Heave Plate Vertical Lips Hydrodynamic Inertia
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Solution Overview
Problem
Existing heave plates used to increase the effective mass of spars in wave energy converters and offshore structures are limited in their ability to enhance hydrodynamic inertia without increasing the size or length scale of the plates, which can be challenging due to considerations of harbor depth, structural strength, and weight.
Innovation Solution
Attaching vertically extending structures to the top and bottom surfaces of heave plates to increase the effective mass by enhancing the volume of fluid moved during motion, allowing for a larger natural resonance period without enlarging the spar or plate size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the size or length scale of heave plates is increased to enhance hydrodynamic inertia, then the effective mass of the spar increases, but the structural complexity and cost increase due to deeper harbor requirements and greater material usage
Solution Approach 1:
The patent applies dimensionality change by transitioning from traditional two-dimensional flat plates to three-dimensional structured plates with vertical columns. This adds a vertical dimension to the plate geometry, increasing the volume of water displaced and thereby enhancing hydrodynamic inertia without requiring an increase in the horizontal footprint of the plate. The structured configuration allows the plate to interact with a larger volume of fluid while maintaining compact overall dimensions.
Solution Approach 2:
The patent employs parameter changes by modifying the geometric parameters of the heave plate - specifically changing from a flat surface to a structured form with vertical columns of specific height and spacing. This geometric parameter modification increases the equivalent volume and surface area that interacts with water, thereby increasing added mass and hydrodynamic inertia without proportionally increasing material usage or structural complexity.
2Weight of moving object
If vertically extending structures are added to heave plates to increase effective mass, then hydrodynamic inertia increases, but the manufacturing complexity and weight of the plate increase
Solution Approach 1:
The patent applies segmentation by dividing the heave plate into modular components - a base plate and multiple vertical columns. This segmented structure allows for simplified manufacturing where columns can be produced separately and attached to the base plate, reducing overall manufacturing complexity compared to creating a single monolithic structured plate. The modular design also facilitates easier assembly and potential standardization of components.
3Strength
If the heave plate is made thicker to provide structural strength, then structural integrity improves, but the added mass decreases and the equivalent volume reduction becomes significant
Solution Approach 1:
The patent resolves this contradiction by shifting from increasing thickness (one-dimensional solution) to adding vertical columns (three-dimensional solution). The vertical columns increase the equivalent volume and hydrodynamic inertia by extending into the vertical dimension, rather than relying on increased plate thickness. This approach maintains structural strength through the columnar framework while preserving or enhancing added mass through increased water displacement volume.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively increases the hydrodynamic inertia of the spar, allowing for a larger natural resonance period and improved power conversion efficiency in wave energy converters and reduced vertical motion in offshore platforms, while maintaining structural integrity and cost-effectiveness.
Implementation Method 1
The added mass that the heave plates contribute is due to the fact that the acceleration or deceleration of the plate requires movement of some volume of fluid around the plate as it moves. The volume of fluid that the plate will move is proportional to the equivalent volume of the plate times some (experimentally determined) factor.
Implementation Method 2
The heave plate is disposed in a plane which is generally transverse (perpendicular) to the up or down direction of motion of the spar for increasing the effective mass of the spar. A plate so attached affects the dynamic behavior of the spar by increasing the effective mass and the viscous drag in the heave (vertical) direction.
Implementation Method 3
The benefit of attaching one, or more, heave plates is to allow for a shorter vertical spar that will still have a heave natural period outside of the prevailing wave period for the operating conditions (so that the spar will not respond to the prevailing wave conditions) and to increase the viscous damping of the spar in order to decrease near-resonance responses.
Data Source
AI summary
Apparatus embodying the invention include a damping plate attached to the submerged end of a spar-like element floating in a body of water. The spar like element tends to move up and down in a vertical direction in response to passing waves. The damping plate has a pair of oppositely facing surfaces extending transversely to the vertical direction of the movement of the spar-like element and vertical structures (“lips”) mounted on the oppositely facing surfaces for increasing the effective mass of water pushed during movement of the damping plate through the water. Damping plates with lips, as per the invention, may be used in wave energy converters to control the relative motion between the spar-like element and a float to increase the energy produced.