Towing Tank Tests Research Articles

Multivariable identification of ship steering and roll motions

This paper addresses identification of a multivariable model describing the rudder-induced surge-sway-yaw-roll dynamics of a fast container ship. The identification problem is formulated and is solved numerically by using a random search minimisation method. Such method, which has to carry out the estimation of a large number of unknown parameters, is based on a suitable implementation of Simulated Annealing, Application of the algorithm to a set of simulated data has proved to be quite successful. The results show that the proposed identification method is a very efficient and easy-to-use tool for determination of ship hydrodynamic derivatives on the basis of full-scale sea trials or from towing-tank tests conducted on scale models.

Performance of a single-beam pulse-to-pulse coherent Doppler profiler

We report on the testing of a single-beam 1.7-MHz coherent Doppler sonar. The system is PC-controlled, using a digital signal processor (DSP) to acquire and extract the velocity and backscatter amplitude data. Results from a series of tow-tank calibration tests demonstrate an accuracy in the order of 5 mm s/sup -1/ for data rates of 10 profiles/second over a 1-2 m range with 1.5-cm range bins. An expression for system accuracy is developed which allows generalization to other pulse-to-pulse coherent Doppler systems. We present data showing the systematic decorrelation of backscatter signals due to particle advection: increased decorrelation is seen in the transducer near-field. Example observations of velocity profiles in laboratory-generated waves are presented.

Boundary layer instability over compliant walls: Comparison between theory and experiment

Theoretical studies have shown that compliant walls are able to attenuate the Tollmien–Schlichting waves that lead to conventional two-dimensional boundary-layer transition. This phenomenon was demonstrated in towing-tank tests conducted by Gaster et al. The results of these experiments also featured a different and very dramatic form of boundary-layer breakdown. We contend that this type of breakdown was due to a hydroelastic mode of instability, namely traveling-wave flutter. In this paper we model the two-layer viscoelastic compliant wall of Gaster et al. and its interaction with the boundary-layer flow using the asymptotic theory of Carpenter and Gajjar; en-type calculations are carried out for the traveling-wave flutter. Excellent agreement is found between the stability characteristics of the TWF mode and the measurements of the new form of breakdown found in the experiments; thus a complete understanding of the physical features found in the experiments is now available. Such understanding is essential for progress to be made in the technological development of compliant panels for transition delay.

An Introduction to Ethnotechnology for Naval Architects: Sea Kayak Design of Yesterday and Tomorrow

The skin-covered kayaks and baidarkas of the Inuit and Aleut peoples are elegant examples of naval architectural technology developed over centuries of experimental refinement. This paper describes the ethnotechnology which lies behind the design of modern sea kayaks and discusses the development of the DeCourcy Duet, a two-hole kayak, which utilizes numerical lines fairing, extensive computer stability calculations and full-scale towing tank testing as part of its design development.

A Study on the Motions in Waves of High-speed Catamarans with Hydrofoils (1st Report)

The motions in waves of high-speed catamarans with hydrofoils were studied through both nonlinear computer simulation and towing tank tests. The category of the ships of our interests is characterized by a set of fully submerged hydrofoils whose dynamic lift support the majority of the ship weight and a set of catamaran hulls whose displacement gives the support for the rest of the ship weight as well as the longitudinal and lateral stability. We describe the longitudinal motions in head and following waves in this first report. The time-domain non-linear computer simulation was based on the strip method for the forces and moments on the hulls. For the dynamic lift of the hydrofoils, the unsteady components stemming from the wave orbital velocity and the ship motions were considered in the quasi-steady way. The simulation results showed good agreements with the towing tank tests in general. Through the simulation runs and the tank tests for the ship Froude number of 1.0 and the wave length to ship length ratios from 1.0 to 4.0, the motions in following waves were found to be significantly larger than those in head waves. In the high following waves (Hw/L=0.06), the fore hydrofoil went out of the water in the downward slopes of the waves and the ship showed large non-linear motions. This kind of wild motions in following waves are described to be a natural tendency of the ships of the subject category. In order to suppress the large motions, we tried controlling the angle of attack of the hydrofoils by feeding the pitch angle and the pitch rate back. Both the simulation and the tank tests showed significant effects of the control. The amplitudes of the pitching motions were reduced to about 30% of those under no control both in head waves and in following waves. Finally, we studied the effects of the hydrofoil configuration with the simulation. Although the studied cases dis not show good improvements of the wild motions in following waves, the developed simulation program in a good tool for designing this kind of ships considering the motions in waves. In the second report, we intend to survey the motions of six degrees of freedom in the waves from various directions.

Sailing Performance of Ocean Cruising Yacht by Full-Scale Sea Test

The sailing performance of a 10.6 m-LOA ocean cruising yacht was measured by sea test and the results were compared with calculated values. The sea test was carried out to examine the steady sailing performance as well as the dynamic performance in waves.First, the steady sailing performance was estimated by calculating the velocity prediction program (VPP). The VPP calculates the equilibrium sailing state of the boat considering the balance of X, Y forces and K, N moments, respectively. The hydrodynamic force coefficients of hull were derived by the towing tank test using 1/4.275 scale model, and the aerodynamic force coefficients of sail were calculated using the results of a wind tunnel test.Then, the sailing state parameters of the full-scale were measured under various wind conditions. The measured items were wind velocity, wind direction, boat velocity, leeway angle, heel angle and rudder angle. These values were compared with the results of VPP. The both results were in good agreement and this indicates that the calculating method and fluid dynamic coefficients for VPP were adequate.Next, The motion of the boat was measured in conjunction with wave measurement using a throw-in type wave meter. A vertical gyro and accelerometers were used for measurement of rolling, pitching and heaving motion of the boat. These data were analyzed by means of spectral analysis, and compared with both model test and numerical calculations. The model test was performed in regular wave conditions at the towing tank. The analyzed results indicated the sail damping effect on the rolling motion quantitatively and the distinctive feature of motion for the sailing cruiser in waves.

Experimental Study by Towing Tank Tests on Propulsive Performances of Rowing of “Ro” (Oriental Sweep)

In order to investigate the propulsive performances of “Ro” that is oriental sweep used to propel a Japanese traditional wooden ship, the authors analyze geometrically the motion of “Ro” when rowing it first of all and make clear the principle of propulsion by “Ro” in the present paper. According to the results of such analysis of the motion of “Ro”, manufacturing of the rowing machine of “Ro” is discussed.The open tests have been carried out by rowing the model “Ro” of 1/3 scale installed on the realized rowing machine. Furthermore the self-propulsion tests of a 4 metres long model ship propelled by “Ro” operated by the rowing machine set-up in the model ship have been performed in the towing tank. As the results of such experiments the hydrodynamic characteristics of “Ro” have been made clear experimentally for the first time. For example, the efficiency of “Ro” is possible to be more than 0.70 in a good case but less than 0.40 in a bad case. In the worst case any thrust cannot be gained. Accordingly the propulsive performances of “Ro” strongly depends on the skill of a rower.

Nonlinear Dynamic Analysis Method of Underwater Line Structure and its Validation

Three-dimensional nonlinear analysis method of underwater line structure is presented and its validity is discussed by direct comparison with experiments. This analysis method is formulated by finite element method and dynamic behavior of the structures are solved in time domain. The motion equation is integrated directly and the method can handle all nonlinearities involved in the dynamic motion of the line structures such as hydrodynamic nonlinearity, geometrical nonlinearity, nonlinear boundary condition and so on. This method is a combination of Newmark's time integration scheme, one of the most reliable scheme, and Newton's iteration scheme for solution of nonlinear equations.Newmark's time integration scheme is an implicit scheme and its relatively complicated form produces a system of nonlinear algebraic equations which must be solved at each time step by iteration. Newton's iteration scheme is effective in solving the nonlinear equations and the analysis method is expected to be more robust against divergence. But direct application of the method requires large matrix of derivatives and time consuming calculation causes inefficiency. In the present method, the matrix of derivatives is decomposed into small band matrices and the nonlinear equations can be solved minimizing the inefficiency in the calculation. Thus the analysis method become robust and efficient by combining the Newmark's and Newton's schemes.So far a number of methods have been published related to the dynamic analysis of underwater line structures. Because of the nonlinearities handled in the analysis methods, these methods should have been tested by comparing the solution with experiments, but the validity of the methods were not tested except some cases. Primary reason is that general purpose instruments to measure the dynamic behaviors of underwater line structures in towing tank model tests were not available or limited. In this paper, development of a general purpose ultrasonic sensor for towing tank tests is described and the validity of the analysis method is discussed by direct comparison with expemimental results obtained from towing tank test. In the ultrasonic instrumentation system, high accuracy is required due to the small size of models and high frequency is employed, and coordinates of maximum 16 points can be determined at accuracy of 1 mm.

Side Forces on a Ship’s Hull

Side forces on a ship traveling at small yaw angles are predicted using slender-body theory. The approach uses the method of matched asymptotic expansions, with a cascade of flat plates as a model for the submarine portion of the ship's hull. Resulting predictions of side force coefficients are then compared with experimentally measured values derived from towing tank tests of a typical (tanker) hull. Correlation between theoretical and experimental results was very good for yaw angles less than 8 deg at low Froude number (Fn = 0.134).

A framework for the laboratory testing of Eulerian current measuring devices

THE DEVELOPMENT of testing techniques and procedures required to understand the performance of devices used to measure water currents has proven to be one of the most difficult and challenging tasks that the oceanographic community faces. It has long been recognized that some type of controllable relative water motion was a necessary element in the process of determining the accuracy of a current meter. A widely accepted solution is the towing tank where a current meter fastened to a moving carriage is moved through still water. A simple measurement of carriage speed over the ground compared to the current meter's flow measurement gives an indication of the accuracy of the device. Although this approach satisfied many, a sense that this technique was not sufficient spawned a few short-lived attempts at simulating time-varying flow conditions and developing deterministic models (transfer functions) for the response of inertial transducers. In addition, mathematical modeling of the motion of buoy moorings was attempted by a variety of investigators. In the late 1960's and early 1970's, the response of a current meter to the complex time-varying ocean environment became a major issue within the oceanographic community. It was clear that this information could not be obtained by simple steady-flow tow tank testing and that either dynamic controllable techniques must be developed or our ability to characterize the measurement environment must be improved.

An Experimental Study on the Motion Control of Semi-Submerged Ships

It is well known that the semi-submerged ship possesses excellent seakeeping qualities in seaways, because of its long natural periods due to the small waterplane area. However, the small waterplane area also causes instability in the longitudinal attitude or large oscillations in following seas. Equipment of some control fins is desirable for making the ship stable at high speed and for reducing the oscillations at resonance.In this paper, the three components of hydrodynamic forces acting on the fin-body configuration were measured firstly by wind tunnel test and towing tank test. These data were analyzed putting emphasis on fin-body interactions and free surface effects.The free running test on the radio controlled SWATH type model were carried out secondly in the seakeeping basin. The trim, sinkage and oscillations in regular waves were measured in various conditions with fin control.The main conclusions obtained in the present study are summarized as follows ;1) The fin-body interaction and downwash effect of the forward fin to the aft fin can be evaluated by the method of Pitts et al.2) The free surface effect on the lift of fin can be estimated by taking into consideration of the flow field around the body which changes with the advance speed.3) The lift generated by the oscillating fin or the lift acting on the fixed fin in regular waves can be evaluated quasi-steadily by using the method mentioned in 1).4) At the free running test on our SWATH ship model, a large bow down phenomenon was observed near Froude number 0.4. This instability can be anticipated by the moment measuring test in towing tank.5) The usefulness of fin control for reducing the oscillations in waves was approved by the free running test.

側壁型ＡＣＶの水上推進性能について ＩＩ

An explanation of the drag characteristics of a Sidewall Air Cushion Vehicle is proposed based on the towing tank tests of an ACV model.The simple model with the flat plate sidewalls has been chosen so that the measured drag can be easity broken down into its components.It is found that the trim of a craft plays a remarkable role in the drag reduction, as well as the cushion pressure which was forcused on our first report. The trim depends on the both wave gattern which is formed by the cushion pressure, and also the additional moment which is adjusted by the ballast and the tbrust line.It is shown that the trim exerts primarily skirt drag and indirectly wave pattern drag. Namely, inadequate trim causes the scooping action by the rear skirts which results in increase of skirt drag at the secondary hump speed (Fu=0.38). When the scooping action by rear skirts is observed, wave pattern drag is reduced relatively, because wave is broken down.The mechanism of drag reduction due to trim adjustment can be explained by the interaction of these factors.The wetting area of sidewalls and skirt drag depend on FROUD Number, cushion pressure, sidewall depth, cushion air gap and trim. The estimation of the wetting area and skirt drag is reached according to experimental data.

Seakeeping dynamics of a single cushion, peripheral cell-stabilized air cushion vehicle

A study of air cushion vehicle (ACV) motion in waves is presented for a single cushion ACV having a cellular, peripheral cell-type skirt system. The craft is considered to be traveling at constant speed while encountering regular waves of arbitrary heading. The dynamic equations for pitch, heave, and roll motions are derived using the cushion and cell air flow equations. These equations are solved numerically using a digital computer. The results are shown as frequency response curves giving steady-state motion response amplitudes as a function of encounter frequency or wavelength for fixed craft speed and wave steepness. The theoretical predictions are then compared with experimental data taken from scale model, towing tank tests in head seas. The comparison shows good agreement for pitch motion, while heave motion damping is overpredicted.

Some towing problems with faired cables

Measurements have been obtained from both wind tunnel and towing tank tests which explain the poor streaming behaviour of certain proprietary cable fairings, which had caused severe towing difficulties at sea. A simple modification applied to the fairings showed marked improvement in behaviour in laboratory tests and in sea trials. The results show the importance of good fairing cross sectional shape in order to develop adequate hydrodynamic restoring moments, and demonstrate the mechanical factors causing friction between cable and fairing.

Comments on "Controlling the Separation of Laminar Boundary Layers in Water: Heating and Suction'

The analytical solution has been applied to 7/100 scale model of the JEFF(A) with the results shown in Fig. 1. The predicted value of the normalized amplitude of the solution (= IC l / a ) is plotted vs encounter frequency and wavelength for a Froude number of 1.15. The magnitude of the wave forcing term and the linear frequency response are also shown separately since these are the factors which generate the heave response. It may be seen that the heave response of the vehicle is controlled by the form of the wave forcing curve, while the predicted linear frequency response is quite flat at this speed for wavelengths greater than the craft length. For comparison, an experimentally determined heave response obtained from towing tank tests as presented in Ref. 3 is included. The experimental curve behaves roughly in the same manner as the theoretical prediction. This suggests that the model may be relied upon to explain physical mechanisms and the influence of design particulars, though not in precise quantitative terms.

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY RESEARCH IN HIGH-SPEED DEVICES FOR THE RECOVERY OF THIN-FILM OIL SPILLS

ABSTRACT The United States Environmental Protection Agency has sponsored two separate research contracts in the field of high-speed devices for the recovery of thin-film oil spills. Both projects involve deflecting oil that is moving relative to the device by means of an air jet so that the resulting oil and water spray can be captured and separated. One project has been conducted by Tetradyne Corporation of Richardson, Texas, and involves the use of air jets to concentrate and subsequently deflect oil into a sump for gravity separation. This device has achieved up to 86% (vol/vol) recovery efficiency at a speed of six FPS in towing tank tests of a full-scale prototype; it is relatively insensitive to waves, small debris, and changes in oil viscosity. The second project has been conducted by Science Applications, Inc., of McLean, Virginia, and involves use of a slightly submerged air jet to deflect oncoming oil in the form of a spray lofted into a rotating polyurethane foam belt used for oil-water separation. Collection efficiencies of up to 83% (wt/wt) have been achieved in towing tank tests of a section of a full-scale prototype at a speed of 5.5 FPS. This device operates satisfactorily in waves and is somewhat sensitive to oil viscosity. Material is presented on the rationale for developing the devices, the testing technology that has been used for these efforts, and the test results for each device.

On Motions of a High Speed Planning Boat in Regular Head Sea

Recent advances in the research of ship motion in a seaway have enabled to predict the ship motion. These researches, however, are restricted to those of displacement type ships such as a merchant ship and a destroyer, and as to behaviours of high speed planing boat in a seaway few available researches have been published.In the present study the towing tank test of a torpedo boat model was carried out in regular head wave and experimental data were discussed along with the results calculated by Ordinary Linear Strip Method (O. S. M.).The conclusions deduced from these studies are as follows, 1) High frequency components appear in pitching and heaving oscillations at higher encounter frequency, that is, at higher speed and shorter wave. In these regions, each mean value of the pitching and heaving oscillation becomes larger compared with the trim angle and vertical displacement in still water.2) The motions calculated by the O. S. M. give good agreement with experimental data for Fn< 0.5, but they do not always for higher Froude number.3) In spite of much higher frequency components in the motions, the amplitudes of pitching and heaving motions are almost proportional to those of the wave, that is, the linearity to wave height is nearly conserved.

Study Of Boundary Layer Turbulence Stimulations Of Ship Models Tested In A Towing Tank

The parer present result of theoretical and experimental investigation of the natural and artificial turbulence timulation of the boundary layer on ship model by towing tank tests. A dependence of the extent of the laminar and transition regions in a boundary layer upon the model hull form is shown. Some practical tips are recommended both for the choice of trip wire and for the correction introduced in the results of model basin test for laminar region of the boundary layer near the trip wire and for its parasite resistance. Introduction of the proposed corrections brings about an essential increase of reliability of ship resistance data derived from the result of model test in the towing tank. Results of this study have been reported at the XII International Towing Tank Conference, Rome, 1969, [1].

Faired Towline Hydrodynamics

A theoretical analysis for determining the hydrodynamic forces on a faired towline is developed. The analysis requires that the hydrodynamic forces acting on an element of the towline be defined as a function of the towlines local inclination angle to the flow, and of the Reynold's number. These hydrodynamic forces are known as loading functions. The analysis is based on consideration of the boundary layer formed on the airfoil shaped cross section used for the towlines. The Reynold's number effect on the loading functions is derived using momentum theory, and requires that the pressure distribution around the airfoil section be defined. Potential flow theory is used, and gives excellent results when compared with pressure distribution measurements made on models. The theoretical loading functions are compared with model data obtained from water channel, tow tank and wind-tunnel tests. The analytical results show excellent correlation with the data. The analysis has been termed Boundary-Layer Loading Functions (BLLF).

HELICOPTERS AND HYDROFOILS— A PROPOSED ASW SYSTEM

Naval Engineers JournalVolume 81, Issue 2 p. 19-22 HELICOPTERS AND HYDROFOILS— A PROPOSED ASW SYSTEM EUGENE H. HANDLER, EUGENE H. HANDLER THE AUTHOR: is Chief, Test and Facilities, Joint Surface Effect Ships Program Office. He was the aircraft hydrodynamics engineer for the Naval Air Systems Command (formerly Bureau of Naval Weapons, Bureau of Aeronautics) from 1954 to 1968. He was responsible for the Navy programs relating to the hydrodynamic aspects of water-based aircraft programs, associated research studies and full scale evaluations of hydro-ski, hydrofoil and hull type aircraft, tilt and vertical floats, amphibious helicopters and air-towed water-borne craft. During World War II he served in the Eighth and Far Eastern Air Forces, then returned to Brown University and received a Masters' degree in Engineering in 1949. Mr. Handler was employed at the Glenn L. Martin Company for several years, primarily with towing tank tests of patrol seaplanes and the P6M mine layer. He left the Martin Company for the Bureau of Aeronautics in 1954.Search for more papers by this author EUGENE H. HANDLER, EUGENE H. HANDLER THE AUTHOR: is Chief, Test and Facilities, Joint Surface Effect Ships Program Office. He was the aircraft hydrodynamics engineer for the Naval Air Systems Command (formerly Bureau of Naval Weapons, Bureau of Aeronautics) from 1954 to 1968. He was responsible for the Navy programs relating to the hydrodynamic aspects of water-based aircraft programs, associated research studies and full scale evaluations of hydro-ski, hydrofoil and hull type aircraft, tilt and vertical floats, amphibious helicopters and air-towed water-borne craft. During World War II he served in the Eighth and Far Eastern Air Forces, then returned to Brown University and received a Masters' degree in Engineering in 1949. Mr. Handler was employed at the Glenn L. Martin Company for several years, primarily with towing tank tests of patrol seaplanes and the P6M mine layer. He left the Martin Company for the Bureau of Aeronautics in 1954.Search for more papers by this author First published: April 1969 https://doi.org/10.1111/j.1559-3584.1969.tb05476.x AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Volume81, Issue2April 1969Pages 19-22 RelatedInformation