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An investigation into the resistance components of high speed displacement catamarans
... Figure 4 reports the comparison between the wet surface modelled by the developed analytical formulation and the values of the reference hull computed by CAD. The total resistance coefficient is modelled as a combination of a friction and a residuary component [19]: ...
... A significant simplification was chosen to model the residuary drag coefficient . A combination of two quadratic formulations with Froude number, for speeds lower and higher than a critical value and linearly function of the operative weight, was adopted: The total resistance coefficient is modelled as a combination of a friction and a residuary component [19]: ...
... Good agreement with CFD computations was observed ( Figure 5) adopting as L wl the full length of the hull (modern A-Cat hulls have an inversed bow shape). The total resistance coefficient is modelled as a combination of a friction and a residuary component [19]: ...
A procedure for the optimization of a catamaran’s sail plan able to provide a preliminary optimal appendages configuration is described. The method integrates a sail parametric CAD model, an automatic computational domain generator and a Velocity Prediction Program (VPP) based on a combination of sail RANS computations and analytical models. The sailing speed and course angle are obtained, with an iterative process, solving the forces and moment equilibrium system of equations. Analytical formulations for the hull forces were developed and tuned against a matrix of CFD solutions. The appendages aerodynamic polars are estimated by applying preliminary design criteria from aerospace literature. The procedure permits us to find the combination of appendages configuration, rudders setting, sail planform, shape and trim that maximise the VMG (Velocity Made Good). Two versions of the sail analysis module were implemented: one adopting commercial software and one based on the use of only Open-Source codes. The solutions of the two modules were compared to evaluate advantages and limitations of the two approaches.
... However, the 30 individual resistance components of a swimmer have yet to be experimentally validated. Thin-ship theory has been successfully applied in conventional naval architecture for quantifying the wave resistance of ships [8,9], for example, but has yet to be applied to swimmer geometries. Thin-ship theory offers the opportunity for accurate results with run times that are two to three orders of magnitude faster than CFD [5]. ...
... Thin-ship Theory (TST) has been used to estimate the wave resistance of ships for several decades [8]. Development to initial work [10,11,12] have enabled the application of TST to vessels of a variety of shapes. ...
... Development to initial work [10,11,12] have enabled the application of TST to vessels of a variety of shapes. Some examples of applying TST to ships include [8,9]. As TST has been shown to provide fast accurate simulations of ship hydrodynamics, applications of TST to swimmer hydrodynamics have also been explored. ...
Quantifying the wave resistance of a swimmer as a function of depth assists in identifying the optimum depth for the glide phases of competition. Previous experiments have inferred how immersed depth influences the drag acting on a swimmer [1], but have not directly quantified the magnitude of wave resistance. This research experimentally validates the use of thin-ship theory for quantifying the 5 wave resistance of a realistic swimmer geometry. The drag and wave pattern of a female swimmer mannequin were experimentally measured over a range of depths from 0.05m to 1.00m at a speed of 2.50 m/s. Numerical simulations agree with experiment to confirm that there were negligible reductions in wave resistance below a depth of 0.40m. Larger swimming pool dimensions are shown to be significant at reducing wave resistance at speeds above 2.0 m/s and depths below 0.40m. 10 Truncating the swimmer’s body at the upper thigh increases the wave resistance at speeds below 2.0m/s but is not significant at higher speeds, indicating that the upper body is the main contributor to the wave system. Numerical experiments indicate that rotating the shoulders towards the surface is more influential than the feet, demonstrating the impact of the upper body on wave resistance.
... Researchers like have developed the original methods as Mitchell [24], Wigley [25] and Eggers [26] and this method can now be applied to a wide range of hull forms. For example, Insel [27,28], Cong and Hsiung [29] among those how have applied the more developed method. The work described here uses the method developed by Insel [27] in which the wave resistance is calculated from the description of the far-field wave system using Eggers coefficients [26]. ...
... For example, Insel [27,28], Cong and Hsiung [29] among those how have applied the more developed method. The work described here uses the method developed by Insel [27] in which the wave resistance is calculated from the description of the far-field wave system using Eggers coefficients [26]. Also, the ship resistance calculation is based on the proposed method by Couser et al. [30,31]. ...
In the current paper, different geometrical parameters of the trimaran hull ship are investigated to achieve the optimal points of geometry parameters. Considering the fixed displacement volume, the values of the longitudinal center of buoyancy, block coefficient, midsection coefficient as well as the side hull length and position are computed and using Lackenby shift transformation, the geometry is reconstructed during the optimization process. It is then necessary to compute the ship resistance of the reconstructed geometry which is hereby accomplished by slender body method. Subsequently, D-optimal method is used for finding the best parameters to achieving minimum resistance at cruise and sprint speeds. Two strategies are pursued to find optimum value of design variable: trimaran hull transformation and separated hull approach. Generally, a hull optimization process takes huge time and depending on the applied methodology, it might take somewhere between 6 months and 2 years. However, through slender body method and design of experiment study, proposed in this paper, the total time of global optimization process is only 1 week. Meanwhile, 9.1% resistance reduction at cruise speed and 2.24% resistance reduction at sprint speed is achieved. Hence, a successful ship hull optimization with suitable computational time and effort is the novelty of the current work. The conducted optimization indicates that two parameters of longitudinal center of buoyancy and block coefficient have significant effect on the total resistance. Comparison of the original and optimized hull signals the validity and superiority of the proposed optimization strategy, which can be extended to other maritime industrial projects.
... Catamarans, due to their favourable performance in efficiency and stability at high speeds, have been widely studied experimentally, theoretically and numerically over the past decades [5][6][7]. A series of model tests were carried out by Insel and Molland [8] and Molland et al. [9] investigating the calm water resistance of fast catamarans with symmetrical demihulls, whereas Zaraphonitis et al. [10] have studied asymmetrical demihulls. Their studies emphasised the effects of demihull dimensions and separation distance on the resistances and motions of the catamarans over a wide range of Froude numbers (0.2 ≤ Fn ≤ 1.0). ...
The present paper investigates numerically the resistance at full-scale of a zero-emission, high-speed catamaran in both deep and shallow water, with the Froude number ranging from 0.2 to 0.8. The numerical methods are validated by two means: a) comparison with available model tests; b) a blind validation using two different flow solvers. The resistance, sinkage and trim of the catamaran, as well as the wave pattern, longitudinal wave cuts and cross-flow fields, are examined. The total resistance curve in deep water shows a continuous increase with the Froude number while in shallow water, a hump is witnessed near the critical speed. This difference is mainly caused by the pressure component of total resistance, which is significantly affected by the interaction between the wave systems created by the demihulls. The pressure resistance in deep water is maximised at a Froude number around 0.58, whereas the peak in shallow water is achieved near the critical speed (Froude number ≈ 0.3). Insight into the underlying physics is obtained by analysing the wave creation between the demihulls. Profoundly different wave patterns within the inner region are observed in deep and shallow water. Specifically, in deep water, both crests and troughs are generated and moved astern as the increase of the Froude number. The maximum pressure resistance is accomplished when the secondary trough is created at the stern, leading to the largest trim angle. In contrast, the catamaran generates a critical wave normal to the advance direction in shallow water, which significantly elevates the bow and creates the highest trim angle as well as pressure resistance. Moreover, significant wave elevations are observed between the demihulls at supercritical speeds in shallow water which may affect the decision for the location of the wet deck.
... Catamarans, due to their favourable performance in efficiency and stability at high speeds, have been widely studied experimentally, theoretically and numerically over the past decades [5][6][7]. A series of model tests were carried out by Insel and Molland [8] and Molland et al. [9] investigating the calm water resistance of fast catamarans with symmetrical demihulls, whereas Zaraphonitis et al. [10] have studied asymmetrical demihulls. Their studies emphasised the effects of demihull dimensions and separation distance on the resistances and motions of the catamarans over a wide range of Froude numbers (0.2 ≤ Fn ≤ 1.0). ...
This paper numerically investigates the resistance at full-scale of a zero-emission, high-speed catamaran in both deep and shallow water, with the Froude number ranging from 0.2 to 0.8. The numerical methods are validated by two means: (a) Comparison with available model tests; (b) a blind validation using two different flow solvers. The resistance, sinkage, and trim of the catamaran, as well as the wave pattern, longitudinal wave cuts and crossflow fields, are examined. The total resistance curve in deep water shows a continuous increase with the Froude number, while in shallow water, a hump is witnessed near the critical speed. This difference is mainly caused by the pressure component of total resistance, which is significantly affected by the interaction between the wave systems created by the demihulls. The pressure resistance in deep water is maximised at a Froude number around 0.58, whereas the peak in shallow water is achieved near the critical speed (Froude number ≈ 0.3). Insight into the underlying physics is obtained by analysing the wave creation between the demihulls. Profoundly different wave patterns within the inner region are observed in deep and shallow water. Specifically, in deep water, both crests and troughs are generated and moved astern as the increase of the Froude number. The maximum pressure resistance is accomplished when the secondary trough is created at the stern, leading to the largest trim angle. In contrast, the catamaran generates a critical wave normal to the advance direction in shallow water, which significantly elevates the bow and creates the highest trim angle, as well as pressure resistance. Moreover, significant wave elevations are observed between the demihulls at supercritical speeds in shallow water, which may affect the decision for the location of the wet deck.
... The Delft Systematic Yacht hull series provides a significant amount of information on the hydrodynamics of parametrically varied sailing craft hull forms (Gerritsma and Keuning, 1992;Keuning and Sonnenberg, 1998 (Insel and Molland, 1992;Molland et al., 2011). These hull forms are slender, round 795 bilged and possessed transom sterns. ...
The aim of this thesis is to quantify how Polynesian seafaring technology, climate and season may have influenced the length of the “long pause” between the 35 settlement of West and Central East Polynesia. Current literature has not investigated the performance of Polynesian seafaring technology at the time of the long pause and how this could influence colonisation, or how uncertainty propagates through the marine weather routing process. Of interest is how Polynesian seafaring technology could have contributed towards the length of 40 the long pause and how competing factors and sources of uncertainty could have influenced the result.
A review of Polynesian seafaring technology has allowed the performance of the earliest recorded voyaging canoe, the Tongiaki to be predicted. A novel methodology was developed to quantify the influence of weather, performance and 45 numerical uncertainty on the minimum time taken to complete a specific voyage. The ability to use Bayesian Belief Networks (BBNs) to model the reliability within the routing algorithm was shown to improve the chances of completing a voyage using an autonomous sailing craft, a modern naval architectural problem. By applying the novel methodology it was found that the Tongiaki was only able 50 to complete voyages between Samoa and Aituitaki, the voyage bridging West and East Polynesia, under El Niño conditions. The windward ability of a canoe was found to be more influential than speed increases from simulations generated by using a parametric voyaging canoe model. The trend in simulated Polynesian canoe performance mirrors that seen in the spatial development in Polynesian 55 seafaring technology.
... Determining the interference effect in the past was difficult, as separating ϕ and σ required the availability of high-performance computing and experimental tools (Insel and Molland, 1992). For practical purposes, ϕ and σ are combined into a viscous interference factor (β), where: ...
A
computational fluid dynamics investigation was carried out on a slender body
catamaran to determine the effect of pressure and flow velocity changes for
varied hull separations. The investigation was conducted using an NPL 4a model
with a slenderness (length to breadth) ratio of about 11 together with the use
of a commercial code (CFX) with hull separations of S/L = 0.3 and 0.4 along
with a variation in Reynolds numbers of 2.86×105, 3.43×105, 4.01×105, and
4.44×105. Pressure and flow velocity around the hull were measured to obtain a
fluid effect attributed to the influence of catamaran hull interference. A
computational fluid dynamics investigation was carried out with the same
configurations as those in the experimental tests. The overall results were in
good agreement, with the order of discrepancy at about 1.76%; the computational
fluid dynamics results were consistently lower than the experimental ones. Both
tests demonstrated a viscous interaction between the hulls and, thus, the form
factors for the demihull and catamaran were properly derived: the form factor
for the demihull (1+k) was 1.254 and for the catamaran (1+?k) was 1.420,
indicating interaction effects of about 13.2%. The form factor for the
catamaran was consistently higher than the demihull, suggesting some viscous
interference between the hulls. The effect of catamaran hull interference
variation can be recognized through the velocity augmentation ratio (?),
pressure change ratio (?), and the viscous interference factor (?). In
addition, the ? value is very helpful for finding out the interference of the
hull on a catamaran when sophisticated experimental and numerical tools are not
available.
... So that the total displacement, Calculation of the coefficient of the ship shape is taken from calculations using the Maxurf software as shown in Table 6 In an experiment to calculate the total resistance value of a catamaran, its hull is assumed to be a demihull ship added to the interference price due to the hull which is S distance from its center line. The value of the total resistance is multiplied by 2 considering the wet surface area (WSA) is in each hull [17]. The total resistance can be calculated with the following formula: After knowing the value of total resistance (RT) then move with the calculation of the power to move the ship. ...
... Однако начало научного подхода к её изучению было положено около 100 лет назад работами W. Froude[147] и J. H. Michell[161]. Развитие компьютерных технологий около 30 лет назад сделало это изучение бестелесным[151,152,165,171,175].Сегодня практически все новые байдарки разработаны с использованием ЭВМ.В работах[156,174] L. Lazauskas и E. O. Tuck предложили алгоритм по нахождению оптимальной длины, ширины и других принципиальных размеров для байдарки-одиночки на различных скоростях, но с учётом установленных международной федерацией гребли (ICF) ограничений. В работе подробно рассмотрены все составляющие гидродинамического сопротивления: волнообразования. ...
The mathematical method developed based on the application of a physical model of the air flows and water flow interaction with an athlete and a boat, which including special algorithms and programs, allows to accurately determine the criterion for an objective assessment of sport results.
For a clear evaluation of the sprint result a new criterion was applied – the characteristic time. The characteristic time equal to the sum of the actual (real) race time and the time increment caused by aero - and hydrodynamic factors.
... On multihull vessels, including catamarans, the problem of resistance is still widely discussed. Several studies on hull distance ratio have been investigated (Insel and Molland, 1992) as well as several experiments on catamaran resistance (Everest, 1968;Pien, 1976;Oving, 1985). This research aims to find the hull separation ratio (clearance) on a catamaran hull model for an N219 seaplane based on biomimetics to optimize the design using an experimental method and CFD simulation. ...
Seaplanes are planes that can take off and land from the surface of
water. Due to their ability to take off and land from the surface of water,
seaplanes need a pair of pontoons in the form of a catamaran hull at the bottom
of seaplanes so that the seaplanes can float above the surface of water.
Research on the catamaran hull model was conducted to examine the effect of istiophorus
platypterus design distance between hulls (clearance) variation on the
total resistance of the catamaran hull model through experimental method and
computational fluid dynamics (CFD) simulation method. There are three values of
clearance (S/L) used in this research: 0.15, 0.2, and 0.25. The most optimal
clearance configuration can be determined using a configuration which has the
lowest total resistance. The results of experiments and simulations show that
the distance between hull variations has a considerable effect on the total
resistance of the catamaran hull model. The catamaran hull, which has the
optimal clearance configuration, will cause the resulting wave interference and
resistance to be small. The model was towed with Froude numbers ranging
from 0.35 to 0.65. The results showed that hull separation made a difference in
the total resistance coefficient on the same experiment configurations. The
configurations with S/L 0.25 showed the least total resistance coefficient,
whereas the configurations with the S/L 0.15 showed the highest total
resistance coefficient. The simulations were conducted with the model with
Froude numbers ranging from 0.35 to 0.65 using 700,000 cells in meshing and an
error rate of 7.6% in convergence.
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