structural mechanics simulation (csm using finite … uk/staticassets/ml... · structural mechanics...

© 2011 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary© 2011 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary

Structural Mechanics Simulation (CSM using finite element analysis)

Mark Leddin

ANSYS UK

© 2011 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary

Agenda

• Structural Mechanics Simulation (CSM using finite

element analysis)

- Structural integrity performance for

complex structures and sub-structures

- Seismic assessment

- Geotechnical engineering

- Thermal bridging

Fluid-Structure-Interaction (FSI)

- Blast loading and structural response

- I-beam structural integrity under thermal loading


Structural integrity performance for complex structures and sub-

structures


ANSYS Mechanical FEA Suite

• Founded in 1970, ANSYS have been

developing generic Mechanical FEA software

for 40 years

• Originally developed for the nuclear industry,

quality was paramount in its design, now

in accordance with ISO quality controls

• ANSYS FEA has the broadest range of

capabilities in the market-place, with

technologies for:

– Linear & Nonlinear (geometric/material)

analyses

– Static, frequency-domain & time-domain

– 0-D to 3-D elements

– Isotropic, anistropic, layered materials

– ....


Product/Technology Description

ANSYS

DesignSpace

ANSYS

Structural

ANSYS

Professional NLT

ANSYS

Mechanical

Linear Structural

Steady State Thermal

Linear Structural


Transient Thermal

Linear Dynamics

Linear Structural

Non-Linear Structural

Linear Dynamics

Nonlinear Dynamics

Linear Structural

Non-Linear Structural

Linear Dynamics

Nonlinear Dynamics


Transient Thermal

Acoustics

Direct Coupled

Solver Technology

ANSYS

Professional NLS

Linear Structural


Nonlinear Structural

Linear Dynamics


Analysis Methods & Solvers

Technology Components

Geometry & Mesh

Materials

Boundaries & Loads

Solution

Post-Processing


ANSYS Structural Mechanics

• Geometry

– Direct CAD Links

• Connect to real CAD models

and create true parametric

analysis

– Create analysis geometry

• Geometry clean-up

• Simplification

• Create Shell & Beam

geometry

– Work with imported files



Elements Technology



Materials Modeling



Solvers

• Structural / Thermal /

Acoustics / ... / Coupled

• Linear / Nonlinear

• Implicit / Explicit

• Evolving to keep pace

with hardware

developments• Multi-core

• 32 & 64 bit

• Clusters

• GPU



• Postprocessing

• Stress, Strain,

Deformation, Creep,

Contact, Reactions.....

• Images

• Tabular data Excel

• Movie files

• Automated report

generation


Submodelling

Submodeling is a finite element

technique that you can use to

obtain more accurate results in

a particular region of a model.

A finite element mesh may be

too coarse to produce

satisfactory results in a given

region of interest. The results

away from this region,

however, may be satisfactory

Jackup Rig


Base model – Beam Elements

Typical structure that is modelled using

beam elements.

Locally high load at deck to leg

interface.

Load applied in example:

Wind load as nodal forces.

Deck interface as point constraint.

Gravity.


Shell model for detailed study


Integral Method


Seismic assessment


Spectrum analysis

Deterministic:

• Response Spectrum

• Single-Point Response Spectrum

• Multi-Point Response Spectrum

• Dynamic Design Analysis Method

Probabilistic:

• Random vibration

• Power Spectral Density (PSD)


Description & Purpose

• It is common to have a large models excited by transient loading.

– e.g., building subjected to an earthquake

– e.g., electronic component subjected to shock loading

• The most accurate solution is to run a long transient analysis.

– “Large” means many DOF. “Long” means many time points.

– In many cases, this would take too much time and compute resources.

• Instead of solving the (1) large model and (2) long transient together, it

can be desirable to approximate the maximum response quickly.


Description & Purpose

Idea: solve the (1) large model and (2) long transient separately and

combine the results.

Large model

Long transient

Large model

Mode extraction

↓

Mode shapes

Small model

Long transient

↓

Response spectrum

Combined solution

Fast, approximateFull solution

Slow, accurate

Large model

Long transient

Transient Analysis Response Spectrum Analysis


Generating the Response Spectrum

ω = 30 Hz

S = 95 m/s2

ω = 50 Hz

S = 138 m/s2

ω = 70 Hz

S = 86 m/s2


Spectral Regions

• Two frequencies can often be identified on a response spectrum

– This divides the spectrum into three regionsmid

frequency

high

frequency

low

frequency

fSP

frequency at peak response

(spectral peak)

fZPA

frequency at rigid response

(zero period acceleration)

1. Low frequency (below fSP)

• periodic region

• modes generally uncorrelated

(periodic) unless closely spaced

2. Mid frequency (between fSP and fZPA)

• transition from periodic to rigid

• modes have periodic component and

rigid component

3. High Frequency (above fZPA)

• rigid region

• modes correlated with input frequency

and, therefore, also with themselves

ZPA


Mode Combination

Whereas the SRSS method takes the following form,

The CQC and ROSE methods introduce a double sum and a correlation

coefficient.

Each method has a formula for the correlation coefficient, ε, which

is based on the frequency and damping of modes i and j

is designed to vary between 1 (fully correlated) and 0 (uncorrelated)

2

1

1

2

N

i

iRR

2

1

1 1

2

1

1

ROSECQC

N

i

N

j

jiij

N

i

N

ij

jiij RRRRRkR


Spectrum analysis


Spectrum analysis -

Static pre-stress


Spectrum analysis –

Modal analysis



RS loading



Results


Geotechnical


Drucker-Prager Plasticity

• Drucker-Prager (DP) plasticity is applicable to granular (frictional) materials such as soils, rock, and concrete.

• Unlike metal plasticity, the yield surface is a pressure-dependent von Mises surface for DP:

where sy is a material yield parameter, sm is the hydrostatic pressure, seqv is von Mises stress, and b is a material constant.

• Plotted in principal stressspace, the yield surface isa cone.

s1

s2

s3

s1 s2 s3

y

eqv

mF ss

bs 3

3


• Cap Drucker-Prager plasticity model applicable to

– Simulation granular materials such as soils

– Powder compaction simulation

– The model has also been utilized for modeling pressure-dependent

plasticity of polymers

• The model is a new addition to the existing Extended Drucker-

Prager model

– Introduce cap for both tension and compression

– Include cap hardening

– Include shear envelope hardening

Cap Drucker-Prager Model


Cap Drucker-Prager Model

Soil excavation analysis using EDP model with Cap

Displacement Plot Plastic Strain Plot


Concrete Model

• The concrete material model in ANSYS can

be used to model brittle materials, such as

concrete, rock and ceramics.

– Both cracking and crushing failure modes

are included.

– Prior to failure, behavior is assumed to be

linear elastic. However, plasticity and/or

creep may be combined with concrete to

provide nonlinear behavior prior to failure.

– This constitutive model is meant for low

tensile strength but high compressive load

carrying capability.

– A “smeared” reinforcement can be

specified via real constants along three

element coordinate directions, or discrete

reinforcements can be separately added

via LINK or COMBIN elements.


Drucker-Prager Plasticity and Concrete

... Concrete Model

• The concrete material can be combined with other nonlinearities:

– Plasticity and creep may be included with concrete. Usually, multilinear elastic or

Drucker-Prager plasticity is used for concrete. Note that the plasticity yield

surface must lie inside the concrete failure surface, otherwise no yielding will

occur.

– The concrete failure surface as plotted in principal stress space is shown on right.

Hence, the

yield surface associated

with any other nonlinear

material behavior (i.e.,

plasticity) must lie inside

of the concrete failure

surface. Otherwise, the

material will completely

fail and never yield.

– Adjustments to stresses

due to plasticity are

performed prior to the

cracking/crushing checks.


ANSYS Procedure for Concrete

• After solution, cracks can be plotted:

Other items such as the

status (unfailed, crush,

open crack, closed

crack), crack orientation

angles, and rebar

solution, can also be

obtained.

In the plot on right, note

that crack orientation

and plane are plotted

per integration point.


Recent Innovation

New Coupled Pore-Pressure

Mechanical Solids

Fluid flow through porous media

Single phase, based on extended Biot-

consolidation theory

Benefits

Allows for modeling of fluid pore

pressure in soils and biomedical

materials

Applications

Bone and prosthetic implants

Foundation and excavation analysis

Geological, Oil & Gas industryImage Courtesy of Archus Orthopedics

Model Courtesy of


Thermal Bridging


Study to compare to EN ISO 10211-1:1995

• Thermal bridges in building construction -- Heat

flows and surface temperatures -- Part 1: General

calculation methods

• 3D Geometry


3D Case

• Mesh

– 20 noded hexahedral

• Options:

– Low order elements

– Tetrahedrals


3D Case

• Boundary conditions

• Alpha 20°C with 5 W/m. °C

• Beta 15°C with 5 W/m. °C

• Delta 0°C with 20 W/m. °C


3D Case

• Results


3D Case – results comparison

BS ANSYS Difference Difference rounded Difference %

U 12.9 12.909 0.009 0.0

V 11.3 11.279 -0.021 0.0

W 16.4 16.363 -0.037 0.0

X 12.6 12.554 -0.046 0.0

Y 11.1 11.074 -0.026 0.0

Z 15.3 15.241 -0.059 -0.1

Alpha 46.3 46.109 0.191 0.4

Beta 14 13.904 0.096 0.7

Gamma 60.3 60.013 0.287 0.5


FSI

Blast Loading on

Structures – Explicit

Dynamics


Because…

► no equilibrium iteration needed

► no convergence problems in highly nonlinear problems

► material failure and erosion easy to realize

► high frequencies are naturally resolved because of

small time steps

► fast solving of system of equations highly scalable in

parallel mode

► implicit-explicit switching capability for efficienty

Why Explicit?

hypervelocity impact

blast in urban environment

ceramic impact

drop testsheet metal forming

ship collision

Ima

ge

s c

ou

rtesy C

ran

field

Univ

ers

ity (D

CM

T,U

K)


ANSYS® AUTODYN®

Ground Shock Urban Blast

Pipe bomb Façade Response

Contact Charge


Blast Effects on Structures

• Euler-Lagrange coupling

– Euler Blast Solver

– Deforming structures (solids, shells, beams)

– Fluid (air) vents through openings generated by blast

• Example Application

– Explosion inside masonry structure


AUTODYN Simulations of a

Brick Store House

• 3 charge sizes

– 24 kg

– 8 kg

– ~ 1 kg

• Two Configurations

– With a reinforced

concrete roof

– Open at the top

• 2 m x 2 m x 2 m

Jon Glanville, Rich Thayer

Century Dynamics Limited

Craig Hoing, Ian Barnes

DOSG


24 kg Trial (with concrete roof)


Structural Response


• Euler-Lagrange Coupling

– Lagrange solvers used for vehicle and soil

– Euler solver for the air blast

– Combined blast and fragment (soil) loading



– Mine blast


In Kabul suicide car bomber rammed bus killing

4 and wounding 29.

Almost all injuries attributed to flying shards of

glass.

To reduce the hazards of flying glass shards,

the German Defense Ministry is assessing

various safety concepts for bus windows using:

Full-scale bus experiments

AUTODYN simulations

Test in Large Blast Simulator

Standard glazing Polycarbonate Glazing


– Blast on windows/glazing




• Air Blast modeled using the Euler Blast solver

• RPG casing (fragments) and wing box components modeled using Lagrange solvers

• Euler-Lagrange coupling used for the blast loading

• Lagrange contact and erosion used for the fragment loading

Courtesy FhG-EMI, Germany


– Blast and fragmentation loading of composite wing


• Procedure (Stage 1)

– Static structural implicit

used to apply gravity

loading


– Bomb blast on bridge

10 м

5 м

1000 kg TNT

FE Model of the Bridge

Courtesy EMT-R, Russia

Stresses

Vertical Displacements

Implicit to Explicit



– Bomb blast on bridge

• Procedure (Stage 2)

– Transfer model and results

to AUTODYN

– Add Euler-FCT, used to

represent air and explosive

– Blast-Structure Interaction

(FSI) solve in AUTODYN

– Determine bridge damage


Damage

Blast Wave Propagation



FSI

I-beam structural integrity

under thermal loading


Description

• Illustrates the setup and simulation of a

simplified fire in a room, and its effect on the

roof structure as time progresses up to 1 hour.

• The simulation uses ANSYS Fluid-Structure

Interaction (FSI) capability to solve for:

– Air and heat flow within the room

– Thermal radiation

– Heat conduction within the structures

– Structural deformation of the support beams

under thermal and mechanical loading

– Elasto-plastic material behaviour


Geometry

• The room is L-shaped, and open only at one end.

• It is about 8m long, and 2.5m high.

• The ceiling is supported by the walls, and 3 steel I-beams.

• The ‘fire’ is positioned on the floor towards the closed end

of the room (idealized simply as a source of hot air).

Open End

4 m

4 m

4 mFire position


Project Schematic

• Project is setup in Workbench

– FSI (2-way coupled) simulation is created by:

• Adding a Transient Structural analysis

• Right-clicking on Setup and selecting:

– Transfer Data to New -> Fluid Flow (CFX)

– Geometry is shared between physics

– Setup and solution information is transferred

too


Geometry

• Multibody parts created, with solid bodies for the

fluid (air) and solid geometry.

– The appropriate bodies can be active or suppressed depending

on which physics you are working with.


Material Properties

• Structural Properties defined in Engineering Materials

– Property tables entered as functions of temperature


Structural Setup

• Frictional Contact added under Connections

– Surface-to-Surface contact between

beams and ceiling.

• Contact offset of 1cm to allow air flow

between surfaces if they separate

– Edge(node)-to-Surface between

beams and fixed support emulating

wall beneath.

– Augmented Lagrange formulation.

– Normal stiffness factor together with

appropriate „pinball‟ radius applied

to give efficient contact convergence.


Structural Setup

• Loads and Constraints are added to model

– Gravity added

– Zero vertical displacement at ceiling edges and at beam supports

(wall support)

– Rigid body dof constraints (for stability)

– Large pressure load added to top surface to simulate effect of

upper storey presence.


Structural Setup

• Analysis Settings added for coupled simulation

– Single step end time = 30s

– Timestep defined by single substep

– Large Deflection = on, for non-linear solution

– Direct solver chosen (should be sparse)

• Fluid-Solid Interfaces added for external surfaces of

beams, and lower surface of ceiling.

– Numbered 1 to 4 (beams are 1-3, and ceiling is no.4)

– These will match to corresponding CFD boundaries for fluid-solid

data transfer

• Nominal Solution fields added to results

– Total Deformation, Equivalent Stress,

and Contact Tool


CFD Setup in CFX

• Domain Physics, Boundary Conditions, and Fluid-

Structure Control setup in CFX-Pre

– Transient Simulation of 1hr, with 30s timesteps.

• Fluid-Structure coupling will occur every timestep

– Single „air‟ fluid material used, with Ideal Gas equation for density

and full buoyancy effects.


CFX Setup

• Domain Physics

– Mesh Deformation initialised to allow for structural movements

– Shear Stress Transport model used to include turbulent effects

– Thermal Energy model added to allow heat transport

– Monte Carlo thermal radiation model included

• Grey spectral model

• Boundary-specific emisivity

• Fluid-Solid Interface Boundaries

– No-slip walls set up at all beams surfaces, and ceiling

– Total Force Density passed to ANSYS, and Displacement received

– Wall Heat Flux passed to ANSYS, and Temperature received


Simultaneous Coupled Solution

• CFX Solver Manager used to start CFX and ANSYS

Mechanical solvers

– MFX framework used to communicate data between solvers

using sockets

– Solver Manager allows simultaneous solution monitoring from

both solvers

– Simulation takes about 2 days to solve


Simultaneous Coupled Solution

CFD Residuals

FEA ResidualsCoupling

Residuals

FEA Output CFD Output

Temperature

Probes

Displacement

Probes


Processing with CFD-Post

• Simultaneous processing of Fluid and Structural results

– Structural Stress

– Structural Displacement

– Temperature of both air

and solid structures

– Air velocity distribution



• Examine Beam displacement with time– Beams and ceiling slowly droop into domain. This is due to thermal expansion, and a

reduction in the stiffness due to temperature and plasticity effects.



• Examine Beam temperature– Examine distribution across beam, and relative contributions of convective and

radiative heat flux, at a point in time.


Post-Processing with ANSYS

• Examine potential for structural failure– Beams and ceiling can be examined for stress and plastic strain, to see when and

where failure may occur.


Conclusions

• ANSYS can solve the complete fluid-structure-

thermal interaction scenario of a fire in an enclosed

room.

• It has the tools to include complex geometric and

physical details.

• The coupled software has not been tested for the

collapse process itself, and difficulties are

specifically anticipated in sustaining two-way

coupling during impact between structures during

the collapse (if that occurs).

• However, the coupled software is able to analyze

events up to collapse, and the structural software can

analyze the collapse.


Overall Conclusions

• Wide range of proven technology

– Elements

– Materials

– Solvers

• Choice of FSI methodlogy

– Fully coupled

– Iterative

• One common platform taking advantage of

– Robust meshing

– Bi-directional CAD

structural mechanics simulation (csm using finite … uk/staticassets/ml... · structural mechanics...

Documents