Pub Date : 2020-06-01DOI: 10.12989/OSE.2020.10.2.131
M. S. Patel, M. S. Liew, Z. Mustaffa, Abdurrasheed Said Abdurasheed, A. Whyte
The objective of this study was to evaluate the downtime cost of side-by-side offloading operations in Malaysian waters. With the help of a numerical time domain tool, the structure and cable response of moored FPSO vessel was simulated for heading and beam sea-states under irregular waves. The weather downtime was assessed by comparing the response under operational wave condition with the pre defined industrial safe offloading criteria. Additionally, two cases of cable failure were simulated for each sea-state. The novel study on downtime cost was presented for three different location of Malaysia subcontinent for which the location specific wave scatter diagram facilitated to estimate the probability of occurrence of operational wave condition. It was concluded that an unpredictable increment in wave height by 0.5 m can significantly impact the production cost.
{"title":"Downtime cost analysis of offloading operations under irregular waves in Malaysian waters","authors":"M. S. Patel, M. S. Liew, Z. Mustaffa, Abdurrasheed Said Abdurasheed, A. Whyte","doi":"10.12989/OSE.2020.10.2.131","DOIUrl":"https://doi.org/10.12989/OSE.2020.10.2.131","url":null,"abstract":"The objective of this study was to evaluate the downtime cost of side-by-side offloading operations in Malaysian waters. With the help of a numerical time domain tool, the structure and cable response of moored FPSO vessel was simulated for heading and beam sea-states under irregular waves. The weather downtime was assessed by comparing the response under operational wave condition with the pre defined industrial safe offloading criteria. Additionally, two cases of cable failure were simulated for each sea-state. The novel study on downtime cost was presented for three different location of Malaysia subcontinent \u0000for which the location specific wave scatter diagram facilitated to estimate the probability of occurrence of operational wave condition. It was concluded that an unpredictable increment in wave height by 0.5 m can significantly impact the production cost.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"10 1","pages":"131-161"},"PeriodicalIF":0.9,"publicationDate":"2020-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44726179","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}
Pub Date : 2020-06-01DOI: 10.12989/OSE.2020.10.2.227
Cyj Chen, Chia-Yen Hsieh, A. Smith, Dariush Alako, Lallit Pandey, Tim Chen
This paper deals with the problem of the global stabilization for a class of tension leg platform (TLP) nonlinear control systems. Problem and objective: Based on the relaxed method, the chaotic system can be stabilized by regulating appropriately the parameters of dither. Scope and method: If the frequency of dither is high enough, the trajectory of the closed-loop dithered chaotic system and that of its corresponding model the closed-loop fuzzy relaxed system can be made as close as desired. Results and conclusion: The behavior of the closed-loop dithered chaotic system can be rigorously predicted by establishing that of the closed-loop fuzzy relaxed system.
{"title":"AI based control theory for interaction of ocean system","authors":"Cyj Chen, Chia-Yen Hsieh, A. Smith, Dariush Alako, Lallit Pandey, Tim Chen","doi":"10.12989/OSE.2020.10.2.227","DOIUrl":"https://doi.org/10.12989/OSE.2020.10.2.227","url":null,"abstract":"This paper deals with the problem of the global stabilization for a class of tension leg platform (TLP) nonlinear control systems. Problem and objective: Based on the relaxed method, the chaotic system can be stabilized by regulating appropriately the parameters of dither. Scope and method: If the frequency of dither is high enough, the trajectory of the closed-loop dithered chaotic system and that of its corresponding model the closed-loop fuzzy relaxed system can be made as close as desired. Results and conclusion: The behavior of the closed-loop dithered chaotic system can be rigorously predicted by establishing that of the closed-loop fuzzy relaxed system.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"10 1","pages":"227"},"PeriodicalIF":0.9,"publicationDate":"2020-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43210496","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}
Pub Date : 2020-06-01DOI: 10.12989/OSE.2020.10.2.201
Mohammad Barzegar, D. Palaniappan
A systematic numerical comparative study of the performance of semicircular and rectangular submerged breakwaters interacting with solitary waves is the basis of this paper. To accomplish this task, Nwogu's extended Boussinesq model equations are employed to simulate the interaction of the wave with breakwaters. The finite difference technique has been used to discretize the spatial terms while a fourth-order predictor-corrector method is employed for time discretization in our numerical model. The proposed computational scheme uses a staggered-grid system where the first-order spatial derivatives have been discretized with fourth-order accuracy. For validation purposes, five test cases are considered and numerical results have been successfully compared with the existing analytical and experimental results. The performances of the rectangular and semicircular breakwaters have been examined in terms of the wave reflection, transmission, and dissipation coefficients (RTD coefficients) denoted by K_R, K_T, K_D. The latter coefficient K_D emerges due to the non-energy conserving K_R and K_T,. Our computational results and graphical illustrations show that the rectangular breakwater has higher reflection coefficients than semicircular breakwater for a fixed crest height, but as the wave height increases, the two reflection coefficients approach each other. On the other hand, the rectangular breakwater has larger dissipation coefficients compared to that of the semicircular breakwater and the difference between them increases as the height of the crest increases. However, the transmission coefficient for the semicircular breakwater is greater than that of the rectangular breakwater and the difference in their transmission coefficients increases with the crest height. Quantitatively, for rectangular breakwaters the reflection coefficients K_R are 5-15% higher while the diffusion coefficients K_D are 3-23% higher than that for the semicircular breakwaters, respectively. The transmission coefficients K_T for rectangular breakwater shows the better performance up to 2.47% than that for the semicircular breakwaters. Based on our computational results, one may conclude that the rectangular breakwater has a better overall performance than the semicircular breakwater. Although the model equations are non-dissipative, the non-energy conserving transmission and reflection coefficients due to wave-breakwater interactions lead to dissipation type contribution.
{"title":"Numerical study on the performance of semicircular and rectangular submerged breakwaters","authors":"Mohammad Barzegar, D. Palaniappan","doi":"10.12989/OSE.2020.10.2.201","DOIUrl":"https://doi.org/10.12989/OSE.2020.10.2.201","url":null,"abstract":"A systematic numerical comparative study of the performance of semicircular and rectangular submerged breakwaters interacting with solitary waves is the basis of this paper. To accomplish this task, Nwogu's extended Boussinesq model equations are employed to simulate the interaction of the wave with breakwaters. The finite difference technique has been used to discretize the spatial terms while a fourth-order predictor-corrector method is employed for time discretization in our numerical model. The proposed computational scheme uses a staggered-grid system where the first-order spatial derivatives have been discretized with fourth-order accuracy. For validation purposes, five test cases are considered and numerical results have been successfully compared with the existing analytical and experimental results. The performances of the rectangular and semicircular breakwaters have been examined in terms of the wave reflection, transmission, and dissipation coefficients (RTD coefficients) denoted by K_R, K_T, K_D. The latter coefficient K_D emerges due to the non-energy conserving K_R and K_T,. Our computational results and graphical illustrations show that the rectangular breakwater has higher reflection coefficients than semicircular breakwater for a fixed crest height, but as the wave height increases, the two reflection coefficients approach each other. On the other hand, the rectangular breakwater has larger dissipation coefficients compared to that of the semicircular breakwater and the difference between them increases as the height of the crest increases. However, the transmission coefficient for the semicircular breakwater is greater than that of the rectangular breakwater and the difference in their transmission coefficients increases with the crest height. Quantitatively, for rectangular breakwaters the reflection coefficients K_R are 5-15% higher while the diffusion coefficients K_D are 3-23% higher than that for the semicircular breakwaters, respectively. The transmission coefficients K_T for rectangular breakwater shows the better performance up to 2.47% than that for the semicircular breakwaters. Based on our computational results, one may conclude that the rectangular breakwater has a better overall performance than the semicircular breakwater. Although the model equations are non-dissipative, the non-energy conserving transmission and reflection coefficients due to wave-breakwater interactions lead to dissipation type contribution.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"10 1","pages":"201-226"},"PeriodicalIF":0.9,"publicationDate":"2020-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41505671","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}
Pub Date : 2020-06-01DOI: 10.12989/OSE.2020.10.2.163
A. C. Oliveira, R. G. Pestana
Considering the huge demand of several types of subsea equipment, as Christmas Trees, PLEMs (Pipeline End Manifolds), PLETs (Pipeline End Terminations) and manifolds for instance, a critical phase is its installation, especially when the equipment goes down through the water, crossing the splash zone. In this phase, the equipment is subject to slamming loads, which can induce impulsive loads in the installation wires and lead to their rupture. Slamming loads assessment formulation can be found in many references, like the Recommended Practice RP-N103 from DNV-GL (2011), a useful guide to evaluate installation loads. Regarding to the slamming loads, RP-N103 adopt some simplifying assumptions, as considering small dimensions for the equipment in relation to wave length, in order to estimate the slamming coefficient CS used in load estimation. In this article, an experimental investigation based on typical subsea structure dimensions was performed to assess the slamming coefficient evaluation, considering a more specific scenario in terms of application, and some reduction of the slamming coefficient is achieved for higher velocities, with positive impact on operability.
{"title":"Experimental assessment of slamming coefficients for subsea equipment installations","authors":"A. C. Oliveira, R. G. Pestana","doi":"10.12989/OSE.2020.10.2.163","DOIUrl":"https://doi.org/10.12989/OSE.2020.10.2.163","url":null,"abstract":"Considering the huge demand of several types of subsea equipment, as Christmas Trees, PLEMs (Pipeline End Manifolds), PLETs (Pipeline End Terminations) and manifolds for instance, a critical phase is its installation, especially when the equipment goes down through the water, crossing the splash zone. In this phase, the equipment is subject to slamming loads, which can induce impulsive loads in the installation wires and lead to their rupture. Slamming loads assessment formulation can be found in many references, like the Recommended Practice RP-N103 from DNV-GL (2011), a useful guide to evaluate installation loads. Regarding to the slamming loads, RP-N103 adopt some simplifying assumptions, as considering small dimensions for the equipment in relation to wave length, in order to estimate the slamming coefficient CS used in load estimation. In this article, an experimental investigation based on typical subsea structure dimensions was performed to assess the slamming coefficient evaluation, considering a more specific scenario in terms of application, and some reduction of the slamming coefficient is achieved for higher velocities, with positive impact on operability.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"10 1","pages":"163"},"PeriodicalIF":0.9,"publicationDate":"2020-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42626533","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}
Pub Date : 2020-03-01DOI: 10.12989/OSE.2020.10.1.111
K. Sadeghi, Fatemeh Nouban
A simplified algorithm is proposed for fast estimation of the material quantities required for the construction of rubble-mound breakwaters. The proposed algorithm is able to employ only the data available at feasibility study phase such as the maximum draught of the design ship selected to transport the cargos to the harbor despite, because at the feasibility phase, information for the planned harbor is likely to be very limited. A linear-constant waterdepth model together with a proposed section configuration for the breakwaters, which is customary for harbors, is considered to calculate the quantity of materials. The numerical simulation of the wave characteristics has been verified using the recorded wave data collected by a buoy installed near the Neka harbor in Caspian Sea waters. A case study has been also applied to four harbors to validate the proposed algorithm. The estimated weights using the proposed linear-constant and multi-linear waterdepth models were compared using the bathymetry maps and layouts of these harbors. A computer program, written in QBasic language, has been developed to simulate the wave characteristics and to estimate the material quantities needed to construct a rubble-mound breakwater. The obtained results show that taking into account the acceptable accuracies normally applied to the feasibility study and conceptual design phases, the proposed algorithm is sufficiently accurate and highly effective for the conceptual estimation of materials
{"title":"A simplified algorithm for conceptual estimation of the material quantities of rubble-mound breakwaters","authors":"K. Sadeghi, Fatemeh Nouban","doi":"10.12989/OSE.2020.10.1.111","DOIUrl":"https://doi.org/10.12989/OSE.2020.10.1.111","url":null,"abstract":"A simplified algorithm is proposed for fast estimation of the material quantities required for the construction of rubble-mound breakwaters. The proposed algorithm is able to employ only the data available at feasibility study phase such as the maximum draught of the design ship selected to transport the cargos to the harbor despite, because at the feasibility phase, information for the planned harbor is likely to be very limited. A linear-constant waterdepth model together with a proposed section configuration for the breakwaters, which is customary for harbors, is considered to calculate the quantity of materials. The numerical simulation of the wave characteristics has been verified using the recorded wave data collected by a buoy installed near the Neka harbor in Caspian Sea waters. A case study has been also applied to four harbors to validate the proposed algorithm. The estimated weights using the proposed linear-constant and multi-linear waterdepth models were compared using the bathymetry maps and layouts of these harbors. A computer program, written in QBasic language, has been developed to simulate the wave characteristics and to estimate the material quantities needed to construct a rubble-mound breakwater. The obtained results show that taking into account the acceptable accuracies normally applied to the feasibility study and conceptual design phases, the proposed algorithm is sufficiently accurate and highly effective for the conceptual estimation of materials","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"10 1","pages":"111-129"},"PeriodicalIF":0.9,"publicationDate":"2020-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48086587","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}
Pub Date : 2020-03-01DOI: 10.12989/OSE.2020.10.1.087
S. Junianto, M. Mukhtasor, R. Prastianto, C. Jo
Catamaran has recently been a choice to support a typical vertical axis turbine in floating tidal current energy conversion system. However, motion responses associated with the catamaran can reduce the turbines efficiency. The possibility to overcome this problem is to change the catamaran parameter by varying and simulating the demi-hull separations to have lower motion responses. This simulation was undertaken by Computational Fluid Dynamic (CFD) using potential flow analysis. Cases of demi-hull separation were considered, with ratios of demi-hull separation (S) to the breadth of demi-hull (B), S⁄B of 3.45, 4.95, 6.45, 7.2 and 7.95. In order to compare to the previous works in the literature, the regular wave was set with wave height of 0.8 m. Furthermore, the analysis was carried out by irregular waves with significant wave height, Hs, of about 0.09 to 1.5 m and the wave period, T, of about 1.5 to 6 s or corresponding to the wave frequency, w, of about 1.1 to 4.2 rad/s. The wave spectrum was derived from the equation of the International Towing Tank Conference (ITTC). For the case of turbines-loaded catamaran under consideration, the new finding is that the least significant amplitude response can be satisfied at the ratio S⁄B of 7.2. This study indicates that selecting a right choice of demi-hull separation ratio could contribute in reducing motion responses of the tidal current turbines-loaded catamaran.
{"title":"Effects of demi-hull separation ratios on motion responses of tidal current turbines-loaded catamaran","authors":"S. Junianto, M. Mukhtasor, R. Prastianto, C. Jo","doi":"10.12989/OSE.2020.10.1.087","DOIUrl":"https://doi.org/10.12989/OSE.2020.10.1.087","url":null,"abstract":"Catamaran has recently been a choice to support a typical vertical axis turbine in floating tidal current energy conversion system. However, motion responses associated with the catamaran can reduce the turbines efficiency. The possibility to overcome this problem is to change the catamaran parameter by varying and simulating the demi-hull separations to have lower motion responses. This simulation was undertaken by Computational Fluid Dynamic (CFD) using potential flow analysis. Cases of demi-hull separation were considered, with ratios of demi-hull separation (S) to the breadth of demi-hull (B), S⁄B of 3.45, 4.95, 6.45, 7.2 and 7.95. In order to compare to the previous works in the literature, the regular wave was set with wave height of 0.8 m. Furthermore, the analysis was carried out by irregular waves with significant wave height, Hs, of about 0.09 to 1.5 m and the wave period, T, of about 1.5 to 6 s or corresponding to the wave frequency, w, of about 1.1 to 4.2 rad/s. The wave spectrum was derived from the equation of the International Towing Tank Conference (ITTC). For the case of turbines-loaded catamaran under consideration, the new finding is that the least significant amplitude response can be satisfied at the ratio S⁄B of 7.2. This study indicates that selecting a right choice of demi-hull separation ratio could contribute in reducing motion responses of the tidal current turbines-loaded catamaran.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"10 1","pages":"87-110"},"PeriodicalIF":0.9,"publicationDate":"2020-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47790093","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}
Pub Date : 2020-03-01DOI: 10.12989/OSE.2020.10.1.025
A. Jasper, Akaawase T. Bernard, O. Gudmestad
A study of the wave conditions for the Asabo offshore location at the Qua Iboe oil field in Eastern Nigeria has been carried out. Statistical analysis was applied to three (3) years of data comprising spectral periods, Tp and significant wave heights, Hs. The data was divided into two (2); data from October to April represents one set of data and data from May to September represents another set of data. The results were compared with similar studies at other locations offshore of West Africa. It was found that there is an absence of direct swellwaves from the Southern Ocean reaching the location under study (the Asabo site). This work suggests that the wave system is largely emanating from the North Atlantic storms. The presence of numerous islands near the Asabo location shields the site from effects of storms from south west and therefore swells from the Southern Ocean. It is noted that the local wind has little or no contribution. An Hs maximum of 2 m is noted at the Asabo offshore location. It is found that the Weibull distribution best describes the wave distribution at Asabo. Thus, the Weibull distribution is suggested to be adequate for long term prediction of extreme waves needed for offshore design and operations at this location.
{"title":"Sea state description of Asabo offshore in Nigeria","authors":"A. Jasper, Akaawase T. Bernard, O. Gudmestad","doi":"10.12989/OSE.2020.10.1.025","DOIUrl":"https://doi.org/10.12989/OSE.2020.10.1.025","url":null,"abstract":"A study of the wave conditions for the Asabo offshore location at the Qua Iboe oil field in Eastern Nigeria has been carried out. Statistical analysis was applied to three (3) years of data comprising spectral periods, Tp and significant wave heights, Hs. The data was divided into two (2); data from October to April represents one set of data and data from May to September represents another set of data. The results were compared with similar studies at other locations offshore of West Africa. It was found that there is an absence of direct swellwaves from the Southern Ocean reaching the location under study (the Asabo site). This work suggests that the wave system is largely emanating from the North Atlantic storms. The presence of numerous islands near the Asabo location shields the site from effects of storms from south west and therefore swells from the Southern Ocean. It is noted that the local wind has little or no contribution. An Hs maximum of 2 m is noted at the Asabo offshore location. It is found that the Weibull distribution best describes the wave distribution at Asabo. Thus, the Weibull distribution is suggested to be adequate for long term prediction of extreme waves needed for offshore design and operations at this location.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"10 1","pages":"25-47"},"PeriodicalIF":0.9,"publicationDate":"2020-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44611373","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}
Pub Date : 2020-03-01DOI: 10.12989/OSE.2020.10.1.067
Karun Klaycham, Panisara Nguantud, Chainarong Athisakul, S. Chucheepsakul
The main goal of this study is to investigate the free vibration analysis of a large sag catenary with application to the jumper in hybrid riser system. The equation of motion is derived by using the variational method based on the virtual work principle. The finite element method is applied to evaluate the numerical solutions. The large sag catenary is utilized as an initial configuration for vibration analysis. The nonlinearity due to the large sag curvature of static configuration is taken into account in the element stiffness matrix. The natural frequencies of large sag catenary and their corresponding mode shapes are determined by solving the eigenvalue problem. The numerical examples of a large sag catenary jumpers are presented. The influences of bending rigidity and large sag shape on the free vibration behaviors of the catenary jumper are provided. The results indicate that the increase in sag reduces the jumper natural frequencies. The corresponding mode shapes of the jumper with large sag catenary shape are comprised of normal and tangential displacements. The large sag curvature including in the element stiffness matrix increases the natural frequency especially for a case of very large sag shape. Mostly, the mode shapes of jumper are dominated by the normal displacement, however, the tangential displacement significantly occurs around the lowest point of sag. The increase in degree of inclination of the catenary tends to increase the natural frequencies.
{"title":"Free vibration analysis of large sag catenary with application to catenary jumper","authors":"Karun Klaycham, Panisara Nguantud, Chainarong Athisakul, S. Chucheepsakul","doi":"10.12989/OSE.2020.10.1.067","DOIUrl":"https://doi.org/10.12989/OSE.2020.10.1.067","url":null,"abstract":"The main goal of this study is to investigate the free vibration analysis of a large sag catenary with application to the jumper in hybrid riser system. The equation of motion is derived by using the variational method based on the virtual work principle. The finite element method is applied to evaluate the numerical solutions. The large sag catenary is utilized as an initial configuration for vibration analysis. The nonlinearity due to the large sag curvature of static configuration is taken into account in the element stiffness matrix. The natural frequencies of large sag catenary and their corresponding mode shapes are determined by solving the eigenvalue problem. The numerical examples of a large sag catenary jumpers are presented. The influences of bending rigidity and large sag shape on the free vibration behaviors of the catenary jumper are provided. The results indicate that the increase in sag reduces the jumper natural frequencies. The corresponding mode shapes of the jumper with large sag catenary shape are comprised of normal and tangential displacements. The large sag curvature including in the element stiffness matrix increases the natural frequency especially for a case of very large sag shape. Mostly, the mode shapes of jumper are dominated by the normal displacement, however, the tangential displacement significantly occurs around the lowest point of sag. The increase in degree of inclination of the catenary tends to increase the natural frequencies.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"10 1","pages":"067"},"PeriodicalIF":0.9,"publicationDate":"2020-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49297005","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}
Pub Date : 2020-03-01DOI: 10.12989/OSE.2020.10.1.001
Y. H. Kumar, R. Vijayakumar
Hydrodynamic Drag of Surface combatants pose significant challenges with regard to fuel efficiency and exhaust emissions. Stern flaps have been used widely as an energy saving device, particularly by the US Navy (Hemanth et al. 2018a, Hemanth Kumar and Vijayakumar 2018b). In the present investigation the effect of flap turning angle on drag reduction is numerically and experimentally studied for a high-speed displacement surface combatant fitted with a stern flap in the Froude number range of 0.17-0.48. Parametric investigations are undertaken for constant chord length & span and varying turning angles of 5 10 & 15. Experimental resistance values in towing tank tests were validated with CFD. Investigations revealed that pressure increased as the flow velocity decreased with an increase in flap turning angle which was due to the centrifugal action of the flow caused by the induced concave curvature under the flap. There was no significant change in stern wave height but there was a gradual increase in the stern wave steepness with flap angle. Effective length of the vessel increased by lengthening of transom hollow. In low Froude number regime, flow was not influenced by flap curvature effects and pressure recovery was marginal. In the intermediate and high Froude number regimes pressure recovery increased with the flap turning angle and flow velocity.
水面战舰的水动力阻力对燃油效率和废气排放提出了重大挑战。船尾襟翼已被广泛用作节能装置，特别是在美国海军(Hemanth et al. 2018a, Hemanth Kumar and Vijayakumar 2018b)。本文对高速排水量水面舰艇在弗劳德数0.17 ~ 0.48范围内安装尾翼时，尾翼转角对减阻的影响进行了数值和实验研究。参数调查进行了恒定的弦长和跨度和不同的转角5 - 10和15。利用CFD对拖曳槽试验的阻力值进行了验证。研究表明，随着襟翼转角的增大，流速减小，压力增大，这是由于襟翼下的凹曲率引起气流的离心作用。尾波高度变化不明显，但尾波陡度随桨叶角度的增加而逐渐增大。通过延长尾梁中空，增加了容器的有效长度。在低弗劳德数状态下，流动不受襟翼曲率影响，压力恢复很小。在中、高弗劳德数工况下，压力恢复随襟翼转角和流速的增大而增大。
{"title":"Effect of flap angle on transom stern flow of a High speed displacement Surface combatant","authors":"Y. H. Kumar, R. Vijayakumar","doi":"10.12989/OSE.2020.10.1.001","DOIUrl":"https://doi.org/10.12989/OSE.2020.10.1.001","url":null,"abstract":"Hydrodynamic Drag of Surface combatants pose significant challenges with regard to fuel efficiency and exhaust emissions. Stern flaps have been used widely as an energy saving device, particularly by the US Navy (Hemanth et al. 2018a, Hemanth Kumar and Vijayakumar 2018b). In the present investigation the effect of flap turning angle on drag reduction is numerically and experimentally studied for a high-speed displacement surface combatant fitted with a stern flap in the Froude number range of 0.17-0.48. Parametric investigations are undertaken for constant chord length & span and varying turning angles of 5 10 & 15. Experimental resistance values in towing tank tests were validated with CFD. Investigations revealed that pressure increased as the flow velocity decreased with an increase in flap turning angle which was due to the centrifugal action of the flow caused by the induced concave curvature under the flap. There was no significant change in stern wave height but there was a gradual increase in the stern wave steepness with flap angle. Effective length of the vessel increased by lengthening of transom hollow. In low Froude number regime, flow was not influenced by flap curvature effects and pressure recovery was marginal. In the intermediate and high Froude number regimes pressure recovery increased with the flap turning angle and flow velocity.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"10 1","pages":"001"},"PeriodicalIF":0.9,"publicationDate":"2020-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48993803","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}
Pub Date : 2020-03-01DOI: 10.12989/OSE.2020.10.1.049
S. Bal
In this study, the effects of inclined shaft angle on the hydro-acoustic performance of cavitating marine propellers are investigated by a numerical method developed before and Brown's empirical formula. The cavitating blades are represented by source and vortex elements. The cavity characteristics of the blades such as cavitation form, cavity volume, cavity length etc., are computed at a given cavitation number and at a set advance coefficient. A lifting surface method is applied for these calculations. The numerical lifting surface method is validated with experimental results of DTMB 4119 model benchmark propeller. After calculation of hydrodynamic characteristics of the cavitating propeller, noise spectrum and overall sound pressure level (OASPL) are computed by Brown's equation. This empirical equation is also validated with another numerical results found in the literature. The effects of inclined shaft angle on thrust coefficient, torque coefficient, efficiency and OASPL values are examined by a parametric study. By modifying the inclination angles of propeller, the thrust, torque, efficiency and OASPL are computed and compared with each other. The influence of the inclined shaft angle on cavity patterns on the blades are also discussed.
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