1 2 Ship Resistance Components Mm545 Sep2012

7/31/2019 1 2 Ship Resistance Components Mm545 Sep2012

1/33

Ship Resistance and Powering

Ship Resistance

Components

MM545 M.A. Kotb

9/29/2012 1


2/33


MM545 M.A. Kotb

9/29/2012 2

Ships operate on the interface between air and water

AIR=1.2 kg/m3

Under water part

Above water part

Weight

Buoyancy

Air-WaterInterfacep=patm=const

Water=1000 kg/m3


3/33


MM545 M.A. Kotb

9/29/2012 3

When the Ship is not moving (just floating)

AIR

Air-WaterInterface

Water

Weight

Buoyancy

and water and air is still ..


4/33


MM545 M.A. Kotb

9/29/2012 4

No motion No Resistance

AIR

Air-WaterInterface

Water

Weight

Buoyancy

When the Ship is not moving (just floating)


0xF

0

0

WB

Fz

x

z


5/33


MM545 M.A. Kotb

9/29/2012 5

Now get ready the Ship is about to move

AIR

Air-WaterInterface

Water

What do we observe ?

Weight

Buoyancy



6/33


MM545 M.A. Kotb

9/29/2012 6

Observations

Water

Water rubbing against the ships surface

AIR

Air-WaterInterface

Weight

Buoyancy

Still water is no longer still

Waves are generated

Eddies are formed

water rubbing


7/33


MM545 M.A. Kotb

9/29/2012 7

making resistance-Wave


8/33


MM545 M.A. Kotb

9/29/2012 8


9/33


MM545 M.A. Kotb

9/29/2012 9


10/33


11/33


MM545 M.A. Kotb

9/29/2012 11

Resistance to ship motion1. Resistance coming from Air

2. Resistance coming from water

Air-WaterInterface

AIR

Waves are generated

Eddies are formed

Water

3. Resistance coming air water interface


12/33


MM545 M.A. Kotb

9/29/2012 12

Resistance to ship motion1. Resistance coming from Air


Air-WaterInterface

AIR

Waves are generated

Eddies are formed

Water


Neglect due to low density


13/33


MM545 M.A. Kotb

9/29/2012 13

Resistance to ship motion


Air-WaterInterface

AIR

Waves are generated

Eddies are formed

Water


Frictional Resistance RF

Eddy makingResistance RE

Wave makingl Resistance RW


14/33


MM545 M.A. Kotb

9/29/2012 14

Skin Frictional ResistanceEddy Making Resistance

Frictional Resistance and Eddy Making Resistance


15/33


MM545 M.A. Kotb

9/29/2012 15

Total Ships Resistance

Skin FrictionalResistance RF

Eddy MakingResistance REMR

Wave MakingResistance RWMR

Rtotal = RF +REMR +RWMR


16/33


MM545 M.A. Kotb

9/29/2012 16

Total Ships Resistance

Skin FrictionalResistance RF

Eddy MakingResistance REMR

Wave MakingResistance RWMR

Rtotal = RF +REMR +RWMRResiduaryResistance RR Rtotal = RF +RR


17/33


MM545 M.A. Kotb

9/29/2012 17

Total Resistance

RF

RR

RT= RF + RR

VS


18/33


MM545 M.A. Kotb

9/29/2012 18

AIR

Air-WaterInterface

Water

Thank You for Your Attention!


19/33


Factors Affecting Ship

Resistance

MM545 M.A. Kotb

9/29/2012 19


20/33


MM545 M.A. Kotb

9/29/2012 20

Total Resistance

RF

RR

RT= RF + RR

VS


21/33


MM545 M.A. Kotb

9/29/2012 21

Factors Affecting Ship Resistance

Neglected abovewater part

Still water

RT= f(x1, x2, x3, ....)

What are x1,x2,x3,etc ?

Under the assumption Assume

The Question isAIR

Air-Water

Interface

VS

WaterRT


22/33


MM545 M.A. Kotb

9/29/2012 22


AIR

Air-Water

Interface

Water

RT

VS

1.Ship Speed Vs

L

2.Ship Size L

Density

3.Water density

Viscosity

4.Water Viscosity

G

ravityg

5.Gravity g

Pressure p

6.Water Pressure p


23/33


MM545 M.A. Kotb

9/29/2012 23


AIR

Air-Water

Interface

Water

RT

VS

a

TR rfedcba

pgLVR mrb

T VR

c

T LR d

TR m

e

T gR f

T pR

Hence,


24/33


MM545 M.A. Kotb

9/29/2012 24


fedcba

T pgLVR mr

AIR

Air-Water

Interface

Water

VS

Gravityg

RT

LDensity

Viscosity

Pressure p


25/33


MM545 M.A. Kotb

9/29/2012 25


Define

m

r LV

R

s

n

Non dimensional quantity

Reynold Number AIR

Air-WaterInterface

Water

RT

VS

LViscosity

Gravity

g

Pressure pDensity


26/33


MM545 M.A. Kotb

9/29/2012 26


Define

gL

VF sn


Froudes Number

VS

Gravityg

AIR

Air-WaterInterface

Water

RT

Viscosity

Pressure pDensityL


27/33


MM545 M.A. Kotb

9/29/2012 27


Define

2

5.0 s

TT

SV

RC

r

Total Resistance Coeff.


Wetted Surface Area SAIR

Air-Water

Interface

Water

VS

Gravityg

LDensity

Viscosity

Pressure pRT


28/33


MM545 M.A. Kotb

9/29/2012 28


Using Dimensional Analysis

fedcbaT pgLVR mr

Can be written as:AIR

Air-Water

Interface

Water

VS

Gravityg

RT

LDensity

Viscosity

Pressure p


29/33


MM545 M.A. Kotb

9/29/2012 29


gLVLVf

SVR ss

s

T ,5.0

2m

r

r

CTRn Fn

nnT FRfC ,

Hence,


30/33


MM545 M.A. Kotb

9/29/2012 30

Total Resistance

RFT RRR

Divide by

2

5.0 sSVr

2225.05.05.0 s

R

s

F

s

T

SV

R

SV

R

SV

R

rrr

RFT CCC


31/33


MM545 M.A. Kotb

9/29/2012 31


nnT FRfC ,

RFT CCC Hence,

nF RfC nR FfC

Recall,

But

and,


32/33


MM545 M.A. Kotb

9/29/2012 32


FsF

s

FF

CSVR

SV

RC

2

2

5.0

5.0

r

r

nF

RfC nR

FfC

RsR

s

RR

CSVR

SV

RC

2

2

5.0

5.0

r

r

Frictional Resistance Residuary Resistance


33/33


MM545 M.A. Kotb

9/29/2012 33

AIR

Air-WaterInterface

Water

Thank You for Your Attention!

1 2 Ship Resistance Components Mm545 Sep2012

Documents

Transcript of 1 2 Ship Resistance Components Mm545 Sep2012