Energy Envelope Research Articles

Hydraulic fracture studies of reservoirs with an emphasis on pore fracture geometry studies by developing fracture and Microseismic estimations

Nondestructive measurements and evaluation has great significance in various domains of science, engineering and technology. The ob- jective of this research is to investigate the anisotropic behavior in a sandstone sample from non-invasive tests using Laser Doppler Vi- brometer coupled with Piezoelectric Transducer and to validate these results using a laboratory scale controlled hydraulic fracturing ar- rangement. High-resolution 3-component single-point seismograms were generated for the core sample using a combination of 1 MHz Piezoelectric Transducer as a source of elastic waves that travel within the reservoir rock sample and Laser Doppler Vibrometer as the re- ceiver. Hilbert transforms of the 3-component data were calculated to obtain the complex signal. Shear wave splitting phenomenon due to anisotropy in rock was examined and the resultant S H and S V wave polarizations were measured. Elastic tensor for the core sample was subsequently determined from the velocity picks within the Hilbert energy envelope followed by the estimation of Thomsen’s parameters. The hodogram analysis was performed to assess the process of shear wave splitting in the rock sample that detects the anisotropy of the medium and this, in turn, specifies the characteristics of weakness planes. Laboratory scale controlled hydraulic fracturing was performed to verify whether the fractures propagate along the anisotropic planes of weakness. Real-time fracture detection was carried out during this process and its propagation features were studied. The fractured core sample was imaged under the slice Computed Tomography scan machine to perceive the mode and propagation of fractures in the rock specimen.

Subsurface Structure of Long Valley Caldera Imaged With Seismic Scattering and Intrinsic Attenuation

AbstractWe image seismic intrinsic ( ) and scattering ( ) attenuations in Long Valley Caldera, California, by analyzing more than 1,700 vertical component waveforms from local earthquakes. Observed energy envelopes are fit to the diffusion model and seismic attenuation images are produced using two‐dimensional space weighting functions. Low intrinsic and low scattering attenuation anomalies in the center south of the caldera correspond to the location of an earthquake swarm in 2014. We identify high intrinsic and high scattering attenuation anomalies in the fluid‐rich western and eastern areas of the caldera. From a comparison with other geophysical images (magnetotellurics and seismic tomography) we attribute these anomalies to a hydrothermal system (high attenuation). Average to high attenuation values are also observed at the adjacent Mammoth Mountain (southwest of the caldera) and may also have a hydrothermal origin. High intrinsic attenuation at low frequencies to the west of the Hartley Springs Fault may be produced by the magmatic system that produced the Inyo Craters. Seismic attenuation imaging provides insights into subsurface structures that are complementary to velocity and conductivity images.

Enhanced stochastic averaging of non-integrable nonlinear systems subjected to stochastic excitations

Stochastic averaging method based on energy envelope for a non-integrable system reduces the dimension of dynamic systems, while preserving the nonlinearity in system behavior and its stochasticity arising from input excitations. However, this approach for a general system neglects effects of off-diagonal damping components, considers a lumped effect of diagonal damping entries, and assumes independent stochastic excitations for involved degrees of freedom. These constraints may limit the application of stochastic averaging as nonlinear systems often do not satisfy these conditions. This paper addresses these shortcomings and proposes a new strategy to derive an equivalent nonlinear stochastic system. For this purpose, an equivalent excitation intensity and modified damping parameters are derived by equating drift and diffusion components of the modified and the original system through the method of weighted residuals using high order moments of system velocities. The proposed approach, called enhanced stochastic averaging, is demonstrated for a one-story building on a raft foundation in loose sand subjected to lateral stochastic excitations. Results, such as probability density function at different intensity levels, indicate that the enhanced stochastic averaging method significantly improves the analytical predictions of the probabilistic properties of system responses compared to the conventional stochastic averaging method.

Reliability Estimation of Stochastic Dynamical Systems with Fractional Order PID Controller

In this paper, the reliability of stochastic dynamical systems under Gaussian white noise excitations with fractional order proportional–inegral–derivative (FOPID) controller is estimated. First, the FOPID controller is approximated by a set of combination of displacement and velocity based on the generalized van der Pol transformation. Then, the stochastic averaging method of energy envelope is applied to obtain a diffusive differential equation, from which the Backward Kolmogorov equation, governing the conditional reliability function, and the Generalized Pontryagin equation, governing the statistical moments of first-passage time, are derived from the averaged equation and solved numerically. Finally, in the two examples, the critical parameters in the FOPID controller are shown to be capable of improving the reliability of the stochastic dynamical system apparently, and all numerical results are verified to be efficient and correct by the Monte Carlo simulation.

An Algorithm for Heart Rate Extraction From Acoustic Recordings at the Neck

Heart rate is an important physiological parameter to assess the cardiac condition of an individual and is traditionally determined by attaching multiple electrodes on the chest of a subject to record the electrical activity of the heart. The installation and handling complexities of such systems does not prove feasible for a user to undergo a long-term monitoring in the home settings. A small-sized, battery-operated wearable monitoring device is placed on the suprasternal notch at neck to record acoustic signals containing information about breathing and cardiac sounds. The heart sounds obtained are heavily corrupted by the respiratory cycles and other external artifacts. This paper presents a novel algorithm for reliably extracting the heart rate from such acoustic recordings, keeping in mind the constraints posed by the wearable technology. The methodology constructs the Hilbert energy envelope of the signal by calculating its instantaneous characteristics to segment and classify a cardiac cycle into S1 and S2 sounds using their timing characteristics. The algorithm is tested on a dataset consisting of 13 subjects with an approximate data length of 75 h and achieves an accuracy of 94.34%, an RMS error of 3.96 bpm and a correlation coefficient of 0.93 with reference to a commercial device in use.

Numerically Calculated 3D Space-Weighting Functions to Image Crustal Volcanic Structures Using Diffuse Coda Waves

Seismic coda measurements retrieve parameters linked to the physical characteristics of rock volumes illuminated by high frequency scattered waves. Space weighting functions (SWF) and kernels are different tools that model the spatial sensitivity of coda envelopes to scattering and absorption anomalies in these rock matrices, allowing coda-wave attenuation ( Q c o d a ) imaging. This note clarifies the difference between SWF and sensitivity kernels developed for coda wave imaging. It extends the SWF previously developed in 2D to the third dimension by using radiative transfer and the diffusion equation, based on the assumption that variations of Q c o d a depend solely on variations of the extinction length. When applied to active data (Deception Island, Antarctica), 3D SWF images strongly resemble 2D images, making this 3D extension redundant. On the other hand, diffusion does not efficiently model coda waveforms when using earthquake datasets spanning depths between 0 and 20 km, such as at Mount St. Helens volcano. In this setting, scattering attenuation and absorption suffer tradeoffs and cannot be separated by fitting a single seismogram energy envelope for SWF imaging. We propose that an approximate analytical 3D SWF, similar in shape to the common coda kernels used in literature, can still be used in a space weighted back-projection approach. While Q c o d a is not a physical parameter of the propagation medium, its spatially-dependent modeling allows improved reconstruction of crustal-scale tectonic and geological features. It is even more efficient as a velocity independent imaging tool for magma and fluid storage when applied to deep volcanism.

Trajectory control and random vibration control of nonlinear system with dielectric elastomer actuator

Dielectric elastomer actuators have gained extensive attention in scientific and industrial communities with the rapid development of soft robot technology. There still remain some questions on the control aspect of nonlinear system with dielectric elastomer actuator. The first is whether the soft actuator can successfully drive the primary structure to track an arbitrary prescribed trajectory. The second is how to suppress the random vibration around the equilibrium position when the primary structure is disturbed by external excitation. This article seeks the answers for these two questions. By directly solving the governing equation of motion, an open-loop control technique is designed to track a prescribed trajectory. The effectiveness of the trajectory tracking technique is investigated and the limitation is illustrated by the influence of inertia of the primary structure. Based on the stochastic averaging of energy envelope and stochastic dynamic programming principle, a clipped control strategy is proposed by slightly adjusting the voltage in real time to suppress the random vibration around the equilibrium position. The good effectiveness and high robustness of the clipped control strategy are verified numerically. This work may provide some guidelines for the control aspect of nonlinear systems with dielectric elastomer actuators.

Wavelet‐based fundamental heart sound recognition method using morphological and interval features

Accurate and reliable recognition of fundamental heart sounds (FHSs) plays a significant role in automated analysis of heart sound (HS) patterns. This Letter presents an automated wavelet-based FHS recognition (WFHSR) method using morphological and interval features. The proposed method first performs the decomposition of phonocardiogram (PCG) signal using a synchrosqueezing wavelet transform to extract the HSs and suppresses the murmurs, low-frequency and high-frequency noises. The HS delineation (HSD) is presented using Shannnon energy envelope and amplitude-dependent thresholding rule. The FHS recognition (FHSR) is presented using interval, HS duration and envelope area features with a decision-rule algorithm. The performance of the method is evaluated on PASCAL HSs Challenge, PhysioNet/CinC HS Challenge, eGeneralMedical databases and real-time recorded PCG signals. Results show that the HSD approach achieves an average sensitivity (Se) of 98.87%, positive predictivity (Pp) of 97.50% with detection error rate of 3.67% for PCG signals with signal-to-noise ratio of 10 dB, and outperforms the existing HSD methods. The proposed FHSR method achieves a Se of 99.00%, Sp of 99.08% and overall accuracy of 99.04% on both normal and abnormal PCG signals. Evaluation results show that the proposed WFHSR method is able to accurately recognise the S1/S2 HSs in noisy real-world PCG recordings with murmurs and other abnormal sounds.

High-port low-latency optical switch architecture with optical feed-forward buffering for 256-node disaggregated data centers.

Departing from traditional server-centric data center architectures towards disaggregated systems that can offer increased resource utilization at reduced cost and energy envelopes, the use of high-port switching with highly stringent latency and bandwidth requirements becomes a necessity. We present an optical switch architecture exploiting a hybrid broadcast-and-select/wavelength routing scheme with small-scale optical feedforward buffering. The architecture is experimentally demonstrated at 10Gb/s, reporting error-free performance with a power penalty of <2.5dB. Moreover, network simulations for a 256-node system, revealed low-latency values of only 605nsec, at throughput values reaching 80% when employing 2-packet-size optical buffers, while multi-rack network performance was also investigated.

A Semi-Analytical Method for the PDFs of A Ship Rolling in Random Oblique Waves

The PDFs (probability density functions) and probability of a ship rolling under the random parametric and forced excitations were studied by a semi-analytical method. The rolling motion equation of the ship in random oblique waves was established. The righting arm obtained by the numerical simulation was approximately fitted by an analytical function. The irregular waves were decomposed into two Gauss stationary random processes, and the CARMA (2, 1) model was used to fit the spectral density function of parametric and forced excitations. The stochastic energy envelope averaging method was used to solve the PDFs and the probability. The validity of the semi-analytical method was verified by the Monte Carlo method. The C11 ship was taken as an example, and the influences of the system parameters on the PDFs and probability were analyzed. The results show that the probability of ship rolling is affected by the characteristic wave height, wave length, and the heading angle. In order to provide proper advice for the ship's manoeuvring, the parametric excitations should be considered appropriately when the ship navigates in the oblique seas.

The positive binding energy envelopes of low-mass helium stars

The positive binding energy envelopes of low-mass helium stars

Interband Absorption and Photoluminescence in the Cylindrical Layered CdS/HgS/CdS Heterostructure

Within the approximation of an isotropic effective mass, the one-particle states of charge carriers in the layered CdS/HgS/CdS heterostructure are considered. It is shown that under conditions in which the strong-quantization regime is realized in the HgS layer, the spatial localization of charge carriers is realized there with the maximum probability. The energy spectrum and envelopes of the wave functions of the electron and hole states are computed in the structure under consideration. The interband optical absorption is computed, when the system is a layered cylindrical quantum dot and when there is a free motion of the charge carriers along the symmetry axis. For the same cases, the photoluminescence spectrum is also considered.

A Novel R Peak Detection Method for Mobile Environments

With the development of the portable electrocardiogram (ECG) sensor, R peaks can be monitored during various physical activities in mobile environment. However, such ECG signals contain real-world noise, complicating the accurate detection of R peak. In this paper, we propose a novel approach for R peak detection in ECG signals with real-world noise by using signal envelop filtering (SEF) and Shannon energy envelope with the Savitzky–Golay filter (SEE-SG). SEF was designed to diminish abrupt peaks due to movement by adjusting its amplitude based on an automatically determined threshold. SEE-SG was used to enhance the QRS-complex. We first designed the experimental protocol for physical activity (sit, walk, and ascend), namely, normal ECG in a physical activity database, and validated our method by using the ECG data of 23 subjects. Moreover, to avoid overtuning on our database, we validated the proposed method using two public databases: the MIT-BIH QT database (QTDB) and Noise Stress Test Database (NSTDB). The experimental results show promising performance on QTDB (SE and P+: 99.96% and ER: 0.08%), NSTDB (SE: 94.07%, P+: 93.45, and ER: 12.57%), and NPADB (SE: 99.95%, P+: 99.78%, and ER: 0.27%). We also assessed our method by comparing the absolute differences of R–R intervals and heart rates between actual and detected R peaks. In conclusion, as the proposed method achieved noise robustness and reliable performance on R peak detection during physical activities, it can be used to monitor a user’s ECG and cardiac health information accurately in daily life.

A comparative study of the stochastic averaging method and the path integration method for nonlinear ship roll motion in random beam seas

In this paper, the energy-based stochastic averaging method and the path integration method are applied to study the stochastic response of the nonlinear roll motion in random beam seas. Specifically, the Markov diffusion theory is applied to describe the random roll motion such that the probabilistic properties of the ship roll motion are governed by the Fokker–Planck (FP) equation. The stochastic averaging method focuses on the roll energy envelope process and reduces the difficulty in calculating the stochastic response via a dimensional reduction of the original system. In contrast, the path integration method is based on the Markov property of the original dynamical system and provides approximate solutions to the FP equation by linking the explicitly known local solutions. Although the stochastic averaging technique is well established in the study of the stochastic responses of various dynamical systems, its accuracy for determining the high-level roll response has not yet been a focus of study. This paper aims to provide a comparative study for the performance of the two above-mentioned methods; additionally, the advantages and shortcomings of using each method for studying the nonlinear roll motion in beam seas are demonstrated by practical calculations.

Energy envelope maintenance among patients with myalgic encephalomyelitis and chronic fatigue syndrome: Implications of limited energy reserves.

The Energy Envelope Theory of myalgic encephalomyelitis and chronic fatigue syndrome postulates that individuals with myalgic encephalomyelitis and chronic fatigue syndrome may experience some increase in functioning if their level of exertion consistently remains within the limits of their available energy. Findings of several studies support this theory; however, the current study is the first to explore how an individual's initial level of available energy may influence the relation between energy envelope maintenance and level of functioning. The functioning, activity, and symptomatology of six groups of individuals with myalgic encephalomyelitis and chronic fatigue syndrome were compared. Groups were created based upon level of available energy (higher or lower) and energy envelope adherence (underextended, within, overextended). Results indicate that, as expected, individuals with myalgic encephalomyelitis and chronic fatigue syndrome who had higher available energy also had better functioning than individuals with lower available energy; however, this relation was less pronounced for individuals who were overexerting themselves. These results are consistent with the Energy Envelope Theory, and they suggest that overexertion was particularly impactful for individuals with higher levels of available energy.

Effect of electric field on the ratio between the rashba and dresselhaus parameters in III–V heterostructures

The size-quantized energy subbands and envelope wave functions for [001] quantum wells based on zinc-blende III–V semiconductors are numerically calculated using the eight-band Kane model and finite-difference discretization scheme in coordinate space. The effect of the quantum-well band parameters and external electric field oriented along the structure growth direction on the ratio between the Rashba and Dresselhaus spin–orbit coupling parameters is studied. It is demonstrated that at certain electric-field values the spin–orbit coupling parameters in GaAs/InGaAs structures can be equal, which ensures the condition for forming stable spin helices. In addition, it is established that the spin–orbit coupling linear in wave vector in symmetric GaAs/InGaAs wells can disappear under certain well widths and barrier chemical compositions.

Influence of envelope waveform on ITD sensitivity of neurons in the auditory midbrain.

Interaural time differences (ITDs) conveyed by the modulated envelopes of high-frequency sounds can serve as a cue for localizing a sound source. Klein-Hennig et al. (J Acoust Soc Am 129: 3856, 2011) demonstrated the envelope attack (the rate at which stimulus energy in the envelope increases) and the duration of the pause (the interval between successive envelope pulses) as important factors affecting sensitivity to envelope ITDs in human listeners. Modulated sounds with rapid attacks and long pauses produce the lowest ITD discrimination thresholds. The duration of the envelope's sustained component (sustain) and the rate at which stimulus energy falls at the offset of the envelope (decay) are only minor factors. We assessed the responses of 71 single neurons, recorded from the midbrains of 15 urethane-anesthetized tri-colored guinea pigs, to envelope shapes in which the four envelope components, i.e., attack, sustain, decay, and pause, were systematically varied. We confirmed the importance of the attack and pause components in generating ITD-sensitive responses. Analysis of neural firing rates demonstrated more neurons (49/71) show ITD sensitivity in response to "damped" stimuli (fast attack and slow decay) compared with "ramped" stimuli (slow attack and fast decay) (14/71). Furthermore, the lowest threshold for the damped stimulus (91 μs) was lower by a factor of 4 than that for the temporally reversed ramped envelope shape (407 μs). The data confirm the importance of fast attacks and optimal pause durations in generating sensitivity to ITDs conveyed in the modulated envelopes of high-frequency sounds and are incompatible with models of ITD processing based on the integration of sound energy over time.NEW & NOTEWORTHY Using single-neuron electrophysiology, we show that the precise shape of a sound's "energy envelope" is a critical factor in determining how well midbrain neurons are able to convey information about auditory spatial cues. Consistent with human behavioral performance, sounds with rapidly rising energy and relatively long intervals between energy bursts are best at conveying spatial information. The data suggest specific sound energy patterns that might best be applied to hearing devices to aid spatial listening.

Reliability‐based control algorithms for nonlinear hysteretic systems based on enhanced stochastic averaging of energy envelope

SummaryCurrent reliability‐based control techniques have been successfully applied to linear systems; however, incorporation of stochastic nonlinear behavior of systems in such control designs remains a challenge. This paper presents two reliability‐based control algorithms that minimize failure probabilities of nonlinear hysteretic systems subjected to stochastic excitations. The proposed methods include constrained reliability‐based control (CRC) and unconstrained reliability‐based control (URC) algorithms. Accurate probabilistic estimates of nonlinear system responses to stochastic excitations are derived analytically using enhanced stochastic averaging of energy envelope proposed previously by the authors. Convolving these demand estimates with capacity models yields the reliability of nonlinear systems in the control design process. The CRC design employs the first‐level and second‐level optimizations sequentially where the first‐level optimization solves the Hamilton–Jacobi–Bellman equation and the second‐level optimization searches for optimal objective function parameters to minimize the probability of failure. In the URC design, a single optimization minimizes the probability of failure by directly searching for the optimal control gain. Application of the proposed control algorithms to a building on nonlinear foundation has shown noticeable improvements in system performance under various stochastic excitations. The URC design appears to be the most optimal method as it reduced the probability of slight damage to 8.7%, compared with 11.6% and 19.2% for the case of CRC and a stochastic linear quadratic regulator, respectively. Under the Kobe ground motion, the normalized peak drift displacement with respect to stochastic linear quadratic regulator is reduced to 0.78 and 0.81 for the URC and CRC cases, respectively, at comparable control force levels. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Vibration response characterisation and fault-size estimation of spalled ball bearings

Research efforts have increased to investigate the ability to quantify localised bearing faults, ie spalls. These efforts revolve around extending the useful service life of the bearing after the detection of spalls. A number of studies have investigated a linear correlation between the size of spalls and three geometric points that may be recognised in the vibration response: the entry into the spall; the exit from the spall; and a third impact point between the first two. The time difference between these points, calculated using different signal processing techniques, has been widely exploited for quantifying spall size. Currently, there are two main challenges: the first is to enhance the entry point, which typically has weak excitation; the second is to distinguish the impact and the exit points investigated in the literature based on the spall size. However, for practical applications, there is no prior rough estimation of the fault size (ie small or large) and a method is needed for the interpretation of responses. This paper provides insights into the movement of the rolling element within the spall region and shows that the rolling element strongly strikes the bearing races at a minimum of two points. A new technique is then presented to quantify the spall and determine the inherent scaling factor without comparison to any reference data. The technique is based on evaluating two root-mean-square (RMS) energy envelopes, one for the vibration signal and one for a numerical differentiation of this signal. A geometric scaling factor is then used to give a generalised quantification for the small and large spalls. Serviceable estimations of spall size have been achieved for several seeded faults measured on two dissimilar test-rigs provided by the German Aerospace Centre (DLR) and the University of New South Wales (UNSW).

Fault diagnosis of rolling bearing based on improved CEEMDAN and distance evaluation technique

In order to accurately identify the fault conditions of rolling bearing, this paper presents a fault diagnosis method based on improved complete ensemble empirical mode decomposition with adaptive noise (CEEMDAN) and distance evaluation technique. In this method, to effectively extract potential fault-related information, vibration signals of rolling bearing in different fault conditions are decomposed into a set of intrinsic mode functions (IMFs) through improved CEEMDAN. The first eight IMFs containing most fault information are selected for extracting fault features. The original feature set is obtained including energy values, singular values and envelope sample entropy values. Then distance evaluation technique is implemented for selecting sensitive feature set and discarding irrelevant or redundant features. Subsequently, the sensitive feature set is fed into support vector machine (SVM) for automatically identifying rolling bearing fault conditions. The simulation results demonstrate that improved CEEMDAN is able to solve the problem of mode mixing and achieve a numerically negligible reconstruction error. Meanwhile experimental consequences indicate that the proposed method can acquire higher identification accuracy, as well as reduce the classifier computational burden.