Title: A Simulation Study for Mode Selection by Means of MultipleElement Ultrasonic Transducers Acting from
1A Simulation Study for Mode Selection by Means of
Multiple-Element Ultrasonic Transducers Acting
from the Section of a Waveguide
- by Karim Jezzine and Alain Lhémery
- French Atomic Energy Commission
- CEA - Saclay
2- Context guided wave (GW) testing and mode
selection - Simulation of GW generation by a transducer
mounted on the section - Mode selection principle and simulation results
3GUIDED WAVE TESTING
4MODE SELECTION
How to select a single mode in this configuration?
5- Context guided wave (GW) testing and mode
selection - Simulation of GW generation by a transducer
mounted on the section - Mode selection principle and simulation results
6SIMULATION TOOLS FOR GW
All these terms can be obtained thanks to
calculations based on the Semi-Analytical Finite
Element Method (guide of arbitrary section
normal crack).
7VALIDATION OF THE MODEL
8- Context guided wave (GW) testing and mode
selection - Simulation of GW generation by a transducer
mounted on the section - Mode selection principle and simulation results
9MODE SELECTION
Theoretical observation If both the normal and
tangential stress of the selected mode could be
imposed on the section, only this mode would be
generated.
In practiceThe transducer is modelled as a
source of normal stress with zero tangential
stress imposed (piezo transducer with viscous
fluid coupling)
10MODE SELECTION PRINCIPLE
- (1) Find modes showing frequencies at which the
tangential stress is zero or negligible with
respect to normal stress. - (2) Use a multiple-element ultrasonic transducer
to reproduce the normal stress profile of the
mode at these frequencies.
- Waveguide geometries investigated
- cylindrical (rod, tube) Pochhammer modes
- plate Lamb modes
- rectangular
- Two frequencies have been identified as
favourable to mode selection - (1) So-called universal frequency strictly
zero tangential stress - Lamé modes in a plate (Lamb 1917)
- Axisymmetric modes in a cylinder or tube (Hudson
1943) - Identified for several modes in a rectangular
waveguide (Jezzines PhD 2006) - (2) Frequency close to a maximum of group
velocity negligible tangential stress - Symmetric and antisymmetric modes in a plate
- Axisymmetric modes in a cylinder or tube
- Identified for several modes in a rectangular
waveguide
11UNIVERSAL FREQUENCIES IN A CYLINDER
Identification of universal frequencies for
axisymmetric modes in a steel cylinder of radius
10 mm
Phase velocity Vjw/bn
Group velocity Vgdw/dbn
(km/s)
(km/s)
6
4
2
(MHz)
2
1
(MHz)
12DISCRETISATION OF THE SOURCE
Mode chosen L(0,5) fu51.09 MHz
z
Distribution of normal stress szz(r)
L(0,5) discretised with 5 elements
Imposed normal stress (zero crossing respected)
Multiple-element transducer
(mm)
13SIMULATION RESULTS
z
ExcitationToneburst centered on fu5 with 10
relative bandwidth
d20 mm
Emitter
Cylindrical guide
Receiver
Imposed normal stress at z0
(µs)
14FREQUENCY OF MAX GROUP VELOCITY
Identification of the maxima of group velocity
for axisymmetric modes in a steel cylinder of
radius 10 mm
Minimisation of tangential stress
15DISCRETISATION OF THE SOURCE
Mode chosen L(0,5) fMaxVg50.77 MHz
z
Distribution of normal stress szz(r)
L(0,5) discretised with 6 elements
Multiple-element transducer
16SIMULATION RESULTS
z
ExcitationToneburst centered on fMaxVg5 with
10 relative bandwidth
d20 mm
Emitter
Cylindrical guide
Receiver
Imposed normal stress at z0
(µs)
17ACCOUNT OF A NORMAL CRACK
Axisymmetric normal crack
(A) fc900 kHz
(B) fc1140 kHz
(C) fc771 kHz
0
d/2
0
d/2
0
d/2
(a) Full crack (pa)
(b) Partial crack (p3a/4)
(c) Partial crack (pa/2)
(µs)
18SUMMARY PRESENT WORK
Summary - Two methods of mode selection
using multiple-element transducers mounted on
the section of an elastic waveguide proposed.
- Their performances have been assessed thanks
to simulations based on the semi-analytical
finite element method.
- Present work
- - Industrial transfer - Manufacturing of the
transducer - - Experimental validation
19(No Transcript)
20VALIDATION OF THE MODEL
21COMPARISON OF BOTH METHODS
Universal frequency or frequency of Vg Max ?
22Phase velocity Vfw/bn
(km/s)
EMAT, Comb probe, interdigital transducer, rings
of transducers for pipe inspection Constant
wavelength imposed
Variable angle beam probe Constant phase
velocity imposed
(MHz)
23z 500mm
z 250mm
0
d/2
Standard Exc.
0
d/2
Ideal Exc.
0
d/2
5 rings
24z 500 mm
z 250 mm
Standard Exc.
Ideal Exc
6 rings
25(No Transcript)
26E/R
p
z 0.5 m
27SOURCE OF NORMAL STRESS
z
guide axis
28z zl
z 0