• Nuclear Engineering and Technology
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• v.55 no.8
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• pp.3088-3101
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• 2023

A pressurized vessel-pipe-safety valve (PVPSV) combination is a commonly used configuration in nuclear power plants, and a good numerical model is essential for the system design, sizing and performance optimization. However, owing to the large-scale and cross-scale features, it is still a challenge to build a system level numerical model with both high accuracy and efficiency. To overcome this, a novel system level modeling method which can synthesize the advantages of various models is proposed in this paper. For system modeling, the analytical approach, the method of characteristics (MOC) and the surrogate model approach are respectively adopted to predict the dynamics of the pressure vessel, the connecting pipe and the safety valve, and different models are connected through data interfaces. With this system model, dynamic simulations were carried out and both the stable and the unstable system responses were obtained. For the model verification purpose, the simulation results were compared with those obtained from experiments and full CFD simulations. A good agreement and a better efficiency were obtained, verifying the ability of the model and the feasibility of the modeling method proposed in this paper.

• Proceedings of the Korea Information Processing Society Conference
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• 2023.11a
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• pp.528-529
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• 2023

Due to vast points and irregular structure, labeling full points in large-scale point clouds is highly tedious and time-consuming. To resolve this issue, we propose a novel point-based transformer network in weakly-supervised semantic segmentation, which only needs 0.1% point annotations. Our network introduces general local features, representing global factors from different neighborhoods based on their order positions. Then, we share query point weights to local features through point attention to reinforce impacts, which are essential in determining sparse point labels. Geometric encoding is introduced to balance query point impact and remind point position during training. As a result, one point in specific local areas can obtain global features from corresponding ones in other neighborhoods and reinforce from its query points. Experimental results on benchmark large-scale point clouds demonstrate our proposed network's state-of-the-art performance.

• Geophysics and Geophysical Exploration
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• v.16 no.4
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• pp.211-216
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• 2013

In general, smoothing filters regularize functions by reducing differences between adjacent values. The smoothing filters, therefore, can regularize inverse solutions and produce more accurate subsurface structure when we apply it to full waveform inversion. If we apply a smoothing filter with a constant coefficient to subsurface image or velocity model, it will make layer interfaces and fault structures vague because it does not consider any information of geologic structures and variations of velocity. In this study, we develop a selective smoothing regularization technique, which adapts smoothing coefficients according to inversion iteration, to solve the weakness of smoothing regularization with a constant coefficient. First, we determine appropriate frequencies and analyze the corresponding wavenumber coverage. Then, we define effective maximum wavenumber as 99 percentile of wavenumber spectrum in order to choose smoothing coefficients which can effectively limit the wavenumber coverage. By adapting the chosen smoothing coefficients according to the iteration, we can implement multi-scale full waveform inversion while inverting multi-frequency components simultaneously. Through the successful inversion example on a salt model with high-contrast velocity structures, we can note that our method effectively regularizes the inverse solution. We also verify that our scheme is applicable to field data through the numerical example to the synthetic data containing random noise.

• Journal of the Korea Concrete Institute
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• v.27 no.5
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• pp.471-480
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• 2015

The building structure is planned to maximize the use of space in recent. It was developed of a hybrid OCB (Optimized Composite Beam) for trying to take advantage of the maximize space. The OCB is composed of the steel h-beam section reinforced by open strands in negative moment zone and the psc concrete section in positive zone. Flexural behaviors of typical architectural bybrid OCB section was investigated. The 15 m OCB specimen was tested under three point static loading system. Following results are obtained from the tests; 1) The OCB with 15 m span develop initial flexural crackings under the 171% of full service loading. 2) Overall deflections of OCB under the service loads are less than those of the allowable limit in KCI Code provision. 3) The crack patterns, failure mode and ultimate load capacity of test specimen and F.E. model in this paper and they are compared to each other. The OCB is verified of structural reliability from the experimental results.

• 한국연소학회:학술대회논문집
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• 2004.11a
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• pp.141-145
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• 2004

The objective of the present study is to conduct model combustion tests for various injectors to identify their combustion stability characteristics. Three different double swirl coaxial injectors with variation of a recess length have been tested for the comparative study of CH flame structure and dynamic characteristics. Gaseous oxygen and mixture of gaseous methane and propane have been employed for simulating actual propellants used for a full-scale thrust chamber. Upon test results, the direct comparison between various types of injectors can be realized for the selection of the best design among prospective injectors.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.1774-1785
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• 2011

In this paper, Rigid Reinforced Roadbed(RRR) which is expected to have highly applicability to railroad roadbed, was introduced and field tests results were analyzed. Full scale model with 5m height concerning a single track railroad roadbed was constructed. The model had four different sections, which was to assess the effect of geogrid length, spacing, and connection method on deformation characteristics of RRR. Laser displacement meter, earth pressure cell, piezometer, and strain gauge were installed in order to analyze the behavior of reinforced embankment during construction. Horizontal displacements caused by compaction at each section were 20~30% below the displacement limit that of general reinforced retaining wall, which showed that RRR was very stable structure. Maximum tensile strength of reinforcement was withing 10% of the long-term design strength.

• Steel and Composite Structures
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• v.14 no.1
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• pp.21-39
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• 2013

The paper presents a numerical investigation, done with the computer program SAFIR, in order to obtain simpler finite element models for representing the behaviour of the partially protected composite steel concrete slabs in fire situations, considering the membrane action. Appropriate understanding and modelling of the particular behaviour of composite slabs allows a safe approach, but also substantial savings on the thermal insulation that has to be applied on the underlying steel structure. The influence of some critical parameters on the behaviour and fire resistance of composite slabs such as the amount of reinforcing steel, the thickness of the slab and the edge conditions is also highlighted. The results of the numerical analyses are compared with the results of three full scale fire tests on composite slabs that have been performed in recent years.

• Structural Engineering and Mechanics
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• v.22 no.3
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• pp.351-370
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• 2006

In this study, the earthquake damage response of the concrete arch dams was investigated including dam-reservoir interaction. A continuum damage model which is a second-order tensor and includes the strain softening behavior was selected for the concrete material. Fluid-structure interaction problem was modeled by Lagrangian approach. Sommerfeld radiation condition was applied to the truncated boundary of reservoir. The improved form of the HHT-${\alpha}$ time integration algorithm was used in the solution of the equations of motion. The arch dam Type 5 was selected for numerical application. For the dynamic input, acceleration records of the 10 December 1967 Koyna earthquake were chosen. These records were scaled with earthquake acceleration scale factor (EASF) and then used in the analyses. Solutions were obtained for empty and full reservoir cases. The effects of EASF and damping ratio on the response of the dam were studied.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.555-560
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• 2002

The structure of Chosun-ilbo Boopyung factory was desined as exposed concrete. The self compacting concrete(non-vibrating concrete) must be applied to this case because the exposed concrete wall is very thin(200mm) and high(6m), Laboratory tests and semi mock-up test were performed for optimum mix design of the self compacting concrete. As a result, the optimum mixes were observed at the 3-component types(ope, fly-ash, slag powder) that Vp$\geq$0.175, Vw/Vp$\geq$0.95, W=170~175$kgf/m^3$ and B=500~540$kgf/m^3$ Based on this result. we make plan that the pilot productions of batcher plant, the full-scale mock up tests and site application.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.561-564
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• 1999

The uniform state of prestress in a fully prestressed concrete members shows reductions of more than half of the initial prestress in the construction and coupling joint vicinity. Especially, at a zone x/d=0.2 above the construction joint where at the edge of the member, a quite localized reduced stress state of 1/3 of uniform stress is encountered. Five full-scale test specimens were segmentally constructed and post-tensioned and analytic models is used to verify and validate measured test results. The encountered highly nonuniform stress/strain state in the coupling joint vicinity requires special design consideration for the successful application of tendon couplers.