dynamics analysis and improvement of screed based on ...€¦ · the study [2] analyzed the...

Dynamics Analysis and Improvement of Screed

based on Computer Simulation

*Jian Sun and Guiyun Xu College of Mechanical and Electrical Engineering, China University of Mining and Technology, Xuzhou, China

*Corresponding author, Email: [email protected], [email protected]

Xin Wang Ifm Electronic Gmbh, Essen, Germany

Email: [email protected]

Abstract—Screed is the main working component device in a

paver, it plays a very important role in the quality of

construction regardless its performance is good or not. This

study analyzes the paver screed’s dynamic characteristics

and calculates its natural frequency and natural mode of

vibration based on finite element technology. Modification

method proved to have optimized the screed structure. The

results show that the more the screed’s structural strength is

increased the more the natural frequency of bending and

torsional deformation is enhanced. The mode frequency is

greater than the working frequency (50Hz), which means

that the screed structure can avoid resonance effectively and

improve the quality of road paving.

Index Terms—Paver Screed, Finite Element, Natural

Frequency, Computer Simulation

I. INTRODUCTION

With the rapid development of highway construction,

the requirement of pavement also increases. It is

important for development of China's road construction

machinery, especially for paving road construction

machinery. Asphalt paver is special machines that evenly

pave the asphalt mixture on the roadbed and pavement

that have been repaired with certain width and thickness

according to the engineering requirements, and make the

material compaction and ironing. It combines mechanical,

hydraulic and electrical technology in one bodies, is one

of the special equipment with high technical content and

complex structure in the road machinery. It widely used

in roads, airports, mines, hydroelectric dam, port and

other projects. The screed is one of the main working

components of a paver, its role is to mix paving materials,

such as asphalt concrete transported by auger, stabilized

soil, to realize leveling, shaping and pre-compaction.

Screed is in direct contact with the road surface when the

paver paving, so the state of the screed will directly

influence the road after paving. Paver’s screed is a hard

heavy component which could produce constant force.

The screed’s stiffness is very important regarding the

compaction and smoothness of pavement. If the strength

and rigidity of screed are insufficient, the caused

vibration would seriously affect the performance and

quality of the road paving [1]. Therefore, the design of

screed should have the desirable features and

considerable rigidity to prevent distortion of the screed,

so to ensure flatness of attenuation of the screed elevation

within the allowable range.

The study [2] analyzed the structure of vibration

mechanism, and established the solid assembly model of

screed by 3D software, and also discussed the installation

position of the screed vibrators. Li Ziguang et al. [3]

analyzed the dynamical properties of paver cantilever

structure, and conducted modal analysis based the

ANSYS. Subsequently, the innate frequency along with

the vibration mode is detected. Modal analysis is an

important way to structure dynamic design. As each order

natural frequency of the paver suspension arm increases,

the deformation of frame increases gradually. Bending

vibration of suspension arm institutions mainly

concentrated in the end, and central accompanied the

torsional vibration along the z-axis. In the process of

construction, it should be as far as possible avoided that

the working frequency close to the natural frequency of

the suspension arm structure, in order to avoid the system

resonance. The study [4] analyzed the main structure and

working principle of ironing plate, and put forward that

the working state of the screed is the theoretical basis of

its design. Regarding the rational design of ironing plate

structure, stiffness and geometric parameters are key

factors to guarantee the good condition of paver during

paving operation. Li Gang et al. [5] put the ironing plate

composed of two degrees of freedom dynamic system

and established dynamics model of screed. The model of

the ironing plate is simplified as the linear vibration of

longitudinal symmetry plane rigid beam. The dynamic

problems of screed were studied by computer simulation,

and the dynamic characteristics are analyzed as well.

In recent years, there are many scholars who have

made a research on the paver screed, and obtained certain

achievements, but there is a lack of computerized

modeling analysis and dynamic characteristics study of

the iron tablets. In this study, visualization 3D digital

model of screed is created in the PTC environment and

imported into the finite element analysis software

ANSYS for analysis and calculation based on the

prototype structure screed. The natural frequency and

548 JOURNAL OF MULTIMEDIA, VOL. 8, NO. 5, OCTOBER 2013

© 2013 ACADEMY PUBLISHERdoi:10.4304/jmm.8.5.548-556

natural mode of vibration of screed is calculated based on

finite element technology, and the modification method

proved to have optimized the screed structure. Through

structure improvement of iron tablets, the bending,

torsion deformation and natural frequency of screed is

greatly improved, and each order natural frequency was

greater than operating frequency (50 Hz), thus can avoid

resonance effectively and prevent vibration. So, the study

has quite significance to improve the screed’s

performance and the pavement quality through the

structure dynamic analysis, as well as the optimization of

the modal parameters of screed.

II. DYNAMICS MODELING OF SCREED

A. Structure and Composition of Screed

In this paper, the width of iron plate is set 3.0m for

example for analysis. This screed mainly composes of left

and right ironing plate frame, left and right suspension,

lateral connecting rod, camber adjustment, the tamper

mechanism and the eccentric vibration mechanism [6].

They are shown in figure 1.

Figure 1. Structural representation of the screed

Left and right ironing plate frame are hinged by a pin

shaft, then fixed by two supports. Left and right

suspensions are respectively connected with the left and

right frames by bolts. The lateral connecting rod connects

between the right and left suspension to enhance the

mechanism stiffness. The double-tamper mechanism is in

the front of the flatiron-box, it could realize the initial

compaction of the paving mixture by the movement of

vibration beam driven by the rotation of eccentric shaft,

its rotation frequency is generally from 0 to 25Hz [7].

Eccentric vibrating mechanism mainly make use of the

centrifugal force generated by eccentric shaft mounted on

the screed rotary motion to drive the vibration of the

screed, which results in the compaction and surface

finishing while paving hybrid materials. The vibration

frequency ranges from 0 to 50 Hz [8].

B. Dynamic Model of Screed

Regarding to the analysis on dynamic characteristics of

large complicated structures, the establishment of

mechanical model is very important. The actual structure

and loading mode of screed should be took into

consideration when simplifying mechanics model, so that

the mechanical model can be a very good simulation to

the real situation of structure. As the structure of screed

device is very complex, so first create solid models in

Pro/E, and then import into the finite element analysis

software ANSYS for analysis and calculation [9].

Definition of material properties are shown in Table 1.

TABLE I. MATERIAL PARAMETERS

Attribute Value

Density 7.85e-006 kg/mm3

Young’s Modulus 2.0e+005 N/mm2

Poisson’s Ratio 0.3

In order to maintain the accuracy and control the scale

of computation, it is necessary for ironing plate structure

to be appropriately simplified and transform processing

when building up geometric model. Considering the

double tamper mechanism and eccentric vibration

mechanism for the solid shaft and thick plate structure,

the modal properties have little effect on the overall

ironing plate, and the structure is complex, so they are

ignored in the finite element model. While the small hole

and chamfering also have little effect on the results so

they are ignored too. The establishment of FEM model is

shown in figure 2.

Figure 2. Finite element model of the screed

III. DYNAMICS SIMULATION OF SCREED

A. Natural Characteristic Analysis

The actual structure in the engineering is a continuum,

the quality and the elastic parameters are continuously

distributed, it is discretized into a finite discrete system

with multiple degrees of freedom by means of the finite

element method. Then the system dynamics equations are

established using the Lagrange equation, it is expressed

as following:

( ) ( ) ( ) ( )M t C t K t P t (1)

where M is structural mass matrix, C is structural

damping matrix, K is structural stiffness matrix, δ(t) is

generalized coordinates vector, P(t) is structural load

vector.

Calculation of natural frequency and vibration modes

of the structure is a basic problem in dynamic analysis.

Calculation of dynamic response by superposition will

also use these two parameters. Assuming that the

damping and external force is zero, the (1) can be

expressed as following:

0M K (2)

System's inherent frequency and modal vibration mode

is obtained by the characteristic equation.

2( ) 0K M (3)

where ω is the natural frequency, is eigenvector. We

can see that the natural frequency of the system increases

monotonically with the system stiffness meanwhile

decreases monotonically with the system quality.

JOURNAL OF MULTIMEDIA, VOL. 8, NO. 5, OCTOBER 2013 549

© 2013 ACADEMY PUBLISHER

Equation (3) can be obtained by generalized

eigenvalues 2det( ) 0K M or standard eigenvalues

AX IX .

By the standard eigenvalues AX IX , when A is n

order real symmetric positive definite or positive

semidefinite matrix, which has n real eigenvalues, it is


N N-1 2 1 0 (4)

For the generalized eigen value problem, 2det( ) 0K M , which can be solved by trigonometric

process on K or M, and the solution can be obtained

separately.

2 2 2

1 N 2 N-1 N 11 ; 1 ; ; 1 (5)

2 2 2

1 1 2 2 N N; ; ; (6)

Thus, N eigenvalues is obtained by solving the

generalized eigenvalues, the order is as following:

2 2 2 2

N N-1 2 1 0 (7)

Among them, 1 2 N, , , are known as the first,

second, ... N order natural frequencies, and the

corresponding feature vectors 1 2 N, , , are known as

the first, second, ... , N order natural frequency.

TABLE II. MODE CALCULATION RESULTS OF SCREED

Order Frequency(Hz) Mode of vibration

1 0 Rigid translation along the z-axis

2 3.203E-03 Rigid translation along the x-axis

3 0.1004 Rigid translation along the y-axis

4 1.1628 Rigid rotation around

the y-axis

5 1.8532 Rigid rotation around the z-axis

6 2.1956 Rigid rotation around

the x-axis

7 45.492 Front and rear bent swing of tie rod

8 47.846 Up and down bent

swing of tie rod

9 60.344 Front and rear twist of screed

10 76.343 Left and right swing

of screed

11 83.593 Up and down twist

of screed

12 97.41 Up and down twist of screed and suspension swing

Any one of eigenvectors i can show a corresponding

vibration mode of the frequency ωi, and any order

frequency ωi and its feature vector ia respectively

satisfy (3). Where a is an arbitrary constant, so ia is also

the feature vector. So, every mode of vibration can only

determine the mode shape, but not the amplitude.

The analysis of vibration problems using finite element

method is to solve the (3). In the general finite element

analysis, the system has many degrees of freedom. When

studying the dynamic response of the system, often only a

few lower eigenvalues and corresponding eigenvectors

need to be known, so, there is some efficient algorithm

that adapt to this characteristics has been developed,

among which the subspace iteration method and inverse

iteration method are is widely used. Because Lanczos

algorithm has high computational efficiency, so it is more

suitable for solving problems with large eigenvalue.

B. Simulation Results of Screed

The inherent characteristics of the screed is calculated

by finite element analysis software ANSYS. The first 12

order modal frequency of screed is shown in Table 2.

The screed 7 to 12 order vibration modes are shown in

figure 3.

The first six vibration modes of screed are rigid modes,

which are rigid motion along the x, y, z axis and rigid

rotation around the x, y, z axis. Only the spring is

deformed when rigid body moving, the natural frequency

depends on the ironing plate quality and spring stiffness.

From the beginning of the seventh order model, the

screed’s vibration modes are the main bending

deformation and swinging of structure. The excitation

source of screed mainly comes from vibration that the

tamper mechanism and the eccentric vibration

mechanism transfer to the body. The excitation frequency

design value of the tamper device can be changed within

0~25 Hz, and the excitation frequency design value of

eccentric vibration mechanism can be changed within

0~50 Hz, therefore it only needs to pay attention to the

frequency of 0~50 Hz.

From the analysis of the inherent characteristics of the

screed, the ironing plate’s 7 and 8 order modal

frequencies are within 0~50 Hz, and the 9 order modal

frequency is close to 50 Hz. When the working frequency

is close to the natural frequency, mechanism resonance

tends to occur. The 7 and 8 order modals are mainly rod

deformation, so the rod strength should be strengthened.

The 9 order modal shows that iron plate rigidity is weak.

IV. STRUCTURAL DYNAMICS MODIFICATION OF

SCREED

Structural dynamics modification refers to that the

dynamic characteristics of original structure do not meet

the requirements and need to be modified to meet the

given requirements. Under the condition of the original

structure modal parameters being known, make local

changes to the structure, and with a quick and easy way

to get modification modal parameters, namely the

reanalysis of problems of structure. Modification of the

mechanical structure dynamics is designed to optimize

the dynamic of structure to make the structural dynamic

stress parameters more reasonable and improve the

performance of mechanical. For this section, the modal

model is used to modify the finite element model of

screed.

The sensitivity degree of the structural parameters base

on the eigenvalues and eigenvectors can be calculated

through sensitivity analysis for structural dynamic

characteristics, and the influence on the dynamic

characteristics of the structure system can also be found

out, so with the modified structure we can get twice the

result with half the effort.



a). The 7 order vibration mode b). The 8 order vibration mode

c). The 9 order vibration mode d). The 10 order vibration mode

e). The 11 order vibration mode f). The 12 order vibration mode

Figure 3. The 9 to 12 order vibration mode of screed

According to the results of finite element analysis, the

first two order natural frequencies of tie rod are low,

while the work deformation is great, so it needs dynamic

modification. Application for the sensitivity analysis

method modifies the tie rod parameters.

In structural dynamic optimization and modification

technology, when the dynamic characterization of some

structure parameters does not meet the requirements, the

structure needs to be changed. For example, when the

natural frequency is close to the operating frequency, it

would need to modify the structural physical parameters

M, K and C. How to obtain ΔM, ΔK, ΔC to make ωi

maximum in certain direction is the very problem need to

be solved by the sensitivity analysis.

In mathematical sense, the concept of sensitivity can

be defined more broadly. Assume that F(pm) is about pm

multivariate function, the differential sensitivity of the l

order can be expressed as following:

'

m

m

l l

FS F p

p

(8)

m

m

l l

FS F p

p

(9)

Equation (8) and Equation (9) are called the l order

sensitivity of F to pm. In the dynamic modification of

structure, F can represent any dynamic characteristic,

generally represent physical parameters, structural

parameters can also be expressed. When F is the

characteristic value or characteristic vector, the

corresponding sensitivity is called the characteristic

sensitivity; when F is the response, the corresponding



a). The 1 order vibration mode

b). The 2 order vibration mode

c). The 3 order vibration mode

d). The 4 order vibration mode



e). The 5 order vibration mode

f). The 6 order vibration mode

Figure 4. The first six vibration modes comparison of rod

sensitivity is known as response sensitivity; when F is the

frequency response function, the corresponding

sensitivity is called the frequency response function

sensitivity;

The first order sensitivity characteristics value that

relative physical parameters F can be expanded through

M, K and C.

2

m m m m

Ti

i i i i

M C K

p p p p

(10)

On a certain order eigenvalue, the parts that with large

deformation of the mode are known as the sensitive parts,

change the physical parameters of these sites will obtain

the value sensitivity larger feature.

Sensitivity of modal frequencies and damping

sensitivity can be obtained by eigenvalue sensitivity. In

this study, only the modal frequency sensitivity is studied.

Given that the natural modes have been normalized to

structure quality, make dimensionless processing for the

design parameters of structure: Set p0j as the initial

parameter value, the modified value of structure is


0(1 ) ( 1,2, , )j j jp p j n (11)

where pj represents the modified parameter value of the

structure, j represents a structure parameter that needs to

be modified. So, the sensitivity of model natural

frequency can be obtained [10].

0ij j ij j ij

j j

f f f

(12)

where fij(αj) is the i-th natural frequency after the j-th

Structural parameters modified, fij(0j) is the i-th natural

frequency before the j-th Structural parameters modified.

A. Simulation Results of Dynamics Modification for Tie

Rod

According to the engineering experience, there are two

ways to improve the structure stiffness of tie rod, one is

to modify the section size of rod, and the other is to

increase the preload on the tie rod.

Structure dynamic modification was carried out on the

tie rod, and the structural parameters are regarded as

design variables. Rod diameter and wall thickness as the

design variables, considering the sensitivity of modal

frequency with respect to the design variables of the rod,

the calculation results are shown in Table 3.

TABLE III. THE SENSITIVITY VALUE

Parameters Sensitivity value

1 Order 2 Order

Rod diameter(φ Dg) 0.681 0.668

Wall thickness (δg) -1.092 -1.043

From table 3, increasing the stick wall thickness won't

make the natural frequency of the pull rod increasing,

instead it reduces the pull rod natural frequency due to

increase of rod quality; increasing rod diameter can



effectively improve the natural frequency of the pull rod.

Through the analysis, to determine the pull rod

modification method is that rod diameter increase by 60

mm to 80 mm while wall thickness keeps unchanged. The

preload is added to the rod when working. The modal

analysis comparison results of modification on pull rod

are shown in Table 4, and the 1 to 6 order modal shape

comparison of pull rod is shown in figure 5.

TABLE IV. NATURAL FREQUENCY COMPARISON OF TIE ROD

Order

Original modified

Mode of vibration Frequency (Hz)

Frequency (Hz)

1 38.154 52.42 Front and rear bent

swing

2 44.519 58.808 Up and down bent

swing


twist

4 132.18 196.63 Up and down bent

twist


twist swing

6 270.52 416.97 Up and down bent twist swing

According to table 4 and figure 5, after structural

modification, the 1 and 2 order bending frequency of pull

rod is greater than the working frequency range of 50 Hz.

Rod dynamic performance has been greatly improved and

the excessive vibration phenomena of pull rod also has

been avoided effectively in construction process.

B. Simulation Results of Dynamics Modification for

Screed

From 9 to 12 of order bending and twist deformation

mode of screed, we can see that iron plate overall rigidity

is not enough, and the deformation of the suspension is

bigger, so it is necessary to carry out the structural

improvement to eliminate the modal near the operating

frequency. According to the engineering experience and

comparative analysis, the screed structure changes as

following: adopting statically indeterminate structure,

increasing 2 inclined support bars between the ironing

plate frame and suspension and adding reinforcing rib on

the right and left suspension [11]. The modified structure

is shown in figure 5, and the modified finite element

model of the structure is shown in figure 6.

Figure 5. Modified structure of the screed

Figure 6. Modified finite element model of the screed

The modal analysis results before and after

modification of screed is shown in Table 5, and the 7 to

12 order modal shape comparison of screed is shown in

figure 7.

a). The 7 order vibration mode b). The 8 order vibration mode

c). The 9 order vibration mode d). The 10 order vibration mode



e). The 11 order vibration mode f). The 12 order vibration mode

Figure 7. The 7 to 12 order vibration modes of screed after modified

TABLE V. NATURAL FREQUENCY COMPARISON OF SCREED

Order Original modified

Frequency (Hz) Frequency (Hz)

1 0 0

2 3.203E-03 6.81E-04

3 0.1004 0.07543

4 1.1628 1.0611

5 1.8532 1.6931

6 2.1956 2.121

7 45.492 53.512

8 47.846 56.835

9 60.344 68.498

10 76.343 99.728

11 83.593 105.86

12 97.41 126.06

From the analysis result, due to the increase of the

local quality of the system and the spring stiffness

constant for the modification screed, the rigid body

motion frequency of improved screed is lower than that

of the original structure. From the beginning of the

seventh order, modal vibration mode of screed is the

main deformation of bending and swinging, and the

natural frequency of iron plate bending deformation

depends on the structure stiffness. After the dynamic

modification of the screed, the natural frequency is

increased, and the 7, 8 order natural frequency is greater

than the operating frequency (50 Hz). Comparing each

order modal vibration mode of screed before and after

improvement, it can be seen that the deformation of

improved iron plate decrease significantly. We can draw

conclusion that with statically indeterminate structure and

changing the frame size can effectively increase the iron

plate stiffness.

V. CONCLUSIONS

This paper establishes the finite element model of the

screed to simulate and study the dynamic characteristics

of the system. Sensitivity analysis method is applied to

modify the tie rod parameter, and it is found that

increasing the tie rod diameter can effectively improve

the inherent frequency of tie rod. The screed structure is

optimized by adopting statically indeterminate structure,

adding 2 inclined support bars between the ironing plate

frame and suspension and adding reinforcing rib on the

right and left suspension. From the analysis of the

inherent characteristics of the screed before and after

improvement, we can see that bending and torsion natural

frequency of improved screed has been greatly improved,

and the natural frequency is greater than the operating

frequency 50 Hz, which could effectively avoid

resonance and improve the screed’s performance.

Dynamic simulation of structure is an effective method

for structural design and dynamic modification; it will

play an important role in the dynamic design and analysis

of structure.

ACKNOWLEDGMENT

The research work is supported by A Project Funded

by the Priority Academic Program Development of

Jiangsu Higher Education Institutions.

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[9] W. Shi, “The basic steps of finite element analysis,”

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Jian Sun was born in Jiansu, China, in 1975. He is a Ph.D.

candidate in College of Mechanical and Electrical Engineering,

China University of Mining and Technology, Xuzhou, China.

His research interest is mechanical dynamic simulation.

Guiyun Xu was born in Jiansu, China, in 1962. She is a

Professor in College of Mechanical and Electrical Engineering,

China University of Mining and Technology, Xuzhou, China.

Her research interests include the computer simulation and

optimization, robot mechanism and automation control.



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dynamics analysis and improvement of screed based on ...€¦ · the study [2] analyzed the...

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