A simple time-domain numerical model is established to consider the interfacial solitary wave actions on submerged body and the body’s vertical motion. The vertical drag and inertial force on the moving submerged body induced by interfacial solitary wave is computed by Morison equation. The motion equation is solved by the fourth-order Runge-Kutta method. A horizontal submerged slender circular cylinder beneath the interface with forward speed is considered in this paper. The calculations show that when the depression internal solitary wave keeps close to the submerged body, the vertical forces on the body, including interfacial solitary wave force and buoyance, change greatly and the body moves downward with a great displacement in a short time. The main reason which results in the great vertical motion is the decrease of buoyance when submerged body moves into the less density water layer. It can be concluded that the great threat to submarine’s navigation is the density variation caused by interfacial solitary wave. The parameter effect of forward speed of the submerged body is also investigated.
{"title":"Vertical Motion Response of a Submerged Body Induced by Interfacial Solitary Waves","authors":"Y. Gou, Rongquan Wang, B. Teng","doi":"10.1115/OMAE2018-78706","DOIUrl":"https://doi.org/10.1115/OMAE2018-78706","url":null,"abstract":"A simple time-domain numerical model is established to consider the interfacial solitary wave actions on submerged body and the body’s vertical motion. The vertical drag and inertial force on the moving submerged body induced by interfacial solitary wave is computed by Morison equation. The motion equation is solved by the fourth-order Runge-Kutta method. A horizontal submerged slender circular cylinder beneath the interface with forward speed is considered in this paper. The calculations show that when the depression internal solitary wave keeps close to the submerged body, the vertical forces on the body, including interfacial solitary wave force and buoyance, change greatly and the body moves downward with a great displacement in a short time. The main reason which results in the great vertical motion is the decrease of buoyance when submerged body moves into the less density water layer. It can be concluded that the great threat to submarine’s navigation is the density variation caused by interfacial solitary wave. The parameter effect of forward speed of the submerged body is also investigated.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"61 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122402451","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Jun Y. Lee, Jasmin B. T. McInerney, F. Hardjanto, S. Chai, R. Cossu, Z. Leong, A. Forrest
When a subsea pipeline is laid on an uneven seabed, the pipeline can have an initial elevation, potentially compromising its on-bottom stability; scouring due to flow conditions around the pipe can further exacerbate the problem. We assess the capability of the two-phase Eulerian-Eulerian OpenFOAM solver, twoPhaseEulerFoam, in terms of predicting the equilibrium scour depth beneath a pipe at different initial elevations under a steady current for the live bed condition. The predictions were found to be in good agreement with published experimental and numerical results; however, similar to a recent study involving another two-phase Eulerian-Eulerian model, the scour time scale was under-predicted. The predicted equilibrium scour depth was seen to decrease with an increase in the initial pipe elevation. The numerical results were also compared to predictions that were made using previous empirical equations. The most comprehensive equation to date showed a good agreement with the present numerical results. We conclude that this open-source solver, twoPhaseEulerFoam, can be used to predict the equilibrium scour depth beneath subsea pipelines, with short computation times and negligible mesh dependency.
{"title":"Two-Phase Model for Simulating Current-Induced Scour Beneath Subsea Pipelines at Different Initial Elevations","authors":"Jun Y. Lee, Jasmin B. T. McInerney, F. Hardjanto, S. Chai, R. Cossu, Z. Leong, A. Forrest","doi":"10.1115/OMAE2018-77245","DOIUrl":"https://doi.org/10.1115/OMAE2018-77245","url":null,"abstract":"When a subsea pipeline is laid on an uneven seabed, the pipeline can have an initial elevation, potentially compromising its on-bottom stability; scouring due to flow conditions around the pipe can further exacerbate the problem. We assess the capability of the two-phase Eulerian-Eulerian OpenFOAM solver, twoPhaseEulerFoam, in terms of predicting the equilibrium scour depth beneath a pipe at different initial elevations under a steady current for the live bed condition. The predictions were found to be in good agreement with published experimental and numerical results; however, similar to a recent study involving another two-phase Eulerian-Eulerian model, the scour time scale was under-predicted. The predicted equilibrium scour depth was seen to decrease with an increase in the initial pipe elevation. The numerical results were also compared to predictions that were made using previous empirical equations. The most comprehensive equation to date showed a good agreement with the present numerical results. We conclude that this open-source solver, twoPhaseEulerFoam, can be used to predict the equilibrium scour depth beneath subsea pipelines, with short computation times and negligible mesh dependency.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"35 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"124079273","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A preliminary investigation of a low-weight carrying marine platform concept was conducted by means of experiments and approximate theories. The platform consists of a circular elastic tube with circular cross-section, covered with an air-supported membrane deck. A vertical skirt is added along the circumference of the model to avoid air-leakage. We refer to this concept as floating solar island. Solar islands have recently gained interest. The models were subjected to waves. Both regular and irregular wave tests were conducted. Tests with the absence of the membrane (floater only) were also conducted. The general behaviour and failure modes were investigated. Failure modes include over-topping with flooding as consequence, as well as out-of-water incidents and membrane wear with air leakage as consequence. A systematic variation of wave conditions revealed for which wave conditions flooding occured. Out-of-water incidents of the skirt were not observed. Vertical accelerations were measured at eight positions along the circumference of the model, and the heave, pitch and first flexible mode motions were re-constructed by modal theory. The modal responses were compared to theory based on linear potential flow assumption, both for the floater model only, and with simplified theory accounting for the air-cushion of the island in heave. The theory was able to predict the global behaviour reasonably well, although important discrepancies were observed. More detailed studies, involving experiments with more instrumentation and development of theory, must be conducted in case deeper understanding of this relatively complex, hydro-elastic concept is needed.
{"title":"Investigation of an Air-Cushion Supported Solar Island","authors":"T. Kristiansen, P. Borvik","doi":"10.1115/OMAE2018-78533","DOIUrl":"https://doi.org/10.1115/OMAE2018-78533","url":null,"abstract":"A preliminary investigation of a low-weight carrying marine platform concept was conducted by means of experiments and approximate theories. The platform consists of a circular elastic tube with circular cross-section, covered with an air-supported membrane deck. A vertical skirt is added along the circumference of the model to avoid air-leakage. We refer to this concept as floating solar island. Solar islands have recently gained interest. The models were subjected to waves. Both regular and irregular wave tests were conducted. Tests with the absence of the membrane (floater only) were also conducted. The general behaviour and failure modes were investigated. Failure modes include over-topping with flooding as consequence, as well as out-of-water incidents and membrane wear with air leakage as consequence. A systematic variation of wave conditions revealed for which wave conditions flooding occured. Out-of-water incidents of the skirt were not observed. Vertical accelerations were measured at eight positions along the circumference of the model, and the heave, pitch and first flexible mode motions were re-constructed by modal theory. The modal responses were compared to theory based on linear potential flow assumption, both for the floater model only, and with simplified theory accounting for the air-cushion of the island in heave. The theory was able to predict the global behaviour reasonably well, although important discrepancies were observed. More detailed studies, involving experiments with more instrumentation and development of theory, must be conducted in case deeper understanding of this relatively complex, hydro-elastic concept is needed.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131392458","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The open source potential flow BEM solver Nemoh (developed at École Centrale de Nantes) is widely used today, notably for the development of wave energy converters. The use of a linear potential flow theory allows quick estimations of the hydro-dynamic properties of the device, such as its added mass or its radiation damping. Nonetheless, their computation with Nemoh can still be time consuming and could be optimized to facilitate the R&D process. Many wave energy converter concepts present symmetric shapes: for instance rotational symmetry for point absorbers or translation invariance for cylindrical shapes. These symmetries can be exploited in the BEM solver to significantly speed up the computations. In this paper, the mathematical effect of symmetries on the BEM resolution will be discussed and some results of its implementation in Nemoh will be presented.
开源的势流BEM求解器Nemoh(在École Centrale de Nantes开发)今天被广泛使用，特别是用于波浪能转换器的开发。线性势流理论的使用允许快速估计装置的流体动力特性，例如其增加的质量或其辐射阻尼。尽管如此，他们使用Nemoh的计算仍然很耗时，可以优化以促进研发过程。许多波能转换器概念呈现对称形状:例如点吸收器的旋转对称或圆柱形的平移不变性。这些对称性可以在边界元求解器中得到利用，大大加快了计算速度。本文将讨论对称性对边界元分辨率的数学影响，并给出其在Nemoh上实现的一些结果。
{"title":"Using the Floating Body Symmetries to Speed Up the Numerical Computation of Hydrodynamics Coefficients With Nemoh","authors":"M. Ancellin, F. Dias","doi":"10.1115/OMAE2018-77924","DOIUrl":"https://doi.org/10.1115/OMAE2018-77924","url":null,"abstract":"The open source potential flow BEM solver Nemoh (developed at École Centrale de Nantes) is widely used today, notably for the development of wave energy converters. The use of a linear potential flow theory allows quick estimations of the hydro-dynamic properties of the device, such as its added mass or its radiation damping. Nonetheless, their computation with Nemoh can still be time consuming and could be optimized to facilitate the R&D process.\u0000 Many wave energy converter concepts present symmetric shapes: for instance rotational symmetry for point absorbers or translation invariance for cylindrical shapes. These symmetries can be exploited in the BEM solver to significantly speed up the computations. In this paper, the mathematical effect of symmetries on the BEM resolution will be discussed and some results of its implementation in Nemoh will be presented.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130626064","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A 3D numerical two-phase flow model based on solving Unsteady Reynolds-averaged Navier-Stokes (URANS) equations has been used to simulate spilling breaking waves and steep waves past a monopile structure at a 1:10 slope. The volume of fluid (VOF) method is employed to capture the free surface and the k–ω Shear-Stress Transport (k–ω SST) turbulence model is used to simulate the turbulence effects. Mesh and time-step refinement studies have been conducted. The numerical results of wave forces on the structure are compared with the experimental data from Irschik et al. (2004) to validate the numerical model, and the numerical results are in good agreement with the measured data. The wave forces on the structure at different KC numbers are discussed in terms of the generation of the slamming force. The secondary load cycles are observed after the wave front past the structure. The pressure and velocity distribution, as well as the characteristics of the vortices around the structure at four important instants, are studied.
采用求解非定常reynolds -average Navier-Stokes (URANS)方程的三维两相流数值模型，模拟了1:10坡度单桩结构的溢出破碎波和陡浪。采用流体体积法(VOF)捕获自由表面，采用k -ω剪切应力输运(k -ω SST)湍流模型模拟湍流效应。已经进行了网格和时间步细化研究。将波浪力作用在结构上的数值结果与Irschik et al.(2004)的实验数据进行了比较，验证了数值模型，数值结果与实测数据吻合较好。讨论了不同KC数下结构所受波浪力的产生。在波阵面经过结构后观察到二次荷载循环。研究了四个重要时刻的压力和速度分布以及结构周围涡的特性。
{"title":"CFD Simulations of Spilling Breaking Waves and Steep Waves Past a Monopile Structure at Different KC Numbers","authors":"Shengnan Liu, M. Ong, C. Obhrai","doi":"10.1115/OMAE2018-77604","DOIUrl":"https://doi.org/10.1115/OMAE2018-77604","url":null,"abstract":"A 3D numerical two-phase flow model based on solving Unsteady Reynolds-averaged Navier-Stokes (URANS) equations has been used to simulate spilling breaking waves and steep waves past a monopile structure at a 1:10 slope. The volume of fluid (VOF) method is employed to capture the free surface and the k–ω Shear-Stress Transport (k–ω SST) turbulence model is used to simulate the turbulence effects. Mesh and time-step refinement studies have been conducted. The numerical results of wave forces on the structure are compared with the experimental data from Irschik et al. (2004) to validate the numerical model, and the numerical results are in good agreement with the measured data. The wave forces on the structure at different KC numbers are discussed in terms of the generation of the slamming force. The secondary load cycles are observed after the wave front past the structure. The pressure and velocity distribution, as well as the characteristics of the vortices around the structure at four important instants, are studied.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"604 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126900558","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Monopiles installed by impact driving are the preferred system for the foundation of offshore wind turbines in water depths up to 40 m. The vibration technique as alternative installation method has big advantages regarding piling noise and installation time. Much experience exists for the design and installation of impact driven piles. Within the research project ZykLaMP, the lack of experience concerning vibrated monopiles shall be faced by means of large-scaled model investigations regarding the lateral load-bearing behavior. Therefore, open ended steel pipe piles (L = 2.4 m, Dpile = 0.6 m) are installed into dense sand by means of impact and vibratory pile driving and then subjected to cyclic lateral loading. This paper focusses on pile driving predictions and measurements during the installation process. Pile driving post-predictions were carried out based on a simple force equilibrium approach. Model piles were installed using two different vibro hammers with different eccentric moments and one impact hammer. Measurements of strains and accelerations were carried out to investigate dynamic movements during pile driving. Earth pressure transducers were used to investigate the development of soil stresses due to the installation process. Measurements show that even at high acceleration amplitudes a refusal to vibratory driving may occur at a certain penetration depth. Soil stresses in the vicinity of the pile decrease to about 50 % due to vibratory driving which is one reason for the friction fatigue phenomenon. Drivability studies using the force equilibrium model give rough predictions about whether or not a pile can be driven to a certain penetration depth but are quite sensitive to input parameters. For the model tests, post-predictions gave reasonable results.
通过冲击驱动安装的单桩是水深达40米的海上风力涡轮机基础的首选系统。振动技术作为一种替代的安装方法，在桩噪声和安装时间方面有很大的优势。冲击灌注桩的设计与安装已有很多经验。在ZykLaMP研究项目中，应通过对横向承载行为的大规模模型研究来解决振动单桩缺乏经验的问题。因此，采用冲击和振动打桩的方式将L = 2.4 m, Dpile = 0.6 m的开端钢管桩安装在密砂中，然后进行循环侧向荷载。本文着重介绍了在安装过程中的打桩预测和测量。基于简单的力平衡方法进行了打桩后预测。模型桩采用两种不同偏心弯矩的振动锤和一种冲击锤安装。进行了应变和加速度测量，以研究打桩过程中的动力运动。土压力传感器用于研究安装过程中土体应力的变化。测量表明，即使在高加速度幅值的情况下，在一定的侵彻深度也可能出现振动驱动的拒绝。振动驱动使桩附近土体应力降低50%左右，这是产生摩擦疲劳现象的原因之一。利用力平衡模型进行的可打性研究对桩能否打入一定的贯深给出了粗略的预测，但对输入参数相当敏感。对于模型测试，后预测给出了合理的结果。
{"title":"Scale Model Investigations on Vibro Pile Driving","authors":"P. Stein, Nils Hinzmann, J. Gattermann","doi":"10.1115/OMAE2018-77081","DOIUrl":"https://doi.org/10.1115/OMAE2018-77081","url":null,"abstract":"Monopiles installed by impact driving are the preferred system for the foundation of offshore wind turbines in water depths up to 40 m. The vibration technique as alternative installation method has big advantages regarding piling noise and installation time. Much experience exists for the design and installation of impact driven piles. Within the research project ZykLaMP, the lack of experience concerning vibrated monopiles shall be faced by means of large-scaled model investigations regarding the lateral load-bearing behavior.\u0000 Therefore, open ended steel pipe piles (L = 2.4 m, Dpile = 0.6 m) are installed into dense sand by means of impact and vibratory pile driving and then subjected to cyclic lateral loading. This paper focusses on pile driving predictions and measurements during the installation process.\u0000 Pile driving post-predictions were carried out based on a simple force equilibrium approach. Model piles were installed using two different vibro hammers with different eccentric moments and one impact hammer. Measurements of strains and accelerations were carried out to investigate dynamic movements during pile driving. Earth pressure transducers were used to investigate the development of soil stresses due to the installation process.\u0000 Measurements show that even at high acceleration amplitudes a refusal to vibratory driving may occur at a certain penetration depth. Soil stresses in the vicinity of the pile decrease to about 50 % due to vibratory driving which is one reason for the friction fatigue phenomenon.\u0000 Drivability studies using the force equilibrium model give rough predictions about whether or not a pile can be driven to a certain penetration depth but are quite sensitive to input parameters. For the model tests, post-predictions gave reasonable results.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"58 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115036430","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mobile jack-up rigs are frequently cantilevered over production jacket platforms to drill new wells or rework existing well for the offshore oil and gas at shallow and middle water depths. The proximity of the rig to the existing fixed platform will affect the performance of pile foundations of the platform and may cause some distress to the adjacent pile foundation by spudcan penetration. With the increasing accidents with respect to the spudcan penetration and spudcanpile interaction caused severe economic losses in offshore engineering of China, solving these problems is an urgent and significance assignment at present. Since the spudcan-pile interaction is a typical offshore geotechnical large strain large deformation problem, a numerical approach based on the large strain technique is a valid solution tool for evaluating spudcanpile interaction. The paper addresses additional responses of the adjacent pile induced by spudcan penetration in single clay profile and clay overlying sand profile using two different large strain large deformation numerical approaches. One is called two-stage approach. Firstly, ALE (Arbitrary Lagrangian Eulerian) approach is used to the displacement field of soil is calculated at the free field without adjacent piles, and then bending moments of piles investigate through conventional beam-column model. Another is CEL (Coupled Eulerian Lagrangian) approach to analyze the adjacent pile responses induced by spudcan penetration through three dimensional numerical model including spudcan, soil profile and adjacent pile. The feasibility of two approaches was verified through comparison between numerically predicted and experimentally measured results. Variations of pile bending moment induced by spudcan penetration are demonstrated with different pile length, spudcan-pile clearance and soil profiles. Comparisons of the numerically predicted pile bending moment and the experimentally measured values show that the both are close agreement for the different spudcan-pile clearance at the spudcan penetration depth of less than 15m in NC soil profiles. However, an apparent discrepancy lays on that the second positive peak bending moment from the numerical calculation by the beam-column model moves up to a higher depth than the measurement for the 40m pile length.
{"title":"Response Study of Jacket Piles Induced by Spudcan Penetration","authors":"Shuzhao Li, Zhongchang Wang, Xu Jia, Linlin He","doi":"10.1115/OMAE2018-78337","DOIUrl":"https://doi.org/10.1115/OMAE2018-78337","url":null,"abstract":"Mobile jack-up rigs are frequently cantilevered over production jacket platforms to drill new wells or rework existing well for the offshore oil and gas at shallow and middle water depths. The proximity of the rig to the existing fixed platform will affect the performance of pile foundations of the platform and may cause some distress to the adjacent pile foundation by spudcan penetration. With the increasing accidents with respect to the spudcan penetration and spudcanpile interaction caused severe economic losses in offshore engineering of China, solving these problems is an urgent and significance assignment at present. Since the spudcan-pile interaction is a typical offshore geotechnical large strain large deformation problem, a numerical approach based on the large strain technique is a valid solution tool for evaluating spudcanpile interaction. The paper addresses additional responses of the adjacent pile induced by spudcan penetration in single clay profile and clay overlying sand profile using two different large strain large deformation numerical approaches. One is called two-stage approach. Firstly, ALE (Arbitrary Lagrangian Eulerian) approach is used to the displacement field of soil is calculated at the free field without adjacent piles, and then bending moments of piles investigate through conventional beam-column model. Another is CEL (Coupled Eulerian Lagrangian) approach to analyze the adjacent pile responses induced by spudcan penetration through three dimensional numerical model including spudcan, soil profile and adjacent pile. The feasibility of two approaches was verified through comparison between numerically predicted and experimentally measured results. Variations of pile bending moment induced by spudcan penetration are demonstrated with different pile length, spudcan-pile clearance and soil profiles. Comparisons of the numerically predicted pile bending moment and the experimentally measured values show that the both are close agreement for the different spudcan-pile clearance at the spudcan penetration depth of less than 15m in NC soil profiles. However, an apparent discrepancy lays on that the second positive peak bending moment from the numerical calculation by the beam-column model moves up to a higher depth than the measurement for the 40m pile length.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121389648","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Courbois, Emmanuel Tcheuko, B. Bouscasse, Young-Myung Choi, O. Kimmoun, R. Mariani
Wave drift loads play a key role in station-keeping analysis of floating offshore structures. However, conventional radiation/diffraction tools have some limitations especially when the structure has sharp edges, requiring more extended validation. In this paper, a series of CFD computations are performed on a 2D simplified shape representing a rectangular-pontoon, with or without a horizontal damping plate. In the present study, the structure is considered to be fixed (radiation effects are not included). For validation, the results of CFD are compared with the results of experiments. The model tests are performed at the wave canal with an equivalent configuration. The drift forces are derived from the reflected and transmitted waves thanks to far field formulation. The incident, reflected and transmitted waves are separated by using a multi “sensors” method. The dissipation of wave energy is also investigated. The analysis is performed on two different model configurations: with and without the presence of a bottom damping plate. The effect of the damping plate on the wave energy dissipation and drift forces are discussed. The results obtained allows for a better understanding and will allow the study on more complex configurations.
{"title":"Study of Viscous Effects on Wave Drift Forces on a Rectangular Pontoon With a Damping Plate by Using CFD Code OpenFOAM","authors":"A. Courbois, Emmanuel Tcheuko, B. Bouscasse, Young-Myung Choi, O. Kimmoun, R. Mariani","doi":"10.1115/OMAE2018-78053","DOIUrl":"https://doi.org/10.1115/OMAE2018-78053","url":null,"abstract":"Wave drift loads play a key role in station-keeping analysis of floating offshore structures. However, conventional radiation/diffraction tools have some limitations especially when the structure has sharp edges, requiring more extended validation. In this paper, a series of CFD computations are performed on a 2D simplified shape representing a rectangular-pontoon, with or without a horizontal damping plate. In the present study, the structure is considered to be fixed (radiation effects are not included). For validation, the results of CFD are compared with the results of experiments. The model tests are performed at the wave canal with an equivalent configuration. The drift forces are derived from the reflected and transmitted waves thanks to far field formulation. The incident, reflected and transmitted waves are separated by using a multi “sensors” method. The dissipation of wave energy is also investigated. The analysis is performed on two different model configurations: with and without the presence of a bottom damping plate. The effect of the damping plate on the wave energy dissipation and drift forces are discussed. The results obtained allows for a better understanding and will allow the study on more complex configurations.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"53 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116189747","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present recent progress on the development of a new fully nonlinear potential flow (FNPF) model for estimation of nonlinear wave-body interactions based on a stabilised unstructured spectral element method (SEM). We introduce new proof-of-concepts for forced nonlinear wave-body interaction in two spatial dimensions to establish the methodology in the SEM setting utilising dynamically adapted unstructured meshes. The numerical method behind the proposed methodology is described in some detail and numerical experiments on the forced motion of (i) surface piercing and (ii) submerged bodies are presented.
{"title":"Nonlinear Wave-Body Interaction Using a Mixed-Eulerian-Lagrangian Spectral Element Model","authors":"C. Monteserin, A. Engsig-Karup, C. Eskilsson","doi":"10.1115/OMAE2018-77692","DOIUrl":"https://doi.org/10.1115/OMAE2018-77692","url":null,"abstract":"We present recent progress on the development of a new fully nonlinear potential flow (FNPF) model for estimation of nonlinear wave-body interactions based on a stabilised unstructured spectral element method (SEM). We introduce new proof-of-concepts for forced nonlinear wave-body interaction in two spatial dimensions to establish the methodology in the SEM setting utilising dynamically adapted unstructured meshes. The numerical method behind the proposed methodology is described in some detail and numerical experiments on the forced motion of (i) surface piercing and (ii) submerged bodies are presented.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"53 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126708445","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Economics decision drives the operation of ocean-wave energy converters (WEC) to be in a “farm mode”. Control strategy developed for a WEC array will be of high importance for improving the aggregate energy extraction efficiency of the whole system. Model-predictive control (MPC) has shown its strong potential in maximizing the energy output in devices with hard constraints on operation states and machinery inputs (See Ref. [1–3]). Computational demands for using MPC to control an array in real time can be prohibitive. In this paper, we formulate the MPC to control an array of heaving point absorbers, by recasting the optimization problem for energy extraction into a convex Quadratic Programming (QP) problem, the solution of which can be carried out very efficiently. Large slew rates are to be penalized, which can also guarantee the convexity of the QP and improve the computational efficiency for achieving the optimal solution. Constraints on both the states and the control input can be accommodated in this MPC method. Full hydro-dynamic interference effects among the WEC array components are taken into account using the theory developed in [4]. Demonstrative results of the application are presented for arrays of two, three, and four point absorbers operating at different incident-wave angles. Effects of the interacting waves on power performance of the array under the new MPC control are investigated, with simulations conducted in both regular and irregular seas. Heaving motions of individual devices at their optimal conditions are shown. Also presented is the reactive power required by the power takeoff (PTO) system of the array to achieve optimality. We are pleased to contribute this article in celebration of our collegiality with Professor Bernard Molin on the occasion of his honoring symposium.
{"title":"Performance of a Wave-Energy-Converter Array Operating Under Model-Predictive Control Based on a Convex Formulation","authors":"Qian Zhong, R. W. Yeung","doi":"10.1115/OMAE2018-78739","DOIUrl":"https://doi.org/10.1115/OMAE2018-78739","url":null,"abstract":"Economics decision drives the operation of ocean-wave energy converters (WEC) to be in a “farm mode”. Control strategy developed for a WEC array will be of high importance for improving the aggregate energy extraction efficiency of the whole system. Model-predictive control (MPC) has shown its strong potential in maximizing the energy output in devices with hard constraints on operation states and machinery inputs (See Ref. [1–3]). Computational demands for using MPC to control an array in real time can be prohibitive. In this paper, we formulate the MPC to control an array of heaving point absorbers, by recasting the optimization problem for energy extraction into a convex Quadratic Programming (QP) problem, the solution of which can be carried out very efficiently. Large slew rates are to be penalized, which can also guarantee the convexity of the QP and improve the computational efficiency for achieving the optimal solution. Constraints on both the states and the control input can be accommodated in this MPC method. Full hydro-dynamic interference effects among the WEC array components are taken into account using the theory developed in [4]. Demonstrative results of the application are presented for arrays of two, three, and four point absorbers operating at different incident-wave angles. Effects of the interacting waves on power performance of the array under the new MPC control are investigated, with simulations conducted in both regular and irregular seas. Heaving motions of individual devices at their optimal conditions are shown. Also presented is the reactive power required by the power takeoff (PTO) system of the array to achieve optimality.\u0000 We are pleased to contribute this article in celebration of our collegiality with Professor Bernard Molin on the occasion of his honoring symposium.","PeriodicalId":106551,"journal":{"name":"Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics","volume":"83 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-06-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125597376","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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