Journal of Vibroengineering
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Verification of new method for automatic thickness measurement of melanocytic skin tumours by high frequency ultrasound
Get PDFHistological thickness of cutaneous melanoma (CM), known as the Breslow index (pT), represents the most important prognostic factor. The objective of this study is to evaluate the reliability of automatic algorithm based on B-scan image processing of 22 MHz ultrasound (US) for measuring the thickness of CM and melanocytic nevi (MN). The thickness of CM (n = 54) and MN (n = 91) has been measured manually (mT) and automatically (aT) using an algorithm based on B-scan image processing of 22 MHz US. All melanocytic skin tumours (MST) were surgically excised and their histological thicknesses (pT) according to Breslow were evaluated. The investigated parameters were expressed as medians with interquartile range (IQR) because of their asymmetric distribution, Spearman’s correlation coefficient was determined as well. An agreement between values of mT/aT and mT/pT was evaluated by using the Bland-Altman plots. We found a good agreement of aT and mT with the moderate bias of 0.08 mm and relatively small range (95 % CI –0.01 to 0.18) in CM, accordingly 0.03 mm (95 % CI 0.00 to 0.07 mm) regarding MN. The medians of mT/pT in cases of CM and MN were 0.96 mm (IQR: 0.65-1.52) / 0.97 (IQR: 0.66-1.62) and 0.51 mm (IQR: 0.37-0.67) / 0.69 mm (IQR: 0.46-1.01) respectively. The parameters of the thickness correlated better in CM (r = 0.86) than in MN (r = 0.64) cases. The difference between manual (mT) and automatic (aT) measurements while evaluating the thickness of MST was non-significant. Therefore, automatic algorithm based on B-scan image processing of 22 MHz US is a reliable tool for measuring the thickness of MST by less experienced operators
Joint sparse representation based classification of rub-impact in rotating machinery with multiple acoustic emission sensors
Get PDFAcoustic emission (AE) technique has been widely used for the classification of rub-impact in rotating machinery due to its high sensitivity, wide frequency response range and dynamic detection property. However, it is still unsatisfied to effectively classify the rub-impact in rotating machinery under complicated environment using traditional classification method tailored to a single AE sensor. Recently, motivated by the theory of compressed sensing, a sparse representation based classification (SRC) method has been successfully used in many classification applications. Moreover, when dealing with multiple measurements the joint sparse representation based classification (JSRC) method could improve the classification accuracy with the aid of employing structural complementary information from each measurement. This paper investigates the use of multiple AE sensors for the classification of rub-impact in rotating machinery based on the JSRC method. First, the cepstral coefficients of each AE sensor are extracted as the features for the rub-impact classification. Then, the extracted cepstral features of all AE sensors are concatenated as the input matrix for the JSRC based classifier. Last, the backtracking simultaneous orthogonal matching pursuit (BSOMP) algorithm is proposed to solve the JSRC problem aiming to get the rub-impact classification results. The BSOMP has the advantages of not requiring the sparsity to be known as well as deleting unreliable atoms. Experiments are carried out on real-world data sets collected from in our laboratory. The results indicate that the JSRC method with multiple AE sensors has higher rub-impact classification accuracies when compared to the SRC method with a single AE sensor and the proposed BSOMP algorithm is more flexible and it performs better than the traditional SOMP algorithm for solving the JSRC method
Dynamical response of fractional-order nonlinear system with combined parametric and forcing excitation
Get PDFA dynamical analysis of a Mathieu-van der Pol-Duffing nonlinear system with fractional-order derivative under combined parametric and forcing excitation is studied in this paper. The approximate analytical solution is researched for 1/2 sub harmonic resonance coupled with primary parametric resonance based on the improved averaging approach. The steady-state periodic solution including its stability condition is established. The equivalent linear stiffness coefficient (ELDC) and equivalent linear damping coefficient (ELSC) for this nonlinear fractional-order oscillator are defined. Then, the numerical simulations are presented in three typical cases by iterative algorithms. The time history, phase portrait, FFT spectrum and Poincare maps are shown to explain the system response. Some different responses, such as quasi-periodic, multi-periodic and single periodic behaviors are observed and investigated. The results of comparisons between the numerical solutions and the approximate analytical solutions in three typical cases show the correctness of the analytical solutions. The influences of the fractional-order parameters on the system dynamical response are researched based on the ELDC and ELSC. Through analysis, it could be found that the increase of the fractional-order coefficient would result in the rightward and downward movements of the amplitude-frequency curves. The increase of the fractional-order coefficient will also move the bifurcation point rightwards and will make the existing range of steady-state solution larger. It could also be found that the ELSC will become larger and ELDC smaller when the fractional order is closer to zero, so that the decrease of the fractional order would make the response amplitude larger. At last, the detailed conclusions are summarized, which is beneficial to design and control this kind of fractional-order nonlinear system
Investigation assembly state of spindle bearing based on improved maximum correlated kurtosis deconvolution and support vector machine
Get PDFAiming at the skew and misalignment between the inner and outer rings of the spindle bearing during the installation process, a new method for detecting the spindle bearing assembly state is proposed combined an improved maximum correlated kurtosis deconvolution (IMCKD) and support vector machine (SVM). The vibration and impulse signals induced by bearing assembly skew or dislocation are quite weak. In this paper, the collected vibration signals were preprocessed by IMCKD algorithm with optimized parameters between the normal and skewed state of the outer rings at first, which aims to deconvolve periodic impulse characteristic and enhance the periodic impulse component from a new assembly spindle vibration signal. Then, wavelet packet decomposition method was adopted to extract the characteristic energy value of different frequency bands, and the eigenvector of the assembly state of the spindle bearing was calculated. Furthermore, the support vector machine classification method is implemented to analyze the eigenvectors under different assembly states. Finally, the proposed method was verified by experimental results. The results show that the IMCKD and SVM methods can effectively detect the bearing assembly skew state of the spindle with an accuracy of more than 95 %
Intelligent modeling of double link flexible robotic manipulator using artificial neural network
Get PDFThe paper investigates the application of the Artificial Neural Network (ANN) in modeling of double-link flexible robotic manipulator (DLFRM). The system was categorized under multi-input multi-output. In this research, the dynamic models of DLFRM were separated into single-input single-output in the modeling stage. Thus, the characteristics of DLFRM were defined separately in each model and the coupling effect was assumed to be minimized. There are four discrete SISO model of double link flexible manipulator were developed from torque input to the hub angle and from torque input to the end point accelerations of each link. An experimental work was established to collect the input-output data pairs and used in developing the system model. Since the system is highly nonlinear, NARX model was chosen as the model structure because of its simplicity. The nonlinear characteristic of the system was estimated using the ANN whereby multi-layer perceptron (MLP) and ELMAN neural network (ENN) structure were utilized. The implementation of the ANN and its’ effectiveness in developing the model of DLFRM was emphasized. The performance of the MLP was compared to ENN based on the validation of the mean-squared error (MSE) and correlation tests of the developed models. The results indicated that the identification of the DLFRM system using the MLP outperformed the ENN with lower mean squared prediction error and unbiased results for all the models. Thus, the MLP provides a good approximation of the DLFRM dynamic model compared to the ENN
On the equations of the analytical dynamics of the quasi-3D plate theory of I. N. Vekua type and some their solutions
Get PDFThe plate theory of Nth order is constructed on the background of the Lagrangian variational formalism of analytical dynamics of continuum systems and the dimensional reduction approach of I. N. Vekua – A. A. Amosov. The plate model is defined within the configuration space, the set of field variables, and the Lagrangian density. The field variables are determined by the coefficients of the biorthogonal expansion of the spatial displacement vector field with respect to the dimensionless normal coordinate. The dynamic equations are derived as Lagrange equations of the second kind of the two-dimensional continuum system. The dynamics of the plane elastic layer is considered as an example, the normal wave propagation is described on the basis of refined plate theories of various orders, and the convergence of approximate solutions to the exact solution of the three-dimensional elastodynamics problem is analyzed for different wavenumbers
Intelligent identification method for whole aero-engine connection stiffness
Get PDFA novel intelligent identification method for determining connection stiffness values of the aircraft engine vibration model is proposed. Firstly, a dynamic finite element model of an aero-engine is established. The stiffness values of supports and mountings are taken as the connection parameters to be optimized, and then the natural frequencies of the whole machine are obtained under different connection stiffness values by finite element simulations. The regression function, which is from the stiffness to the natural frequency, is constructed in the support vector machines method. Then, the genetic algorithm is applied to a multi-objective optimization. Based on the real natural frequencies (which can be obtained by a modal test), a fitness function of multi-objective optimization of genetic algorithm is established. Using the real number coding method, the connection stiffness values of the whole machine are finally identified. An aero-engine rotor tester with casing is taken as an example to verify the method. According to the results of a modal test, the stiffness values of the supports and mountings are identified, and the results show the method effectiveness
Effects of the type of exercise performed on the vibration delivered during whole-body vibration exercises
Get PDFWhile the internal load factors of whole-body vibration training have been widely investigated, the study of external load magnitude has been overlooked. Thus, the aim of the present study was to evaluate differences in whole-body vibration stimulus magnitude between static/dynamic whole-body vibration training at various vibration conditions. Four Pro 5 Plate vibration platforms were exposed to twelve different vibration conditions and a triaxial USB Impact X250-2 accelerometer was used to measure platform acceleration during each condition. Paired samples t-test was calculated to evaluate differences among amplitude, frequency, time of acceleration and time of deceleration of each platform at each vibration condition and during static (squat of 90° knee flexion) or dynamic exercise (from stand to 90° knee flexion squat). Also, the intra-class correlation coefficients were examined in order to assess the inter-instrument reliability. Peak-to-peak amplitude, frequency, time of acceleration and deceleration of the vibration platform were not modified by the type of exercise performed. Moreover, the four platforms tested showed high repeatability values during the execution of free vibration, static or dynamic squat in all vibration conditions. This study confirms that the vibration delivered by the Pro 5 Plate vibration platform is not modified during the realization of static or dynamic exercises
Performance improvement of a sigma-delta modulator using fractional-order disturbance observer
Get PDFThis paper proposes a novel design of a high order closed-loop Sigma-Delta modulator using a fractional-order disturbance observer, which can reduce the influence of possible dispersions of the sensing element and offset the effect of the external disturbance. The proof mass can maintain near its position of equilibrium by using the proposed fractional-order disturbance observer, which ensures a better control of the proof mass displacement, and the small proof mass displacement can enhance the sensor resolution and the overall system performance. Fractional-order disturbance observer possesses stronger robust stability of interference elimination, because the introduction of fractional calculus makes Q-filter expanding from an integer domain to a real-number domain. Experimental results from the proposed architecture shows an increase of more than 2X improved in signal quantization noise ratio compared to the pure high-order closed-loop Sigma-Delta modulator, and also the proposed Sigma-Delta modulator with a fractional-order disturbance observer improves the performance of disturbance attenuation and system robustness
Semi analytical solution of a rigid pavement under a moving load on a Kerr foundation model
Get PDFThis paper analyzes the dynamic response of assumedly rigid road pavement under a constant velocity of traffic loads moving on its surface. The model of the rigid road pavement is a damped rectangular orthotropic plate which is supported by an elastic Kerr foundation. Semi-analytical solutions of the dynamic deflection of an orthotropic plate, with semi rigid boundary conditions are presented by using governing differential equations. The natural frequencies and mode shapes of the system are then, solved by using the modified Bolotin method considering two transcendental equations as the results of solving the solution of two auxiliaries Levy’s plate type problems. The moving traffic loads modeled by varying the amplitudes of dynamic transverse concentrated loads harmonically. Numerical studies on the soil types, foundation stiffness models, varying constant velocities and loading frequencies are conducted to show the effects of the dynamic response behaviors of the plates. The results show that the dynamic responses of the rigid road pavement influenced significantly by the type foundation stiffness models and velocity of the moving load