Stress Estimation Method Research Articles

The in situ stress prediction of a fractured shale reservoir based on amplitude variation with angle and azimuth inversion: A case study from Southwest China

In situ stress estimation of a shale reservoir is critical for the design of shale hydraulic fracturing and wellbore stability analysis. Fractured shales have orthogonal anisotropy (OA) because of the presence of vertical fractures and lamination. However, the existing in situ stress estimation method mainly focuses on transversely isotropic media. To accommodate orthogonally anisotropic media, an in situ stress estimation method is developed by using amplitude variation with angle and azimuth inversion and linear-slip theory. First, an orthogonal anisotropic medium is introduced to characterize the fractured shale by using a linear-slip model, and then we formulate a reflection coefficient approximation for OA media to perform the seismic inversion. Next, a fracture weakness inversion strategy that incorporates the vertically transverse isotropic background is developed to obtain the stiffness matrix of the media. Finally, the in situ stresses of the OA medium are formulated by using a stress-strain relationship. Inversion tests and a real data application indicate that our method is effective.

Development of fatigue prediction system for bogie frame using a dynamic analysis model based on high‐speed and high‐precision stress estimation method

AbstractDespite ensuring the integrity of bogie frames for railway vehicles via nondestructive inspections during periodic maintenance, the possibility of fatigue cracks occurring at locations other than the predetermined inspection points cannot be dismissed. Therefore, fatigue cracks can be prevented more efficiently by assessing the overall degree of fatigue damage to the entire bogie frame and determining the results via nondestructive inspections. In this study, dynamic stresses in the bogie frame during running were estimated via finite element dynamic analysis by using the axle box acceleration as input, and the degree of fatigue damage and life were calculated from the waveform of the estimated stresses. Furthermore, we developed a bogie frame fatigue prediction system based on a high‐speed and high‐precision stress calculation method. The developed system visualized the overall relative life.

In situ stress estimation in quantitative micro-elastography.

In quantitative micro-elastography (QME), a pre-characterized compliant layer with a known stress-strain curve is utilized to map stress at the sample surface. However, differences in the boundary conditions of the compliant layer when it is mechanically characterized and when it is used in QME experiments lead to inconsistent stress estimation and consequently, inaccurate elasticity measurements. Here, we propose a novel in situ stress estimation method using an optical coherence tomography (OCT)-based uniaxial compression testing system integrated with the QME experimental setup. By combining OCT-measured axial strain with axial stress determined using a load cell in the QME experiments, we can estimate in situ stress for the compliant layer, more accurately considering its boundary conditions. Our proposed method shows improved accuracy, with an error below 10%, compared to 85% using the existing QME technique with no lubrication. Furthermore, demonstrations on hydrogels and cells indicate the potential of this approach for improving the characterization of the micro-scale mechanical properties of cells and their interactions with the surrounding biomaterial, which has potential for application in cell mechanobiology.

Horizontal transverse isotropy anisotropic parameter inversion via azimuthal seismic velocity anisotropy and its application to anisotropic 3D in-situ stress estimation

Anisotropic parameter inversion in horizontal transverse isotropy (HTI) media plays an important role in predicting the fracture density and the anisotropic in-situ stress for unconventional reservoirs. The current industry practice is to use the azimuthal PP-wave reflection coefficient to estimate the HTI anisotropic parameters. Based on the linear slip theory, we develop an innovative approach that uses azimuthal P-wave phase velocity to calculate HTI anisotropic parameters, which presents superiority over the conventional azimuthal PP-wave reflection coefficient inversion. Specifically, we first verify that the azimuthal P-wave phase velocity is for the HTI elliptical fitting than the azimuthal PP-wave reflection coefficient using the analytical formulations. Second, we sort the prestack wide-azimuth data into offset vector tile sectors and perform amplitude-variation-with-offset inversion at each azimuth. Third, we apply an elliptical fitting to the obtained azimuthal P-wave phase velocities to estimate the HTI anisotropic parameters, fracture density, and fracture direction. Fourth, based on the HTI mechanical earth model, we formulate a cost-effective 3D in-situ stress estimation method using the obtained elastic parameters and fracture compliance. Finally, field examples from the Zhaotong area, China, demonstrate that the estimated fracture density and anisotropic in-situ stress are more accurate and have higher resolution compared with conventional methods. The dominant stress regime in the study area is a strike-slip faulting regime with a governing orientation of northeast–southwest and presents good alignments with well logs, which demonstrates the reliability and accuracy of our method for predicting fracture density and anisotropic in-situ stress.

Further investigating the performance of crop water stress index for maize from baseline fluctuation, effects of environmental factors, and variation of critical value

To further analyze the accuracy and applicability of empirical (CWSI_E) and theoretical (CWSI_T) crop water stress index calculation methods, study was conducted at the USDA-ARS Limited Irrigation Research Farm (LIRF), Colorado, USA during two maize growing seasons in 2013 and 2015. The growth stage and seasonal changes of non-water-stressed baseline (NWSB) and non-transpiration baseline (NTB), the effects of environmental factors, and the estimation performances of water stress, grain yield, and WUE were analyzed. Results show that significant correlations (p < 0.001) with vapor pressure deficit (VPD) were found for two baselines, however, the distributions with the changes of VPD and growth stage and seasonal changes of NWSB and NTB were different between two methods. Specifically, neither growth stage nor growing season significantly affects the baselines of CWSI_E, indicating that the baselines of the empirical method were more stable than those of the theoretical method. The lower baselines and smaller difference between NWSB and NTB were more likely to be observed in the theoretical method than the empirical method. The greater CWSI values were observed for the theoretical method because of the relatively smaller difference between NWSB and NTB. VPD with values greater than 1.5 kPa may a suitable environmental criterion to be used to indicate the applicability of the two CWSI methods for crop water stress estimation. Both methods could track maize water stress with R2 of 0.55 for CWSI_E and 0.49 for CWSI_T (n = 236) with sap flow measurements and could estimate grain yield with the highest R2 of 0.95 and WUE with the highest R2 of 0.87 (n = 24). However, greater values and a clear downtrend for three one-hour periods were observed for CWSI_T because of the relatively smaller difference between NWSB_T and NTB_T. This study contributes to the knowledge in the area of stable and accurate monitoring of crop water status based on CWSI.

Convergence study of stabilized non-ordinary state-based peridynamics for elastic and fracture problems

Non-ordinary state-based peridynamics simulates crack propagation while avoiding the imposition of additional criteria to describe the responses at discontinuities. However, an incomplete coverage by the sphere of a horizon near the boundaries and crack surfaces could cause the boundary effect. In this study, the boundary effects occurring in the stress concentration region are investigated in δ- and m-convergence tests for elastic deformation and crack propagation. Three types of boundary imposition methods are investigated in m-convergence and the method showing the fastest convergence is applied to fracture problems. The weighted average stress estimation is proposed for the damage criterion to reduce the variation in the crack paths in the convergence test, and the weight function is defined as a parameter that can change the shape of the function into three different forms: linear, bilinear, and constant. The fracture simulation is performed in an L-shaped panel with varying geometrical parameters. As a result, the bilinear weighted average stress estimation reduces the variation in the crack path compared to the conventional arithmetic average estimation method. Therefore, the proposed weighted average stress estimation method increases the accuracy of the crack path prediction and will enlarge the application area for fracture simulation using peridynamics.

Modified Tributary Area and Pressure Arch Theories for Mine Pillar Stress Estimation in Mountainous Areas

This paper describes a parametric study using discrete element modeling (DEM) of partial mining in a mountain terrain with in situ pillars for overburden support. For room and pillar mining or strip pillar mining, the accurate estimation of pillar stress is essential to ensure pillar stability and mine safety. Classical mine design methods such as the tributary area theory (TAT) and the pressure arch theory (PAT) are commonly used to calculate the pillar stress for mines under a relatively flat terrain. However, mine sites with uneven terrains can result in nonuniform stress distributions in the mine system and the classical methods may underestimate the pillar stresses by several times. In this paper, 1200 DEM mine models with terrains that include either a single slope or a valley, have been constructed. Through rigorous numerical modeling, the effects of several design parameters are identified: The influence factors, influence range, and mechanism of the concentrated pillar stresses computed from the models indicate that the shape of an extended pressure arch (EPA) can dictate the accuracy of the TAT and PAT methods. Based on the EPA estimation, a pillar stress estimation method is proposed for the design of mines in mountainous terrains. This paper updated the method of terrain-induced pillar stress concentrations with an improved EPA theory, and the gap between PAT and TAT theories is addressed by further discussion on their relationship and applicability.

Stress Estimation of Concrete Dams in Service Based on Deformation Data Using SIE–APSO–CNN–LSTM

The stress behavior of key parts of concrete dams is related to the safe operation of the dam. However, the stress sensors in concrete are susceptible to aging and failure with increasing service life. Estimating the structural stress under sensor failure or data loss scenarios for concrete dams in service is essential and complex. This study presents a stress estimation method driven by the observation data. Firstly, a one-to-one correspondence exists between dam deformation reflecting the load effect and structural stress. Estimating the structural stress by simulating load effects with dam deformation is more convenient when it is hard to simulate complex load effects directly. Therefore, based on the observed data before stress sensor failure, the spatial–temporal relationship between structure stress and multi-point deformations of a concrete dam is developed using convolutional neural networks (CNN) and long short-term memory (LSTM). An improved particle swarm optimization algorithm combined with swarm information entropy (SIE–APSO) is proposed simultaneously for tuning the network’s hyperparameter and accelerating the convergence. Finally, the stress estimation of the target part of the concrete dam in service is obtained. The case shows that it is valid and feasible. The RMSE decreased by approximately 21–58%, MAPE decreased by 19–58%, and ARV decreased by 22–94% compared with the load-stress relationship model.

Wall Shear Stress Estimation for 4D Flow MRI Using Navier-Stokes Equation Correction.

This study introduces a novel wall shear stress (WSS) estimation method for 4D flow MRI. The method improves the WSS accuracy by using the reconstructed pressure gradient and the flow-physics constraints to correct velocity gradient estimation. The method was tested on synthetic 4D flow data of analytical Womersley flow and flow in cerebral aneurysms and applied to in vivo 4D flow data acquired in cerebral aneurysms and aortas. The proposed method's performance was compared to the state-of-the-art method based on smooth-spline fitting of velocity profile and the WSS calculated from uncorrected velocity gradient. The proposed method improved the WSS accuracy by as much as 100% for the Womersley flow and reduced the underestimation of mean WSS by 39 to 50% for the synthetic aneurysmal flow. The predicted mean WSS from the in vivo aneurysmal data using the proposed method was 31 to 50% higher than the other methods. The predicted aortic WSS using the proposed method was 3 to 6 times higher than the other methods and was consistent with previous CFD studies and the results from recently developed methods that take into account the limited spatial resolution of 4D flow MRI. The proposed method improves the accuracy of WSS estimation from 4D flow MRI, which can help predict blood vessel remodeling and progression of cardiovascular diseases.

A NEW EMPIRICAL APPROACH TO ESTIMATE THE RATIO OF HORIZONTAL TO VERTICAL IN-SITU STRESS AND EVALUATION OF ITS EFFECT ON THE STABILITY ANALYSIS OF UNDERGROUND SPACES

In-situ stress is one of the most important input data to study stability analysis of underground and surface geomechanical projects. The measured vertical stress has a linear relation with depth. The average value of unit weight (g) was obtained 0.026 MN/m3 (2.56 ton/m3) using 1041 test results of different rocks with 0.001 difference with 0.027 MN/m3 which is a reliable coefficient for estimating vertical stress. The ratio of horizontal (sh) to vertical (sv) stress (K =sh/sv) is estimated by theoretical and empirical methods. The results showed that the estimating ratio of horizontal to vertical stress (K) by a theoretical method such as Terzaghi and Richard is much smaller than 1, and the estimation of the K value utilizing empirical methods such as Hoek and Brady is much greater than 1, with its value even approaching 4 in the near ground surface. To overcome the lack of an applicable comprehensive relation for the estimation of the K ratio and improve the shortcomings of previous methods, a new empirical relation was developed to estimate the K ratio utilizing a significant number of in-situ test results. Stability analysis of Masjed Soleyman powerhouse caverns was carried out by numerical modelling for five values of the K ratio obtained by previous stress estimation methods and this study. The in-situ stress estimation method (K ratio changes) showed a significant effect on stresses, displacements, strains, depth of the plastic zone and significantly affect the stability analysis and support system design of the powerhouse and transformer caverns.

Including effect of bending stress parallel to the crack plane on a developed local limit load model

A plate containing a semi-elliptical surface crack is selected as a typical surface crack case to investigate the effects of the bending stress parallel to the crack plane on the limit load and elastic-plastic J. Elastic and elastic-plastic FE analyses are used to obtain J values for the surface-cracked plate under stress normal to the crack plane or under biaxial stress plus through-thickness bending with/without bending stress parallel to the crack plane. The results show that the applied bending stress parallel to the crack plane does not affect the elastic J, and, therefore, the stress intensity factor (SIF), but it does affect the elastic-plastic J. A reference stress estimation method considering the bending stress parallel to the crack plane is developed, which shows good correlation to the elastic-plastic J for cases with/without the bending stress parallel to the crack plane. This method is then used to extend the developed local limit load model to include the effect of the bending stress parallel to the crack plane.

The Computational Method of Estimating Vibration Stress Levels for GTE Compressor Blades

At present, the process of designing a GTE involves a large amount of computational modeling. With the help of computational modeling, it is possible to predict a behavior of an engine part during engine operations before conducting experimental studies. For example, the numerical dynamic behavior analysis of compressor blades and prediction of dynamic stress levels during fluctuations in free modes are urgent problems. A high level of dynamic stress in the compressor blades in resonant modes can break a blade and stop an engine. In this paper, we propose a simple vibration stress estimation method for the compressor blades based on the calculation of natural frequencies and vibration forms. The method is based on a comparative analysis and scaling of stresses by the value of the total potential or kinetic energy. This estimation method is valid for local changes in the blade geometry, which do not lead to changes in the natural frequencies and vibration forms of the blades, assuming that the geometry change does not change the level of the aerodynamic excitation of the blade or its damping. At the stage of development or revision of the blade, a large number of variants of the blade geometry needs to be analyzed in order to reduce dynamic stresses. The proposed vibration stress estimation method has shown its high efficiency in developing and refining the geometry of the compressor blade. The vibration stress estimation method was tested using the rotor blade of a high-pressure compressor. As a result of the experimental study of the rotor blade, a high level of vibration stresses exceeding the permissible level was found for natural frequencies and vibration forms. To reduce the vibration stresses, measures were proposed to modify the geometry of the blade. For the modified blade geometry, the vibration stress estimation was performed with a prediction of the vibration stress values based on the manifested vibration forms. In order to verify the estimated vibration stress change, an experimental study of the modified blade was conducted. The vibration stress estimation method for the compressor blades was successfully verified.

Local stress fields in solids estimated by acoustical emission method

Based on the Zhurkov’s kinetic concept of solids’ fracture a local internal stress estimation method is introduced. Stress field is computed from the time series of acoustic emission intervals between successive signals. For the case of two structurally different materials the time evolution of these stresses is examined. It is shown that temporal changes of these stresses’ accumulation law may serve as a precursor of incoming macroscopic fracture.

A time‐dependent stress and strain estimation method for notched components of power‐law creep materials under combined primary and secondary loads

AbstractFinite element analyses on notched beams and axis‐symmetric pipes of power‐law creep materials subjected to combined primary and secondary loads are performed in this work. In view of the characteristics of time‐dependent strain energy density at notches under combined loads, a time‐dependent stress and strain estimation method to address the primary and secondary loads has been proposed by considering the stress ratio between the reference stress devoted by primary stress and the total reference stress. The applicability of the modified method to notched components with different geometrical configurations and load conditions is discussed. Good agreement between the results of inelastic analysis and the modified method is observed.

Basic Study on Stress Estimation Method by using ECG and Facial Image Analysis

Basic Study on Stress Estimation Method by using ECG and Facial Image Analysis

О полях напряжений в гетерогенных средах, определяемых методом акустической эмиссии

Local internal stress estimation method based on the S.N. Zhurkov kinetic concept of solids fracture is introduced. The stress field is computed from the time series of acoustic emission intervals between the successive signals. For the case of two structurally quite different materials the time evolution of this stress is examined.

A time-dependent stress and strain estimation method for notched components under displacement-controlled condition

To address accurately creep responses of notched components under displacement-controlled condition, a time-dependent stress and strain estimation method (i.e. modified Neuber’s method) for notched components under displacement-controlled condition has been proposed, with the deformation characteristics at the far field (i.e. the uniform part) of the component considered. The applicability of the proposed method to notched plates with different geometrical configurations is verified, providing more accurate stress and strain predictions of the notched component than the general Neuber’s rule.

Assessment on Stress Estimation Method for Creep Evaluation of Components at Elevated Temperature Within Elastic Analysis Routine

Abstract An accurate stress estimation for creep evaluation is essential for the long-term safe operation of components at elevated temperature. In general, the section-dependent parameter Kt is defined in elastic analysis routine to account for the reduction in extreme fiber bending stress due to the effect of creep action. A constant value is provided for each cross section in ASME III-5 code, but this may induce underestimation or overestimation of the representative stress of the component due to the relevance of parameter Kt to many factors. Therefore, it is essential to re-examine the validity of the parameter Kt in ASME III-5 code for an adequate creep evaluation. In this work, numerical analyses on beam models with a rectangular section are conducted to calculate parameter Kt, and effects of related factors to the parameter Kt are included. The results reveal that the parameter Kt is closely related to the design life, loading level, operation temperature, and loading combinations. It can be higher than that for the pure bending moment (or tensile loading) with the introduction of the tensile loading (or the bending moment). Meanwhile, the parameter Kt may be higher than the value (i.e., 1.25) in ASME III-5 code for a longer design life, a higher loading level, and a higher operation temperature, inducing an overestimation of the representative stress. On the contrary, a smaller value than 1.25 can be found, inducing an underestimation of the representative stress for creep evaluations.

Basic study on estimation method of wall shear stress in common carotid artery using blood flow imaging

In this paper, we propose a method for adaptive selection of the kernel size used in estimation of the wall shear stress (WSS) based on flow velocity profiles obtained by the blood flow imaging method based on enhancement of RF echo signals from blood cells using a singular value decomposition based clutter filter. Two simulation phantom experiments with the Field II program were performed to validate the proposed method. In the simulation experiments, the average bias error (BE) between the WSSs estimated by the conventional method and theoretical one was 16.5%. The proposed method could reduce the average BE to 12.3%. Also, the proposed method was applied to RF echo signals from a common carotid artery (CCA) of a healthy male subject. The WSSs in the CCA were estimated during one cardiac cycle and in a range similar to that in previous reports.

Stress Estimation Using Digital Image Correlation with Compensation of Camera Motion-Induced Error.

Measurement of stress levels from an in-service structure can provide important and useful information regarding the current state of a structure. The stress relaxation method (SRM) is the most conventional and practical method, which has been widely accepted for measuring residual stresses in metallic materials. The SRM showed strong potential for stress estimation of civil engineering structures, when combined with digital image correlation (DIC). However, the SRM/DIC methods studied thus far have practical issues regarding camera vibration during hole drilling. To minimize the error induced by the camera motion, the imaging system is installed at a distance from the specimen resulting in the low pixel density and the large extent of the inflicted damage. This study proposes an SRM/DIC-based stress estimation method that allows the camera to be removed during hole drilling and relocated to take the after-drilling image. Since the imaging system can be placed as close to the specimen as possible, a high pixel density can be achieved such that subtle displacement perturbation introduced by a small damage can be acquired by DIC. This study provides a detailed mathematical formulation for removing the camera relocation-induced false displacement field in the DIC result. The proposed method is validated numerically and experimentally.