• Journal of the Society of Naval Architects of Korea
• /
• v.35 no.3
• /
• pp.71-78
• /
• 1998

Recently, modern long-stroke diesel engines with small number of cylinders have been installed for energy saving and simpler maintenance. These kinds of low speed diesel engine produce large torsional vibration in the shafting, which induces the excessive vibratory stresses in the shafting and large propeller thrust variation. This thrust variation excites vibrations of the shafting and superstructure in the longitudinal direction. Up to now the deteriministic analysis of coupled vibration of marine shafting system has been performed. In this paper probabilistic analysis method of the marine diesel propulsion shafting system under coupled axial and torsional vibrations is presented. For the purpose of this work, the torsional and axial vibration excitations of engine and propeller are assumed to be probabilistic while the lateral excitation is assumed to be deterministic. The probabilistic analysis is based on a response surface and Monte-Carlo simulation. Numerical results based on the proposed method are compared with results calculated using the conventional deterministic analysis method. The results obtained make it clear that the proposed method gives a substantial increase in information about shafting behaviour as compared with the deterministic method.

• Journal of the Society of Naval Architects of Korea
• /
• v.34 no.3
• /
• pp.53-60
• /
• 1997

Generally, a safety estimation based on the buckling strength is carried out to evaluate the strength of plate members in the design process of ship hull structures and more accurate and efficient tool for the buckling strength estimation of enormous plate members of ship structure is naturally demended for saving design process. While, in the reason that the design codes of classification societies do not consider the various effects or include some effects roughly, considerate safe side results are suggested occasionally. In this study, advanced buckling strength estimation system prepared various classification buckling evaluation codes and new evaluation code considering the effects of in-plane tension, plate boundary condition, lateral load & residual stress is developed using the window management system of engineering workstation. Additionally maximum deflection estimation formula is equipped for the increase of fabrication reliability of thin plate ship structure. From this evaluation system, more reliable buckling safety of plate panel will be guaranteed in the ship hull design stage. In order to expand the use of this system pc version system will be developed sooner or later.

• Tunnel and Underground Space
• /
• v.11 no.3
• /
• pp.225-236
• /
• 2001

The roughness of rock joint is one of the most important parameters in developing the shear resistance and the tendency of dilation. Due to the damage accumulated with shearing displacement, the roughness angle is lowered continuously. It is known that dilation, shear strength hardening, and softening are directly related to the degradation of asperities. Much effort has been directed to incorporate the complicated damage mechanism of asperities into a constitutive model fur rock joints. This study presents an elasto-plastic formulation of joint behavior including elastic deformability, dilatancy and asperity surface damage. It is postulated that the plastic portion of incremental displacement 7an be decomposed into contributions from both sliding along the asperity surface and damage of asperity. Numerical cyclic shear tests are presented to illustrate th? performance of the derived incremental stress-displacement relation. A laboratory cyclic shear test is also simulated. Numerical examples reveal that the elasto-plastic joints model is promising.

• Journal of Korean Society of Steel Construction
• /
• v.10 no.2 s.35
• /
• pp.221-232
• /
• 1998

This study presents a fatigue line with a plastic rotational angle to a great extent of plastic strain of Low-Cycle-Fatigue period, such as earthquake, etc. This fatigue line with a plastic rotational angle is measured and analysed more simply in practice rather than Woehler's fatigue line which is developed in stress variation of the structure. It shows that the slope of fatigue line with a plastic rotational angle is equal to that with plastic strain through the experiments by proving the correlation that the plastic strain ratio is directly proportional to the plastic rotational angle in plastic hinge. The theory is induced by Manson and Coffin strain fatigue line, and the experiments are tested by ECCS. The location of the plastic hinge is achieved and accurate plastic strain ratio is calculated through FEM.

• 한국해양학회지
• /
• v.21 no.4
• /
• pp.203-210
• /
• 1986

A linear parallel transport model is formulated and applied to an idealized Yellow Sea, With this simple analytical model, the hither-to suspected upwind flow phenomena in the southern Yellow Sea can be reasonably explained. In deep waters where the local depth exceeds a critical depth (Hc=53m in the present model sea), pressure gradient force dominates over wind stress and contributes to an upwind flow. The estimated upwind flow velocity increases with wind speed and a maximum upwind flow occurs along the axis of the Yellow Sea embayment. For the typical south wind of 5-10 knots in summer, the upwind (southward) flow velocity along the axis of the Yellow Sea is estimated to be 1-5cm s$\^$-1/. While, for the typical north wind of 10-15 knots in winter, the upwind (northward) flow velocity is 5-12cm s$\^$-1/. These velocity ranges can be served as rough estimates for the intrusion velocity of the Yellow Sea Bottom Cold Water in summer and the Yellow Sea Warm Current in winter, respectively.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.11 no.6
• /
• pp.87-94
• /
• 2007

Reuse of recycled aggregate from demolished concrete structure is beneficial and necessary from the viewpoint of environmental preservation and effective utilization of resources. The most important mechanical properties of recycled aggregate concrete (RAC) are the compressive strength, the tensile and the flexural strengths, the bond strength and the elastic modulus of such concrete. In particular, the stress-strain relation and fracture process of RAC in compression is especially important in theoretical and numerical analysis as well as engineering design of RAC structures. In this paper, to clarify the characteristics of fracture process in RAC, acoustic emission(AE) method is applied to detect micro-cracking in concrete under compression. From AE parameters, it is found that cracking and fracture behaviors in recycled aggregate concrete fairly differ from that of normal and recycled sand concrete.

• Journal of the Korean Geosynthetics Society
• /
• v.12 no.1
• /
• pp.11-19
• /
• 2013

Coarse-grained soils are typical engineering materials commonly used in many civil engineering applications such as structural fills, subgrade and drainage fills for dam, railway and bridge. Various researches have been performed with related to constitutive laws for numerical analysis of such structures. This paper presents a parametric study for a constitutive model for coarse grained materials. The model is a kind of the bounding surface models based on critical state theory. A distinct feature of the model is to capture the response of coarse-grained materials with different void ratios and confining pressures using a single set of model parameters. The model behavior is defined with a set of elastic parameters, critical state parameters, and model-specific parameters. The parametric study was performed for the model-specific parameters. The result of parametric study shows that the model is capable to capture stress-dilatancy behavior and kinematic-hardening under non-associative plastic flow.

• Polymer(Korea)
• /
• v.26 no.1
• /
• pp.105-112
• /
• 2002

The low actuation voltage and quick bending response of IPMC(ion-exchange polymer metal composite) are considered attractive for the construction of various types of actuators. In this study, in order to develop a new type actuators by using the IPMC platinum electrode of IPMC are fabricated by using electroless impregnation-reduction method plating. As the platinum-plating times are increased, IPMC performance was improved in terms of bending displacement and force due to the enhanced surface conductivity. In addition, we investigated the basic actuation characteristics of resonance frequency and actuator length as well as the effect of water uptake and ion mobility. Using the classical laminate theory(CLT), a modeling methodology was developed to predict the deformation, bending moment, and residual stress distribution of anisotropic IPMC thin plates. In this modeling methodology, the internal stress evolved by the unsymmetric distribution of water inside IPMC was quantitatively calculated and subsequently the bending moment and the curvature were estimated for various geometry of IPMC actuator.

• Journal of Korean Association for Spatial Structures
• /
• v.9 no.3
• /
• pp.75-82
• /
• 2009

This paper investigates the variation of post-buckling behaviours of spatial structures after sizing optimization with linear assumptions. The mathematical programming technique is used to produce the optimum member size of spatial structures against external load. Total weight of structure is considered as the objective function to be minimized and the displacement occurred at loading point and member stresses of structures are used as the constraint functions. The finite difference method is used to calculate the design sensitivity of objective function with respect to design variables. The post-buckling analysis carried out by using the geometrically nonlinear finite element analysis code ISADO-GN. It is found to be that there is a huge difference between the post buckling behaviours of the initial and optimized structures. Therefore, the stability of optimized spatial structures with linear assumption should be throughly checked by appropriate nonlinear analysis techniques. Finally, the present numerical results are provided as benchmark test suite for future study of large spatial structures.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.27 no.2
• /
• pp.87-94
• /
• 2014

In solid mechanics, the peridynamics theory has provided a suitable framework for material failure and damage propagation simulation. Peridynamics is computationally expensive since it is required to solve enormous nonlocal interactions based upon integro-differential equations. Thus, multiscale coupling methods with other local models are of interest for efficient and accurate implementations of peridynamics. In this study, peridynamic models are restricted to regions where discontinuities or stress concentrations are present. In the domains characterized by smooth displacements, classical local models can be employed. We introduce a recently developed blending scheme to concurrently couple bond-based peridynamic models and the Navier equation of classical elasticity. We demonstrate numerically that the proposed blended model is suitable for point loads and static fracture, suggesting an alternative framework for cases where peridynamic models are too expensive, while classical local models are not accurate enough.