• Ocean Systems Engineering
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• v.13 no.4
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• pp.385-399
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• 2023

A collision between a ship and an offshore platform may result in structural damage and closure; therefore, damage analysis is required to ensure the platform's integrity. This paper presents a damage assessment of a three-legged jacket platform subjected to ship collisions using the industrial finite element program Bentley SACS. This study considers two ships with displacements of 2,000 and 5,000 tons and forward speeds of 2 and 6.17 meters per second. Ship collision loads are applied as a simplified point load on the center of the platform's legs at inclinations of 1/7 and 1/8; diagonal bracing is also included. The jacket platform is modelled as beam elements, with the exception of the impacted jacket members, which are modelled as nonlinear shell elements with elasto-plastic material and constant isotropic hardening to provide realistic dented behavior due to ship collision load. The structural response is investigated, including kinetic energy transfer, stress distribution, and denting damage. The simulation results revealed that the difference in leg inclination has no effect on the level of localized denting damage. However, it was discovered that a leg with a greater inclination (1/8) resists structural displacement more effectively and absorbs less kinetic energy. In this instance, the three-legged platform collapses due to the absorption of 27.30 MJ of energy. These results provide crucial insights for enhancing offshore platform resilience and safety in high-traffic maritime regions, with implications for design and collision mitigation strategies.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.5
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• pp.835-840
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• 2020

In this paper, we described the verification results on method by using the computer simulation and practical experiment for reduction of total radiated power (TRP) measurement time consuming tens of hours. TRP measurements are used in the 5G band in order to exactly evaluate the wireless communication equipment, but it takes a long measurement time because of dense sampling interval. Moreover, if there are various beam forming scenarios, the total measurement time increases exponentially. Therefore, the world-wide research on reduction method of the TRP measurement time is intensively on going. The verified method in this paper is to calculate the TRP through effective isotropical radiated power (EIRP). At first, the relation of TRP and EIRP was investigated, and an antenna for testing was designed and constructed. And, the amount of error was analyzed through simulation and measurement. The analysed results showed that the derived TRP through EIRP has very small error. This method could be applied for TRP measurements of 5G wireless communication equipments.

• Structural Engineering and Mechanics
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• v.27 no.6
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• pp.713-739
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• 2007

Nowadays computers can perform symbolic computations in addition to mere number crunching operations for which they were originally designed. Symbolic computation opens up exciting possibilities in Structural Mechanics and engineering. Classical areas have been increasingly neglected due to the advent of computers as well as general purpose finite element software. But now, classical analysis has reemerged as an attractive computer option due to the capabilities of symbolic computation. The repetitive cycles of simultaneous - equation sets required by the finite element technique can be eliminated by solving a single set in symbolic form, thus generating a truly closed-form solution. This consequently saves in data preparation, storage and execution time. The power of Symbolic computation is demonstrated by six examples by applying symbolic computation 1) to solve coupled shear wall 2) to generate beam element matrices 3) to find the natural frequency of a shear frame using transfer matrix method 4) to find the stresses of a plate subjected to in-plane loading using Levy's approach 5) to draw the influence surface for deflection of an isotropic plate simply supported on all sides 6) to get dynamic equilibrium equations from Lagrange equation. This paper also presents yet another computationally efficient and accurate numerical method which is based on the concept of derivative of a function expressed as a weighted linear sum of the function values at all the mesh points. Again this method is applied to solve the problems of 1) coupled shear wall 2) lateral buckling of thin-walled beams due to moment gradient 3) buckling of a column and 4) static and buckling analysis of circular plates of uniform or non-uniform thickness. The numerical results obtained are compared with those available in existing literature in order to verify their accuracy.

• Computers and Concrete
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• v.3 no.4
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• pp.213-233
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• 2006

Over the past years techniques for non-linear analysis have been enhanced significantly via improved solution procedures, extended finite element techniques and increased robustness of constitutive models. Nevertheless, problems remain, especially for real world structures of softening materials like concrete. The softening gives negative stiffness and risk of bifurcations due to multiple cracks that compete to survive. Incremental-iterative techniques have difficulties in selecting and handling the local peaks and snap-backs. In this contribution, an alternative method is proposed. The softening diagram of negative slope is replaced by a saw-tooth diagram of positive slopes. The incremental-iterative Newton method is replaced by a series of linear analyses using a special scaling technique with subsequent stiffness/strength reduction per critical element. It is shown that this event-by-event strategy is robust and reliable. First, the model is shown to be objective with respect to mesh refinement. Next, the example of a large-scale dog-bone specimen in direct tension is analyzed using an isotropic version of the saw-tooth model. The model is capable of automatically providing the snap-back response. Subsequently, the saw-tooth model is extended to include anisotropy for fixed crack directions to accommodate both tensile cracking and compression strut action for reinforced concrete. Three different reinforced concrete structures are analyzed, a tension-pull specimen, a slender beam and a slab. In all cases, the model naturally provides the local peaks and snap-backs associated with the subsequent development of primary cracks starting from the rebar. The secant saw-tooth stiffness is always positive and the analysis always 'converges'. Bifurcations are prevented due to the scaling technique.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.6
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• pp.545-554
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• 2000

Compton X-ray backscatter technique has been used to quantitatively assess the impact damage in quasi-isotropic laminated composites and to obtain a cross-sectional profile of impact-damaged laminated composites from the density variation of the cross section. An adaptive filter is applied to the Compton backscattering data for the reconstruction and noise reduction from many sources including quantum noise, especially when the SNR(signal-to-noise ratio) of the image is relatively low. A nonlinear reconstruction model is also proposed to overcome distortion of the Compton backscatter image due to attenuation effects, beam hardening, and irregular distributions of the fibers and the matrix in composites. Delaminations masked or distorted by the first few delaminations near the front surface are detected and characterized both in width and location, by application of an error minimization algorithm.

• Journal of Biomedical Engineering Research
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• v.40 no.5
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• pp.165-170
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• 2019

Cancer cells are different from normal cells in terms of life cycle, behavior, and growth patterns. Cancer cells can migrate freely in the body through blood vessels and lymph nodes. The cancer cells easily interact with various substrates including extracellular matrix and vessels and they can differentiate in the new environment. However, it is not well known about the adhesion preference of cancer cells on the substrate and the mechanism of their interaction. In this study, we prepared the nano-, micro-patterned substrates using E-beam lithography techniques. MCF-7 cells were tested on the substrates to find out their adhesion preference. The substrates were made by polydimethylsiloxane (PDMS) with specific patterns including pillars with a diameter of 500 nm, 700 nm, $3{\mu}m$ and $5{\mu}m$. MCF-7 cells were seeded on the substrates and incubated for 24 hours. As a result, this study clearly demonstrated that the MCF-7 cells preferred 700 nm patterning.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.163-163
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• 2000

In this research, we used the ion irradiation technique which has an advantae in improving intentionally the properties of surface and interface in a non-equilibrium, instead of the conventional annealing method which has been known to improve the material properties in the equilibrium stat. Cu/Co multilayered films were prepared on SiN4/SiO2/Si substrates by the electron-beam evaporation for the Co layers and the thermal evaporation for the Cu layers in a high vacuum. The ion irradiation with a 80keV Ar+ was carried out at various ion doses in a high vacuum. Hysteresis loops of the films were investigated by magneto-optical polar Kerr spectroscopy at various experimental conditions. The change of atomic structure of the films before and after the ion irradiation was studied by glancing angle x-ray diffraction, and the intermixing between Co and Cu sublayers was confirmed by Rutherford backscattering spectroscopy. The surface roughness and magneto-resistance were measured by atomic force microscopy and with a four-point probe system, respectively. During the magneto-resistance measurement, we changed temperature and the direction of magnetization. From the results of experiments, we found that the change at the interfaces of the Cu/Co multilayered film induced by ion irradiation cause the change of magnetic properties. According to the change in hysteresis loop, the surface inplane component of magnetic easy axis was isotropic before the ion irradiation, but became anisotropic upon irradiation. It was confirmed that this change influences the axial behavior of magneto-resistance. Especially, the magneto-resistance varied in accordance with an external magnetic field and the direction of current, which means that magneto-resistance also shows the uniaxial behavior.

• Computational Structural Engineering
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• v.8 no.4
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• pp.87-97
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• 1995

For the same configuration of two-dimensional finite element models, 6-node element exhibits stiffer bending stiffness than 8-node element. This is true in the relation between 16-node element and 20-node element for three-dimensional model. This stiffening phenomenon comes from the elimination of several mid nodes from full-node elements. Therefore, this may be called 'relative stiffness stiffening phenomenon'. It seems that there are a couple of ways to correct the stiffening effect, however, we could find only one effective method-the method of modification of Gauss sampling points-which passes the patch test and does not alter other kinds of stiffness, such as extensional stiffness. The quantity of modification is a function of Poisson's ratios of the constituent materials. We could obtain two modification equations, one for plane stress case and the other for plane strain case. This method can be extended to 3-dimensional solid elements. Except the exact plane strain cases, most 3-dimensional plates could be modeled successfully with 16-node element modified by the equation for the plane stress case. The effectiveness of the modification method is checked by applying it to several examples with excellent improvements. In numerical examples, beams with various boundary conditions are subjected to static and time-dependent loads. Free and forced motion analyses of beams and plates are also tested. The beam and plate may be composed of isotropic multilayers as well as a single layer.

• Journal of Korean Association for Spatial Structures
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• v.6 no.4 s.22
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• pp.81-92
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• 2006

This paper presents exact solutions for the free vibrations and buckling of rectangular plates having two opposite, simply supported edges subjected to linearly varying normal stresses causing pure in-plane moments, the other two edges being free. Assuming displacement functions which are sinusoidal in the direction of loading (x), the simply supported edge conditions are satisfied exactly. With this the differential equation of motion for the plate is reduced to an ordinary one having variable coefficients (in y). This equation is solved exactly by assuming power series in y and obtaining its proper coefficients (the method of Frobenius). Applying the free edge boundary conditions at y=0, b yields a fourth order characteristic determinant for the critical buckling moments and vibration frequencies. Convergence of the series is studied carefully. Numerical results are obtained for the critical buckling moments and some of their associated mode shapes. Comparisons are made with known results from less accurate one-dimensional beam theory. Free vibration frequency and mode shape results are also presented. Because the buckling and frequency parameters depend upon Poisson's ratio ( V ), results are shown for $0{\leq}v{\leq}0.5$, valid for isotropic materials.