Showing papers on "Beam (nautical) published in 1980"

Slow Drift-Oscillations of a Ship in Irregular Waves

Abstract: A procedure to calculate horizontal slow drift excitation forces on an infinitely long horizontal cylinder in irregular beam sea waves is presented. The hydrodynamic boundary-value problem is solved correctly to second order in wave amplitude. Results in the form of second order transfer functions are presented for different two-dimensional shapes. It is concluded that Newman's approximative method is a practical way to calculate slow drift excitation forces on a ship in beam sea and suggested that it may be used in a more general case. Applications of the results for moored ships are discussed.

Antisymmetric vibration of ship hulls

Abstract: When investigating the antisymmetric response of a ship to waves it is necessary to describe its behaviour in dynamical terms. In practice this requires that natural frequencies and principal nodes be calculated. A numerical technique which is based on the assumption that the hull moves in vacuo as a nonuniform Timoshenko beam was therefore devised. This technique admits coupling of bending and twisting, and also contains an allowance for warping stiffness. The vibration problem of a conservative uniform beam is solved exactly. The solution provides accurate data against which the numerical method can be tested. the numerical method is also shown to agree with results predicted by Ohtaka, Kumai, Ushijima and Ohji, both for a uniform beam and a ship hull. These writers used a technique in which no allowance is made for warping stiffness. Finally it is shown how a direct check can be made of the orthogonality of computed nodes. Order from BSRA as No. 54,322.

Scaffold bracket and hanger therefor

Abstract: A scaffolding bracket for supporting a platform against the wall of a ship or the like has a tapered U-shaped support beam having opposed pairs of apertures in the sides near one end thereof, the support beam is adjustable relative to a wall engaging plate. The wall engaging plate has a pair of keyhole apertures which connect to a pair of metallic studs which are secured to the wall of the ship or the like by welding means. The plate has a flange, the opposed sides of which define a segment of a circle about which the support beam is adjustably pivoted. The flange has a series of apertures at spaced apart intervals which cooperate with the pairs of apertures near the end of the support beam thus allowing the support beam to be pivotably adjusted in increments of five or ten degrees around the circle segment. In order to permit the bracket to be used on the inside wall as well as the outside wall of a ship, the flange is constructed to define a half circle about which the support beam is adjustably pivoted by a series of spaced apertures therein.

Ship manoeuvrability in strong wind

Abstract: The conventional method of estimating the upper limit of wind velocity at which a ship is manoeuvrable is by the solution of equilibrium equations of steady ship motion, but the method is not realistic because the steered motion of a ship in wind is unsteady. In this study, the Authors investigate the manoeuvrability of a ship in wind both by solving non-linear equations of motion numerically (with a digital computer) and by carrying out a steering test with a manoeuvring simulator. From these investigations, a more realistic upper limit of wind velocity is obtained. By comparing this value with that estimated by equilibrium equations, it is shown that, in the beam and quarter winds that are most difficult in ship manoeuvring, this realistic upper limit of wind velocity is nearly equal to the limit estimated by the equilibrium equations of steady motion for a ship whose rudder angle is kept at 15 deg. By using this relationship, the upper limit of wind velocity for several ships of different types is shown graphically in the article. The effects of shallow water, rudder area, waves, uniform current, and fluctuating wind, upon the upper limit of wind velocity, are also discussed. Order from BSRA as No. 54,224.

Ship with multi-part hull - is of variable beam and has lengthwise partitions and locking connectors allowing sideways movement of parts

Abstract: The ship with a multi-part hull, and beam variable in service, has the two or more parts (1) of the hull, independently buoyant, jointed along or parallel to (2) the centreline. Where the number of parts is even, these are mirror-images in plan but not in themselves symmetrical. For an uneven number, a symmetrical part is inserted centrally between the others. Transverse links (3) connect the parts so that they can be moved laterally relative to each other and locked, lying parallel, in variouspositions. The mating faces of the parts have interlocking lengthwise corrugations (4).

The use of bench test results for calculating roll response of the tank stabilized ship

Abstract: A method is presented whereby the results of bench tests of the passive tank may be used to calculate the stabilised ship roll response to beam seas. It is shown that slightly modified equations for the roll motion of a ship equipped with a U-tube roll stabiliser, represent the behaviour of a ship fitted with any type of stabiliser tank. The equations contain three unknown tank parameters which can be determined from the results of bench tests. The approach is believed to be simple and sufficiently accurate for the prediction of stabilised ship motion during the design stage for most tanks.

Ship vibrations in random seas

Abstract: A general analysis of ship dynamics in random seas is presented. The analysis covers the steady-state wave-induced response and the transient-state slam-induced (whipping) response. Wave-induced response includes with the rigid-body modes (seakeeping) and the hull flexural modes (springing). The strip theory by Salvesen, Tuck, and Faltinsen is used to determine the hydrodynamic forces. The ship structure is idealized by finite beam elements with the lumped-parameter system. The normal-mode approach is used to calculate the vibration characteristics and dynamic response. Statistics of both wave-induced loads and responses are characterized by Zero-mean Gaussian processes. By spectral analysis, the wave-induced responses can be predicted for a ship moving in random seas. The slamming impacts as the input to the ship are treated as a nonstationary filtered Poisson process. The output slam-induced (whipping) response process can be determined by passing such a nonstationary process through the time-invariant ship system or by using a Markov process. Two ship examples are studied. The 1000-ft (305 m) Great Lakes ore carrier Stewart J. Cort is used for the calculation of the wave-induced response, and the 525-ft (160 m) SS Gopher Mariner is used for the calculation of the slam -induced (whipping) response.

Diffraction of waves around a ship

Abstract: The diffraction problem of a fixed slender ship in incident regular sinusoidal deep-sea waves coming from any direction is formulated. The waves are assumed to be of the same order of magnitude as the beam of the ship. Zero Froude number is assumed. The boundary-value problem is linearized with respect to the wave amplitude and solved by the method of matched asymptotic expansions. A solution valid for all wave headings is found. The solution involves solving a two-dimensional Helmholtz equation problem for cross sections along the ship. The Helmholtz equation problem is solved by a new fast integral representation method. Numerical solution procedures are given. The pressure distribution for different wave headings and wave lengths is calculated and compared with experiments. The agreement between theory and experiments is found to be satisfactory.

Control system of ultrasoniccwave beam

Abstract: PURPOSE:To obtain an ultrasonic-wave beam with narrow width, by actualizing actual arc phasing by providing with time delay or phase delay corresponding to the distance of distances from each trembler up to an arbitray point of a short distance field region. CONSTITUTION:Trembler groups 3-1,...,3-N are circularly arranged. When adding time delay corresponding to distances e1, e2, e4, e5 from each trembler up to a circular arc in the case when drawing a circular are AB from a point P at r2 distance from the trembler 3-3, ultrasonic waves are focussed at the point P, and the width of an ultrasonic-wave beam in a line S containing the point P becomes narrow as shown in width a.

A novel icebreaker concept

Abstract: With the new concept the icebreaking process differs considerably from that with conventional icebreakers The main feature is the flat bottomed bow with a beam greater than that of the ship and with sharp edges at the sides Curves of ice resistance and power required show the advantages of the new hull form The results of the model tests in open waters are compared with those of vessels with conventional shapes Order from NSFI as No 22357

Loading method of heavy cargo

Abstract: PURPOSE:To simplify cargo work by using a floating body adjustable by ballast. CONSTITUTION:A floating body 4 adjustable in the ballast level 4' is prepared and positioned on the outside of a base vessel 3 adjustable by ballast alongside a pier 2. When a beam 5 is stretched almost horizontally between the pier 2 and the floating body 4, a heavey cargo 1 is placed on the side of the beam 5. As the cargo 1 is moved to the upper part of the base vessel 3 by the driving of a winch 7, the ballast level 4' is adjusted according to the changing of the load to the floating body 4 for keeping the beam 5 essentially horizontal. Then, the base vessel 3 is floated up by lowering the ballast level 3'. After the heavy cargo 1 is supported by the tops of extended jacks 10, the beam 5 is drawn back to the side of the pier 2 and jackds 10 are contracted.

Flexion measuring device for long beam

Abstract: PURPOSE:To obtain a flexion measuring device which can be applied even in the water or when no stable point is available by measuring the level depth difference within the linking tube which bends along with the long beam and thus measuring the flexion amount at each part of the long beam CONSTITUTION:Linking tube A made of the synthetic resin or the like is attached in a body to long beam B to bend together with B Tube A consists of vertical tube 1 plus upper and lower horizontal tubes 2 and 3 with a fixed space between them, and contains liquid W like the water or the like inside Level gauge 4 is inserted within tube 1, and orifice 5 is provided within tube 3 to control the movement W Thus the signal of the liquid level height detected by gauge 4 is transmitted to analysis recording part C And the reference water level such as the liquid level height at the long beam support part plus the liquid level depth difference to the liquid level height at each measuring point are calculated at operation part 7 and via amplifier 6 to be recorded to recorder 8 In such way, the flexion amount can be measured easily even in the water or when no stable point is available