Assessment of Hydrodynamic Tools for R/V Athena Model 5365 in Calm Water

2017 ◽  
Author(s):  
Anne Fullerton ◽  
Charles Weil ◽  
Evan Lee ◽  
Minyee Jiang ◽  
Fredrick Stern ◽  
...  
Keyword(s):  
Dynamic Response ◽  
Structural Design ◽  
High Speed ◽  
Irregular Waves ◽  
Impact Loads ◽  
Empirical Methods ◽  
Regular Waves ◽  
Hull Form ◽  
Calm Water ◽  
Naval Surface Warfare

Current structural design methods for high speed naval craft rely heavily on empirical methods. Though these methods have been employed reliably for a number of years, it is likely that an unknown level of conservatism exists in the prediction of impact loads. A better physical understanding of the dynamic response of high speed craft in seas would allow for increased structural optimization. The publicly releasable hull form Naval Surface Warfare Center Carderock Division (NSWCCD) Model 5365 (R/V Athena) was chosen to facilitate release of results to various computational teams. Model 5365 was tested in calm water, regular waves, and irregular waves. After reviewing data from the first test in 2014, it was determined that the model should be modified to enable towing from the longitudinal center of gravity. Model 5365 was then modified and re-tested using with added calm water speeds, and additional wave conditions. Calm water results from this test are presented with uncertainty analysis for resistance, heave, and trim.

The Transverse Plane Motions of Ships

1991 ◽  
Vol 28 (02) ◽  
pp. 55-72
Author(s):  
Bruce L. Hutchison
Keyword(s):  
Transverse Plane ◽  
Irregular Waves ◽  
Hydrodynamic Coefficients ◽  
Important Process ◽  
Regular Waves ◽  
Hull Form ◽  
Fishing Vessels ◽  
Transverse Stability ◽  
Roll Axis ◽  
The One

A detailed exposition of the kinematics of the transverse plane motions of ships is provided, with particular attention to the important process of total transverse acceleration in vessel coordinates. The loci of sway, sway velocity and sway acceleration are shown to follow hyperbolic distributions with respect to elevation in both regular and irregular waves. In regular waves the transverse acceleration in earth-fixed and vessel-fixed coordinates are shown to be congruent with a vertical shift in elevation of g/ω2 = λ/(2π). Expressions are given for the elevations minimizing transverse plane processes in regular and irregular waves. In long waves the elevation minimizing total transverse acceleration in vessel coordinates is shown to be g/ωn2 = g[Tn/ /(2π)]2 below the waterline. This is the roll center, which should be used in the traditional analysis of foundation loads. Its location, far below the keel for most vessels, is surprising. The elevation (OP) of the roll axis, which must be used when solving the one-degree-of-freedom equation for roll, is given and is shown to require hydrodynamic coefficients for sway as well as roll. In general, OP does not correspond to an elevation that minimizes any of the transverse plane processes. The effect of hull form, transverse stability and natural roll period on transverse plane motions are examined in an attempt to resolve the dichotomy of views between those who favor ships with low GMT and long natural roll periods and those who favor high GMT with short natural roll periods. It is demonstrated that large values of the beam-to-draft ratio (6/7) with low natural roll periods are advantageous at modest elevations above the waterline. This explains the favorable offshore experience in vessels meeting this description, such as tugs, supply vessels and fishing vessels. At higher elevations long natural periods are shown to present a clear advantage, which supports the preference for low GMT for large passenger vessels, containerships and ships with deck-loads of logs. The trends identified would seem to support the conjecture that, with regard to natural roll period, there is a "forbidden middle" that should be avoided in design.

Experimental appraisal of hydrodynamic performance and motion of a single-stepped high-speed vessel in calm water and regular waves

2020 ◽  
pp. 095440622096812
Author(s):  
Sayyed Mahdi Sajedi ◽  
Parviz Ghadimi ◽  
Aliakbar Ghadimi ◽  
Mohammad Sheikholeslami
Keyword(s):  
High Speed ◽  
Single Step ◽  
Hydrodynamic Performance ◽  
Sea Waves ◽  
Regular Waves ◽  
Height Range ◽  
Step Model ◽  
Speed Range ◽  
Calm Water ◽  
Laboratory Models

High-speed vessels exhibit various motions and accelerations in calm water and sea waves. For examining the behavior of high-speed vessels, it is possible to examine these movements in laboratory models. In this paper, a single-step model in calm water is experimentally tested and compared with a model of no step. The speed range of these vessels is 1 m/s to 9 m/s equivalent to Beam Froude numbers of 0.43 to 3.87. During these experiments, the resistance parameters, trim, bow, and stern rise-up as well as the center of the gravity are measured. The non-step model has longitudinal instability at a speed of 8 m/s. This instability is avoided when the vessel is equipped by a transversal step. The vessel's trim and resistance are also reduced in the planing mode in calm water. Subsequently, hydrodynamic performance and its seakeeping condition in the planing regime are investigated for both vessels in regular waves. The single-step and non-step vessels are tested in the wavelength range of [Formula: see text], and the wave height range of 6 to 18 centimeters. It is observed that stepped vessel experiences lower motions and bow accelerations and less added resistance in comparison to the non-stepped vessel.

scholarly journals Theoretical and Experimental Study on Nonlinear Hydroelastic Responses and Slamming Loads of Ship Advancing in Regular Waves

2018 ◽  
Vol 2018 ◽  
pp. 1-26 ◽  
Author(s):  
Jialong Jiao ◽  
Yulin Zhao ◽  
Yufei Ai ◽  
Chaohe Chen ◽  
Tianhui Fan
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Irregular Waves ◽  
Green Water ◽  
Design Stage ◽  
Regular Waves ◽  
Restoring Force ◽  
Wave Basin ◽  
Hull Structure ◽  
Hydrodynamic Wave

Wave loads estimation and structural strength evaluation are the fundamental work at the ship design stage. The hydroelastic responses and slamming strength issues are also concerned especially for large-scale high-speed ships sailing in harsh waves. To accurately predict the wave-induced motions and loads acting on the ship sailing in regular waves, a fully coupled 3D time-domain nonlinear hydroelasticity theory is developed in this paper. The vibration modal characteristics of the flexible hull structure derived by the 3D finite element method (FEM) and simplified 1D nonuniform Timoshenko beam theory are firstly described. The hydrostatic restoring force and hydrodynamic wave force are calculated on the real-time wetted surface of hull to address geometric nonlinearity due to the steep wave and large amplitude motions. The bow slamming and green water loads acting on the ship in severe regular waves are estimated by the momentum impact method and dam-breaking method, respectively. Moreover, a small-scaled segmented ship model is designed, constructed, and tested in a laboratory wave basin to validate the hydroelasticity algorithm. The results predicted by theoretical and experimental approaches are systemically compared and analyzed. Finally, future work for predictions of ship hydroelasticity and slamming loads in irregular waves is prospected.

Sailing Yacht Performance in Calm Water and in Waves

1993 ◽  
Author(s):  
J. Gerritsma ◽  
J. A. Keuning ◽  
A. Versluis
Keyword(s):  
Model Experiment ◽  
Irregular Waves ◽  
Current Interest ◽  
Added Resistance ◽  
Hull Form ◽  
Wide Range ◽  
Calm Water ◽  
Added Resistance In Waves ◽  
Sailing Yacht ◽  
Calculated Analysis

The Delft systematic Yatch Hull Series has been extended to a total of 39 hull form variations, covering a wide range of length displacement ratios and other form of parameters. The total set of model experiment results, upright and heeled resistance as well as sideforce and stability, had been analysed and polynomial expressions to approximate these quantities are presented. In view of the current interest in the performance of sailing yachts in waves, the added resistance in irregular waves of 8 widely different hull variations has been calculated. Analysis of the results shows that the added resistance in waves strongly depends on the product of displacement-length ratio and the gyradius of the pitching motion.

scholarly journals Computational and experimental determination of waterjet aeration exposure in waves

2020 ◽  
Vol 4 (394) ◽  
pp. 21-30
Author(s):  
Tatyana A. Dyakova ◽  
Sergey O. Rozhdestvensky ◽  
Nikolai V. Marinich ◽  
Alexey A. Rudnichenko
Keyword(s):  
Numerical Simulation ◽  
Video Camera ◽  
Full Scale ◽  
Irregular Waves ◽  
Head Wave ◽  
Hydrodynamic Characteristics ◽  
Regular Waves ◽  
Seakeeping Performance ◽  
Calm Water ◽  
Air Penetration

Object and purpose of research. The object of research was a model of a fast seaworthy boat with discretevariable bottom deadrise and two waterjet propulsors. The purposes of research were to experimentally determine hydrodynamic characteristics of the model in calm water and head regular waves corresponding to the irregular waves of sea states 3 and 4, as well as to determine the possibility of air penetration to waterjet inlets for two variants of their arrangement on model bottom in head-wave conditions, numerical simulation of the full-scale boat movement in oblique irregular waves (sea state 4) for two variants of waterjet arrangement, with an assessment of waterjet duct aeration exposure. Materials and methods. Model hydrodynamics was estimated experimentally by means of towing tests in highspeed seakeeping basin in calm water and head regular waves using standard test equipment; air penetrations were recorded by a GO PRO digital video camera installed on the model above the water inlets. Numerical simulation of the full-scale boat movement was carried out in Star-CCM+ CFD package. Main results. The study yielded the curves of towing resistance, running trim and sinkage versus model speed in calm water and head regular waves of different length for two longitudinal CG positions, as well as the areas of air penetration to waterjet inlets on model bottom. Analysis of the experimental data enabled the estimation of attainable speed for the boat with displacement of 50 and 29 tf in waves for given delivered power. Numerical simulation of the full-scale boat movement in oblique irregular waves for two variants of waterjet arrangement has also been carried out. Conclusion. The results have shown that seakeeping performance of the boat is quite satisfactory and that the most obvious way to mitigate air penetrations is to reduce the speed. Other important factors were shifting the waterjet inlet towards the transom and to the CL, as well as shifting the longitudinal CG forward. The obtained results can be used to select the position of the waterjet inlets on boat bottom in order to increase waterjet efficiency. Using the methods of numerical hydrodynamics, the characteristics of the waterjets have been obtained, the probability and volumes of air penetrations to waterjet ducts (for different variants of waterjet arrangement) at several angles of oblique irregular waves have been estimated.

Empirical Methods for Predicting Lift and Heel Moment for a Heeled Planing Hull

2014 ◽  
Vol 30 (04) ◽  
pp. 175-183
Author(s):  
Carolyn Q. Judge
Keyword(s):  
High Speed ◽  
Experimental Program ◽  
Naval Academy ◽  
Forward Speed ◽  
Empirical Methods ◽  
Empirical Relationships ◽  
Planing Craft ◽  
Underwater Photography ◽  
Calm Water ◽  
Transverse Stability

Even in calm water, high-speed vessels can display unstable behaviors such as chine walking, sudden large heel, and porpoising. Large heel angle can result in the loss of transverse stability at high forward speed. When a planing craft begins to plane, the hydrodynamic lift forces raise the hull out of the water, reducing the underwater geometry. An experimental program at the U.S. Naval Academy has been designed to investigate the transverse stability of planing hulls. An experimental mechanism to force a planing hull model in heave and roll motion was designed and built. The first model tested was a wooden prismatic planing hull model with a constant deadrise of 20, a beam of 1.48 ft (0.45 m), and a total length of 5 ft (1.52 m). The model was held at various heel and running draft positions while fixed in pitch, yaw, and sway. The tests were done at two model speeds, for one model displacement, five fixed heel angles, and five fixed running heave positions. The lift and sway forces, along with the heel moment, were measured and underwater photography was taken of the wetted surface. This article presents a set of equations based on empirical relationships for calculating the lift and heel moment for a prismatic planing hull at nonzero heel angles.

Comparative Performance of Optimum High Speed SWATH and Semi-SWATH in Calm Water and in Waves

2015 ◽  
Author(s):  
S. Brizzolara ◽  
G. Vernengo ◽  
L. Bonfiglio ◽  
D. Bruzzone
Keyword(s):  
High Speed ◽  
Hydrodynamic Performance ◽  
Forward Speed ◽  
Comparative Performance ◽  
Hull Form ◽  
High Speeds ◽  
Head Waves ◽  
Calm Water ◽  
Minimization Algorithms ◽  
Ranse Solver

The hydrodynamic performance of unconventional SWATH and Semi-SWATH for high speed applications are analyzed and compared in this paper. Bare hull resistance in calm water is estimated by an inviscid boundary element method with viscous corrections and verified by a fully turbulent, multiphase unsteady RANSE solver. Motions response in head waves, calculated by a frequency domain 3D panel method with forward speed effects are also evaluated and compared. Both considered hulls are the best designs coming from full parametric hull form optimization procedures, based on CFD solvers for the estimation of their hydrodynamic performance and driven by evolutionary minimization algorithms. The SWATH has twin parabolic struts and an unconventional underwater shape, the semi-SWATH has a slender triangular waterline, a bulbous shape in the entrance body which gradually morph into a U-section with a shallow transom in the run body. In general, as expected, the Semi-SWATH hull shows a lower drag at high speeds while the single strut SWATH is superior at lower speeds. As regards seakeeping, the SWATH shows unbeatable lower pitch and heave motions in shorter waves, where the Semi-SWATH evidences a double peaked RAO. More detailed analysis and conclusion are drawn in the paper.

Experimental Analysis on Flow around Fin Assisted Semi SWATH

2015 ◽  
Vol 74 (5) ◽  
Author(s):  
Arifah Ali ◽  
Adi Maimun ◽  
Yasser M. Ahmed ◽  
Rahimuddin Rahimuddin ◽  
Mohamad Pauzi A. Ghani
Keyword(s):  
Froude Number ◽  
High Speed ◽  
Water Resistance ◽  
Wave Pattern ◽  
Resistance Test ◽  
Hull Form ◽  
Wave Interference ◽  
Calm Water ◽  
Water Test ◽  
Zero Degree

Demand on High Speed Craft (HSC) is increasing due to development of inland transportation. Therefore, many analysis have been conducted to evaluate performance of this modern ship. One of the important analysis is calm water resistance test. Resistance component of the hull and wave pattern around the hull are obtained from the calm water test. These criteria are important in analyzing flow around hull, especially on wave interference between the hulls. In this paper, flow around hull has been studied for one model of Semi SWATH hull form with fin stabilizers installation by performing calm water resistance test in deep water. The fore fin angle is fixed to zero degree while the aft fin angle is varied to 0, 5 and 15 degree. The effects of fin angle to resistance criteria and flow around hull are investigated. Wave height has been recorded using longitudinal wave probe during resistance test. For each configuration, the investigation is conducted with range of Length Froude Number from 0.34 to 0.69. From the analysis, it is found that flow around the hull of Semi SWATH is affected by fin angle and the effect is various depend on the Froude number.

scholarly journals Experimental Study on Motion Behavior and Longitudinal Stability Assessment of a Trimaran Planing Hull Model in Calm Water

2021 ◽  
Vol 9 (2) ◽  
pp. 164
Author(s):  
Jin Zou ◽  
Shijie Lu ◽  
Hanbing Sun ◽  
Liru Zan ◽  
Jiuyang Cang
Keyword(s):  
High Speed ◽  
Longitudinal Direction ◽  
Longitudinal Stability ◽  
Hull Form ◽  
Average Mass ◽  
Calm Water ◽  
Special Vehicle ◽  
Lift Enhancement ◽  
Resistance Decrease ◽  
Relationship Of

In this study, a high-speed planing trimaran hull form is designed, and the effects of different displacements and gravity longitudinal layouts on the performance of the trimaran planing hull in calm water are experimentally investigated in the towing tank of the China Special Vehicle Research Institute. Based on previous work, an innovative inner tunnel appendage hydroflap is mounted in the inner aft tunnel, located 1/8 L from the transom in the longitudinal direction with attack angles of 0° and 4°, respectively. Furthermore, a regular stern flap is mounted on the transom close to the chine. The towing test results show that, as the gravity center moves forward, the high-speed region resistance of the planing trimaran increases and the longitudinal stability is also strengthened. Further, the total resistance of the planing trimaran with a heavier displacement is larger while the average mass resistance declines; i.e., the resistance efficiency is improved. The results also indicate that the inner tunnel hydroflap and stern flap enhance the aft hull hydrodynamic lift and tunnel aerodynamic lift. As a result, mounting aft hull lift enhancement appendages can affect the bottom and inner tunnel pressure distribution and then cause a slight resistance decrease in the low-speed region. The value relationship of resistance between groups of appendages for the attached hull and bare hull is reversed at a speed of about Froude number 3.0. Although the aft hull lift enhancement appendages result in a higher resistance cost in the high-speed region, the longitudinal stability is effectively promoted and the occurrence speed of porpoising results in a delay of 1 to 2 m/s.

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