Container Stack Frequency Monitoring for Lashing Fatigue Alerts
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Solution Overview
Problem
Current systems for monitoring the dynamics of shipping containers on cargo ships fail to accurately account for the dynamic modal responses and natural frequencies of container stacks, leading to potential lashing and twist lock failures due to increased lateral accelerations and mechanical play, which can result in reduced lashing capacity and increased snap loads.
Innovation Solution
A monitoring system that includes load cells with high sampling rates to detect natural frequencies and resonance modes, coupled with processors to analyze tension data and provide alerts for potential overloading, using load pins and adapters to interface with existing lashing systems, and incorporating accelerometers and gyroscopes to measure ship movements, enabling real-time detection of container stack dynamics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If standard industry loading software assumes quasi-static response and static loads, then calculation simplicity is maintained, but dynamic modal responses and natural frequencies of container stacks are not accurately captured
Solution Approach 1:
The patent transitions from static assumptions to dynamic analysis by incorporating the natural frequencies and modal responses of container stacks. The system considers the dynamic behavior of containers during sea voyages, accounting for vibrations and resonances that occur at specific frequencies, thereby accurately capturing dynamic modal responses that were previously ignored.
Solution Approach 2:
The patent changes the fundamental parameters of the analysis from static loads to dynamic loads that vary with time and frequency. By introducing frequency-dependent parameters and considering the spectral characteristics of sea waves, the system accurately models the dynamic response of container stacks under various sea conditions.
2Stability of the object's composition
If connections between containers are assumed rigid, then structural stability is simplified, but mechanical play in twistlocks and lashings is not accounted for
Solution Approach 1:
The patent applies different connection characteristics to different parts of the container stack. Rather than assuming uniform rigid connections throughout, the system considers localized mechanical play in twistlocks and lashings at specific connection points, allowing for realistic modeling of connection behavior where rigidity varies by location and connection type.
Solution Approach 2:
The patent models connections as dynamic elements rather than static rigid constraints. The mechanical play in twistlocks and lashings is represented as dynamic gaps that open and close during vessel motion, affecting the natural frequencies and modal responses of the container stack in a frequency-dependent manner.
3Ease of manufacture
If lashing capacity is calculated based on static loads, then design simplicity is maintained, but snap loads due to dynamic responses are not predicted
Solution Approach 1:
The patent performs preliminary dynamic analysis to identify critical natural frequencies and modal responses of container stacks before finalizing lashing design. By predicting dynamic amplification factors and snap loads in advance, the system enables designers to select appropriate lashing capacities that account for dynamic effects rather than relying solely on static calculations.
Solution Approach 2:
The system incorporates feedback from dynamic response analysis into the lashing design process. By continuously evaluating the interaction between container stack dynamics and lashing forces across different frequency ranges, the system refines lashing capacity recommendations to ensure reliability under dynamic sea conditions.
4Quantity of substance
If container stack height is increased to maximize cargo capacity, then shipping efficiency is improved, but lateral accelerations at the top of stacks increase leading to failure
Solution Approach 1:
The patent analyzes the dynamic behavior of tall container stacks by considering their natural frequencies and modal responses. The system identifies critical height thresholds where parametric roll resonances occur and lateral accelerations become excessive, enabling optimization of stack height to balance cargo capacity with safety under various sea conditions.
Solution Approach 2:
The patent examines how changing the height parameter of container stacks affects their dynamic characteristics. By analyzing the relationship between stack height, natural frequencies, and lateral accelerations, the system determines optimal height ranges that maximize cargo capacity while avoiding resonant conditions that lead to connection failures.
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 system effectively measures and predicts potential overloading, reducing the risk of lashing and twist lock failures by accurately accounting for dynamic responses and providing timely alerts, thereby enhancing the safety and stability of container stacks under varying wave conditions.
Implementation Method 1
load cells coupled to a lashing that secures shipping containers stacked on a cargo ship
Implementation Method 2
incorporating accelerometers and gyroscopes to measure ship movements
Implementation Method 3
load cells with high sampling rates to detect natural frequencies and resonance modes
Data Source
AI summary
A system includes several load cells, each coupled to a lashing that secures shipping containers, accelerometer cells, each coupled to a shipping container at the top of a stack, and an inclinometer cell coupled to a cargo ship. The cells are configured to transmit data to a computer. All the cells comprise a processor programmed to acquire a time series of measurements and, preferably, decompose the time series into a sum of sinusoidal signals, each having a frequency and an amplitude. Alternatively, the computer can be programmed to decompose the time series. The computer is programmed to identify the signal components caused by the roll of the cargo ship or by resonances in shipping container stacks. The computer estimates cumulated damages caused by fatigue in the lashings and/or twist locks. The system is used to trigger alarms and/or schedule maintenance.