming target image with the reference target block image, but has critical problems, so called a false-peak problem and a drift phenomenon (correlator walk-off. The false-peak problem is generally caused by highly correlated background pixels with similar intensity of a moving target and the drift phenomenon occurs when tracking errors accumulate from frame to frame because of the nature of the correlation process. At first, the false-peaks problem for the ordinary correlation-based video tracking is investigated using a simple mathematical analysis. And, we will suggest a robust selective-attention correlation measure with a gradient preprocessor combined by a drift removal compensator to overcome the walk-off problem. The drift compensator adaptively controls the template block size according to the target size of interest. The robustness of the proposed method for practical application is demonstrated by simulating two real-image sequences.