• Journal of the Society of Naval Architects of Korea
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• v.38 no.4
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• pp.23-29
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• 2001

An Obstacle Avoidance System(OAS) of Underwater Vehicle(UV) in diving and steering plane is investigated. The concept of Imaginary Reference Line(IRL), which acts as the seabed in the diving plane, is introduced to apply the diving plane avoidance algorithm to the steering plane algorithm. Furthermore, the distance to the obstacle and the slope information of the obstacle are used for more efficient and safer avoidance. As for the control algorithm, the sliding mode controller is adopted to consider the nonlinearity of the equations of motion and to get the robustness of the designed system. To verify the obstacle avoidance ability of the designed system, numerical simulations are carried out on the cases of some presumed three-dimensional obstacles. The effects of the sonar and the clearance factor used in avoidance algorithm are also investigated. Through these, it is found that the designed avoidance system can successfully cope with various obstacles and the detection range of sonar is proven to bea significant parameter to the performance of the avoidance.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.2
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• pp.639-643
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• 2018

As electronic systems become smaller and more portable, the need for power conversion continues to increase. In addition, system stability must be ensured from switching noise due to power conversion efficiency and power conversion system miniaturization. Therefore, countermeasures to reduce switching noise during power conversion are essential. In this paper, a DC/DC buck converter circuit is constructed, and the characteristics of switching noise generated when changing the parts layout in a four-layer printed circuit board (PCB) structure with a reference plane are compared and analyzed. In addition, switching noise characteristics were compared and analyzed through simulations when the parts layout was different in a two-layer PCB structure from which the reference planes were removed. As a result, it was confirmed that the radiated emissions characteristic is reduced by 12dB and the conducted emissions characteristic decreased by 7dB to 8dB, according to the current return path in the four-layer PCB structure. Thus, it was confirmed that the noise characteristics can be improved according to the configuration of the current return path when the power conversion circuit is designed.

• Geophysics and Geophysical Exploration
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• v.9 no.2
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• pp.171-175
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• 2006

Gravity reduction and Bouguer anomaly are frequently misunderstood by many geoscientists as follows; the observed gravity is reduced to a common datum plane, so that gravity effects by all materials above the datum is removed, therefore, Bouguer anomaly is located on the datum plane. In reality, Bouguer anomaly does not lie on a common datum plane, but is difference between observed gravity and reference gravity at the actual point of measurement. Commonly used gravity reduction formulas are approximate formulas. Here, we introduce complete formulas, and suggest to use them for more accurate results. We also suggest to use not the geoid but the reference ellipsoid as the vertical datum.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.8
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• pp.637-648
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• 2021

This paper aims to propose new reentry guidance for Korean Space plane (KSP). Similar to the Space Shuttle guidance concept, a reference drag profile is first determined to satisfy several flight path constraints and boundary conditions, and the proposed guidance commands are realized in a way to track the predetermined reference drag profile. To this end, the drag dynamics is examined. The investigation uncovers that the dynamics characteristics of the drag and the flight path angle are considerably different. Based on this fact, the proposed guidance commands are determined using the time-scale separation technique and the feedback linearization methodology. The key feature of the proposed guidance lies in its simple structure and a clear working mechanism. Therefore, the proposed method is simple to implement compared to existing methods. Numerical simulations are performed to investigate the performance of the proposed method.

• Smart Structures and Systems
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• v.20 no.5
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• pp.563-572
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• 2017

The safety of structures is closely associated with the structural out-of-plane behavior. In particular, long and slender beam structures have been increasingly used in the design and construction. Therefore, an evaluation of the lateral and torsional behavior of a structure is important for the safety of the structure during construction as well as under service conditions. The current contact measurement method using displacement meters cannot measure independent movements directly and also requires caution when installing the displacement meters. Therefore, in this study, a vision-based system was used to measure the in-plane and out-of-plane displacements of a structure. The image processing algorithm was based on reference objects, including multiple targets in Lab color space. The captured targets were synchronized using a load indicator connected wirelessly to a data logger system in the server. A laboratory beam test was carried out to compare the displacements and rotation obtained from the proposed vision-based measurement system with those from the current measurement method using string potentiometers. The test results showed that the proposed vision-based measurement system could be applied successfully and easily to evaluating both the in-plane and out-of-plane movements of a beam including twisting rotation.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.40 no.3
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• pp.123-129
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• 2014

Objectives: The aim of this study was to verify the concordance of the measurement values when the same cephalometric analysis method was used for two-dimensional (2D) cephalometric radiography and three-dimensional computed tomography (3D CT), and to identify which 3D Frankfort horizontal (FH) plane was the most concordant with FH plane used for cephalometric radiography. Materials and Methods: Reference horizontal plane was FH plane. Palatal angle and occlusal plane angle was evaluated with FH plane. Gonial angle (GA), palatal angle, upper occlusal plane angle (UOPA), mandibular plane angle (MPA), U1 to occlusal plane angle, U1 to FH plane angle, SNA and SNB were obtained on 2D cephalmetries and reconstructed 3D CT. The values measured eight angles in 2D lateral cephalometry and reconstructed 3D CT were evaluated by intraclass correlation coefficiency (ICC). It also was evaluated to identify 3D FH plane with high degree of concordance to 2D one by studying which one in four FH planes shows the highest degree of concordance with 2D FH plane. Results: ICCs of MPA (0.752), UOPA (0.745), SNA (0.798) and SNB (0.869) were high. On the other hand, ICCs of gonial angle (0.583), palatal angle (0.287), U1 to occlusal plane (0.404), U1 to FH plane (0.617) were low respectively. Additionally GA and MPA acquired from 2D were bigger than those on 3D in all 20 patients included in this study. Concordance between one UOPA from 2D and four UOPAs from 3D CT were evaluated by ICC values. Results showed no significant difference among four FH planes defined on 3D CT. Conclusion: FH plane that can be set on 3D CT does not have difference in concordance from FH plane on lateral cephalometry. However, it is desirable to define FH plane on 3D CT with two orbitales and one porion considering the reproduction of orbitale itself.

• The Journal of the Acoustical Society of Korea
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• v.17 no.2E
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• pp.47-52
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• 1998

An analysis of dynamic responses is carried out on monoclinic anisotropic system due to a buried harmonic line source. The load is in the form of a normal stress acting along an arbitrary axis on the plane of symmetry within the orthotropic materials: In case that the line load is acting along the symmetry axis normal to the plane of symmetry, plane wave equation is coupled with verital shear wave and longitudinal wave. However, if the line load is acting along an arbitrary axis normal to the plane of symmetry, plane wave equation is coupled with vertical shear wave, longitudinal wave and horizontal shear wave. We first considered the equation of motion in a reference coordinate system, where the line load is coincident with a symmetry axis of the orthotropic material. Then the equation of motion is transformed into one with respect to general coordinate system with azimuthal angle by using transformation tensor. Plane wave solutions of monoclinic systems are derived for infinite media. Finally complete solutions for the plane harmonic wave are obtained by calculating the inverse of the integral transforms, in which bulk wave poles are avoided by deforming the contour of the integration to the complex plane. Numerical results for examples of orthotropic material belonging to monoclinic symmetry are demonstrated.

• Earthquakes and Structures
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• v.6 no.5
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• pp.515-537
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• 2014

Current seismic codes (e.g. the NTC08 Italian code and the EC8 European code) adopt a performance-based approach for both the design of new buildings and the assessment of existing ones. Different limit states are considered by verifying structural members as well as non structural elements and facilities which have generally been neglected in practice. The key role of non structural elements on building performance has been shown by recent earthquakes (e.g. L'Aquila 2009) where, due to the extensive damage suffered by infills, partitions and ceilings, a lot of private and public buildings became unusable with consequent significant socio-economic effects. Furthermore, the collapse of infill panels, particularly in the case of out-of-plane failure, represented a serious source of risk to life safety. This paper puts forward an infill model capable of accounting for the effects arising from prior in-plane damage on the out-of-plane capacity of infill panels. It permits an assessment of the seismic performance of existing RC buildings with reference to both structural and non structural elements, as well as of their mutual interaction. The model is applied to a building type with RC framed structure designed only to vertical loads and representative of typical Italian buildings. The influence of infill on building performance and the role of the out-of-plane response on structural response are also discussed.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.10a
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• pp.416-421
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• 2004

Off-line feedrate scheduling is presented as the advanced technology to regulate cutting forces at the desired level through change of feedrates. In rough cutting, the feedrate scheduling aims at reducing the machining time, which is the most important factor for better productivity. Thus, the largest force which can avoid breakage of tool shank and tooth is a reference force for feedrate scheduling in rough cutting. In this paper, a calculation method of the reference cutting force for feedrate scheduling is developed. This model calculates rupture plane of tooth using the FEM analysis of a tool and computes the reference force using the transverse rupture strength of a tool. Experiments validate that the presented feedrate scheduling model reduced machining time drastically and regulate cutting forces at the reference cutting force.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.20 no.1
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• pp.19-27
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• 1990

The primary objective of this study was to analyze the hard and soft tissue profile and comparison of the both sexes in Korean adults using roentgenocephalometry. The subjects were 122 males and 116 females from 18 to 22 years of age selected on the basis of their excellent occlusion and harmonious profile. It was an investigation about the interrelationships in the angles which consisted of Frankfort horizontal plane (FH plane), Sella Nasion plane (SN plane), Nasal floor plane (NF plane) and Mandibular plane (Md plane) as reference planes, and of the axial inclinations of the upper anterior tooth to Nasal floor plane (NF Plane) and of the lower anterior tooth to Mandibular plane (Md Plane). Among the 14 categories estabilishied on the soft tissue land marks, the 6 categories were studied for the relationship to Frankfort horizontal plane (FH Plane), and the 8 categories were studied for the soft tissue contour. The results were as follows: 1. Among 8 measured angles in the hard tissue, the angle of FH-Md, NF-Md and SN-Md were greater in females than in males. 2. The axial inclinations of the anterior teeth to NF Plane and Md plane were slightly greater in males than In females. 3. Among 14 measured angles in the soft tissue, the angles of G-Sn-P and E-Pog-Sn were greater in males, and FH-G-Sn, GㆍSn-Sn. Pog and Pog-Sn-P were greater in females. 4. In males, the variability of measured values in both lips region were high.