A Numerical Investigation Into the Value of Added Mass Coefficient for Circular Cylinders

2005 ◽  
Author(s):  
H. Karadeniz
Keyword(s):  
Hydrodynamic Pressure ◽  
Added Mass ◽  
Offshore Structures ◽  
Circular Cylinders ◽  
Element Formulation ◽  
Fluid Structure Interactions ◽  
Shells Of Revolution ◽  
Fluid Structure ◽  
Mass Coefficient ◽  
Added Masses

This paper presents a general axi-symmetrical solid element to be used mainly for the calculation of added masses of water surrounding members of offshore structures, and in general, for multi-purposes such as analyses of shells of revolution, circular beams and plates, axi-symmetrical structures and soils, plane stress/strain problems. Since one element type is used for modeling of different media such as structures, soil and water, the element is very suitable to solve interaction problems. The element is derived parametrically so that changing values of parameters can generate flexible geometrical shapes in exact forms. In the element formulation, a constant shear locking is used to solve bending problems of beam like structures. A similar fluid element is also formulated to analyze fluid-structure interactions and to determine added masses of co-vibrating water. The added mass is calculated from hydrodynamic pressures, which are produced by fluid-structure interactions. In the paper, a special solution algorithm is presented for the coupled eigenvalue problem of the interaction. An analytic calculation of the added mass is also presented for members along which a constant variation of hydrodynamic pressure occurs. A couple of examples are provided to demonstrate applications of the elements explained. Added mass coefficients of offshore structural members (tubular members) are investigated for practical uses.

Supporting New Insight in Pipeline Hydrodynamics Using Stochastic Approaches on External Corrosion Damage

2010 ◽  
Author(s):  
Zahiraniza Mustaffa ◽  
Pieter van Gelder
Keyword(s):  
Field Data ◽  
Corrosion Damage ◽  
Circular Cylinders ◽  
Fluid Structure Interactions ◽  
Fluid Structure ◽  
Subsea Pipeline ◽  
Structure Interaction ◽  
Actual Field ◽  
External Flows ◽  
External Corrosion

Several recent discoveries in the fluid-structure interactions between the external flows and circular cylinders placed close to the wall have added new values to the hydrodynamics of unburied marine pipelines on a seabed. The hydrodynamics of waves and/or currents introduced vortex flows surrounding the pipeline. External corrosions formed in marine pipelines were assumed to be partly contributed by such fluid-structure interactions. The spatial consequences of such interactions were of interest of this study. This paper summarized some experimental and numerical works carried out by previous researchers on these new discoveries. Actual field data were utilized in this study to support this hypothesis. The characteristics of corrosion orientations in the pipelines were studied comprehensively using stochastic approaches and results were discussed. Results adopted from the field data acknowledged well to the hypothesis from the reported literature. The updated knowledge from this fluid-structure interaction is hoped to be given more attention by the industry and perhaps to be incorporated into the current subsea pipeline designs.

Investigations on the Fluid-Structure Interactions of Fishing Nets

2006 ◽  
Author(s):  
Hans-Joachim Winkel ◽  
Mathias Paschen
Keyword(s):  
Theoretical Models ◽  
Transverse Force ◽  
Circular Cylinders ◽  
Fluid Structure Interactions ◽  
Calculation Methods ◽  
Fluid Structure ◽  
Long Time ◽  
Helical Strakes

Modern nets consist of meshes made of threads or twines with spirals or helical strakes. Fluid-structure interactions have been investigated in Rostock for a long time applying different theoretical models. Because of great net flexibility there is a need of calculation methods which consider the main physical qualities. This is done by the approximation of wake of threads by results from circular cylinders and influence of circulation, which is known from measurements of transverse force. Results of measurements with two models with and without spirals are given for comparison.

Comparison of Strong and Partioned Fluid Structure Code Coupling Methods

2005 ◽  
Author(s):  
E. Longatte ◽  
V. Verreman ◽  
Z. Bendjeddou ◽  
M. Souli
Keyword(s):  
Energy Conservation ◽  
Coupled System ◽  
Added Mass ◽  
Point Of View ◽  
Numerical Dissipation ◽  
Fluid Structure Interactions ◽  
Fluid Structure ◽  
Coupling Procedure ◽  
Flow Induced Vibrations ◽  
Structure Code

As far as flow-induced vibrations are concerned, fluid structure interactions and fluid elastic effects are involved. They may be characterized by parameters like added mass, added damping and added stiffness describing fluid and flow effects on structure motion. From a numerical point of view, identifying these parameters requires numerical simulation of coupled fluid and structure problems. To perform such a multi-physics computation, several numerical methods can be considered involving either a partitioned or a monolithic fluid structure code coupling procedure. Monolithic process is a fully implicit method ensuring the energy conservation of the coupled system. However its implementation may be difficult when specific methods are required for both fluid and structure solvers. The partitioned procedure does not feature the same disadvantage because fluid and structure computations are staggered in time. However a specific attention must be paid to the energy conservation of the full coupled system and one must choose code coupling schemes in order to avoid or to reduce as much as possible numerical dissipation polluting the results. In the present paper, several techniques for fluid structure code coupling are compared. Several configurations are considered and numerical results are discussed in terms of added mass and damping for structures vibrating in fluid at rest. These results contribute to the validation of a full fluid structure code coupling procedure with many possible applications in the fields of fluid structure interactions and flow-induced vibrations.

Influence of hydrodynamic effects on iceberg collisions

1990 ◽  
Vol 17 (3) ◽  
pp. 329-337 ◽  
Author(s):  
Michael Isaacson ◽  
Kevin McTaggart
Keyword(s):  
Added Mass ◽  
Offshore Structures ◽  
Ocean Engineering ◽  
Iceberg Drift ◽  
Added Masses ◽  
Waves And Currents ◽  
Fixed Structure ◽  
Wave Induced ◽  
Hydrodynamic Effects ◽  
Selection Of

This paper examines various hydrodynamic effects which should be considered when analyzing iceberg collisions with a fixed structure. Iceberg added mass is among the hydrodynamic parameters that must be known to evaluate collision severity. Effective added mass is shown to vary with collision duration and recommendations are made for the selection of added masses to be used in iceberg collision design. Iceberg impact velocities are influenced by waves and currents, which can both be significantly influenced by the presence of a large structure. Wave-driven iceberg drift motions are shown to be more sensitive than current-driven motions to the presence of a structure. The contribution of wave-induced oscillatory motions to impact velocity is also discussed. Key words: added mass, hydrodynamics, ice impact, icebergs, ocean engineering, offshore structures.

Interaction Between Two Bodies Translating in an Inviscid Fluid

1991 ◽  
Vol 35 (01) ◽  
pp. 1-8
Author(s):  
L. Landweber ◽  
A. T. Chwang ◽  
Z. Guo
Keyword(s):  
Translational Motion ◽  
Closed Form Solution ◽  
Added Mass ◽  
Form Solution ◽  
Circular Cylinders ◽  
Integral Approach ◽  
Inviscid Fluid ◽  
Added Masses ◽  
Two Bodies ◽  
Good Agreement

The equations of motion of two bodies in translational motion in an inviscid fluid at rest at infinity are expressed in Lagrangian form. For the case of one body stationary and the other approaching it in a uniform stream, an exact, closed-form solution in terms of added masses is obtained, yielding simple expressions for the velocity of the moving body as a function of its relative position and for the interaction forces. This solution is applied to the case of a rectangular cylinder approaching a cylindrical one, for which the added-mass coefficients had been previously obtained in a companion paper by an integral-equation procedure. In order to compare results with those in the literature, and to evaluate the accuracy of the present procedures, results were calculated for a pair of circular cylinders by these methods as well as by successive images. Very good agreement was found. Comparison with published results showed good agreement with the added mass but very poor agreement on the forces, including disagreement as to whether the forces were repulsive or attractive. The discrepancy is believed to be due to the omission of terms in the Bernoulli equation which was used to obtain the pressure distribution and then the force on a body. The Lagrangian formulation is believed to be preferable to the pressure-integral approach because it yields the hydrodynamic force directly in terms of the added masses and their derivatives, thus requiring the calculation of many fewer coefficients.

scholarly journals FORCES FROM FLUID FLOW AROUND OBJECTS

1974 ◽  
Vol 1 (14) ◽  
pp. 106 ◽  
Author(s):  
John H. Nath ◽  
Tokuo Yamamoto
Keyword(s):  
Fluid Flow ◽  
Flow Direction ◽  
Added Mass ◽  
Circular Cylinders ◽  
Plane Boundary ◽  
Viscous Effects ◽  
Local Flow ◽  
Direction Parallel ◽  
Mass Coefficient ◽  
Added Mass Coefficient

All hydrodynamic forces on submerged objects are shown to be due to the acceleration effects of the fluid flow. However, it is useful to consider separately the influence from the various ambient flow and local flow conditions. At times certain aspects of the flow can be ignored, which simplifies the analysis. Examples are developed for circular cylinders near a plane boundary with a flow direction parallel to the boundary and perpendicular to the cylinder. Potential flow theory predicts that large vertical forces exist away from the boundary when the cylinder is against the boundary and that large negative forces exist toward the boundary when the cylinder is positioned a small distance from the boundary, when the viscous effects are small. When the cylinder is near the boundary, the added mass coefficient is the same regardless of the direction of the flow, providing the flow is perpendicular to the cylinder. In addition, the added mass coefficient is much larger for cylinders near the boundary than when they are in a free stream. Good agreement between theory and laboratory experimentation was obtained for various coefficients with waves on horizontal cylinders near a plane boundary.

Hydrodynamic forces on fixed submerged cylinders

1992 ◽  
Vol 436 (1896) ◽  
pp. 13-32 ◽  
Keyword(s):  
Theoretical Calculations ◽  
Fluid Velocity ◽  
Longitudinal Velocity ◽  
Added Mass ◽  
Offshore Structures ◽  
Rate Of Change ◽  
Circular Cylinders ◽  
Inertia Force ◽  
Wave Loads ◽  
Zonal Harmonic

Wave loads on the cylindrical members of fixed offshore structures are generally calculated by using Morison’s Equation. The inertia force component of this equation is conventionally quoted in a form derived from theoretical calculations for a uniformly accelerating fluid. In this paper the correct form for the inertia force in a general fluid flow is derived from first principles by pressure integration and, independently, from earlier work, by energy arguments. It is shown that, for the thin cylinder limiting case, the transverse force on a circular cylinder is incorrectly given by the conventional approach, in that the product of transverse fluid velocity (in the direction of the required force) with the longitudinal velocity gradient should be added to the water particle acceleration, when computing the added-mass component of the force. Axial divergence, in other words, appears to play the role of a rate-of-change of added mass. It is shown that the mathematical origin of this extra term is the classical three-dimensional flow feature of a ‘zonal harmonic’, which produces a convective fluid acceleration but zero loading. A more elaborate formula is derived for non-circular cylinders, and the nature of point loads occurring at cylinder ends is also discussed.

scholarly journals Modelling capsizing icebergs in the open ocean

2020 ◽  
Vol 223 (2) ◽  
pp. 1265-1287
Author(s):  
P Bonnet ◽  
V A Yastrebov ◽  
P Queutey ◽  
A Leroyer ◽  
A Mangeney ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Aspect Ratio ◽  
Added Mass ◽  
Open Ocean ◽  
Contact Dynamics ◽  
Cfd Simulations ◽  
Fluid Structure ◽  
Aspect Ratios ◽  
Glacier Front ◽  
Added Masses

Summary At near-grounded glacier termini, calving can lead to the capsize of kilometre-scale (i.e. gigatons) unstable icebergs. The transient contact force applied by the capsizing iceberg on the glacier front generates seismic waves that propagate over teleseismic distances. The inversion of this seismic signal is of great interest to get insight into actual and past capsize dynamics. However, the iceberg size, which is of interest for geophysical and climatic studies, cannot be recovered from the seismic amplitude alone. This is because the capsize is a complex process involving interactions between the iceberg, the glacier and the surrounding water. This paper presents a first step towards the construction of a complete model, and is focused on the capsize in the open ocean without glacier front nor ice-mélange. The capsize dynamics of an iceberg in the open ocean is captured by computational fluid dynamics (CFD) simulations, which allows assessing the complexity of the fluid motion around a capsizing iceberg and how far the ocean is affected by iceberg rotation. Expressing the results in terms of appropriate dimensionless variables, we show that laboratory scale and field scale capsizes can be directly compared. The capsize dynamics is found to be highly sensitive to the iceberg aspect ratio and to the water and ice densities. However, dealing at the same time with the fluid dynamics and the contact between the iceberg and the deformable glacier front requires highly complex coupling that often goes beyond actual capabilities of fluid-structure interaction softwares. Therefore, we developed a semi-analytical simplified fluid-structure model (SAFIM) that can be implemented in solid mechanics computations dealing with contact dynamics of deformable solids. This model accounts for hydrodynamic forces through calibrated drag and added-mass effects, and is calibrated against the reference CFD simulations. We show that SAFIM significantly improves the accuracy of the iceberg motion compared with existing simplified models. Various types of drag forces are discussed. The one that provides the best results is an integrated pressure-drag proportional to the square of the normal local velocity at the iceberg’s surface, with the drag coefficient depending linearly on the iceberg’s aspect ratio. A new formulation based on simplified added-masses or computed added-mass proposed in the literature, is also discussed. We study in particular the change of hydrodynamic-induced forces and moments acting on the capsizing iceberg. The error of the simulated horizontal force ranges between 5 and 25 per cent for different aspect ratios. The added-masses affect the initiation period of the capsize, the duration of the whole capsize being better simulated when added-masses are accounted for. The drag force mainly affects the amplitude of the fluid forces and this amplitude is best predicted without added-masses.

scholarly journals A simplified fluid structure interaction model for the assessment of ship hard grounding

2021 ◽  
Author(s):  
Sang Jin Kim ◽  
Jung Min Sohn ◽  
Pentti Kujala ◽  
Spyros Hirdaris
Keyword(s):  
Structural Damage ◽  
Rapid Assessment ◽  
Interaction Model ◽  
Fluid Structure Interactions ◽  
Hydrodynamic Properties ◽  
Surrounding Water ◽  
Fluid Structure ◽  
Source Codes ◽  
Added Masses ◽  
Restoring Forces

AbstractThe structural damage of ships in navigational accidents is influenced by the hydrodynamic properties of surrounding water. Fluid structure interactions (FSI) in way of grounding contact can be idealized by combining commercial FEA tools and specialized hydrodynamic solvers. Despite the efficacy of these simulations, the source codes idealizing FSI are not openly available, computationally expensive and subject to limitations in terms of physical assumptions. This paper presents a unified FSI model for the assessment of ship crashworthiness following ship hard grounding. The method uses spring elements for the idealization of hydrostatic restoring forces in 3 DoF (heave, pitch, roll) and distributes the added masses in 6 DoF on the nodal points in way of contact. Comparison of results against the method of Kim et al. (2021) for the case of a barge and a Ro–Ro passenger ship demonstrate excellent idealization of ship dynamics. It is concluded that the method could be useful for rapid assessment of ship grounding scenarios and associated regulatory developments.

Sign in / Sign up

Export Citation Format

Share Document