Cable Strakes for Rain-Wind Vibration Control
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Solution Overview
Problem
Cables supporting structures like bridges and antennas experience undesirable vibrations due to wind and rain, which can lead to damage and fatigue, and existing solutions like viscous or frictional dampers do not effectively prevent rain-wind induced rivulets that alter the aerodynamic profile and exacerbate vibrations.
Innovation Solution
The design of strakes on the cable's outer surface, where each strake is shorter than the circumference and less than 5% of the diameter, arranged transversely to the longitudinal direction, increases streamwise vorticity, reduces wake formation, and prevents rivulet formation, thereby minimizing drag and vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If viscous or frictional dampers are introduced to bridge cables, then vibrations are reduced, but rain-wind induced rivulets are not prevented and the aerodynamic profile is not improved
Solution Approach 1:
The cable surface is segmented into multiple discrete strakes arranged in a specific pattern. Each strake acts as an independent element that collectively modifies the aerodynamic profile, preventing rivulet formation while maintaining vibration reduction capabilities
Solution Approach 2:
Strakes serve as intermediary elements between the cable surface and the rain-wind flow. These protrusions intercept and redirect the flow, preventing direct contact between rain-wind rivulets and the cable surface, thereby eliminating the root cause of aerodynamic profile changes
2Reliability
If strakes are made longer to better prevent rivulets, then aerodynamic properties improve, but drag force increases
Solution Approach 1:
The strake length parameter is optimized to be less than the circumference of the cable. This specific parameter range generates sufficient streamwise vorticity to prevent rivulet formation while minimizing wake formation and drag force. The height parameter is also controlled at less than 5% of cable diameter to balance effectiveness with drag reduction
3Ease of manufacture
If strakes are arranged parallel to the longitudinal direction for simplicity, then manufacturing is easier, but rivulet prevention and vibration reduction are less effective
Solution Approach 1:
The strakes are arranged in an asymmetric pattern relative to the cable's longitudinal axis, with specific angular orientations designed to maximize streamwise vorticity generation. This asymmetric arrangement is highly effective at preventing rivulet formation and reducing vibrations, overcoming the manufacturing simplicity advantage of parallel alignment
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 configuration significantly improves aerodynamic properties, reduces drag, prevents rain-wind induced rivulets, and inhibits ice/snow shedding, effectively minimizing vibrations and ensuring safer structural integrity under varying weather conditions.
Implementation Method 1
the streamwise vorticity generated by the strake is increased. This is desirable as it reduces the wake formed leeward relative to the cable, which reduces cable drag
Implementation Method 2
if the strakes are provided so that they extend in a direction transverse to the longitudinal direction of the cable causes rain-wind generated rivulets to be prevented
Data Source
Figure 1~3
Figure 4~5
AI summary
The invention provides a construction comprising a structural element and at least one cable (100) arranged in tension to carry at least a part of the weight of the structural element. The cable defines an outer surface (102) onto which a plurality of strakes (104) form protrusions for reducing rain and wind induced vibrations. Each strake has a height being a distance from a strake root part connected to the outer surface of the cable and a strake end part terminating the strake outwards form the cable, a width being transverse to the height, and a length transverse to the height and width and along which length the strake is connected to the cable. The length of each strake is shorter than the circumference of the outer surface, and the height is less than 5 percent of the diameter of the cable.