• Structural Engineering and Mechanics
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• 제64권5호
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• pp.621-640
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• 2017

This paper reports the numerical investigation conducted to study the influence of Local-Distortional (L-D) interaction mode buckling on post buckling strength erosion in fixed ended lipped channel cold formed steel columns. This investigation comprises of 81 column sections with various geometries and yield stresses that are carefully chosen to cover wide range of strength related parametric ratios like (i) distortional to local critical buckling stress ratio ($0.91{\leq}F_{CRD}/F_{CRL}{\leq}4.05$) (ii) non dimensional local slenderness ratio ($0.88{\leq}{\lambda}_L{\leq}3.54$) (iii) non-dimensional distortional slenderness ratio ($0.68{\leq}{\lambda}_D{\leq}3.23$) and (iv) yield to non-critical buckling stress ratio (0.45 to 10.4). The numerical investigation is carried out by conducting linear and non-linear shell finite element analysis (SFEA) using ABAQUS software. The non-linear SFEA includes both geometry and material non-linearity. The numerical results obtained are deeply analysed to understand the post buckling mechanics, failure modes and ultimate strength that are influenced by L-D interaction with respect to strength related parametric ratios. The ultimate strength data obtained from numerical analysis are compared with (i) the experimental tests data concerning L-D interaction mode buckling reported by other researchers (ii) column strength predicted by Direct Strength Method (DSM) column strength curves for local and distortional buckling specified in AISI S-100 (iii) strength predicted by available DSM based approaches that includes L-D interaction mode failure. The role of flange width to web depth ratio on post buckling strength erosion is reported. Then the paper concludes with merits and limitations of codified DSM and available DSM based approaches on accurate failure strength prediction.

• 한국수자원학회논문집
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• 제41권6호
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• pp.575-585
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• 2008

수자원의 계획 평가 관리 및 수공구조물의 설계를 위해서는 정확하고 신뢰성 높은 유량 자료가 필수적이다. 본 연구에서는 Chiu의 유속분포와 최대유속 추정을 이용하여 하천유량을 계산하는 새로운 방법을 제시하였다. 기존 면적유속법과 비교 검토한 바, 본 연구에서 개발한 방법은 기존 유속면적법과 매우 유사한 하천유량을 보였다. Price-AA를 이용하여 유속을 측정할 경우 측선의 수심에 따라 정해진 지점에서 유속을 측정하여야 하는데, 본 연구에서 제시한 방법을 이용하면 임의의 측선과 측점에서 유속을 측정하여도 정확한 유량계산이 가능하다. 그러나 흐름 단면이 매우 복잡하거나 좌우의 비대칭성이 심한 경우에는 엔트로피 개념의 Chiu의 유속분포가 실제 자연하천의 흐름분포에서 멀어지고 유량산정에 Chiu의 유속분포의 정확도가 떨어지기 때문에 본 연구에서 제시한 방법을 적용하기 어렵다.

• 한국산학기술학회논문지
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• 제15권3호
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• pp.1756-1763
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• 2014

하천을 횡단하는 관로를 매설할 경우 하상변동으로 인해 관로가 드러나는 사고가 발생할 수 있으며 이를 방지하기 위해서는 안전한 매설경로를 분석할 필요가 있다. 본 연구에서는 금강을 횡단하는 도수관로의 안전한 매설구간 선정을 위해 2차원 수치모형을 이용하여 흐름해석 및 하상변동 분석을 수행하였다. 20년 빈도 홍수량을 적용한 모의 결과, 전반적으로 하상이 퇴적되는 것으로 나타났으나 교각의 영향을 받는 구간에서는 관로 매설 깊이 2 m 이상의 침식이 발생하는 것으로 나타났다. 극한 호우 사상에서도 교각 상류와 근접한 부근에서 관로매설 위치까지 침식이 발생하는 것으로 나타났다. 따라서 교각위치에서 상류 약 140 m 까지는 교각의 영향으로 하상침식이 매설된 관로에 영향을 미칠 것으로 예상된다. 상류 150 m 이후에 위치한 관로 횡단경로들은 하상 침식에 대해 상대적으로 안정적일 것으로 판단되어 안전을 고려하여 이를 도수관로 횡단경로의 최적구간으로 선정하였다.

• Structural Engineering and Mechanics
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• 제33권4호
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• pp.503-527
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• 2009

This paper presents experimental results on the behaviour and ultimate load of fifteen pipes and six roof panels made of ferrocement. Additional results from three roof panels, carried out by others, are also compared with this research results. OPC cement, natural sand and galvanised iron wire mesh were used for the construction of 20 mm thick specimens. The pipe length was 2 m and roof panel length was 2.1 m. The main variables studied were the number of wire mesh layers which were 1, 2, 3, 4 and 6 layers, the inner pipe diameter which were 105, 210 and 315 mm, cross sectional shape of the panel which were channel and box sections and the depth of the edge beam which were 95 mm and 50 mm. All specimens were simply supported and tested for pure bending with test span of 600 mm at mid-span. Tests revealed that increasing the number of wire mesh layers increases the flexural strength and stiffness. Increasing the pipe diameter or depth of edge beam of the panel increases the cracking and ultimate moments. The change in the pipe diameter led to larger effect on ultimate moment than the effect of change in the number of wire mesh layers. The box section showed behaviour and strength similar to that of the channel with same depth and number of wire mesh layers.

• 한국광학회지
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• 제17권5호
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• pp.430-436
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• 2006

1550nm 파장대역에서 편광에 관계없이 동작하는 $Ti:LiNbO_3\;2{\times}2$ 삽입/분기 광 멀티플렉서를 구현하였다. 소자는 두 개의 입 출력 광도파로, 두 개의 편광모드분리기, 두 개의 편광모드 변환기 그리고 전기광학효과로 파장을 가변시킬 수 있는 전극으로 구성되었다. TE, TM 편광에 대해서 단일모드 특성을 갖는 채널 광도파로는 x-cut $LiNbO_3$에 Ti 확산 방법으로 제작하였으며, 채널 광도파로 위에 배열된 $SiO_2$ 패드의 전단 스트레인을 이용하여 위상정합 편광모드변환기를 구현하였다. 한편 전기광학효과를 이용하여 파장을 가변시키기 위해서 전압을 인가하여 광도파로의 복 굴절률을 변화시켰다. 0.094nm/V 파장가변률과 최대 17nm 파장을 가변시켰으며, 8.2dB 부 모드레벨과 3.72nm FWHM을 측정하였다.

• 지구물리
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• 제5권1호
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• pp.19-27
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• 2002

장풍 폐광산의 갱내수와 폐광석 적치장에서 발생되는 산성광산폐수에 의한 침출수의 유동경로와 지화학적 특성을 알아보기 위해 지구물리탐사(자연전위, 전자탐사, 전기비저항, 탄성파굴절법)를 수행하여 그 결과를 지화학 물시료분석(pH, EC, ${SO_4}^{-2}$, 중금속 함량) 자료와 상관·분석하였다. 갱구에 수직 방향의 2개 측선에서 실시한 전기비저항 쌍극자탐사 결과 갱구에서 북서 방향으로 저비저항대가 이어지는데 이것은 갱구에서 지하로 유입된 산성광산폐수에 의한 침출수가 폐석더미와 기반암의 경계를 따라 이동하여 하천 방향으로 유입되어 나타나는 현상으로 해석된다. 이와 같은 양상은 전기비저항 수직탐사, 자연전위, 전자탐사의 반응 결과들에서 보이는 북서방향의 이상대 및 북서쪽에서 상대적으로 높은 값을 보이는 EC, 중금속함량, ${SO_4}^{-2}$의 분포와도 잘 상관된다.

• Nuclear Engineering and Technology
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• 제55권11호
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• pp.3973-3982
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• 2023

As for two-phase flow in rectangular channels, the flow regimes especially like churn-turbulent and annular flow are significant for the physical problem like Countercurrent Flow Limitation (CCFL). In this study, the rectangular channels with cross-sections of 4 × 66 mm, 6 × 66 mm, 8 × 66 mm are adopted to investigate the flow regimes of air-water vertical upward two phase flow under adiabatic condition. The gas and liquid superficial velocities are 0 ≤ j_g ≤ 20m/s and 0.25 ≤ j_f ≤ 3m/s respectively which covering bubbly to annular flow. The flow regimes are identified by random forest algorithm and the flow regime maps are obtained. As the results, the transitional void fraction from slug to churn turbulent flow fluctuate from 0.47 to 0.58 which is significantly affected by the dimensional size of channel and flow rate. Besides, the void fraction at transitional points from churn-turbulent (slug) to annular flow are 0.66-0.67, which are independent with the gap size. Furthermore, a new criteria of slug to churn-turbulent flow is established in this study. In addition, by introducing the interfacial force model, the criteria of churn-turbulent (slug) flow to annular flow is verified.

• Steel and Composite Structures
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• 제50권5호
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• pp.515-529
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• 2024

Cold-formed steel (CFS) is a popular choice for construction due to its low cost, durability, sustainability, resistance to high environmental and seismic pressures, and ease of installation. The beam-column connections in residential and medium-rise structures are formed using self-drilling screws that connect two CFS channel sections and a gusset plate. In order to increase the moment capacity of these CFS screwed beam-column connections, stiffeners are often placed on the web area of each single channel. However, there is limited literature on studying the effects of stiffeners on the moment capacity of CFS screwed beam-column connections. Hence, this paper proposes a new test approach for determining the moment capacity of CFS screwed beam-column couplings. This study describes an experimental test programme consisting of eight novel experimental tests. The effect of stiffeners, beam thickness, and gusset plate thickness on the structural behaviour of CFS screwed beam-column connections is investigated. Besides, nonlinear elasto-plastic finite element (FE) models were developed and validated against experimental test data. It found that there was reasonable agreement in terms of moment capacity and failure mode prediction. From the experimental and numerical investigation, it found that the increase in gusset plate or beam thickness and the use of stiffeners have no significant effect on the structural behaviour, moment capacity, or rotational capacity of joints exhibiting the same collapse behaviour; however, the capacity or energy absorption capacities have increased in joints whose failure behaviour varies with increasing thickness or using stiffeners. Besides, the thickness change has little impact on the initial stiffness.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2015년도 학술발표회
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• pp.237-237
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• 2015

The district of Marlborough has had more than its share of river management projects over the past 150 years, each one uniquely affecting the geomorphology and flood hazard of the Wairau Plains. A major early project was to block the Opawa distributary channel at Conders Bend. The Opawa distributary channel took a third and more of Wairau River floodwaters and was a major increasing threat to Blenheim. The blocking of the Opawa required the Wairau and Lower Wairau rivers to carry greater flood flows more often. Consequently the Lower Wairau River was breaking out of its stopbanks approximately every seven years. The idea of diverting flood waters at Tuamarina by providing a direct diversion to the sea through the beach ridges was conceptualised back around the 1920s however, limits on resources and machinery meant the mission of excavating this diversion didn't become feasible until the 1960s. In 1964 a 10 m wide pilot channel was cut from the sea to Tuamarina with an initial capacity of $700m^3/s$. It was expected that floods would eventually scour this 'Wairau Diversion' to its design channel width of 150 m. This did take many more years than initially thought but after approximately 50 years with a little mechanical assistance the Wairau Diversion reached an adequate capacity. Using the power of the river to erode the channel out to its design width and depth was a brilliant idea that saved many thousands of dollars in construction costs and it is somewhat ironic that it is that very same concept that is now being used to deal with the aggradation problem that the Wairau Diversion has caused. The introduction of the Wairau Diversion did provide some flood relief to the lower reaches of the river but unfortunately as the Diversion channel was eroding and enlarging the Lower Wairau River was aggrading and reducing in capacity due to its inability to pass its sediment load with reduced flood flows. It is estimated that approximately $2,000,000m^3$ of sediment was deposited on the bed of the Lower Wairau River in the time between the Diversion's introduction in 1964 and 2010, raising the Lower Wairau's bed upwards of 1.5m in some locations. A numerical morphological model (MIKE-11 ST) was used to assess a number of options which led to the decision and resource consent to construct an erodible (fuse plug) bank at the head of the Wairau Diversion to divert more frequent scouring-flows ($+400m^3/s$)down the Lower Wairau River. Full control gates were ruled out on the grounds of expense. The initial construction of the erodible bank followed in late 2009 with the bank's level at the fuse location set to overtop and begin washing out at a combined Wairau flow of $1,400m^3/s$ which avoids berm flooding in the Lower Wairau. In the three years since the erodible bank was first constructed the Wairau River has sustained 14 events with recorded flows at Tuamarina above $1,000m^3/s$ and three of events in excess of $2,500m^3/s$. These freshes and floods have resulted in washout and rebuild of the erodible bank eight times with a combined rebuild expenditure of $80,000. Marlborough District Council's Rivers & Drainage Department maintains a regular monitoring program for the bed of the Lower Wairau River, which consists of recurrently surveying a series of standard cross sections and estimating the mean bed level (MBL) at each section as well as an overall MBL change over time. A survey was carried out just prior to the installation of the erodible bank and another survey was carried out earlier this year. The results from this latest survey show for the first time since construction of the Wairau Diversion the Lower Wairau River is enlarging. It is estimated that the entire bed of the Lower Wairau has eroded down by an overall average of 60 mm since the introduction of the erodible bank which equates to a total volume of $260,000m^3$. At a cost of $$0.30/m^3$ this represents excellent value compared to mechanical dredging which would likely be in excess of $$10/m^3$. This confirms that the idea of using the river to enlarge the channel is again working for the Wairau River system and that in time nature's "excavator" will provide a channel capacity that will continue to meet design requirements.

• Bulletin of the Korean Chemical Society
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• 제31권2호
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• pp.315-326
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• 2010

This study examined the overlapping resonances in the systems involving 1 open and 2 closed channels using the phase-shifted version of multichannel quantum-defect theory (MQDT). The results showed that 21 patterns for the q reversals in the autoionization spectra are possible depending on the relative arrangements of the two simple poles and roots of the quadratic equations. Complete cases could be generated easily using the q zero planes determined using only 3 asymmetric spectral line profile indices. The transition of the spectra of the coarse interloper Rydberg series from the lines into a structured continuum by being dispersed onto the entire Rydberg series was found. The overall behavior of the time delays was found to be governed by the dense Rydberg series, which is quite different from the one of the autoionization cross sections that is governed by an interloper, indicating that different dynamics prevail for them. This is in contrast to the two channel system where both quantities behave similarly. The dynamics obtained in the presence of overlapping resonances is as follows. The absorption process is instant and dominated by a transition to the interloper line. This process is followed by rapid leakage into the dense Rydberg series, which has a longer residence time before ionization than that of the interloper state. This is because the orbiting period is proportional to $\upsilon^3$ so that an excited electron has a shorter lifetime in the interloper state belonging to a lower member of the Rydberg series.