Quadruple Flow and Acoustic Coincident Resonance of Rotating Bladed Disks Interacting With Stationary Elements

In recent years it has been discovered that besides non-uniform flow excitation such as from stator wakes; acoustic pressure pulsation can be a concern, especially for high pressure centrifugal compressor impellers. This has been termed “triple coincidence” and explains rare failures and likely a reason, at least partially, for some previous undocumented failures. Bladed disk interaction resonance discovered by the author in the mid 1970’s can be avoided such as for centrifugal impellers as needed, depending on vibratory mode involved, available damping, and potential excitation level. Especially for stages having vanes in the diffuser near impeller tips, concern for high cycle fatigue is very high as certain numbers of vanes combined with number of rotating blades can give correct phase to excite a highly responding mode. Intentional mistuning of disk-dominated modes has potential for reducing response. A similar but more complex interaction is with transverse acoustic modes having a specific number of nodal diameters. In this case acoustic gas modes in cavities at sides of impellers can match rotating acoustic pulsations at BPF (blade passing frequency) and/or harmonics, termed Tyler-Sofrin modes with increased noise. Also acoustic mode matching impeller structural mode can give the triple coincidence causing resonant response of the impeller. The concern for this coincidence is often difficult to evaluate. For some cases, calculations give enough evidence to modify number of vanes or blades to correct a possible cause of a fatigue failure. This coincidence can add to the direct response, e.g. from either upstream wakes or downstream diffuser vane interacting “potential flow” excitation, herein termed “quadruple coincidence resonance”. Dimensions of impeller side cavities are axisymmetric and are set by aerodynamics, so that outer and inner radii define transverse modes with small radial dimensional changes available. Often a minor aerodynamic performance compromise can be used to change designs to avoid serious resonances, e.g. revise numbers of vanes and/or blades, avoid the response of a matching diameter mode or have a different less responsive mode to alleviate concern. Besides turbomachinery e.g. compressors and pumps, some other methods as described could be utilized for any cavity that has diametrical mode shapes, or possibly other patterns for pressure pulsation frequencies. These modification(s), including patent-pending method, PCT/US2018/020880 described herein can alleviate if not eliminate concern for any mechanism having structural vibration excitation and/or environmental noise issues.

Effect of Angular Acceleration and Unbalance Force Orientation on the Backward Whirl in Cracked Rotors

Rotors have wide applications in several aerospace and industrial heavy-duty systems. In most of these applications, the rotating system reaches its steady state operational speed after the passage through at least one of its critical rotational speeds. In real-life applications, the probable appearance of a residual slight unbalance in the system could cause an elevation in vibration amplitudes at the critical rotational speeds. Accordingly, propagation of cracks in rotating shafts usually influences the level of these vibration amplitudes during start-up and cost-down operations. For such rotating systems, the critical whirl speeds are usually associated with forward and backward whirl responses where it has been always assumed that the backward whirl zone should precede the forward whirl zone. Here, two configurations of cracked rotor-disk systems are considered to study the effect of the angular acceleration and the unbalance force vector orientation with respect to the crack opening direction on the whirl response at the backward whirl zone of rotational speeds. The obtained numerical simulation results are verified through a robust experimental testing for system startup operations. The backward whirl zone is found here to appear immediately after the passage through the critical forward whirl rotational speed. The onset of the backward whirl is also found to be associated with a sharp drop in vibration whirl amplitudes. This backward whirl zone is found to be significantly affected by the unbalance force angle vector orientation and the shaft angular acceleration. More importantly, this zone of backward whirl orbits is not found to be preceding the critical forward whirl zone for the considered cracked shaft-disk configurations.

Elasto-Plastic Modeling of Beams for Impedance Based Structural Health Monitoring

The structural health monitoring by piezoelectric wafer active sensor (PWAS) using electromechanical impedance method used for monitoring of structure. In present work impedance method of elasto-plastic beam structure is studied. In order to model the effect of a plastic in beam, the moment-curvature relationship for elasto-plastic region for loading and unloading is used. The finite difference method is used to discretize beam with piezoelectric. The piezoelectric actuator is modeled by equivalent moment. Then output current of piezoelectric sensor is calculated. Firstly, elastic modeling of beam is considered that this is leads to linear system equation. In linear system, time domain system equations are calculated and Fourier transform of current output obtained, and then impedance of PWAS in frequency domain is calculated. Secondly, the elasto-plastic of beam is modeled. This phenomenon leads to the nonlinear system equations. These nonlinear equations are solved using finite difference method for any harmonic voltage applied to actuator. Then impedance of PWAS is calculated. Two methods are used to detect elasto-plastic modeling on PWAS impedance. At the first, frequency response of elastic beam as intact model is compared with elasto-plastic results in a desired frequency range. Second, only frequency response of one harmonic is computed with its super-harmonics. Finally, the detection method of linear is compared with nonlinear model.

Nonlinear Vibration Analysis of a Fractional Viscoelastic Euler-Bernoulli Microbeam

Nonlinear vibration of a simply-supported Euler-Bernoulli microbeam with fractional Kelvin-Voigt viscoelastic model subjected to harmonic excitation is investigated in this paper. For small scale effects the modified strain gradient theory is used. For take into account geometric nonlinearities the Von karman theory is applied. Beam equations are derived from Hamilton principle and the Galerkin method is used to convert fractional partial differential equations into fractional ordinary differential equations. Problem is solved by using the method of multiple scales and amplitude-frequency equations are obtained for primary, super-harmonic and sub-harmonic resonance. Effects of force amplitude, fractional parameters and nonlinearity on the frequency responses for primary, super-harmonic and sub-harmonic resonance are investigated. Finally results are compared with ordinary Kelvin-Voigt viscoelastic model.

A Holey Cavity for High-Capacity Ultrasound Imaging

Compressive sensing (CS) theory states that, if certain conditions are met, a signal can be retrieved at a sampling rate that is lower than what Nyquist theorem requires. Among these conditions are the sparsity of the signal and the incoherence of the sensing matrix, which is constructed based on how the sensing system is designed. One effective method to render the sensing matrix incoherent is to use random processes in its construction. Diverse approaches have been proposed to randomize the sensing matrix including transmission at random transmitter positions and spectral coding with the use of a physical structure that responds very differently at disparate frequencies. In this work, a holey cavity with various frequency modes is used to spectrally code the ultrasound wave fields. Then, with the use of CS theory and simulations, it is shown that the sensing system that is equipped with such a cavity performs meaningfully better than a regular system in terms of sensing capacity, beam focusing, and imaging. What is more, the validity of Born approximation is investigated in this work to show its extent of applicability in imaging relatively small targets. Due to computational limitations, the simulation domain has been selected to be comparatively small; yet, the achieved results evidently show the concept and warrant further studies on holey cavities in ultrasound imaging, including their fabrication and experimental corroboration. The decrease in the number of measurements necessary for correct image reconstruction can make ultrasound sensing systems more efficient in size and scan time in a variety of applications including medical diagnosis, non-destructive testing, and monitoring.

Application of a Resonant Metamaterial Line Array in Ultrasound Compressive Imaging

Acoustic metamaterials have been proposed for numerous applications including subwavelength imaging, impedance matching, and lensing. Yet, their application in compressive sensing and imaging has not been fully investigated. When metamaterials are used as resonators at certain frequencies, they can generate random radiation patterns in the transmitted and received waves to and from a target. Compressive sensing favors such randomness inasmuch as it can increase incoherence by decreasing the amount of mutual information between any two different measurements. This study aims at assessing whether the use of resonating metamaterial unit cells in a single-layered array between a number of ultrasound transceivers and targets can improve the sensing capacity, point-spread function of the sensing array (their beam focusing ability), and imaging performance in pointlike target detection. The theoretical results are promising and can open the way for more efficient metamaterial designs with the aim of enhancing ultrasound imaging with lower number of transceivers compared to the regular systems.

Objective Evaluation of FCV Interior Sound Quality During Acceleration

While driving a FCV during acceleration, many sorts of sounds could be heard, which influence the interior sound quality. A typical FCV is taken as a sample, four interior noises generated under the acceleration operation are collected in the whole vehicle semi-anechoic chamber, and the noise sample database of diesel engine radiation noise is established after preprocessing. Based on sound quality theory (physical and psychoacoustic features), the Kernel Principal Component Analysis (KPCA) is used to extract the key objective features mainly influencing the sound quality, which realize the dimension reduction target; the variations of objective features are analyzed to qualitatively analyze the law of the sound quality varying during acceleration. According to the objective evaluation of FCV interior sound quality, combining with FCV operating parameters, the influencing law of the FCV sound quality could be obtained.

Different Definitions of Entropy for Statistical Energy Analysis

This paper explores several definitions of entropy that stem from the fields of statistical mechanics and thermodynamics for vibrating structures. This paper shows that these definitions are equivalent in the context of mechanically vibrating systems. However, one is more suitable for statistical energy analysis. This work is motivated by the usefulness of the entropy concept towards developing a framework for the statistical treatment of vibroacoustic systems. Specifically, entropy provides a thermodynamic framework to justify the methodology of statistical energy analysis.

The Study of Holey Cavity in the Application of Thermoacoustics Imaging

Microwave-induced Thermoacoustics (TA) sensing has the potential to be a breakthrough in subsurface imaging applications. This is because it combines the advantages of high contrast of microwave imaging and high resolution of ultrasound imaging. However, state-of-the-art TA hardware requires that the receiving transducer is scanned in a linear or rotational fashion in order to be able to collect enough orthogonal data needed to produce a TA image possessing high-spatial resolution both in range and cross-range. This process is slow, increases the detection time, and adds an extra complexity to the system. In order to address these problems, a Compressive Sensing (CS) methodology is presented in this paper as a mechanism to reduce the minimum number of data samples required to reconstruct a sparse signal. Furthermore, in order to reduce the mutual information shared by different measurements, a holey cavity structure is proposed to be used to perform 4D coding. In this work, the TA imaging theory is introduced; and the impact that the holey cavity parameters have in the imaging performance is studied. The imaging results in this work are carried out using a distributed Alternating Direction Method of Multipliers (ADMM) algorithm, capable of using norm-1 and norm-2 regularizers; and they reveal the effectiveness of the proposed holey-cavity and CS TA imaging approach.

Deep Convolutional Neural Network for Early Disk Crack Diagnosis Under Variable Speed

Aero engine is essentially the heart of an airplane. However, the high temperature and high pressure working environment of the aero engine can easily lead to fatigue cracks in turbine disks, and result in serious accidents. Therefore, early disk crack diagnosis is very important to guarantee safe flight of the airplane and reduce its maintenance cost, which, however, is challenging due to the difficulty in building a complex physical model under variable operating speeds. To tackle this problem, a novel deep convolutional neural network (CNN)-based method is proposed for early disk crack diagnosis. CNN, as one of the deep learning structures, can learn deep-seated features directly and automatically from the raw data without the need of physical model or prior knowledge. It shows the potential to deal with the challenge of early disk crack diagnosis. Since the proposed diagnosis method is signal-level, the collected vibration signals can be input into the CNN architecture directly without the need of feature extractor. In this paper, the vibration signals at both the beginning and the end of the test are used for training the CNN model, then the rest signals are input into the trained model as test data to diagnose when the incipient disk crack is generated. Experimental study conducted on the fatigue test of a real turbine disk has proved the effectiveness and robustness of the proposed method for early disk crack diagnosis. Meanwhile, comparison study with some state-of-the-art methods is also performed, and further highlights the superiority of the proposed method.