Naval architecture

Source: Wikipedia, the free encyclopedia.
"Naval engineering" redirects here. For the physical construction of ships and other floating vessels, see
Ocean engineering
.
Reconstruction of a 19th-century naval architect's office, Aberdeen Maritime Museum
Curriculum of Naval Architecture
General Course of Study leading to Naval Architecture degree

Naval architecture, or naval engineering, is an

statutory
and non-statutory requirements.

Main subjects

The word "vessel" includes every description of

transportation on water.[3] The principal elements of naval architecture are detailed in the following sections.[4]

Hydrostatics

Body plan of a ship showing the hull form

trim (the measure of the longitudinal inclination of the vessel) and stability (the ability of a vessel to restore itself to an upright position after being inclined by wind, sea, or loading conditions).[5]

Hydrodynamics

Flotation and stability

Main articles: ship motions, ship stability, initial stability, secondary stability, and limit of positive stability
Translations
Axes of a ship and rotations around them

While atop a liquid surface a floating body has 6 degrees of freedom in its movements, these are categorized in either translation or rotation.

  • Translation
    • Sway: transverse
    • Surge: fore and aft
    • Heave: vertical
  • Rotation
    • Yaw: about a vertical axis
    • Pitch or trim: about a transverse axis
    • Roll or heel: about a fore and aft axis

Longitudinal stability for longitudinal inclinations, the stability depends upon the distance between the center of gravity and the longitudinal meta-center. In other words, the basis in which the ship maintains its center of gravity is its distance set equally apart from both the aft and forward section of the ship.

While a body floats on a liquid surface it still encounters the force of gravity pushing down on it. In order to stay afloat and avoid sinking there is an opposed force acting against the body known as the hydrostatic pressures. The forces acting on the body must be of the same magnitude and same line of motion in order to maintain the body at equilibrium. This description of equilibrium is only present when a freely floating body is in still water, when other conditions are present the magnitude of which these forces shifts drastically creating the swaying motion of the body.[6]

The buoyancy force is equal to the weight of the body, in other words, the mass of the body is equal to the mass of the water displaced by the body. This adds an upward force to the body by the amount of surface area times the area displaced in order to create an equilibrium between the surface of the body and the surface of the water.

The stability of a ship under most conditions is able to overcome any form or restriction or resistance encountered in rough seas; however, ships have undesirable roll characteristics when the balance of oscillations in roll is two times that of oscillations in heave, thus causing the ship to capsize.[7]

Structures

Cutaway of the structure of a US Navy WWII destroyer escort

Structures involves selection of material of construction, structural analysis of global and local strength of the vessel, vibration of the structural components and structural responses of the vessel during motions in seaway. Depending on type of ship, the structure and design will vary in what material to use as well as how much of it. Some ships are made from glass reinforced plastics but the vast majority are steel with possibly some aluminium in the superstructure.[6]

The complete structure of the ship is designed with panels shaped in a rectangular form consisting of steel plating supported on four edges. Combined in a large surface area the Grillages create the hull of the ship, deck, and bulkheads while still providing mutual support of the frames. Though the structure of the ship is sturdy enough to hold itself together the main force it has to overcome is longitudinal bending creating a strain against its hull, its structure must be designed so that the material is disposed as much forward and aft as possible.[6]

The principal longitudinal elements are the deck, shell plating, inner bottom all of which are in the form of grillages, and additional longitudinal stretching to these. The dimensions of the ship are in order to create enough spacing between the stiffeners in prevention of buckling. Warships have used a longitudinal system of stiffening that many modern commercial vessels have adopted. This system was widely used in early merchant ships such as the

Isherwood System.[6]

The arrangement of the Isherwood system consists of stiffening decks both side and bottom by longitudinal members, they are separated enough so they have the same distance between them as the frames and beams. This system works by spacing out the transverse members that support the longitudinal by about 3 or 4 meters, with the wide spacing this causes the traverse strength needed by displacing the amount of force the bulkheads provide.[6]

Arrangements

Functional areas of a destroyer

Arrangements involves

concept design, layout and access, fire protection, allocation of spaces, ergonomics and capacity
.

Construction

Shipbuilding with steel, 1973

glass-reinforced plastic. The process of construction is thought-out cautiously while considering all factors like safety, strength of structure, hydrodynamics, and ship arrangement. Each factor considered presents a new option for materials to consider as well as ship orientation. When the strength of the structure is considered the acts of ship collision are considered in the way that the ships structure is altered. Therefore, the properties of materials are considered carefully as applied material on the struck ship has elastic properties, the energy absorbed by the ship being struck is then deflected in the opposite direction, so both ships go through the process of rebounding to prevent further damage.[8]

Science and craft

Smooth ship lines

Traditionally, naval architecture has been more craft than science. The suitability of a vessel's shape was judged by looking at a half-model of a vessel or a prototype. Ungainly shapes or abrupt transitions were frowned on as being flawed. This included rigging, deck arrangements, and even fixtures. Subjective descriptors such as ungainly, full, and fine were used as a substitute for the more precise terms used today. A vessel was, and still is described as having a ‘fair’ shape. The term ‘fair’ is meant to denote not only a smooth transition from fore to aft but also a shape that was ‘right.’ Determining what is ‘right’ in a particular situation in the absence of definitive supporting analysis encompasses the art of naval architecture to this day.

Modern low-cost digital

Computational Fluid Dynamics
is being applied to predict the response of a floating body in a random sea.

The naval architect

Naval architect at work

Due to the complexity associated with operating in a marine environment, naval architecture is a co-operative effort between groups of technically skilled individuals who are specialists in particular fields, often coordinated by a lead naval architect.[9] This inherent complexity also means that the analytical tools available are much less evolved than those for designing aircraft, cars and even spacecraft. This is due primarily to the paucity of data on the environment the marine vehicle is required to work in and the complexity of the interaction of waves and wind on a marine structure.

A naval architect is an engineer who is responsible for the design, classification, survey, construction, and/or repair of ships, boats, other marine vessels, and offshore structures, both commercial and military, including:

Cutaway of a nuclear submarine

Some of these vessels are amongst the largest (such as

aircraft carriers
), and highly valued movable structures produced by mankind. They are typically the most efficient method of transporting the world's raw materials and products. Modern engineering on this scale is essentially a team activity conducted by specialists in their respective fields and disciplines. Naval architects integrate these activities. This demanding leadership role requires managerial qualities and the ability to bring together the often-conflicting demands of the various design constraints to produce a product which is fit for the purpose.[10]

In addition to this leadership role, a naval architect also has a specialist function in ensuring that a safe, economic, environmentally sound and

seaworthy
design is produced. To undertake all these tasks, a naval architect must have an understanding of many branches of engineering and must be in the forefront of high technology areas. He or she must be able to effectively utilize the services provided by scientists, lawyers, accountants, and business people of many kinds.

Naval architects typically work for

Classification societies, regulatory bodies (Admiralty law), navies
, and governments.

See also

References

  1. ^ "Careers in Naval Architecture". www.rina.org.uk. Archived from the original on 2017-10-20. Retrieved 2019-08-13.
  2. ISBN 0-7506-4988-7
  3. ISBN 92-801-4167-8
  4. ISBN 0-939773-00-7
  5. ^ "EN342". www.usna.edu.
  6. ^ a b c d e Tupper, Eric (1996). Introduction to Naval Architecture. Oxford, England: Butterworth-Heinemann.
  7. doi:10.1016/j.oceaneng.2016.02.010
    .
  8. doi:10.1016/j.tws.2017.02.022
    .
  9. ^ American Society of Naval Engineers Archived December 26, 2008, at the Wayback Machine. Naval engineering brochure.
  10. ^ "Job Family Standard for Professional Work in the Engineering and Architecture Group, U.S. Office of Personnel Management, pp. 43–45" (PDF). Archived from the original (PDF) on 2009-05-12.

Further reading

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