• The Korean Journal of Malacology
• /
• v.32 no.3
• /
• pp.189-195
• /
• 2016

The growth of manila clam Ruditapes philippinarum inhabiting culturing ground was studied in west coast Gomso tidal flat of Korea, from August 2000 to July 2001. The density of the clam was the highest in November 2000, showing a monotonic decrease afterwards over the study period. Mean density was $1,224ind./m^2$ during the study period. Size frequencies of the clam showed a unimodal distribution, and its mode increased with shell growth over time. Although the growth of shell length of manila clam was monotonic, the growth rates decreased between July 2001 and February 2002 and increased from March 2002. The biomass of the clam also increased with time, in which the increments becoming larger since March 2002. The clam shell length had linear relationship to shell height, and had logarithmic relationship to total weight, meat wet weight, dry meat weight, and AFDW. Condition index of the clam increased continuously until April, decreasing afterwards in 2001. The pattern was similar in 2002. Based on fluctuations in condition index, the spawning time of manila clam in Gomso tidal flat is inferred to be between May and October. These results suggested that optimal harvests can be made before summer season when growth decreased and mass mortality occurred, after 24 months of seed shell release.

• Applied Biological Chemistry
• /
• v.43 no.4
• /
• pp.260-265
• /
• 2000

To determine the quality change of the irradiated eggs during storage, fresh shell eggs were irradiated using $^{60}Co$ at 0, 1, 5, 10, 30 kGy and stored for 30 days. The york index, color, pH, viscosity, egg weight, and SDS-PAGE profile of the irradiated eggs were examined. During storage, york index values of the irradiated eggs and the control were decreased and the increase of dose decreased yolk index. However, the yolk index values were increased temporarily at 10 kGy and 30 kGy. The yolk color had a bright yellow with increases in dose level and there was no significant change during storage. The albumen viscosities were decreased with increases in dosage and were decreased during storage. Also, the albumen pH values of the irradiated eggs were higher than that of the control and were increased during storage. The weight losses of eggs were increased during storage and there were no significant changes by dose level. SDS-PAGE profile of the egg white proteins of the shell eggs showed the change in molecular weight distribution and had aggregation pattern as well as degradation. CD and fluorescence spectroscopy study showed changes in the secondary and tertiary structure of egg white proteins by ${\gamma}-irradiation$. Therefore, this study clearly indicates that irradiation dose of eggs should be appropriate to prevent the loss of egg qualities.

• Structural Engineering and Mechanics
• /
• v.85 no.4
• /
• pp.545-562
• /
• 2023

In this work, superharmonic and subharmonic resonance of rotating stiffened FGM truncated conical shells exposed to harmonic excitation in a thermal environment is investigated. Utilizing classical shell theory considering Coriolis acceleration and the centrifugal force, the governing equations are extracted. Non-linear model is formulated employing the von Kármán non-linear relations. In this study, to model the stiffener effects the smeared stiffened technique is utilized. The non-linear partial differential equations are discretized into non-linear ordinary differential equations by applying Galerkin's method. The method of multiple scales is utilized to examine the non-linear superharmonic and subharmonic resonances behavior of the conical shells. In this regard, the effects of the rotating speed of the shell on the frequency response plot are investigated. Also, the effects of different semi-vertex angles, force amplitude, volume-fraction index, and temperature variations on the frequency-response graph are examined for different rotating speeds of the stiffened FGM truncated conical shells.

• Earthquakes and Structures
• /
• v.26 no.4
• /
• pp.299-309
• /
• 2024

The present paper develops application of third-order shear deformation theory (TSDT) and modified couple stress theory (MCST) to size-dependent bending analysis of a functionally graded cylindrical micro-shell. The radial and axial displacement components are described based on TSDT for more accurate analysis. The effect of small scales is accounted based on MCST. The principle of virtual work is used for derivation of bending governing equations. The solution is presented for a simply-supported boundary condition to account the influence of various important parameters such as micro length scale parameter, in-homogeneous index and some dimensionless geometric parameters such as length to radius and length to thickness ratios on the bending results. A comparative analysis is presented to examine the effect of order of employed shear deformation theory on the axial and radial displacements.

• Geomechanics and Engineering
• /
• v.36 no.2
• /
• pp.99-109
• /
• 2024

Studying the dynamic behavior of axially moving cylindrical shells in hygro-thermal environments has important theoretical and engineering value for aircraft design. Therefore, in this paper, considering hygro-thermal effect, the nonlinear forced vibration of an axially moving cylindrical shell made of functionally graded materials (FGM) is studied. It is assumed that the material properties vary continuously along the thickness and contain pores. The Donnell thin shell theory is used to derive the motion equations of FGM cylindrical shells with hygro-thermal loads. Under the four sides clamped (CCCC) boundary conditions, the Gallekin method and multi-scale method are used for nonlinear analysis. The effects of power law index, porosity coefficient, temperature rise, moisture concentration, axial velocity, prestress, damping and external excitation amplitude on nonlinear forced vibration are explored through parametric research. It can be found that, the changes in temperature and humidity have a significant effect. Increasing in temperature and humidity will cause the resonance position to shift to the left and increase the resonance amplitude.

• Journal of Ecology and Environment
• /
• v.30 no.2
• /
• pp.109-119
• /
• 2007

The effect of water flow on the growth of Gafrarium tumidum was studied in the field using open cages constructed with stainless steel net and perspex in which holes were drilled. Cages with different flows (25, 50 and 75% of the control) were made by varying the area of perspex being drilled. Reduction in flow rate was directly proportional to the undrilled area, and the mean flow rate of the different treatment groups varied from 3.12 cm/s for the 25% exposure to 12.48 cm/s for the control cages. At the end of the 3-month experiment, no significant differences in sediment characteristics were found among the treatments. Growth in shell length, shell weight and tissue dry weight was, however, positively correlated with flow rate. Percentage increases ranged from $3.0{\sim}8.3%$ for shell length, $9.9{\sim}23.1%$ for shell weight and $17.2{\sim}53.3%$ for tissue dry weight. Condition index of the clam was not significantly different among the treatments. Seston depletion effect could reduce growth in G. tumidum only when water flow was reduced to 25% of the control. G. tumidum also exhibited different responses in shell and tissue growth at low flow rates, in which shell growth continued to decrease as flow rate decreased whereas tissue growth was relatively independent of low flows at 25 and 50% of the control. It was suggested that when seston flux was reduced at slow flows, it would be a better strategy for G. tumidum to channel energy for gonad development instead of shell growth during the reproductive stage.

• Steel and Composite Structures
• /
• v.36 no.4
• /
• pp.463-480
• /
• 2020

Although detailed shell analysis is suitable to predict the ductile crack initiation life of steel members, such detailed method adds time expense and complexity. In order to simply predict the ductile crack initiation life of stiffened steel bridge piers, a total of 33 cases are simulated to carry out the parametric analyses. In the analysis, the effects of the width-to-thickness ratio, slenderness ratio, plate thickness and so on are considered. Both shell analyses and beam analyses about these 33 cases are conducted. The plastic strain and damage index obtained from shell and beam analyses are compared. The modified factor β_s is determined based on the predicted results obtained from both shell and beam analyses in order to simulate the strain concentration at the base corner of the steel bridge piers. Finally, three experimental results are employed to verify the validity of the proposed method in this study.

• Structural Engineering and Mechanics
• /
• v.61 no.2
• /
• pp.231-244
• /
• 2017

The aim of this study is to develop a semi-analytical method to investigate fluid-structure coupling of concentric double shells with different lengths and elastic behaviours. Co-axial shells constitute a cylindrical circular container and a baffle submerged inside the stored fluid. The container shell is made of functionally graded materials with mechanical properties changing through its thickness continuously. The baffle made of steel is fixed along its top edge and submerged inside fluid such that its lower edge freely moves. The developed approach is verified using a commercial finite element computer code. Although the model is presented for a specific case in the present work, it can be generalized to investigate coupling of shell-plate structures via fluid. It is shown that the coupling between concentric shells occurs only when they vibrate in a same circumferential mode number, n. It is also revealed that the normalized vibration amplitude of the inner shell is about the same as that of the outer shell, for narrower radial gaps. Moreover, the natural frequencies of the fluid-coupled system gradually decrease and converge to the certain values as the gradient index increases.

• The Korean Journal of Malacology
• /
• v.29 no.3
• /
• pp.217-223
• /
• 2013

The morphological relations and physiological characteristics of the triploid and diploid oysters (Crassostrea gigas) in Taean area, west coast of Korea, were investigated from May 2012 to April 2013. Mophometric analysis indicated that the triploid oysters have the same shell length to shell height ratio but higher shell depth to shell height ratio than diploids. Consistent with morphological characteristics, triploid oysters showed greater values of fatness, condition index and RNA/DNA ratio during the period of experiment. The DNA concentration in adductor muscle and mantle of triploid were either lower or equal to the nucleic acids of diploid. However, RNA/DNA ratio were significantly higher than diploid. It appears that RNA/DNA ratio could be a useful indicator of health condition of triploid and diploid oysters when taken in correlation with the morphological indices.

• Structural Engineering and Mechanics
• /
• v.68 no.6
• /
• pp.721-733
• /
• 2018

The modal frequency responses of functionally graded (FG) sandwich doubly curved shell panels are investigated using a higher-order finite element formulation. The system of equations of the panel structure derived using Hamilton's principle for the evaluation of natural frequencies. The present shell panel model is discretised using the isoparametric Lagrangian element (nine nodes and nine degrees of freedom per node). An in-house MATLAB code is prepared using higher-order kinematics in association with the finite element scheme for the calculation of modal values. The stability of the opted numerical vibration frequency solutions for the various shell geometries i.e., single and doubly curved FG sandwich structure are proven via the convergence test. Further, close conformance of the finite element frequency solutions for the FG sandwich structures is found when compared with the published theoretical predictions (numerical, analytical and 3D elasticity solutions). Subsequently, appropriate numerical examples are solved pertaining to various design factors (curvature ratio, core-face thickness ratio, aspect ratio, support conditions, power-law index and sandwich symmetry type) those have the significant influence on the free vibration modal data of the FG sandwich curved structure.