• Wind and Structures
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• v.36 no.3
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• pp.161-174
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• 2023

The analytical model of tornado vortices plays an essential role in tornado wind description and tornado-resistant design of civil structures. However, there is still a lack of guidance for the selection and application of tornado analytical models since they are different from each other. For single-cell tornado vortices, this study conducts a comparative study on the velocity characteristics of the analytical models based on numerically simulated tornado-like vortices (TLV). The single-cell stage TLV is first generated by Large-eddy simulations (LES). The spatial distribution of the three-dimensional mean velocity of the typical analytical tornado models is then investigated by comparison to the TLV with different swirl ratios. Finally, key parameters are given as functions of swirl ratio for the direct application of analytical tornado models to generate full-scale tornado wind field. Results show that the height of the maximum radial mean velocity is more appropriate to be defined as the boundary layer thickness of the TLV than the height of the maximum tangential mean velocity. The TLV velocity within the boundary layer can be well estimated by the analytical model. Simple fitted results show that the full-scale maximum radial and tangential mean velocity increase linearly with the swirl ratio, while the radius and height corresponding to the position of these two velocities decrease non-linearly with the swirl ratio.

• Geomechanics and Engineering
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• v.31 no.3
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• pp.237-248
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• 2022

Nowadays, more and more subway tunnels were planed and constructed underneath the ground of urban cities to relieve the congested traffic. Potential damage may occur in existing tunnel if the new tunnel is constructed too close. So far, previous studies mainly focused on the tunnel-tunnel interactions with circular shape. The difference between circular and horseshoe shaped tunnel in terms of deformation mechanism is not fully investigated. In this study, three-dimensional numerical parametric studies were carried out to explore the effect of different tunnel shapes on the complicated tunnel-tunnel interaction problem. Parameters considered include volume loss, tunnel stiffness and relative density. It is found that the value of volume loss play the most important role in the multi-tunnel interactions. For a typical condition in this study, the maximum invert settlement and gradient along longitudinal direction of horseshoe shaped tunnel was 50% and 96% larger than those in circular case, respectively. This is because of the larger vertical soil displacement underneath existing tunnel. Due to the discontinuous hoop axial stress in horseshoe shaped tunnel, significant shear stress was mobilized around the axillary angles. This resulted in substantial bending moment at the bottom plate and side walls of horseshoe shaped tunnel. Consequently, vertical elongation and horizontal compression in circular existing tunnel were 45% and 33% smaller than those in horseshoe case (at monitored section X/D = 0), which in latter case was mainly attributed to the bending induced deflection. The radial deformation stiffness of circular tunnel is more sensitive to the Young's modulus compared with horseshoe shaped tunnel. This is because of that circular tunnel resisted the radial deformation mainly by its hoop axial stress while horseshoe shaped tunnel do so mainly by its flexural rigidity. In addition, the reduction of soil stiffness beneath the circular tunnel was larger than that in horseshoe shaped tunnel at each level of relative density, indicating that large portion of tunneling effect were undertaken by the ground itself in circular tunnel case.

• Steel and Composite Structures
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• v.50 no.3
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• pp.265-280
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• 2024

The collapse behavior observed in single-story beam-column assembly (SSBCA) do not accurately represent the actual overall stress characteristic of multi-story frame structure (MSFS) under column loss scenario owing to ignoring the interaction action among different stories, leading to a disconnection between the anti-collapse behaviors of "components" and "overall structures", that is, the anti-collapse performance of frame structures with two different structural scales has not yet formed a combined force. This paper conducts a numerical and theoretical study to explore the difference of the collapse behaviors of the SSBCA and MSFS, and further to reveal the internal force relationships and boundary constraints at beam ends of models SSBCA and MSFS. Based on the previous experimental tests, the corresponding refined numerical simulation models were established and verified, and comparative analysis on the resistant-collapse performance was carried out, based on the validated modeling methods with considering the actual boundary constraints, and the results illustrates that the collapse behaviors of the SSBCA and MSFS is not a simple multiple relationship. Through numerical simulation and theoretical analysis, the development laws of internal force in each story beam under different boundary constraints was clarified, and the coupling relationship between the bending moment at the most unfavorable section and axial force in the composite beam of different stories of multi story frames with weld cover-plated flange connections was obtained. In addition, considering the effect of the yield performance of adjacent columns on the anti-collapse bearing capacities of the SSBCA and MSFS during the large deformation stages, the calculation formula for the equivalent axial stiffness at the beam ends of each story were provided.

• Smart Structures and Systems
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• v.33 no.1
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• pp.1-16
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• 2024

The investigation on vehicle-bridge coupling system (VBCS) is crucial in bridge design, bridge condition evaluation, and vehicle overload control. A real-time hybrid testing (RTHT) method for VBCS (RTHT-VBCS) is proposed in this paper for accurately and economically disclosing the dynamic performance of VBCSs. In the proposed method, one of the carriages is chosen as the experimental substructure loaded by servo-hydraulic actuator loading system in the laboratory, and the remaining carriages as well as the bridge structure are chosen as the numerical substructure numerically simulated in one computer. The numerical substructure and the experimental substructure are synchronized at their coupling points in terms of force equilibrium and deformation compatibility. Compared to the traditional iteration experimental method and the numerical simulation method, the proposed RTHT-VBCS method could not only obtain the dynamic response of VBCS, but also economically analyze various working conditions. Firstly, the theory of RTHT-VBCS is proposed. Secondly, numerical models of VBCS for RTHT method are presented. Finally, the feasibility and accuracy of the RTHT-VBCS are preliminarily validated by real-time hybrid simulations (RTHSs). It is shown that, the proposed RTHT-VBCS is feasible and shows great advantages over the traditional methods, and the proposed models can effectively represent the VBCS for RTHT method in terms of the force equilibrium and deformation compatibility at the coupling point. It is shown that the results of the single-degree-of-freedom model and the train vehicle model are match well with the referenced results. The RTHS results preliminarily prove the effectiveness and accuracy of the proposed RTHT-VBCS.

• Journal of radiological science and technology
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• v.37 no.1
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• pp.15-20
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• 2014

This study was to evaluate clinical feasibility of biodegradable polymeric membrane for interventional procedure in preliminary study. Bio-degradable polymetric membrane was produced into a solution by mixing hyaluronic acid powder with NaOH solution in a heating mantle. Three different concentrations of contrast media (10, 20, and 30 vol%) were added to the produced soluble powder, and vertical agitation was performed for 12 hours at a speed of 100 to 200 rpm at a room temperature. It was freeze dried for 24 hours at a temperature $80^{\circ}C$. Pressure on the freeze dried sample was exerted by a hydraulic press in order to form the freeze dried sample into a membrane. The membrane produced with varying contrast medium concentration was visually examined by a scanning electron microscope and radiographically inspected. Under the visual examination, the higher the concentration of contrast medium, the rougher the surface. Radiographic transparency was similar under all conditions of fluoroscopic radiography, simple radiography, and serial radiography. In conclusion, this preliminary study verified that bio-degradable membrane produced with hyaluronic acid was a material with clinical usability.

• Journal of the Korea Organic Resources Recycling Association
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• v.8 no.4
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• pp.93-99
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• 2000

Treatment of shaving scrap, a chrome containing solid scrap generated by leather manufacturing process, has been so far depended on mainly incineration, soil landfill and ocean dumping, which give bad impact on environment and cause pollution. Shaving scrap generates from the mechanical work for controlling the final thickness of leather and its main components are collagen protein and pan of chromium compound. For the purpose of reusing this leather waste as resources, researches in connection with collagen fiber recovery, gelable protein recovery and liquid fertilizer is being speedily progressed. In the experiment, shaving scrap went through wet pulverizing treatment by physical and chemical methods. Then, making the leather sheet evenly, it is mixed with natural latex and every kind of binding materials in the container, and the mixtures were passed through experimental hydraulic press machine and applied to Fourdrinier machine respectively. Lastly, a test for fading out physical strength and properties of multiple-purpose of leather-like material was performed on a continuous leather sheet prepared by the experiment. In result, the physical strength and properties of leather-like material showed noticeable differences according to mixing ratio of binding materials, beating methods and the Ends of binding materials selected, and generally tear strength was the weakest property among others. Also, by the pilot scale experiment in sequence, it was possible to manufacture recycled goods made of soft and hard types of leather-like material with various performances.

• Journal of the Korean Geotechnical Society
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• v.34 no.7
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• pp.39-49
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• 2018

Jacked pile that involves the use of hydraulic jacks to press the piles into the ground is free from noise and vibration, and is possibly installed within a limited construction area. Thus, as an alternative to conventional pile driving methods, pile jacking could become widely accepted for the construction projects in urban area (e.g., reconstruction or remodeling construction projects). Great concern has arisen over the prediction of axially loaded jacked pile behavior. Against this background, a series of pile load tests were hence conducted on a jacked steel pipe pile installed in weathered zone (i.e., weathered soil and weathered rock). From the test results, base resistance and shaft resistance for each test condition were evaluated and compared with the values predicted by the previous driven pile resistance assessment method. Test results showed that the previous driven pile resistance assessment method highly underestimated both the base and shaft resistances of a jacked pile; differences were more obviously observed with the shaft resistance. The reason for this discrepancy is that a driven pile normally experiences a larger number of loading/unloading cycles during installation, and therefore shows significantly degraded stiffness of surrounding soil. Based on the results of the pile load tests, particular attention was given to the modification of the previous driven pile resistance assessment method for investigating the axially loaded jacked pile behavior.

• Ocean Systems Engineering
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• v.6 no.1
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• pp.23-60
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• 2016

The major objective of this study was to develop further understanding of 3D nearshore hydrodynamics under a variety of wave and tidal forcing conditions. The main tool used was a comprehensive 3D numerical model - combining the flow module of Delft3D with the WAVE solver of XBeach - of nearshore hydro- and morphodynamics that can simulate flow, sediment transport, and morphological evolution. Surf-swash zone hydrodynamics were modeled using the 3D Navier-Stokes equations, combined with various turbulence models (${\kappa}-{\varepsilon}$, ${\kappa}-L$, ATM and H-LES). Sediment transport and resulting foreshore profile changes were approximated using different sediment transport relations that consider both bed- and suspended-load transport of non-cohesive sediments. The numerical set-up was tested against field data, with good agreement found. Different numerical experiments under a range of bed characteristics and incident wave and tidal conditions were run to test the model's capability to reproduce 3D flow, wave propagation, sediment transport and morphodynamics in the nearshore at the field scale. The results were interpreted according to existing understanding of surf and swash zone processes. Our numerical experiments confirm that the angle between the crest line of the approaching wave and the shoreline defines the direction and strength of the longshore current, while the longshore current velocity varies across the nearshore zone. The model simulates the undertow, hydraulic cell and rip-current patterns generated by radiation stresses and longshore variability in wave heights. Numerical results show that a non-uniform seabed is crucial for generation of rip currents in the nearshore (when bed slope is uniform, rips are not generated). Increasing the wave height increases the peaks of eddy viscosity and TKE (turbulent kinetic energy), while increasing the tidal amplitude reduces these peaks. Wave and tide interaction has most striking effects on the foreshore profile with the formation of the intertidal bar. High values of eddy viscosity, TKE and wave set-up are spread offshore for coarser grain sizes. Beach profile steepness modifies the nearshore circulation pattern, significantly enhancing the vertical component of the flow. The local recirculation within the longshore current in the inshore region causes a transient offshore shift and strengthening of the longshore current. Overall, the analysis shows that, with reasonable hypotheses, it is possible to simulate the nearshore hydrodynamics subjected to oceanic forcing, consistent with existing understanding of this area. Part II of this work presents 3D nearshore morphodynamics induced by the tides and waves.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.258-258
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• 2019

계산 격자에 기반하여 천수 흐름을 모의할 때, 그 격자에 담긴 물의 양을 정확하게 파악할 필요가 있다. 예를 들어, 초기조건으로 수위가 부여된다면 계산격자의 기하 특성에 맞추어 흐름 변수인 수심이나 흐름 단면적으로 바꾸어야하기 때문이다. 필요에 따라서는 모의 결과를 수위로 보이거나 격자 속 수심을 계산에 사용할 수도 있으므로 그 역변환도 고려되어야 한다. 2차원의 삼각형 계산격자에 대해서는 물의 부피와 수위 관계(volume/free-surface relationship)가 이미 정확(exact)하게 구명되어 있다(Hwang, 2017, J. KWRA). 그런데 1차원 문제의 횡단면에서 흐름 단면적과 수위의 관계(area/free-surface relationship)는 수위로부터 면적 환산에 대해서는 정확하나 그 역변환은 그렇지 않다. 매 시간 단계에서 갱신된 흐름 단면적으로부터 수위를 환산하기 위해 미리 작성된 면적-수위 자료를 이용한 선형 보간이 적용된다(Goodell, 2011, The RAS Solution). 이때, 환산 정확도는 자료의 해상도에 의존된다. 다행히 하천 횡단면 대부분을 채워 흐르는 홍수모의에서는 이 문제가 그리 심각하지는 않다. 심지어 수위가 복단면 저수로 턱에 걸쳐있어 흐름단면적이 급변하는 경우에도 환산 수위의 정확도는 크게 훼손되지 않는다. 그러나 미미한 환산 오차일지라도 그로 인해 수위가 저수로 턱을 넘거나 그보다 작을 수 있다. 이 경우, 홍수터의 잠김여부에 따라 수면폭(top width)이 실제 계산 결과에 비해 크게 달라질 수밖에 없다. 수면폭 오차는 그것을 이용하여 결정되는 수리 수심(hydraulic depth)이나 평균 하상고(mean bed level)의 산정에도 전파된다. 이 연구에서는 하천 횡단면에서 수위와 흐름 단면적 사이의 환산 정확도를 크게 높일 수 있는 기법을 제시하였다. 먼저 하천 횡단면에서 주어진 수위에 대해 흐름 단면적을 산정할 수 있는 알고리듬을 보였다. 또한, 횡단면에서 수위와 흐름 단면적의 관계가 단조 증가 함수(monotonically increasing function)임에 착안하여 그 역변환에 대해 해 찾기(root finding) 방법의 하나인 Brent 기법을 적용하였다. 이 기법은 주어진 구간에서 도함수가 알려져 있지 않은 경우에 대해서도 효과적으로 해를 찾을 수 있는 것으로 알려져 있다(Press et al., 2002, Numerical Recipes in C, 2nd Ed.). 내성천 하류 수계의 333개 단면에서 수면폭에 대한 상대 오차를 살펴보면, 선형 보간에 의한 기존 방법으로는 면적-수위 자료의 수가 1,000개가 되어도 그 최대치가 1% 이내에 들지 않은 반면, 이 연구에서 제시한 기법으로 면적-수위 자료 없이도 1% 이내로 줄어드는 것을 확인하였다. 다만, 반복 계산에 의한 계산 시간의 증대를 피할 수 없다. 미리 작성된 면적-수위 자료를 이용하면 계산 비용을 줄일 수 있으며, 약 35개의 구간으로 나누었을 때 비용 대비오차가 적절하였다. 이 연구는 한국건설기술연구원(주요사업 과제번호: 20190116-001)의 지원에 의한 것이다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.3
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• pp.543-560
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• 2018

With the increased development in downtown underground space facilities that vertically cross under a railway at a shallow depth, the demand for non-open cut method is increasing. However, most construction sites still adopt the pipe roof method, where medium and large diameter steel pipes are pressed in to form a roof, enabling excavation of the inside space. Among the many factors that influence the loosening region and loads that occur while pressing in steel pipes, the size of the pipe has the largest impact, and this factor may correspond to the magnitude of load applied to the underground structure inside the steel pipe roof. The super equilibrium method (SEM) has been developed to minimize ground disturbance and loosening load, and uses small diameter pipes of approximately 114 mm instead of conventional medium and large diameter pipes. This small diameter steel pipe is called an SEM pile. After SEM piles are pressed in and the grouting reinforcement is constructed, a crossing structure is pressed in by using a hydraulic jack without ground subsidence or heaving. The SEM pile, which plays the role of timbering, is a fore-poling pile of approximately 5 m length that prevents ground collapse and supports surface load during excavation of toe part. The loosening region should be adequately calculated to estimate the spacing and construction length of the piles and stiffness of members. In this paper, we conducted a comparative analysis of calculations of loosening load that occurs during the press-in of SEM pile to obtain an optimal design of SEM. We analyzed the influence of factors in main theoretical and empirical formulas applied for calculating loosening regions, and carried out FEM analysis to see an appropriate loosening load to the SEM pile. In order to estimate the soil loosening caused by actual SEM-pile indentation and excavation, a steel pipe indentation reduction model test was conducted. Soil subsidence and soil loosening were investigated quantitatively according to soil/steel pipe (H/D).