Crane Winch Control for Dynamic Load Reduction
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Solution Overview
Problem
Offshore cranes experience high dynamic loads during sea lifts due to stochastic vessel heave motions, leading to potential overloading and increased risks of damage, which existing methods struggle to mitigate effectively.
Innovation Solution
A method that determines the resonance frequencies of the crane boom and load system, generates damping motion through winch control, and adds this damping to the operator-controlled motion to counteract dynamic oscillations, using feedback from tension forces and tuning of PI-type winch speed controllers to absorb vibration energy at specific resonance frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a skilled crane operator manually selects optimal heave phase for load pickup, then peak loads can be reduced, but the risk of overloading remains due to stochastic vessel heave motions and human mistakes
Solution Approach 1:
The system uses real-time feedback from accelerometers and tension sensors to detect vessel heave phase and dynamically adjust winch operation. The feedback loop continuously monitors actual conditions and automatically corrects for stochastic variations, eliminating the need for manual judgment and ensuring consistent optimal timing for load pickup regardless of sea conditions.
Solution Approach 2:
The patent replaces manual operator control with an automated electronic control system that uses sensors, processors, and actuators. The mechanical decision-making process is substituted with electronic detection of heave phase through accelerometers and automated winch control, eliminating human error and providing more precise control over the load pickup timing.
2Productivity
If load is lifted off vessel deck while vessel is moving downwards, then sea lift operation can proceed, but jerk can make peak load exceed allowable maximum
Solution Approach 1:
The system performs preliminary detection of the optimal heave phase using accelerometers and tension sensors before initiating load pickup. By identifying the precise moment when vessel downward motion is minimal, the system prepares the winch to lift the load at the optimal timing, preventing excessive jerk and peak loads before they occur.
Solution Approach 2:
The control system dynamically adjusts winch operation based on real-time vessel motion conditions. Rather than using fixed timing, the system continuously adapts to changing heave phases, adjusting the load pickup timing to match the instantaneous vessel motion state, thereby minimizing dynamic loads under varying sea conditions.
3Reliability
If load chart limitations are applied to lower overloading risk, then safety is improved, but operational weather window is reduced leading to higher costs
Solution Approach 1:
The system replaces static load chart limitations with dynamic load management that adapts to real-time sea conditions. By continuously monitoring vessel heave phase and automatically adjusting winch operation, the system maintains safe load levels regardless of weather conditions, eliminating the need to restrict operations based on predetermined weather thresholds.
Solution Approach 2:
The invention changes the operational parameters from fixed load limits to dynamically adjusted timing and force control. Instead of restricting operations based on weather parameters, the system modifies the temporal parameters of load pickup timing and the force application rate, allowing safe operation across a broader range of weather conditions.
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 reduces dynamic peak loads, enhancing safety and operational flexibility by dampening resonance oscillations and extending the operational weather window.
Implementation Method 1
automatic generation of a damping motion in at least one of said winches, that counteract dynamic oscillations in the crane
Implementation Method 2
determining the resonance frequencies of the coupled crane boom and load system
Implementation Method 3
the top winch speed controller is tuned to absorb vibration energy most efficiently around the lowest crane resonance frequency and where the hoist winch speed controller is tuned to absorb vibration energy most efficiently around the highest crane resonance frequency
Data Source
AI summary
A method and related device for reducing resonant vibrations and dynamic loads of cranes, where vertical motion of a pay load is controlled by a boom winch and a hoist winch. In an embodiment, the method includes determining resonance frequencies of the crane boom and pay load from inertia data of the boom and stiffness on at least the boom and hoist ropes, the resonance frequencies including a first frequency and a lower second frequency. In addition, the method includes automatically modifying the motion of the boom winch or the hoist winch to induce a damping inducing winch motion in the boom or hoist winch, by tuning a proportional integral (PI)-type boom winch speed controller or a PI-type hoist winch speed controller. The boom winch speed controller is tuned to absorb energy at the second frequency, the hoist winch speed controller is tuned to absorb energy at the first frequency.