• Journal of Environmental Health Sciences
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• v.23 no.4
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• pp.133-138
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• 1997

The technology of removing phosphorous, considered as one of the most important control nutrients causing eutrophication in various water bodies, have been investigated by many researchers. Recently, phosphorous crystallization process is emerging as a new technology for phosphorous removal. In this study, waste oyster shells which can be easily obtained from the ocean, were used as a seed crystal, and their effects of several physical/chemical factors on the phosphorous removal efficiencies were examined by batch tests. Ca$^{2+}$ and pH affected phosphorous crystallization process using waste oyster shells. As alkalinity of wastewater increased, phosphorous removal efficiencies gradually decreased. Phosphorous removal efficiencies were increased, as specific area and contact efficiency per unit area of waste oyster shells were increased. In case of high temperature, phosphorous crystallization process was rapidly advanced and phosphorous removal efficiencies were increased. Dependig on X-ray diffraction analysis, it was showed that generation materials extracted from the surface of waste oyster shells with short reaction time were dominated by $CaHPO_4\cdot 2H_2O$, but progressed to $Ca_5(OH)(PO_4)_3$. The SEM observation reveals that the evident variations were hardly seen, but particle sizes of waste oyster shells were relatively bigger and showed forms of smaller plate than before.

• Journal of Soil and Groundwater Environment
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• v.26 no.1
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• pp.17-23
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• 2021

In order to investigate change of shear strength of coastal muddy sediment by mixing pretreated oyster shells with different pyrolysis temperatures and particle sizes, a vane shear test was carried out. The shear strength of the sediment with oyster shells pyrolyzed at 800℃ was twice higher than that of the control, with a maximum shear strength of ca. 0.2 kPa. The Ca2+ concentration in the pore water was the highest at sediment with oyster shells pyrolyzed at 800℃ with a concentration of ca. 790 mg/L. From the above results, it is concluded that the application of the oyster shells pyrolyzed at 800℃ can affect the increase in shear strength of coastal sediments through the aggregation of clay particles and pozzolanic reactions with sediments.

• Structural Engineering and Mechanics
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• v.84 no.6
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• pp.767-782
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• 2022

In this paper, the nonlinear vibration behavior of the spiral stiffened multilayer functionally graded (SSMFG) cylindrical shells exposed to the thermal environment and a uniformly distributed harmonic loading using a semi-analytical method is investigated. The cylindrical shell is surrounded by a nonlinear viscoelastic foundation consisting of a two-parameter Winkler-Pasternak foundation augmented by a Kelvin-Voigt viscoelastic model with a nonlinear cubic stiffness. The distribution of temperature and material constitutive of the stiffeners are continuously changed through the thickness direction. The cylindrical shell has three layers consisting of metal, FGM, and ceramic. The interior layer of the cylindrical shell is rich in metal, while the exterior layer is rich in ceramic, and the FG material is located between two layers. The nonlinear vibration problem utilizing the smeared stiffeners technique, the von Kármán equations, and the Galerkin method has been solved. The multiple scales method is utilized to examine the nonlinear vibration behavior of SSMFG cylindrical shells. The considered resonant case is 1:3:9 internal resonance and subharmonic resonance of order 1/3. The influences of different material and geometrical parameters on the vibration behavior of SSMFG cylindrical shells are examined. The results show that the angles of stiffeners, temperature, and elastic foundation parameters have a strong effect on the vibration behaviors of the SSMFG cylindrical shells.

• Steel and Composite Structures
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• v.45 no.3
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• pp.349-367
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• 2022

In this research, an approach combining a semi-analytical method and an analytical method is presented to investigate the static and dynamic post-buckling behavior of the sandwich functionally graded (FG) porous cylindrical shells exposed to external pressure. The sandwich cylindrical shell considered is composed of a viscoelastic core and two FG porous (FGP) face layers. The viscoelastic core is made of Kelvin-Voigt-type material. The material properties of the FG porous face layer are considered continuous through each face thickness according to a porosity coefficient and a volume fraction index. Two types of sandwich FG porous viscoelastic cylindrical shells named Type A and Type B are considered in the research. Type A shell has the porosity evenly distributed across the thickness direction, and Type B has the porosity unevenly distributes across the thickness direction. The FG face layers are considered in two cases: outside metal surface, inside ceramic surface (OMS-ICS), and inside metal surface, outside ceramic surface (IMS-OCS). According to Donnell shell theory, von-Karman equation, and Galerkin's method, a discretized nonlinear governing equation is derived for analyzing the behavior of the shells. The explicit expressions for static and dynamic critical buckling loading are thus developed. To study the dynamic buckling of the shells, the governing equation is examined via a numerical approach implementing the fourth-order Runge-Kutta method. With a procedure presented by Budiansky-Roth, the critical load for dynamic post-buckling is obtained. The effects of various parameters, such as material and geometrical parameters, on the post-buckling behaviors are investigated.

• Journal of the Korea Organic Resources Recycling Association
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• v.7 no.1
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• pp.13-21
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• 1999

The purposes of this research were to evaluate the character of laboratory wastewater, and to examine the utilization of waste egg shells for neutralization and removal of heavy metals. Waste egg shells are excellent at neutralizing acidic wastewater, because they have alkaline minerals such as calcium. It must be seemed that removal rate of heavy metals were very influenced by adsobent dosage and adsorbate concentrations, because waste egg shells acted as precipitation and adsorption. If we reflected the adsorption capacity(k) and adsorption(1/n) of Freundlich isotherm, we couldn't consider waste egg shells as a good adsorbent. In view of these results, it showed that wastes containing the similar compositions as waste egg shells could utilize the neutralization, precipitation and adsorption of heavy metals in laboratory wastewater.

• Journal of Korean Society of Steel Construction
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• v.12 no.2 s.45
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• pp.187-196
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• 2000

In this paper, stability analysis is carried out for the out of plane behaviors under compressive loads to the direction of the generator in anisotropic cylindrical shells. It is not easy to obtain the analytic solutions about the stability analysis of anisotropic cylindrical shells consisted of composite materials. For solving this problems, this paper used the finite difference method which is one of the numerical methods. Geometrical property of cylindrical shells transforms the compressive loads into the inplane behaviors. This paper studied the change of stiffness in the direction of the circumferential and stability of shells according to change of fiber angle, curvature, subtended angle and aspect ratio. From result of this study, anisotropic cylindrical shells under compressive loads to the direction of the generator vary greatly with respect to the change of the circumferential stiffness. Therefore, it will be more safe to strengthen the circumferential stiffness of anisotropic cylindrical shells under compressive loads.

• Journal of Korean Association for Spatial Structures
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• v.4 no.4 s.14
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• pp.113-128
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• 2004

A three-dimensional (3-D) method of analysis is presented for determining the free vibration frequencies and mode shapes of solid paraboloidal and complete (that is, without a top opening) paraboloidal shells of revolution with variable wall thickness. Unlike conventional shell theories, which are mathematically two-dimensional (2-D), the present method is based upon the 3-D dynamic equations of elasticity. The ends of the shell may be free or may be subjected to any degree of constraint. Displacement components $u_r,\;u_{\theta},\;and\;u_z$ in the radial, circumferential, and axial directions, respectively, are taken to be sinusoidal in time, periodic in ${\theta}$, and algebraic polynomials in the r and z directions. Potential (strain) and kinetic energies of the paraboloidal shells of revolution are formulated, and the Ritz method is used to solve the eigenvalue problem, thus yielding upper bound values of the frequencies by minimizing the frequencies. As the degree of the polynomials is increased, frequencies converge to the exact values. Convergence to four digit exactitude is demonstrated for the first five frequencies of the complete, shallow and deep paraboloidal shells of revolution with variable thickness. Numerical results are presented for a variety of paraboloidal shells having uniform or variable thickness, and being either shallow or deep. Frequencies for five solid paraboloids of different depth are also given. Comparisons are made between the frequencies from the present 3-D Ritz method and a 2-D thin shell theory.

• Culinary science and hospitality research
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• v.19 no.2
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• pp.1-10
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• 2013

This study was conducted to investigate the quality characteristics of dumpling shells with white lotus leaf powder added to them (WLL 0%, 1%, 2%, 3%, 4%). Water binding capacity and moisture content of dumpling shells were not significantly different. Solubility in $50^{\circ}C$, $60^{\circ}C$ and $70^{\circ}C$ of dumpling dough has decreased because of the addition of WLL. Swelling power of all groups has increased because of increased amount of WLL content and temperature. The mass, volume and water absorption rate of cooked dumpling shells decreased while the turbidity of cooked dumpling shells increased with the addition of WLL. L and b value of dumpling shells significantly decreased and a value of dumpling shells significantly increased because of increased amount of WLL contents. Hardness and adhesiveness of dumpling shells significantly increased in WLL2 and WLL3 groups. Cohesiveness, springiness, gumminess and chewiness of cooked dumpling shells were not significantly different according to the additions of WLL. In sensory evaluation, color, flavor, white lotus leaf flavor, taste and overall acceptability significantly increased in WLL3. Stickiness, softness, chewiness of cooked dumpling shells were not significantly different according to the additions of WLL. Overall, the result of this study indicates that the dumpling shell containing 3% WLL powder was most preferred among the groups.

• Wind and Structures
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• v.8 no.6
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• pp.443-454
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• 2005

Wind loading is very important, even dominant in some cases, to large-span single-layer reticulated shells. At present, usually equivalent static methods based on quasi-steady assumption, as the same as the wind-resistant design of low-rise buildings, are used in the structural design. However, it is not easy to estimate a suitable equivalent static wind load so that the effects of fluctuating component of wind on the structural behaviors, especially on structural stability, can be well considered. In this paper, the effects of fluctuating component of wind load on the stability of a single-layer reticulated spherical shell model are investigated based on wind pressure distribution measured simultaneously in the wind tunnel. Several methods used to estimate the equivalent static wind load distribution for equivalent static wind-resistant design are reviewed. A new simple method from the stability point of view is presented to estimate the most unfavorable wind load distribution considering the effects of fluctuating component on the stability of shells. Finally, with comparisive analyses using different methods, the efficiency of the presented method for wind-resistant analysis of single-layer reticulated shells is established.

• Steel and Composite Structures
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• v.17 no.4
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• pp.453-470
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• 2014

This article is the result of an investigation on the influence of a Pasternak elastic foundation on the stability of exponentially graded (EG) cylindrical shells under hydrostatic pressure, based on the first-order shear deformation theory (FOSDT) considering the shear stresses. The shear stresses shape function is distributed parabolic manner through the shell thickness. The governing equations of EG orthotropic cylindrical shells resting on the Pasternak elastic foundation on the basis of FOSDT are derived in the framework of Donnell-type shell theory. The novelty of present work is to achieve closed-form solutions for critical hydrostatic pressures of EG orthotropic cylindrical shells resting on Pasternak elastic foundation based on FOSDT. The expressions for critical hydrostatic pressures of EG orthotropic cylindrical shells with and without an elastic foundation based on CST are obtained, in special cases. Finally, the effects of Pasternak foundation, shear stresses, orthotropy and heterogeneity on critical hydrostatic pressures, based on FOSDT are investigated.