• Journal of Advanced Marine Engineering and Technology
• /
• v.41 no.2
• /
• pp.150-155
• /
• 2017

Many engineering issues are caused because of sloshing phenomena. Numerical solution methods including the computational fluid dynamics (CFD) technique, are used to analyze these sloshing problems. In this study, a numerical technique was used to analyze sloshing impact loads in a prismatic tank under forced horizontal motion. The volume-of-fraction (VOF) method was adopted to model the sloshing flow. Six cases were used to compare the effects of the natural frequencies of a simple rectangular and prismatic tank, with impact pressure on the prismatic tank wall. This study also investigated the variable pressure loads and sloshing phenomena in prismatic tanks when the frequencies were changed. The results showed that the average of the peak pressure value for ${\omega}^{\prime}1=4.24=4.24$ was 22% higher than that of ${\omega}_1=4.6$.

• International Journal of Automotive Technology
• /
• v.2 no.1
• /
• pp.25-31
• /
• 2001

It is necessary to understand the combustion process and cycle-by-cycle variation in combustion to improve the engine stability and consequently to improve the fuel economy and exhaust emissions. The pressure related parameters instead of mass fraction burned were compared for the effect of initial combustion pressures on the following combustion and the analysis of cycle-by-cycle variation in combustion for two pen injected SI engines. The correlation between IMEP and pressures at referenced crank angles showed almost the same trends for equivalence ratios, but the different mixture preparations indicated different tendency. The dependency of IMEP on pressure at the referenced crank angles increases as the mixture becomes leaner for both engines. The mixture distribution in the combustion chamber was varied with the coolant temperature and intake valve deactivation due to the evaporation of fuel and air motion. The correlation between pressure related parameters were also compared for the coolant temperatures and air motion.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.11a
• /
• pp.527-533
• /
• 2000

It is investigated that the characteristics of rotating cantilevered composite beam with a breathing crack. In the present study, the crack is modeled as a breathing crack which opens and closes with the motion of the unidirectional graphite-fiber reinforced polyimide beam. For the finite element analysis, the cracked element is modelled by the local flexibility matrix calculated on the basis of fracture mechanics using Castiligano theorem. Rotating beam is considered only transverse bending motion so that the element includes two degrees of freedom per node such as the transverse deflection and slope. The time history and frequency response function of the beam with a breathing crack are studied by Newmark direct time integration method and FFT(Fast Fourier Transform)simulation. Effects of various parameters such as the crack depths, crack locations, ply angles, volume fraction ratios, and rotating speeds of the beam are also studied. Numerical results indicate that it is more reliable to be modelled as a breathing crack than an open crack.

• Computers and Concrete
• /
• v.23 no.5
• /
• pp.303-309
• /
• 2019

This study investigates axisymmetric fractional vibration of an isotropic hyperelastic semi-linear thin disc with a view to examine effects of finite deformation associated with the material of the disc and effects of fractional vibration associated with the motion of the disc. The generalized three-dimensional equation of motion is reduced to an equivalent time fraction one-dimensional vibration equation. Using the method of variable separable, the resulting equation is further decomposed into second-order ordinary differential equation in spatial variable and fractional differential equation in temporal variable. The obtained solution of the fractional vibration problem under consideration is described by product of one-parameter Mittag-Leffler and Bessel functions in temporal and spatial variables respectively. The obtained solution reduces to the solution of the free vibration problem in literature. Finally, and amongst other things, the Cauchy's stress distribution in thin disc under finite deformation exhibits nonlinearity with respect to the displacement fields whereas in infinitesimal deformation hypothesis, these stresses exhibit linear relation with the displacement field.

• Structural Engineering and Mechanics
• /
• v.88 no.4
• /
• pp.355-368
• /
• 2023

Employing the non-local strain gradient theory (NSGT), this paper investigates the nonlinear resonance characteristics of functionally graded material (FGM) nanoshells with initial geometric imperfection for the first time. The effective material properties of the porous FGM nanoshells with even distribution of porosities are estimated by a modified power-law model. With the guidance of Love's thin shell theory and considering initial geometric imperfection, the strain equations of the shells are obtained. In order to characterize the small-scale effect of the nanoshells, the nonlocal parameter and strain gradient parameter are introduced. Subsequently, the Euler-Lagrange principle was used to derive the motion equations. Considering three boundary conditions, the Galerkin principle combined with the modified Lindstedt Poincare (MLP) method are employed to discretize and solve the motion equations. Finally, the effects of initial geometric imperfection, functional gradient index, strain gradient parameters, non-local parameters and porosity volume fraction on the nonlinear resonance of the porous FGM nanoshells are examined.

• Education of Primary School Mathematics
• /
• v.5 no.2
• /
• pp.111-119
• /
• 2001

Over the years, the benefits of instructional manipulatives in mathematics education have been verified by classroom practice and educational research. The purpose of this paper is to introduce how the instructional material, specifically, geoboard could be used and integrated in elementary mathematics classroom in order to develop student's mathematical concepts and process in terms of the following areas: (1) Number '||'&'||' Operation : counting, fraction '||'&'||' additio $n_traction/multiplication (2) Geometry : geometric concepts (3) Geometry : symmetry '||'&'||' motion (4) Measurement : area '||'&'||' perimeter (5) Probability '||'&'||' Statistics : table '||'&'||' graph (6) Pattern : finding patterns Further, future study will continue to foster how manipulatives will enhance children's mathematics knowledge and influence on their mathematics performance.

• The Bulletin of The Korean Astronomical Society
• /
• v.43 no.1
• /
• pp.54.3-54.3
• /
• 2018

In this study, we perform a statistical investigation on the kinematic classication of 4264 coronal mass ejections (CMEs) from 1996 to 2015 observed by SOHO/LASCO C3. Using the constant acceleration model, we classify these CMEs into three groups; deceleration, constant velocity, and acceleration motion. For this, we devise four dierent classication methods by acceleration, fractional speed variation, height contribution, and visual inspection. Our major results are as follows. First, the fractions of three groups depend on the method used. Second, about half of the events belong to the groups of acceleration and deceleration. Third, the fractions of three motion groups as a function of CME speed classied by the last three methods are consistent with one another. Fourth, according to the last three methods, the fraction of acceleration motion decreases as CME speed increases, while the fractions of other motions increase with speed. In addition, the acceleration motions are dominant in low speed CMEs whereas the constant velocity motions are dominant in high speed CMEs.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.25 no.6
• /
• pp.293-303
• /
• 2021

Seismic fragility functions for unreinforced masonry buildings were derived based on the incremental dynamic analysis of eight representative inelastic numerical models for application to Korea's earthquake damage estimation system. The effects of panel zones formed between piers and spandrels around openings were taken into account explicitly or implicitly regarding stiffness and inelastic deformation capacity. The site response of ground motion records measured at the rock site was used as input ground motion. Limit states were proposed based on the fraction of structural components that do not meet the required performance from the nonlinear static analysis of each model. In addition to the randomness of ground motion considered in the incremental dynamic analysis explicitly, supplementary standard deviation due to uncertainty that was not reflected in the fragility assessment procedure was added. The proposed seismic fragility functions were verified by applying them to the damage estimation of masonry buildings located around the epicenter of the 2017 Pohang earthquake and comparing the result with actual damage statistics.

• Journal of The Korean Astronomical Society
• /
• v.55 no.3
• /
• pp.67-74
• /
• 2022

In this study, we perform a statistical investigation of the kinematic classification of 4,264 coronal mass ejections (CMEs) from 1996 to 2015 observed by SOHO/LASCO C3. Using the constant acceleration model, we classify these CMEs into three groups: deceleration, constant velocity, and acceleration motion. For this, we devise three different classification methods using fractional speed variation, height contribution, and visual inspection. The main results of this study can be summarized as follows. First, the fractions of three groups depend on the method used. Second, about half of the events belong to the groups of acceleration and deceleration. Third, the fractions of three motion groups as a function of CME speed are consistent with one another. Fourth, the fraction of acceleration motion decreases as CME speed increases, while the fractions of other motions increase with speed. In addition, the acceleration motions are dominant in low speed CMEs whereas the constant velocity motions are dominant in high speed CMEs.

• Advances in nano research
• /
• v.17 no.1
• /
• pp.61-73
• /
• 2024

This paper presents nonlinear vibration analysis of a composite cylindrical shell. The core of the shell is made of functionally graded (FG) porous materials and layers is fabricated of carbon nanotubes (CNTs) reinforced nanocomposites. To increase the accuracy of results, neutral surface position is considered. First-order shear deformation theory is used as displacement field to derive the basic relations of equation motions. In addition, von-Karman nonlinear strains are employed to account geometric nonlinearity and to enhance the results' precision, the exact position of the neutral surface is considered. To governing the partial equations of motion, the Hamilton's principle is used. To reduce the equation motions into a nonlinear motion equation, the Galerkin's approach is employed. After that the nonlinear motion equation is solved by multiple scales method. Effect of various parameters such as volume fraction and distribution of CNTs along the thickness directions, different patterns and efficiency coefficients of porous materials, geometric characteristics and initial conditions on nonlinear to linear ratio of frequency is investigated.