Reverse-Pyramid Hoist Cables for Offshore Crane Load Positioning
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Solution Overview
Problem
Existing cranes face challenges in accurately positioning heavy loads due to swinging and bending issues, especially in offshore windfarm installations, where wave-induced motion and wind cause objects to swing uncontrollably, and tugger cables lack the capacity to compensate for these movements effectively.
Innovation Solution
A crane design with a main boom hoist assembly and jib hoist assembly, featuring multiple-fall arrangements of hoist cables and heave compensation mechanisms, allowing coordinated control of the hoisting system to stabilize and position loads by distributing the vertical load over three cables, forming a reverse pyramid shape to minimize swinging and reduce bending stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If heave compensation mechanisms are used to compensate wave-induced motion, then the crane can operate in offshore conditions, but the load still swings uncontrollably due to insufficient prevention capability
Solution Approach 1:
The system applies preliminary anti-action by using heave compensation mechanisms to counteract wave-induced motion before it causes significant load swinging. The anti-swinging cables and control system work proactively to prevent excessive swing development, rather than merely reacting to swings after they occur.
Solution Approach 2:
The control system continuously monitors load position and cable tensions, using this feedback information to dynamically adjust the hoisting system and anti-swinging cable forces. This closed-loop control enables real-time correction of load position and suppression of swinging motions.
2Ease of operation
If tugger cables are used to translate the load horizontally, then load positioning can be adjusted, but the cables lack capacity to prevent swinging and control heavy loads
Solution Approach 1:
The system merges the functions of load support and horizontal positioning by integrating the hoisting system with anti-swinging cables that also provide positioning capability. The multiple cables work together in a coordinated manner, with the control system managing their interactions to achieve both support and positioning functions simultaneously.
Solution Approach 2:
The hoist cables serve multiple functions: supporting the load vertically, controlling horizontal position through coordinated tension adjustments, and preventing swinging motions. This multi-functionality eliminates the need for separate systems for each function, improving overall system efficiency.
3Device complexity
If the crane uses a single hoist cable to lift heavy loads, then the structure is simpler, but the load positioning accuracy decreases due to swinging and bending
Solution Approach 1:
The single hoist cable is segmented into multiple parallel cables (first, second, and third hoist cables) that share the load. This segmentation distributes the mechanical stresses, reduces swinging motions, and improves positioning accuracy while maintaining structural manageability through systematic arrangement.
Solution Approach 2:
The system uses a composite cable arrangement combining multiple cables with different functional roles (primary support cables and anti-swinging cable) working together. This composite structure leverages the strengths of each cable to achieve superior load control and positioning compared to a single cable system.
4Length of moving object
If the crane operates with tall boom to reach high positions, then the lifting height increases, but the bending stress on the boom increases under heavy loads
Solution Approach 1:
The anti-swinging cables act as counterbalancing elements that reduce the effective load on the boom by supporting part of the weight and counteracting swinging forces. This reduces the bending moment and stress on the boom structure, enabling safe operation at greater heights with heavy loads.
Solution Approach 2:
The system transitions from vertical load support to a multi-dimensional control system where cables are arranged in three-dimensional space with specific geometric relationships. This spatial arrangement creates mechanical advantages that reduce boom stress while maintaining lifting capability.
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
The crane achieves more accurate and efficient load positioning by minimizing swinging and reducing bending stresses, enabling the handling of heavier loads with less stress on the crane structure, even in challenging offshore conditions.
Implementation Method 1
the hoist cables and the anti-swinging cables together define a reverse pyramid shape when viewed from above, with the object suspended at the apex
Implementation Method 2
distributing the vertical load over three cables
Implementation Method 3
The hoist winch is provided with heave compensation, e.g. by embodying the hoist winch as an AHC winch or by means of heave compensating cylinders operating on the unwound section of the hoist cable
Data Source
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AI summary
A wave-induced motion compensating crane (1; 101) comprising a hoist assembly, wherein at least two departure sheaves (62) are mounted at opposite lateral sides of the jib (35), and wherein the object suspension device is supported both by two hoist cables (63a, b) extending laterally from the jib and a third hoist cable (53) that runs via another departure sheave (52), wherein the hoist assembly is adapted to, hoist and/or lower the object suspension device with an object (7) connected thereto, between a lower position and a position at a height up to the departure sheaves while the hoist cables together define a reverse pyramid, diverging upwards in between the object suspension device and the departure sheaves.