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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
Reducing the bottom-hole differential pressure by vortex and hydraulic jet methods
Get PDFReducing the bottom-hole differential pressure (BHDP) of a gas/oil well and so as to reduce the “chip hold-down effect” can significantly improve the rate of penetration (ROP). The fluid vortex and hydraulic jet methods are used to reduce the BHDP while the wellbore pressure is unchangeable to prevent wellbore instability. The depressurization theories of the two hydraulic pressure drawdown methods are studied. The structures, depressurization mechanism, depressurization capacity, and the current researches and developments of the hydraulic pressure drawdown tools, including the vortex tools and the jet hydraulic pressure drawdown tools (JHPDTs), are analyzed. Using field tests and flow field numerical calculation methods, the key factors which affect depressurization capacity of the vortex tools and the JHPDTs, and the design principles of the vortex bit and the jet pump bit are proposed. Different depressurization methods and structures are simulated, which shows the vortex and jet pump combination bit with 106 mm distance is preferable
Analysis and implementation of adaptive filtered-X LMS algorithm based on reference signal self-extraction
Get PDFBy comparing conventional FXLMS (filtered-X least mean square) control algorithms, the present paper introduces an improved adaptive vibration control FXLMS algorithm based on reference signal self-extraction. It overcomes the problem of reference signal which correlated with external excitation signal is needed to be predicted in advance, namely, the reference signal is extracted from structural vibration in real time in the process of control algorithm. Its theoretical basis is: get an original vibration signal estimation using the error signal of the system and the estimation value is taken as the reference signal of adaptive filtering. In addition, to verify the feasibility and advantage of the proposed algorithm, we simulate solar panels with piezoelectric smart flexible plate and construct the corresponding experimental platform. Finally, the results presented in this paper demonstrate that the proposed algorithm is feasible, effective and achieve improvement with significantly faster convergence speed and better control effect compared with other algorithms
Flutter analysis for wing structure using finite element modeling with equivalent stiffness
Get PDFThe aim of this study is to find a rapid and accurate method for wing flutter prediction in the early stage of aircraft design. A method using the concept of equivalent stiffness is presented for the modal and flutter analysis of a wing. The concept of equivalent stiffness method is that the stringer-stiffened panels in wing structures are replaced by unstiffened panels with the same stiffness, and accordingly the complicacy of the finite element (FE) modeling for wing structures can be reduced substantially. The key of the method is on computation of the stiffness matrices of the unstiffened panels with the equivalent mechanical properties of the stringer-stiffened panels. A regional aircraft wing is used for a case study to verify the accuracy of this method. Both the detailed FE model and the FE model with equivalent stiffness for the wing structure are created and analyzed in MSC.Patran/Nastran. The numbers of elements and degrees of freedom in the FE model with equivalent stiffness are reduced to one-tenth of those in the detailed wing FE model. The complicacy of the detailed FE modeling of the wing structure, such as modeling stringers and handling irregular surface, is avoided in the FE model with equivalent stiffness. The results show that the natural frequencies, mode shapes and flutter speed from the two models are in a good agreement. Satisfactory accuracy and rapid modeling of the FE model with equivalent stiffness make it suitable for wing flutter prediction in conceptual and preliminary aircraft design
Application of the discrete wavelet transform and probabilistic neural networks in IC engine fault diagnostics
Get PDFAround the world are continued attempts to use the vibroacoustic phenomena for purposes of diagnosis of machine condition. Particularly important becomes non-invasive methods including methods based on vibration and acoustic signals. Vibroacoustic phenomena, which relates to the working of technical objects, includes all necessary information connected with the technical condition. The biggest difficulty is the transformation of registered vibroacoustic signals and creation on their basic measures, which will be non-sensitive to any type of interference occurring during the operation of objects and recording signals. To the group of technical objects, for which are already conducted numerous studies all over the world, connected with use of vibroacoustic phenomena for diagnostic purposes which relates to the automotive drive systems, including combustion engines. Combustion engines during its working generate a whole range of vibroacoustic phenomena bringing information on the proper operation of the engine, as well as on condition of each of its elements. In a combustion engine, there are many sources of vibroacoustic phenomena, which contributes to the disruption of diagnostic information. The development of appropriate methods for vibroacoustic signal processing and complete diagnostic systems may allow future extension of the on-board diagnostics OBD system – currently in used cars. The most interesting would be the development of complex system for diagnosing the condition of the individual elements of the car engine operating by basing on information from vibroacoustic signals. In this article are shown results of research, which aim is to diagnose damages of mechanical elements of car combustion engine using vibration signals and artificial neural networks
3-D calibration method and algorithm for freehand image of phased array ultrasonic testing
Get PDFPhased array ultrasonic testing (UT) is an advanced technique applying ultrasound wave vibration theory to detect the flaw in tested materials by imaging. In this research, computer 3-D visualization of the flaw through calibrating the ultrasonic phased array image is proposed. 3-D calibration for ultrasonic phased array image is a procedure to calculate the spatial transformation matrix, spatial relationship between the US image plane and the tracker attached to the UT probe. The calibration method depends on a cross-string phantom and the corresponding algorithm. The phantom with a set of crosses guiding the operator quickly to find the scanning plane. The ten string crosses in the scanning plane provide the coordinates and spatial vectors for the calibration algorithm, thus the calibration algorithm can be realized based on the least-squares fitting method of the homologous points matching. Select the points having different distances and angles with the reference point to calculate the matrix and average them as the final result. The results show that the scanning plane positioning time is no more than 5 s. The precision and the accuracy results are the same as that is obtained through the other published methods in the medical 3-D ultrasound image calibration. The results make the 3-D flaw model reconstruction possible in phased array ultrasonic NDT. It will reduce the difficulties in the flaw recognizing and localization
Identification of modal parameter of nonlinear system from seismic response data using amplitude-dependent time series model
Get PDFThe present work develops a novel procedure of establishing an amplitude-dependent time series model for a nonlinear system and estimating the instantaneous modal parameters of the system from the dynamical responses. The undetermined coefficient in an amplitude-dependent autoregressive with exogenous input (amplitude-dependent ARX) model are assumed as functions of amplitude and are expanded by shape functions constructing by moving least-squares with polynomial basis functions. The amplitude of dynamical responses could be obtained by Hilbert transform. The instantaneous modal parameters of the system are directly estimated from the coefficient in the amplitude-dependent ARX model. The feasibility of the procedure is demonstrated by processing numerically simulated dynamic responses of a nonlinear system. The proposed scheme is demonstrated to be superior to time-varying ARX model and recursive method in identifying modal parameters. Finally, the proposed approach is applied to process measured data for a frame specimen subjected to a series of base excitations in shaking table tests. The specimen was damaged during testing. The identified modal parameters are consistent with observed physical phenomena
Modeling the coupled flexural and torsional vibrations in rotating machines in transient states
Get PDFThe paper presents an example of modelling of coupled flexural, torsional and longitudinal vibrations occurring during the startup of machine consisting of rotors and elastic shaft. The authors’ Simulink block library was used, by which one can model the serial rotating mechanical power transfer systems in any configuration. The main element of the library being development is the rigid rotor model with six degrees of freedom elaborated by the authors. The authors proposed a method for the decoupling equations of motion of the rotor, which allowed their use in Simulink. The general concept of the library assumes division of the rotating system of rigid components (inertial) and elastic components. In this sense, the methodology used is similar to the transfer matrix method developed by Myklestadt and Prohl. The library is open, it can be expanded by new blocks with a particular functionality (bearings, couplings, dampers, drive elements), while maintaining the established structure of signals and method of joining inertial blocks with elastic blocks. In comparison with existing systems of vibration analysis of rotating machinery based on FEM, the major advantages of the Simulink library being developed are: definitely smaller number of degrees of freedom needed to describe the motion, which shortens the simulation times; and the possibility to combine with ready libraries available in Matlab
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