The interceptor hydrodynamic analysis for controlling the porpoising instability in high speed crafts

A well-known instability of the high-speed planing crafts is the porpoising instability. This instability involves periodic, coupled heave/pitch oscillations possibly experienced in a planing vessel at high speeds. The porpoising can be controlled by using external devices. Interceptors are vertical blades installed symmetrically at the aft of the craft and have been introduced as a trim control appendage. Here, based on numerical methods and Savitsky porpoising theory, the effects of hydrodynamic interceptors on the porpoising control are investigated. Using computational fluid dynamics, the pressure distribution created by interceptor and its effects on porpoising are computed and then discussed. To model the flow around the vessel model, the Reynolds Average Navier Stokes (RANS) equations are applied. The work deals with craft with and without an interceptor at different heights. A dynamic grid mode involving two degrees of freedom is used. The results show that the interceptor causes an intense pressure at the stern bottom. It also decreases the trim and resistance of the vessel and increases the lift force coefficient which directly affects the porpoising instabilities. Based on the results, the interceptor can completely control the porpoising phenomenon.     

An experimental study of interceptors for drag reduction on high-performance sailing yachts

Interceptors have been widely used in recent years in fast ferries and small high-speed leisure and commercial craft for ride and trim control, and steering. In the context of high-performance sailing yachts, they first appeared in 2008 on the yacht Ecover 3 which was dismasted while leading the Vendee Globe Challenge race. However, in spite of their popularity in power craft, few studies have been published investigating the impact of interceptors on vessel performance, and apparently none in the case of sailing yachts. In the current study, interceptors are compared with an aerodynamic device known as a Gurney flap. It is shown that interceptors are generally substantially smaller than Gurney flaps. A comprehensive experiment programme is presented exploring the impact of interceptors on the performance of an Open 60 yacht hull. Results show a marked reduction in calm-water resistance over a wide speed range, with benefits of 10–18% in the speed range between 8 and 20 knots, accompanied by reduced sinkage and trim. The gains observed are much larger than those observed in powercraft, and also substantially greater than those achievable through trim changes by moving ballast longitudinally. The benefits appear to be largely sustained in small waves.     

The spray volume shed by an uncambered planing hull in steady planing

Earlier papers (Payne, 1981 a,b,c) have developed what might be called a virtual mass theory which in principle permits the forces on any planing hull form to be calculated. In the present paper, this methodology is extended to calculate the thickness and momentum of the jet or spray sheet thrown off by the planing surface. For a two-dimensional flat planing plate—the only case where comparison is possible—the theory gives essentially the same result as that of Pierson and Leshnover (1948). For a three-dimensional flat plate and prismatic hulls, the results seem physically reasonable.For the small trim angles associated with efficient planing, on a weightless inviscid fluid the total pressure drag of any hull can be reduced to close to zero by deflecting the jet rearwards and parallel to the undisturbed surface, the residual resistance being due to the cross-flow force which varies as (trim angle)².     

A combined method for the hydrodynamic characteristics of planing crafts

The prediction of the total resistance of planing crafts at high speeds is very important. In this paper, a combined method is investigated for determining the hydrodynamic characteristics of planing crafts in the calm water. The study consists of a potential-based boundary element method (BEM) for the induced pressure resistance, the boundary layer theory for the frictional resistance and practical method for the spray resistance. The planing surface is represented by a number of elements with constant velocity potential at each element. The unknown-induced pressure is obtained by using the free surface elevation condition and the Kutta condition at the transom stern. Hydrodynamic-induced resistance and lift are determined by the calculated dynamic pressure distributions. The boundary layer analysis method is based on calculations of the momentum integral equation applied to obtain the frictional resistance. A particular practical approach is introduced to present the region of the upwash geometry for the spray. A numerical program has been developed for the present research and applied to the hull form of the craft. Four different hull forms of Series 62 model 4666 planing craft are presented. It is shown that the present combined method is efficient and the results are in good agreement with the experimental measurements over a wide range of volumetric Froude numbers.     

Planing and impacting plate forces at large trim angles

Added mass theory has been shown to give excellent agreement with experimental measurements on planing surfaces at normal planing angles [e.g. Payne, P.R. (1982, Ocean Engng9, 515–545; 1988, Design of High-Speed Boats, Volume 1: Planning. Fishergate. Inc., Annapolis, Maryland)] and to agree exactly with more complex conformal transformations where such a comparison is possible. But at large trim angles, it predicts non-transient pressures that are greater than the free-stream dynamic pressure and so cannot be correct. In this paper, I suggest that the reason is because, unlike a body or a wing in an infinite fluid, a planing plate only has fluid on one side—the “high pressure” side. So the fluid in contact with the plate travels more slowly as the plate trim angle (and therefore static pressure) increases. This results in lower added mass forces than Munk, M. (1924) The Aerodynamic Forces on Airship Hulls (NACA TR-184) and Jones, R. T. (1946) Properties of Low-Aspect-Ratio Pointed Wings at Speeds Below and Above the Speed of Sound (NACA TR-835) originally calculated for wings and other bodies in an infinite fluid.For simplicity of presentation, I have initially considered the example of a triangular (vertex forward) planning plate. This makes the integration of elemental force very simple and so the various points are made without much trouble. But the penalty is that there seem to be no experimental data for such a configuration; at least none that I have been able to discover. But at least the equations obtained in the limits of zero and infinite aspect ratio, small trim angles (τ) and τ = 90° all agree with established concepts and the variation of normal force with trim angle looks like what we would expect from our knowledge of how delta wings behave in air.I then employed the new equation to calculate the force on a rectangular planing surface at a trim angle τ, having a constant horizontal velocity u_o and a vertical impact velocity of ż. This happens to have been explored experimentally by Smiley, R. F. [(1951) An Experimental Study of Water Pressure-Distributions During Landings and Planing of a Heavily Loaded Rectangular Flat Plate Model (NACA TM 2453)] up to trim angles of τ = 45°, and so a comparison between theory and experiment is possible. The results of this comparison are encouraging, as is also a comparison with the large trim angle planing plate measurements of Shuford, C. L. [(1958) A Theoretical and Experimental Study of Planing Surfaces Including Effects of Cross Section and Plan Form (NACA Report)].As two practical applications, I first employed the new equations to calculate the “design pressures” needed to size the plating of a transom bow on a high-speed “Wavestrider” hull. The resulting pressures were significantly different to those obtained using semi-empirical design rules in the literature. Then I used the theory to critically review data obtained from tank tests of a SES bow section during water impact to identify how the “real world” of resilient deck plating diverged from the “model world” of extreme structural rigidity.     

紫扇贝和海湾扇贝杂交家系的生长和通径分析

以紫扇贝(Argopecten purpuratus)和海湾扇贝(Argopecten irradians irradians)为亲本,建立了紫扇贝自交(ZZ)、海湾扇贝自交(HH)、紫扇贝(卵)×海湾扇贝(精)(ZH)和海湾扇贝(卵)×紫扇贝(精)(HZ)共4个试验家系.在养殖60、127 d时测定壳高、壳长、壳厚和体质量,并分析各养殖时期影响体质量的主要因素.结果表明:在各养殖时期,2杂交家系子代的壳高、壳厚以及体质量均表现出生长优势(P＜0.01),因此认为通过紫扇贝和海湾扇贝杂交方式是改善扇贝的良好方法.通径分析的结果表明,对于自交家系,壳长是影响体质量的主要影响因素,但对于杂交家系HZ来说,壳长(60 d)和壳厚(127 d)对体质量的决定作用最大;在杂交家系ZH,60 d时壳长和壳厚的协同作用对体质量的决定作用最大,127d时壳高的决定作用最大.因此对于两个杂交家系的选育,应按照不同性状对体质量的决定系数选择各时期的优势性状,以使子代的杂种优势充分表现.     

On the Applicability of Similarity Theory for the Stable Atmospheric Boundary Layer over Complex Terrain

Micrometeorological measurements in the atmospheric boundary layer over a hilly forest terrain have been made on a meteorological tower at several levels from the forest canopy top to a height that exceeds the height of trees almost seven times. A semiempirical length scale depending on the local topography features and the underlying surface type has been proposed and calculated. This scale has been shown to allow the universal functions of the Monin–Obukhov similarity theory to be corrected for a stable atmospheric boundary layer over complex terrain without substantial modification when compared to the universal functions over a homogeneous surface with small roughness elements. This approach can be used to refine the methods for calculating turbulent momentum fluxes from profile measurements over spatially inhomogeneous landscapes.     

Characteristics of the boundary layer at the bottom of a solitary wave

The results of direct numerical simulations of the boundary layer generated at the bottom of a solitary wave are described. The numerical results, which agree with the laboratory measurements of Sumer et al. (2010) show that the flow regime in the boundary layer can be laminar, laminar with coherent vortices and turbulent. The average velocity and bottom shear stress are computed and the results obtained show that the logarithmic law can approximate the velocity profile only in a restricted range of the parameters and at particular phases of the wave cycle. Moreover, the maximum value of the bottom shear stress is found to depend on the dimensionless wave height only, while the minimum (negative) value depends also on the dimensionless boundary layer thickness. Diagrams and simple formulae are proposed to evaluate the minimum and maximum bottom shear stresses and their phase shift with respect to the wave crest.     

基于Savitsky法滑行艇航行姿态参数影响研究

高速滑行艇处于滑行状态时的阻力性能一直是滑行艇水动力性能研究的重点和难点。首先采用半经验半理论的Savitsky法对棱柱形滑行艇的航行姿态与阻力进行研究分析,计算纵倾结果与试验结果吻合良好。然后改变滑行艇的长宽比、重心纵向位置与底部斜升角参数,进一步研究三种参数变化对滑行艇航行姿态与阻力性能的影响。研究结果表明:基于半经验半理论的Savitsky方法可用于棱柱形滑行艇的阻力性能分析;在高速阶段,长宽比、重心纵向位置与底部斜升角参数对阻力影响较大。     

A Unified Computational Method for Simulating Dynamic Behavior of Planing Vessels

High speed planing hulls have complex hydrodynamic behaviors. The trim angle and drafts are very sensitive to speed and location of the center of gravity. Therefore, motion simulation for such vessels needs a strong coupling between rigid body motions and hydrodynamic analysis. In addition, free surface should be predicted with good accuracy for each time step. In this paper, velocity and pressure fields are coupled by use of the fractional step method. On the basis of integration of the two-phase viscous f...     

Observation and measurement of the bottom boundary layer flow in the prebreaking zone of shoaling waves

In this paper, the characteristics of the bottom boundary layer flow induced by nonlinear, asymmetric shoaling waves, propagating over a smooth bed of 1/15 uniform slope, is experimentally investigated. Flow visualization technique with thin-layered fluorescent dye was first used to observe the variation of the flow structure, and a laser Doppler velocimeter was then employed to measure the horizontal velocity, U.The bottom boundary layer flow is found to be laminar except within a small region near the breaking point. The vertical distribution of the phase-averaged velocity U at each phase is non-uniform, which is directly affected by the mean velocity, . The magnitude of increases from zero at the bottom to a local positive maximum at about z/δ2.02.5 (where z is the height above the sloping bottom and δ is the Stokes layer thickness), then decreases gradually to zero at z/δ6.07.0 approximately, and finally becomes negative as z/δ increases further. Moreover, as waves propagate towards shallower water, the rate of increase in the maximum onshore oscillating velocity component is greater than that of the offshore counterpart except near the breaking point. The free stream velocities in the profiles of the maximum onshore and offshore oscillating velocity components, and are found to appear at z/δ≥6.0. This implies that, if the Stokes layer thickness is used as a length scale, the non-dimensionalized boundary layer thickness remains constant in the pre-breaking zone. Although is greater than and the asymmetry of the maximum free stream velocities (i.e. ) increases with decrease of water depth, a universal similar profile can be established by plotting z/δ versus ( ) or ( ). The final non-dimensional profile is symmetric and unique for the distributions of the maximum onshore and offshore oscillating velocity components within the bottom boundary layer, which are induced by nonlinear, asymmetric shoaling waves crossing the pre-breaking zone.     

The normal force on a flat planing plate, including low length to beam ratios

A previous paper (Payne, 1980) developed the theory of a slender planing surface from first principles, and found it to agree with experiment without the need for “factors determined from experiments”. The theory broke down, however, for low wetted length to beam ratios because the flow is then no longer two-dimensional in character in respect to a section normal to the flow. It is in a transition to the condition where, at very small length to beam ratios, it is two-dimensional in a vertical plane parallel to the flow, rather than normal to it.In the present paper we determine, albeit somewhat heuristically, the virtual mass coefficient of a flat plate in the transition region. This is then employed to compute the normal force on a planing plate in both steady state and transient motion. For both conditions the agreement with the available experimental data is within the accuracy of the data.Both theory and experiment lead to the conclusion that certain traditional concepts in the of trim angle and Pierson's suggestion that ‘wetted length’ is more fundamental than the length of intersection with the still water surface. The widespread acceptance of this latter suggestion has meant that a key parameter in the present theory—the nominal or undisturbed water intersection length—is almost never measured in modern experiments. Thus, since we could not find any modern data, we had to appeal to the classical experimental papers which originated the scientific study of planing in the thirties and forties. Oddly, the earliest papers gave data which had much less scatter than the later papers.     

The vertical structure of the atmospheric boundary layer over the central Arctic Ocean

The tropopause height and the atmospheric boundarylayer （PBL） height as well as the variation of inversion layer above the floating ice surface are presented using GPS （global position system ） radiosonde sounding data and relevant data obtained by Chinas fourth arctic scientific expedition team over the central Arctic Ocean （86°-88°N, 144°-170°W） during the summer of 2010. The tropopause height is from 9.8 to 10.5 km, with a temperature range between -52.2 and -54.10C in the central Arctic Ocean. Two zones of maximum wind （over 12 m/s） are found in the wind profile, namely, low- and upper-level jets, located in the middle troposphere and the tropopause, respectively. The wind direction has a marked variation point in the two jets from the southeast to the southwest. The average PBL height determined by two methods is 341 and 453 m respectively. These two methods can both be used when the inversion layer is very low, but the results vary significantly when the inversion layer is very high. A significant logarithmic relationship exists between the PBL height and the inversion intensity, with a correlation coefficient of 0.66, indicating that the more intense the temperature inversion is, the lower the boundary layer will be. The observation results obviously differ from those of the third arctic expedition zone （800-85° N）. The PBL height and the inversion layer thickness are much lower than those at 870-88° N, but the inversion temperature is more intense, meaning a strong ice- atmosphere interaction in the sea near the North Pole. The PBL structure is related to the weather system and the sea ice concentration, which affects the observation station.     

A Unified Computational Method for Simulating Dynamic Behavior of Planing Vessels

High speed planing hulls have complex hydrodynamic behaviors. The trim angle and drafts are very sensitive to speed and location of the center of gravity. Therefore, motion simulation for such vessels needs a strong coupling between rigid body motions and hydrodynamic analysis. In addition, free surface should be predicted with good accuracy for each time step. In this paper, velocity and pressure fields are coupled by use of the fractional step method. On the basis of integration of the two-phase viscous flow induced stresses over the hull, acting loads (forces and moments) are calculated. With the strategy of boundary-fitted body-attached mesh and calculation of 6-DoF motions in each time step, time history of ship motions including displacements, speeds and accelerations are evaluated. For the demonstration of the software capabilities, circular cylinder slamming is simulated as a simple type of water slamming. Then, a high-speed planing catamaran is investigated in the case of steady forward motion. All of the results are in good concordance with experimental data. The present method can be widely implemented in design as well as in performance prediction of high-speed vessels.     

基于风廓线雷达观测的台风“天兔”边界层演变特征研究

垂直探测台风边界层特征对于认清台风结构具有重要意义。基于1319号台风“天兔”途经的三个边界层风廓线雷达站的观测资料,结合探空数据,本文分析了“天兔”的边界层径向、切向风特征,结果表明：1）最大切向风速出现在眼区附近,在“天兔”稳定维持为强台风级别期间,最大切向风速基本稳定在1800 m高度左右,随着登陆后强度的迅速减弱,最大切向风速减弱、最大切向风速垂直范围缩小;2）最大风速所在高度和台风入流层顶高基本相近,大于依据理查森数或位温梯度所判断出的边界层高度,而基于信噪比（SNR）或其梯度所判断的混合层高度时常偏低;3）“天兔”登陆前边界层高度可以达到2100 m以上,在台风级别及以上时,各站观测到的边界层高度变化不大,基本在1200～1600 m之间,登陆后随着台风强度的减弱,边界层高度迅速减小。     

The differences between a wing and a planing plate in two-dimensional flow

The normal force coefficient on a flat planing surface having arbitrary heave and pitch motion in two-dimensional flow is compared with the lift coefficient of a thin wing in an infinite fluid. Despite the totally different derivations, they are found to be identical (at large Froude numbers and low trim angles and allowing for the wing's interaction with twice as much fluid) at low reduced frequencies. For higher frequency motions, the wing's angle of attack induced lift and its pitch and heave damping are less than those of a planing surface, but the acceleration terms remain identical. The differences at the higher reduced frequencies are due to the fact that, in invisad irrotational flow, the planning plate cannot leave a vortex wake, whereas a wing does.It seems to follow that the “virtual mass” planing hull analysis can be applied to “quasi-static” problems involving wings and bodies in an infinite fluid without the slenderness restriction originally imposed by Jones (1946). Certainly, it is remarkable that the so called “quasi-steady” forces on a two-dimensional wing can be obtained in a few lines of elementary analysis. On the other hand, the method fails entirely when used to compute the pitching moment on a two-dimensional plate, even though it has been found to give good results for the three-dimensional case (Payne, 1981c).This work is offered as a very incomplete study of an intriguing relationship between two very different bodies of analysis. Much more work will need to be done before the relationship between the two approaches will be fully understood.     

Calculating the Wave Force on Partially Immersed Large-Scale Horizontal Cylinders

Large-scale interceptors constitute the main structure of offshore self-driven floating marine litter collection devices,and the structural stability of such interceptors under the action of waves directly influences the overall safety of the device.When the ratio of the diameter of a horizontal cylinder in such interceptors to the incident wavelength is larger than 0.25,the wave force can be calculated by using the diffraction theory,by considering the problem as that of the interaction between the waves and a partially immersed large-scale horizontal cylinder.In this study,an analytical approach to calculate the wave force on a partially immersed large-scale horizontal cylinder was formulated by using the stepwise approximation method.Physical model tests were conducted to investigate the effects of different factors(wave height,period,and immersion depth)on the wave force on a large-scale horizontal cylinder under conditions involving short-period waves.The results show that both horizontal and vertical wave forces on the cylinder increase as the wave height(immersion depth)increases in most cases.The vertical wave force decreases with the decrease of the period.For the horizontal wave force,it increases with the decrease of the period when the wavelength is larger than the diameter of the cylinder and decreases with the decrease of the period when the wavelength is smaller than the diameter of the cylinder.     

Full-range equation for wave boundary layer thickness

Full-range equation covering all the flow regimes in a wave boundary layer is proposed for the boundary layer thickness. The results are compared with the available experimental data and good agreement has been found. In case of wave boundary layers, there are three definitions of boundary layer thickness in use. Therefore, the full-range equation is derived for three of the definitions. The findings of this study may be useful in calculating suspended sediment transport in coastal environments and studying wave–current combined motion.     

长江河口区边界层参数的观测与分析

2003年11月在长江口南槽用ADCP进行定点水文观测,结果表明研究区为不规则半日潮,在水流转向期流速较低时常出现悬沙浓度峰值。根据流速对数剖面分布模型与悬沙分布模型,分别计算了海底边界层参数,其中潮周期内摩阻流速可达0.15 m/s,粗糙长度为0.01~1.2 m,拖曳系数为10-3~10-4,边界层厚度为2~4 m,悬沙的沉降速率为0.2~6 mm/s。