• Journal of Advanced Marine Engineering and Technology
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• v.34 no.5
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• pp.695-702
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• 2010

Numerical analysis information will be very useful to improve fluid system. General information about an internal gas flow is presented by numerical analysis approach. Relating with hydrogen compressing system, which have an important role in hydrogen energy utilization, this should be a useful tool to observe the flow quickly and clearly. Flow characteristic analysis, including pressure and turbulence kinetic energy distribution of hydrogen gas coming to the cylinder of a reciprocating compressor are presented in this paper. Suction-passage model is designed based on real model of hydrogen compressor. Pressure boundary conditions are applied considering the real condition of operating system. The result shows pressure and turbulence kinetic energy are not distributed uniformly along the passage of the Hydrogen system. Path line or particles tracks help to demonstrate flow characteristics inside the passage. The existence of vortices and flow direction can be precisely predicted. Based on this result, the design improvement, such as reducing the varying flow parameters and flow reorientation should be done. Consequently, development of the better hydrogen compressing system will be achieved.

• Journal of Biosystems Engineering
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• v.19 no.1
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• pp.17-21
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• 1994

This reasearch was performed to provide the fundamental intonation for the mechanization of Korean pine cone harvest when the shoot shearing method is adopted. Shear force and stress of pine cone shoots were measured and analyzed for this purpose. Samples are selected along their harvesting time and tested in 17 levels of shoot diameter from 10 to 26mm with 1mm increment. 1) Shear force-deformation characteristics showed that shoot reached its rupture point after 2 to 4 of bio-yield points. It was supposed that these multiple bio-yield points were caused by the discrete compression of wood parts which are composed of water, nutrient, resin, etc. 2) Required shear force to shear shoot was proportional to the square of shoot diamter, however, shear force for shoots of early harvesting time(Aug. 31) was proportional to the shoot diameter. Variance of shear force was increased as the harvesting time was delayed. Shear forces were distributed from 468N(Aug. 31, 12mm dia) to 4153N(Aug. 31, 26mm dia) disregarding the sampling date. 3) The average shear stresses by sampling dates were 744,822, and 883N/m2, respectively, and for the earlier shoot samples shear stress was quite smaller than the others. Shear stress was proportional to shoot diameter squared, and the effect of shoot diameter on the shear stress was decreased as harvesting time was delayed.

• Korean Journal of Optics and Photonics
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• v.13 no.3
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• pp.235-239
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• 2002

A novel ultra-narrow linewidth DFB laser in the extended FBG ring cavity having kHz linewidth is presented. The method of linewidth compression was realized by introducing an extended fiber ring cavity into the cavity between the external FBG and the Bragg grating inside a DFB laser diode. Optimum optical feedback control was achieved by using an optical circulator and a variable optical attenuator to prevent mode hopping induced by spatial hole burning. To prove the validity of the proposed scheme, a self-heterodyne measurement set-up with fiber delay line of 63 km was utilized for the ultra-narrow linewidth measurement. A 3 dB linewidth of less than 3 kHz was demonstrated, which is resolution limited performance. This linewidth is equivalent to 3 dB linewidth of 2$\times$10$^{-8}$ nm.

• The Journal of Korean Academy of Prosthodontics
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• v.9 no.1
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• pp.29-34
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• 1969

Occlusal force is a critical factor affecting the condition and structure of the periodontium. When the occlusal forces exceed the physiologic adaptive capacity of the tissues, tissue damage ensues. Such damage is referred to as trauma from occlusion. Excessive pressure causes compression, degeneration and realignment of the periodontal ligament fibers so that they are paralleled perpendicular to the tooth and bone. By inducing excessive occlusal forces with a high amalgam filling on rat's molar, the author observed histologic alterations of the periodontal ligament fibers by means of Hematoxylin-eosin, Van Gieson and Aldenyde fuchsin stainings. The results of the study were observed as follows: 1) The excessive occlusal forces altered arrangement of the collagenous fibers. 2) The arrangement of the oblique fibers showed appreciable differences between the control group and the group subjected to 10 days experimental trauma from occlusion. 3) The realignment of the transseptal fibers was not found. 4) The arrangement of the oblique fibers after 15 days of trauma from occusion was similar to that of 10 days experimental group. 5) The oxytalan fibers were more abundant at the cementum rather than at the alveolar bone. 6) The excessive occlusal forces produced funnel-shaped widening of the oxytalan fibers, which followed wavy course. 7) The oxytalan fibers appeared to be distributed mainly around the middle third of the root rather than that of the apical third of the root during the experimental trauma from occlusion.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.13 no.2
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• pp.355-361
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• 2009

This paper proposes a new basic unit level rate control algorithm which generates the output bits corresponding to the target bits. The H.264 standard uses various coding modes and optimization methods to improve the compression performance, which makes it difficult to control the generated traffic accurately. In the proposed scheme, the allocated bits to a frame are distributed to all basic units properly to encode each basic unit according to the bit budget. After encoding the frame, the encoding parameters are adjusted according to the difference between the target and the resulting values. It is shown by experimental results that the new algorithm can generate output bit rates accurately corresponding to the target bit rates with the PSNR performance better than that of the existing rate control algorithm.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.10
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• pp.4618-4639
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• 2018

One of the most innovative paradigms for the next-generation of wireless cellular networks is the cloud-radio access networks (C-RANs). In C-RANs, base station functions are distributed between the remote radio heads (RHHs) and base band unit (BBU) pool, and a communication link is defined between them which is referred as the fronthaul. This leveraging link is expected to reduce the CAPEX (capital expenditure) and OPEX (operating expense) of envisioned cellular architectures as well as improves the spectral and energy efficiencies, provides the high scalability, and efficient mobility management capabilities. The fronthaul link carries the baseband signals between the RRHs and BBU pool using the digital radio over fiber (RoF) based common public radio interface (CPRI). CPRI based optical links imposed stringent synchronization, latency and throughput requirements on the fronthaul. As a result, fronthaul becomes a hinder in commercial deployments of C-RANs and is seen as one of a major bottleneck for backbone networks. The optimization of fronthaul is still a challenging issue and requires further exploration at industrial and academic levels. This paper comprehensively summarized the current challenges and requirements of fronthaul networks, and discusses the recently proposed system architectures, virtualization techniques, key transport technologies and compression schemes to carry the time-sensitive traffic in fronthaul networks.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.603-610
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• 2003

The influence of Poisson's ratio on the tensile strength of brittle materials is neglected in many studies. When brittle materials are loaded in compression or impact, substantial tensile stresses are induced within the materials. These tensile stresses are responsible for splitting failure of the materials. In this paper, the state of stress in a spherical particle due to two diametrically opposed forces is analyzed theoretically. A simple equation for the state of stress at the center of the particle is obtained. An analysis of the distribution of stresses along the z-axis due to distributed pressures and concentrated forces, and on diametrically horizontal plane due to concentrated forces, shows that it is reasonable to propose the tensile stress at the center of the particle at the point of failure as a tensile strength of the particle. Moreover, the tensile strength is a function of the Poisson's ratio of the material. As the state of stress along the z-axis in an irregular specimen tends to be similar to that in a spherical particle compressed diametrically with the same force, this tensile strength has some validity for irregular particles as well. Therefore, it can be proposed as the tensile strength for brittle materials generally. The effect of Poisson's ratio on the tensile strength is discussed.

• Steel and Composite Structures
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• v.22 no.1
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• pp.203-216
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• 2016

To study the stress concentration factors (SCFs) of concrete-filled tubular Y-joints subject to in-plane bending, experiments were used to investigate the hot spot stress distribution along the intersection between chord and brace. Three concrete-filled tubular chords forming Y-joints were tested with different reinforcing components, including doubler-plate, sleeve, and haunch-plate reinforcement. In addition, an unreinforced joint was also tested for comparison. Test results indicate that the three different forms of reinforcement effectively reduce the peak SCFs compared with the unreinforced joint. The current research suggests that the linear extrapolation method can be used for chords, whereas the quadratic extrapolation method must be used for braces. The SCF is effectively reduced and more evenly distributed when the value of the axial compression ratio in the chord is increased. Furthermore, the SCFs obtained from the test results were compared to predictions from some well-established SCF equations. Generally, the predictions from those equations are very consistent for braces, but very conservative for concrete-filled chords.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2001.11a
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• pp.21-27
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• 2001

Springs are widely utilized in machine element. To find out stiffness of frustum-shaped coil spring, the space beam theory using the finite element method is adopted in this paper In three dimensional space, a space frame element is a straight bar of uniform cross section which is capable of resisting axial forces, bending moments about two principal axes in the plane of its cross section and twisting moment about its centroidal axis. The corresponding displacement degrees of freedom are twelve. To find out load vector of coil spring subjected to distributed compression, principle of virtual work is adapted The displacements of nodal points due to small increment of force are calculated by the finite element method and the calculated nodal displacements are added to coordinates of nodal points. The new stiffness matrix of the system using the new coordinates of nodal points is adopted to calculate the another increments of nodal displacements, that is, the step by step method is used in this paper. The results of the finite element method are fairly well agreed with those of various experiments. Using MATLAB program developed in this paper, spring constants and stresses can be predicted by input of few factors.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.472-477
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• 2003

This study was performed to investigate the behavior of vapor phase of fuel mixtures with different piston cavity diameters in a optically accessible engine. The images of vapor phases were measured in the motoring engine using exciplex fluorescence method. The conventional engine was modified as GDI engine with swirl flow. Fuel was injected into atmospheric nitrogen to prevent quenching phenomenon by oxygen. Injection pressure is 5.1MPa. Two dimensional spray fluorescence image of vapor phases was acquired to analyze spray behavior and fuel distribution inside of cylinder. Three injection timings were set at BTDC $180^{\circ}$, $60^{\circ}$and $60^{\circ}$. With a fuel injection timing of BTDC $60^{\circ}$, fuel-rich mixture was concentrated in near the cavity center. With a fuel injection timing of BTDC $60^{\circ}$, fuel-rich mixture level in the center region was highest in the S-type during the late compression stroke. With a fuel injection timing of BTDC $180^{\circ}$, fuel was not affected in a piston cavity and generally distributed as homogeneous mixture.