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S. Kelakunjal
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Slamming of deformable structures on water free surface
Two-way coupled fluid-structure modelling : A numerical study
Slamming — the impulsive loading that occurs when a structure meets the water surface at high relative velocity governs the design of ship bottom and bow plating and underlies a wider family of marine impact problems, from wet-deck slamming to LNG sloshing. When the impacted structure is compliant, its deformation feeds back on the flow and can reduce the local peak load, but predicting that mitigation efficiently remains an open problem. This thesis develops and validates two fluid–structure interaction models of the folding-flap wedge devised by Hendriksen (2022), a controlled abstraction of bottom slamming in which two keel-hinged plates, restrained by calibrated springs, fold under impact so that structural compliance can be varied independently of deadrise angle and entry velocity.
The first model resolves the flow in detail: a fixed-grid Navier–Stokes/volume-of-fluid simulation (on ComFLOW) representing the folding keel as two interactively moving plates sharing a hinge, used as a high-fidelity model on a small number of cases. The second is a fast, two-dimensional boundary element method with constant-strength source panels, governed by the measured torsional spring. This model is run first and covers the full test matrix. The flap-opening moment is derived from the rate of change of that added mass rather than from re-integrated pressure, making the coupling momentum-consistent. A preliminary analytical reduced-order model gives the integrator skeleton and a rigid-limit check.
Both models are validated against experimental records. The boundary element model spans the full fourteen-case matrix of spring stiffness, entry velocity, and deadrise, reproducing measured keel and panel pressures to a mean error of about 12% and per-plate flap rotation to a mean model-to-experiment ratio of about 7% error. The resolved ComFLOW simulation targets selected rigid and deformable cases at 10° and 20° deadrise. Both models capture the flap's light, oscillatory motion about a small positive mean, with periods matching the analytical wet natural period.
The central finding: peak pressure is fixed within the first fraction of a millisecond, before the flap folds, and is nearly insensitive to the spring; deformation instead reflects the slam impulse integrated against the spring. Because the slam is of shorter duration than the flap's wet period, the response is impulsive, so peak fold lags the pressure peak. A discretely compliant body thus mitigates outboard and integrated loads. The two models prove complementary, and recommendations follow for effective structural stiffness, three-dimensional and asymmetric extensions, and aerated, fully hydroelastic impacts. ...
The first model resolves the flow in detail: a fixed-grid Navier–Stokes/volume-of-fluid simulation (on ComFLOW) representing the folding keel as two interactively moving plates sharing a hinge, used as a high-fidelity model on a small number of cases. The second is a fast, two-dimensional boundary element method with constant-strength source panels, governed by the measured torsional spring. This model is run first and covers the full test matrix. The flap-opening moment is derived from the rate of change of that added mass rather than from re-integrated pressure, making the coupling momentum-consistent. A preliminary analytical reduced-order model gives the integrator skeleton and a rigid-limit check.
Both models are validated against experimental records. The boundary element model spans the full fourteen-case matrix of spring stiffness, entry velocity, and deadrise, reproducing measured keel and panel pressures to a mean error of about 12% and per-plate flap rotation to a mean model-to-experiment ratio of about 7% error. The resolved ComFLOW simulation targets selected rigid and deformable cases at 10° and 20° deadrise. Both models capture the flap's light, oscillatory motion about a small positive mean, with periods matching the analytical wet natural period.
The central finding: peak pressure is fixed within the first fraction of a millisecond, before the flap folds, and is nearly insensitive to the spring; deformation instead reflects the slam impulse integrated against the spring. Because the slam is of shorter duration than the flap's wet period, the response is impulsive, so peak fold lags the pressure peak. A discretely compliant body thus mitigates outboard and integrated loads. The two models prove complementary, and recommendations follow for effective structural stiffness, three-dimensional and asymmetric extensions, and aerated, fully hydroelastic impacts. ...
Slamming — the impulsive loading that occurs when a structure meets the water surface at high relative velocity governs the design of ship bottom and bow plating and underlies a wider family of marine impact problems, from wet-deck slamming to LNG sloshing. When the impacted structure is compliant, its deformation feeds back on the flow and can reduce the local peak load, but predicting that mitigation efficiently remains an open problem. This thesis develops and validates two fluid–structure interaction models of the folding-flap wedge devised by Hendriksen (2022), a controlled abstraction of bottom slamming in which two keel-hinged plates, restrained by calibrated springs, fold under impact so that structural compliance can be varied independently of deadrise angle and entry velocity.
The first model resolves the flow in detail: a fixed-grid Navier–Stokes/volume-of-fluid simulation (on ComFLOW) representing the folding keel as two interactively moving plates sharing a hinge, used as a high-fidelity model on a small number of cases. The second is a fast, two-dimensional boundary element method with constant-strength source panels, governed by the measured torsional spring. This model is run first and covers the full test matrix. The flap-opening moment is derived from the rate of change of that added mass rather than from re-integrated pressure, making the coupling momentum-consistent. A preliminary analytical reduced-order model gives the integrator skeleton and a rigid-limit check.
Both models are validated against experimental records. The boundary element model spans the full fourteen-case matrix of spring stiffness, entry velocity, and deadrise, reproducing measured keel and panel pressures to a mean error of about 12% and per-plate flap rotation to a mean model-to-experiment ratio of about 7% error. The resolved ComFLOW simulation targets selected rigid and deformable cases at 10° and 20° deadrise. Both models capture the flap's light, oscillatory motion about a small positive mean, with periods matching the analytical wet natural period.
The central finding: peak pressure is fixed within the first fraction of a millisecond, before the flap folds, and is nearly insensitive to the spring; deformation instead reflects the slam impulse integrated against the spring. Because the slam is of shorter duration than the flap's wet period, the response is impulsive, so peak fold lags the pressure peak. A discretely compliant body thus mitigates outboard and integrated loads. The two models prove complementary, and recommendations follow for effective structural stiffness, three-dimensional and asymmetric extensions, and aerated, fully hydroelastic impacts.
The first model resolves the flow in detail: a fixed-grid Navier–Stokes/volume-of-fluid simulation (on ComFLOW) representing the folding keel as two interactively moving plates sharing a hinge, used as a high-fidelity model on a small number of cases. The second is a fast, two-dimensional boundary element method with constant-strength source panels, governed by the measured torsional spring. This model is run first and covers the full test matrix. The flap-opening moment is derived from the rate of change of that added mass rather than from re-integrated pressure, making the coupling momentum-consistent. A preliminary analytical reduced-order model gives the integrator skeleton and a rigid-limit check.
Both models are validated against experimental records. The boundary element model spans the full fourteen-case matrix of spring stiffness, entry velocity, and deadrise, reproducing measured keel and panel pressures to a mean error of about 12% and per-plate flap rotation to a mean model-to-experiment ratio of about 7% error. The resolved ComFLOW simulation targets selected rigid and deformable cases at 10° and 20° deadrise. Both models capture the flap's light, oscillatory motion about a small positive mean, with periods matching the analytical wet natural period.
The central finding: peak pressure is fixed within the first fraction of a millisecond, before the flap folds, and is nearly insensitive to the spring; deformation instead reflects the slam impulse integrated against the spring. Because the slam is of shorter duration than the flap's wet period, the response is impulsive, so peak fold lags the pressure peak. A discretely compliant body thus mitigates outboard and integrated loads. The two models prove complementary, and recommendations follow for effective structural stiffness, three-dimensional and asymmetric extensions, and aerated, fully hydroelastic impacts.