| dc.description.abstract | The project, Coastal Highway E39, introduces the concept of Submerged Floating Tube Bridge (SFTB). The bridge is simplified as tandem cylinders with longitudinal length-diameter ratio L/D = 3.2, diameter D=1.0 and span-wise length l = 6D. The tandem cylinders are subjected by a linearly varying profile called Shear Flow, with a shear rate K=0.2, gradient G=0.1 1/s and center-line velocity Uc=0.5. The flow problems are analyzed numerical with OpenFOAM, for two-dimensional (2D) domains with Reynolds number (Re) 100, 300 and 500, and three-dimensional (3D) domains with Reynolds number (Re) 100 and 500.
The numerical analysis is performed with a laminar solver, where mean values for drag - and lift coefficients are found with root mean square values. The oscillation periods (Tv) [s], frequencies (fv) [1/s] and Strouhals numbers (St) are found behind each cylinder, with use of Power Spectral Density (PSD) curves. ParaView is used to visualize the distribution of velocity U, pressure P and vorticity in z-direction.
Results obtained for flow problem with Reynolds number 100 are approximately identical for both 2D and 3D domains, since there are no 3D effects occurring for this Reynolds number. When increasing the Reynolds number (Re), one must take in account the 3D effects occurring span-wise. The thesis discusses the effects of a shear flow versus a uniform flow, and the effect of having tandem configurations versus a single cylinder.
Tandem cylinders will experience drag forces on each cylinder, with oscillating lift forces close to zero. A uniform - or shear flow will move around the tandem cylinders, with some vorticity and approximately no velocities in-between the cylinders. Turbulent behaviour is observed downstream, when a shear flow is subjected on the tandem configuration. When subjecting a flow towards a single cylinder, the alternating vortex sheddings will occur for an earlier time instant, compared to tandem flow problems. Pressure distribution around tandem cylinders follows the same pressure curve, when subjected either to a shear - or a uniform flow. The pressure magnitude and fluctuation values are larger around the cylinders, when subjected to shear flow.
Designing Submerged Floating Tube Bridges (SFTB), one must understand the flow behaviour in-between the tandem configuration and flow phenomena downstream when subjected to a shear flow versus a uniform flow. | |
