[2008]
[2008] [01 [01- -2][02 2][02- -1][02 1][02- -2] 2]
Planning Procedure of Naval Architecture Planning Procedure of Naval Architecture
& Ocean Engineering
& Ocean Engineering
& Ocean Engineering
& Ocean Engineering
September, 2008 September, 2008 Prof.
Prof. Kyu Kyu- -Yeul Yeul Lee Lee
Department of Naval Architecture and Ocean Engineering Department of Naval Architecture and Ocean Engineering Department of Naval Architecture and Ocean Engineering, Department of Naval Architecture and Ocean Engineering,
Seoul National University of College of Engineering Seoul National University of College of Engineering
2008_Hydrostatic pressure and Force(Moment) on a floating body 2008_Hydrostatic pressure and Force(Moment) on a floating body 2008_Hydrostatic pressure and Force/Moment on a floating body 2008_Hydrostatic pressure and Force/Moment on a floating body
Part 1. Stability & Trim [01
[01- -2],[02 2],[02- -1],[02 1],[02- -2] 2]
Hydrostatic Pressure and Force/Moment Hydrostatic Pressure and Force/Moment Hydrostatic Pressure and Force/Moment Hydrostatic Pressure and Force/Moment on a floating body
on a floating body
2008_Hydrostatic pressure and Force(Moment) on a floating body
2008_Hydrostatic pressure and Force(Moment) on a floating body NAOE/SNU 2008_Hydrostatic pressure and Force/Moment on a floating body
2008_Hydrostatic pressure and Force/Moment on a floating body
부력
부력(Buoyancy) (Buoyancy)
“Archimedes Principle”
“Archimedes Principle”
Archimedes’ Principle
Archimedes Principle Archimedes Principle
y “유체 속에 있는 물체가 받는 부력의 크기는 그 물체가 밀어낸 유체의 무게와 같고 그 방향은 중력과 반대 방향이다”
① 아르키메데스의 원리
물체의 부력 = 물체가 밀어낸 유체의 중량(배수량; Displacement)
② 평형 상태 이 물체에 작용하는 모든 합력과 모멘트가 W
② 평형 상태 ( 이 물체에 작용하는 모든 합력과 모멘트가 0) 물체의 부력 - 물체의 중량=0
③ ∴배수량 = 물체의 중량
gV W = ρ
−
= Δ
G: 중심, B: 부심 W 중력 Δ 부력
G
W: 중력, Δ: 부력 B
ρ: 유체의 밀도
V: 유체 속에 잠겨있는 물체의 부피
B
Δ
2008_Hydrostatic pressure and Force(Moment) on a floating body 2008_Hydrostatic pressure and Force(Moment) on a floating body 2008_Hydrostatic pressure and Force/Moment on a floating body 2008_Hydrostatic pressure and Force/Moment on a floating body
물체의 부피 Δ
압력의
압력의 개념을 개념을 도입한 도입한 부력계산 부력계산
※ 압력(Pressure) : 단위 면적에수직으로 작용하는 힘 즉, 힘을 구하기 위해서는 압력에 면적과
그 작용면의 법선 벡터(Normal Vector)를 곱해야 함
좌표계 설정에 따라 값이 이므로 를 붙임
9 아래 물체에 작용하는 수직방향의 정적인 힘은?
: 물체 윗면의 미소 면적에 작용하는 힘
dS P
d F
Top=
Top⋅ n
1⎟⎟ ⎞
⎜⎜ ⎛ P
Top= P
atm− ρ g ⋅ 0
좌표계 설정에 따라 z값이 (-)이므로( -)를 붙임 Æ 아래쪽으로 갈수록 압력이 커짐
z
y
atm
Top
P
P =
n
1: Normal vector⎟⎟ ⎠
⎜⎜ ⎝ n
1= k −
h y
Bottom
P
dS
: Areagz
P
P =
atm− ρ
dS P
d F = ⋅ n ⎟⎟ ⎠
⎜⎜ ⎞
⎝
⎛
=
−
= k n
gh P
P
Bottom atmρ
dS P
d F
Bottom=
Bottom⋅ n
2: 물체 아랫면의 미소 면적에 작용하는 힘
⎠
⎝ n
2= k d
d
d F = F
Top+ F
Bottom∫∫
∫ ( P P ρ gz )
) (
) (
2 1
dS gh P
dS P
dS P
dS P
atm atm
Bottom Top
Bottom Top
− +
−
=
⋅ +
⋅
=
ρ k k
n n
∫∫
−
= ρ g n zdS
∫∫
∫ =
=
SB
dS P
d F n
F , ( P = P
static= − ρ gz )
선형화 한 Bernoulli eq.
전체 정적 압력에서 대기압을 뺀 순수 유체 정압력
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) ( gh dS dS
gh = − ⋅
−
= ρ k k ρ
: 대기압에 의한 힘이 서로 상쇄됨
∫∫
SB
dS ρ g
ρgz t
P ∂
Φ
− ∂
−
= ρ
선형화 한 Bernoulli eq.
static
P P
dynamicgz P
gz
P
atm− ρ ) −
atm= − ρ
(
선박에
선박에 작용하는 작용하는 유체의 유체의 정적 정적 압력 압력(Hydrostatic pressure) (Hydrostatic pressure)과 과 부력 부력(Buoyancy) (Buoyancy) -
-수학적 수학적 접근 접근
좌현으로 기울어진 상태
(선박을 정면에서 바라봄)
Hydrostatic force (Surface force)
: 표면에 작용하는 모든 힘을 적분하여 구함
9 미소 면적에 작용하는 힘 :
( : wetted surface)
S ′
dS P
d P
d F = ⋅ S = ⋅ n
9 미소 면적에 작용하는 힘 :
( : wetted surface)
S
Bξ z z′
y 여기서 P는 hydro static pressure, P
static이다.
9 T t l f
r S d
ξ
4y′
O O′
S
Bd F = P
static⋅ n dS = − ρ gz ⋅ n dS
gz P
P =
static= − ρ
∫∫
−
=
SB
dS z
g n
F ρ
∫∫
=
SB
dS Pn F
9 Total force :
S
d
( : wetted surface)S
B Hydrostatic Moment : (모멘트)=(거리) X (힘)
B B
9 미소 면적에 작용하는 모멘트 : dS
P Pd
d F = S = n
(미소 면적에 작용하는 힘)
P P =
t ti( ) dS
P dS
P d
d M = r × F = r × n = r × n
9 Total moment : r
F r
M d
d = ×
(미소 면적)(미소면적에 작용하는 모멘트)
dS gz P
P
staticρ n
−
=
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( )
∫∫ ×
−
=
SB
dS z
g r n
M ρ
( )
∫∫ ×
=
SB
dS P r n M
r
왜 r이 먼저 오는가? (좌표축에서 양의 방향을 고려함)
작용하는 모멘트)
선박에
선박에 작용하는 작용하는 유체의 유체의 정적 정적 압력 압력(Hydrostatic pressure) (Hydrostatic pressure)과 과 부력 부력(Buoyancy) (Buoyancy) -
-수학적 수학적 접근 접근
9 Hydrostatic force (Surface force)
∫∫
−
= g z n dS F ρ
1) Erwin Kreyszig, Advanced Engineering Mathematics 9th,Wiley,Ch10.7(p458~463) 2) Erwin Kreyszig, Advanced Engineering Mathematics 9th,Wiley,Ch9.9(p414~417)
( : wetted surface)
S
∫∫
SB
dS ρ g
⎞
⎛
divergence theorem
1)사용하면,
( : wetted surface)
S
∫∫∫ ⎜ ⎛ ∂ z ∂ z ∂ z ⎟ ⎞
⎟⎟ ⎠
⎜⎜ ⎞
⎝
⎛ ∫∫ ⋅ = ∫∫∫ ∇
V S
fdV dA
f n
∫∫∫ ∇
2)=
V
zdV ρ g
F ⎟⎟ ⎠
⎜⎜ ⎞
⎝
⎛ =
∂ + ∂
∂ + ∂
∂
= ∂
∇ i j k k
z z y
z x
z z
∫∫∫
= k ρ g dV
2)
: 물에 잠긴 물체의 부피에 해당하는 물의 무게를 수면과 수직 방향으로 받음
∫∫∫
V) gV (t ρ
= k
선박의 운동 시, 시간에 따라 배수 용적V가달라지므로, V는 시간에 대한 함수 V(t)임
(≒아르키메데스의 원리)
※ (-)부호가 사라진 이유
: Divergence theorem은 면의 외향 단위 벡터를 기준으로 한다
2008_Hydrostatic pressure and Force(Moment) on a floating body
2008_Hydrostatic pressure and Force(Moment) on a floating body NAOE/SNU 2008_Hydrostatic pressure and Force/Moment on a floating body
2008_Hydrostatic pressure and Force/Moment on a floating body
: Divergence theorem은 면의 외향 단위 벡터를 기준으로 한다.
부력 계산시 사용하는 Normal vector는 내향 단위 벡터이므로,
(−)를 곱한 뒤, Divergence theorem을 적용해야 한다.
유체입자에
유체입자에 작용하는 작용하는 압력 압력//힘 힘
① 뉴턴 유체(Newtonian fluid)③ 비점성 유동(Invicid flow)
④ 비회전 유동(Irrotational flow) 9Assumption
②Stokes Assumption
1) RTT : Reynold Transport Theorem 2) SWBM : Still Water Bending Moment 3) VWBM : Vertical Wave Bendidng Moment
FF.K: Froude- krylov force FD: Diffraction force FR: Radiation force
2 2
, :
dt d dt
d x
x a V x
=
=
변위 따른 시간에 유체입자의
9유체입자의 운동방정식 Newton’s 2
ndLaw
④ 비회전 유동(Irrotational flow)
전단 응력 Curl과 회전
Lagrangian &
Eulerian Description
y
z
M
유체입자3자유도 (회전 3자유도 X)
3) VWBM : Vertical Wave Bendidng Moment dt2
dt
Cauchy equation
Navier-Stokes equation
Euler equation
Bernoulli equation Newton s 2 Law
= ∑
Pmx F
, ,
body P surface P
= F + F
P 1 Mass ∂Φ
2
Φ 0
∇
L l
③
②④
④
① ,②
m
M
유체입자 (P)Particle 6자유도
(S)Ship
1
22 ( )
P g z F t
t ρ
∂Φ + + ∇Φ + =
∂ Mass
Conservation Law
2
Φ = 0
∇
Laplace Equation
미시적 유도/
거시적 유도(RTT1))
Velocity potential
( V = ∇ Φ )
2008_Hydrostatic pressure and Force(Moment) on a floating body 2008_Hydrostatic pressure and Force(Moment) on a floating body
7
유체
유체 입자의 입자의 운동 운동 방정식 방정식 정리 정리
(Cauchy eq. ~ Bernoulli eq.)
(Cauchy eq. ~ Bernoulli eq.)
1) 전단응력이 전단변형율(의 시간변화율)에 비례하는 유체 2) 선형 변형과 등방 팽창에 의한 점성 계수 μ,λ의 관계식을 정의함(Cauchy eq Bernoulli eq ) (Cauchy eq Bernoulli eq )
① 뉴턴 유체
1)(Newtonian fluid)
Cauchy Equation : d
ρ dt V = ρ + ∇ • σ
g , ( V = [ u v w , , ]
T)
) 선형 변형과 등방 팽창에 의한 점성 계수 μ, 의 관계식을 정의함
= 0
•
∇
∂ +
∂ ρ ρ V t
Continuity
Equation
(질량보존)① 뉴턴 유체
)(Newtonian fluid)
Navier-Stokes Equation :
(in general form) 1 ( )
23
d P
ρ dt = ρ − ∇ + μ ⎛ ⎜ ⎝ ∇ ∇ + ∇ ⎞ ⎟ ⎠
V g i V V
② Stokes assumption
2)∇ V 0
⑦ incompressible flow constant 0
t ρ = ⎛ ⎜ ⎝ ∂ ∂ ρ = ⎞ ⎟ ⎠
③ 비점성 유동 (Invicid flow) Euler Equation : ρ d V = g ρ − ∇ P
(in general form) dt ⎝ 3 ⎠
( μ = 0 ) ∇ V • ⑥ = irrotational flow 0
( V = ∇Φ )
Euler Equation : P L l
dt ρ g ∇ ρ
④ barotropic flow
( ) P ρ ρ =
Euler Equation : ∂ V ∇ B
V ⎛ ⎜ B 1
2+ + ∫ dP
2 2+ +
2 2⎞ ⎟
Laplace
Equation ∇
2Φ = 0
⑤ Steady flow ⑥ Unsteady, irrotational flow t 0
⎛ ∂ = ⎞
⎜ ∂ ⎟
⎝ ⎠
V
2 2
, 0
q
⎛ = ∇Φ ⎞
⎜ ⎟
⎜ = ∇Φ = ⎟
⎝ ⎠
V
ω Euler Equation :
(Another form) B
t + ∇ = ×
∂ V ω ,
2,
2 2 2 2B 2 q gy q u v w
= + + ρ = + +
⎜ ⎟
⎝ ∫ ⎠
Bernoulli equation
(case1)
Constant
B = Bernoulli
equation
(case2)
1
22 ( )
gy dP F t
t ρ
∂Φ + ∇Φ + + =
∂ ∫
⎝ ⎠
1
22
q gy dP C
ρ
⎛ ⎞
+ + =
⎜ ⎟
⎝ ∫ ⎠
⑦ Incompressible flow
( ρ = constant )
Newtonian fluid Stokes assumption Invicid flow
Unsteady flow
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along streamlines and vortex lines
( ρ constant ) ⑦ Incompressible flow Bernoulli
equation
(case3)
1
22 ( )
gy P F t
t ρ
∂Φ + ∇Φ + + =
∂
y
Irrotational flow
Incompressible flow
Bernoulli equation
Bernoulli equation의 의 F(t) F(t)의 의 의미와 의미와 계기 계기 압력 압력 1) 1)
1) 계기 압력 : 전체 압력에서 대기압을 뺀 압력
Bernoulli Equation z
atm
Top
P
P = 1
22 ( )
P g z F t
t ρ
∂Φ + + ∇Φ + =
∂
☞ 항등식
h y
항등식 P
9 만약 정적인 상태인 경우를 고려하면
⎞
⎛ Φ ∂
Bottom
P
P ( )
g z F t
+ =
⎟ ⎠
⎜ ⎞
⎝
⎛ = ∇ Φ =
∂ Φ
∂ 0 , 0
0 t
= Φ
1
22
Bottom atm
P P
t ρ gz ρ
∂Φ + + ∇Φ + =
∂
9 물체 바닥에서의 압력은?
g z F t ( ) ρ + =
항등식 이므로 , z = 0 일 때도 성립 P
ρ ρ
1
22
atm Fluid atm
P P P
+ gz
∂Φ + + ∇Φ + =
( ) ∂
P
atmρ = F t
z=0일 때 압력 = 대기압(Patm)
1
22 0
Fluid
P gz
t ρ
∴ ∂Φ + + ∇Φ + =
∂
2 g
t ρ ρ
∂
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1
22
P
atmP g z
t ρ ρ
∴ ∂Φ + + ∇Φ + =
∂
‘계기 압력’
※ Bernoulli equation에서 우변 F(t)=0 으로 표기한 경우, 압력 P는 대기압을 뺀 유체만의 압력임을 의미함
9
유체입자에
유체입자에 작용하는 작용하는 압력 압력//힘 힘
① 뉴턴 유체(Newtonian fluid)③ 비점성 유동(Invicid flow)
④ 비회전 유동(Irrotational flow) 9Assumption
②Stokes Assumption
1) RTT : Reynold Transport Theorem 2) SWBM : Still Water Bending Moment 3) VWBM : Vertical Wave Bendidng Moment
FF.K: Froude- krylov force FD: Diffraction force FR: Radiation force
2 2
, :
dt d dt
d x
x a V x
=
=
변위 따른 시간에 유체입자의
9유체입자의 운동방정식 Newton’s 2
ndLaw
④ 비회전 유동(Irrotational flow)
전단 응력 Curl과 회전
Lagrangian &
Eulerian Description
y
z
M
유체입자3자유도 (회전 3자유도 X)
3) VWBM : Vertical Wave Bendidng Moment dt2
dt
Cauchy equation
Navier-Stokes equation
Euler equation
Bernoulli equation Newton s 2 Law
= ∑
Pmx F
, ,
body P surface P
= F + F
Mass L l
③
②④
④
① ,②
m
M
유체입자 (P)Particle 6자유도
(S)Ship
P 1
∂Φ
2
9유체력 계산 Mass
Conservation Law
Laplace Equation
Velocity potential
미시적 유도/
거시적 유도(RTT1))
1
22 ( )
P g z F t
t ρ
∂Φ + + ∇Φ + =
0 ∂
2
Φ =
∇ ( V = ∇ Φ )
Linearization
Φ
R
∂
D I T
Φ +
Φ +
Φ
=
Φ
(Incident wave potential) (Diffraction velocity potential) (Radiation velocity potential)⎟⎠
⎜ ⎞
⎝
⎛ ∇Φ =0 2
1ρ 2
∫∫
SPn dS ρgz t
P
T∂ Φ
− ∂
−
= ρ
Fluid
=
F = F
static+ F
F.K+ F
D+ F
R( : wetted surface)
S
B∫∫
SB2008_Hydrostatic pressure and Force(Moment) on a floating body
2008_Hydrostatic pressure and Force(Moment) on a floating body NAOE/SNU
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파랑
파랑 중 중 선박이 선박이 받는 받는 힘 힘
1) Erwin Kreyszig, Advanced Engineering Mathematics, Wiley, 2005, Ch 12.1 (pp 535~538)
2
Φ = 0
∇ , ( V = ∇ Φ )
9 Laplace Equation
2 0
2 2 2 2
2Φ+∂ Φ+∂ Φ =
∂
9 파랑 중 선박 주위 유체의 운동
: 유체장의 운동으로 인해 유체 입자의 속도,가속도,압력이
y z
y z
2 2
2 ∂ ∂
∂x y z
장 동 , ,
변하게 되고, 선박 표면의 유체 입자가 선박에 가하는 압력도 변하게 된다.
정지상태 교란
선형화
1)된 wave로 분해
9 입사파가 선박에 의해 교란되지 않는다고 가정함
9 Total Velocity Potential
Incident wave velocity potential( ) Φ
Iz
+
9 입사파가 선박에 의해 교란되지 않는다고 가정함
Ä 입사파에 의한 velocity potential Φ
T= Φ
I+ Φ
D+ Φ
RSuperposition Theorem
L l ti 은 선형
y
+
9 선박의 존재로 인하여 교란된 파(wave). 물체 고정 Ä 산란파에 의한 velocity potential
Fixed
Diffraction velocity potential
( ) Φ
DLaplace equation은 선형
방정식이므로, 각의 해를 더한 것 (superposition)도 해가 된다
1).
y z
+
Radiation velocity potential
( ) Φ
R2 2 2
2 2 2
0
x y z
∂ Φ ∂ Φ ∂ Φ + + =
∂ ∂ ∂
2 2
∂ Φ ∂ Φ
z
2008_Hydrostatic pressure and Force(Moment) on a floating body 2008_Hydrostatic pressure and Force(Moment) on a floating body
9 정수 중에서 선박의 강제 진동으로 인해 발생하는 파 (wave)
Ä 기진력에 의한 velocity potential
11
2 2
0
y z
∂ Φ ∂ Φ + =
∂ ∂
y
선박에
선박에 작용하는 작용하는 유체력 유체력
R D I
Φ Φ
Φ
: Incident wave velocity potential : Diffraction potential: Radiation potential
FF.K: Froude- krylov force FD: Diffraction force FR: Radiation force
2
Φ = 0
0 ∇
1 ∇ Φ
2Φ
∂ P
9 Bernoulli Equation 9 Laplace Equation
y z
2 ∇ Φ + = 0 +
∂ + P ρgz
t ρ
ρ
Linearization
R D
I + Φ + Φ
Φ
= Φ
Linear combination
ρgz
P ∂
Φ
− ∂
−
= ρ
Linearization
⎟ ⎠
⎜ ⎞
⎝
⎛
∂ Φ + ∂
∂ Φ + ∂
∂ Φ
− ∂
−
= ρgz ρ
I D RLinear combination
of Basic solutions Basic solutions
Fluid
P ρg t
ρ ∂ ⎟
⎜ ⎠
⎝ ∂ t ∂ t ∂ t ρg ρ
static
= P
dS P d F = n
dS
R D
K
F
P P
P + +
+
.유체입자가 표면에 작용하는 압력
P
Fluid
하나의 유체 입자가
F
d = F
static+ F
F K+ F
D+ F
Rdynamic
P
Fluid
∫∫ P
Fluid
= n dS
: 하나의 유체 입자가
F
선박 표면에 가하는 힘
dS F d
: 미소 면적
n
: 미소 면적의 Normal 벡터R D
K F
static .
선박의 침수 표면 전체에 대하여 적분
(유체입자가 선박에 작용하는 힘과 모멘트)
( : wetted surface)S
BFluid
∫∫
SB Fluid2008_Hydrostatic pressure and Force(Moment) on a floating body
2008_Hydrostatic pressure and Force(Moment) on a floating body NAOE/SNU 2008_Hydrostatic pressure and Force(Moment) on a floating body
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(유체입자가 선박에 작용하는 힘과 모멘트)
9 유체입자 하나에 작용하는 Body force 와 Surface force로부터 구한 압력을 선박
의 침수 표면 전체에 대해 적분하여 선박에 작용하는 유체력을 계산함
선박의
선박의 6 6자유도 자유도 운동 운동 방정식 방정식 유도 유도
① 뉴턴 유체(Newtonian fluid)③ 비점성 유동(Invicid flow)
④ 비회전 유동(Irrotational flow) 9Assumption
②Stokes Assumption
1) RTT : Reynold Transport Theorem 2) SWBM : Still Water Bending Moment 3) VWBM : Vertical Wave Bendidng Moment
FF.K: Froude- krylov force FD: Diffraction force FR: Radiation force
2 2
, :
dt d dt
d x
x a V x
=
=
변위 따른 시간에 유체입자의
9유체입자의 운동방정식 Newton’s 2
ndLaw
④ 비회전 유동(Irrotational flow)
전단 응력 Curl과 회전
Lagrangian &
Eulerian Description
y
z
M
유체입자3자유도 (회전 3자유도 X)
3) VWBM : Vertical Wave Bendidng Moment dt2
dt
Cauchy equation
Navier-Stokes equation
Euler equation
Bernoulli equation Newton s 2 Law
= ∑
Pmx F
, ,
body P surface P
= F + F
Mass L l
③
②④
④
① ,②
m
M
유체입자 (P)Particle 6자유도
(S)Ship
P 1
∂Φ
2
9선박의 6자유도 운동 방정식 9유체력 계산
Mass Conservation
Law
Laplace Equation
Velocity potential
미시적 유도/
거시적 유도(RTT1))
1
22 ( )
P g z F t
t ρ
∂Φ + + ∇Φ + =
0 ∂
2
Φ =
∇ ( V = ∇ Φ )
① Coordinate system 정의 (
Global & Body-fixed coordinate)
Linearization
Φ
R
∂
D I T
Φ +
Φ +
Φ
=
Φ
(Incident wave potential) (Diffraction velocity potential) (Radiation velocity potential)② Newton’s 2
ndLaw
∑
⎟⎠
⎜ ⎞
⎝
⎛ ∇Φ =0 2
1ρ 2
ρgz t
P
T∂ Φ
− ∂
−
= ρ
= ∑
SMx F = F
body S,+ F
surface S,R D K
F t ti
it
F F F F
F + + + +
=
Fluid
gravity
F
F +
= F
Fluid= ∫∫
SPn dS = F
static+ F
F.K+ F
D+ F
R( : wetted surface)
S
BR D K
F static
gravity
F F F F
F + +
.+ +
x B x A F
F + − −
=
restoring exciting( M + A ) x + B x = F
restoring+ F
exciting9Shear force(S.F.) 및 bending moment(B.M.)
( M + A ) a
z(x )
z
x
Sh f (S F ) 계산 (az: z방향 가속도)
∫∫
SB2008_Hydrostatic pressure and Force(Moment) on a floating body 2008_Hydrostatic pressure and Force(Moment) on a floating body
( )
restoring excitingcf) 선형화 된 복원력
( M + A ) x + B x + Cx = F
exciting) ( F
restoring= − Cx
) ( )
( )
( x F x Bv x
F
restoring+
exciting−
zShear force(S.F.) 계산 Ð(적분) Bending moment(B.M.) ( z
(vz : z방향 속도) .
S.F
B .M .
x1
z방향
성분 13
선박의
선박의 6 6자유도 자유도 운동 운동 방정식 방정식 유도 유도
R D I
Φ Φ
Φ
: Incident wave velocity potential : Diffraction potential: Radiation potential
FF.K: Froude- krylov force FD: Diffraction force FR: Radiation force
9 선박에 작용하는 유체력
R D
K F static
Fluid S
B
dS
P n F F F F
F = ∫∫ = +
.+ +
y z
B
9 선박의 6자유도 운동방정식
: 유체입자 하나에 작용하는 (Body force) 와 (Surface force)로부터 구한 압력을 선박의 침수 표면 전체에 대해 적분하여 선박에 작용하는 유체력을 계산함
9 선박의 6자유도 운동방정식
Newton’s 2
ndLaw
=
= ∑ F
x
M (Body Force) + (Surface Force)
선박의 Surface force로 작용
dS P d F = n
dS
Surface force
Body force
기타 외부에서 작용하는 외력Fluid
gravity
F
F +
= + F
external: 하나의 유체 입자가 선박 표면에 가하는 힘
F d
R D
K F
static
F F F
F +
.+ +
Gravity
+
= F x M
Restoring
F F
waveexcitingF
R= − M
Ax − B x
added Damping
static external dynamic
external,
F
,F +
+
dS
: 미소 면적n
: 미소 면적의 Normal 벡터static external dynamic
external A
exciting wave static
gravity
)
, ,( F F F M x B x F F
x
M = + + − − + +
added mass
Damping Coefficient
[ x y z φ θ ψ ]
T= x
2008_Hydrostatic pressure and Force(Moment) on a floating body
2008_Hydrostatic pressure and Force(Moment) on a floating body NAOE/SNU 2008_Hydrostatic pressure and Force/Moment on a floating body
2008_Hydrostatic pressure and Force/Moment on a floating body
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( M + M
A) x + B x + Cx = F
waveexciting+ F
external,dynamic+ F
external,staticLinearization
, ( F
restoring= ( F
gravity+ F
static) ≈ − Cx )
[ x , y , z , φ , θ , ψ ]
= x
heave z
sway y
surge x
: : :
yaw pitch roll
: : : ψ θ φ
matrix coeff.
restoring 6 6 :
matrix coeff.
damping 6 6 :
matrix mass added 6 6 :
×
×
× C B MA
Ex) Heave motion of ship
Ex) Heave motion of ship – – step 1 step 1
9
Mass-Spring-Damper system
Z
X
g M
k
p g p y
① k
m z F =
m : mass
m
g
z
kmz F
gravity
= F
= − mg k
′′
mg
By Newton’s 2
ndlaw,
m ′′ z = F
= mg k
2008_Hydrostatic pressure and Force(Moment) on a floating body 2008_Hydrostatic pressure and Force(Moment) on a floating body 2008_Hydrostatic pressure and Force/Moment on a floating body 2008_Hydrostatic pressure and Force/Moment on a floating body
Ex) Heave motion of ship
Ex) Heave motion of ship – – step 2 step 2
9
Mass-Spring-Damper system
0
B
static static S
P dS ρ gV
= ∫∫ =
F n k
9Archimedes’ Principlestatic
= ρ gV
0F k
Z
X
p g p y
g M
k
V
0②
gravity
= − mg F
k
m: mass
V0 : submerged volume SB: submerged surface area
ρ: density of sea water
m z F = s
0m 0
ks
0−
m
dS P dF= n
dS static
+F gV
0ρ
+ k
: static equilibrium
0 ( z 0)
= ∵ =
mz F
gravity
= F
= − mg k z
m ′′ z = F
k
mg
: force exerted by the infinitesimal
dS F d
: infinitesimal submerged surface area
: static equilibrium
0 ( z 0)
= ∵ =
= 0
m z = F
= mg k − k ks
0) 0 ( ∵ z ′′ =
2008_Hydrostatic pressure and Force(Moment) on a floating body
2008_Hydrostatic pressure and Force(Moment) on a floating body NAOE/SNU 2008_Hydrostatic pressure and Force/Moment on a floating body
2008_Hydrostatic pressure and Force/Moment on a floating body
: force exerted by the infinitesimal fluid element on
F d
n
: normal vector ofdS dS
0
: static equilibrium
)
0
( z ∵
Ex) Heave motion of ship
Ex) Heave motion of ship – – step 3 step 3
Z 9
Mass-Spring-Damper system
B
static static S
P dS
= ∫∫
F n
9Archimedes’ Principlestatic
= ρ gV
0F k
0 addtional bouyancy
ρ gV
= k F +
external static,
F
Z
X
p g p y
g M
k
V
0③
restoring force
0 addtional bouyancy
ρ g
z
external static,
F
additional
buoyancy caused by additional displacement z
gravity
= − mg F
k
m: mass
V0 : submerged volume SB: submerged surface area Awp : waterplane area
ρ: density of sea water
m z F =
z
0s
m
0
z
kz ks −
−
0m
addtional bouyancy
gA
WPρ
= − F
z
if, z is small
k
static
+F gV
0ρ
+ k
mz F
gravity
= F
= − mg k
,
mg
external static
F external static,
+F
external static, wp
+F
ρ gA
− z
+F ρ gA z
WP
= − z k
, k = ρ gA
WPm ′′ z = F
0 ( z 0)
= ∵ =
external static, wp
+F
ρ gA
= − z
external static,
+F
= − z k
0 external static,
mg ks kz
= k − k − k F +
external static,
=− kz k F +
= 0 ( ∵ z ′′ = 0 )
2008_Hydrostatic pressure and Force(Moment) on a floating body 2008_Hydrostatic pressure and Force(Moment) on a floating body 2008_Hydrostatic pressure and Force/Moment on a floating body 2008_Hydrostatic pressure and Force/Moment on a floating body
( )
Ex) Heave motion of ship
Ex) Heave motion of ship – – step 4 step 4
Z 9
Mass-Spring-Damper system
B
static static S
P dS
= ∫∫
F n
9Archimedes’ Principlestatic
= ρ gV
0F k
external static,
F
0 addtional bouyancy
ρ gV
= k F +
Z
X
p g p y
g M
k
V
0z
external static,
F
④
restoring force
0 addtional bouyancy
ρ g
additional
buoyancy caused by additional displacement z
gravity
= − mg F
k
m: mass
V0 : submerged volume SB: submerged surface area Awp : waterplane area
ρ: density of sea water
m z F =
z
0s
m 0
z
kz ks −
−
0m
F addtional bouyancy
gA
WPρ
= − F
z
if, z is small
k
static
+F gV
0ρ
+ k
mz F
gravity
= F
= − mg k
external static,
+F
external static, wp
+F
ρ gA
− z
+F ρ gA z
,
mg
external static
F
m ′′ z = F
mg ks kz
= k k k +F
WP
= − z k
, k = ρ gA
WPLi i d
external static, wp
+F
ρ gA
= − z
, k = ρ gA
WPexternal static,
+F
= − z k
mg ks
0kz
= k − k − k
=− k kz
external static,
+F
external static,
+F
m z ′′ + k z = 0
Oscillation by the restoring force0 ( z 0)
= ∵ =
Linearized Restoring Force
2008_Hydrostatic pressure and Force(Moment) on a floating body
2008_Hydrostatic pressure and Force(Moment) on a floating body NAOE/SNU 2008_Hydrostatic pressure and Force/Moment on a floating body
2008_Hydrostatic pressure and Force/Moment on a floating body
( )
Ex) Heave motion of ship
Ex) Heave motion of ship – – step 4 step 4
Z 9
Mass-Spring-Damper system
B
static static S
P dS
= ∫∫
F n
9Archimedes’ Principlestatic
= ρ gV
0F k
0 WP
gV gA
ρ ρ
= k − z
Z
X
p g p y
g M
k
V
0z
④
restoring force
0 0
WP
gV k ρ
= k − z
gravity
= − mg F
k
m: mass
V0 : submerged volume SB: submerged surface area Awp : waterplane area
ρ: density of sea water
m z F =
z
0s
m 0
z
kz ks −
−
0정수 중 선박의 강제
m운동에 의해 발생한 힘 k
static
+F gV
0ρ
+ k
mz F
gravity
= F
= − mg k − ρ gA
wpz ρ gA z
mg
m ′′ z = F
mg ks kz
= k k k
gA
wpρ
= − z
= − z k
mg ks
0kz
= k − k − k
=− k kz
m z ′′ + k z = 0
Oscillation by the restoring forceShip will oscillate forever?
E i di i t d b di ti
Radiation Force
B
radiation radiation S
P dS
= ∫∫
F n
2008_Hydrostatic pressure and Force(Moment) on a floating body 2008_Hydrostatic pressure and Force(Moment) on a floating body 2008_Hydrostatic pressure and Force/Moment on a floating body 2008_Hydrostatic pressure and Force/Moment on a floating body
Energy is dissipated by radiation wave
Ex) Heave motion of ship
Ex) Heave motion of ship – – step 5 step 5
Z 9
Mass-Spring-Damper system
B
static static S
P dS
= ∫∫
F n
9Archimedes’ Principlestatic
= ρ gV
0F k
0 WP
gV gA
ρ ρ
= k − z
z
Z
X
p g p y
g M
k
V
0z
0 0
WP
gV k ρ
= k − z
⑤k k
restoring force
z
radiation
= − c
F z
gravity
= − mg F
k
m: mass
V0 : submerged volume SB: submerged surface area Awp : waterplane area
ρ: density of sea water
m z F =
정수 중 선박의 강제
운동에 의해 발생한 힘 z
0s
m
0
z
kz ks −
−
0m
z
− c ′ z
k
static
+F gV
0ρ
+ k
mz F
gravity
= F
= − mg k − ρ gA
wpz ρ gA z
Dashpot
z z mg
radiation
+F
− z c
cz m ′′ z = F
gA
wpρ
= − z
= − z k Radiation Force
B
radiation radiation S
P dS
= ∫∫
F n
− z c
− z c
opposite to velocitym z = F
− k cz′
ks
0kz
− k − k
= mg k
− k cz′
− k kz
=
2008_Hydrostatic pressure and Force(Moment) on a floating body
2008_Hydrostatic pressure and Force(Moment) on a floating body NAOE/SNU 2008_Hydrostatic pressure and Force/Moment on a floating body
2008_Hydrostatic pressure and Force/Moment on a floating body
= − z c
c : damping coefficient