scholarly journals Hydrodynamics of Moonpool-Type Floaters: A Theoretical and a CFD Formulation

Energies ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 570
Author(s):  
Anargyros S. Mavrakos ◽  
Dimitrios N. Konispoliatis ◽  
Dimitrios G. Ntouras ◽  
George P. Papadakis ◽  
Spyros A. Mavrakos

Moonpool-type floaters were initially proposed for applications such as artificial islands or as protecting barriers around a small area enabling work at the inner surface to be carried out in relatively calm water. In recent years, a growing interest on such structures has been noted, especially in relation to their use as heaving wave energy converters or as oscillating water column (OWC) devices for the extraction of energy from waves. Furthermore, in the offshore marine industry, several types of vessels are frequently constructed with moonpools. The present paper deals with the hydrodynamics of bottomless cylindrical bodies having vertical symmetry axis and floating in a water of finite depth. Two computation methods were implemented and compared: a theoretical approach solving analytically the corresponding diffraction problem around the moonpool floater and a computational fluid dynamics (CFD) solver, which considers the viscous effects near the sharp edges of the body (vortex shedding) as non-negligible. Two different moonpool-type configurations were examined, and some interesting phenomena were discussed concerning the viscous effects and irregularities caused by the resonance of the confined fluid.

2015 ◽  
Vol 784 ◽  
pp. 373-395 ◽  
Author(s):  
Izolda V. Sturova

The problems of radiation (sway, heave and roll) of surface and flexural-gravity waves by a submerged cylinder are investigated for two configurations, concerning; (i) a freely floating finite elastic plate modelling an ice floe, and (ii) two semi-infinite elastic plates separated by a region of open water (polynya). The fluid of finite depth is assumed to be inviscid, incompressible and homogeneous. The linear two-dimensional problems are formulated within the framework of potential-flow theory. The method of mass sources distributed along the body contour is applied. The corresponding Green’s function is obtained by using matched eigenfunction expansions. The radiation load (added mass and damping coefficients) and the amplitudes of vertical displacements of the free surface and elastic plates are calculated. Reciprocity relations which demonstrate both symmetry of the radiation load coefficients and the relation of damping coefficients with the far-field form of the radiation potentials are found. It is shown that wave motion essentially depends on the position of the submerged body relative to the elastic plate edges. The results of solving the radiation problem are compared with the solution of the diffraction problem. It is noted that resonant frequencies in the radiation problem correlate with those frequencies at which the reflection coefficient in the diffraction problem has a local minimum.


1995 ◽  
Vol 18 (1) ◽  
pp. 151-170 ◽  
Author(s):  
D. D. Bhatta ◽  
M. Rahman

Wave forces and moments due to scattering and radiation for a vertical circular cylinder heaving in water of finite depth are derived analytically. These are derived from the total velocity potential which can be decomposed as two velocity potentials; one due to scattering in the presence of an incident wave on fixed structure (diffraction problem), and the other due to radiation by the heave motion on calm water (radiation problem). For each part, the velocity potential is derived by considering two regions, namely, interior region and exterior region. The complex matrix equations are solved numerically to determine the unknown coefficients to compute the wave loads. Some numerical results are presented for different depth to radius and draft to radius ratios.


1986 ◽  
Vol 30 (03) ◽  
pp. 147-152
Author(s):  
Yong Kwun Chung

When the wavelength of the incident wave is short, the total surface potential on a floating body is found to be 2∅ i & O (m-l∅ i) on the lit surface and O (m-l∅ j) on the shadow surface where ~b i is the potential of the incident wave and m the wave number in water of finite depth. The present approximation for wave exciting forces and moments is reasonably good up to X/L ∅ 1 where h is the wavelength and L the characteristic length of the body.


Author(s):  
Yuri I. Biba ◽  
Zheji Liu ◽  
D. Lee Hill

A complete effort to redesign the aerodynamic characteristics of a single-stage pipeline compressor is presented. The components addressed are the impeller, diffuser region, and the volute. The innovation of this effort stems from the simultaneous inclusion of both the noise and aerodynamic performance as primary design parameters. The final detailed flange-to-flange analysis of the new components clearly shows that the operating range is extended and the tonal noise driven by the impeller is reduced. This is accomplished without sacrificing the existing high efficiency of the baseline machine. The body of the design effort uses both Computational Fluid Dynamics (CFD) and vibro-acoustics technology. The predictions are anchored by using the flange-to-flange analysis of the original design and its experimental performance data. By calculating delta corrections and assuming that these deltas are approximately the same for the new design, the expected performance is extrapolated.


2015 ◽  
Author(s):  
Joshua Counsil ◽  
Kevin McTaggart ◽  
Dominic Groulx ◽  
Kiari Boulama

A study has been undertaken to test the value of unsteady Reynolds-averaged Navier-Stokes (URANS) and traditional semi-empirical methods in the face of complex ship roll phenomena, and provide insight into the selection of bilge keel span for varying roll amplitudes. The computational fluid dynamics (CFD) code STAR-CCM+ is employed and two-dimensional submerged bodies undergoing forced roll motion are analyzed. The spatial resolution and timestepping scheme are validated by comparison with published numerical and experimental studies. The model is then applied to a fully-submerged circular cylinder with bilge keels of varying span and undergoing roll motion at varying angular amplitudes. Extracted hydrodynamic coefficients indicate that in general, increasing displacement amplitude and bilge keel span yields increased added mass and increased damping. The relationship is complex and highly dependent upon vortex interactions with each other and the body. The semi-empirical methods used for comparison yield good predictions for simple vortex interactions but fail where viscous effects are strong. Hence, URANS methods are shown to be necessary for friction-dominated flows while semi-empirical methods remain useful for initial design considerations.


2005 ◽  
Vol 49 (02) ◽  
pp. 144-158 ◽  
Author(s):  
F. Kara ◽  
D. Vassalos

The Ship Stability Research Centre, Department of Naval Architecture and Marine Engineering, The Universities of Glasgow and Strathclyde, Scotland, UKA linearized three-dimensional potential flow formulation in time domain is applied to calculate wave-making resistance of ships in calm water. Steady-state perturbation potentials for resistance are obtained as the steady-state limit of the surge radiation impulse response function using the transient free surface source distribution over the body surface. Five different vessels are used to validate the present numerical approximation. The results, including steady-state wave-making resistance, sinkage force, trim moment, and wave profile along the waterline, are compared with other published numerical and experimental results.


1980 ◽  
Vol 24 (01) ◽  
pp. 60-65
Author(s):  
A. J. Smits ◽  
S. P. Law ◽  
P. N. Joubert

A wide range of experimental pressure distributions along axisymmetric bodies was compared with the results of Landweber's potential flow calculation method. Apart from certain viscous effects, some discrepancies were found, and it is shown that blockage corrections are of the right order to account for these discrepancies. The calculation method was also used to show that the pressure distribution over the nose of the body is largely independent of the tail shape, and vice versa.


Energies ◽  
2019 ◽  
Vol 12 (2) ◽  
pp. 261 ◽  
Author(s):  
Andres G. ◽  
Juan S. ◽  
Omar López ◽  
Laura Suárez C, ◽  
Jaime A. Escobar

Globalization has led to an increase in the use of small copters for different activities such as geo-referencing, agricultural fields monitoring, survillance, among others. This is the main reason why there is a strong interest in the performance of small-scale propellers used in unmanned aerial vehicles. The flow developed by rotors is complex and the estimation of its aerodynamic performance is not a trivial process. In addition, viscous effects, when the rotor operates at low Reynolds, affect its performance. In the present paper, two different computational methods, Computational Fluid Dynamics (CFD) and the Unsteady Vortex Lattice Method (UVLM) with a viscous correction, were used to study the performance of an isolated rotor of a quadcopter flying at hover. The Multi Reference Frame model and transition S S T κ - ω turbulence model were used in the CFD simulations. The tip vortex core growth was used to account for the viscous effects in the UVLM. The wake structure, pressure coefficient, thrust and torque predictions from both methods are compared. Thrust and torque results from simulations were validated by means of experimental results of a characterization of a single rotor. Finally, figure of merit of the rotor is evaluated showing that UVLM overestimates the efficiency of the rotor; meanwhile, CFD predictions are close to experimental values.


The method of integral equations is used here to calculate the virtual mass of a half-immersed cylinder heaving periodically on water of finite constant depth. For general sections this method is more appropriate than the method of multipoles; particular sections that are considered are the circle and the ellipse. Green’s theorem is applied to the potential and to a fundamental solution (wave source) satisfying the conditions at the free surface, at the bottom and at infinity, but not necessarily on the body. An integral equation for the potential on the body only is thus obtained. For the simplest choice of fundamental solution the method breaks down at a discrete infinite set of frequencies, as is well known. When the fundamental solution was modified, however, a different integral equation could be obtained for the same unknown function and this was found not to break down for the circle and ellipse. The present numerical results are in good agreement with those obtained by the method of multipoles which for the circle is more efficient than the method of integral equations but which is not readily applicable to other sections. Much effort now goes into such calculations.


Author(s):  
Antoine Ducoin ◽  
Yin Lu Young

The objective of this research is to derive and validate scaling relationships for flexible lifting bodies in transitional and turbulent flows. The motivation is to help the design and interpretation of reduced-scale experimental studies of flexible hydrofoils, with focus on the influence of viscous effects on the hydroelastic response. The numerical method is based on a previous validated viscous FSI solver presented in [1]. It is based on the coupling between a commercial Computational Fluid Dynamics (CFD) solver, CFX, and a simple two-degrees-of-freedom (2-DOF) system that simulates the free tip section displacement of a cantilevered, rectangular hydrofoil. To validate the scaling relations, sample numerical results are shown for three geometrically similar models: full scale, 1/2 scale and 1/10 scale. On the fluid side, although the effects of gravity and compressibility are assumed to be negligible, three different methods of scaling the velocity are considered: Reynolds scaling, Froude scaling, and Mach scaling. The three scaling methods produce different velocity scales when the fluid properties and gravitational constant are the same between the model and prototype, which will lead to different scaling for the material properties. The results suggest that by applying Mach scaling (which does not mean the flow is compressible, but simply requires the relative inflow velocity and fluid properties to be the same between the model and the prototype) and Re ≥ 2 × 106, the same material as the full scale could be used, which will lead to similar stress distributions, in addition to similar strains, and hence similar hydroelastic response and failure mechanisms. However, if Re ≤ 2 × 106 and Mach scale is used, a viscous correction is required to properly extrapolate the experimental results to full-scale.


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