• Journal of Ocean Engineering and Technology
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• v.35 no.1
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• pp.50-58
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• 2021

The demand for eco-friendly energy is expected to increase due to the recently strengthened environmental regulations. In particular, the flow inside the pipe used in a cargo handling system (CHS) or fuel gas supply system (FGSS) of hydrogen transport ships and hydrogen-powered ships exhibits a very complex pattern of multiphase-thermal flow, including the boiling phenomenon and high accuracy analysis is required concerning safety. In this study, a feasibility study applying the boiling model was conducted to analyze the multiphase-thermal flow in the pipe considering the phase change. Two types of boiling models were employed and compared to implement the subcooled boiling phenomenon in nucleate boiling numerically. One was the "Rohsenow boiling model", which is the most commonly used one among the VOF (Volume-of-Fluid) boiling models under the Eulerian-Eulerian framework. The other was the "wall boiling model", which is suitable for nucleate boiling among the Eulerian multiphase models. Moreover, a comparative study was conducted by combining the nucleate site density and bubble departure diameter model that could influence the accuracy of the wall boiling model. A comparison of the Rohsenow boiling and the wall boiling models showed that the wall boiling model relatively well represented the process of bubble formation and development, even though more computation time was consumed. Among the combination of models used in the wall boiling model, the simulation results were affected significantly by the bubble departure diameter model, which had a very close relationship with the grid size. The present results are expected to provide useful information for identifying the characteristics of various parameters of the boiling model used in CFD simulations of multiphase-thermalflow, including phase change and selecting the appropriate parameters.

• Journal of Welding and Joining
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• v.25 no.4
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• pp.79-85
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• 2007

The industrial disaster caused by a work-related disease like a Musculoskeletal Disorders(MSDs) becomes a big social problem and increases rapidly. This leads to the degradation of the labor desire and the productivity. Welding work belongs to the work with a high intensity. This paper aims to analyze the welding work in the various positions from a view-point of the burden of the human musculoskeletal system and to propose the desired position with lower burden. For this purpose the real welding work was observed in the shipyard and analyzed using the RULA method, a powerful ergonomics tool. The 3-dimensional simulation model fur this work was also developed. In this model, ergonomics human model and welding work environment were built. This model was verified through the comparison to the real work. This paper showed that the improvement of welding position by changing the location of a stool and using some auxiliary tool can reduce the work intensity remarkably and lead to the decrease of MSDs.

• Journal of the Society of Naval Architects of Korea
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• v.58 no.2
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• pp.73-83
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• 2021

In this study, the numerical investigation of the flow around the SUBOFF submarine model is performed by using the Detached Eddy Simulation (DES) method which is developed based on the SST k-ω turbulence model. At the DES analysis level, complex vortical flows around the submarine model are caused mainly by the vortices due to the appendages and their interactions with the flows from the hull boundary layer and other appendages. The complexity and scale of the vortical flow obtained from the numerical simulations are highly dependent on the grid. The computed local flow properties of the submarine model are compared with the available experimental data showing a good agreement. The DES analysis more reasonably estimates the physical phenomena inherent in the experimental result in a low radius of the propeller plane where vortical flows smaller than the RANS scale are dominant.

• Journal of the Korea Society for Simulation
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• v.19 no.4
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• pp.309-318
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• 2010

Simulation-based acquisition(SBA) is a new acquisition paradigm to deliver combat systems cheaper, faster, and better. ROK MND adopts the vision of SBA and is pushing ahead with dramatic reform. However, ROK MND does not develop the SBA architecture framework which facilitates the reuse of tools and techniques and data software code and algorithms among participants of collaborative environments. In this paper, we propose a conceptual Model of architecture framework for SBA. To do so, we analyse acquisition process of MND and propose the to-be operational view that describes fundamental concept for how Government, Industry, and Academia can collaborate and share information more effectively throughout the acquisition process. Furthermore, we identify the tools and techniques that supports the operational nodes, and propose technical view and all view, too. technical view compose of set of standards that can ensure interoperability among tools, techniques and data, and all view provide an overarching description of the architecture.

• Computers and Concrete
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• v.15 no.5
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• pp.847-864
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• 2015

In this paper, a reaction-diffusion model of carbonation process in self-compacting concrete (SCC) was realized with a consideration of multi-field couplings. Various effects from environmental conditions, e.g. ambient temperature, relative humidity, carbonation reaction, were incorporated into a numerical simulation proposed by ANSYS. In addition, the carbonation process of SCC was experimentally investigated and compared with a conventionally vibrated concrete (CVC). It is found that SCC has a higher carbonation resistance than CVC with a comparable compressive strength. The numerical solution analysis agrees well with the test results, indicating that the proposed model is appropriate to calculate and predict the carbonation process in SCC. The parameters sensitivity analysis also shows that the carbon dioxide diffusion coefficient and moisture field are essentially crucial to the carbonation process in SCC.

• Journal of Information Processing Systems
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• v.9 no.3
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• pp.489-498
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• 2013

In this paper, we propose a common simulation model that can be reused for different performance evaluations of networked virtual environments. To this end, we analyzed the common features of NVEs, in which multiple regions compose a shared space, and where a user has his/her own interest area. Communication architecture can be client-server or peer-server models. In usual simulations, users move around the world while the number of users varies with the system. Our model provides various simulation parameters to customize the region configuration and user movement pattern. Furthermore, our model introduces a way to mimic a lot of users in a minimal experiment environment. The proposed model is integrated with our network framework, which supports various scalability approaches. We specifically applied our model to the interest management and load distribution schemes to evaluate communication overhead. With the proposed simulation model, a new simulation can be easily designed in a large-scale environment.

• Geomechanics and Engineering
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• v.9 no.1
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• pp.25-37
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• 2015

To predict the surface subsidence of salt rock storage, a new surface subsidence basin model is proposed based on the Logistic function from the phenomenological perspective. Analysis shows that the subsidence curve on the main section of the model is S-shaped, similar to that of the actual surface subsidence basin; the control parameter of the subsidence curve shape can be changed to allow for flexible adjustment of the curve shape. By using this model in combination with the MMF time function that reflects the single point subsidence-time relationship of the surface, a new dynamic prediction model of full section surface subsidence for salt rock storage is established, and the numerical simulation calculation results are used to verify the availability of the new model. The prediction results agree well with the numerical simulation results, and the model reflects the continued development of surface subsidence basin over time, which is expected to provide some insight into the prediction and visualization research on surface subsidence of salt rock storage.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.5
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• pp.498-509
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• 2009

Present study is concerned with the simulation of plasticity models for the cyclic stressstrain behavior of aluminum alloy AC4C-T6 that can be used for primary materials of LNG cargo pump. Material model of cyclic hardening and plasticity for aluminum alloy AC4C-T6 was investigated through experiments and numerical simulations. Monotonic tensile and cyclic tension-compression test under symmetric load cycles was performed at both room temperature and cryogenic temperature of $-165^{\circ}C$. Based on the experimental data plastic hardening models were evaluated for isotropic/kinematic/combined hardening. FEA (Finite Element Analysis) models which describe the cyclic stress-strain relationship were evaluated for the simulation of plasticity. An appropriate hardening model is proposed comparing the results of FEA with those of experiments.

• Journal of KIBIM
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• v.6 no.3
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• pp.34-41
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• 2016

The previous studies argue that using the semantic properties of BIM objects is efficient for simulating the behaviors of autonomous, computer agents, called virtual-users, but such assumption is not proven via evidence-based research approaches. Hence, this present study aims to investigate the empirical effects of a human behavior simulation model equipped the semantics of spaces on the architecture-major students' operation and understanding of the simulation system, compared to a typical path-finding model. To achieve the aim, this study analyzed the survey and interview data, collected in the authentic design projects. The analysis indicates that (1) using a simulation model equipped the semantics of spaces helps the students' operation of the simulation, and (2) it also aids understanding the relationship between the variables of spaces and virtual-users (${\alpha}=0.74$). In addition, the qualitative data inform that the advantages of the simulation model that computes the semantics of spaces stem in the automatic behavioral changes of massive numbers of virtual-users, and efficient detection and activation on the what-if situations. The analysis also reveals that the simulation model has shortcomings in orchestrating the complex data structure between the semantics properties of spaces and virtual-users under multi-sequential scenarios. The results of this study contribute to develop a future design system combining BIM with human behavior simulation.

• International conference on construction engineering and project management
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• 2013.01a
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• pp.397-402
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• 2013

In super-tall building construction projects, schedule risk factors which vertically change and are not found in the low and middle-rise building construction influence duration of a project by vertical attribute; and it makes hard to estimate activity or overall duration of a construction project. However, the existing duration estimating methods, that are based on quantity and productivity assuming activities of the same work item have the same risk and duration regardless of operation space, are not able to consider the schedule risk factors which change by the altitude of operation space. Therefore, in order to advance accuracy of duration estimation of super-tall building projects, the degree of changes of these risk factors according to altitude should be analyzed and incorporated into a duration estimating method. This research proposes a simulation model using Monte Carlo method for estimating activity duration incorporating schedule risk factors by weather conditions in a super-tall building. The research process is as follows. Firstly, the schedule risk factors in super-tall building are identified through literature and expert reviews, and occurrence of non-working days at high altitude by weather condition is identified as one of the critical schedule risk factors. Secondly, a calculating method of the vertical distributions of the weather factors such as temperature and wind speed is analyzed through literature reviews. Then, a probability distribution of the weather factors is developed using the weather database of the past decade. Thirdly, a simulation model and algorithms for estimating non-working days and duration of each activity is developed using Monte-Carlo method. Finally, sensitivity analysis and a case study are carried out for the validation of the proposed model.