VIETNAM ACADEMY OF SCIENCE AND TECHNOLOGY
GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY
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NGUYEN VAN QUANG
DEVELOPMENT AND APPLICATION OF SIGNAL
PROCESSING METHODS FOR CRACK DIAGNOSIS OF
BAR STRUCTURES
Major: Engineering Mechanics
Code: 9520101
SUMMARY OF PhD THESIS
Hanoi – 2018
The thesis has been completed at:
Vietnam Academy of Science and Technology
Graduate University of Science and Technology
Supervisor: Assoc. Prof. Dr. Nguyen Viet Khoa
Reviewer 1: Prof. Dr. Hoang Xuan Luong
Reviewer 2: Assoc. Prof. Dr. Luong Xuan Binh
Reviewer 3: Assoc. Prof. Dr. Nguyen Phong Dien
Thesis is defended before the State level Thesis Assessment
Council held at: Graduate University of Science and
Technology - Vietnam Academy of Science and Technology.
At ………... on ……………………………………………..
Hardcopy of the thesis can be found at:
+ Library of Graduate University of Science and Technology
+ National Library of Vietnam
List of the Author’s publications
1. Khoa Viet Nguyen, Quang Van Nguyen. Time-frequency
spectrum method for monitoring the sudden crack of a column
structure occurred in earthquake shaking duration. Proceeding
of the International Symposium Mechanics and Control 2011,
p. 158-172.
2. Khoa Viet Nguyen, Quang Van Nguyen. Wavelet based
technique for detection of a sudden crack of a beam-like bridge
during earthquake excitation. International Conference on
Engineering Mechanics and Automation ICEMA August 2012,
Hanoi, Vietnam, p. 87-95.
3. Nguyễn Việt Khoa, Nguyễn Văn Quang, Trần Thanh Hải,
Cao Văn Mai, Đào Như Mai. Giám sát vết nứt thở của dầm
bằng phương pháp phân tích wavelet: nghiên cứu lý thuyết và
thực nghiệm. Hội nghị Cơ học toàn quốc lần thứ 9, 2012, p.
539-548.
4. Khoa Viet Nguyen, Hai Thanh Tran, Mai Van Cao, Quang
Van Nguyen, Mai Nhu Dao. Experimental study for monitoring
a sudden crack of beam under ground excitation. Hội nghị Cơ
họ V r n i n ng oàn uốc lần thứ 11, 2013, p. 605-614.
5. Khoa Viet Nguyen, Quang Van Nguyen. Element stiffness
index distribution method for multi-cracks detection of a beam-
like structure. Advances in Structural Engineering 2016, Vol.
19(7) 1077-1091.
6. Khoa Viet Nguyen, Quang Van Nguyen. Free vibration of a
cracked double-beam carrying a concentrated mass. Vietnam
Journal of Mechanics, VAST, Vol.38, No.4 (2016), pp. 279-
293.
7. Khoa Viet Nguyen, Quang Van Nguyen, Kien Dinh Nguyen,
Mai Van Cao, Thao Thi Bich Dao. Numerical and experimental
studies for crack detection of a beam-like structure using
element stiffness index distribution method. Vietnam Journal of
Mechanics, VAST, Vol.39, No.3 (2017), pp. 203-214.
1
INTRODUCTION
Crack detection methods based on oscillating signals are usually
based on two main factors: the dynamical characteristics of the
structure and the oscillating signal processing methods. In practice,
the change in dynamical characteristics of the structure caused by the
crack is very small and difficult to detect directly from the oscillating
measurement signal. Therefore, in order to detect these minor
changes, modern signal processing methods are given, which is the
method of signal processing in time-frequency domains. These
methods include the Short-time Fourier Transform (STFT), the
Wavelet Transform (WT) v.v. These methods will analyze signals in
two time and frequency domains. When using these methods, the
signals over time will be represented in the frequency domain while
the time information is retained. Therefore, time-frequency methods
will be useful for analyzing small or distorted variations in the
oscillation signal caused by the crack.
The objective of the thesis
Study the effect of cracks on the dynamic characteristics of the
structure.
Study the applicability of the time-frequency signal processing
method in detecting cracks.
Application and development the processing time-frequency
oscillation signals methods for cracks detection.
Study method
The dynamic characteristics of cracked structures, such as
frequencies, mode shapes will be calculated and studied by finite
element method.
2
The time-frequency signal processing method will be applied to
analyze the simulated vibration signals of the cracked structure.
Develop an oscillating signal processing method to detect
changes in element stiffness to detect the crack.
Carry out some experiments to verify the effectiveness of the
methods.
New findings of the dissertation
The application of wavelet spectral methods for sudden cracks
detection.
The application of wavelet analysis for cracks detection based on
the effect of cracks and concentrated mass..
Proposed a new method using the "Element stiffness index
distribution method" for crack detection of the structure. In this
method, the element stiffness index distribution is calculated
directly from the oscillation signal.
Structure of the thesis
The contents of the thesis include the introduction, the
conclusion, and 5 chapters:
Chapter 1: An overview
Presents an overview of the world's research on cracks detection
methods based on structural dynamics, signal-processing methods in
time-frequency domain for analysis and crack detection.
Chapter 2: Theoretical basic
Provides a theoretical basic of structural dynamics with cracks.
Introduce cracks model of 2-D and 3-D beams.
Chapter 3: Theory of oscillating signal processing methods