• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.2
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• pp.119-128
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• 2018

A numerical method is proposed to simulate level ice interaction with ship in transverse and longitudinal directions in time domain. A novel method is proposed to simulate non-symmetric transverse force in a stochastic way. On the basis of observations from the model tests, the simulation of longitudinal force combines the ice bending force acting on the waterline, submersion force below the waterline and ice friction forces caused by transverse force and ice floes rotation amidships. In the simulations the ship was fixed and towed through an intact ice sheet at a certain speed. The setup of the numerical simulation is similar to the ice tank setup as much as possible. The simulated results are compared with model tests data and the results show good agreement with the measurement.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.9
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• pp.659-668
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• 2008

Combustion instability has been considered as very important issue for developing gas turbine and rocket engine. There is a need for fundamental understanding of combustion instability. In this study, combustion instability was numerically and experimentally investigated in a dump combustor with bluff body. The fuel and air mixture had overall equivalence ratio of 0.9 and was injected toward dump combustor. The pressure oscillation with approximately 256Hz was experimentally obtained. For numerical simulation, the standard k-$\varepsilon$ model was used for turbulence and the hybrid combustion model (eddy dissipation model and kinetically controlled model) was applied. After calculating steady solution, unsteady calculation was performed with forcing small perturbation on initial that solution. Pressure amplitude and frequency measured by pressure sensor is nearly the same as those predicted by numerical simulation. Furthermore, it is clear that a combustion instability involving vortex shedding is affected by acoustic-vortex-combustion interaction. The phase difference between the pressure and velocity is $\pi$/2, and that between the pressure and heat release rate is in excitation range described by Rayleigh, which is obvious that combustion instability for the bluff body combustor meets thermoacoustic instability criterion.

• Korean Journal of Agricultural Science
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• v.43 no.1
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• pp.116-126
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• 2016

The objective of this study is to predict the fuel efficiency of an agricultural tractor. The fuel efficiency of the tractor during rotary tillage was predicted using numerical modeling. A numerical model was developed using Simulation X. Based on tractor power flow, numerical modeling consisted of an engine, transmission, PTO (power take off), and hydraulics. The specifications of major components utilized in the numerical model were the same as those of a 71 kW tractor (field test tractor). The load that was inputted for fuel efficiency prediction into the simulation model was obtained from a field test. Fuel efficiency predictions were conducted by comparing field test results and simulation results. In addition, it was performed by dividing the rotary tillage and steering section. Main results are as follows: first, t-values of engine torque were measured to be 0.31 in the rotary tillage and 0.92 in the steering section. Second, t-values of fuel consumption were measured to be 0.51 and 5.41 in the rotary tillage and the steering section, respectively. Finally, t-values of fuel efficiency were measured to be 1.72 and 40 in the rotary tillage and the steering section, respectively. The results show no significant differences with t-values of less than 5% in the rotary tillage. But, it shows significant differences in the steering section. Therefore, simulation for accurate fuel efficiency prediction requires a suitable algorithm or detailed design of the simulation model in the steering section.

• Computers and Concrete
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• v.9 no.1
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• pp.21-33
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• 2012

This paper presents the numerical simulation of the rigid 12.6 mm diameter kinetic energy ogive-nosed projectile impact on plain and fiber reinforced concrete (FRC) targets with compressive strengths from 45 to 235 MPa, using a three-dimensional finite element code LS-DYNA. A combined dynamic constitutive model, describing the compressive and tensile damage of concrete, is implemented. A modified Johnson_Holmquist_Cook (MJHC) constitutive relationship and damage model are incorporated to simulate the concrete behavior under compression. A tensile damage model is added to the MJHC model to analyze the dynamic fracture behavior of concrete in tension, due to blast loading. As a consequence, the impact damage in targets made of plain and fiber reinforced concrete with same matrix material under same impact velocities (650 m/s) are obtained. Moreover, the damage distribution of concrete after penetration is procured to compare with the experimental results. Numerical simulations provide a reasonable prediction on concrete damage in both compression and tension.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.205-208
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• 2008

The wind load on building surface is numerically investigated. The geometry of target building is a square cross section and aspect ratio (height (H) to width (d)) is 6. On building surface, the pressure was measured, compared to obtained value from numerical simulation. The numerical simulations were done using URANS with three different turbulence models such as v2-f model, k-${\omega}$model, and k-${\varepsilon}$ model, respectively. The v2-f model showed the best agreement with experimental data in simulating mean pressure coefficients on front, rear and side surface. But unsteady characteristics of pressure history measured on surface is shown a discrepancy between experiment and numerical simulation.

• Advances in Computational Design
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• v.3 no.2
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• pp.133-146
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• 2018

The paper discusses numerical analysis of tensile notched specimens with the use of Gurson - Tvergaard - Needleman (GTN) material model. The analysis concerned S235JR and S355J2G3 steel grades, subjected to medium stress state triaxiality ratio, amounting 0.739. A complete procedure for FEM model preparation was described, paying special attention to the issue of determining material constants in the GTN model. An example of critical void volume fraction ($f_c$) experimental determination procedure was presented. Finally, the results of numerical analyses were discussed, indicating the differences between steel grades under investigation.

• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.31-44
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• 2019

This study simulated a control rod assembly (CRA), which is a part of reactor shutdown systems, in immersed and fluid flow conditions. The CRA was inserted into the reactor core within a predetermined time limit under normal and abnormal operating conditions, and the CRA (which consists of complex geometric shapes) drop behavior is numerically modeled for simulation. A full-scale prototype CRA drop test is established under room temperature and water-fluid conditions for verification and validation. This paper describes the details of the numerical modeling and analysis results of the several conditions. Results from the developed numerical simulation code are compared with the test results to verify the numerical model and developed computer code. The developed code is in very good agreement with the test results and this numerical analysis model and method may replace the experimental and CFD method to predict the drop behavior of CRA.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.49-55
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• 2004

This paper addresses a numerical simulation of the flow and heat transfer in a simplified model of helically coiled tube steam generator using a general purpose computational fluid dynamic analysis computer code. The steam generator model is comprised of a cylindrical shell and helically coiled tubes. A cold feed water entered the tubes is heated up, evaporates. and finally become a superheated steam with a large amount of heat transferred continuously from the hot compressed water at higher pressure flowing counter-currently through the shell side. For the calculation of tube side two-phase flow field formed by boiling, inhomogeneous two-fluid model is used. Both the internal and external turbulent flows are simulated using the standard k-e model. The conjugate heat transfer analysis method is employed to calculate the conduction in the tube wall with finite thickness and the convections in the internal and external fluids simultaneously so as to match the fluid-wall-fluid interface conditions properly. The numerical calculations are peformed for helically coiled tubes of steam generator at an integral type pressurized water reactor under normal operation. The effects of tube-side inlet flow velocity are discussed in details. The results of present numerical simulation are considered to be physically plausible based on the data and knowledge from previous experimental and numerical studies where available.

• Transactions of Materials Processing
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• v.22 no.3
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• pp.150-157
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• 2013

Fiber metal laminates (FMLs) are layered materials comprised of thin metal sheets and fiber reinforced plastic (FRP). This paper presents the numerical study of the formability enhancement of FMLs composed of an aluminum alloy and self-reinforced polypropylene (SRPP) composite. In this study, a numerical simulation based on finite element (FE) modeling is proposed to evaluate the formability of FMLs using ABAQUS/Explicit. The FE model, which included a single layer of solid and shell elements to model the blank, used discrete layers of the solid element with a contact model and shell elements with a friction based model for the aluminum alloy-composite interface conditions. This method allowed the description of each layer of FMLs and was able to simulate the interaction between the layers. It is noted through this research that the proposed numerical simulation described properly the formability enhancement of the FMLs and the simulation results showed good agreement with experimental results.

• Wind and Structures
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• v.1 no.4
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• pp.337-349
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• 1998

A numerical and experimental study was performed for the wind flow field in one area, comprising a group of several pavilions separated by passageways, of the EXPO '98 - a World Exposition (Lisbon, Portugal). The focus of this study is the characterization of the flow field to assess pedestrian comfort. The predictions were obtained employing the Reynolds averaged Navier-Stokes equations with the turbulence effects dealt with the ${\kappa}-{\varepsilon}$ RNG model. The discretization of the differential equations was accomplished with the control volume formulation in a Cartesian coordinate system, and an advanced segregated procedure was used to achieve the link between continuity and momentum equations. The evaluation of the overall numerical model was performed by comparing its predictions against experimental data for a square cylinder placed in a channel. The predicted values, for the practical geometry studied, are in a good agreement with the experimental data, showing the performance and the reliability of the ${\kappa}-{\varepsilon}$ RNG model and suggesting that the numerical simulation is a reliable methodology to provide the required information.