Negative Spring Device for Wave Energy Buoy Stiffness
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Solution Overview
Problem
Existing wave energy converters, such as point absorbers, have limited bandwidth and amplitude of movement, restricting their ability to effectively convert wave energy into usable forms over a wide range of frequencies and frequencies, leading to reduced energy output.
Innovation Solution
The use of a negative spring device connected between a buoy and a reference point, which applies a positive force during displacement from the equilibrium position, reducing hydrostatic stiffness and increasing the buoy's amplitude of movement and energy conversion efficiency, allowing for a greater range of wave frequencies to be harnessed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If a standard spring device is used to connect the buoy to the reference point, then the buoy's natural hydrostatic stiffness is maintained, but the range of movement and amplitude of oscillation are limited
Solution Approach 1:
The patent applies a negative spring device that changes the effective stiffness parameter of the buoy system. By introducing a negative spring with negative stiffness, the overall hydrostatic stiffness is reduced, allowing the buoy to oscillate with larger amplitudes and greater range of movement while maintaining system stability through careful tuning of the negative spring characteristics.
2Productivity
If the buoy is pre-tensioned to increase response to waves, then the negative mass effect reduces inertia, but the complexity of the system increases
Solution Approach 1:
The patent employs pre-tensioning of the buoy to create a negative mass effect, where the tensioning force counteracts the buoy's natural mass, effectively reducing its inertia. This allows the buoy to respond more quickly and efficiently to wave forces, improving energy conversion efficiency without requiring additional complex active control systems.
3Adaptability or versatility
If the buoy is designed for large amplitude oscillation, then energy extraction over broader frequency range is improved, but the coupling to energy conversion devices becomes more difficult
Solution Approach 1:
The patent utilizes the dynamic characteristics of the negative spring device to enable the buoy to oscillate with large amplitudes across a broad frequency bandwidth. The negative stiffness property allows the system to adapt its natural frequency and amplitude response dynamically, facilitating easier coupling to energy conversion devices that can operate over varying oscillation ranges.
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 increases the delivered energy by at least 100% and simplifies energy conversion by enabling the buoy to oscillate with larger amplitudes over a broader frequency range, effectively doubling the average power output compared to standard systems.
Implementation Method 1
the spring device is a negative spring device comprising a mechanical spring, wherein the negative spring device is for applying a positive force in the direction of displacement when the buoy moves away from the equilibrium position
Implementation Method 2
wave energy convertor for extracting energy from ocean waves
Implementation Method 3
a buoy arranged to oscillate relative to a reference point about an equilibrium position
Implementation Method 4
With the use of a negative spring a buoy may be made to have an apparent stiffness that is very low for a given range of movement
Data Source
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Figure 5~6
AI summary
A wave energy convertor (1) for extracting energy from ocean waves, comprising: a buoy (2) arranged to oscillate relative to a reference point 3 about an equilibrium position (4); and a negative spring device (10) connected between the buoy (2 )and the reference point (3), wherein the negative spring device (10) is for applying a positive force in the direction of displacement when the buoy (2 )moves away from the equilibrium position (4).