Structural health monitoring requires collection of large number sample data and sometimes high frequent vibration data
for detecting the damage of structures. The expensive cost for collecting the data is a big challenge. The recent proposed
Compressive Sensing method enables a potentially large reduction in the sampling, and it is a way to meet the challenge.
The Compressed Sensing theory requires sparse signal, meaning that the signals can be well-approximated as a linear
combination of just a few elements from a known discrete basis or dictionary. The signal of structure vibration can be
decomposed into a few sinusoid linear combinations in the DFT domain. Unfortunately, in most cases, the frequencies of
decomposed sinusoid are arbitrary in that domain, which may not lie precisely on the discrete DFT basis or dictionary. In
this case, the signal will lost its sparsity, and that makes recovery performance degrades significantly. One way to
improve the sparsity of the signal is to increase the size of the dictionary, but there exists a tradeoff: the closely-spaced
DFT dictionary will increase the coherence between the elements in the dictionary, which in turn decreases recovery
In this work we introduce three approaches for arbitrary frequency signals recovery. The first approach is the continuous
basis pursuit (CBP), which reconstructs a continuous basis by introducing interpolation steps. The second approach is a
semidefinite programming (SDP), which searches the sparest signal on continuous basis without establish any dictionary,
enabling a very high recovery precision. The third approach is spectral iterative hard threshold (SIHT), which is based on
redundant DFT dictionary and a restricted union-of-subspaces signal model, inhibiting closely spaced sinusoids. The
three approaches are studied by numerical simulation. Structure vibration signal is simulated by a finite element model,
and compressed measurements of the signal are taken to perform signal recovery. Comparison of the performance of the
three approaches is made, and future work on design of compressive sampling testing system for vibration signal is
In order to improve inspection result repetition and flaw ration veracity of manual ultrasonic inspection of offshore
platform structure, an ultrasonic phased array inspection imaging technology for NDT of offshore platform structures is
proposed in this paper. Aimed at the practical requirement of tubular joint welds inspection of offshore platform
structures, the ultrasonic phased array inspection imaging system for offshore platform structures is developed, which is
composed of computer, ultrasonic circuit system, scanning device, phased array transducer and inspection imaging
software system. The experiment of Y shape tubular joint model of 60 degree is performed with the ultrasonic phased
array inspection imaging system for offshore platform structures, the flaws characteristic could be exactly estimated and
the flaws size could be measured through ultrasonic phased array inspection imaging software system for offshore
platform structures. Experiment results show that the ultrasonic phased array inspection imaging technology for offshore
platform structures is feasible, the ultrasonic phased array inspection imaging system could detect flaws in tubular joint
model, the whole development trend of flaws is factually imaging by the ultrasonic phased array inspection technology
of offshore platform structures.
Complex stress monitoring test of big scale offshore platform T-shape tubular joint is designed and accomplished. To
assist this study, a finite element model of the T-shape tubular joint is established to predict the complex strain
distribution in the hot spot of the joint. Installation principle and scheme of FBG sensors are proposed. The right angle
FBG strain rosette is developed to measure the principle strain, along with the strain distribution of the hot point, in
comparison with results from strain gauges. The results show that FBG rosette can monitor the principle strain precisely,
and single FBG sensor is acceptable for the hot point strain monitoring. A method is proposed to correct the FBG sensor
measurement for its relatively long sensing gauge. Further experimental results show that a single FBG sensor with data
correction can monitor the hot spot strain of the model. Static test using FBG sensors and strain gauges were designed
and conducted, respectively. Results show that FBG sensors can precisely measure the axial force, the hot spot strain,
and the local strain of the tubular joint model.
In this paper, the vibration damping capacities of cement-based matrix with some additions of multi-walled carbon nanotubes (MWNTs) are investigated with free vibration testing method in an elastic system. The experimental results show that there are positive effects on the critical damping ratio ζ of the cement-based matrix with small amount MWNTs additions. The nanotubes increase the damping ratios (ζ) of the MWNTs reinforced cement composites due to the contribution of excellent frictions among multiple inter-tubes and multi-walled carbon nanotubes-matrix large interface area to damping. The flexural and compressive strength tests of those are subsequently implemented. Results indicate that the nanotubes has the reinforcing function to cement on the flexural strength in some degree, while has the negative impact on its compressive strength.
Aimed at the practical requirement of tubular joints weld inspection of offshore platform structures of Shengli oil field,
the ultrasonic phased array inspection arithmetic for offshore platform structures is proposed. The integrated design of
ultrasonic phased array inspection imaging system for offshore platform structures is completed, the ultrasonic phased
array inspection imaging system for offshore platform structure is integrated on the basis of the each module and the
exploitation of subsystem, which is made up of computer, ultrasonic circuit system, scanning device and phased array
transducer. The ultrasonic phased array inspection experiment of T shape tubular joint model is performed with the
ultrasonic phased array inspection imaging system for offshore platform structures, the flaws characteristic could be
exactly estimated and the flaws size could be measured. Experiment results indicate that the ultrasonic phased array
inspection arithmetic for offshore platform structures is practical, the ultrasonic phased array inspection imaging system
could inspect artificial defects in tubular joint model, such as slag inclusion, crack, gas porosity, etc., the whole
development trend of flaws is factually imaging by the ultrasonic phased array inspection technology of offshore
The ultrasonic phased array inspection imaging system was developed in this paper, which is integrated on the basis
of the each module and the exploitation of subsystem, it is made up of computer, ultrasonic circuit system, scanning
device, phased array transducer and imaging software. The ultrasonic phased array inspection imaging system has the
functions of controlling ultrasonic transmission and reception, controlling sound beam steering and focusing, controlling
scanner moving, receiving flaw information and position formation, restructuring flaw image and commenting damage.
Experiment was done on the fillet weld block of T shape flat plate with some artifical flaws using the ultrasonic phased
array system, the flaws characteristic could be exactly estimated through comparing and analyzing the flaws position in
B-scan image and the waveform feature in A-scan curve, and the flaws size could be measured from the image of C-scan
and D-scan. Experiment results indicate that the flaws detected by the manual ultrasonic inspection technology could be
found over again by the ultrasonic phased array inspection technology, the flaws size measured by the latter is close to
the former, the whole trend of development of flaws are factually imaging by the latter.
Updating the finite element models of structures with semi-rigid joints and boundary are studied. While most researches in this field are on updating semi-rigid joints with moment-rotation effect, in this paper a hybrid finite element to consider both the moment-rotation and shear-displacement effects of joint are proposed. The hybrid element is composed of a beam element with two connections at both ends, and the semi-rigidity of joints of both rotational and shear effects are simulated at the two ends. The stiffness matrix and mass matrix of the hybrid finite element are formulated. A hybrid optimization technique is applied to update structures with semi-rigid joints and boundary. The method proposed is experimentally studied by updating the finite element of a 14-bay beam. The results show that the method can produce an analytical model that better duplicates the dynamic property of actual structure while keep physical connectivity between them.
Since the concept of structural control was proposed by J.P.T. Yao, tremendous progress has been made over the last three decades toward making active structural control a viable technology for enhancing structural functionality and safety against natural hazards such as strong earthquakes and high winds. However, because of the high dimensionality and multiple-input-multi-output nature of civil structure model, it is difficult to design a control strategy to achieve desired stability, robustness with centralized control method. Hierarchical decentralized control strategy is employed in this paper in response to this difficulty. In this approach, the structure to be controlled is divided into a set of substructures. A hierarchical decentralized control consists of two levels: the low-level subsystem by which each substructure is controlled independently by local controllers and local information, and the high-level system that we call it global control system, which takes the outputs of every substructure as its input, and eliminates interconnection among substructures. With LQR active control algorithm in Matlab environment, the centralized control and hierarchical decentralized control strategy are implemented on a 20-storey shear building under dynamic excitation. The simulated results show that both the centralized control and hierarchical decentralized control are able to control the vibration of building. Compared with centralized control, hierarchical decentralized control method has a good control effect with preferably suppressed vibration response and less control force. The study in this paper presents a promising technology for structural vibration control.
Finite element model updating of structures usually results in a nonlinear optimization problem. Finding an optimization technique with high efficiency is one of the key issues for model updating. A hybrid optimization technique is proposed in this paper, which draws together the global searching capability of the chaos-based optimization technique and high searching efficiency of the trust-region optimization method. The hybrid approach is demonstrated to be more efficient and prone to obtain a global minimum as compared to conventional methods using a two dimensional test function. Then this hybrid method is employed to update a 14-bay frame model. An optimization problem for model updating using modal frequencies and modal shapes is formulated. Studies using numerically simulated data and experimental data show that the proposed hybrid optimization technique is very promising for structural model updating.
Artificial Neural Networks (ANNs) have been applied in structural damage detection as a classifier, but generally a capable ANNs has to be trained with a certain amount of samples. When both damage locations and damage extents are to be identified, the amount of training samples is tremendous because of the combinations of damage locations and extents. By wavelet transform of the structure free motion equations, the Residual Wavelet Coefficient Vector (RWCV) is deduced. A damage feature parameter is defined as the ratio between RWCVs in two different frequency bands. This parameter has a unique property that it's sensitive only to damage locations, and is independent of damage extents. The damage feature parameters are then fed to the neural network for damage localization. After the damage sites are detected, the damage extent is further identified by another neural network with RWCVs as inputs. This two-phase approach for damage localization and extent identification can simply the neural network and reduce the training samples tremendously. Finally a numerical example is given for damage detection of a 10 DOFs system using the proposed approach.
Structural fatigue life prediction, especially for the structures in service, is still a world-wide big problem, which is the safety evaluation focus of structural health monitoring system. Generally speaking, by now we have no choice but to rely on the strain-time course to give statistical prediction of structural fatigue life. In this paper, a new kind of structural fatigue life prediction smart sensor, named smart fatigue life gauge, is developed. And its effect of resistance accumulation and statistical expression are studied. Then, the solution of fatigue damage life prediction based on smart fatigue life gauge is given. Results show that the smart fatigue life gauge is prominent in the field of structural health monitoring system.