In recent years, extreme waves have attracted more and more attention due to its threat to offshore and coastal structures. It is essential to obtain further insight into the formation and propagation of the extreme waves. The formation of extreme waves mainly comes from the simultaneous focusing of wave group energy in the ocean. In the present study, the nonlinear characteristics of the extreme wave are experimentally investigated by the wave focusing method. The phase decomposition methods, both two-phases separation and four-phases separation methods, are used to obtain the higher harmonic elevation in the focused wave. The results show that the four-phases separation method can reasonably extract the first four harmonics. With the separated results, the nonlinear analysis of the wave elevation and velocity of the focused wave is carried out. It is found that the harmonics of the wave group focused at the same time, but the wave elevation and energy of higher-order harmonics are smaller than that of the overall wave. The Stokes wave theory can describe the variation of second-order harmonics satisfactorily. However, the Stokes wave theory cannot estimate third-order harmonics accurately. More work should be carried out to figure out the third-order wave interaction occurring during wave focusing. With a distributed wave gauge system, the wave evolution along the wave flume is measured. The evanescent modes significantly influence the wave group’s harmonic structure near the wavemaker. The coefficients of the higher-order harmonics are obtained from the measured elevations. The nonlinear wave elevation of the focused wave can be reconstructed with those coefficients basing on the linear theoretical solution, which is in good agreement with the experimental results.
{"title":"The Harmonic Structure of the Focused Wave in a Wave Flume","authors":"Huixing Gao, Jianjun Zhou, Yang Song, Qinghe Fang","doi":"10.1115/omae2021-62721","DOIUrl":"https://doi.org/10.1115/omae2021-62721","url":null,"abstract":"\u0000 In recent years, extreme waves have attracted more and more attention due to its threat to offshore and coastal structures. It is essential to obtain further insight into the formation and propagation of the extreme waves. The formation of extreme waves mainly comes from the simultaneous focusing of wave group energy in the ocean. In the present study, the nonlinear characteristics of the extreme wave are experimentally investigated by the wave focusing method. The phase decomposition methods, both two-phases separation and four-phases separation methods, are used to obtain the higher harmonic elevation in the focused wave. The results show that the four-phases separation method can reasonably extract the first four harmonics. With the separated results, the nonlinear analysis of the wave elevation and velocity of the focused wave is carried out. It is found that the harmonics of the wave group focused at the same time, but the wave elevation and energy of higher-order harmonics are smaller than that of the overall wave. The Stokes wave theory can describe the variation of second-order harmonics satisfactorily. However, the Stokes wave theory cannot estimate third-order harmonics accurately. More work should be carried out to figure out the third-order wave interaction occurring during wave focusing.\u0000 With a distributed wave gauge system, the wave evolution along the wave flume is measured. The evanescent modes significantly influence the wave group’s harmonic structure near the wavemaker. The coefficients of the higher-order harmonics are obtained from the measured elevations. The nonlinear wave elevation of the focused wave can be reconstructed with those coefficients basing on the linear theoretical solution, which is in good agreement with the experimental results.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"30 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90490411","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}
Sébastien Fouques, S. Lafleche, A. Akselsen, T. Sauder
It is well known that flap wavemakers behave in a nonlinear way when either the flap angle or the flap velocity becomes large. Moreover, the hinge depth should be adapted to the period of the generated waves in order to minimize linear evanescent modes, which may contribute to the formation of nonlinear spurious waves. For example, imposing a sinusoidal motion with a relatively long period and a large amplitude to a short flap will result in a surface elevation composed of a regular wave with the same period as the flap motion, but also of a variety of harmonics with higher frequencies. Second-order harmonics can be predicted theoretically for regular and irregular waves, and they can be corrected by modifying the control signal of the wavemaker. However, there is no theory that can describe nor mitigate effects of orders higher than two. The design of the wavemaker is then essential to generate extreme sea states with good quality and predictability in a laboratory. In this paper, the nonlinearities of flap wavemakers are investigated experimentally for regular and irregular waves generated in SINTEF Ocean’s laboratories. Nonlinearities of order two and three are estimated from times series of the surface elevation measured at different locations by an array of wave probes. Particular focus is put on identifying the effects of the classical second-order correction on the second- and third-order harmonics.
{"title":"An Experimental Investigation of Nonlinear Wave Generation by Flap Wavemakers","authors":"Sébastien Fouques, S. Lafleche, A. Akselsen, T. Sauder","doi":"10.1115/omae2021-63120","DOIUrl":"https://doi.org/10.1115/omae2021-63120","url":null,"abstract":"It is well known that flap wavemakers behave in a nonlinear way when either the flap angle or the flap velocity becomes large. Moreover, the hinge depth should be adapted to the period of the generated waves in order to minimize linear evanescent modes, which may contribute to the formation of nonlinear spurious waves. For example, imposing a sinusoidal motion with a relatively long period and a large amplitude to a short flap will result in a surface elevation composed of a regular wave with the same period as the flap motion, but also of a variety of harmonics with higher frequencies. Second-order harmonics can be predicted theoretically for regular and irregular waves, and they can be corrected by modifying the control signal of the wavemaker. However, there is no theory that can describe nor mitigate effects of orders higher than two. The design of the wavemaker is then essential to generate extreme sea states with good quality and predictability in a laboratory.\u0000 In this paper, the nonlinearities of flap wavemakers are investigated experimentally for regular and irregular waves generated in SINTEF Ocean’s laboratories. Nonlinearities of order two and three are estimated from times series of the surface elevation measured at different locations by an array of wave probes. Particular focus is put on identifying the effects of the classical second-order correction on the second- and third-order harmonics.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"54 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82595180","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}
F. Duan, N. Ma, X. Gu, Yao-hua Zhou, Wang Shangming
The excessive acceleration is one of five stability failure modes for intact stability being discussed at IMO. The excessive acceleration usually occurs in shallow draft state, under which the ship is prone to large nonlinear rolling motion. Therefore, the accurate prediction and evaluation of the acceleration response are required in ship intact stability analysis. This paper proposes a 5-DOF model in time domain to calculate the nonlinear acceleration response of a large container ship. The nonlinear restoring force and wave exciting forces (F-K force) are calculated through pressure integration on instantaneous wetted surfaces. A model test has been carried out to verify the prediction method of ship nonlinear acceleration response in the regular and irregular waves. It turns out the ship nonlinear acceleration response in regular and irregular waves obtained by the nonlinear time domain simulation agrees well with the experimental results. The vulnerability criteria for excessive acceleration are also validated by numerical and experimental results. In addition, the influence factor of ship lateral acceleration is studied. The results show that the prediction accuracy of 5-DOF model is acceptable. However, the accuracy needs to be improved for the condition of short wavelength. The influence of angular velocity can be ignored.
{"title":"Prediction of Nonlinear Acceleration Response of a Large Container Ship and the Validation of Excessive Acceleration Failure Mode","authors":"F. Duan, N. Ma, X. Gu, Yao-hua Zhou, Wang Shangming","doi":"10.1115/omae2021-62685","DOIUrl":"https://doi.org/10.1115/omae2021-62685","url":null,"abstract":"\u0000 The excessive acceleration is one of five stability failure modes for intact stability being discussed at IMO. The excessive acceleration usually occurs in shallow draft state, under which the ship is prone to large nonlinear rolling motion. Therefore, the accurate prediction and evaluation of the acceleration response are required in ship intact stability analysis. This paper proposes a 5-DOF model in time domain to calculate the nonlinear acceleration response of a large container ship. The nonlinear restoring force and wave exciting forces (F-K force) are calculated through pressure integration on instantaneous wetted surfaces. A model test has been carried out to verify the prediction method of ship nonlinear acceleration response in the regular and irregular waves. It turns out the ship nonlinear acceleration response in regular and irregular waves obtained by the nonlinear time domain simulation agrees well with the experimental results. The vulnerability criteria for excessive acceleration are also validated by numerical and experimental results. In addition, the influence factor of ship lateral acceleration is studied. The results show that the prediction accuracy of 5-DOF model is acceptable. However, the accuracy needs to be improved for the condition of short wavelength. The influence of angular velocity can be ignored.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"18 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82866438","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 flow-through porous bodies/structure is one of the more advanced research in the area of energy dissipation in coastal and civil engineering fields. The experiments on the determination of drag coefficient of screens with varying porosities and for the range of flow velocities lead to explore damping ratio in a typical fluid-structure interaction problem. An experimental study has been carried out to assess the drag coefficient of the porous screens as suggested by Keulegan, G. H (1968) [3]. Six different screens with porosities of 4.4%, 6.8%, 9.2% 15%, 20% and 25% are considered. In the experiments, water with a known head from one tank is allowed to flow through a pipe equipped with porous screens into the other tank. Based on the experimental observation, the correlation between Reynolds number and drag coefficient is obtained for all porous screens. The effect of damping nature (damping ratio) of the screen for a particular range of Reynolds number has been explored. As the Reynolds number increases, the drag coefficient decreases with increasing the porosity of the screen. Further, it is understood that the value of the damping ratio decreases with an increasing relative head (H/L).
渗流多孔体/结构是海岸工程和土木工程耗能研究的前沿课题之一。通过确定不同孔隙率筛网的阻力系数和流速范围的实验，探讨了典型流固耦合问题中的阻尼比。Keulegan, G. H(1968)[3]提出了多孔筛网阻力系数的实验研究。考虑了6种孔隙率分别为4.4%、6.8%、9.2%、15%、20%和25%的不同屏幕。在实验中，已知水头的水从一个水箱流出，通过装有多孔筛网的管道流入另一个水箱。在实验观察的基础上，得到了所有多孔筛网的雷诺数与阻力系数的相关关系。探讨了筛网阻尼特性(阻尼比)对特定雷诺数范围的影响。随着雷诺数的增加，阻力系数随筛孔率的增加而减小。此外，阻尼比的值随着相对水头(H/L)的增加而减小。
{"title":"Drag Coefficient for Porous Screen in a Non-Oscillating Perpendicular to Plane-in Flow","authors":"M. S. Bhandiwad, T. Nasar","doi":"10.1115/omae2021-62799","DOIUrl":"https://doi.org/10.1115/omae2021-62799","url":null,"abstract":"\u0000 The flow-through porous bodies/structure is one of the more advanced research in the area of energy dissipation in coastal and civil engineering fields. The experiments on the determination of drag coefficient of screens with varying porosities and for the range of flow velocities lead to explore damping ratio in a typical fluid-structure interaction problem. An experimental study has been carried out to assess the drag coefficient of the porous screens as suggested by Keulegan, G. H (1968) [3]. Six different screens with porosities of 4.4%, 6.8%, 9.2% 15%, 20% and 25% are considered. In the experiments, water with a known head from one tank is allowed to flow through a pipe equipped with porous screens into the other tank. Based on the experimental observation, the correlation between Reynolds number and drag coefficient is obtained for all porous screens. The effect of damping nature (damping ratio) of the screen for a particular range of Reynolds number has been explored. As the Reynolds number increases, the drag coefficient decreases with increasing the porosity of the screen. Further, it is understood that the value of the damping ratio decreases with an increasing relative head (H/L).","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"32 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78949175","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}
Lorenzo Balestra, Ruochen Yang, I. Schjølberg, I. Utne, Ø. Ulleberg
This paper focuses on the use of safety barrier analysis, during the design phase of a vessel powered by cryogenic hydrogen, to identify possible weaknesses in the architecture. Barrier analysis can be used to evaluate a series of scenarios that have been identified in the industry as critical. The performance evaluation of such barriers in a specific scenario can lead to either the approval of the design, if a safety threshold is met, or the inclusion of additional barriers to mitigate risk even further. By conducting a structured analysis, it is possible to identify key barriers that need to be included in the system, intended both as physical barriers (sensors, cold box) and as administrative barriers (checklist, operator training). The method chosen for this study is the Barrier and Operational Risk Analysis (BORA) method. This method, developed for the analysis of hydrocarbon releases, is described in the paper and adapted for the analysis of cryogenic hydrogen releases. A case study is presented using the BORA method, developing the qualitative barrier analysis. The qualitative section of the method can be easily adapted to vessels of different class and size adopting the same storage solution. The barrier analysis provides a general framework to analyze the system and check that the safety requirements defined by the ship operator and maritime certification societies are met.
{"title":"Towards Safety Barrier Analysis of Hydrogen Powered Maritime Vessels","authors":"Lorenzo Balestra, Ruochen Yang, I. Schjølberg, I. Utne, Ø. Ulleberg","doi":"10.1115/omae2021-60451","DOIUrl":"https://doi.org/10.1115/omae2021-60451","url":null,"abstract":"\u0000 This paper focuses on the use of safety barrier analysis, during the design phase of a vessel powered by cryogenic hydrogen, to identify possible weaknesses in the architecture. Barrier analysis can be used to evaluate a series of scenarios that have been identified in the industry as critical. The performance evaluation of such barriers in a specific scenario can lead to either the approval of the design, if a safety threshold is met, or the inclusion of additional barriers to mitigate risk even further. By conducting a structured analysis, it is possible to identify key barriers that need to be included in the system, intended both as physical barriers (sensors, cold box) and as administrative barriers (checklist, operator training). The method chosen for this study is the Barrier and Operational Risk Analysis (BORA) method. This method, developed for the analysis of hydrocarbon releases, is described in the paper and adapted for the analysis of cryogenic hydrogen releases. A case study is presented using the BORA method, developing the qualitative barrier analysis. The qualitative section of the method can be easily adapted to vessels of different class and size adopting the same storage solution. The barrier analysis provides a general framework to analyze the system and check that the safety requirements defined by the ship operator and maritime certification societies are met.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"136 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76390285","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}
Articulated pusher barge vessel is a short-distance transport vessel with good economic performance and practicability, which is widely used in the Yangtze River of China. In this present work, the resistance performance of articulated pusher barge vessel in deep water and shallow water was studied by model tests in the towing tank and basin of Shanghai Ship and Shipping Research Institute. During the experimental investigation, the articulated pusher barge vessel was divided into three parts: the pusher, the barge and the articulated pusher barge system. Firstly, the deep water resistance performance of the articulated pusher barge system, barge and the pusher at design draught T was studied, then the water depth h was adjusted, and the shallow water resistance at h/T = 2.0, 1.5 and 1.2 was tested and studied respectively, and the difference between deep water resistance and shallow water resistance at design draught were compared. The results of model tests and analysis show that: 1) in the study of deep water resistance, the total resistance of the barge was larger than that of the articulated pusher barge system. 2) for the barge, the shallow water resistance increases about 0.4–0.7 times at h/T = 2.0, 0.5–1.1 times at h/T = 1.5, and 0.7–2.3 times at h/T = 1.2. 3) for the pusher, the shallow water resistance increases about 1.0–0.4 times at h/T = 2.7, 1.2–0.9 times at h/T = 2.0, and 1.7–2.4 times at h/T = 1.6. 4) for the articulated pusher barge system, the shallow water resistance increases about 0.2–0.3 times at h/T = 2.0, 0.5–1.3 times at h/T = 1.5, and 1.0–3.5 times at h/T = 1.2. Furthermore, the water depth Froude number Frh in shallow water was compared with the changing trend of resistance in shallow water.
{"title":"Resistance Tests of an Articulated Pusher Barge System in Deep and Shallow Water","authors":"Li Zhang, Lei Xing, Mingyu Dong, Wei-min Chen","doi":"10.1115/omae2021-61754","DOIUrl":"https://doi.org/10.1115/omae2021-61754","url":null,"abstract":"\u0000 Articulated pusher barge vessel is a short-distance transport vessel with good economic performance and practicability, which is widely used in the Yangtze River of China. In this present work, the resistance performance of articulated pusher barge vessel in deep water and shallow water was studied by model tests in the towing tank and basin of Shanghai Ship and Shipping Research Institute. During the experimental investigation, the articulated pusher barge vessel was divided into three parts: the pusher, the barge and the articulated pusher barge system. Firstly, the deep water resistance performance of the articulated pusher barge system, barge and the pusher at design draught T was studied, then the water depth h was adjusted, and the shallow water resistance at h/T = 2.0, 1.5 and 1.2 was tested and studied respectively, and the difference between deep water resistance and shallow water resistance at design draught were compared. The results of model tests and analysis show that: 1) in the study of deep water resistance, the total resistance of the barge was larger than that of the articulated pusher barge system. 2) for the barge, the shallow water resistance increases about 0.4–0.7 times at h/T = 2.0, 0.5–1.1 times at h/T = 1.5, and 0.7–2.3 times at h/T = 1.2. 3) for the pusher, the shallow water resistance increases about 1.0–0.4 times at h/T = 2.7, 1.2–0.9 times at h/T = 2.0, and 1.7–2.4 times at h/T = 1.6. 4) for the articulated pusher barge system, the shallow water resistance increases about 0.2–0.3 times at h/T = 2.0, 0.5–1.3 times at h/T = 1.5, and 1.0–3.5 times at h/T = 1.2. Furthermore, the water depth Froude number Frh in shallow water was compared with the changing trend of resistance in shallow water.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"20 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79466276","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 present research focuses on the experimental and numerical analysis of nonlinear gap resonance which can occur for two side-by-side configured vessels during the offloading operation of Liquified Natural Gas (LNG). The proximity of the FLNG (Floating Liquefied Natural Gas) facility and LNGC (Liquified Natural Gas Carrier) brings about the formation of a long narrow gap region between the two vessels. The model test was carried out in a wave flume with vessels of different sizes to obtain the resonance response at different locations in the gap region with the effects of gap distances and vessel drafts in incident waves of different wave frequencies and wave directions analysed. It was found that certain model configurations produce increased wave amplification between the vessels, these were highlighted and presented and have the possibility of being predicted to prevent the occurrence. The numerical analysis was carried out with the potential flow solver SIMA in the time domain and a calibrated damping factor was assigned to suppress the overestimated wave elevation in the narrow gap region.
{"title":"An Experimental and Numerical Analysis of Gap Resonance Applicable for FLNG Side-by-Side Offloading","authors":"Jideofor Collins Nwafor, Zhiqiang Hu","doi":"10.1115/omae2021-62059","DOIUrl":"https://doi.org/10.1115/omae2021-62059","url":null,"abstract":"\u0000 The present research focuses on the experimental and numerical analysis of nonlinear gap resonance which can occur for two side-by-side configured vessels during the offloading operation of Liquified Natural Gas (LNG). The proximity of the FLNG (Floating Liquefied Natural Gas) facility and LNGC (Liquified Natural Gas Carrier) brings about the formation of a long narrow gap region between the two vessels. The model test was carried out in a wave flume with vessels of different sizes to obtain the resonance response at different locations in the gap region with the effects of gap distances and vessel drafts in incident waves of different wave frequencies and wave directions analysed. It was found that certain model configurations produce increased wave amplification between the vessels, these were highlighted and presented and have the possibility of being predicted to prevent the occurrence. The numerical analysis was carried out with the potential flow solver SIMA in the time domain and a calibrated damping factor was assigned to suppress the overestimated wave elevation in the narrow gap region.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"24 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91516266","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}
F. M. Chagas, B. R. Rachid, B. G. Ambrosio, A. A. Luz, C. Gramcianinov, P. Serrao, R. Camargo, E. Siegle
We present a high-resolution metocean forecast model (Aimar), which provides 24/7 results for the Brazilian coast. The model integrates global model boundary conditions and detailed coastal models, especially for complex geometry areas near ports and major coastal cities. The aim of this paper is to assess the forecast reliability and to present model data compared to in-situ measurements under high energy weather events. Mean wind velocity and direction were investigated during the occurrence of an extratropical cyclone near Brazilian coast. The model has been assessed by comparing its results to two specific events, one for winds and one for waves. Results of the tested wind event show that Aimar results predict the high energy winds in advance of 5 days, while NCEP’s Global Forecast System Ensemble (GFSe) predicted the same event in advance of 2–3 days, for the region of Santos city. Results of the tested wave event show that Aimar forecasts properly represent the wave propagation for complex geometry coasts. The high-resolution coastal model could predict the nearshore state of sea agitation caused by the passage of a cold front. Model agreement with in-situ wave measurements adjacent to Rio de Janeiro-RJ city were considered Excellent and Good, according to statistical parameters R and RMAE. These results show that high-resolution coastal forecast models can be applied to increase the efficiency, resource uses and reduce the risks for marine operations and engineering works.
{"title":"Assessment of Wind and Wave High-Resolution Forecasts During High-Energy Weather Events in the Brazilian Coast","authors":"F. M. Chagas, B. R. Rachid, B. G. Ambrosio, A. A. Luz, C. Gramcianinov, P. Serrao, R. Camargo, E. Siegle","doi":"10.1115/omae2021-62030","DOIUrl":"https://doi.org/10.1115/omae2021-62030","url":null,"abstract":"\u0000 We present a high-resolution metocean forecast model (Aimar), which provides 24/7 results for the Brazilian coast. The model integrates global model boundary conditions and detailed coastal models, especially for complex geometry areas near ports and major coastal cities. The aim of this paper is to assess the forecast reliability and to present model data compared to in-situ measurements under high energy weather events. Mean wind velocity and direction were investigated during the occurrence of an extratropical cyclone near Brazilian coast. The model has been assessed by comparing its results to two specific events, one for winds and one for waves. Results of the tested wind event show that Aimar results predict the high energy winds in advance of 5 days, while NCEP’s Global Forecast System Ensemble (GFSe) predicted the same event in advance of 2–3 days, for the region of Santos city. Results of the tested wave event show that Aimar forecasts properly represent the wave propagation for complex geometry coasts. The high-resolution coastal model could predict the nearshore state of sea agitation caused by the passage of a cold front. Model agreement with in-situ wave measurements adjacent to Rio de Janeiro-RJ city were considered Excellent and Good, according to statistical parameters R and RMAE. These results show that high-resolution coastal forecast models can be applied to increase the efficiency, resource uses and reduce the risks for marine operations and engineering works.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"120 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73301675","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 wave interaction with cylinders placed in proximity results in significant modification of the wave field, wave-induced processes, and wave loading. The evaluation of such a complex wave regime and accurate assessment of the wave loading requires an efficient and accurate numerical model. Concerning the wave scattering types identified by Swan et al. (2015) and lateral progressive edge waves, this paper presents the application of a two-phase Computational Fluid Dynamics (CFD) model to carry out a detailed investigation of nonlinear wave field surrounding a pair of columns placed in the tandem arrangement in the direction of wave propagation and corresponding harmonics. The numerical analysis is conducted using the Unsteady Reynolds-Averaged Navier-Stokes/VOF model based on the OpenFOAM framework combined with the olaFlow toolbox for wave generation/absorption. For the simulations, the truncated cylinders are assumed vertical and surface piercing with a circular cross-section subjected to regular, non-breaking fifth-order Stokes waves propagating with moderate steepness in deep water. Primarily, the numerical model is validated with experimental data provided by ITTC (OEC)[1] for a single cylinder. Future, the given simulations are conducted for different centre-to-centre distances between the tandem large cylinders. The results show the evolution of a strong wave diffraction pattern and consequently high wave amplification harmonics around cylinders are apparent.
波浪与靠近圆柱体的相互作用会导致波场、波致过程和波载荷的显著改变。要对如此复杂的波浪状态进行评估并准确地评估波浪荷载，需要一个高效、准确的数值模型。针对Swan et al.(2015)确定的波散射类型和横向递进边波，本文采用两相计算流体动力学(CFD)模型，对沿波传播方向串列布置的一对柱及其对应谐波周围的非线性波场进行了详细研究。采用基于OpenFOAM框架的非定常reynolds - average Navier-Stokes/VOF模型，结合olaFlow工具箱进行波浪产生/吸收的数值分析。在模拟中，假设截短的圆柱体是垂直的，表面穿透，横截面为圆形，在深水中以中等陡度传播的规则，非破碎的五阶斯托克斯波。首先，利用ITTC (OEC)[1]提供的单缸实验数据对数值模型进行了验证。在此基础上，对串联大气缸之间不同的中心距离进行了仿真。结果表明，在圆柱体周围形成了强波衍射图样，从而产生了明显的高波放大谐波。
{"title":"Numerical Simulation of Wave Interaction With a Pair of Fixed Large Tandem Cylinders Subjected to Regular, Non-Breaking Waves","authors":"M. Mohseni, C. Guedes Soares","doi":"10.1115/omae2021-62089","DOIUrl":"https://doi.org/10.1115/omae2021-62089","url":null,"abstract":"\u0000 The wave interaction with cylinders placed in proximity results in significant modification of the wave field, wave-induced processes, and wave loading. The evaluation of such a complex wave regime and accurate assessment of the wave loading requires an efficient and accurate numerical model. Concerning the wave scattering types identified by Swan et al. (2015) and lateral progressive edge waves, this paper presents the application of a two-phase Computational Fluid Dynamics (CFD) model to carry out a detailed investigation of nonlinear wave field surrounding a pair of columns placed in the tandem arrangement in the direction of wave propagation and corresponding harmonics. The numerical analysis is conducted using the Unsteady Reynolds-Averaged Navier-Stokes/VOF model based on the OpenFOAM framework combined with the olaFlow toolbox for wave generation/absorption. For the simulations, the truncated cylinders are assumed vertical and surface piercing with a circular cross-section subjected to regular, non-breaking fifth-order Stokes waves propagating with moderate steepness in deep water. Primarily, the numerical model is validated with experimental data provided by ITTC (OEC)[1] for a single cylinder. Future, the given simulations are conducted for different centre-to-centre distances between the tandem large cylinders. The results show the evolution of a strong wave diffraction pattern and consequently high wave amplification harmonics around cylinders are apparent.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"92 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81253698","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}
S. Saincher, John Wesly Gongalla, P. Vineesh, V. Sriram
Moonpools are designed to provide a calm environment for lowering of equipment from ships. Considerable research effort has been invested towards understanding water column excitation within a moonpool. However, most recent investigations consider regular waves. The nature of interaction between focused waves and a moonpool is not well-understood; the present work strives to fill this research gap. A series of experiments have been carried out in a 22 m long glass flume in the Department of Ocean Engineering at IIT Madras. Two identical cuboidal boxes were affixed with a 0.15 m gap representing a rectangular moonpool. Focused waves based on a constant steepness spectrum were generated in 0.6 m water depth by a piston-type wave-paddle. The focusing point was set at the center of the moonpool and wave-focusing experiments were performed with and without the twin-body. Wave elevation at various locations along the flume was measured using five wave-gauges. Next, the experiments were numerically replicated using the in-house codes IITM-FNPT2D (for inviscid wave generation) and IITM-RANS3D (for fully viscous wave-structure interaction). Gap-excitation at the instant of focusing has been quantified and correlated with focused wave characteristics and with dynamics of spanwise vortices generated at the edges of the moonpool.
{"title":"Experimental and FNPT-RANS Investigations Into Gap-Excitation and Vortex Dynamics in a Rectangular Moonpool Interacting With Focused Waves","authors":"S. Saincher, John Wesly Gongalla, P. Vineesh, V. Sriram","doi":"10.1115/omae2021-61842","DOIUrl":"https://doi.org/10.1115/omae2021-61842","url":null,"abstract":"\u0000 Moonpools are designed to provide a calm environment for lowering of equipment from ships. Considerable research effort has been invested towards understanding water column excitation within a moonpool. However, most recent investigations consider regular waves. The nature of interaction between focused waves and a moonpool is not well-understood; the present work strives to fill this research gap. A series of experiments have been carried out in a 22 m long glass flume in the Department of Ocean Engineering at IIT Madras. Two identical cuboidal boxes were affixed with a 0.15 m gap representing a rectangular moonpool. Focused waves based on a constant steepness spectrum were generated in 0.6 m water depth by a piston-type wave-paddle. The focusing point was set at the center of the moonpool and wave-focusing experiments were performed with and without the twin-body. Wave elevation at various locations along the flume was measured using five wave-gauges. Next, the experiments were numerically replicated using the in-house codes IITM-FNPT2D (for inviscid wave generation) and IITM-RANS3D (for fully viscous wave-structure interaction). Gap-excitation at the instant of focusing has been quantified and correlated with focused wave characteristics and with dynamics of spanwise vortices generated at the edges of the moonpool.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"21 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81454652","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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：