FINITE ELEMENT MODELING OF ABDOMINAL AORTIC ANEURYSM

MOHD IZZAT BIN SAMSUDIN

Thesis submitted in fulfillment of the requirements

for the award of the degree of

Bachelor of Mechanical Engineering

Faculty of Mechanical Engineering

UNIVERSITI MALAYSIA PAHANG

MEI 2010

ii

SUPERVISOR’S DECLARATION

I hereby declare that I have checked this project and in my opinion, this project is adequate

in terms of scope and quality for the award of the degree of Bachelor of Mechanical

Engineering

Signature:

Name of Supervisor: Mohd Akramin Bin Mohd Romlay

Position: Lecturer

Date: 6 MEI 2010

iii

STUDENT’S DECLARATION

I hereby declare that the work in this project is my own except for quotations and

summaries which have been duly acknowledged. The project has not been accepted for any

degree and is not concurrently submitted for award of other degree.

Signature:

Name: Mohd Izzat Bin Samsudin

ID Number: MA06022

Date: 6 MEI 2010

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ABSTRACT

An aneurysm is an abnormal bulging or widening of a portion of an artery due to weakness in the wall of the aortic wall. This is happening when the mechanical stress exceeds the tensile strength of the tissue. Aneurysm can happens anywhere in parts of our body as long there is an aorta. Nowadays, an accurate decision to predict the rupture of theaneurysm is not is founded yet and usually, clinical doctors will treat the aneurysm base on the aneurysm size. This study is focusing on abdominal aortic aneurysm that is occurring at the area of abdomen aorta. By using the simulation tools, the stress behavior on this region will be analyzed. The normal size of abdomen aorta is about 2 cm and aneurysm can make this aorta to reach to 6 cm. As the size of an aneurysm increases, there is a potential of rupture of aneurysm. This can result in severe hemorrhage or even worst, fatal event. The studies being proceed without experiment but only based on numerical approach. From the previous studies, it was shown that the mechanical behaviors inside aneurysm region would be different compare to the normal blood vessel. It was proves that a large stress distribution appear at both necks and around the aneurysm bulge on the anterior surfaces.Studying the mechanical properties in real AAAs would be useful information to the clinical doctors because it helps them to better understand of aneurysm behavior.

vi

ABSTRAK

Aneurism adalah kejadian ganjil pembengkakan atau pembesaran bahagian arteri disebabkan oleh dinding aorta yang lemah. Kejadian ini berlaku apabila tekanan mekanikal melebihi kekuatan tegangan dinding aorta. Aneurism boleh terjadi di mana-mana bahagian badan kita yang mempunyai salur darah. Pada hari ini, keputusan yang tepat untuk meramal aneurism akan pecah belum masih ditemui dan kebiasaannya, doktor akan merawat aneurism berdasarkan saiz aneurism. Kajian ini akan difokuskan di abdomen aneurism yang berlaku di kawasan salur darah di perut. Dengan mengunakan kaedah simulasi, sifat-sifat tekanan di kawasan ini akan dianalisis. Saiz normal untuk salur darah di bahagian perut adalah 2 cm dan aneurism boleh menyebabkan salur darah ini mencecah 6 cm. Apabila saiz aneurism meningkat, terdapat potensi untuk aneurism pecah. Ini boleh menyebabkan pendarahan atau lebih teruk, kematian. Kajian ini hanya dijalankan dengan pendekatan berdasarkan pengiraan matematik tanpa melibatkan sebarang eksperimen. Berdasarkan kajian lepas, telah ditunjukkan bahawa sifat-sifat mekanikal di dalam bahagian aneurism adalah berbeza dengan salur darah yang normal. Telah dibuktikan bahawa taburan tekanan yang kuat berlaku di kedua-dua pangkal dan sekitar bahagian pembengkakan aneurism. Dengan mengkaji sifat-sifat mekanikal di abdomen aneurism yang sebenar dapat memberikan maklumat-maklumat yang berguna kepada doktor-doktor kerana ini dapat menolong mereka untuk lebih memahami keadaan aneurism.

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TABLE OF CONTENTS

PAGE

SUPERVISOR’S DECLARATION ii

STUDENTS’S DECLARATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES viii

LIST OF FIGURES xiii

LIST OF ABBREVIATIONS xv

CHAPTER 1 INTRODUCTION

1.1 Background 1

1.2 Problem Statement 2

1.3 Project Objective 2

1.4 Project Scope 2

1.5 Thesis Organization 3

CHAPTER 2 LITERATURE REVIEW

2.1 Background 4

2.2 Types of Aneurysm 5

2.2.1 Abdominal Aortic Aneurysm 5

2.2.2 Thoracic Aortic Aneurysm 6

2.2.3 Cerebral Aortic Aneurysm 7

2.3 Risks of Aneurysm 8

2.4 Finite Element Analysis (FEA) 10

viii

2.5 Computational Fluid Dynamics (CFD) 11

2.6 Fluid Structure Iteration (FSI) 12

2.7 Mechanical Behavior in Abdominal Aortic Aneurysm 13

2.7.1 Pressure Behavior in Abdominal Aortic Aneurysm 13

2.7.2 Mechanical Stresses in Abdominal Aortic Aneurysm 16

2.8 Isotropic and Anisotropic Material 18

2.9 Newtonian and Non-Newtonian Fluids 20

2.10 No-Slip conditions 21

2.11 Biomechanics of Abdominal Aortic Aneurysm 21

2.12 Comparison of Peak Wall Stress in Ruptured and Non Ruptured 22

AAA

2.13 Aneurysm Shapes 23

2.14 Conclusion 24

CHAPTER 3 METHODOLOGY

3.1 Background 25

3.2 Geometry and Properties of Models 26

3.3 Boundary Conditions 28

3.4 Simulation 29

3.5 Simulation for Solid Structure 31

3.5.1 Invoking the AUI and Choosing the Finite Element Program 31

3.5.2 Defining Model Control Data 32

3.5.3 Defining the Modeling 34

3.5.4 Defining the Boundary Condition 38

3.5.5 Defining the Material 38

3.5.6 Defining the Elements 39

3.5.7 Generating the ADINA File, Saving the Database 43

3.6 Simulation for fluid structure 44

3.6.1 ADINA-F Model 44

3.6.2 Defining Model Control Data 45

ix

3.6.3 Defining Model Geometry 53

3.6.4 Defining the Boundary Conditions and Loading 55

3.6.5 Defining Material Properties 57

3.6.6 Defining the Elements 58

3.6.7 Generating the ADINA-F Data File, Saving the ADINA-In 59

Database

3.6.8 Running ADINA-FSI 59

3.7 Examining the Solution 62

3.8 Conclusion 64

CHAPTER 4 RESULTS AND DISCUSSION

4.1 Background 65

4.2 Analysis on the Wall Stress 66

4.3 Analysis on the Velocity of AAA 67

4.4 Analysis on the Pressure of AAA 69

4.5 Result from Manipulated Aneurysm Length 72

4.6 Result from Manipulated Aneurysm Diameter 74

4.7 Aneurysm Wall Deformation 76

4.8 Hemodynamic Study in AAA 77

4.9 Vortex Formation of AAA 78

4.10 Machine Manual 80

CHAPTER 5 CONCLUSION

5.1 Conclusion 81

5.2 Limitations 82

5.3 Recommendations 82

REFERENCES 83

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LIST OF TABLES

Table No. Title Page

2.1 Comparison of patient demographics between ruptured and non-ruptured

AAA

7

2.2 Finding on ergonomics design 15

2.3 Recommended work surface height for standing workers 19

2.4 Previous design of Durian Peeler 19

2.5 Comparison for the selected CAD software 26

3.1 Layout for questionnaire 31

3.2 Justification of the questionnaire 31

4.1 Questionnaire response rate 37

4.2 Correspondent’s Details 37

4.3 Respondent’s working style 42

4.4 Findings on section B questionnaire 46

4.5 Respondent’s working posture 48

4.6 Findings on section C questionairre 54

4.7 Respondent’s preferer working accessories 56

4.8 Findings on section D questionairre 59

4.9 Major dimension for the machine 61

4.10 Summary of justification parts for the machine 62

4.11 Comparison between old and new design 66

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LIST OF FIGURE

Figure No. Title Page

2.1 Reach envelopes 9

2.2 Example of tools redesign 11

2.3 Example of using motion-saving mechanism 11

2.4 Provide padding for hand grip 12

2.5 Provide cushioning for feet 13

2.6 Anthropometry data of the male southern Thai population, aged 18–25 23

2.7 Anthropometry data of the female southern Thai population, aged 18–25 24

3.1 Flow chart of the study 29

4.1 Correspondent ages 39

4.2 Correspondent’s gender 40

4.3 Working hours per day 40

4.4 Working experience at current position 41

4.5 Repetitive works among respondents 42

4.6 Break time required 43

4.7 Moving is required 44

4.8 Lifting is required 45

4.9 Strecthing is required 45

4.10 Working position causes back pain 49

4.11 Pains in upper body 49

4.12 Same working positions for the whole day 50

4.13 Sitting is the best working position 51

4.14 Body needs to bend while working 51

4.15 Force concentrate on hand 52

4.16 Upper arm need to be close to the body 53

4.17 Require an adjustable hand held tool 56

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4.18 Require wrapped tool handle 57

4.19 Working materials or tools place in reach envelope 58

4.20 Adjustable tool and material height 58

4.21 The front view of the new designed machine 61

4.22 Part for the machine 64

4.23 The designed machine 65

4.24 Shows the old and new design machine 67

4.25 Show three main sections for the machine 68

xiii

LIST OF ABBREVIATIONS

MSD Musculoskeletal disorders

SME Small and medium enteprise

MARDI Malaysian Agricultural Research and Development Institute

ABSTRACT

An aneurysm is an abnormal bulging or widening of a portion of an artery due to

weakness in the wall of the aortic wall. This is happening when the mechanical stress

exceeds the tensile strength of the tissue. Aneurysm can happens anywhere in parts of

our body as long there is an aorta. Nowadays, an accurate decision to predict the rupture

of the aneurysm is not is founded yet and usually, clinical doctors will treat the

aneurysm base on the aneurysm size. This study is focusing on abdominal aortic

aneurysm that is occurring at the area of abdomen aorta. By using the simulation tools,

the stress behavior on this region will be analyzed. The normal size of abdomen aorta is

about 2 cm and aneurysm can make this aorta to reach to 6 cm. As the size of an

aneurysm increases, there is a potential of rupture of aneurysm. This can result in severe

hemorrhage or even worst, fatal event. The studies being proceed without experiment

but only based on numerical approach. From the previous studies, it was shown that the

mechanical behaviors inside aneurysm region would be different compare to the normal

blood vessel. The effective wall stress showed large variations on the size and form of

aneurysm. It was proves that a large stress distribution appear at both necks and around

the aneurysm bulge on the anterior surfaces. Studying the mechanical properties in real

AAAs would be useful information to the clinical doctors because it helps them to better

understand of aneurysm behavior.

ABSTRAK

Aneurism adalah kejadian ganjil pembengkakan atau pembesaran bahagian arteri

disebabkan oleh dinding aorta yang lemah. Kejadian ini berlaku apabila tekanan mekanikal

melebihi kekuatan tegangan dinding aorta. Aneurism boleh terjadi di mana-mana bahagian badan

kita yang mempunyai salur darah. Pada hari ini, keputusan yang tepat untuk meramal aneurism

akan pecah belum masih ditemui dan kebiasaannya, doktor akan merawat aneurism berdasarkan

saiz aneurism. Kajian ini akan difokuskan di abdomen aneurism yang berlaku di kawasan salur

darah di perut. Dengan mengunakan kaedah simulasi, sifat-sifat tekanan di kawasan ini akan

dianalisis. Saiz normal untuk salur darah di bahagian perut adalah 2 cm dan aneurism boleh

menyebabkan salur darah ini mencecah 6 cm. Apabila saiz aneurism meningkat, terdapat potensi

untuk aneurism pecah. Ini boleh menyebabkan pendarahan atau lebih teruk, kematian. Kajian ini

hanya dijalankan dengan pendekatan berdasarkan pengiraan matematik tanpa melibatkan

sebarang eksperimen. Berdasarkan kajian lepas, telah ditunjukkan bahawa sifat-sifat mekanikal

di dalam bahagian aneurism adalah berbeza dengan salur darah yang normal. Tekanan effektif

menunjukkan perbezaan yang besar berdasarkan saiz dan bentuk aneurism. Telah dibuktikan

bahawa taburan tekanan yang kuat berlaku di kedua-dua pangkal dan sekitar bahagian

pembengkakan aneurism. Dengan mengkaji sifat-sifat mekanikal di abdomen aneurism yang

sebenar dapat memberikan maklumat-maklumat yang berguna kepada doktor-doktor kerana ini

dapat menolong mereka untuk lebih memahami keadaan aneurism.

CHAPTER 1

INTRODUCTION

1.1 BACKGROUND

The aorta is the largest artery in our body. It is the main artery of the body,

supplying oxygenated blood to the circulatory system. In human body, it passes over the

heart from the left ventricles and runs down in front of the backbone. The aneurysm then is

an excessive localized swelling of the wall of the artery. The force of blood pushing against

the weakened or injured walls can cause bulges and fill it with blood. Then it will become

abnormally large its look like the balloons outward. However, certain medical problems,

genetic conditions, and trauma can damage or injure the artery walls. The biomechanics of

aneurysm has been studied with great interest since aneurysm rupture is a mechanical

failure of the degenerated aortic wall and is a significant cause of death in developed

countries (David A. Vorp. 2006).

In these recent years, the number of cases for aneurysm had increases. The study

and research had been in hope to solve this problem. Patients are currently advised repair if

the diameter of the AAA is 5.5 cm or when the aneurysm is symptomatic (A. K.

Venkatasubramaniam et al 2004. The main complication of aneurysm is like compression

of nearby structures such as nerves, which may lead to weakness and numbness. A blood

clot can develop in the aneurysm because blood flow inside the aneurysm is sluggish. The

clot may extend along the entire wall of the aneurysm. A blood clot may break loose, travel

through the bloodstream, and block the arteries. Besides that, the infection can lead the

body to wide illness. The greatest danger of an aneurysm is rupture, which is often a fatal

event.

PROBLEM STATEMENT

Nowadays, the case of rupture of AAAs is increasing every years and it often occurs

without any preceding symptoms. The rupture occurs when the stress acting on the aorta

wall exceeds the strength of the aorta wall itself. It was necessary to establish reliable

criteria of the rupture risk assessment procedures in AAAs for these lesions, and criteria

based on the mechanical field. Besides that, the prediction of rupture happens is not

available yet. The stress distribution caused by pressure in the aorta is one element factor

that influenced the rupture of aneurysm. So it was necessary to study the behavior of these

elements to better understanding of aneurysm.

1.2 PROJECT OBJECTIVE

The objectives of this study are;

To study the computation of the wall stresses in each virtual of AAA.

The investigation of finite element analysis with different geometries of AAA.

Determine the effect of geometry that influence the magnitude and distribution of

the peak wall stress in the aneurysm.

1.3 PROJECT SCOPE

This project is about to investigate the condition of patient with aneurysm with a certain

softwares. In this type of study, only aneurysm from abdominal area were selected. A

models of AAA with fusiform shape were created in 2-dimension modeling with

differences kind of geometry. The studies being proceed without experimentally but only

based on numerical approach. After the models were created, the finite element analysis on

this models will be done. The result from this study will be analyze and be discuss.

1.4 THESIS ORGANIZATION

There are 5 chapters in this thesis and was organized as follow. For each chapter, there

are sub-topics in it.

In the chapter 1, Introduction consists of some information about aneursym, the studies

and the purpose of this study. In addition, this section also includes the objectives of the

study, the scope of study, the project assumption and how this thesis is organized.

Chapter 2, Literature Review is to gather the useful information from journals, books

and articles that are related to aneurysms study. All the information that gathered from this

chapter will be reviewed to simulate the AAA.

Chapter 3, Methodology, is about the method to simulate this project. The details about

how the simulation is running and the properties that had been used will be shown.

Chapter 4, Result and Discussion is about the analysis of collected data from the

simulations. The behavior of result will be analyzed and discuss.

Chapter 5, Conclusion will discuss about the achievment of the study and also either the

project objective is completed or not. The recommendation regarding the project for the

benefits in the future study will be shared.

CHAPTER 2

LITERATURE REVIEW

2.1 BACKGROUND

AAA disease is degenerative process which worst event is the rupture of the vessel

wall that can bring fatal effect. A.K.Venkatasubramaniam et al. (2004) study as cited in J.F.

Rodriguez et al. (2008) shows that the peak wall stresses in the ruptured aneurysms were

found to be about 60% higher than for the non-ruptured aneurysms. Surgically clipping the

aneurysm from the outside cuts off the interior flow and prevents rupture, but invasive

neurosurgery carries well-known risks of mortality and morbidity (G.R.Stuhne and

D.A.Steinman, 2003). Along with this, the reliable method to predict AAA rupture is not

available yet. In this field of study, the stress distribution of AAA in will be investigated

using finite element analysis. Biomechanical studies had suggested that one determinant of

AAA rupture is related to the stress in the wall (J.F. Rodriguez et al. 2008). By studying the

stress distribution of AAA, the impact load that occurs that applied can be determine and

more, it can predict when the rupture is happening. The basic approach of the finite element

method is to divide a complex geometrical structure (AAA) into smaller pieces or elements

(M. Truijers et al. 2007). The stress distribution on each element will be investigated to find

better accurate analysis. Other than that, the data analysis is depending on real situation of

AAA condition itself. There is some consideration should take into the account before the

study is to proceed. Knowledge of the regional distribution of wall thickness and failure

properties in an AAA can help in understanding its natural history, developing methods to

predict rupture risk and in designing vascular prostheses (Madhavan L. Raghavan et al.

2006).

2.2 TYPES OF ANEURYSM

2.2.1 Abdominal Aortic Aneurysm

Abdominal aortic aneurysms (AAA) are aneurysms that occur in the part of the

aorta that passes through the abdomen. Previous research by Fillinger et al (2002) as cited

Steven P. Marra et al (2006) has demonstrated that aortic aneurysm wall stress is strongly

associated with aneurysm rupture risk in AAA. This type of aneurysms may cause a pulsing

sensation in the abdomen and when they rupture, it can causes deep and excruciating pain.

Doctors often detect an aneurysm during an examination or imaging procedure that is done

for another purpose. The drug is given to lower blood pressure and aneurysms that a large

or growing are repaired by either open or endovascular stent-graft surgery.

Figure 2.1: Abdominal aortic aneurysms

Source: http://health.allrefer.com

2.2.2 Thoracic Aortic Aneurysm

Thoracic aortic aneurysms are aneurysms in the part of the aorta that passes through

the chest (thorax). It may not cause symptoms, or they may cause pain, coughing, and

wheezing. Thoracic aortic aneurysm with vertebral erosion is a very rare and potentially

fatal condition (Yosuke Takahashi et al. 2007).Thoracic aortic aneurysms are associated

with a pathologic lesion termed “medial degeneration,” which is described as a no

inflammatory lesion and it was complication of Marfan syndrome and can be inherited in

an autosomal dominant manner of familial thoracic aortic aneurysm (Rumin He MD et al.

2007). If an aneurysm ruptures, people may have excruciating pain that begins high in the

back and spreads down the back and into the abdomen. Aneurysms are often discovered by

chance, but doctors do x-rays, computed tomography, or another imaging procedure to

determine the size. Rupture of an aortic aneurysm represents a life-threatening condition

and most patients die within 6 h after rupture (Johansson G and Markstrom U, 2006)

Figure 2.2: Thoracic Aortic Aneurysms

Source: http://www.vascularweb.org

2.2.3 Cerebral Aortic Aneurysm

A cerebral aneurysm occurs at a weak spot in an artery that supplies blood to the

brain. Once weakened, the artery wall bulges outward and fills with blood. Most

bifurcations of the cerebral vasculature are structurally stable, but a small number develop a

weakness that causes the wall to expand outwards in the region near the flow divider of the

branching artery (M.Kroon and G.A. Holzapfel, 2007). An aneurysm can burst, spilling

blood into the brain. When this happens, permanent brain damage, disability, or death may

occur. Most cases of cerebral aneurysm are caused by congenital factors. Congenital means

that the person was born with the defect. These mean that person has artery walls that are

thinner than normal in some places. It is in these regions that aneurysms develop.

Aneurysms may be caused by other factors, as well. These factors include injury to the

brain, infection and hardening of the arteries. Previous research by Thom T et al (2006) as

cited by Xin Zhou et al (2006) shows that the rupture of cerebral aneurysm is the leading

cause of hemorrhagic stroke and its mortality rate is about 3–4 folds than that of ischemic

stroke within the onset of 30 days.

Figure 2.3: Cerebral Aortic Aneurysm

Source: http://www.web-books.com

2.3 RISKS OF ANEURYSM

It is not clear exactly what causes aneurysms. But some of these factors are the contributors

to aneurysm. These factors causes the walls of the arteries to weaken thus lead to an

aneurysm.

Age

Gender factor

Hypertension

Ischaemic heart disease.

Smoking

Chronic obstructive pulmonary disease

Aneurysms develop slowly over many years and often have no symptoms. Sometimes

people do not realize they have an aneurysm that can lead to rupture. This symptoms

usually happens to the area where aneurysm is occurs. The symptoms of rupture include:

Headache

Anxiety

Clammy skin

Nausea and vomiting

Pain in the abdomen or back, severe, sudden, persistent, or constant. The pain may

radiate to groin, buttocks, or legs.

Ringing in the ears

Pulsating sensation in the abdomen

Rapid heart rate when rising to a standing position

Shock

Table 2.1: Comparison of patient demographics between ruptured and non-ruptured AAA

Source: A. K. Venkatasubramaniam et al. 2004

Non-ruptured AAA (n=15)

Ruptured AAA (n=12)

P (x2)

Age- median years (range)

75 (66–90) 75 (71–84) NS

Sex- Male:female 5:1 5:1 NS

Hypertension (%) 67 25 NS

Ischaemic heart disease (%)

33 50 NS

Smoking (%) 33 57 NS

COPD (% 56 71 NS

COPD, chronic obstructive pulmonary disease. NS, not significant.

2.4 FINITE ELEMENT ANALYSIS (FEA)

Finite element analysis is a powerful computer-based tool widely used by engineers

and scientists for understanding the mechanics of physical systems. Finite element analysis

consists of a computer model of a material or design that is stressed and analyzed for

specific results. Mathematically, the finite element analysis is used for finding approximate

solutions of partial differential equations as well as of integral equations and in order to

present unlimited degrees of freedom of structures by limited degrees of freedom, the

structures are divided into many elements (Aihong (Rachel) Zhao et al. 2007). These

elements are connected by joint called node and make a grid named mesh. Several modern

finite element packages include specific components such as thermal, fluid flow,

electrostatic and structural working environments

Generally, there are two types of analysis that is two-dimensional and three-

dimensional analysis. The structural of finite element analysis usually consist either linear

or nonlinear and it does generally characterize the elements. Usually finite element models

contain tens of thousands and possibly hundreds of thousands of elements, resulting in

hundreds of thousands of (simultaneous) equations (A.K.Venkatasubramaniam et al. 2004).

Usefulness of the finite element analysis result depends highly on the pre-processing stage.

Thus, defining an appropriate physical model such as mathematical model, geometrical

simplifications, material properties, boundary conditions and an adapted mesh in

accordance with simulation goals is a very difficult and time-consuming task. In practice,

the modeling assumptions are still mostly based on the user's experience (E. Bellenger et al.

2008). By using this tool, it significantly improved both the standard of engineering designs

and the methodology of the design process in many industrial applications.