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Axially loaded elements
Published in Peter Knowles, Design of Structural Steelwork, 2018
Theoretically, a thin-walled circular section is the optimum shape but there will be circumstances in which a rectangular hollow section will be more efficient than a circular section, as, for example, when bending is combined with compression. Figure 4.5 shows a comparison of five different rolled sections of approximately equal cross-sectional area listed in descending order of minimum radius of gyration from which it will be observed that the circular hollow section has a minimum radius of gyration over three times and a compressive strength over twice that of the universal beam.
Prediction of the near wall flow behaviours of separation and transition for NREL phase VI wind turbine blade
Published in International Journal of Sustainable Energy, 2023
Kyoungsoo Lee, Ziaul Huque, Chao Sui, Raghava Kommalapati
Although the entire wind turbine system was initially tested in a wind tunnel experimental study, the tower and nacelle were ignored to simplify the CFD model. In this study, only the blade was investigated. The actual taper and twist of the blade were considered to resolve the real 3D flow field. The blade design is incorporated from same group previous work (Lee et al. 2016a), as shown in Figure 2. It is built by a series of original sharp-edged S809 aerofoils from root to tip. This well-documented aerofoil is optimised to be less sensitive to leading edge roughness to improve the wind energy output power (Schreck, Hand, and Fingersh 2001; Hand et al. 2001). Along the entire blade, the minimum chord length is 0.356 m, and the maximum chord length is 0.737 m. The twist axis is located at 30.0% to chord length. The maximum twist angle is 20.04°, which occurs at 25% of the span and decreases to a –2.5° twist at the tip. In addition to the aerofoil, a cylinder with a 0.109 m radius that extends from 0.508 m to 0.883 m also exists, and a transitional part was designed to connect the circular section to the root aerofoil section at radius 1.257 m.
Desert Rose Stone Constructions Covered with Domes in the Souf Region (Algeria)
Published in International Journal of Architectural Heritage, 2022
Cheima Azil, Boualem Djebri, Fabio Fratini, Giulia Misseri, Luisa Rovero
As concerns Brazilian tests, parallelepiped specimens were used, instead of cylindrical ones to make simpler linear cuts. Considering a cylinder inscribed in the parallelepiped specimen, the straight vertical circular section is compressed by a load concentrated at two antipodal points. Thus, tensile stress develops in the direction perpendicular to the load. Through the hypothesis of homogeneous, isotropic, elastic material, at the geometric centre of the circular section, the compression to tension stress ratio is −3, and the failure tensile stress is nearly the same as the uniaxial tensile failure stress. In agreement with ASTM–D 3967 16, the tensile strength is determined considering the following formulation: , where F is failure load and A is the surface of the circle inscribed into the square vertical cross-section under the load (ASTMD3967-16, 2016). The use of parallelepiped instead of cylinder-shaped of the specimen is an approximation owed to the difficulty in cutting the samples. It can be observed that the strain (and therefore stress) to which the parallelepiped sample is subjected in the part under the application of the load during the test, reasonably do not differ much from that suffered by the virtual cylinder enclosed, which obviously was used to calculate the tensile strength. In fact, the sample is in contact with the test machine only where the load is applied (points of the virtual cylinder), while the rest of the external surface is free.
Numerical study on surface distributed vortex-induced force on a flat-steel-box girder
Published in Engineering Applications of Computational Fluid Mechanics, 2018
Xing-Yu Chen, Bin Wang, Le-Dong Zhu, Yong-Le Li
It should be noted that most efforts have been focused on the VIVs of circular cylinders, which are easier to reveal some fundamental mechanisms. A large number of studies adopting wind tunnel tests are contained in several reviews, such as Williamson and Govardhan (2004), Sumner (2010), Bearman (2011) and Wu, Ge, and Hong (2012). And relative full-scale researches of CFD of circular sections are presented at the early twenty-first century (Guilmineau & Queutey, 2002; Kumar & Dalal, 2006; Tamura, 1999). In fact, compared with circular cylinder, VIV of non-circular section has different characteristics. However, limited research can be found for non-circular sections, especially for the flat-steel-box bridge decks. The experimental results of Diana, Resta, Belloli, and Rocchi (2006) indicated significant nonlinear behaviors of the vortex-induced force on a multi-box deck. Sun, Owen, and Wright (2009) testified that 2D simulation with k-ω RANS turbulence model is appropriate to simulate the wind-induced forces on bluff bodies compared with the 3D simulation. The mechanism and vibration reduction of VIV of a box cross section in the presence of aerodynamic countermeasures were discussed by Sarwar and Ishihara (2010), which showed the influences of fairings and flaps. Hallak et al. (2013) discussed the aerodynamic behavior of a girder in the presence of tall vehicles via 2D CFD model. Section and full aero-elastic model experiments of VIV were conducted and the differences between the two testing results were discussed by Sun, Li, and Liao (2013). However, the mechanism of nonlinear vortex-induced vertical force at resonance stability period on flat-steel-box bridge deck has not been studied extensively.