Naval Architecture PPT

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    OCEN 201Introduction to Ocean &

    Coastal EngineeringBasics of Naval Architecture

    Jun [email protected]

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    Ships by Configurations

    Surface displacement: Conventional ships(single hull); Catamaran (double hull, large deck

    area, small displacement, excellent stability).

    Near (above) Surface: Air cushion vehicles;

    Hydrofoils and planning hull craft (smalldisplacement, high speed)

    Submerged: Submersibles; submarines;Underwater habitats; Submerged buoys.

    Semi submersibles: Very deep, small waterplane

    Bottom supported: Temporary & Permanent

    jack-up;

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    Tanker (with a bulbous bow)

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    Small Water-plane Area Twin-Hull (SWATH)

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    Ferry (Catamaran, or SWATH)

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    Container Ship

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    Container Ship

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    Trimaran

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    View from the below

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    Hydrofoil Craft

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    Rules and Regulations

    The rules and regulations are issued by organizations

    which may be divided into three categories:

    -Classification societies: have established standards

    of construction by the production of rules whichhave done much to ensure the safety of ships. (ABS,DNV, BV)

    -Governmental Authorities: concern for the safety

    of ships and the well being of all who sail the ships(behavior of the people). (Coast Guard)

    -International Authorities, IMO (InternationalMaritime Organization)

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    Basic Topics of Naval Architecture

    Hull: Hydrostatic, hydrodynamicperformance (Resistance)*

    Structure: Strength of hull**

    Machinery and Propulsion: Main engine**& propellers*

    Ship Control: (maneuvering, sea keeping)**

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    Deck Machinery**

    Navigation: Sensors & Radar**

    Communications**

    Damage Control:**

    Rigging and Mooring:*

    Economic feasibility:**

    ** Not covered in detail

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    Definition (Terminology):

    Principal Dimensions (length, breadth, depth etc)

    -Length.Lbp ( or Lpp) Length between two perpendiculars

    FPForward perpendicular (vertical line through intersection

    of stem and waterline (w.l).)

    APBackward perpendicular (vertical line through the center

    of rudder pintle)

    LoaOverall Length

    LwlWaterline Length (calculation length)

    also see Table 6-2 at p175 (old edition at p142)

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    W.L.

    A.P

    Loa

    Lwl

    Amid Ship

    Lbp

    F.P.

    Forward Sheer

    After Sheer

    Sheer is the height measured between deck at side and base line.

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    Definition (Terminology):

    Principal Dimensions

    -Breadth, depth & draft. Breadth (moulded) (inside of plate on one side to another side)

    Breadth maximum Depth (measured at midship)

    Camberthe rise of the deck at the centerline. 2% of breadth

    Bilge radius

    Rise of Floor

    Flat of keel (thicker plate)

    Tumber home

    Rake of stem

    Draught and trim

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    Flat of KeelRise of Floor

    Depth

    Moulded

    Breadth

    moulded

    Bilge radius

    Centerline

    Deck

    Base Line (Top of

    Flate keel)

    CamberBreadth Extreme

    Fonder

    w.l.

    Draft (d)

    Mid Cross Section of a ship

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    If W.L. is parallel to the baseline (keel line),

    the ship is floating evenly.

    If not parallel, the ship has a trim.

    Trim = dadf

    Trim (in radians) = (dadf )/ L

    Average draft = (da + df )/ 2

    Free board (f.b) is the distance measured

    downwards from the deck to the W.L.Usually f.b. is minimum at midship

    Minimum f.b is required by International

    Law.

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    Line Drawing:

    Using the methods of descriptive geometry, the form of

    a hull is drawn on a scale (1:50 or 1:200) drawing,

    which is called Lines Drawing, or simply the lines

    or lines plan. (See p34 Figure 3.4 Lines plan).

    Lines drawing mainly consists ofthree plan views

    Sheer plane (Buttock plane, Buttock lines) : parallel

    to the longitudinal central plane (2m, 4m, etc are the

    distances from the center plane)

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    Half-Breadth plane (Water plane, Waterline planes):

    parallel to the base plane (2m, 4m, .are the distance

    form the base plane)

    Body Plan (Ordinate station, Transverse section,

    0-10 bow stern (US), 10-0 (UK)): parallel to the mid-

    section (# of stations indicated the distance from the

    mid-section or bow).

    Diagonals (Bilge Diagonal) Fair form and fairness of line, checking the

    consistency of point, smoothness of lines

    Table of Offsets

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    Line Drawing

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    Hull characteristics (coefficients

    (non-dimensional)

    - Coefficient of Form ( Fatness of a hull)

    Block Coefficient CB

    whereL= Lpp or Lbp and T= Draft

    CB 0.38~0.90 even bigger

    - Midship Section Coefficient

    CM = immersed area of mishap section (A) / (BT)

    0.67~0.98

    BC

    LBT

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    -Prismatic or Longitudinal Coefficient: 0.55~0.80

    -Waterplane Coefficient

    -Displacement /Length Ratio

    BP

    M M

    CCL A L B T C C

    area of water plane0.67 - 0.87

    where --Length of Load water plane

    = Beam of W.P.

    WPCLB

    L

    B

    3 3

    BB

    C LBT B TC

    L L L L

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    -Breadth /Length Ratio :

    -Draft/Length Ratio

    -Draft/Breadth Ratio

    -These coefficients are related to the resistance and

    stabilityof the ship and can be used to estimate

    them empirically.

    B

    L

    T

    L

    T

    B

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    Important Hydro-Static Curves or Relations(see Fig. 6-3, pp148)

    Displacement Curves (displacement [molded, total]

    vs. draft, weight [SW, FW] vs. draft (T))

    Coefficients Curves (CB , CM , CP , CWL, vs. T)

    VCB (KB,ZB

    ): Vertical distance of Center of

    Buoyancy (C.B) to the baseline vs. T

    LCB (LCF,XB

    ): Longitudinal Distance of C.B or

    floatation center (C.F) to the midship vs. T

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    StabilityA floating body reaches to an equilibrium state, if

    1) its weight = the buoyancy2) the line of action of these two forces become collinear.

    The equilibrium: stable, or unstable or neutrally stable.

    Stable equilibrium: if it is slightly displaced from its

    equilibrium position and will return to that position.

    Unstable equilibrium: if it is slightly displaced form its

    equilibrium position and tends to move farther away from

    this position.

    Neutral equilibrium: if it is displaced slightly from this

    position and will remain in the new position.

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    Motion of a Ship:

    6 degrees of freedom

    - Surge

    - Sway

    - Heave

    - Roll

    - Pitch

    - Yaw

    Axis Translation Rotationx Longitudinal Surge Neutral S. Roll S. NS. USy Transverse Sway Neutral S. Pitch S.z Vertical Heave S. (for sub, N.S.) Yaw NS

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    Righting & Heeling Moments

    A ship or a submarine is designed to float in the

    upright position.

    Righting Moment: exists at any angle ofinclination where the forces of weight and buoyancy

    act to move the ship toward the upright position.

    Heeling Moment: exists at any angle of inclination

    where the forces of weight and buoyancy act to

    move the ship away from the upright position.

    F di l t hi

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    G---Center of Gravity, B---Center of Buoyancy

    M--- Transverse Metacenter,

    If M is above G, we will have a righting moment, and

    if M is below G, then we have a heeling moment.

    W.L

    For a displacement ship,

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    For submarines (immersed in water)

    G

    B

    G

    If B is above G, we have righting momentIf B is below G, we have heeling moment

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    Static Stability & Dynamical Stability

    Static Stability: Studying the magnitude of the

    righting moment given the inclination (angle) of the

    ship*.

    (That is, the rolling velocity and energy are notconsidered.)

    Dynamic Stability**: Calculating the amount of work

    done by the righting moment given the inclination ofthe ship.

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    Static Stability1. The initial stability (aka stability at small

    inclination) &,2. the stability at large inclinations.

    The initial stability: studies the right moments or right

    arm at small inclination angles (< 5 degree).

    The stability at large inclination (angle): computes theright moments (or right arms) as function of the inclination

    angle, up to a limit angle at which the ship may lose its

    stability (capsizes). (Cross curves of stability (see Fig.

    6-7 at pp 156) & Curves of Static Stability (see Fig. 6-8

    at pp157) )

    The initial stability is a special case of the latter.

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    Initial stability Righting Arm: A symmetric ship is inclined at a small angle

    d. C.B has moved off the ships centerline as the result of the

    inclination. The distance between the action of buoyancy andweight, GZ, is called righting arm.

    Transverse Metacenter: A vertical line through the C.B

    intersects the original vertical centerline at point,M

    .

    sin

    if 1

    Small angle inclination

    5 0.087266

    GZ GM d

    GMd d

    d

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    Location of the Transverse Metacenter

    Transverse metacentric height : the vertical distance

    between the C.G. andM(GM). It is important as anindex of transverse stability at small angles of inclination.

    GZ is positive, if the moment is righting moment. M

    should be above C.G, ifGZ >0.

    If we know the location ofM, we may find GM, and thus the

    righting arm GZ or righting moment can be determined

    given a small angle d.

    Righting Moment = GZ

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    ; the distance from C.B. to

    ( ) the distance from the baseline to .

    ,

    where is the vertical coordinates of the C.B.

    The vertical distance between the metacenter

    x

    M

    xM B

    B

    IBM BM M

    H KM M

    IKM = H = + Z

    Z

    .

    & C.G,

    xM G B G

    IGM H Z + Z Z

    E l f

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    Examples of

    computing KM

    d

    B

    3

    2

    2

    3

    2

    2

    ) Rectangular cross section

    1, ,

    2 12

    12

    12 2

    ) Triangular cross section

    2 1 1, ,

    3 12 2

    6

    2

    6 3

    B x

    x

    B

    B x

    x

    B

    a

    dZ I LB LBd

    I BBM

    d

    B dKM BM Z

    d

    b

    dZ I LB LBd

    I BBM

    d

    B dKM BM Z

    d

    d

    B

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    Ship Resistance (Drag )

    A ship actually moves at the same time through twofluids, water and air, with widely different density.

    While the lower part of the hull is moving through

    water, the upper part is moving through air. Because

    , the air resistance is usually much smaller

    than the water resistance, except for those aerostatic

    support of hydrodynamic support crafts.

    Summary: Water resistance (submerged part of a hull)

    Air resistance (upper part of hull &

    superstructure)

    a w

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    Types of Water Resistances1. Wave-Making Resistance: Waves are generated on

    the surface of water and spread away from a ship.Waves possess energy. Thus a ship making waves

    means a loss of its energy. Wave-making

    resistance is important to surface ships, especially

    those of high speeds.2. Frictional Resistance: arising due to the viscosity

    of water, i.e. tangential stresses. Because of

    viscosity & velocity gradient in the direction normal

    to the ship hull, there is a mass of fluid beingdragged along with a ship. Energy necessary to drag

    the mass of fluid is the work done by the ship

    against the frictional resistance.

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    3. Eddy-making Resistance: Due to the viscosity of the

    fluid, the flow separates from the surface of a hull and

    eddies (vortices) are formed. These eddies induce the

    changes in the velocity field and thus change the

    normal pressures on a hull. The changes in the

    pressure field around a ship result in the eddy-making

    resistance.

    Air resistance (mainly resulting from wind resistance).

    Appendage resistances: are caused by the appendages

    of a ship, such as propellers, rudders and bilge keels.

    R N F R

    T F R air app

    R R R

    R R R R R

    Naked Ship esistance

    Total

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    Computation of Frictional Resistance

    810

    72

    10

    Re /

    (1947 ATTC line)

    0.242log Re , for Re 4.5 10 .

    0.075 , for Re 10log Re 2

    F

    F

    F

    LV

    CC

    C

    Reynolds Number (non - dimensional)

    Schoenherr formula

    1957 ITTC line formula

    2

    .

    1

    2

    F FF V SC Frictional Resistance

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    Influence of Roughness of a plate on CF

    The formulas for computing CF

    are applied to the flat plates with

    smooth surface. The rough surface (of a ship) will result in theincrease ofC

    F. Roughness (on the surface of a hull) may be

    classified into 3 types.

    1. Structural roughness: caused by welded joints, warviness ofshell plating on the hull. A newly-built ship will have

    (for Schoenherr formula).

    2. Corrosion

    3. Fouling: caused by the attachment of marine organisms such as

    seaweeds, shells and barnacles.

    Corrosion & fouling occur for ships having sailed for a certain

    period of time. They will decrease the velocity of the ship. Ship

    owner will decide when the ship should go to the dock for cleaning.

    0.0004fC

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    Wave-Making ResistanceWave-making resistance is important to

    1. a surface ship (negligible for submarine); &2. its speed is high. Accurately speaking, its Froude # ,

    or in U.S. the speed/length ratio, is high.

    It is noticed that the speed to length ratio is a dimensional

    coefficient, where Vis in knots,L in feet.

    A nautical mile/hr (knot) = 0.5144 m/s.

    R

    VF

    gL

    V

    L

    6

    2

    R

    1 is equivalent to 0.3

    When 0.1, & is negligible.

    When 0.45, , is dominant in .

    1R ( determined via model tests)

    2

    R

    R W W

    R W W T

    W W

    VF

    L

    F C R

    F C V R R

    V SC C

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    Ship Wave Pattern

    Lord Kelvin (1887) considered a single pressure point traveling

    in a straight line over the surface of the water, sending outwaves which combine to form a characteristic pattern.

    Transverse Waves

    Divergence Waves

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    Ship Wave Pattern

    Kelvin wave pattern illustrates and explains many of the

    features ofship waves. Ship wave pattern is similar to the

    combination of two Kelvin wave systems generated by two

    pressure points, with one near the bow and the other near the

    stern.

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    Wave pattern of a ship

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    Wave pattern behind a moving duck

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    Wave Pattern of a small boat (divergence wave pattern)

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    Wave Pattern of a small boat (divergence wave pattern)

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    A Towing Carriage and A Ship Model

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    A Towing Carriage

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    Overview of MarinTeks Shop Model Tank (Norway)

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    Propulsive Devices

    Paddle-Wheels: While the draft varying with ship displacement,

    the immersion of wheels also varies. The wheels may come out

    of water when the ship is rolling, causing erratic course-keeping,

    & they are likely to damage from rough seas.

    Propellers: Its first use was in a steam-driven boat at N.Y. in1804. Advantages over paddle-wheels are,

    1) not substantially affected by normal changes in draft;

    2) not easily damaged;

    3) decreasing the width of the ship, &4) good efficiency driven by lighter engine.

    Since then, propellers have dominated in use of marine

    propulsion.

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    Paddle Wheels Propulsion (Stern)

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    Paddle Wheels Propulsion (Midship)

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    Propeller (5-blade)

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    Propeller (5-blade)& Rudder

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    Jet type: Water is drawn by a pump & delivered sternwards as a

    jet at a high velocity. The reaction providing the thrust. Its use

    has been restricted to special types of ships.

    Other propulsion Devices:

    1. Nozzles (Duct) Propellers: main purpose is to increase the

    thrust at low ship speed (tug, large oil tanker)2. Vertical-Axis Propellers: Advantage is to control the direction

    of thrust. Therefore, the ship has good maneuverability.

    3. Controllable-Pitch Propellers (CCP): The pitch of screw can

    be changed so that it will satisfy all working conditions.4. Tandem and Contra-rotating Propellers: It is used because

    the diameter of a propeller is restricted due to limit of the draft

    or other reasons (torpedo). The efficiency of the propeller

    usually decreases.

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    Jet Propulsion

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    Nozzle Propellers

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    Vertical-Axis Propellers

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    Vertical-Axis Propellers

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    Controllable Pitch Propellers (CPP)

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    Contra-rotating Propellers

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    Type of Ship Machinery (Engine)

    1.Steam Engine

    2.Steam Turbine

    3.Internal combustion engines (Diesel engine)

    4. Gas Turbines

    5. Nuclear reactorsturbine

    Engine (Brake) Power: Measured at right behind the

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    Engine (Brake) Power: Measured at right behind the

    enginePB

    Delivered horsepower (PD

    ): the power delivered to the

    propeller.

    Thrust horsepower (PT):

    =

    - Efficiency of the Propeller in open water

    - Thrust delivered by the propeller

    - Advancing velocity of the propeller

    T D O A

    O

    A

    P P T V

    T

    V

    Efficiency of the shaft

    transfer energy from the engine to the propeller

    D B S SP P

    Effective horsepower (P or EHP):

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    Effective horsepower (PE

    , or EHP):

    RTtotal resistance

    Vsadvance velocity of ship

    / = =

    - quasi-propulsive coefficient (efficiency)

    - Hull coefficient (efficiency)

    E T S

    S TE T H

    A

    E E TD H R O H O

    D T D

    D

    H

    P R V

    V RP P

    V TP P P

    P P P

    Propulsion Efficiency

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    Propulsion Efficiency

    Total propulsion efficiency

    can also be replaced by or

    A more meaningful measure of hydrodynamic performance

    of a propeller is: a quasi-propulsive coefficient,

    ,

    , where is the shaft

    ET S B I

    S

    D

    ED

    D

    DS S

    S

    P P P PP

    P

    P

    P

    P

    transmission efficiency

    and thus, .

    - 98% for ships with main engine aft

    - 97% for ships with main engine amidship

    T D S

    S