Huang Wen-hu

Negative-selection algorithm based approach for fault diagnosis of rotary machinery

The main task of the immune system is to detect and eliminate the non-self materials called antigens such as virus and cancer cells which come from inside and outside of the living system. The negative-selection algorithm proposed which is inspired by the negative-selection mechanism of the immune system is able to detect any change. In this paper, the algorithm is improved to make it suitable for the fault diagnosis of mechanical equipment. Moreover, based on the improved algorithm a new approach of fault diagnosis of rotary machinery is proposed and its feasibility is demonstrated by the on-line fault diagnosis of rotary machinery successfully. In addition, the approach of the novel fault diagnosis can also be applied to other fields.

Research on solid-liquid coupling dynamics of pipe conveying fluid

On the basis of Hamilton principle, the equation of solid-liquid coupling vibration of pipe conveying fluid is deduced. An asymmetrical solid-liquid coupling damp matrix and a symmetrical solid-liquid coupling stiffness matrix are obtained. UsingQR method, pipes nature frequencies are calculated. The curves of the first four orders of natural frequency-flow velocity of pipe waw given. The influence of flowing velocity, pressure, solid-liquid coupling damp and solid-liquid coupling stiffness on natural frequency are discussed respectively. The dynamic respondence of the pipes for stepload with different flow velocity are calculated by Newmark method. It is found that, with the flow velocity increased, the nature frequency of the pipes reduced, increased, reduced again and so on.

Application of rough set theory to fault diagnosis of check valves in reciprocating pumps

This paper investigates the application of rough set theory (RST) to fault diagnosis of check valves in three cylinder reciprocating pumps. Currently the faults are detected by the operator through readings of flowmeters and piezometers on the output pipeline. However the condition of each valve can not be detected in this way. Therefore a method of vibration measurements is used. A simulation pump is used to generate measurement data for several kinds of faults. To obtain the fault characteristics of the valves, the wavelet packet transform (WPT) is introduced as a preprocessing means of extracting time-frequency information from vibration signals. Furthermore, in order to determine the position of the faulty valve, RST is used in the process of fault diagnosis. It is proved that severe leakage and fault positions can be identified and diagnosed by the above method.

Multiple scattering and dynamic stress analysis of elastic waves in a fiber-reinforced composite with interfaces

Based on the theory of elastic dynamics, multiple scattering of elastic waves and dynamic stress concentrations in fiber-reinforced composite are studied. The analytical expressions of elastic waves in different regions are presented. The mode coefficients of elastic waves are determined in accordance with the continuous conditions of displacement and stress on the boundary of the multi-interfaces. By using the addition theorem of Hankel functions, the formula of scattered wave fields in different local coordinates are transformed into those in one local coordinate to determine the unknown coefficients and dynamic stress concentration factors (DSCFs). The influences of the distance between two inclusions, material properties and structural size on the DSCFs near the interfaces are analyzed. As examples, the numerical results of DSCFs near the interfaces for two kinds of fiber-reinforced composites are presented and discussed.

FLEXURAL WAVE PROPAGATION IN NARROW MINDLIN'S PLATE ∗

Appling Mindlin’s theory of thick plates and Hamilton system to propagation of elastic waves under free boundary condition, a solution of the problem was given. Dispersion equations of propagation mode of strip plates were deduced from eigenfunction expansion method. It was compared with the dispersion relation that was gained through solution of thick plate theory proposed by Mindlin. Based on the two kinds of theories, the dispersion curves show great difference in the region of short waves, and the cutoff frequencies are higher in Hamiltonian systems. However, the dispersion curves are almost the same in the region of long waves.Appling Mindlin’s theory of thick plates and Hamilton system to propagation of elastic waves under free boundary condition, a solution of the problem was given. Dispersion equations of propagation mode of strip plates were deduced from eigenfunction expansion method. It was compared with the dispersion relation that was gained through solution of thick plate theory proposed by Mindlin. Based on the two kinds of theories, the dispersion curves show great difference in the region of short waves, and the cutoff frequencies are higher in Hamiltonian systems. However, the dispersion curves are almost the same in the region of long waves.

ELASTIC WAVE SCATTERING AND DYNAMIC STRESS IN COMPOSITE WITH FIBER

Based on the theory of elastic dynamics, multiple scattering of elastic waves and dynamic stress concentrations in fiber-reinforced composite were studied. The analytical expressions of elastic waves in different region were presented and an analytic method to solve this problem was established. The mode coefficients of elastic waves were determined in accordance with the continuous conditions of displacement and stress on the boundary of the multi-interfaces. By making use of the addition theorem of Hankel functions, the formulations of scattered wave fields in different local coordinates were transformed into those in one local coordinate to determine the unknown coefficients and dynamic stress concentration factors. The influence of distance between two inclusions, material properties and structural size on the dynamic stress concentration factors near the interfaces was analyzed. It indicates in the analysis that distance between two inclusions, material properties and structural size has great influence on the dynamic properties of fiber-reinforced composite near the interfaces. As examples, the numerical results of dynamic stress concentration factors near the interfaces in a fiber-reinforced composite are presented and discussed.

ANALYSIS OF NONLINEAR DYNAMIC STABILITY OF LIQUID-CONVEYING PIPES

Nonlinearly dynamic stability of flexible liquid-conveying pipe in fluid structure interaction was analyzed by using modal disassembling technique. The effects of Poisson, Junction and Friction couplings in the wave-flowing-vibration system on the pipe dynamic stability were included in the analytical model constituted by four nonlinear differential equations. An analyzing example of cantilevered pipe was done to illustrate the dynamic stability characteristics of the pipe in the full coupling mechanisms, and the phase curves related to the first four modal motions were drawn. The results show that the dynamic stable characteristics of the pipe are very complicated in the complete coupling mechanisms, and the kinds of the singularity points corresponding to the various modal motions are different.

Controlling oscillation by noncritical eigenvalue assignment

Linear feedback stabilization of nonlinear systems in critical cases (NSICC) is studied in this paper. The noncritical eigenvalues are assumed completely controllable. The stability and linear feedback stabilizability are attacked by means of center manifold method and Lyapunov stability analysis. The construction of linear feedback stabilizing law is given on the basis of noncritical eigenvalue assignment.

A METHOD OF INTERFACE INVERSION IN INHOMOGENEOUS MEDIA

First, an approximate solution of time domain interface scattering field is derived by extending the classical Born approximation in the problem of interface scattering. In accordance with the solution form, a projection density compensation (PDC) inversion method is developed according to the projection slice theorem, which is valid for the cases of inhomogeneous media and wave mode transformation. Finally, in the model of layered media, the calculation algorithm and the simulation inversion comparison results of point defect, crack, and crack on an interface, as well as the experiment method and results in the condition of acoustic wave, are given.

Refined dynamic equations of thick beam bending

In this paper, based on the theory of refined dynamic equations of thick plates bending, applied the differential operator algebra and decomposition of operator spectra, the refined dynamic equation of the beam flexural motion is first obtained by using proper gauge conditions and satisfying the boundary conditions. The refined equation of beams is a fourth-order equation, which governs the generalized displacement functions W , F and f . The dispersion relations, which are from the given beam theory, Euler-Bernoulli beam and Timoshenko beam, respectively, are compared. The refined equations of thick beams and applicable condition are investigated and discussed. Since derivation of the refined dynamic equation is conducted without any assumptions, so the proposed equation of thick beam bending is exact, that can be used to analyze vibration of thick beams at the high frequency and to evaluate the applicable condition of the engineering beam theory.