Pub Date : 2021-09-01DOI: 10.12989/OSE.2021.11.3.217
Arun George, I. Cho
In this study, the three dimensional numerical simulation of a seawater exchange breakwater using the Helmholtz resonator has been carried out in OpenFOAM. When the frequency of the incident wave coincides with one of the natural frequencies of a closed semi-circular resonator, resonance occurs in the resonator. The amplified water elevation in a resonator pushes the seawater periodically into the ocean/port side through the water channel and consequently improves the water quality of the port. The numerical model is based on Reynolds Averaged Navier Stokes equations with SST turbulence model. The VOF (Volume of Fluid) method is used to capture the free surface behavior. The numerical model is validated with model experiments conducted by Cho (2001) in a two-dimensional wave tank for regular waves. Numerical simulations for the prototype model in irregular waves based on the JONSWAP spectrum are also conducted to show whether the proposed seawater exchange breakwater can be feasible to the real seas. It is found that the seawater exchanging rate is greatly enhanced in the low-frequency wave region where the frequency of the Helmholtz resonance situates. If designing the Helmholtz resonator properly, it can supply the clean seawater sustainedly into the port side without additional electric power.
{"title":"Performance evaluation of a seawater exchange breakwater with Helmholtz resonator using OpenFOAM","authors":"Arun George, I. Cho","doi":"10.12989/OSE.2021.11.3.217","DOIUrl":"https://doi.org/10.12989/OSE.2021.11.3.217","url":null,"abstract":"In this study, the three dimensional numerical simulation of a seawater exchange breakwater using the Helmholtz resonator has been carried out in OpenFOAM. When the frequency of the incident wave coincides with one of the natural frequencies of a closed semi-circular resonator, resonance occurs in the resonator. The amplified water elevation in a resonator pushes the seawater periodically into the ocean/port side through the water channel and consequently improves the water quality of the port. The numerical model is based on Reynolds Averaged Navier Stokes equations with SST turbulence model. The VOF (Volume of Fluid) method is used to capture the free surface behavior. The numerical model is validated with model experiments conducted by Cho (2001) in a two-dimensional wave tank for regular waves. Numerical simulations for the prototype model in irregular waves based on the JONSWAP spectrum are also conducted to show whether the proposed seawater exchange breakwater can be feasible to the real seas. It is found that the seawater exchanging rate is greatly enhanced in the low-frequency wave region where the frequency of the Helmholtz resonance situates. If designing the Helmholtz resonator properly, it can supply the clean seawater sustainedly into the port side without additional electric power.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"11 1","pages":"217"},"PeriodicalIF":0.9,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42136334","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 : 2021-09-01DOI: 10.12989/OSE.2021.11.3.203
Amir Syawal Kamis, A. Fuad, A. Ashaari, C. Noor
This research proposes an improved mathematical model which can be used to calculate wheel over point (WOP) for a ship's route optimisation. WOP is a marking made on the charted course to demonstrate where the ship must initiate the course alteration to guarantee that it follows the route. The advance transfer technique (ATT) was used to determine WOP. Through practical exercise, two gaps were identified in ATT. From there, an improved mathematical model, namely ATMM, were developed. A preliminary manoeuvring analysis was then carried out in this study using a ship simulator for ATMM and the existing ATT. Then, the cross-track distance produced by both methods were compared to verify the difference. It was found that the ATMM produced better result in maintaining a ship on its course. This research's mathematical model is expected to be used onboard ship and used in the Electronic Chart Display and Information System to aid navigator in making more effective course alteration.
{"title":"Wheel over point mathematical model","authors":"Amir Syawal Kamis, A. Fuad, A. Ashaari, C. Noor","doi":"10.12989/OSE.2021.11.3.203","DOIUrl":"https://doi.org/10.12989/OSE.2021.11.3.203","url":null,"abstract":"This research proposes an improved mathematical model which can be used to calculate wheel over point (WOP) for a ship's route optimisation. WOP is a marking made on the charted course to demonstrate where the ship must initiate the course alteration to guarantee that it follows the route. The advance transfer technique (ATT) was used to determine WOP. Through practical exercise, two gaps were identified in ATT. From there, an improved mathematical model, namely ATMM, were developed. A preliminary manoeuvring analysis was then carried out in this study using a ship simulator for ATMM and the existing ATT. Then, the cross-track distance produced by both methods were compared to verify the difference. It was found that the ATMM produced better result in maintaining a ship on its course. This research's mathematical model is expected to be used onboard ship and used in the Electronic Chart Display and Information System to aid navigator in making more effective course alteration.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"11 1","pages":"203"},"PeriodicalIF":0.9,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43633172","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 : 2021-09-01DOI: 10.12989/OSE.2021.11.3.275
N. Patil, S. Rajendran
The present work focuses on the development of a numerical body nonlinear time-domain method for estimating the effect of active roll fin stabilizers on ship roll motion in both regular and irregular seaway. The time-domain analysis aims at providing fast and accurate ship responses that will be useful during the design process through accurate estimation of the environmental loads. A strip theory-based approach is followed where the Froude-Krylov and hydrostatic forces are calculated for the exact wetted surface area for every time step. The equations of motions are formulated in the body frame and consider the six degrees of coupled motions. The active fin, rudder, and propeller modules are included in the simulation. This leads to accurate modeling of the system dynamics. The numerical unstabilized roll motion is validated with experimental seakeeping simulations conducted on a Coastal Research Vessel (CRV). The phenomena of Parametric Rolling (PR) is identified during the numerical investigation of the candidate vessel. Besides, a nonlinear PID (NPID) control technique and LQR method is implemented for active roll motion control and its performance is observed in regular as well as irregular waves. The proposed numerical approach proves to be an effective and realistic method in evaluating the 6-DoF coupled ship motion responses.
{"title":"A time-domain method for analyzing the ship roll stabilization based on active fin control","authors":"N. Patil, S. Rajendran","doi":"10.12989/OSE.2021.11.3.275","DOIUrl":"https://doi.org/10.12989/OSE.2021.11.3.275","url":null,"abstract":"The present work focuses on the development of a numerical body nonlinear time-domain method for estimating the effect of active roll fin stabilizers on ship roll motion in both regular and irregular seaway. The time-domain analysis aims at providing fast and accurate ship responses that will be useful during the design process through accurate estimation of the environmental loads. A strip theory-based approach is followed where the Froude-Krylov and hydrostatic forces are calculated for the exact wetted surface area for every time step. The equations of motions are formulated in the body frame and consider the six degrees of coupled motions. The active fin, rudder, and propeller modules are included in the simulation. This leads to accurate modeling of the system dynamics. The numerical unstabilized roll motion is validated with experimental seakeeping simulations conducted on a Coastal Research Vessel (CRV). The phenomena of Parametric Rolling (PR) is identified during the numerical investigation of the candidate vessel. Besides, a nonlinear PID (NPID) control technique and LQR method is implemented for active roll motion control and its performance is observed in regular as well as irregular waves. The proposed numerical approach proves to be an effective and realistic method in evaluating the 6-DoF coupled ship motion responses.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"13 11","pages":"275"},"PeriodicalIF":0.9,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41311529","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 : 2021-09-01DOI: 10.12989/OSE.2021.11.3.237
S. Neelamani, N. Al-Anjari
Experimental investigations were carried out to assess the global wave forces and wave induced moments on slotted vertical barriers (SVB). Fourty two different wave barrier configurations (5%, 10%, 20%, 30%, 40%, 50% and 60% porosities and 1 to 6 number of slotted walls) were tested in random wave fields of JONSWAP spectra for wide range of significant wave heights and peak periods. It is found that the wave force is very sensitive to the change in porosity of the SVB. It is also found that relatively long waves and low porosity on SVB results in the highest wave force and short waves and high porosity on the SVB results in the lowest wave force. For most of the conditions, the wave force on SVB is less than the wave force on a single impervious vertical wall and force reduction to an extent of 20% to 80% is possible for the range of porosity and number of porous walls studied. A predictive equation to estimate the wave induced significant moment is provided with high regression coefficient. The average lever arm for assessing the wave induced moment is 0.6145 times the local water depth.
{"title":"Assessment of global wave forces and moments on porous vertical barriers in random wave fields","authors":"S. Neelamani, N. Al-Anjari","doi":"10.12989/OSE.2021.11.3.237","DOIUrl":"https://doi.org/10.12989/OSE.2021.11.3.237","url":null,"abstract":"Experimental investigations were carried out to assess the global wave forces and wave induced moments on slotted vertical barriers (SVB). Fourty two different wave barrier configurations (5%, 10%, 20%, 30%, 40%, 50% and 60% porosities and 1 to 6 number of slotted walls) were tested in random wave fields of JONSWAP spectra for wide range of significant wave heights and peak periods. It is found that the wave force is very sensitive to the change in porosity of the SVB. It is also found that relatively long waves and low porosity on SVB results in the highest wave force and short waves and high porosity on the SVB results in the lowest wave force. For most of the conditions, the wave force on SVB is less than the wave force on a single impervious vertical wall and force reduction to an extent of 20% to 80% is possible for the range of porosity and number of porous walls studied. A predictive equation to estimate the wave induced significant moment is provided with high regression coefficient. The average lever arm for assessing the wave induced moment is 0.6145 times the local water depth.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"11 1","pages":"237-257"},"PeriodicalIF":0.9,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47966599","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 : 2021-06-01DOI: 10.12989/OSE.2021.11.2.123
Hassiba Ouargli, B. Hamoudi
Numerical simulation of a full-scale ship model, KVLCC2, has been conducted applying the Reynolds Averaged Navier-Stokes (RANS) approach using the STARCCM+ commercial computational fluid dynamics (CFD) software to calculate total resistance, seakeeping and Pitch Moments. Results are obtained for the speed of 15.5 Knots under different sea conditions (calm water, regular waves and irregular waves), The total resistance calculated for the KVLCC2 ship hull in calm water is in a good agreement with the results from experiments and the results for motion (heave and pitch) and added resistance in waves were compared to numerical and experimental findings from previous research with good agreement. In addition to wave excitations, the full-scale ship model was subjected to propeller excitations using the virtual disk model from the CFD software. The body force propeller method, which simplified the full propeller characteristic of the KVLCC2 into a resultant body force, is applied to the virtual disk model. Results are compared with results from the hull-only model. A comparison of the wake results with previous work is also presented.
{"title":"Study of added resistance and seakeeping of KVLCC2 in waves with and without propeller","authors":"Hassiba Ouargli, B. Hamoudi","doi":"10.12989/OSE.2021.11.2.123","DOIUrl":"https://doi.org/10.12989/OSE.2021.11.2.123","url":null,"abstract":"Numerical simulation of a full-scale ship model, KVLCC2, has been conducted applying the Reynolds Averaged Navier-Stokes (RANS) approach using the STARCCM+ commercial computational fluid dynamics (CFD) software to calculate total resistance, seakeeping and Pitch Moments. Results are obtained for the speed of 15.5 Knots under different sea conditions (calm water, regular waves and irregular waves), The total resistance calculated for the KVLCC2 ship hull in calm water is in a good agreement with the results from experiments and the results for motion (heave and pitch) and added resistance in waves were compared to numerical and experimental findings from previous research with good agreement. In addition to wave excitations, the full-scale ship model was subjected to propeller excitations using the virtual disk model from the CFD software. The body force propeller method, which simplified the full propeller characteristic of the KVLCC2 into a resultant body force, is applied to the virtual disk model. Results are compared with results from the hull-only model. A comparison of the wake results with previous work is also presented.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"11 1","pages":"123"},"PeriodicalIF":0.9,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45937284","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 : 2021-06-01DOI: 10.12989/OSE.2021.11.2.185
H. X. Nguyen, V. Dinh, B. Basu
The aim of this paper is to verify the velocity profile and the pressure variation inside the fluid domain over one wavelength obtained from a numerically simulated Smoothed Particle Hydrodynamics model with some exact qualitative results (i.e., increasing/decreasing trend or constant value of a flow field) from a fully nonlinear Euler equation for water wave model. A numerical wave flume has been modeled and a regular wave train is created by the horizontal displacement of a wave paddle on one side of the flume. A passive beach is used to dissipate the energy of the wave on the other side. The extracted numerical results are compared with some recently available exact results from a nonlinear steady water wave model based on the Euler equations for irrotational flow. The flow properties under wave crests, wave troughs, and along the distance from the wave crest to the wave trough over one wavelength are investigated. The horizontal and vertical velocity components and the pressure in the fluid domain agree well with the analytical results.
{"title":"A comparison of smoothed particle hydrodynamics simulation with exact results from a nonlinear water wave model","authors":"H. X. Nguyen, V. Dinh, B. Basu","doi":"10.12989/OSE.2021.11.2.185","DOIUrl":"https://doi.org/10.12989/OSE.2021.11.2.185","url":null,"abstract":"The aim of this paper is to verify the velocity profile and the pressure variation inside the fluid domain over one wavelength obtained from a numerically simulated Smoothed Particle Hydrodynamics model with some exact qualitative results (i.e., increasing/decreasing trend or constant value of a flow field) from a fully nonlinear Euler equation for water wave model. A numerical wave flume has been modeled and a regular wave train is created by the horizontal displacement of a wave paddle on one side of the flume. A passive beach is used to dissipate the energy of the wave on the other side. The extracted numerical results are compared with some recently available exact results from a nonlinear steady water wave model based on the Euler equations for irrotational flow. The flow properties under wave crests, wave troughs, and along the distance from the wave crest to the wave trough over one wavelength are investigated. The horizontal and vertical velocity components and the pressure in the fluid domain agree well with the analytical results.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"11 1","pages":"185"},"PeriodicalIF":0.9,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48252418","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 : 2021-06-01DOI: 10.12989/OSE.2021.11.2.141
N. Hiron, I. Giriantari, L. Jasa, I. Kumara
This paper analyzes the fish-ridge type wind turbine performance and characteristics of energy extraction applied in a low wave Oscillating Water Column (OWC) system. This article contributes to providing a better understanding of the application of OWC and VAWT in a low wave environment. The aerodynamic characteristics of the three-blade fish-ridge turbine in an OWC chamber have been successfully investigated. CFD simulation with Reynolds-Averaged-Stokes (RANS) equations was used to obtain airspeed and air pressure contours under compressed and decompressed conditions in the turbine blades. Experiments on laboratory scale test rig also obtained data. The blade torque and turbine power coefficient at different AoA were validated through the experimental test to obtain numerical equations for the relationship between airspeeds, torque, tip speed ratio, and turbine power. The turbine design was 0.2 m long and 0.1 m wide and with an overlap ratio of 15%. The maximum tested airspeed was 20m/s. We found that the fish-ridge turbine has a homogeneous air velocity distribution and pressure due to the 15% overlap area. The maximum efficiency of the fish-ridge turbine under compressed conditions was 30% at TSR 0.9, while under decompressed conditions, the maximum efficiency reached 28% at TSR 0.6.
分析了鱼脊式风力机在低波振荡水柱系统中的性能和抽能特性。本文有助于更好地理解OWC和VAWT在低波环境中的应用。本文成功地研究了三叶片鱼脊涡轮在空室中的气动特性。利用reynolds - average - stokes (RANS)方程进行CFD仿真，得到了涡轮叶片压缩和解压状态下的空速和气压曲线。在实验室规模的试验台上进行了实验，获得了数据。通过试验验证了不同AoA下的叶片转矩和涡轮功率系数，得到了空速、转矩、叶尖速比和涡轮功率之间关系的数值方程。涡轮设计为长0.2 m，宽0.1 m，重叠比为15%。试验最大空速为20m/s。我们发现，由于15%的重叠面积，鱼脊涡轮具有均匀的风速分布和压力。鱼脊涡轮在压缩工况下的最大效率为30%，TSR为0.9，而在减压工况下，TSR为0.6时的最大效率为28%。
{"title":"Fish-ridge wind turbine aerodynamics characteristics in Oscillating Water Column (OWC) system","authors":"N. Hiron, I. Giriantari, L. Jasa, I. Kumara","doi":"10.12989/OSE.2021.11.2.141","DOIUrl":"https://doi.org/10.12989/OSE.2021.11.2.141","url":null,"abstract":"This paper analyzes the fish-ridge type wind turbine performance and characteristics of energy extraction applied in a low wave Oscillating Water Column (OWC) system. This article contributes to providing a better understanding of the application of OWC and VAWT in a low wave environment. The aerodynamic characteristics of the three-blade fish-ridge turbine in an OWC chamber have been successfully investigated. CFD simulation with Reynolds-Averaged-Stokes (RANS) equations was used to obtain airspeed and air pressure contours under compressed and decompressed conditions in the turbine blades. Experiments on laboratory scale test rig also obtained data. The blade torque and turbine power coefficient at different AoA were validated through the experimental test to obtain numerical equations for the relationship between airspeeds, torque, tip speed ratio, and turbine power. The turbine design was 0.2 m long and 0.1 m wide and with an overlap ratio of 15%. The maximum tested airspeed was 20m/s. We found that the fish-ridge turbine has a homogeneous air velocity distribution and pressure due to the 15% overlap area. The maximum efficiency of the fish-ridge turbine under compressed conditions was 30% at TSR 0.9, while under decompressed conditions, the maximum efficiency reached 28% at TSR 0.6.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"11 1","pages":"141"},"PeriodicalIF":0.9,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46925253","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 : 2021-06-01DOI: 10.12989/OSE.2021.11.2.099
Shan Miao, Yuming Liu, D. Yue
Motivated by many recent discoveries of marginal fields in deep water, this paper presents a novel and economical design concept of a minimal floating platform with around 10,000 cubic tons in displacement. The concept characterizes a simple hull geometry and an excellent seakeeping behavior. It incorporates a damping plate at the keel on the basis of a spar-like floater. The design procedure is explained and illustrated. The paper also describes a new design methodology that is capable of efficiently evaluating the seakeeping performance of the platforms with the viscous damping effect included. We integrate this methodology into an Evolutionary Algorithm (EA) to conduct a multi-objective optimization for our novel design. The hull shape is optimized by minimizing the heave motion in waves without sacrificing the cost in construction and installation. Several potential geometric configurations are considered. The optimization results provide a wealth of information that can be used to support practical design decisions.
{"title":"Optimum design of miniature platforms for marginal fields","authors":"Shan Miao, Yuming Liu, D. Yue","doi":"10.12989/OSE.2021.11.2.099","DOIUrl":"https://doi.org/10.12989/OSE.2021.11.2.099","url":null,"abstract":"Motivated by many recent discoveries of marginal fields in deep water, this paper presents a novel and economical design concept of a minimal floating platform with around 10,000 cubic tons in displacement. The concept characterizes a simple hull geometry and an excellent seakeeping behavior. It incorporates a damping plate at the keel on the basis of a spar-like floater. The design procedure is explained and illustrated. The paper also describes a new design methodology that is capable of efficiently evaluating the seakeeping performance of the platforms with the viscous damping effect included. We integrate this methodology into an Evolutionary Algorithm (EA) to conduct a multi-objective optimization for our novel design. The hull shape is optimized by minimizing the heave motion in waves without sacrificing the cost in construction and installation. Several potential geometric configurations are considered. The optimization results provide a wealth of information that can be used to support practical design decisions.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"11 1","pages":"99"},"PeriodicalIF":0.9,"publicationDate":"2021-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41436404","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 : 2021-03-01DOI: 10.12989/OSE.2021.11.1.043
Amir Bordbar, S. Sharifi, H. Hemida
In the present work, a 3D numerical model is proposed to study local scouring around single vertical piers with different cross-section shapes under steady-current flow. The model solves the flow field and sediment transport processes using a coupled approach. The flow field is obtained by solving the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations in combination with the k-w SST turbulence closure model and the sediment transport is considered using both bedload and suspended load models. The proposed model is validated against the empirical measurements of local scour around single vertical piers with circular, square, and diamond cross-section shapes obtained from the literature. The measurement of scour depth in equilibrium condition for the simulations reveal the differences of 4.6%, 6.7% and 13.1% from the experimental measurements for the circular, square, and diamond pier cases, respectively. The model displayed a remarkable performance in the prediction of scour around circular and square piers where horseshoe vortices (HSVs) have a leading impact on scour progression. On the other hand, the maximum deviation was found in the case of the diamond pier where HSVs are weak and have minimum impact on the formation of local scour. Overall, the results confirm that the prediction capability of the present model is almost independent of the strength of the formed HSVs and pier cross-section shapes.
{"title":"Prediction of scour around single vertical piers with different cross-section shapes","authors":"Amir Bordbar, S. Sharifi, H. Hemida","doi":"10.12989/OSE.2021.11.1.043","DOIUrl":"https://doi.org/10.12989/OSE.2021.11.1.043","url":null,"abstract":"In the present work, a 3D numerical model is proposed to study local scouring around single vertical piers with different cross-section shapes under steady-current flow. The model solves the flow field and sediment transport processes using a coupled approach. The flow field is obtained by solving the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations in combination with the k-w SST turbulence closure model and the sediment transport is considered using both bedload and suspended load models. The proposed model is validated against the empirical measurements of local scour around single vertical piers with circular, square, and diamond cross-section shapes obtained from the literature. The measurement of scour depth in equilibrium condition for the simulations reveal the differences of 4.6%, 6.7% and 13.1% from the experimental measurements for the circular, square, and diamond pier cases, respectively. The model displayed a remarkable performance in the prediction of scour around circular and square piers where horseshoe vortices (HSVs) have a leading impact on scour progression. On the other hand, the maximum deviation was found in the case of the diamond pier where HSVs are weak and have minimum impact on the formation of local scour. Overall, the results confirm that the prediction capability of the present model is almost independent of the strength of the formed HSVs and pier cross-section shapes.","PeriodicalId":44219,"journal":{"name":"Ocean Systems Engineering-An International Journal","volume":"11 1","pages":"43"},"PeriodicalIF":0.9,"publicationDate":"2021-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49664413","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 : 2021-03-01DOI: 10.12989/OSE.2021.11.1.017
M. M. Zaheer, S. D. Hasan, Nazrul Islam, M. Aslam
Articulated loading platforms (ALPs) belongs to a class of offshore structures known as compliant. ALP motions have time periods falling in the wind excitation frequency range due to their compliant behaviour. This paper deals with the dynamic behavior of a double hinged ALP subjected to low-frequency wind forces with random waves. Nonlinear effects due to variable submergence, fluctuating buoyancy, variable added mass, and hydrodynamic forces are considered in the analysis. The random sea state is characterized by the Pierson-Moskowitz (P-M) spectrum. The wave forces on the submerged elements of the platform's shaft are calculated using Morison's Equation with Airy's linear wave theory ignoring diffraction effects. The fluctuating wind load has been estimated using Ochi and Shin wind velocity spectrum for offshore structures. The nonlinear dynamic equation of motion is solved in the time domain by the Wilson-e method. The wind-structure interactions, along with the effect of various other parameters on the platform response, are investigated. The effect of offset of aerodynamic center (A.C.) with the center of gravity (C.G.) of platform superstructure has also been investigated. The outcome of the analyses indicates that low-frequency wind forces affect the response of ALP to a large extent, which otherwise is not enhanced in the presence of only waves. The mean wind modifies the mean position of the platform surge response to the positive side, causing an offset. Various power spectral densities (PSDs) under high and moderate sea states show that apart from the significant peak occurring at the two natural frequencies, other prominent peaks also appear at very low frequencies showing the influence of wind on the response.
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