• Journal of Institute of Control, Robotics and Systems
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• v.19 no.2
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• pp.131-139
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• 2013

In recent years alternative navigation system such as a DBRN (Data-Base Referenced Navigation) system using geophysical information is getting attention in the military navigation systems in advanced countries. Specifically TRN (Terrain Referenced Navigation) algorithm research is important because TRN system is a practical DBRN application in South Korea at present time. This paper presents an integrated navigation algorithm that combines a linear profile-based TRN and INS (Inertial Navigation System). We propose a correlation analysis method between TRN performance and terrain roughness index. Then we propose a conditional position update scheme that utilizes the position output of the conventional linear profile type TRN depending on the terrain roughness index. Performance of the proposed algorithm is verified through Monte Carlo computer simulations using the actual terrain database. The results show that the TRN/INS integrated algorithm, even when the initial INS error is present, overcomes the shortcomings of linear profile-based TRN and improves navigation performance.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.7
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• pp.629-639
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• 2016

Batch process TRN(Terrain Relative Navigation) using an altimeter is a technique to correct position by correlating a series of periodically measured terrain height profile and terrain height candidate profile of the DEM(Digital Elevation Map). However, it is generally known that the performance of TRN is degraded when measured terrain height profile and terrain height candidate profiles of the DEM are similar at hill or repetitive terrain. In this paper, area based terrain slope roughness index[11] is applied and area based terrain curvature roughness index which can detect similarity of terrain in ROI(Region Of Interest) is proposed to overcome this problem. Applying terrain roughness indexes to terrain relative navigation system of lunar lander, it is shown that TRN using area based terrain roughness results in improved performance compared to conventional trajectory based method through simulation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.7
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• pp.891-899
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• 1997

This paper presents the results of a detailed experimental examination of fully developed asymmetric flows between annular tubes with square-ribbed surface roughness. The main emphasis of the research has been on establishing the turbulence structure, particularly in the central region of the channel where the two dissimilar wall flows interact. Measurements have included profiles of time mean velocities, turbulence intensities, turbulent shear stresses, triple velocity correlations, skewness, and flatness. The region of greatest interaction is characterized by strong diffusional transport of turbulent shear stress and kinetic energy from rough toward the smooth wall region, giving rise to an appreciable separation between the planes of zero shear stresses depending on positions of roughness on the walls.

• Journal of Korea Water Resources Association
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• v.37 no.12
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• pp.1055-1063
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• 2004

An unsteady flow model is developed that allows variable roughness coefficient for each computational point according to its spatial position and the discharge. A step function or a power function can be used for functional relation between the discharge and the Manning's roughness coefficient. The model is applied to the reach of the South Han River between the Chungju Dam and Paldang Dam, and model parameters are estimated by optimization. Estimated parameters of both the step function model and the Power function model show that Manning's roughness coefficient decreases as the discharge increases. This tendency is more noticeable for the upstream reach of Yeoju compared to the downstream reach. It turns out that the stages calculated by the variable roughness coefficient model agree better with the observed ones than those by the conventional fixed parameter model.

• Design & Manufacturing
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• v.17 no.4
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• pp.1-7
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• 2023

In the fabrication of curved multi-display glass for automotive use, the surface roughness of the mold is a critical quality factor. However, the difficulty in detecting micro-cutting signals in a micro-machining environment and the absence of a standardized model for predicting micro-cutting forces make it challenging to intuitively infer the correlation between cutting variables and actual surface roughness under machining conditions. Consequently, current practices heavily rely on machining condition optimization through the utilization of cutting models and experimental research for force prediction. To overcome these limitations, this study employs a surface roughness prediction formula instead of a cutting force prediction model and converts the surface roughness prediction formula into experimental data. Additionally, to account for changes in surface roughness during machining runtime, the theory of position variables has been introduced. By leveraging artificial neural network technology, the accuracy of the surface roughness prediction formula model has improved by 98%. Through the application of artificial neural network technology, the surface roughness prediction formula model, with enhanced accuracy, is anticipated to reliably perform the derivation of optimal machining conditions and the prediction of surface roughness in various machining environments at the analytical stage.

• Tribology and Lubricants
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• v.20 no.5
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• pp.284-291
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• 2004

We present a three-dimensional average flow model considering elastic deformation of pad asperities for chemical mechanical planarization. To consider the contact deformation of pad asperities in the calculation of the flow factor, three-dimensional contact analysis of a semi-infinite solid based on the use of influence functions is conducted from computer generated three dimensional roughness data. The average Reynolds equation and the boundary condition of both force and momentum balance are used to investigate the effect of pad roughness and external pressure conditions on film thickness and wafer position angle.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.13 no.2
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• pp.41-48
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• 2014

Direct writing(DW) is a method of patterning materials to a substrate directly, without a mask. It can use a variety of materials and be applied to various fields. Among DW systems, the flow-based type, using a syringe pump and nozzle, is simpler than other types. Furthermore, the range of materials is exceptionally wide. In additive processes, a three dimensional structure is made of stacking layer. Each layer is made of several lines. In this regard, good surface roughness of fabricated layers is essential to three dimensional fabrication. The surface roughness of any fabricated layer tends to change with the dispensing pattern. When multiple layers fabricated by a nozzle dispensing system are stacked, control of the nozzle position from the substrate is important in order to avoid interference between the nozzle and the fabricated layer. In this study, a fluid direct writing system for three dimensional structure fabrication was developed. Experimentsto control the position of the nozzle from substrate were conducted in order to examine the characteristics of the material used in this system.

• Journal of Welding and Joining
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• v.32 no.6
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• pp.22-28
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• 2014

Most publications on friction stir welding describe phenomena or results with given process parameters like feed rate, rotation speed, angle and depth of penetration. But without a complete documentation of tool design, the results under the same process parameters are completely different. For this purpose, the Institute of Cutting and Joining Manufacturing Processes (tff), University of Kassel investigated the influence of tool roughness on the friction stir welding process. Therefore a defined surface finish was produced by turning and die sinking. As basis of comparison the constant parameters were rotation speed, feed rate, tilt angle and a heel plunge depth. Sound butt-welds were produced in aluminium alloy 6082 (AlMgSi1) with 1.5 mm sheet thickness with a turned reference tool with a surface of $Ra=0.575{\mu}m$ in position controlled mode. The surfaces are manufactured from a very fine to a very rough structure, classified by the VDI-classes with differences in the arithmetical mean roughness. It can be demonstrated with the help of temperature measures, that less heat is generated at the surfaces of the shoulder and the pin by the higher roughness due to lower active friction contact surface. This can also be seen in the resulting wormhole defects.

• Wind and Structures
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• v.12 no.4
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• pp.349-381
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• 2009

Since 1998, several institutions have deployed mobile instrumented towers to collect research-grade meteorological data from landfalling tropical cyclones. This study examines the wind flow characteristics from seven landfalling tropical cyclones using data collected from eight individual mobile tower deployments which occurred from 1998-2005. Gust factor, turbulence intensity, and integral scale statistics are inspected relative to changing surface roughness, mean wind speed and storm-relative position. Radar data, acquired from the National Weather Service (NWS) Weather Surveillance Radar - 1988 Doppler (WSR-88D) network, are examined to explore potential relationships with respect to radar reflectivity and precipitation structure (convective versus stratiform). The results indicate tropical cyclone wind flow characteristics are strongly influenced by the surrounding surface roughness (i.e., exposure) at each observation site, but some secondary storm dependencies are also documented.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.591-596
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• 2002

Fused deposition(FD) modeling by Stratasys Inc., is one of the material deposition subfamilies of solid freefrom fabrication(SFF) technologies. In this process, build material in the form of a flexible filament, is heated to a semi-liquid state and extruded from a controlled deposition head onto a fixtureless table in a temperature controlled environment. The position of nozzle is computer controlled relative to the base, which allows geometric complex models to be made to precise dimensions. FDM provide what the part was directly tested by the worker. It provide believable data. This Study is identify to surface roughness by build orientation adjustment. So, the paper is the study on surface roughness by build orientation at FDM.