• Structural Engineering and Mechanics
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• v.64 no.5
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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.

• Journal of Korea Water Resources Association
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• v.41 no.6
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• pp.575-585
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• 2008

It is essential to obtain accurate and highly reliable streamflow data for water resources planning, evaluation and management as well as design of hydraulic structures. A new discharge computation method proposed in this research uses Chiu's velocity distribution and estimation of maximum velocity. This method shows acceptable channel discharges comparing these by the exiting velocity-area method. When velocity-area method is used, it is required to observe velocities at every specified point and vertical line using a velocity meter like Price-AA. If the method proposed in this research, is used, however it is not necessary to observe all point velocities needed in the velocity-area method. But this method can not be applied for the cases of very complex and strongly asymmetric channel cross-sections because Chiu's velocity distribution using entropy concept may be quite biased from that of natural rivers.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.3
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• pp.1756-1763
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• 2014

A water pipeline buried under the riverbed could be exposed by bed erosion, therefore safe crossing sections should be analyzed for preventing damages due to the exposure of pipelines. In this study, flow and bed changes have been simulated using a two-dimensional numerical model for selecting the optimized section of pipeline crossing in the Geum River. As a result of simulation with the 20-year recurrence flood, sediment deposition has been distributed overall in the channel and bed erosion over 2 m has occurred near bridge piers. For the extreme flood simulation, the channel bed near the bridge piers has been eroded down to the buried depth. Therefore, within 140 m upstream of the bridge piers, bed erosion affects a buried pipeline in safety due to bridge pier effects and the crossing section over 150 m upstream of bridge piers is selected as a safe zone of a water pipeline.

• Structural Engineering and Mechanics
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• v.33 no.4
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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.

• Korean Journal of Optics and Photonics
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• v.17 no.5
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• pp.430-436
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• 2006

Polarization-independent $Ti:LiNbO_3\;2{\times}2$ optical add/drop multiplexer for the 1550nm wavelength region is fabricated. The device consists of two input waveguides, two polarization beam splitters. two polarization conversion/electrooptic tuning waveguide sections, and two output waveguides. The single mode channel waveguides for both TE and TM polarizations are fabricated on a x-cut $Ti:LiNbO_3$substrate by Ti diffusion. Spectral section is based on phase-matched polarization conversion due to shear strain induced by a thick $SiO_2$ grating overlay film. An applied voltage tunes the device by changing the waveguide birefringence, hence the optical wavelength at which most efficient polarization conversion occurs. Tuning rate of 0.094nm/V with a maximum range of 17nm has been obtained. The nearest side-lobe is about 8.2dB. The FWHM is 3.72nm.

• Journal of the Korean Geophysical Society
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• v.5 no.1
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• pp.19-27
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• 2002

Geophysical surveys(self-potential, electromagnetic, electrical resistivity, and seismic refraction methods) were performed to delineate the flow channel of leachate from a AMD (acid mine drainage) by correlating the anomalies to geochemical characteristics at an abandoned mine (Jangpoong mine). The geophysical responses attempted to be correlated with water sample analysis data(pH, EC, heavy metals, ${SO_4}^{-2}$). Electrical dipole-dipole resistivity sections represent the low-resistivity zone trending northwest, which indicates the leachate flow by AMD along the contact of the mine waste rock dump and the bedrock. From the overall points of geophysical and geochemical anomalies, it is summarized that the flow channel of leachate by AMD can be successfully imaged with composite interpretations on the geophysical and geochemical studies.

• Nuclear Engineering and Technology
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• v.55 no.11
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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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• v.50 no.5
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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.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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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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• v.31 no.2
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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.