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Shipboard crane digital twin: An empirical study on R/V Gunnerus
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Industry 4.0 is moving forward under technology upgrades, utilizing information technology to improve the intelligence of the industry, whereas Industry 5.0 is value-driven, aiming to focus on essential societal needs, values, and responsibility. The manufacturing industry is currently moving towards the integration of productivity enhancements and sustainable human employment. Such a transformation has deeply changed the human–machine interaction (HMI), among which digital twin (DT) and extended reality (XR) are two cutting-edge technologies. A manufacturing DT offers an opportunity to simulate, monitor, and optimize the machine. In the meantime, XR empowers HMI in the industrial field. This paper presents an XR application framework for DT-based services within a manufacturing context. This work aims to develop a technological framework to improve the efficiency of the XR application development and the usability of the XR-based HMI systems. We first introduce four layers of the framework, including the perception layer with the physical machine and its ROS-based simulation model, the machine communication layer, the network layer containing three kinds of communication middleware, and the Unity-based service layer creating XR-based digital applications. Subsequently, we conduct the responsiveness test for the framework and describe several XR industrial applications for a DT-based smart crane. Finally, we highlight the research challenges and potential issues that should be further addressed by analyzing the performance of the whole framework.
Digital twin technology empowers the digital transformation of the industrial world with an increasing amount of data, which meanwhile creates a challenging context for designing a human–machine interface (HMI) for operating machines. This work aims at creating an HMI for digital twin based services. With an industrial crane platform as a case study, we presented a mixed reality (MR) application running on a Microsoft HoloLens 1 device. The application, consisting of visualization, interaction, communication, and registration modules, allowed crane operators to both monitor the crane status and control its movement through interactive holograms and bi-directional data communication, with enhanced mobility thanks to spatial registration and tracking of the MR environment. The prototype was quantitatively evaluated regarding the control accuracy in 20 measurements following a step-by-step protocol that we defined to standardize the measurement procedure. The results suggested that the differences between the target and actual positions were within the 10 cm range in three dimensions, which were considered sufficiently small regarding the typical crane operation use case of logistics purposes and could be improved with the adoption of robust registration and tracking techniques in our future work.
The conventional approach to dynamic analysis of ship motion response with shipboard operation equipment is usually done by establishing combined equations of motion of the multi-body system. The weakness of such methods is usually associated with the effectiveness of modelling and the simulation efficiency of computing the dynamic ship responses in waves in the time domain. In recent years, time domain simulation of nonlinear ship motion response in waves has become more and more popular. In this paper, we present coupled simulation of a heavy load crane with interactive ship motion responses in waves. The static gravitational forces of the crane system and dynamic excitation forces from the payload are applied to the ship as external forces on varying attack points of the hull during crane operations. Simulation of the crane operation is implemented in the digital twin ship platform and demonstrated meaningful physical behaviours.
This paper introduces a novel co-simulation framework running on the Java Virtual Machine built on a software architecture known as the Entity-Component-System. Popularised by games, this architecture favours composition over inheritance, allowing for greater flexibility. Rather than using a fixed inheritance tree, an entity is defined by its traits, which can be seamlessly changed during simulation. The framework supports the Functional Mock-up Interface standard for co-simulation, as well as the System Structure and Parameterisation standard for defining the system structure. Furthermore, the employed architecture allows users to seamlessly integrate physics engines, plotting, 3D visualisation, co-simulation masters and other types of systems into the framework in a modular way. To show its effectiveness, this paper compares the framework to four similar open-source co-simulation frameworks by simulating a quarter-truck system defined using the System Structure and Parameterisation standard.
This paper presents a novel approach for implementation of a digital twin for condition monitoring of a small-scale knuckle boom crane. The digital twin of the crane is simulated real-time in a nonlinear finite element (FE) program, where the estimated payload weight is used as an input. We implement an inverse method for estimation of the weight as well as its force vector direction based on physical strain gauge measurements. Additional strain gauges were utilized for validation of accuracy of the digital twin and inverse method. Based on a few physical sensor outputs, the digital twin allows for real-time determination of stresses, strains and loads at an unlimited number of hot spots. Therefore a digital twin can be an effective tool for predictive maintenance and product life-cycle management. In addition, condition monitoring of cranes during heavy-lift operations increases safety and reliability.
The presented approach is described in a general manner and is applicable for various robotic manipulators used in the industry.
This paper presents an object-oriented modeling (OOM) approach to model development of marine operation systems, specifically the hydraulic systems of marine cranes. Benefited from the rapid development of computation technology, many modeling and simulation techniques and software tools have proved to be very useful during the product and system development process. However, due to the increasing complexity of the physical systems, many challenges still exist regarding model flexibility, model integration, simulation accuracy, stability, and efficiency. The goal of introducing OOM to complex dynamic systems is to provide flexible, effective, and efficient models for different simulation applications. Previous work presented a virtual prototyping (VP) framework based on the functional mock-up interface (FMI) standard. The advantage of using FMI cosimulation is that modeling and simulation of stiff and strongly coupled systems can be distributed. As a result, the modeling tradeoffs between simulation accuracy and efficiency can be evaluated. The essential features of OOM and its application within dynamic operation system domain are highlighted through a case study. These features include model causality, model encapsulation, and inheritance that facilitate the decomposition and coupling of complex system models for co-simulation. The simulation results based on the proposed VP framework showed speedups in the computation efficiency at the cost of moderate accuracy loss.
Here, we present the concept of an open virtual prototyping framework for maritime systems and operations that enables its users to develop re-usable component or subsystem models, and combine them in full-system simulations for prototyping, verification, training, and performance studies. This framework consists of a set of guidelines for model coupling, high-level and low-level coupling interfaces to guarantee interoperability, a full-system simulation software, and example models and demonstrators. We discuss the requirements for such a framework, address the challenges and the possibilities in fulfilling them, and aim to give a list of best practices for modular and efficient virtual prototyping and full-system simulation. The context of our work is within maritime systems and operations, but the issues and solutions we present here are general enough to be of interest to a much broader audience, both industrial and scientific.
Both marine surface vehicles and underwater vehicles are often equipped with cranes, robotic manipulators or similar equipment. Much attention is given to modeling of both the dynamics of marine vehicles and the dynamics of manipulators, cranes and other equipment. However, less attention is given to the interconnected behaviour of the vehicle and the equipment, even though such equipment may have a considerable impact on the vehicle dynamic behaviour, and therefore risk, or conversely, the vehicle may have a considerable impact on the equipment dynamic behaviour. With main focus on ships equipped with cranes, this paper presents a framework for modeling the interconnected dynamics of rigid body systems, based on Lagrangian dynamics. The resulting equations of motion are implemented as a bond graph template to which any subsystem of interest, such as actuators, hydrodynamics, and controllers may be interfaced. An example on how this framework can be used in order to develop a high fidelity simulator of an offshore installation vessel with a heavy duty crane is presented. This work represents the first bond graph implementation of crane and vessel dynamics where the interconnections are modeled according to true physical rigid body principles without non-physical limitations such as diagonal mass-inertia matrix.
A research vessel (RV) plays an important role in many fields such as oceanography, fisheries and polar research, hydrographic surveys, and oil exploration. It also has a unique function in maritime research and developments. Full-scale sea trials that require vessels, are usually extremely expensive; however, research vessels are more available than other types of ship. This paper presents the results of a time-domain simulation model of R/V Gunnerus, the research vessel of the Norwegian University of Science and Technology (NTNU), using MARINTEK’s vessel simulator (VeSim). VeSim is a time-domain simulator which solves dynamic equations of vessel motions and takes care of seakeeping and manoeuvring problems simultaneously. In addition to a set of captive and PMM tests on a scale model of Gunnerus, full-scale sea trials are carried out in both calm and harsh weather and the proposed simulation model is validated against sea trial data.
Advanced offshore machinery, such as an offshore crane, usually involves several energy domains. Modelling and simulation of multi-domain systems is challenging because of not only the complexity in modelling of the related sub-systems but also the interfacing of these sub-models in an integrated model and the performance of simulating, especially when real-time simulation is required. This paper introduces a modelling approach for offshore crane operations based on the bond graph (BG) method. Specifically, the integrated model includes mechanical properties, hydraulic actuators and control algorithms. For the purpose of testing, particularly of advanced control algorithms, it is necessary and crucial to include the response of physical systems. In this paper, a flexible control algorithm for offshore crane operation, including functions of heave compensation and load anti-sway, was implemented.
The Functional Mockup Interface (FMI) is a tool independent standard for the exchange of dynamic models and for Co-Simulation. The first version, FMI 1.0, was published in 2010. Already more than 30 tools support FMI 1.0. In this paper an overview about the upcoming version 2.0 of FMI is given that combines the formerly separated interfaces for Mod-el Exchange and Co-Simulation in one standard. Based on the experience on using FMI 1.0, many small details have been improved and new features introduced to ease the use and increase the perfor-mance especially for larger models. Additionally, a free FMI compliance checker is available and FMI models from different tools are made available on the web to simplify testing.
This article presents a unified state-space model for ship maneuvering, station-keeping, and control in a seaway. The frequency-dependent potential and viscous damping terms, which in classic theory results in a convolution integral not suited for real-time simulation, is compactly represented by using a state-space formulation. The separation of the vessel model into a low-frequency model (represented by zero-frequency added mass and damping) and a wave-frequency model (represented by motion transfer functions or RAOs), which is commonly used for simulation, is hence made superfluous.
Digitalization has become a key aspect of making maritime industries more innovative, efficient, and fit for future operations. One of the most attractive aspects is the concept of
digital twins
, which refers to digital replicas of physical assets, processes, and systems that can be used as advanced tools for design, operation, and maintenance. This article introduces the development of the digital twin of the research vessel (RV)
Gunnerus
in Norway, which will be a significant scientific and operational achievement for the maritime industry, making efficient and safe offshore operations possible. It enables data exchange safely and easily among different subsystems, modules, and various applications. Thus, the twin ship can provide an integrated view of the ship’s various physical and behavioral aspects in different stages and allow simultaneous optimization of functional performance requirements. In addition, it enables advanced control and optimization, e.g., creating more reliable prediction for flexible objectives (time, output, emissions, fuel consumption), and executing day-ahead and long-term planning for operations. Several related applications are presented in the end to confirm the effectiveness of the digital twin ship system.
This paper presents a state-of-the-art digital twin of a hydraulic actuated winch that is used for heave compensation in offshore applications. The digital twin is used as part of a larger simulation model that involves all necessary components to perform lift planning and, subsequently, determine the corresponding weather window. The winch simulation model is described and verified by means of full-scale measurements. In addition, a set of acceptance criteria are presented that should be used whenever verifying digital twins of heave compensating winches that are to be used for lift planning.
Payload sway for shipboard cranes represents a significant safety concern for deck personnel. In this paper, a generalized trajectory modification strategy is presented that can be applied to a variety of different types of shipboard crane to allow the payload to maintain its desired position with respect to the ship deck in the presence of six degree of freedom (DOF) ship motion, and therefore appear stationary to deck personnel. Initially developed for a five DOF shipboard gantry crane, both a de facto proportional-integral-derivative (PID) controller and a sliding mode controller (SMC) are shown in simulation to be successful at tracking the modified trajectory. The PID controller shows a 64% reduction in the root-mean-square-error (RMSE) between the desired and actual payload positions with the addition of the trajectory modifier, and the SMC shows a 74% reduction. The ship is actuated with six degrees of freedom in the simulations; however, the trajectory modification anti-sway control system only requires the measurement of the ship’s roll and pitch angles.
The trajectory modifier is then applied to a six-DOF shipboard knuckle boom crane, with a dynamic model developed to include the mass and inertia of the actuators. The PID controller only shows a 38% reduction in RMSE and struggles to successfully track the trajectory due to the highly nonlinear dynamics of the knuckle boom crane. The SMC controller shows an 82% reduction in RMSE and appears capable of maintaining the desired payload position with the addition of the trajectory modifier.
To further extend the dynamic model of the knuckle boom crane, first-order transfer functions are applied to govern the response of each actuator. A state-of-the-art sliding mode controller is developed to provide stable control of the system, and shows an 84% reduction in RMSE with the addition of the trajectory modifier. The results therefore indicate that trajectory modification is highly effective at dampening payload sway for shipboard cranes, provided a suitable controller can be developed to allow the crane to accurately track the modified trajectory.
The authors present a virtual simulation of ships and ship-mounted cranes. The simulation is carried out in a Cave Automated Virtual Environment (CAVE). This simulation serves as a training platform for ship-mounted crane operators and as a platform to study the dynamics of ships and ship-mounted cranes under dynamic sea environments. A model of the (Auxiliary Crane Ship) T-ACS 4-6 was built, converted into an OpenGL C++ API, and then ported into the CAVE using DiverseGL (DGL). A six-degrees-of-freedom motion base was used to simulate the actual motion of the ship. The equations of motion of the ship are solved using the Large Amplitude Motion Program (LAMP), and the equations of motion of the crane pay load are numerically integrated; the interaction between the payload and the ship is taken into consideration. A nonlinear delayed-position feedback-control system is applied to the crane, and the resulting simulation is used to compare the controlled and uncontrolled pendulations of the cargo. Our simulator shows a great deal of realism and was used to simulate different ship-motion and cargo transfer scenarios.
This paper presents a digital twin simulation platform, “Nauticus Twinity”, with the vision of providing a more efficient verification scheme for the maritime industry. A digital twin of a vessel consists of a number of simulation models that are continuously updated to mirror its real-life twin. A key feature of the simulation platform is the open architecture allowing integration and co-simulation of models developed by DNV GL and our partners. The platform facilitates new tools for design, classification, verification, commissioning, condition monitoring, and decision-making throughout a vessel’s life cycle. The paper focuses on co-simulation and use of digital twins for the new build phase, and includes an example of how Nauticus Twinity can improve the commissioning and the verification process for complex integrated systems.
Presently, ship-mounted cranes are playing more and more important roles in modern ocean transportation and logistics. Different from traditional land-fixed crane systems, ship-mounted cranes present much more complicated nonlinear dynamical characteristics and they are persistently influenced by different mismatched disturbances due to harsh sea environments, e.g., sea waves, ocean currents, sea winds, and so forth; these unfavorable factors bring about many challenges for the development of effective control schemes. This paper presents a novel nonlinear stabilizing control strategy for underactuated ship-mounted crane systems. Specifically, some novel coordinate change procedures are first introduced to tackle the disturbing terms by transforming the original dynamics into a new form, which facilitates both controller design and stability analysis. After that, a nonlinear control law is constructed to regulate the cargo position to the desired location asymptotically, in the presence of ship roll and heave movements. The boundedness and convergence of the closed-loop signals are proven with Lyapunov-based analysis. To the best of our knowledge, this is the first closed-loop scheme that can achieve asymptotic control results, without linearizing/approximating the original nonlinear dynamics when performing controller design and stability analysis, for underactuated ship-mounted cranes with ship roll and heave movements. Hardware experimental results are included to show that the proposed control method can achieve satisfactory control performance and it admits strong robustness against external perturbations.
The installation and maintenance of offshore wind energy farms is a dangerous field of work. To increase the safety of these operations, the ongoing research project Safe Offshore Operations (SOOP), was launched in 2011. One objective of the project is the development and preparation of specialised simulator training scenarios for offshore personnel. Because of their high degree of realism, commercial simulators are used. Although these simulations are capable of modelling a wide range of situations physically correctly, the special demands of offshore operations on the simulation environment might exceed the boundaries of the implemented mathematical models. To ascertain the validity of the training sessions, custom simulations specialised on the problems at hand are developed and used for comparison with the results of commercial simulators. The current state of development of the implementation and its placing within the project SOOP is presented.
In this paper, an integrated computer simulator tool of rotary crane with ship behavior in consideration of ship sway and load sway is newly built to systemize the state analysis of a shipboard crane. The integrated simulator of shipboard crane was realized by cooperating a component of external force interface routine and fluid analysis software. A transfer control system is conducted by HSA (Hybrid Shape Approach) using STT (Straight Transfer Transformation) method and its effectiveness in suppressing the sway of both ship and load was confirmed by the simulation analysis. A shipboard crane operational training system which we call virtual coach teaching system, is also presented, in order to shorten the training period of amateur operators. The controlled inputs generated from HSA controller which are utilized as the ideal commands are then converted to drive a newly built teaching interface. Subjects are physically coached through the ideal motion of joystick by placing their hand on the teaching interface, thus giving them a kinesthetic understanding on how to transfer a load without exciting the sway of both the ship and load. Performance of subjects was measured in terms of transfer time by conducting an experiment using a newly built virtual driving simulator. Findings from this study indicate that virtual coach teaching is effective in training.
This paper analyzes the dynamics of an offshore boom crane and proposes a high-performance nonlinear controller to drive the system states to track some constructed trajectories. Specifically, by employing Lagrange's method in an attached frame, a dynamic model is obtained for the offshore crane system consisting of the boom and a payload, with specific emphasis on the effect of the vessel's motion on the payload swing. Based on the model, a novel nonlinear control law is designed for the underactuated boom crane, which makes the system states track some planned trajectories successfully, even in the presence of persistent disturbance in harsh sea conditions. The stability of the designed closed-loop system is proven by Lyapunov techniques. Simulation and experimental results are included to demonstrate that the proposed control method significantly reduces the impact of the disturbance in harsh sea conditions.
In this paper, the integrated computer simulator tool of rotary crane with ship behavior in consideration of ship sway and load sway is newly built in order to systemize the state analysis of a shipboard crane. The integrated simulator of shipboard crane was realized by corporating an external force interface routine of a component with Fluid analysis software. The transfer control system is conducted by HSA (Hybrid Shape Approach) using STT (Straight Transfer Transformation) method. The proposal method was confirmed to be effective in order to reduce both the sway of a ship and a load by the simulation analysis.
During offshore installations in harsh sea conditions, the involved crane system must satisfy rigorous requirements in terms of safety and efficiency. The forces resulting from the vertical motion of the vessel have an extensive effect on the overall crane structure and its lifetime. Moreover, vessel motion handicaps the operator during fine positioning of the payload. Hence, an active compensation system for the vertical vessel motion is proposed. An important point to consider for such systems is the time delay between the sensors and actuators, which diminishes performance. To compensate the dead times in the system, a prediction algorithm for the vertical motion of the vessel is proposed in the first part. In the second part, an inversion-based control strategy for the hydraulic-driven winch is formulated that considers the dynamic behavior of the drive system. A feedforward controller compensates the vertical-motion disturbance using the predicted motion. The proposed controller together with the prediction algorithm decouple the motion of the rope-suspended payload from the vessel's motion. The active compensation approach is evaluated with simulation and measurement results.
Mechanical systems with nonlinear geometry
- Dean C. Karnopp