Post on 24-Nov-2014
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
FINITE ELEMENT ANALYSIS OF RESPONSE OF A FLOATING STRUCTURE TO AN UNDERWATER EXPLOSION (UNDEX)
M.Sc. Thesis by
Fatih ARUK
Supervisors: Prof. Dr. Tuncer TOPRAK
Dr. Ergün BOZDAĞ
Examination Date: 09.06.2008
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
What is the importance of UNDEX resistance?
• Warships should last destructive effects of any near underwater explosion.
• Also shipboard systems must be shock hardened to a certain level to ensure combat survivability of both personnel and equipment.
So, shock resistance is a major issue that should be considered during early design phase of...
warships, radars, weapons, torpedos or any other shipboard equipment
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
Shock Trials (Physical Tests);
• Extremely Expensive• Dangerous
• Harmful to the surrounding Environment
• Require years of planning and preparation
• Due to safety risk, shock trials do not test up to the ship’s design limits or even the true wartime shock environment.
• These tests are performed after the first ship is already built.
Shock trials of USS WINSTON S. CHURCHILL (DDG 81) in 2001
• United States Navy spent tens of millions of dollars • Years of planning and preparation
Shipboard eqipment testing; MIL-S 901D (Military Specification for shock testing of ship board equipment)
Shock Test Platform
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
Impact Tests;
expensive experimental tests on simple cylindrical shells and plate structures.
Computational modeling and response, if perfected, can effectively and accurately replace the experimental procedures used to obtain the UNDEX response.
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX Simulation;The shock response of an immersed or floating structure is obtained when subjected to a near UNDEX loading
• Kwon and Cunningham; dynamic responses of stiffened cylinder and beam elementsDYNA3D [Explicit FE Code]+ Underwater Shock Analysis (USA) [BE Code based on DAA]
• 90s Kwon and Fox;the nonlinear dynamic response of a cylinder subjected to side-on underwater explosion
• Sun and McCoy UNDEX analysis of a composite cylinder ABAQUS + a fluid-structure interaction code• Cichocki, Adamczyk, and Ruchwa implemented fluid-
structure interaction phenomenon, pressure wave distribution, and the radiation boundary conditions into ABAQUS.
Three dimensional ship shock trial simulation of a warship was performed by Shin in 2004
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX PHENOMENA;
0 1.5 12 13.5 15 149 150.5 152Radius
(m)
234.4 Mpa
23.4 Mpa
15.2 Mpa
2.3 Mpa1.1 Mpa
Similitude Relations (Pressure versus Time)
1
( )( , )A
cc
aP R t P
Rf
B
c c
c
a v t
R a
( )f e 1
1.338 1.805( ) 0.8251 0.1749f e e 7
;P;R;ca;t
Pressure
, , , ;c cP v A B
Distance to charge (stand-off distance)
Charge radiusTime
Charge constants
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
0 1 2 3 4 5 6
x 10-3
0
2
4
6
8
10
12
14
P(M
pa)
t(s)
Pressure vs. time history for 25kg of HBX-1 charge, standoff distance of 10m
according to Swisdak
according to Price
UNDEX PHENOMENA;Similitude Relations (Pressure versus Time)
Material Source
TNT (1.52 g/cc) Coles (1946) 1.42 992 0.13 0.18
TNT (1.60 g/cc) Farley and Snay (1978) 1.45 1240 0.13 0.23
TNT (1.60 g/cc) Price (1979) 1.67 1010 0.18 0.18
HBX-1 (1.72 g/cc) Swisdak (1978) 1.71 1470 0.15 0.29
HBX-1 (1.72 g/cc) Price (1979) 1.58 1170 0.144 0.24
Pentolite (1.71 g/cc) Thiel (1961) 1.65 1220 0.14 0.23
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
Explosive Gas Bubble
UNDEX PHENOMENA;
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
1
3
5 5
6( 10)
cmT K
D
1
3
max 6 1
3( 10)
cma K
D
Explosive Gas Bubble
UNDEX PHENOMENA;
Gas Bubble Period Max. Gas Bubble Radius
For our case ( MIL-S-901 D; 27.3 kg HBX-1 at 7.3 m depth) T=0.64 s
amax =4.4 m
• Bubble pulses are a strong source of excitation for ships whose bending vibration mode is near to the bubble pulse frequency
• It is especially important for the late time response of the ship
• However, for our case, the first mode of vibration is well above the bubble pulse freq. calcualted above.
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
Explosive Gas Bubble, Geers-Hunter Bubble Model (2002)
UNDEX PHENOMENA;
UNDEX= SHOCK WAVE PHASE + BUBBLE OSCILLATION PHASE
SHOCK WAVE PHASE provides initial conditions for BUBBLE OSCILLATION PHASE
ABAQUS includes Geers-Hunter (2002) model for UNDEX loading.(a fourth-order Runge-Kutta integrator to prescribe the pressure variation)
MIL-S-901 D; 27.3 kg HBX-1 at 7.3 m depth 27.3 kg HBX-1 at 65 m depthPressure variation for two cases (7.3 m and 65 m cases) at stand-off distance (8.7 m)
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX PHENOMENA;Cavitation
Cavitation takes place in water when there is area of near-zero absolute pressure (about 206.8 Pa)
Two types of cavitation occur in an UNDEX event;
‘bulk’ cavitation;a large volume of low pressure due to reflections from sea surface
‘local’ cavitation;a small zone of low pressure at fluid-structure interaction surface.
The effect of cavitation on the response of the floating structures is important and must be properly modeled to obtain physically meaningful results.
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
1234
6315.2
6096
7620
9144
12192
2,3,41
UNDEX PHENOMENA;Cavitation
‘bulk’ cavitation
0i atm stc RP P P P Cavitation condition:
2 1j j
cf
R Rt
c
( , ) 0F x y
( , ) 0G x y
Equations of lower and upper cavitation boundaries:
EXPLOSION VARIATIONS ACCORDING TO MIL-S-901 D
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX PHENOMENA;Cavitation
‘local’ cavitation
Taylor plate theory
Assumptions;• The plate is rigid• The shock wave is planar
p i rv v v
i f f i
r f f r
P c v
P c v
pp t i r
dvm P P P
dt
max2 2p tp f f p i
dvm c v P P e
dt
1
max
A
cc
aP P
R
max2( )
(1 )t t
pp
Pv t e e
m
max2( )
1t t
p
PP t e e
f f
p
c
m
As becomes large (a lightweight plate), cavitation occurs faster.
ln
1cavt
1 1maxmax
2p
f f
Pv
c
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX PHENOMENA;Cavitation
‘local’ cavitation
pp atm
dvm P
dt cavt t
max( ) ( )atmp cav p
p
Pv t t t v
m
cavt t
max2( )
(1 )t t
pp
Pv t e e
m
max2( )
1t t
p
PP t e e
cavt t
cavt t
Incident and total pressures behind, and velocity of shock platform subjected to through-centerline UNDEX of 50 kg of HBX-1 charge at 30 m depth.
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
Elements of UNDEX Simulation;
Acoustic EquationsEquilibrum equation for small motions of a compressible, adiabatic fluid with velocity-dependent momentum loses;
0f ff
p
u u
x The slow flow assumption is accurate for
steady fluid velocities up to Mach 0.1
Acoustic Constitutive Equation;
f fp K
ux
Acoustic Constitutive Equation for cavitating fluid;
v f fp K
ux
max ,v c op p p p linear
nonlinear
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
Elements of UNDEX Simulation;Formulation of Direct Integration, Coupled Acoustic-Structural Analysis
0f ff
p
u u
x f fp K
u
x
1 10
f f f f
pp p
K K
x x
Introducing a variational field δp, integrating over entire body and applying Green’s theorem yields;
1 10
f fpf f f fV S S
p pp p p dV p T dSK K
xx x
1f
f
pT
x n u nx
Boundary traction term
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
Elements of UNDEX Simulation;Formulation of Direct Integration, Coupled Acoustic-Structural Analysis
fpSthe value of the acoustic pressure isprescribed;
ftSprescribes motion of the fluidparticles, modeling pressure wave
0f
ftT T x n u
0p
fiSthe radiating acoustic boundary,waves passing exclusively outward
1 1
1 1fiT p p
c a
x
fsS acoustic-structural interactionf m n u n u
mfsT
x n u
Acoustic Boundary Conditions
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
Elements of UNDEX Simulation;Formulation of Direct Integration, Coupled Acoustic-Structural Analysis
0
1 1
1 1
1 10
f ft
fi fs
f f f fV S
m
S S
p pp p p dV pT dSK K
p p p dS p dSc a
x x
n u
:
0fs t
m m m mc
V V V
m m
S S
dV dV dV
p dS dS
σ u u u u
u n u t
the final variational statement for the acoustic medium
the virtual work statement for a structure.
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
Elements of UNDEX Simulation;Formulation of Direct Integration, Coupled Acoustic-Structural Analysis
The Discretized Finite Element Equations
interpolation functions
P Pp H p
m N Nuu N 1,2,...N up to the number of displacement degrees of freedom.
1,2,...P up to the number of pressure nodes
[ [ ]] ff f ff sM p C p K p u PS
[ ] [ ]Ts f ss ssM u C u K u p PS
I Sp p p
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
Surface-Based Acoustic-Structural Interaction Procedure
( ) ( ( ))fs
m iN N N
iS
p dS A N m
in u n x P x u ( ) ( ( ))fs
m iN N N N
iS
p dS p A N u n n x P x
Elements of UNDEX Simulation;Formulation of Direct Integration, Coupled Acoustic-Structural Analysis
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
( , ) j oI j x j
f
R Rp t p t p
c
x x
j s jR x x
s ox j
s j
p
x xx
x x
Note that the source point sx should be located out of the fluid domain.
Incident Wave Loading
Elements of UNDEX Simulation;Formulation of Direct Integration, Coupled Acoustic-Structural Analysis
o s oR x x
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
Elements of UNDEX Simulation;Mesh Refinement
For reasonable accuracy, at least six representative internodal intervals of the acoustic mesh should fit into the shortest acoustic wavelength present in the analysis. Eight or more will be better.
maxL ; maximum linear element length
f f fc K ; the speed of sound
;the number of linear elements per acoustic wavelength
maxf ; max. frequency of excitation which can be simulated accurately
maxmin max
fcfn L
minn
max
max
1500
8 0.053750
m sf
mf Hz
We used an element size of about 50 mm around the acoustic-structural interface. The element size increases up to 150 mm at outer fluid regions.
Meshing whole fluid medium with 50 mm elements would result in about 16 million elements!
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
Explicit Time Integration
Elements of UNDEX Simulation;
( 1) ( )1 1
( ) ( )2 2
( )2i iN N
ii
i
Nt tu uu
( 1) ( ) ( 1) 1( )
2
N N Ni i i
iu u t u
• An explicit central-difference time integration rule is used;
• Each increment is relatively inexpensive because there is no solution for a set of simultaneous equations.
• The time increments must be quite small so that the accelerations are nearly constant during an increment.
• A lumped mass matrix is used because its inverse is simple to compute.
1
( ) ( ) ( )N NJ J Ji i iu M P I
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
Advantages of the explicit time integration method;
Explicit Time Integration
Elements of UNDEX Simulation;
• Well-suited to solving high-speed dynamic events
• No global tangent stiffness matrix. Iterations and tolerances are not required.
Stability of Explicit Integration;max
2t
2max max
max
21t
The Stable Time Increment Estimation;
If damping included;
minLt
c
2sc
(1 )(1 2 )
Ev
v v
2(1 )
E
v
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
Structural Damping
Explicit Time Integration
Elements of UNDEX Simulation;
[ ] [ ] [ ]s R s R sC M K
Mass Proportional Damping
Stiffness Proportional Damping
2 2R iR
ii
In names of natural freq.;
damps lower frequencies
damps higher frequencies
Effects of damping on the stable time increment in Explicit Analysis
2max max
max
21t
maxmax
max2 2RR
R has greater effect on stable time increment
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS METHODOLOGY
UNDEX TEST PARAMETERS FROM MIL-S-901D
MIL-S-901Dspecification which covers shock testing requirements for ship board machinery, equipment, system and structures.
heavyweight shock testing platform27.2 kg HBX-1
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX TEST PARAMETERS FROM
MIL-S-901D
UNDEX FE MODEL GENERATION
FLUID-STRUCTURE INTERACTION FE
ANALYSIS
CORRELATION OF UNDEX RESPONSES AND VALIDATION OF
NUMERICAL CODE
CONDUCT UNDEX TEST
SHORT DURATION DYNAMIC RESPONSE
Equivalent?
SHORT DURATION DYNAMIC RESPONSE
NO
MODIFY UNDEX MODEL/ANALYSES
PARAMETERS
YES
UNDEX ANALYSIS METHODOLOGY
UNDEX CORRELATION METHODOLOGY
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS METHODOLOGY
SUBMODELING ANALYSIS
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
MODELING AND ANALYSIS
Weight; about 39 tones
CAD MODELING; CATIA V15
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
MODELING AND ANALYSISMESHING; ABAQUS CAE
Number of nodes: 140316
Number of elements:142327 Linear quadrilateral elements of type S4R
Connections were imposed by means of kinematic couplings
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
MODELING AND ANALYSISGENERATING A REDUCED (COARSE) MODEL for tryouts and acoustic mesh convergence studies; HYPERMESH
Number of nodes: 7858
Number of elements: 8229 Linear quadrilateral elements of type S4R538 Linear triangular elements of type S3R
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
MODAL ANALYSIS
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS WITH REDUCED (COARSE) MODELFLUID MESH CONVERGENCE ANALYSIS
Boundary Conditions
1
1
f f
f
c K
1
1
2f f f f
fa K
Plane type radiating surfaces;
1f
0
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS WITH REDUCED (COARSE) MODELFLUID MESH CONVERGENCE ANALYSIS
Acoustic-Structural InteractionInitial Static PressureIncident Wave (UNDEX) Loading
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS WITH REDUCED (COARSE) MODELFLUID MESH CONVERGENCE ANALYSIS
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS WITH REDUCED (COARSE) MODELFLUID MESH CONVERGENCE ANALYSIS
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS WITH REDUCED (COARSE) MODELANALYSIS WITH DEFORMABLE PLATFORM
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS WITH REDUCED (COARSE) MODELANALYSIS WITH DEFORMABLE PLATFORM; EFFECT OF DAMPING
1.5R
0.5 6R E
For first two modes; % 0.4
For the first torsional and bending modes ; 0.25 % and 0.15 %
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS WITH REDUCED (COARSE) MODELANALYSIS WITH DEFORMABLE PLATFORM; EFFECT OF DAMPING
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS WITH MAIN (FINE) MODEL
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS WITH MAIN (FINE) MODELEFFECT OF MESH REFINEMENT AROUND ACOUSTIC-STRUCTURAL INTERACTION REGION
Mesh Convergence Analysis;
Element size; 150 mm
Number of nodes; 1059260
DFT Analysis of Incident Pressure Waves;
Element size; 50 mm
Number of nodes; 4198257
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS WITH MAIN (FINE) MODELEFFECT OF MESH REFINEMENT AROUND ACOUSTIC-STRUCTURAL INTERACTION REGION
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS WITH MAIN (FINE) MODELEFFECT OF CAVITATION
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS WITH MAIN (FINE) MODELEFFECT OF STRUCTURAL DAMPING 1.5R 0.5 6R E
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS WITH MAIN (FINE) MODEL
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
UNDEX ANALYSIS WITH MAIN (FINE) MODEL
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
SUBMODELING ANALYSIS
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
CONCLUSION AND OUTLOOK
• Fluid mesh size has important effect on the structural response and should be selected carefully for accurate results; Mesh Convergence Study DFT analysis of loadings
• Though it requires a nonlinear fluid behavior which adds to the cost
of the analyses, including cavitation is a must to obtain physically meaningful results.
• The effect of damping was also shown to be important for peak acceleration estimation in the late time response of the platform.
• Submodeling analysis can bu run to obtain converged stress-strain results at some sub-region of the structure.
• Experimental work is a must for the validation of the numerical code used and of the analysis procedure followed in this study. The work done in this work will provide the basis for the future experimental work.
İTÜ
Faculty of Mechanical Engineering
Mech. Eng. Fatih ARUK
aruk@itu.edu.tr
END OF THE PRESENTATION
QUESTIONS?