Vilmar Æsøy

HOT SURFACE ASSISTED COMPRESSION IGNITION OF NATURAL GAS IN A DIRECT INJECTION DIESEL ENGINE

Burning natural gas in a direct injection diesel engine, requires a special arrangement to secure ignition. In this study a hot surface assisted ignition concept is investigated in a constant volume combustion bomb and a test engine with the objective to develop a better understanding of the mechanisms involved. The experiments show that surface temperature above 1,200 K is required to achieve acceptable ignition, strongly dependent on natural gas composition and system parameters such as injection and hot surface geometry. A mathematical model of the concept is also being developed. Numerical simulations combined with experiments allow one to look closer into the processes, and to expand the test matrix even outside the physical limits of the test engine. This paper will give an outline of the investigation including some results from experiments and numerical simulations. Furthermore some design features concerning interactions between the gas injection parameters and the hot surface will be discussed.

Flexible Modeling And Simulation Architecture For Haptic Control Of Maritime Cranes And Robotic Arm.

This paper introduces a modular prototyping system architecture that allows for the modeling, simulation and control of different maritime cranes or robotic arms with different kinematic structures and degrees of freedom using the Bond Graph Method. The resulting models are simulated in a virtual environment and controlled using the same input haptic device, which also provides the user with a valuable force feedback. The arm joint angles can be calculated at runtime according to the specific model of the robot to be controlled. The idea is to develop a library of crane beams, joints and actuator models that can be used as modules for simulating different cranes. The base module of this architecture is the crane beam model. Using different joint modules to connect several such models, different crane prototypes can be easily built. The library also includes a simplified model of a vessel to which the crane models can be connected in order to get a complete model. Related simulations were carried out using the so-called 20-sim simulator to validate efficiency and flexibility of the proposed architecture. In particular, a two-beam crane model connected to a simplified vessel model was implemented. To control the arm, an omega.7 from Force Dimension was used as an input haptic device.

Modelling And Simulation Of An Offshore Hydraulic Crane.

This paper presents a modeling approach based on Bond Graph (BG) method for offshore hydraulic crane focusing on its hydraulic system characteristics. A hydraulic library is built in the modeling software tool 20-sim using BG elements. The hydraulic submodels are designed according to one specific type of offshore crane, however, they can be easily modified and reused for other similar systems. BG method is a modelling technique for modeling of complex system by describing the energy flow inside the physical system. One of the main benefits of modeling using BG for the hydraulic system is the model provide interfaces to systems of other domains, for example, cooling system, mechanical model, control unit, etc. In this paper it is shown how an integrated BG model of the hydraulic system for a knuckle boom crane is derived and used for simulation. The simulation results proved the validation and effectiveness of the presented modeling approach for simulation of multi-domain systems. INTRODUCTION Cranes are found onboard almost all kinds of vessels and platforms for handling personnel and cargo. Cranes onboard vessels and platforms handling goods between the quayside and vessel or between vessels are normally referred to as offshore cranes. Cranes that are used for handling submerged loads as well e.g. launch and recovery of submersibles or installation of subsea hardware, are normally referred to as subsea cranes. Compare to land based cranes with a solid fixed base, offshore and subsea cranes are subject to significant dynamic forces from the resulting payload sway directly or indirectly caused by the vessel motion. As field testing in offshore industry is expensive and time consuming to carry out and constrained by many factors such as weather condition and vessel availability, modeling and simulation become a crucial part for product design, testing and analysis. On one hand, offshore cranes are mostly hydraulic actuated due to the consideration for stable performance and safety redundancy. On the other hand, it is rather delicate to model and control hydraulic systems because of the complex dynamic behavior and nonlinear aspect of fluid energy transfer. Many studies on hydraulic system modeling dedicated to one or several specific components. There are many software tools available for modelling and simulation of hydraulic systems. Modelling tools used in former researches include SimHydraulic from MathWorks (Vĕchet and Krejsa 2009), Easy5 from MSC (Li et al. 2011), SimulationX from ITI (En et al. 2013), 20-sim from Controllab (Aridhi et al. 2013), etc. These programs provide standard libraries for hydraulic components which can be parameterized and modified to certain levels. The generalized models are not designed for a specific system which means they might be over-complicated thus compromise the simulation efficiency. It is possible, to a certain level, to create new specific models for components that are not included in these libraries from these software tools, but that’s not always the best way. Take 20-sim as example, a hydraulic library is developed according to the Modelica hydraulic library. The library doesn’t include all the valves in a crane system. Instead of using BG elements, the models are written in a way which is difficult for the users to understand and edit. In this paper we present a modeling approach for offshore hydraulic crane system based on BG method. The submodels are created from scratch using basic BG elements and are completely open for editing as detailed as necessary depending on the simulation purpose. Another reason of choosing 20-sim as the modelling tool is using BG method complex systems, e.g. an offshore hydraulic crane, involving multiple energy domains can be modelled and integrated. The rest of the paper starts with introducing the basics of the BG method and the hydraulic system of the Proceedings 28th European Conference on Modelling and Simulation ©ECMS Flaminio Squazzoni, Fabio Baronio, Claudia Archetti, Marco Castellani (Editors) ISBN: 978-0-9564944-8-1 / ISBN: 978-0-9564944-9-8 (CD) kunckle boom crane. Then, the modelling of the main components using BG is described and the results from the simulation of the model are presented. Finally, the conclusion and future work is discussed. BOND GRAPH METHOD BG method as a general approach for modeling interacting systems is based on identifying the energetic structure in a system. A system can be decomposed into a few basic physical properties depending on what is going to be studied, and then the system can be described by interrelated idealized elements. The energy or power interaction between two elements is called a “power bond” represented by a half arrow. Another type of bond called “signal bond” represented by a full arrow indicates a signal flow at negligible power. A power bond is defined by two variables with generalized names of “effort” and “flow”, of which the product is power. Table 1 lists a number of energy domains and their corresponding power variables. Table 1 Common used BG energy domains Energy Domain Effort (e) Flow (f) Name Unit Name Unit Mechanical translation Force N Linear velocity m/s Mechanical rotation Torque Nm Angular velocity rad/s Electrical Voltage V Current A Hydraulic Pressure Pa Volume flow m/s Thermal Temperature K Entropy flow W/°C Magnetic Magnetomotive force A Flux rate Wb/s Chemical Chemical potential J/mol Reaction rate Mol/s Roughly speaking, the basic elements account for energy supply based on supply of effort and flow (Se-element and Sf-element), potential and kinetic energy storage (Celement, I-element), energy dissipation (R-element) and energy transform (TF-element) or conversion (GYelement). In addition to the basic elements describing the boundary components, the interconnection in between two elements is described using an ideal 1junction or 0-junction element, which neither store nor dissipate the energy. In brief, a 1-junction has equal flow on all bonds adjoining and the sum of efforts equals to zero, while a 0-junction is just the opposite: the effort is the same and the sum of flow is zero. The essence of defining an element is to establish the relation of the energy variables. Below Figure 1 so-called tetrahedron of state, illustrates the basic 1-port elements relating the energy variables (Pedersen and Engja 2008). Figure 1: Tetrahedron of state for basic 1-port elements OFFSHORE CRANE HYDRAULIC SYSTEM The hydraulic system of a common offshore knuckle boom crane is studied in this paper. The crane consists of three joints actuated by a hydraulic motor and two hydraulic cylinders (Figure 2). Figure 2: Offshore hydraulic knuckle boom crane When considering the complexity of the model, it is vital that the simulation can be done in real time. Thus the hydraulic system schematic is simplified to include only the main components at a level corresponding to the characteristics that shall be studied (Figure 2). The main components of the crane hydraulic system include a Hydraulic Power Unit (HPU), pipelines, valves (compensator, 4/3proportional direction valve, load control valve), cylinders, and motors. Figure 3: Hydraulic system schematic BOND GRAPH MODELING OF CRANE HYDRAULIC SYSTEM After identified the main components of the hydraulic system, in this chapter modeling of these components using BG elements is described. The hydraulic submodels are created based on the basic principles of fluid dynamics (ASSOFLUID 2007). To reduce the complexity of the overall model, the model of each component is also simplified. Fluid inertia and flexibility are dominant in the pipeline and cylinder chambers, thus neglected in the other components. As mentioned, BG method is modelling approach by describing the energy flow of the system. In the hydraulic domain, the key principle is to establish the connection of pressure and flow through the system. HPU (pump) The HPU of the crane mainly consist of a pressure compensated pump, which maintains a preset pressure at its outlet by adjusting its delivery flow in accordance with the pressure at any given time. If the system pressure is less than the pressure set point, the pump outputs its flow proportional to the pressure deviation. In the BG method a pump is modelled as a flow source element (Sf-element). The Sf-element has one output power port associated with the pump outlet. The effort and flow relationship is given by the following equations:

Distributed Co-Simulation of Maritime Systems and Operations

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.

Virtual Prototyping of Maritime Systems and Operations

While in aerospace and automotive industry, airplanes and cars are built in quantity, in maritime industry ships and offshore platforms are built uniquely such that even sister ships can be significantly different from each other. Hence, building a full scale prototype to test, verify, and demonstrate effectiveness of new innovative solutions, is not an option in maritime sector. Model testing and simulation of separate modules have been practiced in many applications successfully, however, capturing the complete interaction of different modules in a maritime system is not straight forward. To best of our knowledge, the modeling and simulation of a maritime system to the extent where the complete system, including the mutual interactions, is not accomplished yet. A maritime system incorporates a wide variety of components from different engineering fields and in order to develop a simulation framework for such a complex system, an interdisciplinary effort is needed from different branches of science including but not limited to hydrodynamics, machinery and power systems, structural engineering, navigation and control. This paper aims to introduce a joint effort from different research institutes, universities, and industrial partners to shed a light on the different issues in virtual prototyping in maritime systems and operations. It summarizes some of the available frameworks for virtual prototyping, and ends with a numerical simulation of a generic hull model coupled with propellers, propeller actuators, DP controller, thrust loss calculations, wind, waves and current, performed with the current implementation of our Virtual Prototyping Framework (VPF).© 2016 ASME

A Multi-Body Dynamic Model Based on Bond Graph for Maritime Hydraulic Crane Operations

This paper presents a bond graph model of a maritime crane lifting system comprised of a 3DOFs crane with three revolute joints, a winch, a segment of wire, and a pendulum load. The multi-body model contains the dynamic properties of the system and 3D animation of the operational behaviors. Lagrange’s method was used to derive the dynamic equations of the multi-body crane. Lagrange’s equations provide a clean elegant form for implementation using a special type of bond graph called IC-field. The model based on the bond graph contains interfaces to other domain models, e.g. input devices, control systems, hydraulic actuators, and sensors. Maritime crane operations are challenging due to the impact of heavy lifting, system stiffness and load sway resulted from the unstable working platform. The industry increasingly demands an overall virtual environment for modeling and simulation of maritime operations. The accomplishment will highly increase the efficiency and effectiveness of product and system design, new component and control algorithm testing, and operator training. The multi-body dynamic model is the core building block for modeling and simulation of maritime crane operations.Copyright

Integrated multi-domain system modelling and simulation for offshore crane operations

Abstract 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.

Lifting Operations for Subsea Installations Using Small Construction Vessels and Active Heave Compensation Systems: A Simulation Approach

Sub-sea installation operations require a high level of accuracy and control in order to avoid misalignment and possible collisions between modules on the sea bed. To reduce costs, smaller and lighter construction vessels are now performing these operations. The most critical parts of the operation are lift-off from the deck, passing through the splash zone, and landing sensitive equipment on the sea bed. The hazards are: high dynamic loads, resonance effects, and slack line snap. Therefore, in this study, modeling and simulation are applied to optimize design parameters and develop operational procedures for each operation to reduce risk of failure. Further, the same models can be used in operator simulator training.Modeling and simulation of interactive multi body systems is a rather complex task, involving the vessel as a moving platform, lifting equipment such as cranes and winches, guiding devices, lifting cables and payload behavior in air, all while partly to fully submerged. It is a multi-physics problem involving hydrodynamics, mechanics, hydraulics, electronics, and control systems. This paper describes an approach to link the different models to simulate the operations including interactions between the sub-systems. The paper focuses on the modeling approach used to connect the various dynamic systems into the complete operating system. The work is in its initial phase, and some of the sub-systems models are not complete. The models are described in this paper and will be included in future work. Some initial operational examples are included, to show how the models work together.Copyright

A Hardware-In-The-Loop Simulator For Offshore Machinery Control System Testing.

The paper presents a concept to develop a simulator for testing of the control systems of automated handling systems for offshore vessels. The concept is based on using Bond Graph for numeric modelling of physical systems, then implementing the model on a platform which can run and visualize simulations and communicate with the target control system in real time. A simulator is implemented and tested for a Launch and Recovery System (LARS) from Rolls-Royce Marine. The intention for this simulator is to provide a platform for development and testing of the control system without having a full scale physical system available, as that can be both practically difficult and an expensive way of performing testing. The simulator can also serve as a platform operational training as well as testing and monitoring the performance of the machinery system effectively, in particularly the characteristics of the hydraulic components during runtime.

Low Emission LNG Fuelled Ships for Environmental Friendly Operations in Arctic Areas

Environmental restrictions now favor cleaner fuels, and Natural gas (LNG) is one of the most promising alternative fuels. Highly efficient natural gas fuelled engines have been developed since around 1990. These engines are now entering maritime applications, offering significant emission reductions, both in a local and global perspective. Using LNG as fuel reduce NOx emissions by up to 90%, SOx and particulate matter (soot) are reduced by 95–100% and CO2 emissions are reduced by up to 25%, when compared to traditional marine fuels. These emission reductions are significant contribution especially in local and regional environments. Using LNG as a clean fuel also offers a significant increase in total energy efficiency. Combining power and heat generation, natural gas fuelled engines for on-shore power generation offer a total thermal efficiency of 80–90%, depending on the waste heat recovery rate. For liquid fuels exhaust heat recovery is limited due to the sulfur content, which may cause acid corrosion. Onboard ships, LNG fuelled engines have potential to utilize waste heat to obtain significant higher thermal efficiency than their diesel engine counterpart.LNG is mainly available from fossil sources, but now also increasingly from renewable sources as bio-gas. For storing and transportation LNG is preferred as less challenging compared to high pressure CNG. On the coast of Norway a LNG distribution system is now being built, supplying a fleet of more than 40 ships. LNG is transported by special designed small LNG carriers from the production plants to a series of main terminals along the coastline. From these main terminals the LNG is distributed by trucks to the local fuelling stations, or for direct fuelling of the ships.This paper will present the basic technology and experiences from this full scale LNG fuel system. The paper will discuss local and global environmental benefits, technical solutions, safety issues, and costs issues related to the distribution system and the on-board fuel installations.Copyright