Papers by Author: Hong Wei Ma

Abstract: Based on the results of confined rheological compression test of unsaturated soil samples, some important characteristics and its effective factors have been discussed by using three-dimensional model. At first, the curves of lateral stress relaxation show the process of correspondence with vertical creep. Secondly, it is lateral total stress, and not effective stress, that is relaxed with time because of the volume viscidity of pore water and the shear viscidity of soil skeleton. At last, the limited steady rheological state of soil is controlled by stress strength.

Abstract: Based on the analysis of movement characteristics of gauge disc cutter in cutterhead of tunneling machine, the motion equation to describe the working behavior of the edge point of gauge disc cutter in tunneling process is deduced by using the method of space coordinate transformation matrix. The motion equation has the advantages of considering more parameters, such as position variables of disc cutter, cutter radius, cutterhead rotating speed and advance speed.

Abstract: A new damage identification method for arch bridge structures under a moving load based on the difference of deflection is presented. The function of the deflection at the mid span of the arch with the changing positions of the moving load is derived using the Moore integral method. It can be concluded from the results that when the moving load is in the area without damage, this target indicates to be linear functions with the cosine of an angle (θ) between moving load and horizontal. Nevertheless, this target is multinomial with the change of cosθ in the damage area. In order to validate the proposed damage detection algorithm, a steel arch modal is simulated, which is proved to be practicable in projects. The results indicate that the location and degree of single damage can be identified accurately.

Abstract: Based on the analysis of movement characteristics of inner disc cutter in tunneling machine cutterhead, a trajectory equation to describe the motion behavior of working edge point of inner disc cutter in the process of tunneling is derived by using the method of space coordinate transformation matrix. The trajectory equation mainly considers the parameters of position variables of disc cutter, cutter radius, cutterhead rotating speed and advance speed.

Abstract: In this paper, the feasibility and sensitivity of damage detection based on dynamic responses of a simply supported beam were examined theoretically and numerically, which were the displacement, velocity and acceleration histories at mid-span on a beam under the moving load. First, the theoretic background of a damage beam vibration subjecting to moving load was briefly described. And then a finite element method was used to calculate the responses of the beam. Using wavelet transform of the dynamic responses, the damage could be identified. Case studies showed that the velocity response was sensitive to the damage and the simulations illustrated the better quality of damage detection by velocity than the ones by displacement and acceleration.

Abstract: In this paper, the technology of attractor phase space in chaotic theory is introduced and applied in the structural damage detection. Firstly the phase plane is constructed with the displacement and acceleration responses. Using the changes of phase plane topology of intact and damaged responses, a new damage index is extracted, and the structural damage existence and severity are identified successfully. Since some of the state variables can not be measured, a method of phase space reconstruction is proposed using single dynamic response. The dynamic responses are directly displayed into phase space, realizing transforming the signals from time domain to space domain. Then using the reconstructed phase space, the damage is diagnosed. The results indicate that the phase space reconstruction method has good robustness to noise, and higher sensitivity compared with traditional modal-based methods. The phase space reconstruction method can calculate the value of the damage index using single dynamic response, so that a single sensor can monitor structural damage existence and severity.

Abstract: In this paper, a wavelet-based pipeline inspection method was illustrated experimentally. Piezoelectric ceramic (PZT5), as sensors, was used to generate and receive the guided wave signal. To be specific, a piezoelectric ring was an excitation sensor in order to generate L(0,2) mode guided wave and 16 evenly distributed piezoelectric patches in pipe circle were the reception sensors. A transverse artificial notch in the pipe wall could be detected successfully by the guided wave. For reducing the noise from the testing signal, a wavelet-based denoise technique was proposed Based on the denoised signal, both location and size of the defect could be identified. The result shows that the crack size identification was in good agreement with the theoretical prediction.

Abstract: Intensive research efforts have been spent on vibration-based structural condition monitoring since structural vibration parameters are closely related to structural stiffness which can be used to identify, locate and quantify structural damage. This makes the vibration-based methods quite attractive for structural condition monitoring. This paper proposes to use strain mode for structural damage identification. A new index named Breach Threshold Value of Damage Levels (BTVDL) is proposed to quantify damage. To demonstrate the proposed method, responses of a circular arch with single and multiple damages are simulated using commercial software ANSYS. The simulated dynamic responses are used to identify the location and degree of the damage of the arch. The results demonstrate that strain mode is more sensitive to damages than others indexes such as frequencies and curvature modes. To further verify the method, a scaled arch model was fabricated and tested in the laboratory. Experimental results also confirm the high sensitivity and accuracy of using strain mode in structural damage identification. It is found that the simulated damages can be reliably identified by using the first two strain modes. The proposed method is more sensitive to damages and can be applied to monitoring structural conditions.

Abstract: The local effect of “softening” at the crack location can be simulated by an equivalent spring connecting the two segments of the beam. As modelling the crack, the non-perfectly rigid clamp is also simulated as a torsional spring of unknown stiffness. Combined with the Bernoulli-Euler theories of beam, the present model is applied to derive the characteristic equation of the cantilever beam under uncertain end conditions related to the crack parameters, namely, the location and the depth of the crack. Based on this characteristic equation, an accurate crack identification method is developed to identify the location and the depth of the crack by minimizing the difference between the analytical and experimental frequency values. The proposed approach is verified by two cantilever beam experiments under ideal boundary conditions and uncertain end conditions. It is found that the location and the depth of the crack can be worked out when at least three natural frequencies are known. For crack identification of the cantilever beam under uncertain end conditions, the identified crack location of the proposed approach is more accurate than the Narkis’ method. Furthermore, the crack depth can also be obtained by the present method.

Abstract: The objective of this study is to show the potential of the crack detection method based on Wavelet Packet Transform (WPT), which is depending on the response at a single point on a beam subject to moving load. In this paper, an ANSYS model of a cracked beam is established. The moving load is transient analyzed by shifting the point of the concentrated force. The response at mid-span of the beam is calculated and wavelet packet transformed. The crack on the beam can be found by the abnormal signal in WPT branches. The size is also estimated by a defined damage index (Dindex) which relates to the energy of the abnormal signal. Finally, the effects of both crack location and wavelet selection on Dindex are discussed in detail.