• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2002년도 봄 학술발표회 논문집
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• pp.401-406
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• 2002

A numerical model is introduced to simulate propagation, reflection, and scattering of elastic waves in solids. The model consists of mass points and linear springs, interconnected with in a lattice structure; hence, its name, the mass-spring lattice model (MSLM). The MSLM has successfully been applied to the numerical simulation and visualization of various elastic wave phenomena involved in ultrasonic nondestructive testing (NDT). This method is useful to simulate, design, or analyze actual testing. Some representative examples of numerical simulation using the MSLM are presented, and future work necessary for its further development Is addressed.

• Structural Engineering and Mechanics
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• 제85권6호
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• pp.729-742
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• 2023

It is a recent attraction to the mechanical scientists to investigate state of wave propagation, buckling and vibration in the sport balls to observe the importance of different parameters on the performance of the players and the quality of game. Therefore, in the present study, we aim to investigate the wave propagation in handball game ball in term of mass of the ball and geometrical parameters wit incorporation of the viscoelastic effects of the ball material into account. In this regard, the ball is modeled using thick shell structure and classical elasticity models is utilized to obtain the equation of motion via Hamilton's principle. The displacement field of the ball model is obtained using first order shear deformation theory. The resultant equations are solved with the aid of generalized differential quadrature method. The results show that mass of the ball and viscoelastic coefficient have considerable influence on the state of wave propagation in the ball shell structure.

• The Journal of the Acoustical Society of Korea
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• 제26권2E호
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• pp.50-55
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• 2007

SBN (Structure-Borne Noise) reduction in resiliently mounted machineries are predicted by using mass-spring model and wave model. In mass-spring model, mount is modeled as a spring, while in wave model, mount is considered as an equivalent elastic rod for taking account into longitudinal wave propagation. The predictions for SBN reduction through mounts are compared to the measurements for four different pumps. It is found that the mass-spring model is valid only in low frequency range below few hundred Hz, while for high frequency ranges longitudinal wave propagation in the mount must be considered to explain the measurements. It is also shown that impedance of the floor slightly affects low frequency behaviour in mass-spring and wave model below 50 Hz - 80 Hz, so that in engineering practice the effect of floor impedance may be neglected in computing mount performance.

• Journal of Forest and Environmental Science
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• 제34권1호
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• pp.50-52
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• 2018

The effect of basal nutrients concentrations and exogenous auxin for root induction from leaves of Sedum takesimense were investigated for mass-propagation. Root induction rates were significantly different from the concentrations of basal salts but not influenced by supplemented IBA in the medium. The lowest concentration of MS basal salts (1/10) was most effective to induce roots from leaves followed 1/5 MS, and 1/2 and full strength MS medium. Supplement of IBA $10{\mu}M$ in the medium did not improve the root induction that resulted no differences compare to the hormone free media. Rooted leaves were transplanted in soil and survived in greenhouse.

• 한국해양공학회지
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• 제21권5호
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• pp.18-24
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• 2007

The environmental value of coastal vegetation has been widely recognized. Coastal vegetation such as reed forests and seaweed performs several useful functions, including maintaining water quality, supporting fish (and, thus, fisheries), protecting beaches and land from wave attack, stabilizing sea beds and providing scenic value. However, studies on the physical and numerical process of wave propagation, sediment transport and bathymetric change are few and far between compared to those on the hydrodynamic roles of coastal vegetation. In general, vegetation flourishing along the coastal areas attenuates the incident waves through momentum exchange between stagnated water mass in the vegetated area and rapid mass in the un-vegetated area. This study develops a numerical model for describing the wave attenuation and sediment transport in a wave channel in a vegetation area. By comparing these results, the effects of vegetation properties, wave properties and model parameters are clarified.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 춘계 학술발표회
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• pp.58-63
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• 2009

Biaxial compression test was conducted on a transversely isotropic synthetic jointed rock model for the understanding of the fracture behaviors of a sedimentary or metamorphic rocks with well developed bedding or foliation in uni-direction. The joint angles employed for the model are 30, 45, and 60 degrees to the horizontal, and the synthetic rock mass was made of early strength cement. From the biaxial compression test, initiation propagation of tensile cracks at norm to the joint angle was found. The propagated tensile cracks eventually developed rock blocks, which was dislodged from the rock mass. Furthermore, the propagation process of the tensile cracks varies with joint angle: lower joint angle model shows more stable and progressive tensile crack propagation. The experiment results were validated from the simulation by using discrete element method PFC 2D. From the simulation, as has been observed from the test, a rock mass with lower joint angle produces wider damage region and rock block by tensile cracks. In addition, a rock model with lower joint angle shows a progressive tensile cracks generation around the opening from the investigation of the interacted tensile cracks.

• Geomechanics and Engineering
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• 제21권3호
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• pp.227-236
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• 2020

Non-destructive exploration using elastic waves has been widely used to characterize rock mass properties. Wave propagation in jointed rock masses is significantly governed by the characteristics and orientation of discontinuities. The relationship between spatial heterogeneity (i.e., joint spacing) and wavelength for elastic waves propagating through jointed rock masses have been investigated previously. Discontinuous rock masses can be considered as an equivalent continuum material when the wavelength of the propagating elastic wave exceeds the spatial heterogeneity. However, it is unclear how stress-dependent long-wavelength elastic waves propagate through a repetitive rock-joint system with multiple joints. A preliminary numerical simulation was performed in in this study to investigate long-wavelength elastic wave propagation in regularly jointed rock masses using the three-dimensional distinct element code program. First, experimental studies using the quasi-static resonant column (QSRC) testing device are performed on regularly jointed disc column specimens for three different materials (acetal, aluminum, and gneiss). The P- and S-wave velocities of the specimens are obtained under various normal stress levels. The normal and shear joint stiffness are calculated from the experimental results using an equivalent continuum model and used as input parameters for numerical analysis. The spatial and temporal sizes are carefully selected to guarantee a stable numerical simulation. Based on the calibrated jointed rock model, the numerical and experimental results are compared.

• 한국자원식물학회지
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• 제15권1호
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• pp.8-17
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• 2002

새 번식방법 개발을 위해 둥굴레 뿌리는 눈이 없어도 부정아가 발생된다는 점에 착안하여 뿌리길이와 굵기에 대한 부정아 발생에 관한 시험 연구를 한 결과는 다음과 같다. 1년차는 뿌리길이가 5cm 경우 66.5%지만 15cm에서는 113% 부정아 발생되었고, 뿌리의 굵기 5mm이하는 98.3%지만 10mm이상은 113.3%로 46.7% 차이를 보였다. 2년차는 부정아 생성률은 15cm에서는 1년차의 3배, 시험구 설치 당시 전혀 눈이 없는 상태에서 4배의 증식을 보였다. 용토는 일반토양 2.6배 보다 모래나 펄라이트가 3.1~3.3배 증식 되었다. 대량번식을 위한 가장 좋은 방법은 10mm 둥굴레 뿌리를 5cm로 절단하여 모래에 식재하는 방법으로 판단된다.

• Journal of Astronomy and Space Sciences
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• 제15권2호
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• pp.307-320
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• 1998

다중 위성 관측을 이용하여 지구 근처에서의 태양물질 방출현상(CME: Coronal Mass Ejection)의 전파 속도와 방향에 대하여 조사하였다. 이를 위해 1994년 11월까지 지구에 영향을 미친 CME 중에서 세 개 이상의 위성에서 관측되고 각 위성들이 충분한 거리를 두고 떨어져 있는 1997년 1월 6-11일과 1997년 11월 4-7일의 두 CME 자료를 선택하였다. 위성들의 위치를 공통 좌표 계로 전환하여 위성간의 거리와 CME에 의한 물리량의 변화 시간을 조사하여 CME의 전파 방향과 속도를 계산하였다. 선택된 자료에 대한 조사 결과 지구 자기권 내부에서 CME 전파 속도가 급격히 줄어들었으며 또한 자기권 외부에서의 CME 전파 방향이 GSE 좌표계상의 -x 방향과 일치함을 알 수 있었다.

• 한국조경학회지
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• 제27권4호
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• pp.50-58
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• 1999

This study was carried out to investigate the growth characteristics and propagation methods of L. obtusiloba as a woody landscape plant. The results are obtained as follows: L. obtusiloba was dioecious shrub and shaped with bush type. Leaves were ovate, obtuse, cordate, 7.05 cm long, 7.20 cm wide, and petiole 2.0 cm long. Flowers of L. obtusiloba were diclinous. Soil acidity ranged from pH 4.06 to 5.53 with the lowest at the Mt. Soo-Ri. Mt. Soo-Ri located near factory district, which was considered to damaged by environmental deteoration. While soil organic matter was highest at Mt. Soo-Ri, inorganic nutrients were low. L. obtusiloba grows in the area with low soil acidity and low content of inorganic. Therefore it seemed to be tolerant to air pollution. L. Obtusiloba was high seed germination rate in the plug box and its shoots were longer than seeding box and softwood cutting of L. obtusiloba showed the rooting rate of 50% at 5,000ppm on June 23. To develop a mass propagation method of Korean native L. obtusiloba through an axillary bud culture as a woody landscape plant, about 2∼3 cm shoots induced from explant were subcultured to new media contained different growth regulators. Shoots multiplied most effectively on a WPM containing 1.0 mg/l BA, producing 5.5 shoots with a shoot length of 2.5 cm per shoot explant.