Ship Section Research Articles

Water entry of a bow-flare ship section with roll angle

The two-dimensional water entry of a bow-flare ship section with constant roll angle, or heel angle, was studied by using a boundary element method. The fully nonlinear free surface conditions and exact body boundary conditions were satisfied. Nonviscous flow separation from the knuckles of the section or from the curved bottom could be simulated. The numerical calculations were compared with existing experimental results. First, the effects of roll angle were investigated and then the characteristics associated with large roll angles were examined in particular. The evolution of the free surfaces and the pressure distributions on the section surface are illustrated and the influence of nonviscous flow separation from the leeward section surface is discussed.

Benchmark study on the use of simplified structural codes to predict the ultimate strength of a damaged ship hull

The objective of the paper is to evaluate the ability of simplified structural analysis methods, based on the Smith formulation to predict the ultimate strength of a damaged ship. Such methods are now widely accepted as a reliable and fast way to obtain the longitudinal strength of an intact ship. In order to extend these methods to damaged ships, first a benchmark study on the intact ship was performed in order for the differences between the methods to be evaluated. Afterwards the methods are applied to the same ship section but with damage, which was defined by removing the structural elements from the affected areas. These, in turn, were obtained from a previous study in which a collision was simulated using a finite element model. Results obtained for the ultimate strength were compared against each other and with the results of the finite element analysis. Aside from some exceptions, the results of the approximate methods agreed well with each other for the intact and damaged conditions. The simplified methods are more conservative than the finite element analysis in hogging while they seem to give a very good approximation to the result for sagging with some of them overestimating this value.

Prediction of Welding Distortions of Stainless Steel Ship

The long-term goal of prediction of welding distortions in ship sections is to specify an optimal welding procedure to minimize distortions due to welding. The equivalent load method based on inherent strain for material of stainless steel is studied in this paper. A fillet welding experiment followed by infrared thermograph is done. Then simplified elastic plastic analysis model is used while combining the inherent strain theory and the experimental results for accurate and efficient analysis. The results of temperature field in FEM have been supported by the experimental data. Furthermore, the distortions of the stainless steel ship structure are calculated by FE analysis.

Efficient calculation of slamming pressures on ships in irregular seas

An efficient method for calculation of the slamming pressures on ship hulls in irregular waves is presented and validated for a 290-m cruise ship. Nonlinear strip theory was used to calculate the ship–wave relative motions. The relative vertical and roll velocities for a slamming event were input to the slamming calculation program, which used a two-dimensional boundary element method (BEM) based on the generalized 2D Wagner formulation presented by Zhao et al. To improve the calculation efficiency, the method was divided into two separate steps. In the first step, the velocity potentials were calculated for unit relative velocities between the section and the water. In the next step, these precalculated velocity potentials were used together with the real relative velocities experienced in a seaway to calculate the slamming pressure and total slamming force on the section. This saved considerable computer time for slamming calculations in irregular waves, without significant loss of accuracy. The calculated slamming pressures on the bow flare of the cruise ship agreed quite well with the measured values, at least for time windows in which the calculated and experimental ship motions agreed well. A simplified method for calculation of the instantaneous peak pressure on each ship section in irregular waves is also presented. The method was used to identify slamming events to be analyzed with the more refined 2D BEM method, but comparisons with measured values indicate that the method may also be used for a quick quantitative assessment of the maximum slamming pressures.

Study of non-linear wave motions and wave forces on ship sections against vertical quay in a harbor

The resonance phenomenon of fluid motions in the gap between ship section, seabed and vertical quay wall is studied numerically and experimentally. The natural frequency of the fluid motions in the gap is derived. A two-dimensional time-domain coupled numerical model is developed to calculate the non-linear wave forces acting on a ship section against vertical quay in a harbor. The fluid domain is divided into an inner domain and an outer domain. The outer domain is the area between the left side of ship section and the incident boundary, where flow is expressed by Boussinesq equations. The rest area is the inner domain, which is the domain beneath the ship section plus the domain between the right side of ship section and vertical quay wall. The flow in the inner domain is expressed by Newton's Second Law. Matching conditions on the interface between the inner domain and the outer domain are the continuation of volume flux and the equality of pressures. The numerical results are validated by experimental data.

Circulation in the central equatorial Atlantic: Mean and intraseasonal to seasonal variability

The zonal equatorial circulation of the upper 700 m in the central tropical Atlantic is studied based on 11 cross‐equatorial ship sections taken at 23–29°W during 1999 to 2005 and on data from a pair of moored Acoustic Doppler current profilers deployed on the equator at 23°W during February 2004 to May 2005. The observations on the equator reveal the existence of two mean westward cores of the Equatorial Intermediate Current below the Equatorial Undercurrent. In contrast to the 2002 moored observations at the same position the intraseasonal variability during the mooring period is dominated by zonal instead of meridional velocity fluctuations.

An estimation and verification of vessel radar cross sections for high-frequency surface-wave radar

The radar cross sections of both small and large ships for high-frequency surface-wave radar (HFSWR) were studied by using the numerical electromagnetics code, and by using measurements from an HFSWR system at Cape Race, Newfoundland, Canada. The results of the study indicated that Teleost, a 2405-ton Canadian Coast Guard ship, and large cargo container vessels (-36000 ton) have comparable RCS values at 3.1 and 4.1 MHz. This was verified by comparing Teleost signals with the reflections of seven cargo-container vessels, identified during an operational evaluation of the HFSWR. The conclusion of the study was that Teleost and the large cargo container vessels had an angle-averaged radar cross section (RCS) of -40 dBm/sup 2/, while small vessels (-1000 tons) could reasonably be characterized by an angle-averaged RCS of -30 dBm/sup 2/, in the lower end of the HF band (3-5 MHz).

Fourier NUBS method to express ship hull form

This article presents a method of numerical expression to draw ship hull forms. Recent developments in research into ship hull optimization need a method to express ship hull form as precisely as possible with a small number of design parameters. This method is based on a combination of the Fourier–sine series expansion and nonuniform B-spline (NUBS) interpolation. The merit of the combination is that it removes the wiggles which are often found when generating a rectangular-type curve, such as the midship section of tanker ship, with a simple Fourier series expansion. Here, the procedure is explained, and then a tanker ship hull is generated. Through the discussion, we show the effectiveness of the method.

Prediction And Analysis Of Critically StressedShip Sections

Whole ship shock analysis (WSSA) is becoming a mandatory requirement in the design of naval platform. One of the key technical challenges in WSSA is the reduction of a complex ship design to a reasonable FE model size. An approach known as “smearing” is commonly used to idealise the ship to a manageable number of DOFs, by using equivalent stiffness. This paper presents a novel technique to study the localized stress and deformation of a ship section using global parameters obtained from the WSSA. A 3D explicit finite element code is used to compute the critically stressed areas in the whole ship and predict the localized stresses in the ship section. This paper expounds the methodology of stress recovery through the conversion of the displacement time history from the whole ship to obtain the stress distribution for the ship section. The expedience of exploiting stress recovery to inspect the localized stresses in the beam and shell elements will also be clearly exemplified. Last but not least, a displacement accuracy comparison will be performed on the ship section and the “unsmeared” whole ship.

Loads and Hydrodynamic Coefficients of the Ship Contours for their Instant Position on Wave Surface

An approximate practical method of calculation nonlinear of the Khaskind -Newman hydrodynamic loads, acting on the ship's hull rolling on the waves with finite amplitude, is grounded. In so doing, the effects of variation of wetted part of the ship's surface and an anharmonicity of the velocity field on it are taken into account. Determination of loads is generally reduced to calculation of hydrodynamic coefficients of ship's sections in their instant positions, namely, the attached masses and damping coefficients. To determine the instant hydrodynamic coefficients in wide range of shapes of ships' sections the multiparameter conformal mapping in the parametric plane and the Ursell technique for the determination of the velocity potential in this plane are used. The parameters of conformal mapping and the amplitudes of hydrodynamic singularities are derived by the least-squares method. The results of comparative calculations for hydrodynamic coefficients of typical ship's sections, ship's sections pitched up to 40◦, sections with bilge keels and bulbous SWATH ship's sections are presented. The agreement of these results is estimated in general as satisfactory and good.

Hull Form Optimization by Shift and Deformation of Ship Sections

A technique for reducing ship wave resistance is presented. It is based on a single B-spline patch which approximates the hull surface. A selected specific change of the B-spline coefficients resembles a smooth shift of the ship sections in the longitudinal direction. An unconstrained Davidson-Fletcher-Powell (DFP) optimization procedure controls the changes. The wave resistance is evaluated by a higher-order Rankine source panel method. The numerical results, shown for Series 60 and the Hamburg Test Case (HTC) containership, prove that the method is appropriate for preliminary hull form design.

On a Method to Calculate Hull Response of High Speed Vessels in Waves Taking Account of Slamming

This paper proposes a new method to simulate slamming impact. loads and ship response of a high-speed vessel in waves. Many non-linear analysis methods have been proposed and reported for simulation of slamming of ships, in which hydrodynamic impact loads are determined by means of Karman type impact model. It means that wrater pile up is not taken account of in water surface impact. process. On the other hand, model experiments and numerical analyses of water impact of wedges show very good agreements with water impact theory by Wagner, in which water pile up plays an important role. This implies that calculation of proper impact loads is not expected by these non-linear analysis methods. A new approach have been tried to improve this inconvenience.Wagner type impact model is adopted in the new method, together with threshold velocity of water impact to judge occurrence of water impact. Threshold velocity of water impact is derived for wedges with various deadrise angles, of which model test was carried out for the validation.A new concept of equi-added-mass lines is introduced to take account of the hull form to compute substantial relative velocity between hull and wave surface. This corresponds to a method to derive relative vertical velocity of an inclined prismatic body with a wedge section advancing forward on calm water surface. Using this method, substantial relative velocity can be computed taking account of ship speed, and loads derived by the method include the lift force induced by ship speed.These are incorporated in a new non-linear analysis method. It is confirmed that loads derived by this method for a ship section are equivalent to the loads derived by Stavovy & Chuang's method, which is so-called an impact theory to calculate three-dimensional impact. pressure. A comparison is made between the results of this method and model tests for hull response of a 40 m patrol boat in regular waves. The results show comparatively good agreements in motions in waves. But, it shows there is much room for improvements in treatments of piled up water and waves the ship induces.This method is applied well to simulate hull response of such high-speed vessels like patrol boats, and this method is expected to apply also to other ships like container ships.

NUMERICAL SIMULATION OF SHIP WAVES IN SHALLOW WATER

Ship waves in shallow water are considerably different from those in deep water.They are greatly influenced by the depth Froude number. In the present paper, the numerical method proposed by Tanimoto et al.(1999) has been confirmed to be applicable to predict ship waves in a shallow water by comparing with experimental data by Kurata et al.(1983).Variations of the maximum wave height by the mid ship section coefficient, the distance from the sailing line and the depth Froude number are discussed together with experimental data.The maximum wave height increases as the depth Froude number increases up to the critical speed condition. In the range of super critical speed, the maximum wave height becomes almost constant or slightly decreasing tendency.

Transient response of floating composite ship section subjected to underwater shock

An analysis of the transient response of a floating composite ship section subjected to underwater shock is presented in this paper. Based on Doubly Asymptotic Approximation (DAA) method, the fluid-structure interaction equation for a partially submerged structure is derived, in which the constitutive relation for composite material is implemented and also the effects of the free surface are included. The coupled fluid-structure equations, relating structure response to fluid impulsive loading, are solved using coupled finite-element and boundary-element codes. Transient stress distribution of the composite ship section induced by the underwater shock is illustrated. The influences of the boundary conditions on the transient response of the ship section subjected to underwater shock is studied; and further more, effects of the charge position, the charge weight and the stand-off distance on the transient stress response are examined.

Description of Ship Form and Evaluation of Ship Performance

Ship form has been expressed using the “OFF-SETS” and “PRINCIPAL PARTICULARS (PRINCIPAL DIMENSIONS)” with “LINES” for about 100 years since the beginning of the modern developments of ship engineering/science.In the field of ship design, ship performance has been estimated and evaluated by means of indirect parameters such as principal dimensions and coefficients. Since these parameters do not give an unique ship form, ship designer has utilize their experience and intuition during the procedure of performance design for improving and determining the ship form. However, how long are we able to pass on the skilful knowledge to the future generation ?In the present paper, the authors propose a method for describing ship form by means of Fourier series called Fourier Descriptors (FD). They will show that FD can determine an arbitrary ship section uniquely and can decompose/reproduce arbitrary 2-dimensional ship section form.As the 1 st step of the performance evaluation, they show the effects of section form on the damping and added mass coefficients of 2-dimensional oscillating bodies that are commonly used in the ship motion estimation with comparing results obtained by means of Lewis Form transformation.

Object-oriented approach to a knowledge-based structural design system

In this article, an Expert System for MIDship section design (ESMID) is developed based on a general-purpose expert system shell. The system focuses on the integration of knowledge-based system and design resources such as an engineering database, graphical user interface, and engineering application programs for the calculation of section modulus and longitudinal strength of ship structure. The validation of the ESMID system was examined and verified by applying the system to the 64K bulk carrier ship. The developed expert system can help a novice engineer in designing the midship section of ship.

A General Algorithm for Dynamic Control of Multilink Robots

One of the major tasks in the development of sophisticated methods for robot control is finding algorithms that are appli cable to a wide range of different robots. Another major task is to find algorithms that can be used for on-line control. Several attempts have been made to solve one or the other of these problems. This article presents a general method for solving both. It can be applied to any redundant or nonredundant robot with rigid subunits connected by revolute joints in a tree-like structure. The number of joints can be chosen arbitrarily large without singularity problems, in contrast to traditional inverse kinematics models. A system based on the presented method needs no modifications when changing from one specifrc robot to another structurally or kinematically completely different robot, only input parameters describing the robot are different. The method is founded on a very general algorithm for finding the Lagrangian equations of motion for a robot subject to a given set of artificial forces. The generality and power of the method are demonstrated by two examples. In the first example the method is used to simulate a 25-degrees-of-freedom (DOF) snake-like robot moving through a maze. In the second example the method is used to control an actual application: an 8-DOF industrial robot system welding a ship section.

A Study of Flow Field around Full Ship Forms in Maneuvering Motion

In the previous report dealing with oblique towing condition, the flow field around tow full ships with different aft hull-forms were investigated by numerical computation and experiments. Thereafter, additional studies of comparison between numerical computation and experiments were carried out for the same ships in steady turning condition. As in the previous investigation, detailed measurement of hydrodynamic pressure on the whole hull surface was executed, and then the longitudinal distribution of sectional lateral force was obtained by integrating the measured pressure along a contour of transverse section of ship's hull at various square stations. The measured pressure on the hull and longitudinal distribution of sectional lateral force were compared with numerical solutions of Navier-Stokes equation. The results are fully described in the present paper. The comparison denotes that agreement between numerical computation and experiments is fairly good. In particular, it should be noted that the difference in hydrodynamic lateral force and turning moment between two ships with different hull-forms can be successfully predicted by numerical computation, and the difference in maneuverability of two ships can be definitely correlated to the difference in lateral force distribution caused by the difference in hull-form by means of numerical computation and experiments as well.

Exposure to Solid Aerosols During Regular MMA Welding and Grinding Operations on Stainless Steel

Tests of air concentrations of solid aerosols during manual metal arc (MMA) welding on stainless steel were carried out at three working sites. In addition to a detailed description of the work situation, samples of welding fume were collected from both the breathing zone and the general air. Air concentrations of total solid aerosols were determined gravimetrically. Total amounts of metal compounds (i.e., nickel (Ni), chromium (Cr), iron, and manganese) and water-soluble hexavalent chromium (CrVI), were determined. The mean fume concentrations during MMA welding were 5.4 mg/m3 inside a ship section, 3.0 mg/m3 at an offshore module, and 2.0 mg/m3in welding shops. The highest concentrations of CrVI were found during MMA welding inside the ship section, with a mean concentration of 140 µg/m3 (range 4–640 µg/m3). CrVIcomprised about 50% of the total Cr by weight. Though the base material contained approximately 20% Cr and 10% Ni, the Cr and Ni contents (µg/mg welding fumes) varied greatly among the different welding sites. Grinding generated a mean concentration of 11 mg/m3, of which Cr was about 10% of the total solid aerosol.

Exposure to Solid Aerosols During Regular MMA Welding and Grinding Operations on Stainless Steel

Tests of air concentrations of solid aerosols during manual metal arc (MMA) welding on stainless steel were carried out at three working sites. In addition to a detailed description of the work situation, samples of welding fume were collected from both the breathing zone and the general air. Air concentrations of total solid aerosols were determined gravimetrically. Total amounts of metal compounds (i.e., nickel (Ni), chromium (Cr), iron, and manganese) and water-soluble hexavalent chromium (CrVI), were determined. The mean fume concentrations during MMA welding were 5.4 mg/m3 inside a ship section, 3.0 mg/m3 at an offshore module, and 2.0 mg/m3in welding shops. The highest concentrations of CrVI were found during MMA welding inside the ship section, with a mean concentration of 140 µg/m3 (range 4–640 µg/m3). CrVIcomprised about 50% of the total Cr by weight. Though the base material contained approximately 20% Cr and 10% Ni, the Cr and Ni contents (µg/mg welding fumes) varied greatly among the different...