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Numerical modelling of the Arctic ocean dynamics with real-time simulation capability is useful for designing, developing, testing, and validating the performance of Dynamically Positioned (DP) and Autonomous ships/offshore platforms. Advanced simulation technology needs to be developed to predict the expected loads on these systems due to the complex interactions with environmental disturbances. This paper presents models of waves, currents, wind, and ice that comply with the real-time simulation requirements and adequately capture the dynamic characteristics of the most relevant physical processes. A 3D dispersive numerical model is deployed to predict the wave parameters to be utilized to compute the wave loads on a ship with known Response Amplitude Operators (RAO). A uniform current load is then incorporated in a superposition manner by using a combined wave-current field dispersion relation capable of expressing the wavenumber of an interactive wave-current field. The mean and the gust wind components are added to the resultant force components. A multiple regression-based ice model is used to predict the loads caused by an ice field characterized by varied ice thickness, concentration, floe size, drift speed and directions. The stationkeeping performance of a generic DP-controlled ship subjected to environmental disturbances is evaluated for a range of environmental conditions. The proposed models can help design, develop, and evaluate dynamic positioning and autonomous ship controllers’ performance. Another application may be developing a realistic simulation environment to train conventional, DP-controlled and autonomous ship operators., 40th International Conference on Ocean, Offshore & Arctic Engineering, OMAE 2021, June 21-30, 2021, Virtual Conference, Online

Sea-ice observation and estimation of ice forces are becoming increasingly important with the increased activities in arctic water. Proper modelling of ice properties and forces is crucial in such cases to ensure safe operations, for example, Dynamic Positioning (DP). This work, therefore, aims at developing algorithms for image processing to extract useful ice properties and subsequently aid the modelling of ice load exerted on a floating platform or a ship. A robust algorithm capable of detecting closely connected and overlapped ice floes with various sizes and shapes is presented, which is the first step for accurate modelling of ice forces. To demonstrate the effectiveness of this approach, image frames processed from videos produced during an experiment using a model ship performed at the National Research Council’s Ocean Coastal and River Engineering Research Centre (NRC-OCRE) in Canada are used. Simulated ice floe images are also used to show the efficiency of the proposed model and compare it with other published work. The model will be extended further to extract and correlate other ice properties with the ice forces and develop a machine learning based ice force prediction model. The predicted force from that model will then be used as a feedforward to Dynamic Positioning (DP) controller with an aim to improve the performance of the controller.

The oil and gas companies extended their activities in the offshore area of the North Seas. The presence of extreme environmental waves imparts extra risks to the operations of the offshore fixed and floating structures in these areas. The operation and safety of these offshore structures are considerably disturbed during the propagation of large waves over the region. The Newfoundland coast experienced very high waves during an intense ever storm in 2018 that brought waves with very large wave heights at various locations. This paper reports the loadings of such high waves on the shaft of a Gravity-Based Structure (GBS). A 3D non-linear dispersive mass, momentum, and energy model (MME) with second-order in wave amplitudes, and OrcaFlex™, a commercial numerical tool are used for the simulation of loads on the structure. The 3D numerical model describes the characteristics of the wavefield in terms of mass, momentum, and energy flux conservation equations. OrcaFlex™ is a 3D non-linear time-domain finite element implicit and explicit software that uses lumped mass elements to simplify equations, has diffraction capability, and makes the computation efficient. In the simulations, parameters for incident wave conditions are varied systematically to study various cases and data comparisons between the two numerical simulators are made. The geometry of the GBS was kept constant. The water depth is assumed to be 80m and the shaft length is 95m with a diameter of 30m. The simulation is carried out for 3 hours in each case. New data and information that would be produced from this work are important for possible use in the design method of a GBS and thus increase structural and operational safety exclusively in the harsh environment or in the existence of freak waves.

Real time estimation of actual and imminent wave fields in the vicinity of ships and floating structures are important for safe and efficient operations. According to the relevant literature, three different approaches have been used practically: the use of wave buoys, ship radars (e.g. X-band and K-band radars) / satellite and ship motions. The present study employs artificial neural networks and machine learning type modelling to extend the previous research on neighboring wave field estimation to consider the relative heading between the ship and the waves. For the different cases evaluated, the proposed machine learning model showed very good prediction for relative heading. Some of the results from this study are presented in this paper., OCEANS 2021, September 20–23, 2021, San Diego, CA, USA

Presence of nomadic ice pieces of various sizes in the North Seas such as, in the Grand Bank area of Newfoundland and Labrador largely inflicts extra threats to the operations and stability of semisubmersible offshore structures (SOS). During stormy weather or in a situation of very large waves, the operation and safety of such SOS are extremely risked when ices pieces propagating alongside with the heavy waves. This paper reports initial findings for the effects of various large waves on the risk of occurrence and severity of ice pieces and topside collisions. OrcaFlexᵀᴹ is a commercial code utilized in this project as the numerical simulator. This is a 3D non-linear time-domain finite element implicit and explicit code that utilizes lumped mass elements to simplify equations and to enhance computational efficiency. The results obtained from the OrcaFlex code are compared with the results predicted by StarCCM+ full scale dispersive commercial code for an alike case. The comparisons of the data show a valuable data match., Oceans Conference & Exposition 2020, October 5th - 30th, 2020 [Held Virtually]

Real time estimation of actual and imminent wave fields in the vicinity of ships and floating structures are important for safe and efficient operations. Historically, three main approaches have been cited in the open literatures with varying degrees of accuracies: the use of wave buoys, ship radars (e.g. X-band and K-band radars) / satellite and ship motions. This paper presents two methods to predict approaching waves using ship motions by employing artificial neural networks and machine learning. Another method based on Short Time Fourier Transform (STFT) of the ship motion data was also used for cross comparison. Both methods were tested in head sea condition only with different ship speeds and sea states. The method based on machine learning estimates the wave elevations as time series, whereas STFT gives its estimates as spectrum. Both methods gave very good results.

There can be many benefits of accessing real time accurate estimates of the surrounding wave field for ships and floating structures. This knowledge is important for operational risk mitigation as well as the safety of the vessel and its cargo. In the open literature, wave buoys, ship radars (including X-band and K-band radars) / satellite scanning and hydrodynamic modeling using ship motions seem to be highlighted among the methods to measure / estimate wave field. In the present study, an alternative approach is developed using ship motions and recent developments in artificial intelligence, namely artificial neural networks and machine learning type modelling. In this paper, machine learning approach is introduced briefly, followed by a description of the artificial neural network model used. The paper reports the results obtained for a near shore science vessel in head seas with various ship speeds and sea states. The preliminary results show very good performance in wave field estimation compared to the actual one using machine learning approach with ship motions.

The motion of the ice pieces of various sizes in the Northern Seas such as, in the Grand Bank area of Newfoundland and Labrador always imposes extra risks to the operations of the offshore fixed and floating structures. In stormy weather, the operation and safety of such offshore structures are greatly affected when heavy waves propagate over the region with drifting ice pieces. This can cause damages to the structures when the interaction between those ice pieces and structures occurs. The range of severity of such damages depends on the harshness of the wave actions and the diversity of the ice pieces. In this paper, small ice pieces of different sizes are used in the simulations of interactions with an offshore Concrete Gravity Based Structure (CGBS). The motions of the ice pieces of various geometries and their dynamic impacts on the structures are studied. The simulations are carried out using a commercial numerical solver to predict the trajectory of the ice pieces around the structures, possible interaction with the CGBS and their consequent loadings on different elements of the structure at interest. The outcomes of the simulations obtained from single and multiple realizations of several wave conditions for the vertical impact loads due to ice pieces colliding with the topside so far. The initial results show that an increase of the significant wave height increases the number of collisions with the structure significantly. The magnitudes of the ice impact forces on the topsides did not follow the same trend. In each data set, the average of the highest one- third of the impact forces increases with the increase of Significant Wave Height / Air Gap ratios. The effects of variations in wave realizations for sea states are reported in the paper. The simulations also show the importance and possibilities of incorporating loads due to a collision of the ice pieces with the topside in the design process of such structures in the ocean., Oceans-2019, October 27-31, 2019, Seattle, Washington

Offshore oil and gas operations are being conducted in harsh environments such as offshore fields around Newfoundland and Labrador. The platforms used in these fields may be exposed to additional risks due the presence of drifting ice pieces in various sizes. To avoid a dangerous collision with a large floating ice, ice management and risk mitigation plans are required firstly. In case of smaller ice pieces (or bergy bits), if they collide with an offshore platform, the combined load of bergy bits and waves may be larger than the typical design wave loads. Hence, it is necessary to predict how these bergy bits may interact with a platform in a given sea state to estimate the combined load for developing a reliable design. In this paper, dynamic interaction between a moving bergy bit and a fixed offshore platform is simulated using CFD (Computation Fluid Dynamics) method. Trajectories and velocities of ice are simulated and compared to understand the hydrodynamic interaction by applying a series of different wave conditions such as wave period, height and relative incident peak location. The simulation outcomes show the importance and possibilities to apply it to the design process of such structures in the ocean., ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering, 17 June 2018, Madrid, Spain

A model of a compressed air energy storage unit is tested for tow-out and installation in the Ocean, Coastal & River Engineering (OCRE) Portfolio of the National Research Council of Canada (NRC). The proposed prototype accumulator is a cylinder of 36 m in diameter and 12 m in height, which will be installed at the bottom of Lake Ontario at about 60 m water depth. The model of the accumulator with scale 1:21.5 was fabricated at the Design and Fabrication Unit of NRC. Appropriate ballast systems were designed and applied for the tow out, installations and release mechanism tests. The model scale test was conducted to examine the hydrodynamic behavior of the accumulator during tow-out and set down operations. NRC’s Towing Tank and Offshore Engineering Basin test facilities were used for the tasks. In this paper only the installation case of the accumulator is reported and discussed. Relevant numerical simulations are also carried out. Comparisons of the numerical results with the experimental results show good agreement for the compared cases., ASME 2018 37th International Conference on Ocean, Offshore and Arctic Engineering, 17 June 2018, Madrid, Spain

Estimation of iceberg impact load is an important design consideration for offshore structures in ice prone regions. Impact velocity is influenced by the complex hydrodynamic interaction between the iceberg or bergy bit and the offshore structure. In order to understand the phenomenon, a two phase, experimental and numerical, study has been conducted. In the first phase, the change in wave loads on different sized spherical model ice masses was investigated for different proximities to a fixed structure and the results published in Sayeed et al. (2017b). This paper describes the results of the second phase study where the change in wave induced motions of free floating ice masses, approaching a fixed structure, is investigated through physical experiments and numerical simulations. The experiments were carried out at the Ocean Engineering Research Center (OERC) of Memorial University of Newfoundland and the motions were measured using an optical tracking system, Qualysis©. The objective is to determine the velocity profiles of approaching ice masses and how that changes prior to impact. The experimental results of motion data show excellent correlation with the force data gathered in the first phase. Similar to previous studies, the separation distance to wavelength ratio is shown to dictate the corresponding wave induced motions. As the body gets close to the structure, the surge motion slows and at the same time the heave motion is increased. Some experiments have also been conducted to understand the effect of initial starting location on the resulting drift velocity. Numerical simulations of the experimental cases, using the commercial CFD software Flow3D©, show good agreement with the experimental data.

Offshore oil and gas operations conducted in harsh environments such offshore Newfoundland may pose additional risks due to collision of smaller ice pieces and bergy bits with the offshore structures, including their topsides in the case of gravity based structures particularly in extreme waves. In this paper, CFD (Computational Fluid Dynamics) prediction for wave loads acting on a bergy bit around a fixed offshore platform is presented. Often the vertical column of a gravity based structure is designed against ice collisions, if operating in such an environment. In practices, topsides are usually protected by being placed sufficiently high from the still water level, away from the reach of the bergy bits. This vertical clearance between the still water level and the topside deck is known an air gap. Hence, the amount of the air gap planned for such an offshore structure is an important factor for the safety of the topsides at a given location. In this study a CFD method is applied to estimate the dynamic response of the bergy bit and provide a reliable air gap to reduce the potential risk of the bergy bit collision. In advance of more complex collision simulations using a free-floating ice for the airgap design, CFD analysis of wave load prediction on a stationary bergy bit is carried out and reported in this paper. In the experiments and CFD simulations, the location of the bergy bit is changed to quantify the change of wave load due to the hydrodynamic interaction between the bergy bit and the platform. Finally, the results of the CFD simulations are compared with the relevant experiment results to confirm the simulation performance prior to the free floating bergy bit simulations., ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering, 25 June 2017, Trondheim, Norway

A study on the loading of an oblique surface wave and a surface current field on a fixed vertical slender cylinder in a 3D flow frame is illustrated in the present paper. The three dimensional expressions describing the characteristics of the combined wave–current field in terms of mass, momentum and energy flux conservation equations are formulated. The parameters before the interaction of the oblique wave-free uniform current and current-free wave are used to formulate the kinematics of the flow field. These expressions are also employed to formulate and calculate the loads imparted by the wave–current combined flow on a bottom mounted slender vertical cylinder. In the present study two different situations are assumed where current is uniform over depth and also acting over a layer of fluid that extends from the free surface to a specified finite depth. In this paper we extend the approach considered in Zaman and Baddour (2004) for the wave–current analysis. Morison et al. (1950) equation is deployed for the load computations in all cases. The above models are utilized to compute the loads and moments on a slender cylinder for a wave with varying range of incidence current field.

In the present research, a 3D dispersive numerical model has been developed and utilized to study the modification of the wave field in the presence of offshore structure. The Alternating Direction Implicit (ADI) algorithm has been employed for the solution of the governing equations. Relevant experiments are carried out in the Offshore Engineering Basin (OEB) of National Research Council (NRC) Canada. OEB is a 3D heavy duty 75m × 32m × 2.8m test facility equipped with modern data acquisition and tracking devices to record experimental data. Total 10 wave probes are deployed to measure the data at different locations in the Basin. Later the numerical results are compared with the experimental results. The comparisons of the numerical results show great agreement with the experimental results., The ASME 35th International Conference on Ocean, Offshore and Arctic Engineering, OMAE2016, June 19-24, 2016, Busan, South Korea

After the termination of the wave making, the characteristics of the existing wave components in a 3D large scale Offshore Engineering wave Basin (OEB) at the National Research Council of Canada have been investigated experimentally. In the generation of any wave in the tank we get the relevant primary wave components along with bounded wave components if the incident primary wave has more than one frequency. Inevitably we also get interacted wave components, natural frequency components of the tank and other free waves. In this paper the tank's natural frequency components, bounded wave components and other free waves after the termination of wave making were investigated using several cases of mono- and bi-chromatic waves. These component energies were then compared with the total energy of the measured primary waves. The magnitudes of the residual undulations are also investigated for mono-, bi- and multichromatic waves over different time segments. Several sets of wave data are analysed to perceive the energy due to natural frequency of the basin, energy transferred to the side bands and the damping rate of the residual waves in the tank with respect to the chosen incident wave conditions. In the analysis it is observed that the energy damping rate varies with the incident wave condition but seems much faster than that of 20 minutes traditional waiting time in between two runs in the OEB. The energies for tank's natural frequency components and other free waves were found to be very small compare to the incident primary wave energies., ASME 2015 34th International Conference on Ocean, Offshore and Arctic Engineering, OMAE 2015, 31 May 2015 through 5 June 2015

A 3D dispersive numerical model has been developed and utilized to study the interacted wave field in the Offshore Engineering Basin (OEB) of National Research Council Canada in the presence of array of structures. The basic physics of the numerical model follows the concept of the depth averaged velocity distribution along with an enhanced dispersion relation. The Alternating Direction Implicit (ADI) algorithm has been employed for the solution of the governing equations. As an application, the model has been used to study the wave propagation in the presence of different combinations of structures where the effects due to the reflection and diffraction are also incorporated. Relevant experiments are carried out in the OEB. Total 10 wave probes are deployed to measure the data at different locations in the Basin. Later the numerical results are compared with the experimental results in the OEB at different probe locations for different wave and structure conditions. The comparisons of the numerical results show great agreement with the experimental results. In this paper the results for regular waves will only be presented and discussed., 2014 Oceans - St. John's, OCEANS 2014, 14 September 2014 through 19 September 2014

The experimental results of the interaction among wave, current and a submerged mound have been reported in this paper. This study is carried out for the cases where the wave is propagating in the following and the opposite direction of the current over a submerged mound of parabolic cross section. The phenomenon is investigated for varying forced currents, mound geometry and relative water depths. It is found that following current amplify the wave height over the mound but reverse current over the whole domain. Other results indicate that current of both directions affect the wave characteristics significantly over the mound.

A mathematical model is established to describe wave-current interaction over uneven sea bottoms. The basic equations of the model are obtained by vertically integrating the continuity equation and the equation of motion for flow over impermeable sea bed of mild slope. Finite difference method is utilized for numerical solutions and the results for a wave-current coexistent field over submerged mound show that the variation of the wave features is fairly significant due to the presence of the current which leads to remarkable drop of the mean water level over the mound and that the waves also affect the mean water level appreciably.

Accurate generation of the primary waves and the reproduction of the group-induced second-order low and high frequency waves have been considered essential for physical i.e. model test in the laboratory. In the laboratory when multi-chromatic primary waves are generated the required bounded waves will be generated naturally at the difference frequencies. In addition to that several unwanted free waves are also generated. The free waves, having the same frequencies of the bounded waves are reproduced due to mismatch of the boundary conditions at the wave paddle. The other two types of free waves are due to the wave paddle displacement and the local disturbances. We carried out physical experiments to identify the second order spurious waves in shallow water in the Offshore Engineering Basin (OEB) at the Institute for Ocean Technology (IOT) of National Research Council (NRC) Canada. In the basin water depths in the range of 0.4m to 0.6m are used for the experiments. The peak wave periods also have varied from 1.133s to 2.145s. In the experiments multi-chromatic waves are used. The drive signals of the wave-makers are generated using first-order and second-order wave generation techniques. Total 14 wave probes are used to capture the data in the wave tank. A NRC-IOT code is used to isolate the primary waves, the bounded waves and the unwanted free waves from the measured data at each wave probe. The measured data are analyzed in this paper to illustrate the differences in the waves generated by two different generation techniques., 30th International Conference on Ocean, Offshore and Arctic Engineering (OMAE2011), 19-24 June 2011, Rotterdam, The Netherlands, Series: ASME Conference Proceedings

Accurate generation of the primary waves and the reproduction of the group-induced second-order low and high frequency waves have been considered essential for physical model test in the laboratory. In the laboratory when bi-chromatic primary waves are generated the required bounded waves will be generated naturally at the difference frequency. In addition to that several unwanted free waves are also generated. The free waves, having the same frequency of the bounded wave are reproduced due to mismatch of the boundary conditions at the wave paddle. The other two types of free waves are due to the wave paddle displacement and the local disturbances. We carried out an extensive experimental program to identify the second order spurious waves in shallow water in the Offshore Engineering Basin (OEB) at the Institute for Ocean Technology (IOT) of National Research Council (NRC) Canada. In the experiments water depths are used in the range of 0.3m to 0.8m. The wave periods also have varied from 0.9s to 2.22s. In the experiments mono- and bi-chromatic waves are used. The drive signals of the wave-maker are generated using first-order and second-order wave generation techniques. Total 14 wave probes are used to capture the data in the wave tank. A NRC-IOT code is used to isolate the primary waves, the bounded waves and the unwanted free waves from the measured data at each wave probe. The measured data are analyzed in this paper to illustrate the differences in the waves generated by two different generation techniques., 29th International Conference on Ocean, Offshore and Arctic Engineering, 6-11 June, 2010, Shanghai, China

A vertically integrated 3D numerical model that uses the concept of depth average velocity distribution with enhanced dispersion characteristics investigates the propagation and transformation of mono- and multi-chromatic waves from a quasi-deep region to shallow water region. A finite difference method has been employed for the numerical computation that follows ADI (Alternating Direction Implicit) algorithm. The local sea bottom is uneven and turns into a moderately shallow water due to presence of a ridge-like bottom near the coast. The bottom configuration is from a location off Nova Scotia coast in Canada. Detail results and discussions are presented., 28th International Conference on Ocean, Offshore, and Arctic Engineering, 31 May - 5 June 2009, Honolulu, Hawaii

The evolution of long-crested surface waves subject to sideband perturbations is investigated with two different numerical models: a direct solver for the Euler equations using a nonorthogonal boundary-fitted curvilinear coordinate system and an FFT-accelerated boundary integral method. The numerical solutions are then validated with laboratory experiments performed in the NRC-IOT Ocean Engineering Basin with a segmented wave-maker operating in piston mode. The numerical models are forced by a point measurement of the free surface elevation at a wave probe close to the wave-maker and the numerical solutions are compared with the measured timeseries of the surface elevation at a few wave probe locations downstream., 27th International Conference on Offshore Mechanics and Arctic Engineering, 15-20 June 2008, Estoril, Portugal

Ocean current might be a useful tool to suppress ocean waves that approach a particular region of interest. A reliable short term sheltering approach might be enough in some areas where a heavy and/or permanent protection system is impractical, considering its usage, duration of deployment and money involved. This study is carried out using a 3D finite difference numerical model. The model is presently developed for long crested waves and uniform current by the vertical integration of the continuity equation and the equations of motion. A semi-implicit finite difference technique is employed for the discretization of the governing equations in time and space. Results are shown in terms of wave height distributions, reflection and transmission coefficients for varying currents, incident wave and current angles.Copyright © 2008 by ASME

A nonlinear numerical model has been formulated to study the propagation of a monochromatic surface wave. The model is formulated through the vertical integration of the continuity equation and the equations of motion. This model is investigated for wave propagation, velocity distribution, energy propagation and varying Courant, Friedrichs and Lewy's (CFL) condition. The applicability of this model for both shallow- and deep-water wave is also examined. The results and analyses are shown in details. The results obtained from the model are compared with the Stokes third-order wave theory and with the relevant experimental data.