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}
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}
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}
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}
Numerical simulations are peformed to model the dynamic motions of a free floating body exposed to water waves. The solid body has low freeboard and draft, and its upper deck can be washed by the steep waves. Thus, the green water phenomenon occurs as large waves interact with the floating body. The aim of the research is to improve the understanding of the green water emerging above the upper deck of a floating plate. A thin floating body with barriers is also modeled. For the case of the body equipped with barriers, no green water occurs. Green water has been seen to affect the wave field and the dynamic motions of the plate. It is observed that when water can wash the upper surface of the floating object, drift speed is slightly decreased as a proportion of the energy of waves is dissipated above the body. Water waves are seen to impact the upper surface of the thin floating body as the green water flows over its upper deck. Furthermore, water is seen to impact the plate as its front edge re-enters the water. The first water impact only occurs when the floating body is not equipped with any barrier. By sampling the numerical simulations, it is observed that the non-dimensional value of the impact pressure, resulting from the green water, is larger for the case of smaller wavelength.
{"title":"Drift Motion of Floating Bodies Under the Action of Green Water","authors":"S. Tavakoli, Luofeng Huang, A. Babanin","doi":"10.1115/omae2021-63017","DOIUrl":"https://doi.org/10.1115/omae2021-63017","url":null,"abstract":"\u0000 Numerical simulations are peformed to model the dynamic motions of a free floating body exposed to water waves. The solid body has low freeboard and draft, and its upper deck can be washed by the steep waves. Thus, the green water phenomenon occurs as large waves interact with the floating body. The aim of the research is to improve the understanding of the green water emerging above the upper deck of a floating plate. A thin floating body with barriers is also modeled. For the case of the body equipped with barriers, no green water occurs. Green water has been seen to affect the wave field and the dynamic motions of the plate. It is observed that when water can wash the upper surface of the floating object, drift speed is slightly decreased as a proportion of the energy of waves is dissipated above the body. Water waves are seen to impact the upper surface of the thin floating body as the green water flows over its upper deck. Furthermore, water is seen to impact the plate as its front edge re-enters the water. The first water impact only occurs when the floating body is not equipped with any barrier. By sampling the numerical simulations, it is observed that the non-dimensional value of the impact pressure, resulting from the green water, is larger for the case of smaller wavelength.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"23 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83227522","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}
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}
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}
This study addresses predicting the relationship between forward speed and propeller speed of an autonomous underwater vehicle (AUV) with a towed flexible cable using multiple regression analysis. Accurate prediction of the propeller speed corresponding to forward speed is important. The prediction requires considering various factors such as the dynamic behavior of a flexible cable, tidal currents, and AUV motions. The regression analysis based on in-service data of the AUV, therefore, established the relation between the forward speed and propeller speed considering the other factors. On the other hand, minimal independent variables in the regression model are desirable to avoid multicollinearity and overfitting. Variable selection based on the t-Test and sparse modeling was carried out to remove insignificant variables. We confirmed that the regression model presented in this study was in agreement with the observed data sufficiently, and the residuals of the regression model followed a normal distribution. The propeller speed predicted by the regression model considering only the forward speed of the AUV was comparable to the result predicted by the CFD calculation, not including the other factors. The result indicates the regression analysis can validate the results based on experiments and a numerical simulation.
{"title":"Modeling Relation Between Forward Speed and Propeller Speed of the Cruising AUV Using Multiple Regression Analysis","authors":"Jun Umeda, T. Fujiwara","doi":"10.1115/omae2021-62350","DOIUrl":"https://doi.org/10.1115/omae2021-62350","url":null,"abstract":"\u0000 This study addresses predicting the relationship between forward speed and propeller speed of an autonomous underwater vehicle (AUV) with a towed flexible cable using multiple regression analysis. Accurate prediction of the propeller speed corresponding to forward speed is important. The prediction requires considering various factors such as the dynamic behavior of a flexible cable, tidal currents, and AUV motions. The regression analysis based on in-service data of the AUV, therefore, established the relation between the forward speed and propeller speed considering the other factors. On the other hand, minimal independent variables in the regression model are desirable to avoid multicollinearity and overfitting. Variable selection based on the t-Test and sparse modeling was carried out to remove insignificant variables. We confirmed that the regression model presented in this study was in agreement with the observed data sufficiently, and the residuals of the regression model followed a normal distribution. The propeller speed predicted by the regression model considering only the forward speed of the AUV was comparable to the result predicted by the CFD calculation, not including the other factors. The result indicates the regression analysis can validate the results based on experiments and a numerical simulation.","PeriodicalId":23784,"journal":{"name":"Volume 6: Ocean Engineering","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78428622","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}
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