| 1. |
- Bilandi, Rasul Niazmand, et al.
(author)
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Dynamic motion analysis of stepless and stepped planing hulls in random waves : A CFD model perspective
- 2024
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In: Applied Ocean Research. - : Elsevier BV. - 0141-1187 .- 1879-1549. ; 149
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Journal article (peer-reviewed)abstract
- Predicting the dynamic responses of planing hulls in real sea conditions is important for identifying how basic design factors influence their seakeeping performance. Hence, there is a pressing need to provide high-fidelity models for predicting the motions of these hulls in random waves, representing actual seas. In this article, a computational-based model for solving viscous fluid flow around the vessel is built to address this problem. Three different planing hulls, denoted as C, C1, and C2, each distinguished by the number of steps incorporated on their bottom surfaces (1 and 2 indicating the respective step count, with case C being the stepless hull), are modeled in a Computational Fluid Dynamics (CFD) tank, allowing for analysis of the effects of steps on dynamic responses of a planing surface operating in random waves. CFD data is compared against those collected in towing tank tests, revealing a satisfactory level of accuracy. Extreme value and gamma distributions are shown to give probabilities of maxima/minima of displacements and vertical acceleration at the center of gravity (CG) for all three hulls. It is shown that the stepless boat may be exposed to lower vertical acceleration at an early planing speed, but at higher planing speeds, a double-stepped design mitigates the vertical acceleration. Nevertheless, the double-stepped hull would experience more significant extreme heave responses across all speeds and may be exposed to less significant extreme pitch responses during the ride at the highest speed compared to the stepless and one-stepped hulls. The skewness of heave and pitch is evaluated, and it is found that the heave response tends to skew toward positive values (upward). This skewness becomes more noticeable with increasing speed but remains insensitive to wave steepness. Additionally, the pitch response at lower planing speeds shows a partial skew towards negative values (bow-down), but eventually, they may also be partially skewed towards positive values at higher speeds. Moreover, a correlation is observed between the kurtosis of responses of different hulls and the occurrence of the 1/100 highest responses, indicating that a kurtosis greater than 3.0 would result in more extreme responses. Overall, this analysis offers practical insights into planing hull behavior in actual sea conditions from a CFD model perspective, highlighting the potential of CFD in simulating this complex problem.
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| 2. |
- Bilandi, R. N., et al.
(author)
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Hydrodynamic study of heeled double-stepped planing hulls using CFD and 2D+T method
- 2020
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In: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 196
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Journal article (peer-reviewed)abstract
- In the current paper, we have developed a method, based on 2D+T theory, to model the performance of doubled-stepped planing hulls in asymmetric conditions. We have performed Computational Fluid Dynamics (CFD) simulations to evaluate the difference between the results of the 2D+T method and CFD. We have validated 2D+T and CFD simulations. The quantitative comparison between the results of both methods shows they predict almost similar heeling moment, resistance and trim angle for a doubled-stepped planing hull. Results of non-stepped and doubled-stepped planing hulls are compared against each other, demonstrating that an increase in heel angle has less influence on the performance of the doubled-stepped planing hull. The heeling moment of a double-stepped planing hull is found to be smaller than a heeling moment of a non-stepped planing hull at early planing speeds, but, by the increase in speed, heeling moment of doubled-stepped planing hulls becomes slightly larger.
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| 3. |
- Dashtimanesh, Abbas, et al.
(author)
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A simplified method to calculate trim and resistance of a two-stepped planing hull
- 2017
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In: Ships and Offshore Structures. - : Informa UK Limited. - 1744-5302 .- 1754-212X. ; 12, s. S317-S329
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Journal article (peer-reviewed)abstract
- In a creative design process of planing craft, stepped hulls could fill a gap in the planing craft industries in response to low drag and high speed demands. However, there exists a need for new computational tools for performance prediction of such hulls. Therefore, in the current work, an attempt has been made to develop a mathematical model for performance prediction of two-stepped hulls. Savitsky's mathematical model has been modified, and in conjunction with linear wake theory, a new mathematical model has been proposed, which would enable prediction of trim, resistance and other parameters related to planing hulls with transverse steps. To validate the proposed model, existing experimental data have been used. The obtained results are in good agreement with experimental data. As such, developed mathematical model can be used in conceptual design phase of stepped hulls with transverse steps.
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| 4. |
- Dashtimanesh, Abbas, et al.
(author)
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A three-dimensional SPH model for detailed study of free surface deformation, just behind a rectangular planing hull
- 2013
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In: Journal of the Brazilian Society of Mechanical Sciences and Engineering. - : Springer Verlag. - 1678-5878 .- 1806-3691. ; 35:4, s. 369-380
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Journal article (peer-reviewed)abstract
- Transom wave behind planing hulls is a complicated physical phenomenon that has lead to computational challenge for many researchers. On the other hand, smoothed particle hydrodynamics (SPH) which is known as a meshless Lagrangian approach can simulate free surface flows with strongly nonlinear physics. Therefore, effort has been made in the current study to develop a 3D-SPH code for three-dimensional simulation of transom stern flow behind a rectangular planing hull. It is also aimed to give some new physical insights into this highly nonlinear problem. Different techniques such as sub particle scale turbulence model and moving least square density filter among others are also implemented. To validate the developed 3D-SPH code, the benchmark problem of dam breaking is investigated. Moreover, to verify the capability of the presented SPH model for transom flow simulation, previous experimental studies at low Froude numbers are considered. Comparisons display good agreement between the numerical results and experimental findings. Furthermore, a detailed discussion about rooster tail formation is presented.
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| 5. |
- Dashtimanesh, Abbas, et al.
(author)
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Digitalization of High Speed Craft Design and Operation Challenges and Opportunities
- 2022
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In: Procedia Computer Science. - : Elsevier BV. - 1877-0509. ; 200, s. 566-576
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Journal article (peer-reviewed)abstract
- In recent years, global demands for safe and sustainable ships led to dramatic changes in maritime industry. Digitalization is expected to play important part in the future. This is supported by analysis of the autonomous ships market which shows that digitalization of large ship types such as tankers and container ships is well on track. Although to date designs of autonomous High Speed Craft (HSC) have been developed, there are only a few studies on the impact of digitalization on design and operations. This is because of the challenging operational profile of these assets across a spread of waterborne activities namely fishing, leisure, patrolling and rescuing. This paper reviews literature of relevance on the potential of digitalization of the HSC sector in the Baltic. An overview of the systems that could be partly digitalized and how technology developments may influence operations are also outlined.
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| 6. |
- Dashtimanesh, Abbas, et al.
(author)
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Effects of step configuration on hydrodynamic performance of one- and doubled-stepped planing flat plates : A numerical simulation
- 2020
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In: Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment. - : SAGE Publications. - 1475-0902 .- 2041-3084. ; 234:1, s. 181-195
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Journal article (peer-reviewed)abstract
- Categorized as one of high-speed marine vehicles, stepped planing hulls have the potential to reach relatively high speed in the sea by decreasing wetted surface. There were and still are some challenges in modeling of these vessels and design of ideal situation of steps. In the current study, a numerical-based method has been used to provide understanding about the effect of step height and its location on hydrodynamic characteristics of double-stepped planing plates. At the first step, one-stepped planing plate is numerically simulated. Results are compared against exiting numerical data, suggesting that results of the current numerical simulation are similar to results of previous numerical simulations. Then, double-stepped planing plates are modeled and pressure distribution, wetted length, free surface elevation and drag over lift ratio are computed. It is seen that, ventilation length behind the step and pressure coefficient are increased when step height of one- and a double-stepped planing plates are increased. It has been shown that, unlike an one-stepped planing plate, drag coefficient of a double-stepped planing plate can be increased when the step height is increased. The effects of the location of the second step on the performance of the planing plate have been explored, showing that this position plays a critical role on hydrodynamic forces. It is demonstrated that when the smallest possible lift force is produced by the middle-body, the plate shows the best performance (highest lift over drag ratio).
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| 7. |
- Dashtimanesh, Abbas, et al.
(author)
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Numerical study on a heeled one-stepped boat moving forward in planing regime
- 2020
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In: Applied Ocean Research. - : Elsevier BV. - 0141-1187 .- 1879-1549. ; 96
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Journal article (peer-reviewed)abstract
- Stepped planing hulls have the potential to reach high-speeds in the sea. The step on the bottom of these vessels influence the pressure distribution and thus stability of the vessel, especially in transverse plane. Understanding the behavior of these vessels in a non-zero heel condition is fundamental in the early stage design. In the current paper, numerical simulation of the viscous flow field around a heeled one-stepped planing hull is performed to evaluate influences of the asymmetric planing on the performance of the vessel. The numerical model is validated in two steps. At the first step, performance of a heeled stepless planing hull operating in calm water is simulated using the numerical model, and the computed data are compared against experimental data. At the second step, the numerical model is used to compute resisatnce anad running attitudes of a one-stepped planing hull in symmetric condition, and the obtained results are compared against experimental measurements. Numerically computed results are in good quantitative agreement with laboratory measurements, showing that the numerical model has reasonable accuracy. On the whole, it has been found that a heeled condition manages a one-stepped vessel to settle at a smaller trim angle. But, unlike stepless boats, large heel angles have less effects on the trim angle at high-speeds since significant negative pressure is caused behind the step by the air, triggering negative pitching moment. It is shown that the resistance of a one-stepped planing hull is increased up to 25% at most of speeds and heel angles when the vessel advances in asymmetric condition. Moreover, this study shows that, the heeling moment of a one-stepped vessel decreases as the speed increases. The extent of reduction in the heeling moment gets more significant by the increase in heel angle at high-speeds, and, as a result, the heeling moment required to keep the vessel at large heel angle is observed to converge to the heeling moment correspanding to small heel angles.
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| 8. |
- Dashtimanesh, Abbas, et al.
(author)
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Oblique-asymmetric 2D1T model to compute hydrodynamic forces and moments in coupled sway, roll, and yaw motions of planing hulls
- 2019
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In: Journal of Ship Research. - : The Society of Naval Architects and Marine Engineers. - 0022-4502 .- 1542-0604. ; 63:1, s. 1-15
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Journal article (peer-reviewed)abstract
- In the present article, it has been tried to compute hydrodynamic forces and moments in coupled sway, roll, and yaw motions of planing hulls. For this purpose, wedge water entry has been considered in its generalized form with vertical, horizontal, and roll velocities. Using potential theory, new added mass formulas for coupled sway, roll, and yaw motion of planing hulls have been derived. Moreover, by introducing oblique-asymmetric 2D1T model and implementing momentum theory, sway force, roll moment, and yaw moment have been computed. The obtained hydrodynamic forces and moments have been compared against experimental results and previous empirical method. It has been observed that the method is accompanied with large errors and under-prediction, in the cases with zero and negative roll angle, especially at a yaw angle of 15°, which is a related limitation of the method. Better accuracy in prediction of sway force and yawing moment is observed at a trim angle of 6° and roll angles of 10° and 20°, especially for small yaw angles. The main sources of errors are found to be as follows. 1) Flow separation from the wedge apex in negative roll angle at large yaw angles, which results in under-prediction of sway force, rolling moment, and yawing moment 2) Tendency of the flow to move from starboard to port at a trim angle of 6° for the vessel with a deadrise angle of 30° at a negative roll angle and yaw angle of 15°, which cannot be simulated by the current method. 3) Reduction of contribution of hydrostatic pressure at a speed coefficient of 4.0, which is not well modeled by the proposed method and results in under-prediction of rolling moment. 4) Over-prediction of center of pressure at a yaw angle of 10° and 15°, which results in under-prediction of yawing moment. 5) Prediction of nonzero values for chine wetted length at roll angles of 10° and 20° for the yawed vessel at a trim angle of 6°, which results in under-prediction of rolling moment. 6) Over-prediction of starboard wetted length at negative roll angle at a trim angle of 6°.
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| 9. |
- Dashtimanesh, Abbas, et al.
(author)
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Performance prediction of two-stepped planing hulls using morphing mesh approach
- 2018
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In: Journal of Ship Production and Design. - : The Society of Naval Architects and Marine Engineers. - 2158-2866 .- 2158-2874. ; 34:3, s. 236-248
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Journal article (peer-reviewed)abstract
- Change in body shape characteristics is one of the ways to reduce the resistance and thereby increasing the speed of planing hulls. Creating the transverse steps is one of these variations. The main reason to use the steps in high-speed planing craft is that the wetted surface of the vessel is divided into small parts with higher width–length ratio in high velocities and in this situation, the generated lift force is more efficient. In this article, by performing a three-dimensional numerical solution, motion characteristics of a two-stepped planing hull with transverse steps in calm water have been examined. For this purpose, the vessel is free to trim and sinkage, and by using the morphing mesh approach, the numerical simulation continued until the equilibrium condition of the two-stepped planing hull is satisfied. Resistance, lift, trim angle, and wetted surface in various velocities have been computed and compared against existing experimental data. Analysis of considered two-stepped hull in calm water shows that the numerical solution for resistance, trim, and lift are relatively precise in comparison to model test data. Furthermore, various hull characteristics such as wetted length of keel, chine wetted length, spray angle and, ventilation length have been investigated.
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| 10. |
- Dashtimanesh, Abbas, et al.
(author)
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Simulation of free surface flow by using SPH method and a comparison study on two different smoothing functions
- 2012
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In: International Journal of Fluid Mechanics Research. - : Begell House. - 2152-5102 .- 2152-5110. ; 39:3, s. 261-271
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Journal article (peer-reviewed)abstract
- Simulation of free surface flow has been an interesting area of research for many years. Various methods and computational algorithms have been developed, so far. In this paper, a numerical model for the two dimensional simulation of free surface motion is presented. The model which is based on a smoothed particle hydrodynamics method is used to solve the Navier - Stokes equation and the free surface flow. Two different smoothing kernels are also implemented in the simulation and compared with each other. The numerical model is also verified by comparing the obtained results against the documented experimental and numerical findings. Relatively good agreement is displayed in the verification phase.
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