Go Oishi, H. Yamaguchi, K. Shimada, Kouichi Kayajima
When conducting model tests in a water tank, available model sizes and wave conditions are determined for each tank, depending on measurement accuracy and tank specifications. For deep-water mooring of a floater, a mooring extent in model scale is presumably over 10 meters in depth, making it difficult to be conducted in small-sized tanks without mooring line truncation. The purpose of the research is to develop a device, which could be used as deep-water mooring system in small-sized tanks. Although the law of geometrical similarity is compelled to quit because of the line truncation, the law of mechanical similarity can be maintained by keeping the same restoring, damping and inertia characteristics as those of the full-scale mooring system obtained by numerical simulations. The mooring device consists of a cylinder, a piston, an orifice, springs, pulleys and weights. A spring attached to the mooring line is to generate required restoring force. The orifice, together with the piston, is to generate required damping forces. Inertia forces are generated by the motions of hanged weights, also by the motion of the fluid inside the cylinder. Even negative inertia forces can be given by adjusting natural frequencies of the weight-spring system. With all these examined elements, the mooring device works like the full-depth mooring system. Particulars of the elements of the device have been determined by numerical simulations of the floater moored in the full-depth condition. It has been confirmed that the mooring device behaves as expected in comparison with forced oscillation tests, where prescribed motions were given to the floater-side end point of the mooring line. A tank test has been conducted of a floater with a turret multipoint-moored with the devices and has been satisfactorily compared with numerical simulations of the full-depth system. With the present research it is verified that the mooring device can well simulate actual deep-water mooring system, which makes it possible for small water tanks to deal with deep water mooring experiments.
{"title":"Development of Water Tank Test Device for Deep-Water Mooring","authors":"Go Oishi, H. Yamaguchi, K. Shimada, Kouichi Kayajima","doi":"10.1115/OMAE2018-77090","DOIUrl":"https://doi.org/10.1115/OMAE2018-77090","url":null,"abstract":"When conducting model tests in a water tank, available model sizes and wave conditions are determined for each tank, depending on measurement accuracy and tank specifications. For deep-water mooring of a floater, a mooring extent in model scale is presumably over 10 meters in depth, making it difficult to be conducted in small-sized tanks without mooring line truncation. The purpose of the research is to develop a device, which could be used as deep-water mooring system in small-sized tanks. Although the law of geometrical similarity is compelled to quit because of the line truncation, the law of mechanical similarity can be maintained by keeping the same restoring, damping and inertia characteristics as those of the full-scale mooring system obtained by numerical simulations.\u0000 The mooring device consists of a cylinder, a piston, an orifice, springs, pulleys and weights. A spring attached to the mooring line is to generate required restoring force. The orifice, together with the piston, is to generate required damping forces. Inertia forces are generated by the motions of hanged weights, also by the motion of the fluid inside the cylinder. Even negative inertia forces can be given by adjusting natural frequencies of the weight-spring system. With all these examined elements, the mooring device works like the full-depth mooring system. Particulars of the elements of the device have been determined by numerical simulations of the floater moored in the full-depth condition. It has been confirmed that the mooring device behaves as expected in comparison with forced oscillation tests, where prescribed motions were given to the floater-side end point of the mooring line.\u0000 A tank test has been conducted of a floater with a turret multipoint-moored with the devices and has been satisfactorily compared with numerical simulations of the full-depth system. With the present research it is verified that the mooring device can well simulate actual deep-water mooring system, which makes it possible for small water tanks to deal with deep water mooring experiments.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","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":"115712693","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}
Green water generated by random waves on a fixed, simplified geometry model structure was measured in a large wave basin. The velocity field of the flow that is aerated and highly turbulent was quantified using the bubble image velocimetry (BIV) technique. BIV utilizes shadow textures created by air-water interfaces as tracers in backlit images recorded by a high speed camera. The tracers in consecutive images are then cross-correlated to obtain the corresponding two-dimensional velocities. Random waves were generated by the JONSWAP spectrum with a significant wave height close to the freeboard. An image-based triggering method was employed to detect the green water events and trigger image acquisition. A total of 179 green water events were collected and categorized into three different types, based on the flow behavior. That includes the collapse of overtopping wave, fall of bulk water, and breaking wave crest. Statistical distributions of maximum green water velocities under random waves were developed, while the lognormal distribution was found as the best fit. By modeling the green water as a dam break flow, the Ritter solution was found to be able to capture the horizontal velocity distribution for the random green water events. A prediction equation for the green water velocity distribution under random waves was also obtained.
{"title":"Green Water Flow on a Fixed Model Structure in a Large Wave Basin Under Random Waves","authors":"Wei-Liang Chuang, Kuang‐An Chang, R. Mercier","doi":"10.1115/OMAE2018-77184","DOIUrl":"https://doi.org/10.1115/OMAE2018-77184","url":null,"abstract":"Green water generated by random waves on a fixed, simplified geometry model structure was measured in a large wave basin. The velocity field of the flow that is aerated and highly turbulent was quantified using the bubble image velocimetry (BIV) technique. BIV utilizes shadow textures created by air-water interfaces as tracers in backlit images recorded by a high speed camera. The tracers in consecutive images are then cross-correlated to obtain the corresponding two-dimensional velocities. Random waves were generated by the JONSWAP spectrum with a significant wave height close to the freeboard. An image-based triggering method was employed to detect the green water events and trigger image acquisition. A total of 179 green water events were collected and categorized into three different types, based on the flow behavior. That includes the collapse of overtopping wave, fall of bulk water, and breaking wave crest. Statistical distributions of maximum green water velocities under random waves were developed, while the lognormal distribution was found as the best fit. By modeling the green water as a dam break flow, the Ritter solution was found to be able to capture the horizontal velocity distribution for the random green water events. A prediction equation for the green water velocity distribution under random waves was also obtained.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"44 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":"114200938","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}
Potential liquefaction of some cargoes (Nickel ore, iron ore, ...) is a major risk for the maritime industry. The difficulties to simulate accurately the behaviour of these materials as well as their interaction with a bulk carrier model leaded us to use a non-Newtonian highly viscous fluid to model a liquefied ore. An experimental approach is presented in this paper. Roll responses of a ship model as well as details on the internal free surface behaviours are investigated for different loading conditions: solid cargo, fresh water and viscous fluids.
{"title":"Experimental Study of Ship Response due to Internal Viscous Cargo Motions","authors":"V. Baudry, J. Rousset","doi":"10.1115/OMAE2018-77502","DOIUrl":"https://doi.org/10.1115/OMAE2018-77502","url":null,"abstract":"Potential liquefaction of some cargoes (Nickel ore, iron ore, ...) is a major risk for the maritime industry. The difficulties to simulate accurately the behaviour of these materials as well as their interaction with a bulk carrier model leaded us to use a non-Newtonian highly viscous fluid to model a liquefied ore. An experimental approach is presented in this paper. Roll responses of a ship model as well as details on the internal free surface behaviours are investigated for different loading conditions: solid cargo, fresh water and viscous fluids.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"11 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":"113963671","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}
Here we present a wealth of comparison data from acoustic backscatter current meters against current meters that use an active acoustic path (the RPS CM04). The data cover a wide range of environmental conditions. Very poor agreement between current meters frequently occurs, presenting as both bias and noise. The causes of the differences remain unproven, although for acoustic profilers deployed in deep water, failure of the assumption of the same flow in all beams is a possible source of significant error. As a result of decade’s worth of comparisons plagued with unexplained differences, we have reduced confidence in the accuracy of current data collected by acoustic backscatter sensors. We therefore avoid (where practical) using these instruments when the application of the current data is for engineering design, where uncertainty in accuracy can have significant cost or risk consequences.
{"title":"Comparison of In Situ Current Measurement Methods, the Accuracy Achieved in the Field and Recommendations for Engineering Design Applications","authors":"G. Bush, Carey Nolan","doi":"10.1115/OMAE2018-77170","DOIUrl":"https://doi.org/10.1115/OMAE2018-77170","url":null,"abstract":"Here we present a wealth of comparison data from acoustic backscatter current meters against current meters that use an active acoustic path (the RPS CM04). The data cover a wide range of environmental conditions. Very poor agreement between current meters frequently occurs, presenting as both bias and noise. The causes of the differences remain unproven, although for acoustic profilers deployed in deep water, failure of the assumption of the same flow in all beams is a possible source of significant error. As a result of decade’s worth of comparisons plagued with unexplained differences, we have reduced confidence in the accuracy of current data collected by acoustic backscatter sensors. We therefore avoid (where practical) using these instruments when the application of the current data is for engineering design, where uncertainty in accuracy can have significant cost or risk consequences.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","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":"130250007","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 study of very long-term ocean climate is of great interest in a number of different applications. In a climate change perspective, estimations of return values of wind and wave parameters to a future climate are of great importance for risk management and adaptation purposes. However, there are various ways of estimating the required return values, which introduce additional uncertainties in extreme weather and climate variables pertaining to both current and future climates. The different approaches that are considered in the present work include the annual maxima approach, the block maxima approach, and the MENU method which is based on the calculation of return periods of various level values from nonstationary time series data. Furthermore, the effect of different modelling choices within each of the approaches will be explored. Thus, a range of different return value estimates for the different data sets is obtained for a field of datapoints. Long-term datasets for an area in the North Atlantic Ocean are used in the present study, derived for project ExWaCli, comprising of 30 years in the present (historic period) and two sets of 30 years in the future (future projections). The comparison between the results of the various approaches reveals a variability of the return period estimates, and an assessment of this is given. Moreover, it seems that a slight shift towards higher extremes in a future wave climate might be possible based on the particular datasets that have been analysed.
{"title":"Comparison of Wind and Wave Extremes in Very Long-Term Climatic Scales","authors":"Christos Stefanakos, E. Vanem","doi":"10.1115/OMAE2018-77581","DOIUrl":"https://doi.org/10.1115/OMAE2018-77581","url":null,"abstract":"The study of very long-term ocean climate is of great interest in a number of different applications. In a climate change perspective, estimations of return values of wind and wave parameters to a future climate are of great importance for risk management and adaptation purposes. However, there are various ways of estimating the required return values, which introduce additional uncertainties in extreme weather and climate variables pertaining to both current and future climates. The different approaches that are considered in the present work include the annual maxima approach, the block maxima approach, and the MENU method which is based on the calculation of return periods of various level values from nonstationary time series data. Furthermore, the effect of different modelling choices within each of the approaches will be explored. Thus, a range of different return value estimates for the different data sets is obtained for a field of datapoints. Long-term datasets for an area in the North Atlantic Ocean are used in the present study, derived for project ExWaCli, comprising of 30 years in the present (historic period) and two sets of 30 years in the future (future projections). The comparison between the results of the various approaches reveals a variability of the return period estimates, and an assessment of this is given. Moreover, it seems that a slight shift towards higher extremes in a future wave climate might be possible based on the particular datasets that have been analysed.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"49 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":"121199623","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 paper studies the path following of a ship sailing in restricted waters based on an output feedback control, which consists of a state feedback control law and an extended updated-gain high-gain observer. According to the separation principle, the state feedback control and the extended updated-gain high-gain observer are designed separately. The state feedback control law is designed based on a robust guaranteed cost control method assuming that system states are measurable. Sufficient conditions are given for the control based on a linear uncertain system. The extended updated-gain high-gain observer, whose gains are updated according to the nonlinear functions of available evaluation errors, is used to reconstruct system states. Then the output feedback control is obtained by replacing states value in the state feedback control law with its estimation yielded by the state observer. Numerical simulations confirm the effectiveness of the proposed control method for the path following of a ship sailing in restricted waters.
{"title":"Path Following of a Ship Sailing in Restricted Waters Based on an Extended Updated-Gain High-Gain Observer","authors":"Jianqin Wang, Z. Zou, Tao Wang","doi":"10.1115/OMAE2018-77795","DOIUrl":"https://doi.org/10.1115/OMAE2018-77795","url":null,"abstract":"The paper studies the path following of a ship sailing in restricted waters based on an output feedback control, which consists of a state feedback control law and an extended updated-gain high-gain observer. According to the separation principle, the state feedback control and the extended updated-gain high-gain observer are designed separately. The state feedback control law is designed based on a robust guaranteed cost control method assuming that system states are measurable. Sufficient conditions are given for the control based on a linear uncertain system. The extended updated-gain high-gain observer, whose gains are updated according to the nonlinear functions of available evaluation errors, is used to reconstruct system states. Then the output feedback control is obtained by replacing states value in the state feedback control law with its estimation yielded by the state observer. Numerical simulations confirm the effectiveness of the proposed control method for the path following of a ship sailing in restricted waters.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"15 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":"122250051","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}
Prediction of extreme wave heights has always been a challenge in both the naval and energy industries. The survivability and safe operation and design of marine vehicles and devices are highly dependent on the probability distribution of the wave heights of extreme waves. In traditional linear approaches, researchers use various probability distribution functions mostly generated from field measurements and are usually modified with some statistical methods to account for the distribution of wave heights. These approaches do not take into account nonlinearity and instability in wave train behavior and solely relies on linear wave theory assumptions and perhaps some second order effects in more advanced probability models. This study emphasizes the application of modulation wavelengths and periods, resulting from modulational instability analysis of the nonlinear Schrödinger equation (NLS). In this study, state-of-the-art nonlinear Fourier analysis (NLFA) based on NLS is employed to calculate the unstable wave components. The resulting rise time and travel distance for such unstable modes and their maximum possible growth amplitudes are used to derive a range of probable occurrences. Numerical simulation results from CFD computations are used to examine the capability of such an approach in predicting the magnitude and location of extreme wave occurrence. It is shown that application of the proposed NLS-based analytical procedure enables a more accurate prediction of the extreme wave field.
{"title":"Nonlinear Deepwater Extreme Wave Height and Modulation Wave Length Relation","authors":"A. Mohtat, S. Yim, A. Osborne, Ming Chen","doi":"10.1115/OMAE2018-78755","DOIUrl":"https://doi.org/10.1115/OMAE2018-78755","url":null,"abstract":"Prediction of extreme wave heights has always been a challenge in both the naval and energy industries. The survivability and safe operation and design of marine vehicles and devices are highly dependent on the probability distribution of the wave heights of extreme waves. In traditional linear approaches, researchers use various probability distribution functions mostly generated from field measurements and are usually modified with some statistical methods to account for the distribution of wave heights. These approaches do not take into account nonlinearity and instability in wave train behavior and solely relies on linear wave theory assumptions and perhaps some second order effects in more advanced probability models. This study emphasizes the application of modulation wavelengths and periods, resulting from modulational instability analysis of the nonlinear Schrödinger equation (NLS). In this study, state-of-the-art nonlinear Fourier analysis (NLFA) based on NLS is employed to calculate the unstable wave components. The resulting rise time and travel distance for such unstable modes and their maximum possible growth amplitudes are used to derive a range of probable occurrences. Numerical simulation results from CFD computations are used to examine the capability of such an approach in predicting the magnitude and location of extreme wave occurrence. It is shown that application of the proposed NLS-based analytical procedure enables a more accurate prediction of the extreme wave field.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"70 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":"122291317","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}
Holistic energy management in the shipping industry involves reliable data collection, systematic processing and smart analysis. The era of digitisation allows sensor technology to be used on-board vessels, converting different forms of signal into a digital format that can be exported conveniently for further processing. Appropriate sensor selection is important to ensure continuous data collection when vessels sail through harsh conditions. However, without proper processing, this leads to the collection of big data sets but without resulting useful intelligence that benefits the industry. The adoption of digital and computer technology, allows the next phase of fast data processing. This contributes to the growing area of big data analysis, which is now a problem for many technological sectors, including the maritime industry. Enormous databases are often stored without clear goals or suitable uses. Processing of data requires engineering knowledge to ensure suitable filters are applied to raw data. This systematic processing of data leads to transparency in real time data display and contributes to predictive analysis. In addition, the generation of series of raw data when coupled with other external data such as weather information provides a rich database that reflects the true scenario of the vessel. Subsequent processing will then provide improved decision making tools for optimal operations. These advances open the door for different market analyses and the generation of new knowledge. This paper highlights the crucial steps needed and the challenges of sensor installation to obtain accurate data, followed by pre and post processing of data to generate knowledge. With this, big data can now provide information and reveal hidden patterns and trends regarding vessel operations, machinery diagnostics and energy efficient fleet management. A case study was carried out on a tug boat that operates in the North Sea, firstly to demonstrate confidence in the raw data collected and secondly to demonstrate the systematic filtration, aggregation and display of useful information.
{"title":"Capturing and Analysing Real-Time Data From Tugs","authors":"Serena Lim, K. Pazouki, A. Murphy, Ben Zhang","doi":"10.1115/OMAE2018-78003","DOIUrl":"https://doi.org/10.1115/OMAE2018-78003","url":null,"abstract":"Holistic energy management in the shipping industry involves reliable data collection, systematic processing and smart analysis. The era of digitisation allows sensor technology to be used on-board vessels, converting different forms of signal into a digital format that can be exported conveniently for further processing. Appropriate sensor selection is important to ensure continuous data collection when vessels sail through harsh conditions. However, without proper processing, this leads to the collection of big data sets but without resulting useful intelligence that benefits the industry. The adoption of digital and computer technology, allows the next phase of fast data processing. This contributes to the growing area of big data analysis, which is now a problem for many technological sectors, including the maritime industry. Enormous databases are often stored without clear goals or suitable uses. Processing of data requires engineering knowledge to ensure suitable filters are applied to raw data. This systematic processing of data leads to transparency in real time data display and contributes to predictive analysis. In addition, the generation of series of raw data when coupled with other external data such as weather information provides a rich database that reflects the true scenario of the vessel. Subsequent processing will then provide improved decision making tools for optimal operations. These advances open the door for different market analyses and the generation of new knowledge. This paper highlights the crucial steps needed and the challenges of sensor installation to obtain accurate data, followed by pre and post processing of data to generate knowledge. With this, big data can now provide information and reveal hidden patterns and trends regarding vessel operations, machinery diagnostics and energy efficient fleet management. A case study was carried out on a tug boat that operates in the North Sea, firstly to demonstrate confidence in the raw data collected and secondly to demonstrate the systematic filtration, aggregation and display of useful information.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"49 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":"114919075","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}
Zhichao Fang, Longfei Xiao, Yi-zhi Guo, Lijun Yang, Wenyue Lu
This paper concerns the estimation of wave run-ups on a fixed surface-piercing square column. Experiments and numerical simulations were carried out under waves of different scattering parameters and steepnesses. The results of the run-up height ratio, force coefficient, velocity field, and scattered wave profile were shown and discussed. The reasonable agreement with the experimental results indicates the capability and reliability of the numerical model in the wave run-up prediction. The nonlinearity under short waves is mainly due to the interaction between the scattered waves and the next incident wave crest, while the wave-induced flow around the column becomes more influential under long waves. These nonlinearities are further intensified under steeper waves, and the run-up height ratio increases consequently. A correction factor of 1.2–1.3 can be applied to estimate the run-up height based on the linear potential prediction, but a higher factor of 1.3–1.4 is necessary under long and steep incident waves.
{"title":"Experimental and Numerical Investigations Into Wave Run-Up on Fixed Surface-Piercing Square Column","authors":"Zhichao Fang, Longfei Xiao, Yi-zhi Guo, Lijun Yang, Wenyue Lu","doi":"10.1115/OMAE2018-77726","DOIUrl":"https://doi.org/10.1115/OMAE2018-77726","url":null,"abstract":"This paper concerns the estimation of wave run-ups on a fixed surface-piercing square column. Experiments and numerical simulations were carried out under waves of different scattering parameters and steepnesses. The results of the run-up height ratio, force coefficient, velocity field, and scattered wave profile were shown and discussed. The reasonable agreement with the experimental results indicates the capability and reliability of the numerical model in the wave run-up prediction. The nonlinearity under short waves is mainly due to the interaction between the scattered waves and the next incident wave crest, while the wave-induced flow around the column becomes more influential under long waves. These nonlinearities are further intensified under steeper waves, and the run-up height ratio increases consequently. A correction factor of 1.2–1.3 can be applied to estimate the run-up height based on the linear potential prediction, but a higher factor of 1.3–1.4 is necessary under long and steep incident waves.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"6 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":"124205801","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}
I. Shugan, S. Kuznetsov, Y. Saprykina, Yang-Yih Chen
We conducted experimental and theoretical studies on Benjamin-Feir (BF) instability and revealed a number of new features of the development of instability on the late stages of wave’s evolution. We employ the reduced (truncated) version of Zakharov equations — the multi-wave near-neighbor resonance model (NN model), which takes into account the most effective quasi-resonances with minimum detuning from exact resonance conditions. We show that near-neighbor model for wave interactions can adequately describe the number of new prominent features of BF instability observed in experiments and it is much simpler than Zakharov equation for computation and analysis. Numerical simulations of the full Zakharov equations confirm the main predictions obtained by the NN modeling and both reasonably correspond to the results of available physical experiments. Strong permanent downshifting of spectral maximum for gentle waves without wave breaking is revealed for twice as narrow side band spectral width in comparison with the most unstable case. Regime of multiple downshifting accompanied by wave breaking is discovered for steep waves. Discrete energy flow to higher spectral components takes a place in breaking and no breaking regimes. Results of numerical simulations of Zakharov and NN models reasonably correspond to each other and to our experimental and field observations on wave modulation.
{"title":"Late Stages in the Development of Modulation Instability of Waves","authors":"I. Shugan, S. Kuznetsov, Y. Saprykina, Yang-Yih Chen","doi":"10.1115/OMAE2018-77504","DOIUrl":"https://doi.org/10.1115/OMAE2018-77504","url":null,"abstract":"We conducted experimental and theoretical studies on Benjamin-Feir (BF) instability and revealed a number of new features of the development of instability on the late stages of wave’s evolution. We employ the reduced (truncated) version of Zakharov equations — the multi-wave near-neighbor resonance model (NN model), which takes into account the most effective quasi-resonances with minimum detuning from exact resonance conditions.\u0000 We show that near-neighbor model for wave interactions can adequately describe the number of new prominent features of BF instability observed in experiments and it is much simpler than Zakharov equation for computation and analysis. Numerical simulations of the full Zakharov equations confirm the main predictions obtained by the NN modeling and both reasonably correspond to the results of available physical experiments.\u0000 Strong permanent downshifting of spectral maximum for gentle waves without wave breaking is revealed for twice as narrow side band spectral width in comparison with the most unstable case. Regime of multiple downshifting accompanied by wave breaking is discovered for steep waves. Discrete energy flow to higher spectral components takes a place in breaking and no breaking regimes. Results of numerical simulations of Zakharov and NN models reasonably correspond to each other and to our experimental and field observations on wave modulation.","PeriodicalId":124589,"journal":{"name":"Volume 7B: Ocean Engineering","volume":"36 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":"116310533","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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