High-speed Displacement Research Articles

Practical Seakeeping Performance Measures for High Speed Displacement Vessels

The seakeeping performance of high-speed displacement vessels is generally assessed, in a probabilistic manner, by using criteria-based measures of merit. Given a set of seakeeping criteria, these measures, such as the Percentage Time of Operation (PTO) and the Seakeeping Performance Index (SPI), could provide an assessment of the operability of the vessel in a specified sea area. The criteria-based measures are based upon the probability of exceeding specified ship motions in a sea environment particular to the vessel's mission. Given the operational area of the vessel, the percentage of time the vessel operates in a particular sea state can be determined by comparing the predicted motions to the motion limiting criteria. However, because the seakeeping criteria are used in a pass/fail manner, the criteria-based procedures give no credit for reducing motions that do not exceed criteria. This may result in misleading conclusions when the relative seakeeping performance of alternative design concepts is compared. It is shown that criteria-free measures, based upon a normalized summation of critical ship responses for a range of ship speeds and wave headings in a specified sea area, may produce more reliable results when the seakeeping performance of alternative designs are compared. This approach also has the clear advantage of not requiring a set of seakeeping criteria, which is subjective in nature. To demonstrate the effect of typical measures of merit on seakeeping performance assessment, six typical high-speed displacement vessel forms are considered in a comparative analysis. Both the criteria-free and criteria-based measures of merit are employed to compare the seakeeping performance of selected vessels. The results indicate that the choice of seakeeping performance measure of merit depends on the nature of seakeeping analysis and criteria-free measures offer a simple, practical, and realistic assessment in comparative seakeeeping studies.

A Simple Method for Predicting the Maximum Squat of a High-Speed Displacement Ship

A simple formula is developed for predicting the maximum squat of a displacement ship as it passes through the transcritical speed range. This is given in terms of a maximum sinkage coefficient, which is almost constant across a wide range of hull forms. Satisfactory agreement is shown with model test results, and it is shown that large stern sinkages in the order of 3 to 6 meters are predicted for frigate and destroyer type hulls in shallow calm water.

InsPulp-I© : An on-line visual inspection system for the pulp industry

This paper presents a Machine Vision System developed for on-line visual pulp inspection under the critical lighting requirements of the UNE-ISO 5350-2 standard. These requirements typically result in a very low dynamic range in the electronic images due to the following: high-speed displacement of the product (up to 2.7 m/s), very high resolution (0.004 mm 2/pixel), and the backlight requirement. This problem has been solved using TDI technology in the acquisition system, made up of several parallel CCD lines that shift their electrical charges in synchronization with the product movement, therefore producing a single line-image with several times more dynamic range. The obtained image has a cross light non-uniformity that is resolved by an image processing algorithm that divides the image into several sub-images that are processed in parallel. The system has been tested in on-line production plants, and has been proven to provide a great improvement over the objectivity and sampling rate limitations of human inspection, thereby realizing a more reliable and trustworthy quality control measurement.

An efficient numerical method for solving ‘2.5D’ ship seakeeping problem

This paper describes a new numerical algorithm for solving 2.5D hydrodynamic theory, which is based on the high-speed slender body assumptions where the free-surface condition is 3D but the control equation and body surface condition are 2D. This numerical algorithm is accomplished using boundary integral equations formed in the inner fluid field domain and outer fluid field domain and matched on a fixed control surface. Theoretically predicted vertical hydrodynamic coefficients by this method is verified by the theoretical results computed by 2.5D theory based on time domain boundary integral equations. This paper also shows that the matched boundary integral equations can be used to calculate the hydrodynamic characteristics of high-speed displacement vessels with a large flare.

Experimental study on the dynamic response of gravity-designed reinforced concrete connections

This paper reports an experimental programme aiming to shed some light on the response of non-seismic RC beam–column joints to excitations of different frequencies. The RC connections tested were designed only for gravity loads, thus rendering the joint cores weaker than the adjoining members when subjected to a lateral load. Altogether, six tests were conducted on full-scale specimens, which were subjected to reversed cyclic displacements applied at different speeds varying from slow quasi-static loading to high-speed dynamic loading as fast as 20 Hz. Although all specimens as expected suffered joint shear failure, the maximum joint shear stresses observed in the tested specimens, despite lacking transverse hoops inside the joint cores, were more than the horizontal shear stresses allowed in ductile RC joints with the same grade of concrete according to the existing seismic design codes. The damage patterns and failures of the specimens showed a better correlation with the residual storey shear stiffness than with the loss of storey shear strength during the repeated cycles. By analysing the test results, this paper also discusses how an inadvertent inertial force develops during high-speed displacement reversals.

Resistance and Wash Wave Measurements On A Series of High Speed Displacement Monohull and Catamaran Forms In Shallow Water

The paper summarises an experimental investigation into the resistance and wash waves of high speed displacement monohulls and catamarans in shallow water. Measurements of total resistance, running trim, sinkage and multiple longitudinal wave cuts were carried out for three round bilge hulls derived from the NPL series and one from Series 64. Parametric changes included length/displacement ratios of 7.4, 8.5 and 9.5, and hull separation/length ratios of 0.2, 0.4 and infinity. The tests were carried out in two depths of shallow water over a length Froude Number range of 0.25 to 1.0 and a depth Froude Number range of 0.5 to 3.0. The wave resistance was derived using wave pattern analysis and the principal particulars of the generated wave system are presented as maximum wave height, period, distribution of energy and direction of wave propagation. The results of the investigation provide a better understanding of the performance of high speed displacement monohulls and catamarans in shallow water, including the influences of speed, water depth, hull separation and length/displacement ratio. The data derived are very suitable for design applications and for the validation of theoretical analyses of ship wave resistance and wash waves.

An investigation of two unexplored periodic error sources in differential-path interferometry

This paper describes two sources of periodic error in differential-path interferometry that have remained largely unexplored: dynamic periodic error that is exhibited by heterodyne interferometer systems under high-speed displacements and intermodulation periodic error caused by amplifier nonlinearity. Dynamic periodic error occurs when the measurement signal, or intended ac interference term, and unwanted dc interference terms, that exist due to frequency leakage in physical implementations of heterodyne interferometers, are both present within the phase measuring electronics’ modulation bandwidth. The situation is similar to the well-documented pseudo-static periodic error observed at low slide speeds, where the intended ac interference, leakage-induced ac interference, and ac reference terms all lie within the modulation bandwidth. The Frequency–Path (F–P) model of the propagation of light from the source to detector for differential-path interferometers is also presented. This model identifies each possible path for each light frequency from the source to detector and predicts the number of interference terms that may be expected at the detector output. We show that, regardless of the interferometer configuration, the behavior of each interference term with respect to optical path changes may be grouped into one of four categories: optical power, ac interference, ac reference, and dc interference. The application of the F–P model to the generic description of periodic error in a single pass, Michelson-type heterodyne interferometer is provided.

Determination of global design loads for large high-speed catamarans

Methods for calculation of design loads for high-speed vessels are investigated. The influence of operational restrictions on design loads is emphasized. Relevant operational criteria for high-speed displacement vessels are discussed. Procedures and criteria for numerical calculation of operational limits are incomplete and should be further investigated. Operational limits and design loads for a 60 m catamaran are calculated on the basis of linear strip theory. Non-linear effects on design loads are assessed from calculations in regular waves. Simplified formulae commonly used by classification societies for prediction of operational limits seem to over-predict the reduction of motions and wave loads at reduced speed. When operational limits typically given by the shipmaster or the operator are used, the design loads found by direct calculations are comparable with design loads given by classification societies. For vertical bending moment and torsion, the use of active foils is found to increase the linear loads. Owing to reduced motions, the foils reduce the non-linear loads and hence the total loads. The effect of non-linear horizontal loads is not investigated but can be important for transverse bending moment.

Fairing of High Speed Displacement Hull Forms by B‐spline Approximation and Fitting

ABSTRACTThis paper presents flexible numerical procedures for fairing hull form design curves which form the three dimensional ship body. The traditional solution to the problem of fairing ship hull forms is to reduce the problem to simultaneous fairing of two dimensional curves on three orthogonal planes, called the section lines, waterlines and buttock lines. However, this process requires excessive time and experienced personnel. Fairing procedures employed in most Computer Aided Ship Design (CASD) software are computerised versions of the manual method and hence have similar drawbacks. The approach adopted in this study is based on approximation of ship lines by B‐splines that are already fair. It is shown that the degree of fairness can be improved by increasing the order of the B‐spline; however, this may result in excessive deviations from the original offset points. A balance between closeness and fairness can be identified by successive applications of B‐spline to original offsets in an iterative manner. Alternatively, B‐spline fitting instead of B‐spline approximation can be applied in order to minimize the deviation from original offset points. For ship hull forms, in order to obtain three dimensional fairness, two dimensional ship lines on three orthogonal planes need to be faired simultaneously The fairing process is first applied to waterlines and the modified offsets are transferred to other planes. The iterative process is repeated until specified degree of fairness is achieved. This procedure is applied for fairing the lines of a distorted mathematical hull form and the parent hull of a high speed hull form series. The results indicate that these procedures are particularly useful for high speed displacement hull forms and can be used as practical design tools in the early stages of ship design.

A laser measurement system for fast and precise positioning.

Recently, there has been an increase in the positioning accuracy required in the production processes for ULSI. For instance, in a wafer stepper for a 4-Mbit DRAM, the required positioning accuracy is said to be more than 0.04μm. There is also a requirement to reduce the positioning times in such processes. To meet these needs, a new laser measurement system which can accurately measure high speed displacement has been developed. When the target's speed is low, its displacement is measured by comparing the phase change of light reflected by the object with the phase modulated by an electro-optic crystal. When the target's speed is high, its displacement is measured using a fringe counting technique. The system achieves an accuracy of ±4nm and a maximum allowab1e measurement speed of 1OOO mm/s.

Fast-acting electrohydraulic digital transducer. Poppet-type on-off valve by making use of a multilayered piezoelectric device.

Intelligent control of an electrohydraulic servo system can be realized comparatively easily by introducing microcomputer. To realize intelligent control systems, it is important to obtain a digital control valve with high transducer-actuator switching speed performance. In the case of a small valve opening, a poppet-type valve has some advantages compared to a spool-type one. The aims of this study are to propose a high-speed displacement control method for the valve poppet and to develop a high-speed digital valve whose switching time is within 100μs. By introducing feed-forward control and providing some improvements, a poppet-type on-off valvd with a high-speed switching response within 70 μs is developed. In application, a two-stage digital servo valve, whose second stage of the spool valve is driven by the high-speed poppet-type on-off valves, is devised.

RESISTANCE PREDICTIONS AND PARAMETRIC STUDIES FOR HIGH‐SPEED DISPLACEMENT HULLS

ABSTRACTHigh‐speed displacement vessels are widely used in most of the smaller navies because they provide low operating costs, combined with performance adequate for policing 200‐nm exclusive econnomic zones. Feasibility designs of these kinds of vessel, such as corvettes and patrol boats, always require calm water resistance estimates. This paper is an attempt to use available data to analyze main hull form parameters that affect the resistance characteristics of the vessel. A few high‐speed roundbilge methodical series (such as the well‐known series 64, NPL‐HSRB, SSPA‐SFDV, HSVA'C' series and Canadian fast surface ship series) as well as some numerical formulas from regression analyses are available for the powering studies of this type of vessel. However, any attempt to design a good highspeed displacement hull by adopting the previously mentioned methodical series has to be carefully examined. The main hull form parameters must be appropriate to the speed range, due to some distinctive resistance characteristics at Froude numbers larger or smaller than 0.45‐0.55. This paper covers some basic considerations of these aspects, by utilizing several computer programs which were developed by the author based on some of the high‐speed round‐bilge methodical series. Finally, other hull form parameters that may affect resistance are discussed.

Theory of High-Speed Displacement Ships with Transom Sterns

A theory has been developed for high-speed displacement ships with transom sterns; it treats the hull as finite in beam and draft, but slender. The flow is assumed to be smooth at the aft waterline and to have a trailing wake. The trailing wake results in substantial residuary resistance at high speeds for normal waterline ships. This is a completely new finding. Calculations are made for ships of highly variable parametric form and the results are given. This residuary is typically reduced by widening the transom. A shallow draft at the transom is also indicated. A comparison of calculated results with existing experimental data shows good agreement.

Resistance prediction of small high-speed displacement vessels: state of the art1

In preliminary ship design studies it is frequently necessary to estimate the calm water resistance characteristics of various hull forms prior to carrying out model tests. For such estimations, use is generally made of results of well-known methodic

Design and Development of the 190-Ton Stable Semisubmerged Platform (SSP)

The general characteristics, design features, predicted performance, and construction highlights of the 190-ton Stable Semisubmerged Platform (SSP) are presented. The SSP is the first large manned version of a high-speed displacement craft concept having a small waterplane area. The SSP was designed to be a work platform for research and testing of advanced naval equipment at the Naval Undersea Center. Its unique design will provide an order-of magnitude improvement in motion reduction over monohulls, as well as provide more deck space and internal volume. The SSP is 89 feet long and has a top operating speed of 25 knots with about 25 tons of payload and fuel. Design of the SSP features two parallel torpedo-like hulls which support an above-water cross structure by means of four vertical surface-piercing struts; two canard fins are located near the hull bows and a cross stabilizing fin is located near the hull sterns. The SSP was constructed at the Coast Guard Shipyard at Curtis Bay, Md.

Developments in High-Speed Marine Craft

Ways of travelling fast and comfortably over water have interested inventors and designers for many years. Recently, impressive and significant developments have led to three relatively unconventional types of highspeed marine craft large enough to serve practical commercial or naval purposes, while some conventional large ships now also have high service speeds. The development of hovercraft, hydrofoil ships and high-speed displacement or planing craft is reviewed in the first section of the lecture, and criteria for assessing the performance of these different types in calm water and in typical service conditions are examined and compared. The purposes for which high-speed marine craft are needed are discussed; these can be divided into passenger and cargo services on short sea ferry routes, container and similar cargo services on longer open water and ocean routes, and special tasks for which high speed, sometimes linked to amphibious capability, can significantly increase effectiveness. Finally, the likely role of high-speed craft in future marine transport and other systems is considered.

Semi-Submerged Ship Form with Minimum Wave Making Resistance

In the previous paper, as a high speed displacement type hull form the author introduced a semi -submerged ship with the minimum wave making resistance being composed of the combination of source distribution, thus consisting of the submerged hull of the Rankine's ovoid and the upper slender body having sectional area of Versine distribution.In this paper, it is attempted to describe the above hull form in a more general manner and in details. There are two or three ways to minimize the wave making resistance of the subject hull form under the arbitrary condition, but there is found not so notable difference between the respective results obtained therefrom in so far as within the practical speed ranges of this hull form theory. Assuming that the sum of theoretical wave making resistance and surface frictional resistance of this hull form to be the total resistance, and when it is tried to seek the hull form with the minimum total resistance, it should come to a semi-submerged ship for delivery at high designed speed range. While on the other hand, when the designed speed is low, the hull form will rather tend to be a general surface ship with a bulbous bow in a ram shape, thereby permitting to secure the lateral stability, thus it is enabled to make the application of this hull form for general vessels.

Series 64 Resistance Experiments on High-Speed Displacement Forms

The speed-length ratios of displacement-type surface ships in the past were limited to under 2.0. In order to perform projected tactical missions, however, the Navy needs ships of much higher speeds resulting in speed-length ratios of 2.0 or above. To gain information in this respect, 27 models of conventional hull forms designated "Series 64" were designed, constructed, and tested at the David Taylor Model Basin. This paper reports the results of the bare hull resistance tests of Series 64 models.

A Study on the Large Bulbous Bow of a High Speed Displacement Ship

A Study on the Large Bulbous Bow of a High Speed Displacement Ship

A Study on the Large Bulbous Bow of a High Speed Displacement Ship

This paper deals with a practical application of “Weveless Bow” theory, has been developed by Prof. T. Inui & T. Takahei.In spite of a high speed practical ship form is treated for the subject of study, the results of experiments and calculations prove that the large bulbous bow according to “Waveless Bow” theory is certainly effective.Seaworthiness and turning qualities on the same ship form will be mentioned in next reports.