This article studies the feasibility of using low-cost materials, techniques, and tools to manufacture a 1/100-scale model of a VLCC. For this purpose, three main aspects were considered to reduce the production costs: 1) the bypass to the fabrication of a mold, by building directly the final hull with mid-density fiber wood; 2) the use of a 3 degrees of freedom computer numerical control (CNC) milling machine to cut and shape the pieces of the hull, which can be easily rented at affordable prices; 3) the automation as much as possible of the process to avoid contracting highly skilled personnel to do manual tasks, which would increase substantially the fabrication costs. The article is based on the practical case study of the fabrication of the KVLCC2 (KRISO Very Large Crude Carrier 2) scale model, which is used to describe the digital models, the milling process, and the finishing work. At the end, the validation of the model is done by comparing the final physical hull surface with the original digital one. This study is mainly directed to small maritime research centers and/or universities, which are interested in performing maneuvering experiments with homemade ship scale models.

A thorough understanding of the interaction of waves with ships is a vital factor in the safe and economical technology design. Considerable advances have been made recently in the modelling of wave hydrodynamics and wave-structure interaction. Wave diffraction analysis using 2D Strip Theory (ST) or 3D Boundary Element Methods (BEM) based on potential flow theory is now standard with linear and second-order theory in the frequency domain. In case an assessment of a new ship roll stabilisation system of the gyroscopic type is seen as desirable, no ready to use numerical tool to predict the performance of the wave-structure interaction is available. Therefore, for smaller vessels with a certain advance speed, such a patrol boats or pleasure crafts further developments must be applied to a BEM method to take into account speed corrections plus a standard ST tool in order to include the roll stabilisation effect that could be attained using a dedicated gyroscopic roll stabilisation system installed aboard. In this framework, the proposed work consists of exploring the application of an adapted BEM method with speed corrections, plus a standard ST to study the wave-structure interactions of an unstabilised ship and a ship fitted with a Gyroscopic Roll Stabilisation (GRS) system by considering the case study of a small patrol boat in a seaway. The main objective of this study is to assess the performance of this GRS concept and calculate the operability index of this class of vessels (percentage of time the vessel complies with user pre-defined limiting criteria) for a certain design point using long term statistics, so that complex non-linear responses in waves will be neglected at this stage.

The paper presents the results of a comparison study between the Fourier and the Hartley transforms for the real-time simulation of the sea surface elevation in 3D. Fourier transforms are currently the most used and efficient method for obtaining realistic ocean scenes in interactive Virtual Environments. Although the Fast Fourier Transform has been the preferred choice for this type of simulations, the study reveals that the Fast Hartley Transform can be a valid alternative, and even have some advantages compared to the former. The study mainly focuses on the performance and memory aspects, which are decisive factors for real-time applications with ocean scenes, such as ship bridge simulators. The methodology to obtain the sea surface elevation in time domain from a sea state defined by a directional wave spectrum is also described. (C) 2018 Elsevier Ltd. All rights reserved.

This article addresses the main requirements and the process of creating the geometry of ship models that fulfil the highly demanding request for realism and performance of the virtual environments currently used in modern ship bridge simulators. It starts with a classification of the ships based on their role in the simulation and on the type of simulator used, and defines the main characteristics of the models. It also discusses the importance of a well-defined workflow and its impact on the modelling time and on the quality of the final product. The article provides contributions in the following areas: identification of the main requirements of polygonal models of ships for ship simulators; effective workflow for ship three-dimensional modelling and identification of most suitable modelling techniques for efficient creation of ship models. The study is supported by real examples of three-dimensional modelling of ships with different sizes and characteristics currently used by the ship manoeuvring simulator in the Centre for Marine Technology and Ocean Engineering of the University of Lisbon.

This paper presents the software architecture of an interface for real-time three-dimensional (3D) collision detection and determination in a maritime Virtual Environment. Interface classes, attributes and functions to compute the collision point, the moment of impact, and the local velocity and normal vectors of the surfaces at the collision point are described. If a physics application programming interface is available, these values can be used to estimate the objects’ responses to the collision. Within the scope of this work, a wrapper was developed and integrated in a 3D Ship Simulator prototype system.

The paper presents a software system for interactive 3D simulations of offloading operations commonly executed in offshore scenarios. The system was developed to simulate an LNG vessel approaching or departing from a FPSO unit or LNG tanker in 3D Virtual Environment. However, it has the capabilities of a global purpose manoeuvring simulator, including state of the art models of manoeuvrability, sea-keeping and sea surface simulations, which are integrated into the system. Additionally to common real-time physically based manoeuvrability simulators, this simulator also includes real-time ship motions calculations. The system architecture is composed of three main modules that support interaction and real-time data exchange with the integrated mathematical models. The manoeuvrability module allows the user to control the steering gear, the main engine and the bow thrusters, through the Virtual Environment. The seakeeping module computes wave induced ship motions in real-time according to ship's position, heading and speed, based on pre-calculated response amplitude operators. The sea surface module generates and simulates sea states defined by wave spectra. The system takes advantage of the programmable capabilities of the graphics processor units to increase the performance and realism of the simulations. The simulator may be used by operation planners and ship masters, as a tool for testing and training different offloading scenarios and approaching manoeuvres.

The paper describes a software system to simulate the ship motions in a crisis situation. The scenario consists of a damaged ship subjected to wave excitation forces generated by a random sea state. The simulation is displayed in an interactive Virtual Environment allowing the visualization of the ship motions. The numerical simulation of the sea surface and ship motions requires intensive computation to maintain the real-time or even the fast-forward simulations, which are the only ones of interest for these situations. Dedicated tools to analyse the ship behaviour in time are also described. The system can be useful to evaluate the responses of the ship to the current sea state, namely the amplitude, variations and tendencies of ship motions, and help the planning and coordination of rescue operations.

The paper presents the sequence of procedures and the main techniques used currently to build a digital geometric model of a ship that fulfils the high demanding requirements for realism and performance of modern 3D ship simulators. The work presented shows that some particular characteristics of a ship, often define how to apply these techniques. It also highlights the importance of a well-defined workflow, and discusses the impact that it may have on the modelling time and quality of the final product. The description of the procedures and subsequent discussion are supported by a real example of 3D modelling of a free fall lifeboat and a tugboat currently used in a ship manoeuvring simulator.

The paper describes a simulation system to support emergency planning decisions when ship flooding occurs. The events of grounding and collision are considered, where the risk of subsequent flooding of hull compartments is very high, and must be avoided or at least minimized. The system is based on a highly optimized algorithm that estimates, ahead in time, the progressive flooding of the compartments according to the current ship status and existing damages. Flooding times and stability parameters are measured, allowing for the crew to take the adequate measures, such as isolate or counter-flood compartments, before the flooding takes incontrollable proportions. The simulation is supported by a Virtual Environment in real-time, which provides all the functionalities to evaluate the seriousness and consequences of the situation, as well as to test, monitor and carry out emergency actions. Being a complex physical phenomena that occurs in an equally complex structure such as a ship, the real-time flooding simulation combined with the Virtual Environment requires large computational power to ensure the accuracy of the simulation results. Moreover, the distress normally experienced by the crew in such situations, and the urgent (and hopefully appropriate) required counter-measures, leave no room for inaccuracies or misinterpretations, caused by the lack of computational power, to become acceptable. For the events considered, the system is primarily used as a decision support tool to take urgent actions in order to avoid or at least minimize disastrous consequences such as oil spilling, sinking, or even loss of human lives.

Although interactive computer-generated ocean scenes based on real wave spectra are impressively realistic, they usually don't exhibit the original sea state's statistical properties. This might be unacceptable for applications in which the sea surface height field's correctness is important, such as 3D ship simulators for training professionals. Researchers have developed a discretization of the wave spectrum that obtains a sea state statistically more equivalent to the original. This method can also improve the scene's visual realism and real-time performance.

The paper describes the conceptual overview, interface specification and object models of a high level architecture framework for real-time simulation of ship towing operations in virtual environments. The framework is based on the IEE Standard for Modeling and Simulation and is composed by modules for generation and simulation of the sea surface, ship manoeuvrability, sea keeping and towing cable behavior. The simulation runs in a distributed virtual environment, with several nodes representing three main types of entities: tug vessel, towed ship and towed cable. The abstract nature of the framework allows the independent change and reuse of each module, mainly through class inheritance and function overriding.

The current paper presents a methodology to compute and represent the ship motions at interactive frame rates, when navigating on a virtual sea defined by a real wave spectrum. The Inverse Discrete Fast Fourier Transform algorithm is used to compute the sum of all ship motions components induced by the waves and get the final irregular ship motion. Currently, this is the most efficient method to simulate the ship motions in interactive ocean simulations using wave spectra to describe the sea states. The visual realism and physical accuracy of the simulations turns this method into a powerful tool for developing interactive ship

This paper presents the research and development work developed by the authors in the field of Visual Interactive Simulations in Maritime Scenarios. Real-time simulation and visualization of physical phenomena such as ship flooding, sea surface deformation and ship motions are addressed. Simulations in distributed virtual environments has been also a topic of research and is therefore presented and discussed. The work aimed mainly the study of new methodologies and techniques in 3D Computer Graphics, Real-time Simulation, Scientific Visualization and Human-Computer Interfaces to analyze and help finding solutions for Marine Engineering problems. The importance and advantages of such approach becomes clear with the development and testing of 3D tools where the physical accuracy and graphical realism are both important and must coexist in an interactive simulation.

This work describes a computer system developed for the fast parametric generation of a 3D model of ship hull structure. The system is intended to be used as a tool for generating an initial product model of the hull structures at the basic design stage. The model provides not only the geometry of the hull and the main structural systems but also data describing the arrangement of plates and stiffeners of the component panels, including scantlings, spacing and materials. The objective of the system is to generate and help to evaluate alternative structural configurations, producing information on total or partial weights and centres of gravity at different levels of detail. For the intended purpose, the ease and speed of generation of a model is much more relevant than a high geometric accuracy, and so it was adopted as a simplified geometric modelling, representing curved shapes with polygonal approximations. The modelling concepts and methodology are discussed and the architecture of the system is presented, describing the main components. Finally, some results are shown from the partial modelling of a real ship that was used for testing and validation of the system.

The decision support tool Virtual Ship is a virtual environment that supports emergency planning decisions in a ship's Damage Control Center. The model considers what could occur when fluids disseminate through a ship's compartments, such as flooding, fire, or contamination.

A survey of several Computer Graphics techniques used currently for wave generation and visualization of the sea surface in Virtual Environments (VE) is presented. A combination of sinusoidal and trochoidal wave functions with different parameters are used to generate several wave trains with diverse directions, frequencies and amplitudes in order to simulate the visual appearance of the ocean surface in different sea status. Supplementary visual effects such as wind, environment reflection, surface roughness, spray and foam may be added in order to increase the realism of the scenario. The scalability of the environment and the increase of performance are achieved with the use of vertex and pixel shaders for the calculation of the surface deformation and roughness respectively. The use of progressive meshes and projected grids as acceleration techniques to represent the sea surface allows extending it to a larger area.