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The modelling of wave-structure interaction (WSI) has significant applications in understanding natural processes as well as securing the safety and efficiency of marine engineering. Based on the technique of Computational Fluid Dynamics (CFD) and the open-source simulation framework - OpenFOAM, this paper provides a state-of-the-art review of WSI modelling methods. The review categorises WSI scenarios and suggests their suitable computational approaches, concerning a rigid, deformable or porous structure in regular, irregular, non-breaking or breaking waves. Extensions of WSI modelling for wave-structure-seabed interactions and various wave energy converters are also introduced. As a result, the present review aims to help understand the CFD modelling of WSI and guide the use of OpenFOAM for target WSI problems.

Parametric excitation in the pitch/roll degrees of freedom (DoFs) can induce dynamic instability in floating cylinder-type structures such as spar buoys, floating offshore wind or wave energy converters. At certain frequency and amplitude ranges of the input waves, parametric coupling between the heave and pitch/roll DoFs results in undesirable large amplitude rotational motion. One possible remedy to mitigate the existence of parametric resonance is the use of dynamic vibration absorbers. Two prominent types of dynamic vibration absorbers are tuned mass dampers (TMDs) and nonlinear energy sinks (NESs), which have contrasting properties with regard to their amplitude and frequency dependencies when absorbing kinetic energy from oscillating bodies. This paper investigates the suppression of parametric resonance in floating bodies utilizing dynamic vibration absorbers, comparing the performance of TMDs against NESs for a test case considering a floating vertical cylinder. In addition to the type of dynamic vibration absorber utilized, the paper also examines the DoF which it acts on, comparing the benefits between attaching the vibration absorber to the primary (heave) DoF or the secondary (pitch) DoF. The results show that the TMD outperforms the NES and that it is more effective to attach the vibration absorber to the heave DoF when eliminating parametric resonance in the pitch DoF.

This study pertains to analysing the dynamical behaviour of a floating body undergoing parametric resonances. A simple vertical cylinder, representing a classical spar-buoy, is considered, limiting its motion to heave and pitch degrees of freedom. Its geometry and mass distribution are chosen such that a 2:1 ratio of heave to pitch/roll natural frequency makes the spar-buoy prone to parametric resonance. The system is then studied by the shooting method, combined with a pseudo-arclength continuation, and the harmonic balance procedure. Results show that an extensive bistable region exists, where stable parametric resonance coexists with a regular resonance response. The analysis also unveiled the existence of stable quasiperiodic motions existing in correspondence of both pitch and heave resonance. Results are qualitatively validated using a model based on the explicit nonlinear Froude–Krylov force calculation.

The oscillating‐water‐column (OWC) spar‐buoy is a type of wave energy converter that may exhibit undesirable large roll and pitch amplitudes caused by a dynamic instability induced by parametric resonance. The occurrence of this phenomenon not only reduces the power extraction but significantly increases the structural loads on the buoy, the turbine rotor and on the mooring system. The paper compares the parametric resonance behaviour of two configurations of an OWC spar‐buoy using experimental data obtained in a wave flume at a scale of 1:100. The configurations investigated were: (1) closed and (2) fully open‐air chamber. The experimental tests covered a wide range of regular and irregular waves, as well as in free decay experiments. Results showed that opening the air chamber reduces the coupling between the buoy and the OWC within, thus shifting the damped natural heave frequency of the system in comparison with the closed chamber configuration. This effect changes parametric resonance characteristics of the two configurations due to the coupling between roll/pitch and heave modes. Moreover, for specific wave frequencies, the occurrence of parametric resonance observed when the chamber is closed do not occur while the air chamber is fully open. These results suggest the possibility of controlling a pressure relief valve installed on top of the device to reduce parametric resonance whenever this dynamic instability is detected.

International audience; The paper presents results from the Collaborative Computational Project in Wave Structure Interaction (CCP-WSI) Blind Test Series 2. Without prior access to the physical data, participants, with numerical methods ranging from low-fidelity linear models to fully non-linear Navier–Stokes (NS) solvers, simulate the interaction between focused wave events and two separate, taut-moored, floating structures: a hemispherical-bottomed cylinder and a cylinder with a moonpool. The ‘blind’ numerical predictions for heave, surge, pitch and mooring load, are compared against physical measurements. Dynamic time warping is used to quantify the predictive capability of participating methods. In general, NS solvers and hybrid methods give more accurate predictions; however, heave amplitude is predicted reasonably well by all methods; and a WEC-Sim implementation, with CFD-informed viscous terms, demonstrates comparable predictive capability to even the stronger NS solvers. Large variations in the solutions are observed (even among similar methods), highlighting a need for standardisation in the numerical modelling of WSI problems.

The purpose of this study was to determine the effect of adding CIDAA to a subpopulation of an HMO that also had an RPM program. Patients taking insulin for >6 months with A1Cs >8.0% were selected from 3 cohorts, RPM + CIDAA (Group A) , RPM alone (Group B) and usual care (Group C) and followed for 6 months. Glucose readings of Group A patients, given a Bluetooth-enabled glucometer, were analyzed with dose adjustment recommendations sent to their providers (2 MDs, 1 PA) that they could accept or modify. Health educators contacted Group A and B patients for each RPM glucose value of 200 mg/dl and counseled them how to avoid subsequent episodes. Non-insulin drugs were not allowed to be added to Group A and B patients. A1C levels were measured at baseline and 6 months. Patient demographics, their A1C responses and alerts are shown in the Table. There were no differences among baseline A1Cs but significant differences from baseline. Groups A vs. B (P = 0.01) and A vs. C (P = 0.001) were significantly different but not B vs. C. All alerts (P = 0.02) and those >200 mg/dl (P = 0.002) were significantly less in Group A vs. B but alerts Disclosure J.S.Pulicharam: None. J.Davidson: None. M.B.Davidson: Other Relationship; Mellitus Health. Funding Mellitus Health, Inc

Measurement uncertainties are inevitable during physical wave tank tests. Therefore, when validating a numerical wave tank against experiments, knowledge of the uncertainties in the physical experiments, and the sensitivity of the body dynamics to such uncertainties, is crucial. Specifically, the inertial properties, as well as the location of the centre of mass (CoM), which are challenging to measure accurately, can have a significant influence on the system dynamics. On the basis of test cases of the Collaborative Computational Project in Wave Structure Interaction Blind Test Series 2, this paper presents a sensitivity analysis of the agreement between experimental and numerical data sets to the quality of the incident, focused wave, as well as the inertial properties and the location of the CoM. A significant influence on the modelled system dynamics can be observed when changing the system parameters, resulting in a variation of the observed error of up to 80 percentage points for pitch motion.

During the development and optimisation of wave energy converters, numerical wave tanks are useful tools, providing detailed insight into the hydrodynamic performance of devices. Specifically, computational fluid dynamics (CFD)-based numerical wave tanks (CNWTs) can deliver high-fidelity, high-resolution results for a wide range of test conditions. However, CNWTs come at significant computational cost and require more man-hours during model setup, compared to lower-fidelity, frequency domain-based models. The computational costs can only be significantly decreased by improving the numerical solvers or by increasing expenditure on computational power. The required man-hours for the model setup, however, can be reduced by streamlining the setup of CNWTs. To this end, the formulation of best-practice guidelines can expedite this streamlining. A step toward such best-practice guidelines is blind tests. This paper presents the CNWT used for the authors’ contribution to the Collaborative Computational Project in Wave–Structure Interaction (CCP-WSI) Blind Test Series 3. In the employed numerical wave tanks, a self-calibrating impulse source wave maker is implemented for wave generation. In addition to the numerical results, and the comparison with the recently disclosed experimental data, the paper presents the spatial and temporal convergence studies, as well as results for the numerical wave maker calibration. The numerical results show average deviations with the experimental data of less than 10%. Furthermore, a correlation between the accuracy of the numerical replication of the wave and the agreement between numerical and experimental device motion is highlighted.

Reviewing the literature of CFD-based numerical wave tanks for wave energy applications, it can be observed that different flow conditions and different turbulence models are applied during numerical wave energy converter (WEC) experiments. No single turbulence model can be identified as an `industry standard’ for WEC modeling. The complexity of the flow field around a WEC, together with the strong dependency of turbulence effects on the shape, operational conditions, and external forces, hampers the formulation of such an `industry standard’. Furthermore, the conceptually different flow characteristics (i.e., oscillating, free surface flows), compared to the design cases of most turbulence models (i.e., continuous single-phase flow), can be identified as a source for the potential lack of accuracy of turbulence models for WEC applications. This communication performs a first step towards analyzing the accuracy and necessity of modeling turbulence effects, by means of turbulence models, within CFD-based NWTs for WEC applications. To that end, the influence of turbulence models and, in addition, the influence of the initial turbulence intensity is investigated based on different wave–structure interaction cases considering two separately validated WEC models. The results highlight the complexity of such a `turbulence analysis’ and the study suggests specific future work to get a better understanding of the model requirements for the flow field around WECs.

This paper addresses the issue of hydrodynamic model identification from recorded tank test data, for a prototype wave energy device. The study focusses on nonlinear Kolmogorov–Gabor polynomial models, with linear models also used as a baseline reference. Six different experimental data sets are employed for model identification and validation, all derived from a JONSWAP input sea state. Compared to identification on numerical data, this study shows that the determination of model structure and orders is not so straightforward, but that consistent and useful computationally efficient models can be obtained. For the particular tests undertaken, in which the prototype device generally behaves as a wave follower, the nonlinear models only show very marginal performance improvement over the linear ones.

The modelling of ocean waves is an integral part of coastal and offshore engineering. Both theoretical and experimental modelling methods are available and are commonly used in support of each other. In particular, due to the difficulty in measuring the velocity throughout the water column, the wave kinematics are often derived, by means of wave theory, from a measurement of the free surface elevation. However, wave theory is often based upon idealistic conditions, such as infinite spatial domains and time lengths. The question therefore arises, how well are the wave kinematics in an experimental wave tank described by wave theory? The present paper compares theoretical solutions against experimental data, for the free surface elevation and the velocity throughout the water column, to assess the ability of Stokes’ wave theory to describe the kinematics of regular waves in a short, physical, wave flume. Experimentally, the free surface elevation is measured with a set of resistive wave probes, while wave kinematic data is acquired with particle image velocimetry (PIV). For this study, ten different regular waves, of varying steepness, are generated in a 35 m long and 0.7 m deep wave flume. The theoretical solutions are computed based on Stokes 2 nd order wave theory. The presented results show error values of the order of 10–20%, indicating validity of the employed wave theory as a function of the reflection coefficient achieved in the physical wave flume. These result highlight the potential inaccuracies incurred in any wave tank if the wave theory is used to derive the kinematics from the free surface elevation without having detailed knowledge of the reflection characteristics at the point of interest in the tank.

Highly accurate and precise heave decay tests on a sphere with a diameter of 300 mm were completed in a meticulously designed test setup in the wave basin in the Ocean and Coastal Engineering Laboratory at Aalborg University, Denmark. The tests were dedicated to providing a rigorous benchmark dataset for numerical model validation. The sphere was ballasted to half submergence, thereby floating with the waterline at the equator when at rest in calm water. Heave decay tests were conducted, wherein the sphere was held stationary and dropped from three drop heights: a small drop height, which can be considered a linear case, a moderately nonlinear case, and a highly nonlinear case with a drop height from a position where the whole sphere was initially abovethe water. The precision of the heave decay time series was calculated from random and systematic standard uncertainties. At a 95% confidence level, uncertainties were found to be very low — on average only about 0.3% of the respective drop heights. Physical parameters of the test setup and associated uncertainties were quantified. A test case was formulated that closely represents the physical tests, enabling the reader to do his/her own numerical tests. The paper includes a comparison of the physical test results to the results from several independent numerical models based on linear potential flow, fully nonlinear potential flow, and the Reynolds-averaged Navier–Stokes (RANS) equations. A high correlation between physical and numerical test results is shown. The physical test results are very suitable for numerical model validation and are public as a benchmark dataset. Highly accurate and precise heave decay tests on a sphere with a diameter of 300 mm were completed in a meticulously designed test setup in the wave basin in the Ocean and Coastal Engineering Laboratory at Aalborg University, Denmark. The tests were dedicated to providing a rigorous benchmark dataset for numerical model validation. The sphere was ballasted to half submergence, thereby floating with the waterline at the equator when at rest in calm water. Heave decay tests were conducted, wherein the sphere was held stationary and dropped from three drop heights: a small drop height, which can be considered a linear case, a moderately nonlinear case, and a highly nonlinear case with a drop height from a position where the whole sphere was initially above the water. The precision of the heave decay time series was calculated from random and systematic standard uncertainties. At a 95% confidence level, uncertainties were found to be very low—on average only about 0.3% of the respective drop heights. Physical parameters of the test setup and associated uncertainties were quantified. A test case was formulated that closely represents the physical tests, enabling the reader to do his/her own numerical tests. The paper includes a comparison of the physical test results to the results from several independent numerical models based on linear potential flow, fully nonlinear potential flow, and the Reynolds-averaged Navier–Stokes (RANS) equations. A high correlation between physical and numerical test results is shown. The physical test results are very suitable for numerical model validation and are public as a benchmark dataset.

The vast majority of numerical wave tank applications are solved using finite volume-based, volume of fluid methods. One popular numerical modelling framework is OpenFOAM and its two phase solvers, interFoam and interIsoFoam, enabling the simulation of a broad range of marine hydrodynamic phenomena. However, in many applications, certain aspects of the entire set of possible hydrodynamic phenomena are not of interest and the reduced complexity could allow the use of simpler, more computationally efficient solvers. One barrier for the application of such alternative solvers is the lack of suitable wavemaking and absorption capabilities, which this paper aims to address. A wavemaking and absorption methodology is presented, which can be applied to different solvers using the same fundamental concept. The implementation is presented for interFoam and interIsoFoam, as well as two other solvers whose use as numerical wave tanks has not previously been reported in the literature, shallowWaterFoam and potentialFreeSurfaceFoam. Parameter studies are performed to guide the user in the use of the methods. Example applications for two industrially relevant test cases are demonstrated; a multi-frequency wave packet focused at one position over flat bottom and regular waves propagating over a submerged shoal. All solvers yielded useful results, but some complex wave transformations in the shoal case were only resolved by the VoF methods. Alternative methods beyond the already well established VoF methods seem worth considering because potential for significant reductions in computational effort exist.

An active control method, to suppress the onset of pitch/roll parametric resonance on an oscillating water column (OWC) spar buoy, is proposed in this paper, which utilises a pressure relief valve at the top of the OWC air chamber. The paper examines the hypothesis that by opening the relief valve, to reduce the air chamber pressure difference and to decouple the dynamics of the spar buoy and the OWC within, the natural pitch/roll frequencies of the system will be shifted, allowing parametric resonance to be cancelled when its onset is detected. The paper reports on experiments, performed to test the stated hypothesis, with a small-scale model OWC spar buoy in a wave flume. Two configurations are considered and tested in a range of monochromatic waves (1) fully closed air chamber; (2) fully open chamber. The results partially confirm the hypothesis, demonstrating that the occurrence of parametric resonance observed for certain wave frequencies when the chamber is closed does not occur when the chamber is open. However, the change in the natural pitch/roll frequencies between the two configurations is very small, and parametric resonance occurs in both confurations for waves with twice this frequency.

The largest challenge for appropriate adjustment of insulin doses for PCPs is lack of time and for patients is provision of enough blood glucose values. Potential solutions to these two issues are CIDAA for PCPs and CGM for patients. The combination of these two innovations was evaluated in a FQHC serving a poor, mostly minority, medically underserved population. Poorly controlled diabetic patients (A1C levels >9.0%) are referred to a specially trained clinical pharmacist (CP). The pharmacy department supported CGM (Free Style Libre Pro) for 13 patients, 10 on basal insulin alone and 3 on basal/bolus who had ≥2 visits. Their downloaded CGM results were analyzed by FDA-cleared CIDAA and a report containing recommendations for dose adjustments that the CP could modify or accept was provided within 30 seconds. The mean number of reports was 4.8 which covered a period of 97 days. The glycemic responses are shown in the Table. Total insulin doses increased by 42%. Conclusion: Analysis of CGM results by CIDAA addresses the two largest challenges of adjusting insulin doses for PCPs and patients. Using both together has the potential of markedly improving A1C levels in poorly controlled insulin-requiring diabetic patients. Disclosure M.B. Davidson: None. J. Davidson: Employee; Self; Mellitus Health.

Results from the CCP-WSI Blind Test Series 3 are presented. Participants, with numerical methods, ranging from low-fidelity linear models to high-fidelity Navier–Stokes (NS) solvers, simulate the interaction between focused waves and floatingstructures without prior access to the physical data. The waves are crest-focused NewWaves with various crest heights.Two structures are considered: a hemispherical-bottomed buoy and a truncated cylinder with a moon-pool; both are taut-moored with one linear spring mooring. To assess the predictive capability of each method, numerical results for heave,surge, pitch, and mooring load are compared against corresponding physical data. In general, the NS solvers appear topredict the behaviour of the structures better than the linearised methods, but there is considerable variation in the results(even between similar methods). Recommendations are made for future comparative studies and development of numericalmodelling standards.

CFD-based numerical wave tank (CNWT) models, are a useful tool for the analysis of wave energy converters (WECs). During the development of a CNWT, model validation is vital, to prove the accuracy of the numerical solution. This paper presents an extensive validation study of a CNWT model for the 1:5 scale Wavestar point-absorber device. The previous studies reported by Ransley et al. [1] and Windt et al. [2] are extended in this paper, by including cases in which the power-take off (PTO) system is included in the model. In this study, the PTO is represented as a linear spring-damper system, providing a good approximation to the full PTO dynamics. The spring stiffness and damping coefficients in the numerical PTO model are determined through a linear least squares fit of the experimental PTO position, velocity and force data. The numerical results for free surface elevation, PTO data (position, velocity, force), generated power and pressure on the WEC hull are shown to compare well with the experimental measurements.

Energy maximising controllers (EMCs), for wave energy converters (WECs), based on linear models, are attractive in terms of simplicity and computation. However, such (Cummins equation) models are normally built around the still water level as an equilibrium point and assume small movement, leading to poor model validity for realistic WEC motions, especially for the large amplitude motions obtained by a well controlled WEC. The method proposed here is to use an adaptive algorithm to estimate the control model online, whereby system identification techniques are employed to identify a linear model that is most representative of the actual controlled WEC behaviour. Using exponential forgetting, the linear model can be regularly adapted to remain representative in changing operational conditions. To that end, this paper presents a novel adaptive controller based on a receding horizon pseudospectral formulation. A case study is presented, providing an preliminary evaluation of the adaptive receding horizon pseudospectral control (ARHPC), using simulations based on both linear hydrodynamic modelling and computational fluid dynamics (CFD). The parameter adaptation is shown to behave as expected in both different simulation environments. The ARHPC is observed to perform well in irregular sea states, absorbing more power than its nonadaptive counterpart. The optimal trajectory calculated by the adaptive model is seen to have a smaller motion and power take-off (PTO) forces, compared to those calculated by the nonadaptive linear control model, due to the increased amount of hydrodynamic resistance estimated by the adaptive model, as identified from the nonlinear viscous CFD simulation.

Scaled model tests are an important step during the research and development of wave energy converters (WECs). While such scaled model tests in physical wave tanks are prone to undesired scaling effects due to e.g. mechanical artefacts and/or fluid effects, numerical wave tanks (NWTs) provide excellent tools for the analysis of WECs across a range of scales, overcoming the limitations of the physical test environment. Simultaneous scaling based on the Froude and Reynolds number is achievable in physical wave tanks only with significant effort, whereas NWTs allow the adjustment of fluid properties, such as viscosity, in an easy manner, thereby catering for Froude and Reynolds similarity. This study exploits the capabilities of a high-fidelity, computational fluid dynamics based, NWT and investigates the hydrodynamic scaling effects for the heaving buoy Wavestar WEC. Various test cases, relevant for WEC applications and with progressively increasing complexity, are considered to develop a comprehensive understanding of the scaling effects. Results show that significant scaling effects occur for the viscous component of the hydrodynamic loads on the WEC hull, while the system dynamics and total (viscous + pressure) loads are relatively unaffected by scaling effects.

Mathematical models are essential for the design and control of offshore systems, to simulate the fluid–structure interactions and predict the motions and the structural loads. In the development and derivation of the models, simplifying assumptions are normally required, usually implying linear kinematics and hydrodynamics. However, while the assumption of linear, small amplitude motion fits traditional offshore problems, in normal operational conditions (it is desirable to stabilize ships, boats, and offshore platforms), large motion and potential dynamic instability may arise (e.g., harsh sea conditions). Furthermore, such nonlinearities are particularly evident in wave energy converters, as large motions are expected (and desired) to enhance power extraction. The inadequacy of linear models has led to an increasing number of publications and codes implementing nonlinear hydrodynamics. However, nonlinear kinematics has received very little attention, as few models yet consider six degrees of freedom and large rotations. This paper implements a nonlinear hydrodynamic and kinematic model for an archetypal floating structure, commonplace in offshore applications: an axisymmetric spar-buoy. The influence of nonlinear dynamics and kinematics causing coupling between modes of motion are demonstrated. The nonlinear dynamics are shown to cause parametric resonance in the roll and pitch degrees of freedom, while the nonlinear kinematics are shown to potentially cause numerical instability in the yaw degree of freedom. A case study example is presented to highlight the nonlinear dynamic and kinematic effects, and the importance of including a nominal restoring term in the yaw DoF presented.

Numerical wave tanks (NWTs) provide efficient test beds for the numerical analysis at various stages during the development of wave energy converters (WECs). To ensure the acquisition of accurate, high-fidelity data sets, validation of NWTs is a crucial step. However, using experimental data as reference during model validation, exact knowledge of all system parameters is required, which may not always be available, thus making an incremental validation inevitable. The present paper documents the numerical model validation of a 1/20 scale Wavestar WEC. The validation is performed considering different test case of increasing complexity: wave-only, wave excitation force, free decay, forced oscillation, and wave-induced motion cases. The results show acceptable agreement between the numerical and experimental data so that, under the well-known modelling constraints for mechanical friction and uncertainties in the physical model properties, the developed numerical model can be declared as validated. Numerical wave tanks (NWTs) provide efficient test beds for the numerical analysis at various stages during the development of wave energy converters (WECs). To ensure the acquisition of accurate, high-fidelity data sets, validation of NWTs is a crucial step. However, using experimental data as reference during model validation, exact knowledge of all system parameters is required, which may not always be available, thus making an incremental validation inevitable. The present paper documents the numerical model validation of a 1/20 scale Wavestar WEC. The validation is performed considering different test case of increasing complexity: wave-only, wave excitation force, free decay, forced oscillation, and wave-induced motion cases. The results show acceptable agreement between the numerical and experimental data so that, under the well-known modelling constraints for mechanical friction and uncertainties in the physical model properties, the developed numerical model can be declared as validated.

Parametric resonance is a dynamic instability due to the internal transfer of energy between degrees of freedom. Parametric resonance is known to cause large unstable pitch and/or roll motions in floating bodies, and has been observed in wave energy converters (WECs). The occurrence of parametric resonance can be highly detrimental to the performance of a WEC, since the energy in the primary mode of motion is parasitically transferred into other modes, reducing the available energy for conversion. In addition, the large unstable oscillations produce increased loading on the WEC structure and mooring system, accelerating fatigue and damage to the system. To remedy the negative effects of parametric resonance on WECs, control systems can be designed to mitigate the onset of parametric resonance. A key element of such a control system is a real-time detection system, which can provide an early warning of the likely occurrence of parametric resonance, enabling the control system sufficient time to respond and take action to avert the impending exponential increase in oscillation amplitude. This paper presents the first application of a real-time detection system for the onset of parametric resonance in WECs. The method is based on periodically assessing the stability of a mathematical model for the WEC dynamics, whose parameters are adapted online, via a recursive least squares algorithm, based on online measurements of the WEC motion. The performance of the detection system is demonstrated through a case study, considering a generic cylinder type spar-buoy, a representative of a heaving point absorber WEC, in both monochromatic and polychromatic sea states. The detection system achieved 95% accuracy across nearly 7000 sea states, producing 0.4% false negatives and 4.6% false positives. For the monochromatic waves more than 99% of the detections occurred while the pitch amplitude was less than 1/6 of its maximum amplitude, whereas for the polychromatic waves 63% of the detections occurred while the pitch amplitude was less than 1/6 of its maximum amplitude and 91% while it was less than 1/3 of its maximum amplitude.

Computational fluid dynamics (CFD)-based numerical wave tanks are valuable tools for the development and evaluation of energy maximising control systems for wave energy converters (WECs). However, the exaggerated body motion amplitude, which can be induced by the energy maximising control system, challenges the commonly applied mesh morphing method in CFD, due to the resulting mesh distortion and subsequent numerical instability. A more advanced mesh motion method is the overset grid method, which can inherently handle large-amplitude body motions and has recently become freely available in the open-source CFD software OpenFOAM. The overset grid method can, therefore, potentially eliminate the mesh distortion problem, hindering the simulation of WECs under controlled conditions. To evaluate the capability of the overset grid method for control studies of WECs in an OpenFOAM numerical wave tank, this paper presents a detailed comparison of the overset grid and mesh morphing methods, considering five test cases of increasing complexity. The test cases range from a static equilibrium test to the modelling of a controlled WEC, and good agreement is demonstrated between the two mesh motion methods, except for the case of the controlled WEC, when the device motion becomes large, and the mesh morphing simulation crashes. The runtimes for overset grid simulations are observed to be approximately double the time required for the mesh morphing simulations.

Computational Fluid Dynamics (CFD) simulations, based on Reynolds-AveragedNavier&ndash, Stokes (RANS) models, are a useful tool for a wide range of coastal and offshore applications,providing a high fidelity representation of the underlying hydrodynamic processes. Generating inputwaves in the CFD simulation is performed by a Numerical Wavemaker (NWM), with a variety ofdifferent NWM methods existing for this task. While NWMs, based on impulse source methods, havebeen widely applied for wave generation in depth averaged, shallow water models, they have notseen the same level of adoption in the more general RANS-based CFD simulations, due to difficultiesin relating the required impulse source function to the resulting free surface elevation for non-shallowwater cases. This paper presents an implementation of an impulse source wavemaker, which is ableto self-calibrate the impulse source function to produce a desired wave series in deep or shallowwater at a specific point in time and space. Example applications are presented, for a NumericalWave Tank (NWT), based on the open-source CFD software OpenFOAM, for wave packets in deepand shallow water, highlighting the correct calibration of phase and amplitude. Furthermore, thesuitability for cases requiring very low reflection from NWT boundaries is demonstrated. Possibleissues in the use of the method are discussed, and guidance for accurate application is given.

Wave energy conversion is an active field of research, aiming to harness the vast amounts of energy present in ocean waves. An essential development trajectory towards an economically competitive wave energy converter (WEC) requires early device experimentation and refinement using numerical tools. OpenFOAM\(^{\textregistered }\) is proving to be a useful numerical tool for WEC development, having been increasingly employed in recent years to simulate and analyse the performance of WECs. This chapter reviews the latest works employing OpenFOAM\(^{\textregistered }\) in the field of wave energy conversion, and then presents the new application, of evaluating energy maximising control systems (EMCSs) for WECs, in an OpenFOAM\(^{\textregistered }\) numerical wave tank (NWT). The advantages of using OpenFOAM\(^{\textregistered }\) for this application are discussed, and implementation details for simulating a controlled WEC in an OpenFOAM\(^{\textregistered }\) NWT are outlined. An illustrative example is given, and results are presented, highlighting the value of evaluating EMCSs for WECs in an OpenFOAM\(^{\textregistered }\) NWT.

Adjusting insulin doses is very challenging for primary care physicians because of infrequent office visits and time constraints at the visit. For patients, frequent office visits are a barrier. We have used FDA-approved, computerized insulin dose adjustment algorithms and remote glucose monitoring to circumvent both of these issues. Diabetic patients in a safety net clinic who took insulin for at least 6 months with A1C levels ?8.0% were enrolled in a study in which an iHealth glucose meter was attached to a smartphone containing an app downloaded from the Web that transmitted the glucose values to a secure, HIPAA-approved server. There the values were analyzed by the algorithms and a report with recommendations for dose changes was generated and sent to a clinic nurse practitioner every 2-3 weeks who could accept or modify the recommendations. A clinic staff individual contacted the patient with the insulin dose changes. Twenty-eight diabetic patients (one type 1) have reached 3 months. Their mean age (± SD) was 55.9 ± 8.6 years, 15 were females and 13 were males. There were 20 Latinos, 4 African-Americans, 3 Caucasians, and 1 Asian. Their insulin regimens were: basal alone - 11, basal/bolus - 14 and self-mixed/split - 3. Non-insulin drugs were not changed. Their baseline A1C levels (± SD) of 10.0% ± 1.2 decreased by 1.9% ± 0.9 to 8.1% ± 1.1 after 3 months. Their total insulin dose increased by 24%. There were no episodes of severe hypoglycemia (requiring 2nd party assistance) nor emergency room visits for hypoglycemia. Conclusion: Remote glucose monitoring utilizing computerized insulin dose adjustment algorithms to analyze glucose values and generating recommendations for dose changes at more frequent intervals markedly improved A1C levels in poorly controlled diabetic patients in the absence of office visits. Disclosure M.B. Davidson: Employee; Self; Insulin Algorithms, Inc. J. Davidson: Employee; Self; Insulin Algorithms.

Mathematical modelling of wave energy devices has many uses, including power production assessment, simulation of device motion and as a basis for model-based control design. Apart from computationally heavy approaches, such as those based on computational fluid dynamics (CFD) and smooth particle hydrodynamics (SPH), the vast majority of models employed in the simulation and analysis of wave energy converters (WECs) are based on boundary-element methods (BEMs). While BEM models have been shown to be useful, they have the inherent limitation that they are linearised around the still water level, with validity only on the immediate vicinity of this equilibrium point. In this paper, we develop a new modelling methodology, which combines the fidelity of CFD models with the computational attractiveness of BEM-type models. This flexible methodology can give representative linear models, or be extended into the nonlinear domain, as desired.

To maximise the energy output of wave energy converters (WECs), large structural motions are desired. When simulating WEC performance in Computational Fluid Dynamics (CFD) based numerical wave tanks, these motions must be explicitly accommodated in the computational domain. Using well established mesh morphing (MM) methods, this explicit accommodation results in deformation of control volumes (CVs)/mesh. Thus, large amplitude WEC oscillations may lead to highly distorted CVs and push MM models beyond the limits of numerical stability. While advanced numerical mesh motion methods, such as overset grids, have been developed in commercial CFD codes to overcome these issues, little use of these methods can be found in WEC analysis. However, recently the overset grid method (OSG) has been made available to a wider user community through its release in the open source CFD environment OpenFOAM [1,2]. To evaluate the performance of the OSG, this paper will compare the classical MM method and the OSG against experimental tank test data of the WaveStar device [3].

For the research and development (R&D) of wave energy converters (WECs), numerical wave tanks (NWTs) provide an excellent numerical tool, enabling a cost-effective testbed for WEC experimentation, analysis and optimisation. Different methods for simulating the fluid dynamics and fluid structure interaction (FSI) within the NWT have been developed over the years, with increasing levels of fidelity, and associated computational expense. In the past, the high computational requirements largely precluded Computational Fluid Dynamics (CFD) from being applied to WEC analysis. However, the continual improvement and availability of high performance computing has led to the steady increase of CFD-based NWTs (CNWT) for WEC experiments. No attempt has yet been undertaken to comprehensively review CNWT approaches for WECs. This paper fills this gap and presents a thorough review of high-fidelity numerical modelling of WECs using CNWTs. In addition to collating the published literature, this review tries to make a step towards a best practice guideline for the applications of CFD in the field of wave energy.

Performing rigorous technical and commercial assessment of wave energy converters (WECs) numerically, before engaging in expensive wave tank and open ocean tests, is vital for the economically successful development of prototypes. To that end, this paper presents a high-fidelity wave-to-wire simulation platform (the HiFiWEC), where a Computational Fluid Dynamics (CFD)-based numerical wave tank is coupled to a high-fidelity power take-off (PTO) model, which enables assessment of WEC performance with greater accuracy than with previous wave-to-wire approaches. A test case, simulating the performance of a heaving point absorber type WEC in realistic conditions, is presented and compared against traditional lower fidelity modelling methods. The WEC response is evaluated with a number of different approaches, including different techniques to model hydrodynamic wave-structure interactions and the power take-off system, and the benefits of the HiFiWEC are highlighted. The results highlight that excessive simplifications in the modelling of the PTO system can lead to significant overestimation in generated energy output, with relative deviations ( ∊ ) of up to 150% compared to the HiFiWEC. In addition, uncertainty in viscous drag parameters added to hydrodynamic models based on boundary element method solvers, reinforce the necessity of CFD-based models for applications where high-fidelity is essential. Finally, it is demonstrated that minor/insignificant inaccuracies in the hydrodynamic model ( ∊ = 0.5 % ) can result in significant differences in the estimation of the final energy generation ( ∊ = 7 % ), highlighting the need for a coupled high-fidelity platform.

Background: Asthma-like symptoms are common in those under physical duress. It has been demonstrated that 21% of athletes with presumed asthma had no objective evidence at assessment (1). Military personnel who develop symptoms of asthma are frequently declared unfit for service pending medical review. This has ramifications for the recruit and leads to avoidable healthcare costs. Aims: · To know the percentage of recruits referred with asthma who have objective evidence at assessment. · To understand the effects of treatment on the ability to return to unrestricted duties in military personnel. Methods: A retrospective review of military personal with a presumed diagnosis of asthma (July 2012 to June 2016). Diagnosis based on more than a 12% improvement of forced expiratory volume in one second (FEV1) to inhaled short acting beta agonist (SABA) and/or a positive methacholine challenge test. Asthma treatment was adjusted in line with British Thoracic Society (BTS) guidelines. Results: 40% (48/121) of presumed asthmatics had no objective evidence of asthma. 60% (44/73) of those with asthma were on no treatment or SABA only. Appropriate treatment meant that post-review 46/50 (92%) patients who were temporarily downgraded were subsequently recommended for unrestricted duties. Conclusions: At referral, the majority of recruits were on no medication or inhaled SABA only. Appropriate treatment allowed a return to unrestricted duties in most cases. Prompt referral for investigation and titration of treatment is likely to reduce time out of service. 1) Dickinson JW et al. Impact of changes in the IOC-MC asthma criteria: a British perspective. Thorax. 2005;60(8):629-32.

Mathematical analysis is an essential tool for the successful development and operation of wave energy converters (WECs). Mathematical models of moorings systems are therefore a requisite in the overall techno-economic design and operation of floating WECs. Mooring models (MMs) can be applied to a range of areas, such as WEC simulation, performance evaluation and optimisation, control design and implementation, extreme load calculation, mooring line fatigue life evaluation, mooring design, and array layout optimisation. The mathematical modelling of mooring systems is a venture from physics to numerics, and as such, there are a broad range of details to consider when applying MMs to WEC analysis. A large body of work exists on MMs, developed within other related ocean engineering fields, due to the common requirement of mooring floating bodies, such as vessels and offshore oil and gas platforms. This paper reviews the mathematical modelling of the mooring systems for WECs, detailing the relevant material developed in other offshore industries and presenting the published usage of MMs for WEC analysis.

The modelling approach presented in this chapter is that of system identification, where models are determined from input/output data measured from the system under study. Models identified from recorded wave energy converter (WEC) data can accurately describe WEC behaviour, provided the data is of a sufficiently high quality. The chapter details generating data for the system identification process and outlines the requirements of the data to ensure representative models are obtained. Different parametric model structures are presented, along with identification algorithms to determine the optimum parameter values for the models. A number of case studies illustrating the use of system identification to obtain numerical models of WECs are given.

In this paper and its companion, the identification of mathematical models describing the behaviour of wave energy devices (WECs) in the ocean is investigated through the use of numerical wave tank (NWT) experiments. This paper deals with the identification tests used to produce the data for the model identification. NWTs, implemented using computational fluid dynamics (CFD), are shown as an effective platform to perform the identification tests. The design of the NWT experiments, to ensure the production of information-rich data for the model identification, is discussed. A case study is presented to illustrate the design and implementation of NWT experiments for the identification of WEC models.

In this paper and its companion, the identification of mathematical models describing the behaviour of wave energy devices (WECs) in the ocean is investigated through the use of numerical wave tank experiments. When the wave amplitude and the WEC displacement are not negligible with respect to the WEC dimensions, nonlinear hydrodynamic effects may appear, and the accuracy of linear hydrodynamic models is reduced, leading to the necessity of introducing some nonlinearities in the model structure. This paper proposes, for WEC modelling, the use of discrete-time nonlinear autoregressive with exogenous input (NARX) models, as an alternative to continuous-time models. Techniques of model identification are also explained and applied to a case study.