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Toru Katayama - One of the best experts on this subject based on the ideXlab platform.
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Some Topics for Estimation of Bilge Keel Component of Roll Damping
Contemporary Ideas on Ship Stability, 2019Co-Authors: Toru Katayama, Yuuki Yoshioka, Takahiro Kakinoki, Shugo Miyamoto, Yoshiho IkedaAbstract:In this paper, two topics of roll damping estimation are introduced. In these topics, Bilge-Keel component of roll damping is focused, because this component is generally most part of viscous roll damping. First topic is the Bilge-Keel component of roll damping under shallow draft and large amplitude roll motion, and an estimation method of the draft effects based on Ikeda’s method is proposed. Second topic is the Bilge-Keel component of roll damping under transitional and non-periodic rolling, an estimation method for time-domain simulation based on Ikeda’s method is introduced and its estimated results are compared with measured results of roll damping in irregular forced rolling.
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Effects of half breadth to draught ratio of hull under water surface on Bilge-Keel roll damping component
Ocean Engineering, 2019Co-Authors: Toru Katayama, Masaki Matsuoka, Toshiya Adachi, Kazuki IkushimaAbstract:Abstract Roll amplitudes of parametric roll in regular head waves are sometimes underestimated by motion calculations including Ikeda's roll damping prediction method, especially for the case of the large roll amplitude caused by high wave height. In this case, generally the ship has significant relative draught changing because of its heave and pitch. It may be said that the effects of the change in relative draught on roll damping is significant. However, in Ikeda's prediction method, the Bilge-Keel component which is the largest component of total roll damping does not take the effects of draught. As the effects of draught, there are at least two related significant effects on the Bilge-Keel roll damping component not fully considers for developing Ikeda's prediction method. They are the effects of underwater hull aspects (: half breadth to draught ratio) and the free surface effects. In this study, as a first attempt, the effects of draught on the Bilge-Keel component are investigated experimentally and numerically by using a 2-dimensional model. And a prediction model of the effects of draught on Bilge-Keel component to collect Ikeda's prediction method is proposed. Moreover, the calculated results by the proposed method are compared with some measured data including the effects of draught and its validity is confirmed.
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Bilge Keel–free surface interaction and vortex shedding effect on roll damping
Journal of Marine Science and Technology, 2017Co-Authors: Burak Yıldız, Toru KatayamaAbstract:Prediction of the roll damping of a ship with Bilge Keels using traditional techniques, such as Ikeda’s method, is no longer sufficient when the Bilge Keels interact with the free surface. The discrepancies occurring between this method and actual roll damping are due to free surface interaction and vortex shedding, which are not considered in this method. Reynolds-averaged Navier–Stokes (RANS) solvers can be used to capture these effects, and the widely used Ikeda’s method can be modified. In this study, two-dimensional (2D) roll damping calculations for a hull section with Bilge Keels, including the free surface effects, are calculated numerically and experimentally for different draft cases. The normal forces acting on the Bilge Keels are calculated numerically to show the free surface effect on Bilge Keel roll damping. The generated vortices and vortex shedding from the Bilge Keels are analyzed to investigate the effect of the Bilge Keels–free surface interaction on the roll damping coefficients. The results show that the RANS solver is capable of predicting the roll damping coefficients in good agreement with experimental results and can be further used to modify Ikeda’s method. It is concluded that the Bilge Keel forces decrease when the Bilge Keels interact with the free surface, whereas Ikeda’s method gives a constant value for each draft condition. The interaction of the Bilge Keels and free surface affects the generation of the vorticity and vortex shedding from the Bilge Keels.
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Bilge Keel free surface interaction and vortex shedding effect on roll damping
Journal of Marine Science and Technology, 2017Co-Authors: Burak Yıldız, Toru KatayamaAbstract:Prediction of the roll damping of a ship with Bilge Keels using traditional techniques, such as Ikeda’s method, is no longer sufficient when the Bilge Keels interact with the free surface. The discrepancies occurring between this method and actual roll damping are due to free surface interaction and vortex shedding, which are not considered in this method. Reynolds-averaged Navier–Stokes (RANS) solvers can be used to capture these effects, and the widely used Ikeda’s method can be modified. In this study, two-dimensional (2D) roll damping calculations for a hull section with Bilge Keels, including the free surface effects, are calculated numerically and experimentally for different draft cases. The normal forces acting on the Bilge Keels are calculated numerically to show the free surface effect on Bilge Keel roll damping. The generated vortices and vortex shedding from the Bilge Keels are analyzed to investigate the effect of the Bilge Keels–free surface interaction on the roll damping coefficients. The results show that the RANS solver is capable of predicting the roll damping coefficients in good agreement with experimental results and can be further used to modify Ikeda’s method. It is concluded that the Bilge Keel forces decrease when the Bilge Keels interact with the free surface, whereas Ikeda’s method gives a constant value for each draft condition. The interaction of the Bilge Keels and free surface affects the generation of the vorticity and vortex shedding from the Bilge Keels.
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A Study on Flow-Memory Effects on Roll Damping for Non Periodic Motion
2016Co-Authors: Jun Umeda, Toru KatayamaAbstract:In order to guarantee the safety of vessels, it is very important to estimate roll motion adequately. However, it is very complicated to calculate roll motion theoretically, because of significant viscous effects on roll damping. It is well known that there is a prediction method of the roll damping proposed by Ikeda et al. It is developed with theoretical and experimental backgrounds for periodical roll motion. Therefore, it is difficult to apply it to estimation of transitional and non-periodical roll motions (i.e. roll motion in irregular waves, broaching to capsize etc.). In the previous studies, it is pointed out that the flow-memory effects and the effects of transient motion on the Bilge Keel component of roll damping are necessary to consider for time domain simulations of non-periodical roll motion. In this study, the Bilge-Keel component of roll damping is focused, because the component is generally most part of total roll damping. In order to estimate Bilge-Keel component of non-periodic roll damping for time domain, the flow-memory effects are investigated by numerically to understand its mechanism. Moreover, based on the result, the roll damping time domain prediction method including the effects of transient motion, which is proposed by Katayama et al. based on Ikeda's method is improved.
Muhammad Agam Thahir - One of the best experts on this subject based on the ideXlab platform.
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stabilitas sampan dengan Bilge Keel pada sudut 30 dan 60 derajat
JURNAL PERIKANAN TROPIS, 2018Co-Authors: Muhammad Agam ThahirAbstract:Pembuatan sampan berbahan ember cat bekas diharapkan dapat menjadi alternatif pengganti kayu yang semakin sulit diperoleh dan pengganti bahan serat fiber yang tidak murah. Namun sampan ini memiliki kekurangan, yakni stabilitasnya yang rendah. Bobotnya yang ringan membuat sampan mudah oleng meskipun hanya beroperasi diperairan yang relatif tenang. Oleh karenanya instalasi sirip peredam oleng ( Bilge Keel ) diharapkan dapat meningkatkan stablitas sampan ini. Tujuan penelitian ini adalah untuk mendapatkan nilai stabililitas sampan dengan instalasi Bilge Keel pada sudut yang berbeda dalam rangka mendapatkan stabilitas sampan yang baik. Ukuran sampan yang dijadikan obyek dalam penelitian ini adalah panjang (LOA) 3,15 m; lebar (B) 0,64 m; dalam (D) 0,30 m. Metode simulasi numerik untuk mendapatkan nilai stabilitas serta beberapa parameter seakeeping ( pitching, roling dan heaving ) digunakan dalam penelitian ini dengan bantuan perangkat lunak yang sesuai. Hasil analisis menunjukkan bahwa terdapat perbedaan stabilitas yang ditunjukkan oleh nilai lengan GZ ( righting arm ) pada sampan yang dipasangi Bilge Keel dengan sudut 30 dan 60 derajat sebesar 0,002 m. Bilge Keel dengan sudut 30 derajat memberikan nilai stabilitas yang lebih besar dibandingkan dengan sudut 60 derajat.
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stabilitas sampan terbuat dari ember cat bekas dengan Bilge Keel pada sudut 30 dan 45 derajat
Jurnal Teknologi Perikanan dan Kelautan, 2017Co-Authors: Muhammad Agam Thahir, Budhi Hascaryo Iskandar, Mohammad ImronAbstract:Used-paint-buckets can be used as an alternative material instead of wood or fibreglass in contructing a canoe. Its light weight and easy to roll, even in relatively calm water, showing of the low stability. In order to increase its stability, Bilge Keels were applied in this canoe. The purpose of this study is to obtain the impact of Bilge Keels application at different angles in order to increase stability. The dimension of the canoe was: the length (LOA) 3.15 m; width (B) 0.64 m; and depth (D) 0.30 m. Numerical simulation method to obtain the value of some stability parameter and seakeeping (pitching, heaving, and rolling) was used in this study. For the wave factor, JONSWAP wave spectrum was used as an input in this numerical simulation. The analysis result showed that there were differences in the stability, indicated by the value of righting arm on the Bilge Keel with 30 and 45 degree as much as 0.001 m. Bilge Keel with an angle of 30 degrees give better stability value compare to 45 degrees. From the analysis of the response amplitude operator (RAO) showed that the rolling, pithcing and heaving motion of the canoe was remain in the normal.
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STABILITAS SAMPAN TERBUAT DARI EMBER CAT BEKAS DENGAN Bilge Keel PADA SUDUT 30 DAN 45 DERAJAT
Bogor Agricultural University, 2017Co-Authors: Muhammad Agam Thahir, Budhi H. Iskandar, Mohammad ImronAbstract:Ember cat bekas dapat dimanfaatkan sebagai alternatif pengganti kayu yang semakin sulit diperoleh dan pengganti bahan serat fiber yang tidak murah dalam pembuatan sampan. Namun sampan ini memiliki kekurangan, yakni stabilitasnya yang rendah. Bobotnya yang ringan membuat sampan mudah oleng meskipun hanya beroperasi di perairan yang relatif tenang. Oleh karenanya instalasi sirip peredam oleng (Bilge Keel) diharapkan dapat meningkatkan stablitas sampan ini. Tujuan penelitian ini adalah untuk mendapatkan nilai stabililitas sampan dengan instalasi Bilge Keel pada sudut yang berbeda dalam rangka mendapatkan stabilitas sampan yang baik. Ukuran sampan yang dijadikan obyek dalam penelitian ini adalah panjang (LOA) 3,15m; lebar (B) 0,64m; dalam (D) 0,30m. Metode simulasi numerik untuk mendapatkan nilai stabilitas serta beberapa parameter seakeeping (pitching, roling dan heaving) digunakan dalam penelitian ini dengan bantuan perangkat lunak yang sesuai. Untuk faktor gelombang, spektrum gelombang JONSWAP digunakan sebagai inputan dalam simulasi numerik. Hasil analisis menunjukkan bahwa terdapat perbedaan stabilitas yang ditunjukkan oleh nilai lengan GZ (righting arm) pada sampan yang dipasangi Bilge Keel dengan sudut 30 dan 45 derajat sebesar 0,001 m. Bilge Keel dengan sudut 30 derajat memberikan nilai stabilitas yang lebih besar dibandingkan dengan sudut 45 derajat. Dari analisis response amplitude operator (RAO) menunjukkan bahwa dengan inputan spektrum gelombang JONSWAP, gerakan rolling, pithcing dan heaving sampan masih berada pada rentang norma
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STABILITY OF A USED-PAINT-BUCKET BOAT EQUIPPED WITH 30 AND 45 DEGREE ANGEL Bilge KeelS
2014Co-Authors: Muhammad Agam Thahir, Budhi Hascaryo Iskandar, Mohammad ImronAbstract:Used-paint-buckets can be used as an alternative material instead of wood or fibreglass in contructing a canoe. Its light weight and easy to roll, even in relatively calm water, showing of the low stability. In order to increase its stability, Bilge Keels were applied in this canoe. The purpose of this study is to obtain the impact of Bilge Keels application at different angles in order to increase stability. The dimension of the canoe was: the length ( LOA ) 3.15 m; width ( B ) 0.64 m; and depth ( D) 0.30 m. Numerical simulation method to obtain the value of some stability parameter and seakeeping (pitching, heaving, and rolling) was used in this study. For the wave factor, JONSWAP wave spectrum was used as an input in this numerical simulation. The analysis result showed that there were differences in the stability, indicated by the value of righting arm on the Bilge Keel with 30 and 45 degree as much as 0.001 m. Bilge Keel with an angle of 30 degrees give better stability value compare to 45 degrees. From the analysis of the response amplitude operator ( RAO ) showed that the rolling, pithcing and heaving motion of the canoe was remain in the normal.
Mohammad Imron - One of the best experts on this subject based on the ideXlab platform.
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stabilitas sampan terbuat dari ember cat bekas dengan Bilge Keel pada sudut 30 dan 45 derajat
Jurnal Teknologi Perikanan dan Kelautan, 2017Co-Authors: Muhammad Agam Thahir, Budhi Hascaryo Iskandar, Mohammad ImronAbstract:Used-paint-buckets can be used as an alternative material instead of wood or fibreglass in contructing a canoe. Its light weight and easy to roll, even in relatively calm water, showing of the low stability. In order to increase its stability, Bilge Keels were applied in this canoe. The purpose of this study is to obtain the impact of Bilge Keels application at different angles in order to increase stability. The dimension of the canoe was: the length (LOA) 3.15 m; width (B) 0.64 m; and depth (D) 0.30 m. Numerical simulation method to obtain the value of some stability parameter and seakeeping (pitching, heaving, and rolling) was used in this study. For the wave factor, JONSWAP wave spectrum was used as an input in this numerical simulation. The analysis result showed that there were differences in the stability, indicated by the value of righting arm on the Bilge Keel with 30 and 45 degree as much as 0.001 m. Bilge Keel with an angle of 30 degrees give better stability value compare to 45 degrees. From the analysis of the response amplitude operator (RAO) showed that the rolling, pithcing and heaving motion of the canoe was remain in the normal.
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STABILITAS SAMPAN TERBUAT DARI EMBER CAT BEKAS DENGAN Bilge Keel PADA SUDUT 30 DAN 45 DERAJAT
Bogor Agricultural University, 2017Co-Authors: Muhammad Agam Thahir, Budhi H. Iskandar, Mohammad ImronAbstract:Ember cat bekas dapat dimanfaatkan sebagai alternatif pengganti kayu yang semakin sulit diperoleh dan pengganti bahan serat fiber yang tidak murah dalam pembuatan sampan. Namun sampan ini memiliki kekurangan, yakni stabilitasnya yang rendah. Bobotnya yang ringan membuat sampan mudah oleng meskipun hanya beroperasi di perairan yang relatif tenang. Oleh karenanya instalasi sirip peredam oleng (Bilge Keel) diharapkan dapat meningkatkan stablitas sampan ini. Tujuan penelitian ini adalah untuk mendapatkan nilai stabililitas sampan dengan instalasi Bilge Keel pada sudut yang berbeda dalam rangka mendapatkan stabilitas sampan yang baik. Ukuran sampan yang dijadikan obyek dalam penelitian ini adalah panjang (LOA) 3,15m; lebar (B) 0,64m; dalam (D) 0,30m. Metode simulasi numerik untuk mendapatkan nilai stabilitas serta beberapa parameter seakeeping (pitching, roling dan heaving) digunakan dalam penelitian ini dengan bantuan perangkat lunak yang sesuai. Untuk faktor gelombang, spektrum gelombang JONSWAP digunakan sebagai inputan dalam simulasi numerik. Hasil analisis menunjukkan bahwa terdapat perbedaan stabilitas yang ditunjukkan oleh nilai lengan GZ (righting arm) pada sampan yang dipasangi Bilge Keel dengan sudut 30 dan 45 derajat sebesar 0,001 m. Bilge Keel dengan sudut 30 derajat memberikan nilai stabilitas yang lebih besar dibandingkan dengan sudut 45 derajat. Dari analisis response amplitude operator (RAO) menunjukkan bahwa dengan inputan spektrum gelombang JONSWAP, gerakan rolling, pithcing dan heaving sampan masih berada pada rentang norma
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STABILITY OF A USED-PAINT-BUCKET BOAT EQUIPPED WITH 30 AND 45 DEGREE ANGEL Bilge KeelS
2014Co-Authors: Muhammad Agam Thahir, Budhi Hascaryo Iskandar, Mohammad ImronAbstract:Used-paint-buckets can be used as an alternative material instead of wood or fibreglass in contructing a canoe. Its light weight and easy to roll, even in relatively calm water, showing of the low stability. In order to increase its stability, Bilge Keels were applied in this canoe. The purpose of this study is to obtain the impact of Bilge Keels application at different angles in order to increase stability. The dimension of the canoe was: the length ( LOA ) 3.15 m; width ( B ) 0.64 m; and depth ( D) 0.30 m. Numerical simulation method to obtain the value of some stability parameter and seakeeping (pitching, heaving, and rolling) was used in this study. For the wave factor, JONSWAP wave spectrum was used as an input in this numerical simulation. The analysis result showed that there were differences in the stability, indicated by the value of righting arm on the Bilge Keel with 30 and 45 degree as much as 0.001 m. Bilge Keel with an angle of 30 degrees give better stability value compare to 45 degrees. From the analysis of the response amplitude operator ( RAO ) showed that the rolling, pithcing and heaving motion of the canoe was remain in the normal.
Burak Yıldız - One of the best experts on this subject based on the ideXlab platform.
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Numerical Investigation of the Effect of Bilge Keel Width on Roll Damping
2017Co-Authors: Burak Yıldız, Hüseyin YilmazAbstract:In this study, the flow around a forced rolling two dimensional hull section with Bilge Keel at free surface is simulated by using RANS solver. Roll damping coefficients are calculated numerically for different Bilge Keel width and validated with experiments to show if RANS code can correctly predict the damping coefficients. The generated vortices around the hull and Bilge Keel are observed by using RANS solver to show the effect on roll damping.
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Bilge Keel–free surface interaction and vortex shedding effect on roll damping
Journal of Marine Science and Technology, 2017Co-Authors: Burak Yıldız, Toru KatayamaAbstract:Prediction of the roll damping of a ship with Bilge Keels using traditional techniques, such as Ikeda’s method, is no longer sufficient when the Bilge Keels interact with the free surface. The discrepancies occurring between this method and actual roll damping are due to free surface interaction and vortex shedding, which are not considered in this method. Reynolds-averaged Navier–Stokes (RANS) solvers can be used to capture these effects, and the widely used Ikeda’s method can be modified. In this study, two-dimensional (2D) roll damping calculations for a hull section with Bilge Keels, including the free surface effects, are calculated numerically and experimentally for different draft cases. The normal forces acting on the Bilge Keels are calculated numerically to show the free surface effect on Bilge Keel roll damping. The generated vortices and vortex shedding from the Bilge Keels are analyzed to investigate the effect of the Bilge Keels–free surface interaction on the roll damping coefficients. The results show that the RANS solver is capable of predicting the roll damping coefficients in good agreement with experimental results and can be further used to modify Ikeda’s method. It is concluded that the Bilge Keel forces decrease when the Bilge Keels interact with the free surface, whereas Ikeda’s method gives a constant value for each draft condition. The interaction of the Bilge Keels and free surface affects the generation of the vorticity and vortex shedding from the Bilge Keels.
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Bilge Keel free surface interaction and vortex shedding effect on roll damping
Journal of Marine Science and Technology, 2017Co-Authors: Burak Yıldız, Toru KatayamaAbstract:Prediction of the roll damping of a ship with Bilge Keels using traditional techniques, such as Ikeda’s method, is no longer sufficient when the Bilge Keels interact with the free surface. The discrepancies occurring between this method and actual roll damping are due to free surface interaction and vortex shedding, which are not considered in this method. Reynolds-averaged Navier–Stokes (RANS) solvers can be used to capture these effects, and the widely used Ikeda’s method can be modified. In this study, two-dimensional (2D) roll damping calculations for a hull section with Bilge Keels, including the free surface effects, are calculated numerically and experimentally for different draft cases. The normal forces acting on the Bilge Keels are calculated numerically to show the free surface effect on Bilge Keel roll damping. The generated vortices and vortex shedding from the Bilge Keels are analyzed to investigate the effect of the Bilge Keels–free surface interaction on the roll damping coefficients. The results show that the RANS solver is capable of predicting the roll damping coefficients in good agreement with experimental results and can be further used to modify Ikeda’s method. It is concluded that the Bilge Keel forces decrease when the Bilge Keels interact with the free surface, whereas Ikeda’s method gives a constant value for each draft condition. The interaction of the Bilge Keels and free surface affects the generation of the vorticity and vortex shedding from the Bilge Keels.
Yichen Jiang - One of the best experts on this subject based on the ideXlab platform.
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Comparison of RANS Method and Discrete Vortex Method on Simulating the Roll Motion of a Ship With Bilge Keels
Volume 9: Offshore Geotechnics; Honoring Symposium for Professor Bernard Molin on Marine and Offshore Hydrodynamics, 2018Co-Authors: Yichen Jiang, Xiaojie Zhao, Zeng Zhihua, Tiezhi Sun, Li Jiawen, Zhi ZongAbstract:The prediction of roll motion of a ship section with Bilge Keels is particularly difficult because the flow separation and vortex shedding under the hull significantly affect the behavior of roll damping. To predict the roll damping and roll motion directly, the numerical models must simulate the fluid viscosity. Recently, Reynolds-averaged Navier–Stokes (RANS) method and Discrete Vortex Method (DVM) have been applied in this area and show promising results. In this paper, we will use both methods to simulate the free roll-decay motion of a ship section with Bilge Keels. The numerical predictions of the roll time histories will be compared with experimental measurements. Besides, the numerically-predicted vorticity distributions at different time instants near a Bilge Keel will be shown and compared. Moreover, the computation times for both numerical methods will also be reported. In this work, we will conduct the comparison for a number of cases that are with different Bilge-Keel heights and Bilge-Keel installation angles. Thus, the accuracies and the computational efficiencies will be evaluated comprehensively.
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Bilge-Keel Influence on Free Decay of Roll Motion of a Realistic Hull
Journal of Offshore Mechanics and Arctic Engineering, 2017Co-Authors: Yichen Jiang, Ronald W. YeungAbstract:The prediction of roll motion of a ship with Bilge Keels is particularly difficult because of the nonlinear characteristics of the viscous roll damping. Flow separation and vortex shedding caused by Bilge Keels significantly affect the roll damping and hence the magnitude of the roll response. To predict the ship motion, the Slender-Ship Free-Surface Random-Vortex Method (SSFSRVM) was employed. It is a fast discrete-vortex free-surface viscous-flow solver developed to run on a standard desktop computer. It features a quasi-three-dimensional formulation that allows the decomposition of the three-dimensional ship-hull problem into a series of two-dimensional computational planes, in which the two-dimensional free-surface Navier–Stokes solver Free-Surface Random-Vortex Method (FSRVM) can be applied. In this paper, the effectiveness of SSFSRVM modeling is examined by comparing the time histories of free roll-decay motion resulting from simulations and from experimental measurements. Furthermore, the detailed two-dimensional vorticity distribution near a Bilge Keel obtained from the numerical model will also be compared with the existing experimental Digital Particle Image Velocimetry (DPIV) images. Next, we will report, based on the time-domain simulation of the coupled hull and fluid motion, how the roll-decay coefficients and the flow field are altered by the span of the Bilge Keels. Plots of vorticity contour and vorticity isosurface along the three-dimensional hull will be presented to reveal the motion of fluid particles and vortex filaments near the Keels.
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Bilge Keel Influence on the Free Decay of Roll Motion of a Three-Dimensional Hull
Volume 7: Ocean Space Utilization; Professor Emeritus J. Randolph Paulling Honoring Symposium on Ocean Technology, 2014Co-Authors: Ronald W. Yeung, Yichen JiangAbstract:The prediction of roll motion of a ship with Bilge Keels is particularly difficult because of the nonlinear characteristics of the viscous damping. Flow separation and vortex shedding caused by Bilge Keels significantly affect the roll damping and the magnitude of the roll response. To predict free response of roll, the Slender-Ship Free-Surface Random Vortex Method (SSFSRVM) developed in Seah & Yeung (2008) [1] was employed. It is a fast free-surface viscous-flow solver designed to run on a standard desktop computer. It features a quasi-three dimensional formulation that allows the decomposition of the three-dimensional hull problem into a series of two-dimensional computational planes, in which the two-dimensional free-surface Navier-Stokes solver FSRVM [2] can be applied. This SSFSRVM methodology has recently been further developed to model multi-degrees of freedom of free-body motion in the time domain. In this paper, we will first examine the effectiveness of SSFSRVM modeling by comparing the time histories of free roll-decay motion resulting from simulations and experimental measurements. Furthermore, the detailed vorticity distribution near a Bilge Keel obtained from the numerical model will also be compared with the experimental PIV images. Next, we will report, based on the time-domain simulation of the coupled hull and fluid motion, how the roll decay coefficients and the flow field are altered by the span of the Bilge Keels. Plots of vorticity contour and vorticity iso-surface along the three-dimensional hull will be presented to reveal the motion of fluid particles and vortex filaments near the Keels.It is appropriate and an honor for me to present this roll-damping research in the Emeritus Professor J. R. Paulling Honoring Symposium. It was from “Randy” that I first acquired the concept of equivalent linear damping. Even more so, I am very grateful for his teaching, guidance and friendship of many years. — R. W. YeungCopyright © 2014 by ASME
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Computational Modeling in Three Dimensions of Multi-DOF Ship Motion in a Viscous Fluid
2014Co-Authors: Yichen JiangAbstract:The prediction of roll motion of a ship with Bilge Keels is particularly difficult because of the nonlinear characteristics of viscous damping. Flow separation and vortex shedding caused by Bilge Keels significantly affect the roll damping and the magnitude of the roll response. To predict roll damping and motion of a ship, the Slender-Ship Free-Surface Random Vortex Method (SSFSRVM) was employed. It is a free-surface viscous-flow solver with low computational cost so that it can run on a standard desktop computer. It features a quasi-three dimensional formulation that allows the decomposition of the three-dimensional hull problem into a sequence of two-dimensional computational planes, in which the two-dimensional free-surface Navier-Stokes solver FSRVM can be applied. In this work, the SSFSRVM methodology has been further developed to model multi-degrees of freedom of free-body motion in the time domain. This version of SSFSRVM model does not require the assumption of small amplitude motion, and is capable of having viscosity turned on or off in the solution procedure. Because FSRVM uses a grid-free formulation, there is no issue with numerical viscosity. We validated the SSFSRVM in simulating the free roll decay motion of a naval vessel without forward speed. The numerically predicted vorticity distributions at different time instants near a Bilge Keel closely matched experimental PIV images. We found that the SSFSRVM model is capable of predicting the roll motion of a hull, and capturing the behavior of the vortical structures in the fluid. Further, we examined how the roll decay coefficients and the flow field were altered by the span of the Bilge Keels, based on the time-domain simulation of the coupled hull and fluid motion. Plots of vorticity contours and iso-surfaces along the three-dimensional hull were presented to reveal the motion of fluid particles and vortex filaments near the Keels. In addition, the generation of the quadratic roll damping was investigated by showing the Bilge-Keel hydrodynamic moment and the pressure distribution on the hull surface and Bilge Keels. Finally, the predicted roll time histories of a naval hull with three different forward speeds were compared with those obtained from experimental measurements. The numerical predictions were in good agreement with the experimental measurements for all three speeds. In addition, the numerical model also successfully produced the divergent waves with the same angles as those measured in the experiment, and accurately predicted the locations of the peaks and troughs of the divergent waves. The motion of the sonar-dome and Bilge-Keel vortex filaments, as well as their interactions, were presented to investigate the effect of forward speed. Significant influences of forward speed on the roll motion and roll damping were noted and explained.