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Wind-induced self-excited vibrations of a twin-deck bridge and the effects of gap-width
K.C.S. Kwok,P.A. Hitchcock,X.R. Qin,Y.L. Xu,C.H. Fok 한국풍공학회 2007 Wind and Structures, An International Journal (WAS Vol.10 No.5
A series of wind tunnel sectional model dynamic tests of a twin-deck bridge were conducted at the CLP Power Wind/Wave Tunnel Facility (WWTF) of The Hong Kong University of Science and Technology (HKUST) to investigate the effects of gap-width on the self-excited vibrations and the dynamic and aerodynamic characteristics of the bridge. Five 2.9 m long models with different gap-widths were fabricated and suspended in the wind tunnel to simulate a two-degrees-of-freedom (2DOF) bridge dynamic system, free to vibrate in both vertical and torsional directions. The mass, vertical frequency, and the torsional-to-vertical frequency ratio of the 2DOF systems were fixed to emphasize the effects of gap-width. A free-vibration test methodology was employed and the Eigensystem Realization Algorithm (ERA) was utilized to extract the eight flutter derivatives and the modal parameters from the coupled free-decay responses. The results of the zero gap-width configuration were in reasonable agreement with the theoretical values for an ideal thin flat plate in smooth flow and the published results of models with similar cross-sections, thus validating the experimental and analytical techniques utilized in this study. The methodology was further verified by the comparison between the measured and predicted free-decay responses. A comparison of results for different gap-widths revealed that variations of the gap-width mainly affect the torsional damping property, and that the configurations with greater gap-widths show a higher torsional damping ratio and hence stronger aerodynamic stability of the bridge.
Optimal wind-induced load combinations for structural design of tall buildings
C.M. Chan,F. Ding,K.T. Tse,M.F. Huang,K.M. Shum,K.C.S. Kwok 한국풍공학회 2019 Wind and Structures, An International Journal (WAS Vol.29 No.5
Wind tunnel testing technique has been established as a powerful experimental method for predicting wind-induced loads on high-rise buildings. Accurate assessment of the design wind load combinations for tall buildings on the basis of wind tunnel tests is an extremely important and complicated issue. The traditional design practice for determining wind load combinations relies partly on subjective judgments and lacks a systematic and reliable method of evaluating critical load cases. This paper presents a novel optimization-based framework for determining wind tunnel derived load cases for the structural design of wind sensitive tall buildings. The peak factor is used to predict the expected maximum resultant responses from the correlated three-dimensional wind loads measured at each wind angle. An optimized convex hull is further developed to serve as the design envelope in which the peak values of the resultant responses at any azimuth angle are enclosed to represent the critical wind load cases. Furthermore, the appropriate number of load cases used for design purposes can be predicted based on a set of Pareto solutions. One 30-story building example is used to illustrate the effectiveness and practical application of the proposed optimization-based technique for the evaluation of peak resultant wind-induced load cases.
Lee, J,Jung, H-S,Nam, H-C,Kwok, S-K,Ju, J H,Park, K-S,Kim, H-Y,Park, S-H Scientific Medical Division, Macmillan Press Ltd 2012 Lupus Vol.21 No.12
<P>Colitis in patients with systemic lupus erythematosus (SLE) is quite rare. It can be caused by intestinal vasculitis, mesenteric vascular thrombosis, concomitant inflammatory bowel disease or infectious colitis. It is important to make an accurate and early diagnosis as the treatments for each condition differ and a delayed diagnosis can result in life-threatening complications. However, non-specific gastrointestinal symptoms make a timely diagnosis challenging. Amoebic colitis is a rare condition in patients with SLE. Here we present a case of fulminant amoebic colitis in a patient with SLE which was initially misdiagnosed as ischemic colitis due to intestinal vasculitis. Her colitis was complicated with multiple intestinal perforations, disseminated intravascular coagulation and acute respiratory distress syndrome; but in the end, the patient was successfully treated with metronidazole and paromomycin.</P>
Kim, J.-Y.,Kwok, S.-K.,Hur, K.-H.,Kim, H.-J.,Kim, N. S.,Yoo, S.-A.,Kim, W.-U.,Cho, C.-S. Blackwell Publishing Ltd 2008 Clinical and experimental immunology Vol.152 No.2
<P>Summary</P><P>Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that has been demonstrated to regulate the apoptosis of several cell types. Dysregulated apoptosis of fibroblasts has been implicated in a variety of fibrotic diseases, including systemic sclerosis (SSc). In this study, we investigated the role of MIF in the apoptosis of dermal fibroblasts. The concentrations of MIF were measured in sera and in culture supernatants of peripheral blood mononuclear cells (PBMCs) and dermal fibroblasts by enzyme-linked immunosorbent assay. The degree of apoptosis was determined by colorimetric assay, and signalling pathways were examined by Western blot. The results showed that serum levels of MIF were significantly higher in patients with SSc (<I>n</I> = 47) than in healthy controls (<I>n</I> = 56). Stimulation of PBMCs by anti-CD3 and anti-CD28 increased the production of MIF by fourfold over the constitutive levels. SSc dermal fibroblasts produced higher amounts of MIF than normal dermal fibroblasts. When treated with sodium nitroprusside (SNP), SSc dermal fibroblasts showed a lower degree of apoptosis compared with normal dermal fibroblasts. Exogenous MIF (1–100 ng/ml) inhibited SNP-induced apoptosis of dermal fibroblasts dose-dependently. Both extracellular regulated kinase (ERK) inhibitor (PD98059) and protein kinase B (Akt) inhibitor (LY294002) almost completely blocked the inhibitory effect of MIF on apoptosis. Furthermore, MIF increased the expression of Bcl-2, phospho-ERK and phospho-Akt activity in dermal fibroblasts. Taken together, our data suggest that MIF released by activated T cells and dermal fibroblasts decreases the apoptosis of dermal fibroblasts through activation of ERK, Akt and Bcl-2 signalling pathways, which might be associated with excessive fibrosis in SSc.</P>
Large-eddy simulation and wind tunnel study of flow over an up-hill slope in a complex terrain
C. F. Tsang,Kenny C. S. Kwok,Peter A. Hitchcock,Desmond K. K. Hui 한국풍공학회 2009 Wind and Structures, An International Journal (WAS Vol.12 No.3
This study examines the accuracy of large-eddy simulation (LES) to simulate the flow around a large irregular sloping complex terrain. Typically, real built up environments are surrounded by complex terrain geometries with many features. The complex terrain surrounding The Hong Kong University of Science and Technology campus was modelled and the flow over an uphill slope was simulated. The simulated results, including mean velocity profiles and turbulence intensities, were compared with the flow characteristics measured in a wind tunnel model test. Given the size of the domain and the corresponding constraints on the resolution of the simulation, the mean velocity components within the boundary layer flow, especially in the stream-wise direction were found to be reasonably well replicated by the LES. The turbulence intensity values were found to differ from the wind tunnel results in the building recirculation zones, mostly due to the constraints placed on spatial and temporal resolutions. Based on the validated mean velocity profile results, the flow-structure interactions around these buildings and the surrounding terrain were examined.