The pendulous installation method of a manifold has a first phase that can be considered as a free fall in water. Of course, this is not free due to the fluid action. The consequence is that the manifold may oscillate rotationally which characterizes a fluttering behavior. However, the manifold is a complex body with non-uniform shape, several modules, porosity etc. Hence, in order to improve the understanding of the fluttering, this work presents advances in the observation of flow induced rotation on a flat plate in uniform flow. This has been started experimentally and subsequently numerical models yielded a confirmation of quasi-steady observations. The experimental results were obtained at the Laborato´rio de Ondas e Correntes (LOC) [Laboratory of Waves and Current] in COPPE/Federal University of Rio de Janeiro. The drag and lift forces coefficients and the center of pressure have been obtained for angles of attack θ = 0°–90° and for different Reynolds numbers.
The Vortex Induced Vibration (VIV) of cylindrical lines that may occur when the lines are submitted to currents has been extensively discussed in the past few years and its behavior has become well known. However, it is not so well known that the vibrations may occur in a current-less situation, induced by the lateral motion of the structure itself. The present work refers to the last as the Vortex Self-Induced Vibration, the VSIV. This occurrence has been made clear in the LOC/COPPE/UFRJ (Laboratory of Waves and Currents of COPPE, the Graduate School of Federal University of Rio de Janeiro) by specifically designed tests. In these tests, a totally submerged horizontal cylinder was submitted to harmonic forced oscillations, being free to move in the transverse direction of the forced excitation. The VSIV then showed up, with the cylinder segment, describing vertical trajectories in two (vertical 8-shape), three, four, etc., almost circular trajectories (called the rings in the work). Subsequently, the work shows that the measurements in full scale with the VIV bottle on a Steel Catenary Riser in the PETROBRAS 18 platform also indicate the existence of the VSIV. The tests were carried out with Keulegan-Carpenter equal to 10, 20 and 30 and for several amplitudes. The response of the cylinder was represented in non-dimensional parameters corresponding to the amplitude, the excitation and the response frequencies.
This paper aims to discuss the effectiveness of a new passive kind of VIV (Vortex Induced Vibrations) suppression. Moreover, the proposed solutions leads to a significant drag reduction when compared with conventional proposals (strakes for instance). The concept of guided porosity is applied in experimental tests conducted with low mass ratio cylindrical models. The works also shows that the job (VIV control and drag reduction) is achieved without moving parts, in contrast with segmented fairings. It also advances in terms of the omnidirectional solution. Initially, the concept is discussed in terms of the potential theory. Then experimental results are presented in terms of displacements and forces.
The offshore petroleum industry has great technological challenges as new field discoveries are made in increasing water depths. Risers of systems having little space between its elements, subjected to current reach static deflections that depend on the wakes formed by the each riser. Depending on the relative position, each riser will be submitted to a stronger or weaker effect from each neighbor. This work presents results from experiments with flexible jumpers submitted to current. The clashing between the lines caused by the wake interference is the focus of the work. The work presents results in terms of minimum distance between the jumpers comparing experimental results to a numerical code that applies automatically the Huse’s formula for the drag coefficients. It also discusses the validity of this theory. As expected, during the tests the jumpers presented Vortex Induced Vibration (VIV), VIV under Interference (VIV-UI) and friction after contact. The results can be extrapolated to real cases and shows the possibility of clashing on closely spaced systems, putting in evidence other phenomena related to it.
This paper addresses the flow induced rotation phenomena of plates hinged to allow flow induced rotating about their vertical axis. Different transversal shape configurations are studied. The aim of this study is to simplify the fluttering problem that may occur with falling objects in water during installation of offshore devices. The investigation intent is to propose an optimized configuration for stabilizing the fluttering motion of pendulous installation method of manifolds. The experiments and dimensional analysis confirmed that natural frequency is linearly proportional to the incoming flow velocity and inversely proportional to the flat plate width, and also the equivalent harmonic angle of rotation for small oscillation angles is approximately constant in different velocities. Experiments show that the bluffer plates (plate with two stabilizers and plate with stabilizers and nose), by increasing of period of rotation and also decreasing of equivalent harmonic angle of rotation have stabilizing effect in the fluttering motion of falling objects.
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