• Journal of Advanced Navigation Technology
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• v.10 no.3
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• pp.205-212
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• 2006

In this paper, the numerical methods of searching the optimal position of optical phase conjugator (OPC) and the optimal dispersion coefficients of fiber sections are proposed, which are able to effectively compensate overall channels in $8{\times}40$ Gbps WDM system with non zero - dispersion shifted fiber (NZ-DSF) as an optical fiber. And the compensation characteristics in the system with two induced optimal parameters are compared with those in the system with the currently used mid-span spectral inversion (MSSI) in order to verify the availability of the proposed methods. It is confirmed that the compensation extents of the distorted 8-channel signals are improved within 2 dB power penalty by applying the induced optimal parameters into WDM system. It is also confirmed that two optimal parameters less related with the searching procedure of these optimal values, only if these depend on each other.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.3
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• pp.83-90
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• 2010

Composite materials can be used economically and efficiently in civil engineering applications when standards and procedure for analysis, design, construction and quality control are to be established. Bridge systems, including the girders and cross-beams, and concrete decks behave as the specially orthotropic plates. For such systems with sections, boundary conditions other than Navier solution types, it is very difficult to obtain its analytical solution. To design the bridge made by the composite materials, cross-section was used as the form-core shape for economical reason and finite difference method was used for output of the stress value. The Tsai-Wu failure criterion for stress space is used. In this paper, the rate of tensile strength reduction due to increased size was considered. And also numerical study is made for these cases.

• Journal of the Korean Institute of Gas
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• v.8 no.2 s.23
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• pp.54-60
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• 2004

In this paper, the maximum von Mises stress and maximum displacement of the corner protection and secondary bottom structures have been analyzed using a finite element analysis technique. The design criterion of the comer protection is 1,500Pa for a normal nitrogen gas purging process at the beginning stage of start-up procedure. This pressure is very safe for the structure safety of the comer protection and secondary bottom plates. The corner protection and secondary bottom plates fabricated by $9\%$ nickel steel sheet may plastically be distorted and fractured for the increased gas pressure of 8,475Pa, which produces the maximum von Mises stress of 833MPa and maximum displacement of 1.9m at the center of secondary bottom plate.

• Journal of Ocean Engineering and Technology
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• v.34 no.5
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• pp.285-293
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• 2020

This study evaluated the Hook-up installation of an offshore site construction process, which is the final step in an offshore site installation process. During Hook-up installation, the offshore structure can have a detrimental effect on the work stability due to low-frequency motion. Moreover, economic costs can be incurred by the increase in available days of a tugboat. Therefore, this study developed a numerical analysis program to assess the dynamic behavior of mooring systems during hook-up installation to analyze the generally performed installation process and determine when the tugboat should be released. In this program, the behavior of an offshore structure was calculated using Cummin's time-domain motion equation, and the mooring system was calculated by Lumped mass method (LMM). In addition, a tugboat algorithm for hook-up installation was developed to apply the Hook-up procedure. The model used in the calculations was the barge type assuming FPSO (Floating production storage and off-loading) and has a taut mooring system connected to 16 mooring lines. The results of the simulation were verified by comparing with both MOSES, which is a commercial program, and a calculation method for restoring coefficient matrix, which was introduced by Patel and Lynch (1982). Finally, the offset of the structure according to the number of tugboats was calculated using the hook-up simulation, and the significant value was used to represent the calculation result.

• Advances in nano research
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• v.8 no.1
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• pp.83-94
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• 2020

An analytical formulation and solution process for the buckling analysis of porous magneto-electro-elastic functionally graded (MEE-FG) beam via different thermal loadings and various boundary conditions is suggested in this paper. Magneto electro mechanical coupling properties of FGM beam are taken to vary via the thickness direction of beam. The rule of power-law is changed to consider inclusion of porosity according to even and uneven distribution. Pores possibly occur inside FGMs due the result of technical problems that lead to creation of micro-voids in these materials. Change in pores along the thickness direction stimulates the mechanical and physical properties. Four-variable tangential-exponential refined theory is employed to derive the governing equations and boundary conditions of porous FGM beam under magneto-electrical field via Hamilton's principle. An analytical model procedure is adopted to achieve the non-dimensional buckling load of porous FG beam exposed to magneto-electrical field with various boundary conditions. In order to evaluate the influence of thermal loadings, material graduation exponent, coefficient of porosity, porosity distribution, magnetic potential, electric voltage and boundary conditions on the critical buckling temperature of the beam made of magneto electro elastic FG materials with porosities a parametric study is presented. It is concluded that these parameters play remarkable roles on the buckling behavior of porous MEE-FG beam. The results for simpler states are proved for exactness with known data in the literature. The proposed numerical results can serve as benchmarks for future analyses of MEE-FG beam with porosity phases.

• Structural Engineering and Mechanics
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• v.72 no.1
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• pp.113-129
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• 2019

A four-variable shear deformation refined plate theory has been proposed for dynamic characteristics of smart plates made of porous magneto-electro-elastic functionally graded (MEE-FG) materials with various boundary conditions by using an analytical method. Magneto-electro-elastic properties of FGM plate are supposed to vary through the thickness direction and are estimated through the modified power-law rule in which the porosities with even and uneven type are approximated. Pores possibly occur inside functionally graded materials (FGMs) due the result of technical problems that lead to creation of micro-voids in these materials. The variation of pores along the thickness direction influences the mechanical properties. The governing differential equations and boundary conditions of embedded porous FGM plate under magneto-electrical field are derived through Hamilton's principle based on a four-variable tangential-exponential refined theory which avoids the use of shear correction factors. An analytical solution procedure is used to achieve the natural frequencies of embedded porous FG plate supposed to magneto-electrical field with various boundary condition. A parametric study is led to carry out the effects of material graduation exponent, coefficient of porosity, magnetic potential, electric voltage, elastic foundation parameters, various boundary conditions and plate side-to-thickness ratio on natural frequencies of the porous MEE-FG plate. It is concluded that these parameters play significant roles on the dynamic behavior of porous MEE-FG plates. Presented numerical results can serve as benchmarks for future analyses of MEE-FG plates with porosity phases.

• Smart Structures and Systems
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• v.9 no.6
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• pp.505-534
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• 2012

The present work deals with second order statistics of post buckling response of piezoelectric laminated composite cylindrical shell panel subjected to hygro-thermo-electro-mechanical loading with random system properties. System parameters such as the material properties, thermal expansion coefficients and lamina plate thickness are assumed to be independent of the temperature and electric field and modeled as random variables. The piezoelectric material is used in the forms of layers surface bonded on the layers of laminated composite shell panel. The mathematical formulation is based on higher order shear deformation shell theory (HSDT) with von-Karman nonlinear kinematics. A efficient $C^0$ nonlinear finite element method based on direct iterative procedure in conjunction with a first order perturbation approach (FOPT) is developed for the implementation of the proposed problems in random environment and is employed to evaluate the second order statistics (mean and variance) of the post buckling load of piezoelectric laminated cylindrical shell panel. Typical numerical results are presented to examine the effect of various environmental conditions, amplitude ratios, electrical voltages, panel side to thickness ratios, aspect ratios, boundary conditions, curvature to side ratios, lamination schemes and types of loadings with random system properties. It is observed that the piezoelectric effect has a significant influence on the stochastic post buckling response of composite shell panel under various loading conditions and some new results are presented to demonstrate the applications of present work. The results obtained using the present solution approach is validated with those results available in the literature and also with independent Monte Carlo Simulation (MCS).

• Advances in nano research
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• v.5 no.4
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• pp.281-301
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• 2017

In this disquisition, an exact solution method is developed for analyzing the vibration characteristics of magneto-electro-elastic functionally graded (MEE-FG) beams by considering porosity distribution and various boundary conditions via a four-variable shear deformation refined beam theory for the first time. Magneto-electroelastic properties of porous FG beam are supposed to vary through the thickness direction and are modeled via modified power-law rule which is formulated using the concept of even and uneven porosity distributions. Porosities possibly occurring inside functionally graded materials (FGMs) during fabrication because of technical problem that lead to creation micro-voids in FG materials. So, it is necessary to consider the effect of porosities on the vibration behavior of MEE-FG beam in the present study. The governing differential equations and related boundary conditions of porous MEE-FG beam subjected to physical field are derived by Hamilton's principle based on a four-variable tangential-exponential refined theory which avoids the use of shear correction factor. An analytical solution procedure is used to achieve the natural frequencies of porous-FG beam supposed to magneto-electrical field which satisfies various boundary conditions. A parametric study is led to carry out the effects of material graduation exponent, porosity parameter, external magnetic potential, external electric voltage, slenderness ratio and various boundary conditions on dimensionless frequencies of porous MEE-FG beam. It is concluded that these parameters play noticeable roles on the vibration behavior of MEE-FG beam with porosities. Presented numerical results can be applied as benchmarks for future design of MEE-FG structures with porosity phases.

• Journal of the Korean Society of Safety
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• v.34 no.5
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• pp.87-94
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• 2019

This study deals with the reliability analysis approach of the temporary structure that can consider the uncertainty in rotational stiffness at the joints of the members, for which the semi-rigid connections are modelled as rotational spring and its coefficient is treated as a random variable following uniform distribution. In addition, this study introduces a computational procedure of the effective length coefficient for more accurate buckling load according to connection conditions of the supporting members attached to the joint. From the results of this study, it can be seen that the failure probability of the joint-hinge model (Case 1) presented in the design standard is higher than that of the practical model (Case 5) considering the rotational stiffness at the joints. This implies that the design standard leads to a conservative design of the temporary structure. The results also confirmed that the failure probability of the vertical member, i.e., the most critical member, can be further reduced when the base connection is provided with a fixed end. The comparative results between FORM, SORM and MCS further demonstrated that FORM can have a high level of numerical efficiency while ensuring the accuracy of the solution, compared with SORM and MCS. Based on these results, the proposed approach can be used as an accurate and efficient reliability analysis method of the three dimensional temporary structure.

• The Korean Journal of Pain
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• v.34 no.4
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• pp.479-486
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• 2021

Background: Prior studies have reported that 40%-90% of the patients with celiac plexus-mediated visceral pain benefit from the neurolytic celiac plexus block (NCPB), but the predictive factors of response to NCPB have not been evaluated extensively. This study aimed to identify the factors associated with the immediate analgesic effectiveness of NCPB in patients with intractable upper abdominal cancer-related pain. Methods: A retrospective review was performed of 513 patients who underwent NCPB for upper abdominal cancer-related pain. Response to the procedure was defined as (1) a decrease of ≥ 50% or ≥ 4 points on the numerical rating scale (NRS) in pain intensity from the baseline without an increase in opioid requirement, or (2) a decrease of ≥ 30% or ≥ 2 points on the NRS from the baseline with simultaneously reduced opioid consumption after NCPB. Logistic regression analysis was performed to determine the factors associated with successful responses to NCPB. Results: Among the 513 patients included in the analysis, 255 (49.8%) and 258 (50.2%) patients were in the non-responder and responder group after NCPB, respectively. Multivariable logistic regression analysis showed that diabetes (odds ratio [OR] = 0.644, P = 0.035), history of upper abdominal surgery (OR = 0.691, P = 0.040), and celiac metastasis (OR = 1.496, P = 0.039) were the independent factors associated with response to NCPB. Conclusions: Celiac plexus metastases, absence of diabetes, and absence of prior upper abdominal surgery may be independently associated with better response to NCPB for upper abdominal cancer-related pain.