Slide 1

GROUP 1Instructor: Manikandan HMODELING SHIP COLLISIONS USING FINITE ELEMENT ANALYSIS

BITS PilaniPilani Campus1SIJO VM2012A4PS012PJEEVAN RENJITH 2012A4PS251PHARISANKAR 2012A4PS043PJ V N KARTIK 2012A4PS291PNIKHIL GUPTA 2012A4PS227PPRATIK DHAR 2012A4PS296PANAND SEKHAR 2012A4PS370PLOKVISHRUTT BISHNOI 2012A4PS307PGroup:BITS Pilani, Pilani CampusOwing to increasing vessel traffic, ship collisions (especially with offshore platforms) have been on a rise in recent years.There is a need to re-evaluate the current design parameters to improve the robustness and safety of the vessel.

PROJECT BACKGROUND

BITS Pilani, Pilani CampusAround 200-400 ship accidents happen every year.Statistics

BITS Pilani, Pilani CampusTo analyze a collision involving high non-linearity, contact, friction and rupture.Determine appropriate non-linear finite element modeling approach and appropriate values for some of the key analysis variables.Predict structural resistance (i.e., force vs. penetration). Detailed finite element analysis (FEA) for calculating structural damage. Ascertain failure criteria and suggest design modifications.

PROJECT OBJECTIVEBITS Pilani, Pilani Campus Pressure hulls are the main load bearing structures of naval submarines, and autonomous underwater vehicles (AUVs). A pressure hull is a structure that is designed to withstand the compressive forces associated with hydrostatic pressureLITERATURE REVIEW:BITS Pilani, Pilani CampusPRESSURE HULL- Inside the outer hull there is a strong hull, or pressure hull, which actually withstands the outside pressure and has normal atmospheric pressure inside. The pressure hull is generally constructed of thick high-strength steel with a complex structure and high strength reserve, and is separated with watertight bulkheads into several compartments. Pressure hullBITS Pilani, Pilani CampusAnalysis of the collision and grounding accidents can be classified into two parts, namely the external dynamics and internal mechanics. The external dynamics deals with the rigid body global motion of ships under action of the collision or grounding forces and the hydrodynamic pressures acting on the wet surface.The internal mechanics includes evaluation of the structural failure response of the involved ships during the collision or grounding accident.

BITS Pilani, Pilani CampusPROJECT ROADMAPFEA of ship designs and understanding collision based deformationAcquainting with ANSYS, design software and conducting basic simulationsDesigning relevant ship vessel Non linear FEM simulation in ANSYS LS-DYNA Analyze post-processing results and plot force-penetration diagramsSuggest suitable design modificationsBITS Pilani, Pilani CampusStatic Loads -Hydrostatic pressure, Weights of the ship components, Cargo and Ballast loads. Wave moments and forces coming due to ship components are also considered as static loads. Dynamic Load - Hydrodynamic Pressure due to waves, Wind Loads and other operational Loads like loads due to underwater Explosion, Machinery operational loads etc.

LOADS ON SHIPSBITS Pilani, Pilani CampusThermal Loads and Complex Non-Linear Static and Dynamic Loads-Analysis of Forward part of the ship due to slamming loadsCollision analysis-Supply vessel, with a specified velocity collides at the corner of the offshore barge. The contact regions between two vessels have been established by contact and target elements. The geometric and material non-linearity has been taken care off. The results include elastic deflection, permanent deformation / damage and stress values.

BITS Pilani, Pilani CampusThe speed of collision is sufficiently low to avoid large inertial effects and dynamic buckling. The level of damage can then be analyzed based on the demand for energy dissipation, which is obtained from an external mechanics analysis.Co-efficient of friction ranges from 0.3-0.5 AssumptionsBITS Pilani, Pilani CampusDetermine appropriate finite element modeling approachDetermine appropriate values for some of the key analysis variablesPredict structural resistance (i.e., force vs. penetration)Simulate the observed behavior (i.e., tearing, bucking, etc.)Selecting the modelBITS Pilani, Pilani CampusBITS Pilani, Pilani CampusMATERIAL MODEL

General MethodologyDetermine appropriate finite element modelling approach Determine appropriate values for some of the key analysis variables Predict structural resistance (i.e., force vs. penetration) Ascertain post collision behaviour ( i.e., failure criteria )

CONTACT MODELING

In these problems a force normal to the contacting surfaces acts on the two bodies when they touch each other. If there is friction between the surfaces, shear forces may be created that resist the tangential motion (sliding) of the bodies.MASTER AND SLAVE SURFACES The concept of master and slave surfaces are important if surface to surface contact formulation is used.

THEORY BEHIND IMPACT DEFORMATIONConsider an impact between a deformable sphere and deformable flat plateWhere m is the mass of sphere and is the change in distance between two points in sphere.Under static condition, the force acting on the specimen when there is deformation is given by

HULL DESIGNDimensions 10m*10m*5mBulbous bow-2.5m(radius)Structure made of steelFeatures used- Fillets, Draft, ExtrudeImported to ANSYS.

Platform and Assembly DesignDimensions- 8m*8m*1mUpper and lower cover thickness -10cm7 equispaced plates placed perpendicular to each other between upper and lower coverThickness of each plate = 10 cmHull and platform oriented and the assembly was matedStructural steel was used for both hull and platform

Hollow Hull Collision

Benchmark simulation-1Non linear elastic collision of a cylinder with a hemispherical heads with the platformInitial velocity= 20 m/secBilinear Isotropic hardening modelling usedAutomeshing featureStructural steel was used for both solids

Result

Benchmark simulation-2Non linear plastic collision of a cylinder with a hemispherical heads with the platformInitial velocity= 20 m/secBilinear Isotropic hardening modelling usedAutomeshing featureStructural steel was used for both solids

Explicit Dynamics SimulationHull was made to collide with the offshore platform.The assembly was imported from solidworks into ansys.Non linear analysis with automeshing

MATERIAL PROPERTIESCompressive Yield Strength Pa - 2.5e+008Tensile Yield Strength Pa - 2.5e+008Tensile Ultimate Strength Pa - 4.6e+008Young's Modulus Pa - 2.e+011Poisson's Ratio 0.3Bulk Modulus Pa - 1.6667e+011Shear Modulus Pa - 7.6923e+010

Explicit Dynamics Simulation

RESULTSObject NameTotal DeformationEquivalent StressDefinitionTypeTotal DeformationEquivalent (von-Mises) StressDisplay Time5.5001e-003 s6.2858e-003 sResultsMinimum0. m0. PaMaximum0.20007 m0. PaMinimum Occurs OnPart 2Part 1Maximum Occurs OnPart 1Minimum Value Over TimeMinimum0. m0. PaMaximum0. m2.0629e+006 PaMaximum Value Over TimeMinimum0. m0. PaMaximum2.3218 m1.4972e+009 PaInformationIntegration Point ResultsHollow Hull CollisionThe hollow hull was made using Shell command in SolidWorksThe angle of the bow was varied and corresponding simulations were doneAngles of the bow used were 15, 17.5 and 20 degrees.INTERNAL ENERGY Vs PENETRATION

Internal energy- Energy absorbed by the wall.Penetration proportional to velocity and hence Internal energy directly proportional to penetrationINTERNAL ENERGY Vs Penetration for different speeds

PENETRATION Vs TIME for different cone angles

TimeCone angles-12.5, 15 and 17.5 degreesFORCE Vs Time

More elements => More accuracy and hence the force distribution becomes uniformInternal Energy Vs Penetration for friction ratio variation

Internal energy dissipation increases with increase in friction ratio(co-efficient).CONCLUSIONInvestigate the parameters on the ship collisions and to provide effective guidelines on the implementation of finite element codes.The ship structural design has very significant influence on the collision resistance. The collision energy absorption capability depends on the thickness of outer shell, inner shell.The bow of the striking ship should not be assumed rigid.

CONCLUSIONThe benchmarking problems gave the project a direction to proceed in. Rough estimates were obtained which laid the foundation for conceptualizing the design of the ship hull.Two kinds of designs were considered for further simulations namely, solid and hollow hull models.Simulations conducted on both kinds of extreme designs gave a broad idea of the implications of variations in shell thickness and hull nose radius on post collision properties.The radius of the hull and the velocity of the striking vessel were varied and the optimum shell thickness ascertained from various simulation results is 0.256m and the radius of the bow is 1.678m.

THANK YOU