• Journal of Advanced Marine Engineering and Technology
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• v.33 no.1
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• pp.71-80
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• 2009

The response characteristics of EHA systems are sensitive to the temperature change of working fluid because the temperature of working fluid causes the variation of system parameters such as effective bulk modulus and viscous friction coefficient. In this paper, a precise position control of EHA system using the adaptive sliding mode control system is suggested. The adapted system parameters such as effective bulk modulus and viscous friction coefficient can be used for monitoring failures in the EHA system which has potential applications in the industrial fields. Not only the accuracy of adapted system parameters but also the improved performance and robustness in a given reference position of the cylinder are verified by computer simulation using AMESim software.

• Structural Monitoring and Maintenance
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• v.3 no.2
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• pp.129-144
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• 2016

We present a methodology to validate with monitoring data finite element models of existing concrete dams: numerical analyses are performed to assess the structural response under the effects of seasonal loading conditions, represented by hydrostatic pressure on the upstream-downstream dam surfaces and thermal variations as recorded by a thermometers network. We show that the stiffness effect of the rock foundation and the surface degradation of concrete due to aging are crucial aspects to be accounted for a correct interpretation of the real behavior. This work summarizes some general procedures developed by this research group at Politecnico di Milano on traditional static monitoring systems and two significant case studies: a buttress gravity and an arch-gravity dam.

• Ocean Systems Engineering
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• v.3 no.2
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• pp.149-165
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• 2013

Tension leg platforms (TLP's) are highly nonlinear due to large structural displacements and fluid motion-structure interaction. Therefore, the nonlinear dynamic response of TLP's under hydrodynamic wave loading is necessary to determine their deformations and dynamic characteristics. In this paper, a numerical study using modified Morison Equation was carried out in the time domain to investigate the influence of nonlinearities due to hydrodynamic forces and the coupling effect between all degrees of freedom on the dynamic behavior of a TLP. The stiffness of the TLP was derived from a combination of hydrostatic restoring forces and restoring forces due to cables and the nonlinear equations of motion were solved utilizing Newmark's beta integration scheme. The effect of wave characteristics was considered.

• Journal of Ocean Engineering and Technology
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• v.14 no.2
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• pp.28-35
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• 2000

In this paper a complicated structural behavior in collision and its effect of energy transmission to the collision bulkhead was examined through a methodology of the numerical simulation to obtain a ideal bow construction and a location of collision bulkhead against heat on collision. At present the bow structure is normally designed in consideration of its specific structural arrangement and internal and external loads in these areas such as hydrostatic and dynamic pressure wave impact and bottom slamming in accordance with the Classification rules and the specific location of collision bulkhead by SOLAS requirement. By these studies the behavior of the bow collapse due to collision was synthetically evaluated for the different size of tankers and its operational speed limits and by the results of these simulation it provides the optimal design concept for the bow construction to prevent the subsequent plastic deformation onto or near to the collision bulkhead boundary and to determine the rational location of collision bulkhead.

• Journal of Korean Port Research
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• v.14 no.2
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• pp.219-231
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• 2000

In this paper a complicated structural behavior in collision and its effects of energy translation to the collision bulkhead was examined through a methodology of the numerical simulation to obtain a ideal bow construction and a location of collision bulkhead against head on collision. In the present the bow structure is normally designed in consideration of its specific structural arrangements and internal and external loads in these area such as hydrostatic and dynamic pressure, wave impact and bottom slamming in accordance with the Classification rules, and the specific location of collision bulkhead by SOLAS requirement. By these studies the behavior of the bow collapse due to collision was synthetically evaluated for the different size of tankers and its operational speed limits, and by the results of these simulation it provides the optimal design concept for the bow construction to prevent the subsequent plastic deformation onto or near to the collision bulkhead boundary and to determine the rational location of collision bulkhead.

• Ocean Systems Engineering
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• v.12 no.4
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• pp.413-437
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• 2022

An innovative concept for wet-transportation and stepwise installation of mono-bucket foundation for 15 MW offshore wind turbine is proposed. Case studies for two different mono-bucket and wrap-buoy dimensions are conducted and their hydrostatic and hydrodynamic performances are compared for both wet-towing and lowering operations. The intact stability and transient responses are analyzed in detail for various stages of lowering operation. Wave-induced motion statistics during wet tow in sea state 4 (highest operational window) are checked. The proposed concept is found to be feasible and can be an alternative cost-effective solution without using heavy-lift crane vessel in practice.

• Proceedings of the Korean Society of Applied Pharmacology
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• 1996.04a
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• pp.119-130
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• 1996

We review the factors which regulate the depth and composition of the human airway surface liquid (ASL). These include secretion from airway submucosal glands, ion and fluid transport across the surface epithelium, goblet cell discharge, surface tension and transepithelial gradients in osmotic and hydrostatic pressure. We describe recent experiments in which we have used low temperature scanning electron microscopy of rapidly frozen specimens to detect changes in depth of ASL in response to submucosal gland stimulation. We also present preliminary data in which X-ray microanalysis of frozen specimens has been used to determine the elemental composition of ASL.

• Tunnel and Underground Space
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• v.13 no.5
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• pp.397-402
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• 2003

Generally it is likely that rock mass properties are expressed not by a mean value but by values with variation due to its characteristic uncertainty. This characteristic is one of the most important parts for the design of undergound structures, but yet to be fully examined. Stochastic finite element method (SFEM) is contrary to deterministic finite element method in its concept as the former has been developed in order to take the randomness of structural systems into account. Using SFEM, the response variability of structural system can be obtained and it leads probabilistic stability of structure to be analyzed. In this study, displacement response variability of circular opening with hydrostatic stress field are analyzed in terms of rock mass properties having a certain mean and a standard deviation using the SFEM. The analyzed response variability shows that the necessity of probabilistic stability analysis of underground structures using reliable mean value and standard deviation of deformation modulus.

• Ocean Systems Engineering
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• v.4 no.4
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• pp.327-342
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• 2014

The tension leg platform (TLP) is one of the compliant structures which are generally used for deep water oil exploration. With respect to the horizontal degrees of freedom, it behaves like a floating structure moored by vertical tethers which are pretension due to the excess buoyancy of the platform, whereas with respect to the vertical degrees of freedom, it is stiff and resembles a fixed structure and is not allowed to float freely. In the current study, a numerical study for square TLP using modified Morison equation was carried out in the time domain with water particle kinematics using Airy's linear wave theory to investigate the effect of changing the tether tension force on the stiffness matrix of TLP's, the dynamic behavior of TLP's; and on the fatigue stresses in the cables. The effect was investigated for different parameters of the hydrodynamic forces such as wave periods, and wave heights. The numerical study takes into consideration the effect of coupling between various degrees of freedom. The stiffness of the TLP was derived from a combination of hydrostatic restoring forces and restoring forces due to cables. Nonlinear equation was solved using Newmark's beta integration method. Only uni-directional waves in the surge direction was considered in the analysis. It was found that for short wave periods (i.e., 10 sec.), the surge response consisted of small amplitude oscillations about a displaced position that is significantly dependent on tether tension force, wave height; whereas for longer wave periods, the surge response showed high amplitude oscillations that is significantly dependent on wave height, and that special attention should be given to tethers fatigue because of their high tensile static and dynamic stress.

• Journal of Ocean Engineering and Technology
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• v.29 no.1
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• pp.56-61
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• 2015

To improve the accuracy of a machine, research needs to be conducted on the relationship between the output variables and design variables of a spindle-shaped part from the thermal and static viewpoints. Therefore, research was carried out by examining the correlation of each variable to find the optimum conditions. Moreover, DOE (design of experiments) was extensively used. The model used in this study was a grinding spindle to which a hydrostatic bearing was applied. This model was used in a preliminary analysis based on the experimental results of the previous studies. The influences of the output variables and design variables were compared through a main effect analysis. Generated response surfaces were applied to the Kriging model. To optimize the model, a screening method was selected. In comparison with the initial model, the deformation of the optimized model designed by DOE decreased by 4.1 μm, while the thermal deformation decreased by 1.2 μm. Therefore, it was efficient to design a spindle-shaped part through DOE to improve the accuracy of the machine.