PD & GT and I & W

Advanced FEA Compaction

Model Using CEL Method

Liqun Chi, Ph.D.

Machine and Machine Systems

Research and Advanced Engineering

Product Development & Global Technology

Caterpillar Inc.

Greg Zhang

Compactors &Wheel Dozers

Performance & Controls

Industrial & Waste Group

Caterpillar Inc.

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Slide 2Outlines

Brief Introduction of of Motivation

Material Models for Refuse

FEA Compaction Model Development

Early Model with Smooth Drum

Tip Models using Lagrangian Method

Latest CEL models

Model Validation

Introduction on Model Applications

Future Model Development Need

Q & A

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Slide 3Real World Problems

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Slide 4Motivation

Develop VPD Model to predict the compactor performance

Compaction Performance

Machine Mobility

Drive train requirement – Wheel Torque

Fuel Consumption (coupling with other software)

To define the optimum operation procedures

Able to determine the optimum wheel configuration for a

particular market

Guide the Basic Machine Configuration Specs

Improving Current Products

New Product Development

Guide the powertrain design:

Reliability

Fuel efficiency (coupling with other software)

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Slide 5

Force

Refuse

Mechanical Behavior of Refuse – Barrel Tests

Mechanical behavior of waste under applied load

Elasto-Plastic behavior – reversible elastic rebound

and permanent, irreversible plastic deformation

Elastic rebound is stress dependent

Work-hardening plastic deformation behavior –

hyperbolic or exponential shape

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Slide 6Testing Shear Strength of Waste Material

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Slide 7Crushable Foam Material Models for Refuse

Characteristics:

Volumetric hardening

Non-associated flow rules

User Material Subroutine

Stress dependent elasticity

q

ppc

a

1

po-pt poc

Yield surfacesPlastic potential

0222 Bppqf oa

222 pqg

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Slide 8Material Model Validation - VUMAT

Single Element

Lagrangian Mesh

CEL Mesh

0 200 400 600 800 1000 1200

To

tal S

tra

in

Test Data Lag Model CEL Model

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Slide 9Early Models with Smooth Drums

Study the feasibility of the model ABAQUS v5.8 first release with

contact algorithm

Explored both ABAQUS/Standard

and ABAQUS/Explicit

Run time with the computer power

at the time

Excises of Early Model Model validation in laboratory soil bin

with artificial soils

Sizing the drum and powertrain

Competitive Studies

Study optimum optional procedures

Model Description: FEA-based model with ABAQUS/Explicit

Rolling the the wheel on the deformable

ground

Analytical rigid surface for the drum

Friction-type wheel/ground interface

Multiple layers for ground model

Controlled the wheel motion (rotational and

translational).

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Slide 10Soil Bin Validation

Scaled model of smooth drum

Artificial Soil Mix

Soil Model – Drucker-Prager’s Cap Model

Soil Behavior

Triaxial tests

One dimensional compression tests

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Slide 11New Laboratory Soil Bin Facility at Technical Center

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Slide 12Early Model with Smooth Drum – Machine Size

The effect of machine

passes

The effect of machine

weight

Determine the optimum

operation procedures

0 1 2 3

Number of Machine Passes

Re

fus

e D

en

sit

y

CAT816 CAT826 CAT836

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Slide 13

60 cm Layer

Early Smooth Drum Model - Effect of Layer Thickness

90 cm Layer

120 cm Layer

CAT 836 with three passes

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Slide 14Field Validation Test – (US Landfill)

Drive Shaft Torque and Speed

GPS - Measure Speed

GPS Survey for Layer thickness, slopes and density

Crusher Barrel

Tests

(refuse compaction

behavior)

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Slide 15Field Validation Test – US Landfill

Level Ground

5:1 Slope

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Slide 16Early Model with Smooth Drum – Stress Under Wheel

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Slide 17Early Model with Smooth Drum – Volumetric Strain

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Slide 18Results with Smooth Drum Models

Model Accurately Predicted Average Density Change

Model Prediction of Wheel Torque is Significantly Lower

Not Able to Consider the Effects of Detailed Wheel Design (tips shapes, number of

tips and tip arrangement)

0 2 4 6Machine passess

De

ns

ity

Field data

Model

5:1 Slope

0 1 2 3 4 5

Machine passes

De

ns

ity

Field data

Model

Level Ground

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Slide 19Tip Model – Lagrangian Mesh

ALE Method Automatic remeshing (moving the location of nodes,

no nodes or element added, and the node on the

material boundary followings the material deformation)

Various mesh smoothing algorithms (volume average,

Poisson equation, and combination of these methods)

Advection of mass, momentum, and energy

Flexible control of remeshing frequencies

Not able to find an effective remeshing method for

our problem

Model Description

Wheel model included detailed tip shape

and tip arrangement pattern

General finer mesh to accommodating the

tip shape

VUMAT was used for the model

Mesh distortion was key problem with

Lagrangian mesh

Methods Explored for Distortion Control

Solid Section Distortion Control

Distortion control option at “Solid

Section”

With “Enhanced Hourglass” Control

Limited Success

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Slide 20Model with Tips – Lagrangian Method

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Slide 21Model with Tips – Lagrangian Method

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Slide 22Model with Tips – Lagrangian Method

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Slide 23Lagrangian Mesh Tip Model Validation

Limited Success of Distortion

Control in Lagrangian

Formulation

Only single machine pass

And with gentle slope

With relatively small wheel

slips

Much Improved Model

Predictions

Accurate wheel torque

prediction for first pass

(including torque split

between front and rear

axles)

Accurate the average

density prediction for first

pass

0

20

40

60

80

100

120

140

160

Front Rear

Re

lati

ve

Wh

ee

l T

orq

ue

, %

Model Dataset 1 Dataset 2 Dataset 3

Wheel Torque during 1st Pass

3 fwd trips

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Slide 24CEL Method

Coupled Eulerian-Lagrangian (CEL) Formulation:

Lagrangian phase Remeshing phase

The CEL method is based on an operator split of the governing equations, resulting in a

traditional Lagrangian phase followed by an Eulerian, or transport, phase.

Lagrangian phase of the increment- nodes temporarily fixed within the material, and

elements deform with the material.

Eulerian phase of the increment - deformation is suspended, elements with

significant deformation are automatically remeshed. Mass and momentum

advections between neighboring elements are computed.

Eulerian mesh did not follow material – need to construct the surface for contact

Void and partially filled elements

Elements can be filled with different materials

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Slide 25Field Validation Test - China

Spreading Field compaction test

In-site compression testSurvey

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Slide 26CEL Landfill Compaction Model

Eulerian Mesh

Special Eulerian element (EC3D8R – 3D analysis only)

Generally finer than Lagrangian mesh for similar analysis

Cover the region the material potential can move into – void element

Eulerian-Lagrangian Contact

General Contact in Explicit – Penalty Method

Surface of Eulerian mesh is defined using material instance

No need to define contact interactions between Eulerian materials

Boundary Conditions

Define material flow at Eulerian nodes/Boundary Surface

No displacement type constrain at Eulerian node

ABAQUS internal crushable foam model for top loose refuse

Precompacted Layer

Base

Loose Refuse

Void LayerCompactor Wheels

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Slide 27CEL Model Simulation - Video

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Slide 28Model Validation – Samples of Machine Data

FWD FWD FWD

RVS RVS

RVS

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Slide 29

0 1 2 3 4

Machine Passes

Den

sit

y Field Data

Model (F-R-F-R)

Model (R-F-R-F)

Model Validation – Compaction Prediction

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Slide 30

1 2 3 4

Machine Pass

To

tal W

he

el T

orq

m

Field Data - Trip 1

Field Data - Trip 2

Field Data - Trip 3

Model

Forward – Reverse – Forward – Reverse (6% Downhill Slope during Forward)

Model Validation – Wheel Torque

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Slide 31

Reverse – Forward – Reverse - Forward (6% Downhill Slope during Forward)

1 2 3 4

Machine Pass

To

tal W

he

el T

orq

ue

Field Data - Trip 1

Field Data - Trip 2

Field Data - Trip 3

Model

Model Validation – Wheel Torque

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Slide 32

1 2 3 4

Machine Pass

Mach

ine S

peed

Field Trip 1

Field Trip 2

Field Trip 3

Model

Forward – Reverse – Forward – Reverse (6% Downhill Slope during Forward)

Model Validation – Machine Speed

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Slide 33CEL Model to Simulate Drawbar Test

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Slide 34WTL VPD Modeling Domain

Environment

Machine

Real World

Dynasty

Abaqus Explicit

Virtual World

Performance

Structure

•Compaction

•Traction

•Steering

•Braking

•Cooling

•Productivity

•Fuel efficiency

•Stress

•Fatigue

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Slide 35Landfill Compactor Performance Model

•Traction Coefficient

•Rolling Resistance

•Rolling Radius

FEA Landfill

Compaction Model

Dynasty Machine

System Model

P&C

•Productivity

•Fuel Efficiency

3D Tire Model

Cooling

•Heat

Power Train, Structure

•Loads

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Slide 36Typical Model Applications

Tip/wheel designs to achieve optimized machine performance,

power train, cooling and structural integrity

China specific wheel/tip designs to suit the characteristics of

Chinese waste

Belly guard designs to reduce drag

Customer support to help market the products

Competitive studies to understand our products’ strengths and

weaknesses.

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Slide 37Summaries & Conclusions

ABAQUS/Explicit is powerful tool for simulating the machine and ground interactions

The CEL method resolved the element distortion problems experienced in the previous

compaction models using Lagrangian method.

The CEL model can simulate multiple passes for the compaction wheels with

detailed tip shapes.

The CEL model can simulate the excessive ground deformation at high wheel slip

The model accurately predicts the average density changes made by landfill compactor

and machine speed.

The CEL model was able to predict the correct trend of changes in wheel torque

between passes and capture the effect of slopes on the wheel torque.

Lower wheel torque with more compacted ground conditions

Correct trend of effect of ground slopes

Lack of material damping for Eulerian elements results in under-prediction of wheel

torque by the current landfill compaction models – numerical material damping for soil

like plastic material models is critical.

The VUMAT was successfully used for simulating the barrel tests. The model accurately

predicted both elastic rebound and permanent plastic strain.

The use of VUMAT of the same material subroutine failed for the full landfill compactor

model. The robustness of using user-defined material subroutine (VUMAT) with Eulerian

elements in ABAQUS needs to be further improved.

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Slide 38

Thank You!

&

Questions?