An Explicit Dynamic Analysis of a ROPAX Vessel under Impulsive

Loading from a VBIEDSpiro J. PahosPhD Candidate

Universities of Glasgow & StrathclydeBiloxi, April 16, 2008

Overview

• Background – Maritime Terrorism & Statistics• Asymmetric Threats at Sea• Approach of the Problem• Air Blast Phenomena• FE Modelling• FE Results• Survivability in a Seaway• Conclusions

Background – Maritime Statistics

Vital Statistics:

• In 2008, 1.6 million British citizens are expected to take a cruise, a 14% growth on 2007

• U.S. citizens accounted for 78% of the industry’s total cruise passengers

• Carnival Cruises expect a 21% growth in EU capacity in 2008 (World Cruise Industry Review, 2008)

• Cruise ship industry yields €10.1b/yr(Business Research and Economic Advisors, 2006)

• More than 66 million ferry pax/yrMore than 9 million cruise pax/yr

(International Maritime Bureau, 2007)

Background – Maritime Terrorism & Piracy

• BC Sanya (1973) (RHIB)• BC Vory (1974) (RHIB) • BC Athena (1976) (RHIB)

BC Eko, BC Riri, and BC Spiro (Limpet Mines)• USS Cole (2000) (RHIB)• MV Limburg (2002) (RHIB)• Super Ferry 14 (2004) (IED)• Seaborne Spirit (2005) (RPG)• INS Hanit (2006) (ASCM)

Background – Maritime Terrorism (cont.)

USS COLE (2000)

• 17 sailors dead, approx. 270kg TNT (RHIB) www.dcfp.navy.mil

Background – Maritime Terrorism (cont.)

MV LIMBURG (2002)

• 1 crew member dead• 90,000 bbls spilled

www.dcfp.navy.mil

Background – Maritime Terrorism (cont.)

SUPER FERRY 14 (2004)

• 116 dead passengers, approx. 4kg TNT (IED)

Background – Maritime Terrorism (cont.)

SEABORNE SPIRIT (2005)

• No casualties• RPG 7, 4.5kg warhead

Source: Navy NewsStand

Background – Maritime Terrorism (cont.)

INS HANIT (2006)

• 4 sailors dead• ASCM, C802 or C701 ~165kg warhead

www.trmilitary.com

Asymmetric Threats at SeaWhat are the threats?

• No measures to prevent a determined attacker• Attacks most likely mounted whilst at a lower state of readiness

Is the threat from attack real?

Since 1945:• over 500 anti-ship missile launchesin action• over 50 countries have a mining capability• Al Qaeda’s Pillars: RHIB, SCUBA teams

Approach of the Problem - Seaborne VBIED General Particulars (m) (ft)

Length Overall 194.4 (638)Length BP 172.2 (564)Beam 28.4 (93.2)Depth (main dk.) 9.7 (31.8)Draught 6.6 (21.6)Fr. Spacing 0.8 (2.6)Web. Fr. Spacing 2.4 (7.8)

Approach of the Problem – Explosion Hazard from VBIED

Bureau of ATF

Approach of the Problem (cont.)Two cases being considered:

Case I: Sedan VBIED, 227kg (500lbs), ZI = 0.3

Case II: Cargo Van VBIED, 1818kg (4000lbs), ZII = 0.15

• Standoff: VBIED is a spherical charge at 0.4m (1.3ft) above deck 3, at 1.9m (6.2ft) from the side shell

• Critical blast load for most Western Navies, Z = 1.5(Reese et al., (1998) and OPNAV (1988)

Air Blast Phenomena

• Friedlander Eq. for open air (positive phase)

• LS DYNA CONWEP Function (TM5-855-1, USACE, (1986))Input: TNT equivalent, charge co-ordinates in the model,

detonation time, charge shape

• CONWEP drawbacks:– No focusing effect– Spherical/hemi-spherical charges– No ground interaction

00

exp1)(t

tt

t

ttPsotP AA

Finite Element Modelling

Modal Analysis

Three domains of impact-pressure actions (NORSOK, 1999)

- Q/S domain, when 3T < τ- Dynamic/impact, when 0.3 < τ < 3T- Impulsive, when τ ≤ 0.3T

Rayleigh Damping• Ship structures c ~ 4% (Didoszak et al., 2004)• Damping in the system is mass driven (Clough & Penzien, 1993)

22nR

n

Rc

n 20sec1

Finite Element Modelling (cont.)

Material Properties of High Tensile Steel

Finite Element Modelling (cont.)

The Property of Viscoplasticity• A property neglected from class societies• Occurrence of plastic flow past yield stress• Cowper - Symonds strain rate model

(Czujko, 2001)

σy

εf

(Jones, 1989)

Finite Element Modelling (cont.)

Failure Criterion

Strain-based failure criterion, Saint Venant’s Theory (Sanford, 2003)

• Failure strain is based on uniaxially - loaded specimens• Experiments at high strain rates are difficult and expensive• Values vary from 0.17 (Wisniewski, 2001) to 0.46 (Servis et al., 2001) can be found in the literature• Strain Failure of this work is taken as 0.22 • Failure occurs once εeff > εf

eff2

31 2 2 1 3 2 2 3 2

1

2

LS DYNA Results – Case I (500lbs)

LS DYNA Results – Case I (500lbs) (cont.)Breached area:6.92m2 (74.5ft2) (deck 3)5.22m2 (56.2ft2) (side shell)

deck 3 side shell

LS DYNA Results – Case I (500lbs) (cont.)DOF Solution (m) Fragment Velocity (m/s)

LS DYNA Results Case I (500lbs)(Animation I)

LS DYNA Results Case I (500lbs)(Animation II)

LS DYNA Results - Case II (4000lbs)

LS DYNA Results - Case II (4000lbs) (cont.)Breached Area17.12m2 (184.3ft2) (deck 3)25.34m2 (272.7ft2) (side shell)48.64m2 (523.5ft2) (deck5)

deck 3 side shell deck 5

LS DYNA Results - Case II (4000lbs) (cont.)DOF solution (m) Fragment velocity (m/s)

LS DYNA Results – Case II (4000lbs) (Animation)

Survivability in a Seaway – GA Plan

Survivability in a Seaway (cont.)

• JONSWAP spectrum, 5 x 10 different sea states were considered (Hs = 4.0, 4.5, 5.0, 5.5, 6.0m)

• Fully loaded departure (KG/GM) = 13.82/3.15) metres • Simulation time: 1800sec (0.5hrs)

• Permeability μ = 0.85 for ER μ = 0.90 for garage

(SOLAS II-2, Reg.7-3)

• The vessel survived in all sea states for Case I • The vessel sunk at Hs = 5.0m for Case II

Survivability in a Seaway (cont.)Case I (500lbs TNT)

Sea State Water Ingress (tonnes) Result

Hs=4.0m 2.16 SurvivedHs=4.5m 2.74 SurvivedHs=5.0m 1.64 SurvivedHs=5.5m 3.93 SurvivedHs=6.0m 16.75 Survived

Case II (4000lbs TNT)Sea State Water Ingress (tonnes) Result

Hs=4.0m 312.43 Survived Hs=4.5m 212.55 SurvivedHs=5.0m 396.07 CapsizedHs=5.5m 5067.12 CapsizedHs=6.0m 5691.50 Capsized

Survivability in a Seaway (cont.)Case II, Hs = 6.00m (Animation)

Conclusions

1. Case I (500lbs), 5.22m2 gash (survived) in all 6 sea statesCase II (4000lbs), 25.34m2 gash (capsized) in Hs=5.00m

2. Side shell plating is the most vulnerable part of the PMB

3. Reliability-based vulnerability requirements need to be addressed

4. The most critical area of a ROPAX vessel is below the waterline and near a bulkhead

5. Shortest time to for ROPAX ferry of 195m to capsize approximately 10mins (Hs=6.00m, Case II)

An Explicit Dynamic Analysis of a ROPAX Vessel under Impulsive

Loading from a VBIEDSpiro J. PahosPhD Candidate

Universities of Glasgow & StrathclydeBiloxi, April 16, 2008