• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.10 no.4
• /
• pp.431-439
• /
• 1998

Falling film absorption process is an important problem in application such as absorption chillers. The presence of waves on the film affects the absorption process significantly. In the present study the characteristics of heat and mass transfer in laminar-wavy falling film were studied numerically. The wavy flow behavior was incorporated in the energy and diffusion equation. The numerical solution indicated that the interfacial wave increased the transfer rates remarkably. Interfacial shear stress and wave frequency seemed to be the dominant factors on the film Nusselt number and Sherwood number in the wavy film. A comparison of the transfer rates of the wavy film to that of the smooth film showed that the mass transfer rate could be increased by more than 50%.

• Journal of Biomedical Engineering Research
• /
• v.16 no.3
• /
• pp.279-288
• /
• 1995

Ultrasonic Doppler systems for the purpose of estimating blood flow velocity, blood flow volume, and flow imaging are commonly used due to advantages of non-invasive and real time observation. Specially, the technical developments of color flow mapping (2-D Doppler) systems have made a relatively rapid progress. However, the 2-D Doppler systems have several problems, such as the range ambiguity, low signal to noise ratio, and slow frame rate. The slow frame rate problem is resolved by using the spatial average which is a method to acquire more data samples for mean frequency estimation. In this paper, spatial average method using the 2nd order sampling instead of quadrature sampling is proposed. The experimental results show that the proposed methods have good performance and easy application to the color flow mapping system.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.4 s.175
• /
• pp.1047-1054
• /
• 2000

A numerical simulation was made to delineate the re-distribution of tonal noise generated from the equally-spaced blade passing frequency (BPF). A pressure-wave model was employed to analyze the tonal noise. An optimal solution for diversifying the tonal peak noise was obtained by rearranging the unequally-spaced blade angles. This was based on the fact that the noise energy is transferred from BPF to the neighboring frequency band. A limit condition for the minimum blade angle spacing was imposed. The unbalancing problem was also considered to avoid the weight bias.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
• /
• 2004.04a
• /
• pp.149-154
• /
• 2004

In the semiconductor and the optical industry a new transport system which can replace the conventional sliding system is required. These systems are driven by magnetic field and conveyer belt. The magnetic field damages semiconductor and contact force scratches the optical lens. The ultrasonic wave driven system can solve these problem. In this paper, the relationship of transporting speed according to the change of flexural beam shape and the effect of transporting speed according to the change of weight and amplification voltage are verified. The vibration behavior of flexural beam in the ultrasonic transport system is experimented using Laser Scanning Vibrometer.

• Journal of the Korean Society for Nondestructive Testing
• /
• v.27 no.3
• /
• pp.262-267
• /
• 2007

Detection of gas leak from a tube is a very important issue in the quality control of machines such as the heat exchanger of an air-conditioner, because leakage of operating gas directly reduces the performance of machines. The acoustic emission (AE) method is a common way to detect leak of gas, however its application under the environment of mechanical vibration is restricted since most AE detectors are very sensitive to external vibration noise. In order to overcome this problem, we propose a method based on the mode analysis of the Lamb wave. In this method, the dominant Lamb mode and its frequency are found first, and then a proper band-pass filter is used to retain only this frequency component. In this way, we could improve the SNR (signal-to-noise ratio) of AE signal generated by gas leak from the tube even under vibratory environment.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.13 no.9
• /
• pp.916-923
• /
• 2002

In this paper, we propose dual-polarization technique which double the system capacity without increasing any other bandwidth. In theory, dual-polarization technique can double system capacity by using an orthogonal electromagnetic wave. However, cross-polarization interference and multipath interference degrade system performance in practice. To cope with this problem, we propose Cross Polarization Interference Canceller(XPIC) for ITS/DSRC system which can mitigate the XPI as well as multipath propagation interference. We also analyze and discuss its performance with relevant computer simulation results.

• Journal of Institute of Control, Robotics and Systems
• /
• v.9 no.2
• /
• pp.145-151
• /
• 2003

A global ultrasonic sensor system for self-localization of a mobile robot is proposed in this paper. The global ultrasonic sensor system consists of three or more ultrasonic transmitters fixed at some positions in the world coordinate and receivers in the moving coordinate of a mobile robot. In this global sensor system it is easy to get state vector of the mobile robot in the world coordinate from the distance information between each ultrasonic transmitter and receiver. An extended kalman filter algorithm is used to process the noisy ultrasonic signal and to estimate the state vector. In case of using several independent ultrasonic transmitters, it is necessary to avoid the cross talk among the ultrasonic waves and to synchronize between each ultrasonic transmitter and receiver. The small sized radio frequency modules are adopted to solve the cross talk and the synchronization problem Computer simulation and experiments are carried out to verify the effectiveness of the proposed ultrasonic sensor system.

• Journal of Korean Institute of Industrial Engineers
• /
• v.31 no.1
• /
• pp.1-9
• /
• 2005

This paper proposes the heuristic algorithm for the generalized GT problems to consider the restrictions which are given the number of machine cell and maximum number of machines in machine cell as well as minimum number of machines in machine cell. This approach is split into two phase. In the first phase, we use the similarity coefficient which proposes and calculates the similarity values about each pair of all machines and sort these values descending order. If we have a machine pair which has the largest similarity coefficient and adheres strictly to the constraint about birds of a different feather (BODF) in a machine cell, then we assign the machine to the machine cell. In the second phase, we assign parts into machine cell with the smallest number of exceptional elements. The results give a machine-part grouping. The proposed algorithm is compared to the Modified p-median model for machine-part grouping.

• 한국정보통신설비학회:학술대회논문집
• /
• 2007.08a
• /
• pp.366-370
• /
• 2007

This paper discusses a most suitable wireless communications system for subway trains on condition that a geo-spatial video system is implemented in subway trains. Geo-spatial video system for subway trains refers to the device that can transfers the images captured by cameras within a subway station building or in and around a subway track to on coming trains wirelessly, which allows the operator in operating room to monitor the state of a platform and a subway track, the flow of passengers, and the condition of passengers getting on and off. To minimize the problem, secure civil safety and prevent accidents and calamity from occurring, a geo-spatial video system for subway trains has been increasingly introduced. The wireless communications systems for GVS for subway trains involve HF(High Frequency), IR(Infra Red), M/W(Micro Wave), wireless LAN approaches. Each has its own strengths/weaknesses, and different vendors have different technology.

• Proceedings of the KIPE Conference
• /
• 2000.07a
• /
• pp.417-420
• /
• 2000

In order to the torque control the indirect flux control was performed by controlling the ratio of e/f and the q-axis flux was estimated by the slip command and q-axis flux was estimated by the slip command and q-axis current in the rotor circuits. Also the frequency was controlled to keep on the q-axis flux to be zero and the constant torque characteristics could be obtained by generation the preset torque. In the induction motor driven by the boltage source inverter with the constant voltage and frequency the speed variation is expressed as a slip So the speed control can be achieved by slip compensation The slip was calculated with a q-flux current filtered by first-order filter and as the result the error problem which may occur in current detection was eliminated