The aim of the paper is to describe an industrial-academic collaboration whose main goal is the design of a new escort tug family characterized by high intact/damage stability margins, good maneuvering capability and stable behavior during escort indirect assistance. The project addresses three main research areas: hydrodynamic design of the hull with escort capability, simulation of the escort capabilities in different operational scenario, development of control logics that will allow autonomous or unmanned operations. The paper describes the methodological approach adopted for the design and will show some preliminary results. The results refer to the first part of the project. CFD calculations and towing tank tests have been performed onto a prototype tug hull in order to assess the hull design and to infer simulation models able to describe the behavior of a family of vessels. In particular, the propulsion and maneuverability aspects in escort operations are deeply investigated. Results of the project will form the bases for the conceptual application to a remotely controlled or autonomous escort tug.

Viscous effects on the low-frequency excitation force on column based platforms are significant in extreme waves. The wave drift force as calculated by a zero-current potential flow radiation/diffraction code becomes negligible for such waves. In the present study, the effect of current and viscous contributions on the slowly varying wave forces are adjusted by a formula developed in the Exwave JIP, see e.g. [1], which is validated against model test results. This paper presents numerical predictions of low frequency horizontal motions of a semi-submersible in combined high waves and current condition. In the simulation model, frequency dependent wave drift forces from radiation/diffraction code are modified by the formula. Static current forces and viscous damping are modelled by the drag term in Morison load formula using relative velocity between current and floater and with force coefficients as recommended by DNVGL-RP-C205 [2]. Low frequency surge responses calculated by the simulation model are compared with model tests for waves only and for combined collinear and noncollinear wave and current conditions.

This paper presents a dynamic analysis model where installation vessel in coupled with the riser system using the SIMA software. The model is used to assess risk and weather limitations for riser replacements performed with SIMOPRO (Simultaneous Marine Operation and Production). The SIMA model has been used in several complex riser replacement operations in the North Sea during 2017, and proven to be a vital support tool for decision making offshore. The analysis supported critical operational decisions that resulted in reduced weather downtime and enabled the marine operations to be completed in a safe and efficient manner, while the platforms were kept in production. In the planning phase the analysis model was used to test specific DP settings to minimize vessel footprint, optimize procedure steps and provide accurate limits to an Activity Specific Operating Guideline (ASOG). The model was further used to verify vessel and riser response subjected to various “emergency situations”, such as wire break and partial or full vessel black-out. The results were used to establish detailed contingency procedures. During the offshore operations, analyses were performed at regular intervals at the vessel with measured and forecasted weather data, to monitor vessel response and predict vessel drift-off trajectories in case of a vessel black-out scenario. The information provided by the DP recorder was fed back into the fully coupled analysis model where the Kongsberg Maritime DP settings were updated to reflect actual vessel system behaviour. The analysis model also provided vessel drift-off predictions in good agreement with real drift-off test results. With the optimized fully coupled analysis model it was then possible to perform simulations of the planned installation steps based on forecasted weather data.

Direct offloading operations from turret moored FPSOs are traditionally performed with dynamic positioned (DP) shuttle tankers with a bow loading hose and hawser line connected to the stern of the production facility. The hawser line restricts the mobility of the shuttle tanker which is often forced to point towards the FPSO. The inherent increased risk of collision in case of a forward drive-off incident has motivated a study for a hawser-less tandem offloading operation. The structural limits of the flexible loading hose allows for larger operational sector and heading flexibility which enables the shuttle tanker to point away from the FPSO and hence reduces the probability of collision. An analysis model with two representative vessels for offloading operations in the North Sea has been developed in order to investigate the new concept. The model includes a compiled version of the DP system core algorithm, extracted from the real time system of both vessels. The new offloading strategy, with heading offset away from the FPSO, has been implemented in an updated control algorithm for the shuttle tanker. Time-domain analysis of the complete tandem offloading system has been simulated with measured wind, waves and current from a HindCast data base. Heading and relative motion between FPSO and shuttle tanker has been extracted and statistically evaluated in order to determine the time for which the shuttle tanker is directed towards the FPSO. The paper demonstrates how a marine simulation model, including core algorithm of the actual DP system and numerous simulations based on historical measured environment, can be used to document the feasibility of a new offloading operation control strategy.

Different research groups have recently tested scaled floating offshore wind turbines including blade pitch control. A test conducted by the University of Stuttgart (Germany), DTU (Denmark) and CENER (Spain) at the Danish Hydraulic Institute (DHI) in 2016 successfully demonstrated a real-time blade pitch controller on the public 10MW TripleSpar semi-submersible concept at a scale of 1/60. In the presented work a reduced-order simulation model including control is compared against the model tests. The model has only five degrees of freedom and is formulated either in the time-domain or in the frequency-domain. In a first step the Morison drag coefficients are identified from decay tests as well as irregular wave cases. The identified drag coefficients depend clearly on the sea state, with the highest ones for the decay tests and small sea states. This is an important finding, for example for the design of a robust controller, which depends on the system damping. It is shown that the simplified model can well represent the dominant physical effects of the coupled system with a substantially reduced simulation time, compared to state-of-the-art models.

The effects of operational wave loads and wind loads on offshore mono pile wind turbines are well understood. For most sites, however, the water depth is such that breaking or near-breaking waves will occur causing impulsive excitation of the mono pile and consequently considerable stresses, displacements and accelerations in the monopile, tower and turbine. As has been shown in earlier, recent publications, Computational Fluid Dynamics (CFD) can be used to accurately analyze wave impacts on offshore wind turbines. However, it is not yet well suited to study the statistical variability of wave impact loads in long-duration sea states, and thus estimate the ULS and ALS loads for which a wind turbine has to be designed. An alternative, simplified approach, is the use of a Morison model in which the kinematics (water particle velocities and accelerations) from a nonlinear wave model are used. For long-crested waves the nonlinear wave model can be run in a 2D mode and is therefore relatively cheap. In this paper model tests for steep and breaking waves on an offshore wind turbine are compared with results from the Morison model. First, a deterministic comparison is made between the wave loads from the model tests and the simulation model (simulating the same 3-hour wave realization as in the basin), which turns out to be difficult because of differences between wave reflections in the wave basin (a physical beach) and the numerical wave model (absorbing boundary condition). Second, a statistical comparison is made by comparing with different wave realizations measured in the wave basin.

During the process of workpiece productions in metal forming industries, it is necessary to control the results of the reshaped piece to ensure its quality. A common procedure of metal plate forming processes is given by the application of an upper and lower die. Therefore, ribbed die configurations can be used. To simulate the forming process of metal workpieces, the Finite Element Method (FEM) is a feasible tool. In this paper, a parametric model of a ribbed die structure is developed with the specification that only small imperfections on the workpiece surfaces will appear after the forming process. The workpieces in this paper are plates with thickness values equal and greater than 20mm. Furthermore, the springback behaviour of the different workpieces will be in the main focus of the proposed analyses. The results of the simulations are used to developed different types of holder configurations instead of the lower die. This concept might further reduce the costs of forming processes of large metal plates.

During the research of propeller-ice contact process, we found that shadowing effect has great influence on the ice loads of propeller blade. Therefore, more study in the shadowing effect would be helpful to solve the complicated propeller-ice contact problem. A numerical simulation model is established based on the coupling of peridynamics and panel method in this paper, and ice force for the whole blade and for blade back and blade face separately are obtained through the calculation of the simulation model. The influence law to ice loads of shadowing effect would be revealed clearly by comparing the loads of blade face with the loads of blade back .On this basis, more research is carried out on the mechanism of shadowing effect. In addition, a new calculation formula for shadowing coefficient is put forward in this paper. The results show that the influence of shadowing effect on propeller loads is well predicted by the calculation result of shadowing coefficient formula.

The Arctic ocean has been the focus of increasing activities in oil and gas, marine traffic and fisheries as the resources in the Arctic area becomes more attractive for exploitation. There have been several studies on the response of ships and structures in ice covered waters, mainly for oil and gas applications. This paper presents a scenario simulation model for fisheries, crab pot retrieval, in partially ice covered waters. Snow crab fisheries in the Barents Sea is an ongoing commercial activity where partial ice covers may drift over crab pots which need retrieval. This scenario is unique in the sense that the ship and ice can be expected to experience wave forcing in addition to the ice–structure interaction. The complexity of such scenarios favor simplified models and a coupled simulation model consisting of ship hydrodynamics, ice hydrodynamics, ice–ice and ice–ship interactions. A case vessel is presented together with a scenario simulation model which is used to assess the ice impact forces during operations and the amount of ice interaction which can be expected in the region where the pot string is retrieved from the ocean.

Polymer flooding dates from the 1960s. Early applications targeted onshore medium-to-heavy oils up to 100 cP, with limited reservoir temperature and water formation salinity. The number of implemented polymer flooding projects followed oil prices. Since its early days, polymer flooding had overcome many technical obstacles. Advances in polymer manufacturing technology, cost reduction and the use of horizontal wells have pushed polymer flooding as a feasible EOR method. A better understanding of the physical phenomena associated with polymer flow through porous media and technology advancement have extended polymer flooding applications to more viscous oil, higher salinity, and temperature level, as well as to offshore prospects. Meaningful advantages of polymer flooding over conventional methods are consolidated in the literature, such as oil recovery anticipation, incremental oil recovery and reduced volumes of injected and produced water to reach a target recovery factor. Despite all technological advances, polymer flooding needs to be tailored for the specific conditions of the target reservoir. Collect and integrate laboratory, simulation, and field information are essential for a successful polymer flooding application. This paper aims to correlate critical information to the various stages necessary for polymer flooding evaluation and production forecast. First, successfully implemented field cases allow the establishment of ranges for the method application. Once the applicability of polymer flooding is certified, the polymer solution to be injected is designed according to the reservoir characteristics and target conditions. Laboratory tests are performed to determine phase mobilities, polymer retention, and polymer degradation. These parameters are assessed through different experiments, and normalized variables provide data integration. Once the required parameters are determined, it is possible to build a base simulation model. History matching this base model to the laboratory data certifies its validity. An upsized analysis of this model is required to include some degradation phenomena. The 1D laboratory model is extended to a 3D model that incorporates permo-porosity distributions to analyze well characteristics in their radius of influence. The final step is large scale simulation and production forecast. Data integration along each stage and among then all allow the tailoring of the polymer flooding to EOR. The use of normalized parameters to evaluate the results is useful for analysis at different scales, from the laboratory to the reservoir. The proposed workflow can contribute to the design, planning, evaluation, and implementation of polymer flooding in a target field.

This paper presents some outcomes from a four years (2013 – 2016) long research project investigating validation of ship specific simulation models. In contrast to the other initiatives such as SIMMAN 2008 [1] and SIMMAN 2014 [2], the R&D project “Sea Trials and Model Tests for Validation of Shiphandling Simulation Models” (SIMVAL [3]) investigates model development and validation methods for specific vessels. For these vessels, the yard’s documentation of manoeuvring characteristic was available for the researchers. In addition, the project has been given permission to perform different sets of sea trials on selected case vessels. As far as possible, these sea trials were designed to document vessel-specific operations such as low-speed manoeuvres and dynamic positioning. Other papers presenting results from the SIMVAL project will be given in a separate session, Session 12–14, in the Torgeir Moan Symposium at OMAE2017.

This paper presents the applications of an efficient hybrid time-domain simulation model for predicting moored Sevan-floater motions in irregular waves and finite water depth. The irregular incident waves are modeled by the extended Boussinesq equations, which can capture wave-wave interactions and the low-frequency long waves accurately in finite and shallow water depth. By imposing the incident wave kinematics on the surface of the floater, a panel model based on Rankine source method is applied for the calculation of wave forces and corresponding floater motions. The contributions from low-frequency components in incident waves as well as their diffraction effects are included in the wave force calculations. Validation of the irregular waves simulated by the present numerical model are performed against experimental data. Then, the simulated moored floater motions are compared with model test results and results based on Newman’s approximation. The general good agreements with experimental results demonstrate the present model can be used as an alternative for this problem while Newman’s approximation shows non-conservative results.

This paper represents the condensed version of an original Master Thesis written in 2016 [1]. The main aim lays in the structural analysis of Tension Leg Platforms (TLP) as support structures for Floating Wind Turbines (FWT). Special focus is given to a methodology study of different static analysis methods for components of a FWT support structure by Finite Element Method (FEM). The analysis considers Ultimate Limit States (ULS) only. Based on a given open source TLP design [2], the support structure is fragmented in its components. Each component is categorized, based on whether it can be analyzed by parametric equations or by computational methods. For the components, verifiable by parametric equations, the relevant standards are examined. The analysis of the decomposed support structure shows that existing standards can be applied for many of the components. One specific tubular joint of the support structure is selected and analyzed by computational methods. Considering the complexity of Finite Element Analysis (FEA) for FWT, the performed methodology study compares and evaluates various simulation methods on how loads are applied onto the structure. The methodology study results show that for ULS consideration, all load driven simulation methods are generally applicable. In the prospect of fatigue analyses further developments and improvements are considered crucial. This especially includes a better coherence of the stiffness representation between global load simulation model and local structural analysis model.

Nowadays, there are more ships equipped with on-board monitoring systems and vessels with many sensors are becoming a standard. Available measurements can be employed for system optimization which play an important role in the vessel power plant configuration. The improvements in the power system design can be based on theoretical (modeling based on physical and empirical laws — for simulation purposes, for example [1]) or data-driven modeling (machine learning, statistical approach [2]). The data-driven models can be supportive confirming theoretical assumptions or simplifications from simulations. They are also helpful to understand the real systems, including vessel dynamic behavior and interactions. Therefore, the combination of simulation and data-driven modeling will be beneficial by identifying relationships that help explain unidentified variations. This approach is recommended when aiming for a more reliable tool for design optimization and to overcome the limitation of the simulation models that all system properties and dynamic effects must be known beforehand. The scope in this work is to present a potential synergy between the simulation and the machine learning approach. A data-driven method can be complementary to a model based on physical and empirical laws. This is shown in the example of power plant model connected with a thruster and vessel model to simulate the typical transit scenario and the data-driven model. The paper proposes a simultaneous analysis of the theoretical and machine learning models to predict the vessel power/speed and study the complex systems’ interactions in more detail, which are essential while exploring the system behavior.

Increased competition and low oil prices coupled with promising prospects for new oil and gas (O&G) reserves in the Arctic region has led to expansion of activities into the offshore Arctic. This brings along new challenges for the offshore logistics that need to be addressed. These challenges impose more stringent requirements for the logistics system setup, especially on the design and operation of vessels. Copying the logistics system and vessels designed for the North Sea operations is not a sustainable way forward. The few existing studies related to Arctic logistics mainly focus on ship technology solutions for cold and ice infested areas or solutions to the area-specific operational challenges for shipping companies. However, there is a need to understand how these solutions are connected and impact each other in a larger offshore supply logistics system, and thus address the challenges of Arctic logistics as a whole. A methodology for quick evaluation of the feasibility and costs of the logistics system in the early stages of offshore supply planning was developed and presented in previous research [1]. It allows for testing the effects of using alternative ship designs and the overall supply fleet composition on system’s cost and performance while satisfying prospective campaign requirements. Safety standards and requirements for emergency preparedness and environmental performance are taken into account while cost effectiveness of the logistics system as a whole is the main quantifiable measure. Building on the new methodology a simulation tool for remote offshore operations has been developed and is presented in current work. Simulation models allow us to consider the dynamic and uncertain nature of variables, such as variation in weekly transport demand, weather impact on sailing times and fuel consumption, and schedule deviations. The evaluation of the performance of a logistic system is done by simulating the logistic operation over a large number of scenarios. Input parameters are weather data generated from historical observations and probability distributions for transport demand. Output from the tool are key performance indicators for: system costs, logistic robustness and emergency preparedness. The tool consists of three main components: simulation of a regular supply logistics operation, simulation of emergency situations, and visualization of the simulated operations. The proposed methodology and tool are tested on real-life cases for offshore supply planning of drilling campaigns in remote areas for one of the major international O&G operators.

Basic principles of the multidisciplinary approach to arctic marine transport systems (MTS) design and analysis are described in the article. The main idea of the approach is to synthesize geographic information system (GIS) technologies, different shipbuilding disciplines, fleet planning instruments and agent-based dynamic simulation models in an integrated software framework on the basis of object-oriented programming. Vessel operation is described as the movement and interaction of independent ships in GIS environment within the framework of the simulation model. MTS operation combines vessel operation itself (routing, determination of speed and fuel consumption, icebreaker escort, etc.) with plenty of external entities (port infrastructure, ice channel freezing process, offshore platform operation, etc.) that could be described as systems with comprehensive logic and physical behavior. Such integration provides a new quality of MTS simulation that allows considering complex interconnection of various subsystems and all the important details of each MTS project. The outline of the program framework to realize such an approach is given, and two case studies are described to demonstrate its capabilities and feasibility.

The present work investigates the transitional flow around a smooth circular cylinder at Reynolds number Re = 140,000. The flow is resolved using the viscous-flow solver ReFRESCO, and distinct mathematical models are applied to assess their ability to handle transitional flows. The selected mathematical models are the Reynolds-Averaged Navier-Stokes equations (RANS), Scale-Adaptive Simulation (SAS), Delayed Detached-Eddy Simulation (DDES), eXtra Large-Eddy Simulation (XLES) and Partially-Averaged Navier-Stokes (PANS) equations. The RANS equations are supplemented with the k–ω Shear-Stress Transport (SST) with and without the Local Correlation Transition Model (LCTM). The numerical simulations are carried out using structured grids ranging from 9.32 × 10 4 to 2.24 × 10 7 cells, and a dimensionless time-step of 1.50 × 10 −3 . As expected, the outcome demonstrates that transition from laminar to turbulent regime is incorrectly predicted by the k–ω SST model. Transition occurs upstream of the flow separation, which is typical of the supercritical regime and so the flow physics is incorrectly modelled. Naturally, all Scale-Resolving Simulation (SRS) models that rely on RANS to solve the boundary-layer, called hybrid models, will exhibit a similar trend. On the other hand, mathematical models capable to resolve part of the turbulence field in the boundary layer (PANS) lead to a better agreement with the experimental data. Furthermore, the k–ω SST LCTM is also able to improve the modelling accuracy when compared to the k–ω SST. Therefore, it might be a valuable engineering tool if its computational demands are considered (in the RANS context). Therefore, the results confirm that the choice of the most appropriate mathematical model for the simulation of turbulent flows is not straightforward and it may depend on the details of the flow physics.

To optimize tower design it is desirable to relax the constraint of having to place natural frequencies outside the rotor and blade passing frequency-bands. A speed exclusion zone algorithm is tested to assess its effectiveness on preventing tower resonance caused by 3p thrust oscillations. The effect of the speed exclusion zone algorithm on power output is also considered. A simulation model adequate for qualitative testing of the algorithm is developed and implemented in the simulation tool Simulink by MathWorks. The model is based on a 10MW offshore wind turbine and includes a simplified representation of rotor aerodynamics, drive-train and generator dynamics and a two-dimesional finite element representation of the tower and support structure. To support simulations a rotor speed controller is implemented together with wind models accounting for wind shear, tower shadow, turbulence and rotational sampling. A significant reduction in tower vibration is seen with a ±10% speed exclusion zone. A exclusion zone width of ±5% is shown to increase tower vibrations in some cases. The speed exclusion zone algorithm will lead to a reduction in power output for a ±10% and ±15% speed exclusion zone. For the ±5% speed exclusion zone no significant change in power output is observed.

In this paper, a numerical model of a braceless semi-submersible floating wind turbine (FWT) is calibrated against model test data. Experimental data from a 1:30 scaled model tested at MARINTEK’s Ocean Basin in 2015 using real-time hybrid model testing (ReaTHM) is used for the calibration of the time-domain simulation model. In these tests, aerodynamic loads were simulated in real-time and applied to the physical model. The simulation model is based on the as-built model at full scale. The hull and turbine are considered as rigid, while bar elements are used to model the mooring system in a coupled finite element approach. Frequency-dependent added mass, radiation damping, and excitation forces/moments are evaluated using a panel method based on potential theory. Distributed viscous forces on the hull and mooring lines are added to the numerical model applying Morison’s equation. The viscous drag coefficients in Morison’s equation are calibrated against selected test data, including decay tests in calm water and test with irregular waves. Simulations show that the drag coefficients change when waves are present. Aerodynamic loads are included as time varying loads applied directly at the hub based on the actual physical loads from the experiment. This way, uncertainties related to the aerodynamic loads in the calibrations are removed. The calibrated numerical model shows good agreement with experimental data.

As the global demand for energy is increasing, oil and gas exploration is moving further north to more remote areas. Offshore activity in these areas is challenging. Arctic-specific environmental conditions, long distances from onshore facilities and general lack of infrastructure are some of the challenges faced. Therefore, new and more robust solutions — both on technological and operational side — are required before commencing operations safely in these areas. In this paper, a helicopter emergency response capacity — with respect to prevailing wind conditions — for operations in the Barents Sea is studied and a method for mapping the rescue capacity in the given area is presented. The goal is to develop a method capable of assessing the probability of a successful rescue at different locations within given time requirements and under prevailing wind conditions. This is accomplished using a simulation model capable to determine how the wind speed and direction affect the search and rescue helicopter operations in the Barents Sea. The simulation model uses historical wind data along a potential route as input for evaluating the flying time to different locations in an area under the given wind conditions. In addition to the wind conditions, the variation in recovery time, and mobilisation time is implemented into the simulation model. By running the simulation model multiple times, probability distributions of the number of personnel which can be recovered within the given time requirements are established. This information is then used to plot isocurves of equal rescue probability on top of a map of the Barents Sea. Based on the results, it is concluded that wind conditions have significant effect on rescue capacity of a helicopter, and thus thorough weather observations should be made before establishing a search and rescue system for a given area.