Journal of Engineering and Thermal Sciences
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An approach for tool health assessment using the Mahalanobis-Taguchi system based on WPT-AR
Get PDFA real-time tool health assessment has a significant implication on reliable machining operations. This paper proposes a health assessment method for tools in milling machine using the Mahalanobis-Taguchi system (MTS) based on wavelet packet transformation and autoregression. In this method, the nonlinear and non-stationary vibration signal from the milling process is first decomposed using wavelet packet transforms. Then, an autoregression (AR) model is constructed for each coefficient of the reconstructed signal, and the parameters as well as variance of the remnants of each AR model are employed to form the initial feature matrix. Singular values of this feature matrix are obtained through singular value decomposition, at which point MTS is employed. In this study, MTS provides (1) a computational scheme based on the Mahalanobis distance for obtaining the health index of a tool, and (2) Taguchi methods to extract the key features and reduce the redundant ones. Finally, the performance and effectiveness of the proposed method are validated by vibration signals acquired from the milling machining process
Stress arch effect on the productivity of the vertical fractured well
Get PDFRock permeability impacts by effective stress. Permeability modulus is used to evaluate the level of permeability reduction due to effective stress change. And the permeability modulus is always obtained by the experiment which assumes that the overburden pressure is constant during production. Actually, the overburden pressure reduces during production due to stress arch effect and it is easy to form a stress arch in the overburden when the reservoir is small and soft compared with surrounding’s rock. Based on the definition of the permeability modulus, we obtain an expression between permeability modulus bγ considering stress arch effect and permeability modulus b0 without stress arch. There lies a linear ship between bγ and b0, which is also proved by the experiment data. Based on the relationship between bγ and b0, a delivery equation for vertical fractured well is established. Compared with the absolute open flow with stress arch ratio of 0, the absolute open flow increases by 2.87 %, 6.79 %, 12.32 %, 20.12 % and 25.44 % for the stress arch ratio of 0.12, 0.28, 0.5, 0.8 and 1, respectively, with permeability modulus b0 of 0.0397 MPa-1. And it increases by 7.31 %, 18.1 %, 34.88 %, 61.02 % and 79.97 % for the stress arch ratio of 0.12, 0.28, 0.5, 0.8 and 1, respectively, when b0= 1. So absolute open flow with high permeability modulus b0 is more sensitive to stress arch ratio. Stress arch also impacts the optimum fracture half-length. Vertical well has the maximum absolute open flow when it has the optimum fracture half-length. The maximum absolute open flow increases with the increasing of stress arch ratio, while optimum fracture half-length decreases with increasing of stress arch ratio for the same permeability modulus b0. Compared with case with no stress arch, the optimum fracture half-length reduces by 2.86 %, 5.7 %, 11.43 %, 17.14 % and 22.86 % for the stress arch ratio of 0.12, 0.28, 0.5, 0.8 and 1 respectively when b0 equals to 0.0397 MPa-1. While the maximum absolute open flow increases by 1.6 %, 3.8 %, 7.16 %, 12.02 % and 15.60 % for the stress arch ratio of 0.12, 0.28, 0.5, 0.8 and 1 respectively. Thus, vertical well considering stress arch needs smaller fracture half-length than that with no stress arch. Meanwhile, the maximum absolute open flow and optimum fracture conductivity both increase as stress arch ratio increases. Compared with the case without stress arch, the optimum fracture conductivity increases by 50 %, while the maximum absolute open flow increases by 21.40 % with stress arch ratio of 0.5 when b0 equals to 0.0397 MPa-1. The stress arch greatly impacts on the stress sensitive permeability, permeability modulus and well performance, which can’t be neglected especially in the low and ultra-low permeability reservoir
Study on the non-uniform contact between the shaft-taper hole and toolholder for a high speed spindle
Get PDFThe drawbar mechanism of a motor built-in high speed spindle with ATC is to provide the clamping force to grip the toolholder for high speed cutting. The connection status between the shaft-taper hole and toolholder is important on the spindle design and manufacture. In this paper, contact analyses of the toolholder and shaft-taper hole using contact elements are conducted. The stresses distribution between the toolholder and shaft-taper hole is then obtained and is used for the subsequent finite element modal analysis. The finite element modal analysis results are verified by the experimental modal testing to guarantee the accuracy of finite element model. Non-uniform contact conditions between the shaft-taper hole and toolholder is addressed especially in this study. Different intensities of resistance to the cutting torque due to different clamping forces, coefficients of friction, contact types and contact rates are provided. The deformations on the shaft and toolholder are also studied in this paper. The results are helpful to design a motor built-in high speed spindle with a suitable clamping force for providing the necessary torque to resist the cutting force and to give a suggestion on the manufacture of toolholder and shaft-taper hole
Estimation of mode shapes expanded from incomplete measurements
Get PDFAnalytically obtained mode shapes do not match with those of the experimental results due to external noise, including modeling and measurement errors. This inconsistency can pose significant difficulties for the subsequent analysis and design. It is impractical to collect the data for the full set of degrees of freedom (DOFs) of a dynamic system. The incomplete data set should be expanded to the full data set. This work provides a method to correct the analytical mode shapes to match the measured modes. We present the updated forms of the parameter matrices based on the estimated mode shape data. A numerical example illustrates the validity of the proposed method
Optimization design of muffler based on acoustic transfer matrix and genetic algorithm
Get PDFSo as to improve the noise reduction performance and the optimization efficiency of the muffler, an optimization design method based on acoustic transfer matrix and genetic algorithm was proposed in this paper, wherein the transmission loss at certain frequency was treated as the optimization objective, and each structural dimension of the muffler as the design variable, the structural optimization design was conducted through genetic algorithm, thus the optimal solutions were eventually obtained; Moreover, single objective optimization and multiple objective optimization were successively performed, with the results compared with each other, through which it could be demonstrated that the result of the latter was superior to that of the former, concretely, the noise was reduced by 21.32 dB
Research on source location of micro-seismic event based on dynamic cluster velocity model
Get PDFA new velocity model based on dynamic cluster was proposed in this paper. During the process of iteration, the sensors can be formed a cluster according to the velocity similitude degree. Based on the assumption that the speeds from source to each sensor in the same cluster are equal, the corresponding objective function was proposed to solve the source location, which didn’t include the velocity parameter. It not only avoided the error from field measurement and the inversion, but also appropriated for the actual situation that the speeds from every source to different sensors are different. By analyzing 24 different cases, the positioning accuracy based on the velocity model proposed in this paper was verified to be preferable and stable, no matter the source is within the region of the sensor’s array or not. Even for the cases of different velocity variation ranges, the velocity model was still reliable.
Comparative study of model updating methods using frequency response function data
Get PDFConstructing accurate finite element models for engineering structures plays a key role in structural dynamic design and analysis. Finite element model updating using frequency response function data arises great attention. In this paper, a comparison of two model updating approaches by using frequency response function data is investigated. The first method is based on sensitivity analysis, which has been regarded as one of the most successful approaches in model updating. The second one is based on the representation of modeling errors as linear combinations of the individual element matrices, which can be used for both error locating and model updating. The basic formulations of these two methods are introduced and the possible solution strategies are discussed. Numerical simulations are conducted to compare the two model updating methods employing the GARTEUR Truss, two aspects effect on the updating solution including magnitude of initial modeling errors and the completeness of measured coordinates are studied. At last, an experimental cantilever beam is updated by adopting the sensitivity method with tested frequency response function, it is shown that the sensitivity method is effective even when the test data are extremely incomplete
Deformation-compensated modeling of flexible material processing based on T-S fuzzy neural network and fuzzy clustering
Get PDFAccording to the factors that influence flexible material processing (FMP), the deformation compensation modeling method based on T-S fuzzy neural network is proposed. This method combines T-S fuzzy reasoning with a fuzzy neural network. Firstly, fuzzy clustering is introduced to extract fuzzy membership functions and the fitness of fuzzy rules of T-S fuzzy neural network antecedent from the past processing data. Secondly, with the steepest descent method, back-propagation iteration is used to calculate the connection weights of the network. The processing of experiments shows that T-S fuzzy neural network modeling is superior to typical T-S model. The angle error and the straightness error processed by NTS-FNN is 40.4 %, 28.8 % lower than those of STS-FNN. The minimum processing time processed by NTS-FNN is lower by 46.1 % than that of STS-FNN
Vibrations of a plate on a two-parameter foundation subjected to moving rectangular loads of varying velocities
Get PDFThe vibrational characteristics of a plate on a two-parameter foundation under moving rectangular loads with variable velocities are investigated, and the general solution for the dynamic deflection of the plate is derived using the double Fourier transform. Employing the fast Fourier Transform, a rigid pavement is chosen to obtain numerical results, which are consistent with those from the classical solution. The effects of initial load velocity, load acceleration, load deceleration and horizontal resistance at the plate bottom on the dynamic deflection are discussed. An expression to predict the critical velocity is derived, and the results from this formula show very good agreement with those from the numerical analysis. The numerical analysis indicates that the maximum dynamic deflection occurs when the load velocity reaches the critical velocity for the plate. The initial velocity, the acceleration and the deceleration of the rectangular load influence the dynamic response, and the dynamic deflection of the plate at the critical velocity decreases significantly as they increases
Experimental investigation of the vibration transmissibility of a magnet-spring vibration isolator under random excitation
Get PDFA magnet-spring vibration isolator comprised of several magnets and mechanical springs has been proved to be highly effective for overcoming the major limitation of a conventional linear vibration isolator in such a way that the stiffness of the isolator is sufficiently large to hold the weight of a load, but becomes much softer under dynamic motion. The vibration transmissibility of this magnet-spring vibration isolator is usually examined using a sinusoidal excitation with a specific frequency because the system is nonlinear. In this paper, the isolation performance of the magnet-spring vibration isolator is further investigated experimentally for the case of random base excitation. The experimental results are compared with the cases of sinusoidal excitation obtained by computer simulations considering both jump-up and jump-down transmissibility curves. The results are interesting: the vibration isolation performance improves as the RMS (Root Mean Square) amplitude of the random base excitation increases; the experimental vibration transmissibility curve of the random excitation is bounded by the jump-up transmissibility curve of the corresponding sinusoidal excitation case