• Journal of Mechanical Science and Technology
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• v.15 no.8
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• pp.1174-1180
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• 2001

Various experimental data, including mixing areas, cross correlation factors, surface flow patterns on nozzle walls, and far field noise spectra, was used to draw a noise control mechanism in a supersonic jet. In the underexpanded case, mixing of the jet air with ambient air was significantly enhanced as presented before, and mixing noise was also dramatically reduced. Screech tones, in the overexpanded case, were effectively suppressed by trailing edge modifications, although mixing enhancement was not noticeable. From mixing and noise performance of nozzles with modified trailing edges, enhancing mixing through streamwise vortices seems an effective way to reduce mixing noise in the underexpanded flow regime. However, screech tones in the overespanded flow regime is well controlled or suppressed by making shock cells and/or spanwise large scale structures irregular and/or less organized by a proper selection of trailing edges. The noise field in the overexpanded flow regime was greatly affected by the symmetricity of the nozzle exit geometry. In the underexpanded flow regime, the effects of the symmetricity of the nozzle exit on mixing were negligible.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.3
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• pp.118-125
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• 1998

Chip control is a major problem in automatic machining process, especially in finish turning operation. In this case, chip breaker is one of the important factors to be determined. As unbroken chips are grown. these deteriorate the surface roughness. and proces automation can not be carried out. In this study to get rid of chip curling problem while turning internal hole. optimal chip breaker is selected from the experiment. The experiment is planned with Taguchi's method that is based on the orthogonal arrary of design factors. From the response table. cutting speed, feedrate, depth of cut and tool geometry turn to be major factors affecting chip formation. Then, optimal chip breaker is selected. and this is verified as good enough for chip control from the experiment.

• Journal of Drive and Control
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• v.14 no.4
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• pp.17-22
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• 2017

In this study, the back-drivability of the single-rod and double-rod type EHAs (Electro-Hydrostatic Actuators) was compared by computer simulation and experiments. The back-drivability of EHAs exhibit non-linear behavior like their force tracking performance. In case of the double-rod type EHA, the back-drivability was mostly influenced by the bulk modulus of oil that changes with the working pressure due to entrapped air. The back-drivability of the single-rod type EHA was directly affected by the operation states of its pilot-operated check valves, while the asymmetrical piston geometry and the non-linear bulk modulus of oil also made the dynamic response in building up the cylinder pressure dependent on the operating conditions.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.2349-2351
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• 2003

This paper reports a novel microfluidic system, by which microfluidic delivery, transport and control can be digitally realized in femtoliter scale. Microelectronic grade $N_2$ from a pressurized canister was passed through HPLC tubing into a micro injector. The micro injector was driven and controlled digitally by the control system that can apply various control parameters such as pulse frequencies. A front-end of micro nozzle was inserted the dyed oil to collect droplets injected. The diameter of a droplet was measured by a microscope and a CCD camera, and then its volume can be calculated on the assumption that the droplet is spherical. The micro nozzles were simply pulled in glass capillary tubes by the micro puller self-made, and the geometry parameters of the micro nozzles can be adjusted easily. Experiments have successfully been carried out, and the results demonstrated that the proposed digital micro injector possesses three significant advantages : precise ultra-small liquid volume in femtoliter scale, digital microfluidic control and micro devices fabricated by simple glass process, not based on IC process.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.11
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• pp.1085-1091
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• 2014

This paper presents the guidance and control design for automatic carrier landing of a UAV (Unmanned Aerial Vehicle). Differently from automatic landing on a runway on the ground, the motion of a carrier deck is not fixed and affected by external factors such as ship movement and sea state. For this reason, robust guidance/control law is required for safe shipboard landing by taking the relative geometry between the UAV and the carrier deck into account. In this work, linear quadratic optimal controller and longitudinal/lateral trajectory tracking guidance algorithm are developed based on a linear UAV model. The feasibility of the proposed control scheme and guidance law for the carrier landing are verified via numerical simulations using X-Plane and Matlab/simulink.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.10
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• pp.1048-1054
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• 2004

The Passive acoustic control is used in various fields, such as structures, automobiles, aircraft and so on. It is used in variety of acoustic field with the absorbing material, as one of the methods which can control the acoustic in optional space. In that case of passive control using this absorption material, it would be important to maximize the control performance of material property, numbers, geometry shape and the attached location of boundary area of the absorbing material. But realistically these variables, specially material Property, have no broad choice. Therefore, the position of absorbing material is the most important variable. In this study, we use the optimization method to minimize acoustic energy of optional space in the interest frequency attaching some absorbing materials to the boundary area. For analysis and optimization, this study uses the FEA and the conjugate gradient method. This optimization process is very efficient and useful in the passive acoustic control.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.6
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• pp.889-897
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• 1986

The purpose of this study is to describe the strategy of machining process suitable for developing adaptive control with constraint of NC-machine tool. The algorithm that controls machining process parameters of every sampling time is established for the constraint of torque in machinig center. To prove this AC algorithm, manual AC-unit control test is used for simulating the on-line AC strategy control. Also machining tests are carried out on a CNC-machining center fitted with the ACC system and compared with the simulated results. The practical effectiveness of the ACC systems so discussed and the reduction of machining time are demonstrated with reference to typical models of cutting workpieces. As a typical model, taper and step geometry model are selected. The computer simulation results have a good agreement with the experimental observation and make it possible to develope a NC-machine tool with an on-line ACC system.

• Journal of Institute of Control, Robotics and Systems
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• v.6 no.9
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• pp.831-835
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• 2000

The uniformity of themperature on a wafer is a wafer is one the most important parameters to conterol the RTF(Rapid Thermal Process) with proper input signals. It is impossible to achieve the uniformity of temperature without the exact estimation of temperature ar all points on the wafer. There fore, it is difficult to understand the internal dynamics as well as the structural complexities of the RTP, which is aprimary obstacle to measure the distributed temperatures on the wafer accurately. Furthermore, it is also hard to accomplish desirable estimation because only a few pyrometers are available in the general equipments. In the paper, a thermal model based on the chamber grometry of the AST SHS200 RTP system is developed to effectively control the thermal uniformity on the wafer. First of all, the estimation method of one-point measurement is developed, which is properly extended to the case of multi-point measurements. This thermal model is validated through simulation and experiments. The proposed work can be utilized to building a run-by -run or a real-time control of the RTP.

• Nuclear Engineering and Technology
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• v.49 no.3
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• pp.484-494
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• 2017

In industrial plants such as nuclear power plants, system operations are performed by embedded controllers orchestrated by Supervisory Control and Data Acquisition (SCADA) software. A targeted attack (also termed a control aware attack) on the controller/SCADA software can lead a control system to operate in an unsafe mode or sometimes to complete shutdown of the plant. Such malware attacks can result in tremendous cost to the organization for recovery, cleanup, and maintenance activity. SCADA systems in operational mode generate huge log files. These files are useful in analysis of the plant behavior and diagnostics during an ongoing attack. However, they are bulky and difficult for manual inspection. Data mining techniques such as least squares approximation and computational methods can be used in the analysis of logs and to take proactive actions when required. This paper explores methodologies and algorithms so as to develop an effective monitoring scheme against control aware cyber attacks. It also explains soft computation techniques such as the computational geometric method and least squares approximation that can be effective in monitor design. This paper provides insights into diagnostic monitoring of its effectiveness by attack simulations on a four-tank model and using computation techniques to diagnose it. Cyber security of instrumentation and control systems used in nuclear power plants is of paramount importance and hence could be a possible target of such applications.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1845-1848
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• 2005

The automatic $CO_2$ welding is a manufacturing process to produce high quality joints for metal and it could provide a capability of full automation to enhance productivity. Despite the widespread use in the various manufacturing industries, the full automation of the robotic $CO_2$ welding has not yet been achieved partly because the mathematical model for the process parameters of a given welding task is not fully understood and quantified. Several mathematical models to control welding quality, productivity, microstructure and weld properties in arc welding processes have been studied. However, it is not an easy task to apply them to the various practical situations because the relationship between the process parameters and the bead geometry is non-linear and also they are usually dependent on the specific experimental results. Practically, it is difficult, but important to know how to establish a mathematical model that can predict the result of the actual welding process and how to select the optimum welding condition under a certain constraint. In this research, an attempt has been made to develop an intelligent algorithm to predict the weld geometry (top-bead width, top-bead height, back-bead width and back-bead height) as a function of key process parameters in the robotic $CO_2$welding. A sensitivity analysis has been conducted and compared the relative impact of three process parameters on bead geometry in order to verify the measurement errors on the values of the uncertainty in estimated parameters.