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1
Li, Shouju, De Li, Lijuan Cao et Zichang Shangguan. « Parameter estimation approach for particle flow model of rockfill materials using response surface method ». International Journal of Computational Materials Science and Engineering 04, no 01 (mars 2015) : 1550003. http://dx.doi.org/10.1142/s2047684115500037.
Texte intégralRésumé :
Particle flow code (PFC) is widely used to model deformation and stress states of rockfill materials. The accuracy of numerical modeling with PFC is dependent upon the model parameter values. How to accurately determine model parameters remains one of the main challenges. In order to determine model parameters of particle flow model of rockfill materials, some triaxial compression experiments are performed, and the inversion procedure of model parameters based on response surface method is proposed. Parameters of particle flow model of rockfill materials are determined according to the observed data in triaxial compression tests for rockfill materials. The investigation shows that the normal stiffness, tangent stiffness and friction coefficient of rockfill materials will slightly increase with increase of confining pressure in triaxial compression tests. The experiments in laboratory show that the proposed inversion procedure behaves higher computing efficiency and the forecasted stress–strain relations agree well with observed values.
2
Chen, Dai Heng, et Lu Yang. « Inversion Behavior for Cylindrical Tubes under Axial Compression ». Advanced Materials Research 430-432 (janvier 2012) : 512–16. http://dx.doi.org/10.4028/www.scientific.net/amr.430-432.512.
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This paper presents an analysis of tube inversion under axial compression by a finite element method with the aim of expressing and calculating the axial stress from the stress equilibrium equation. The state of a cylinder under internal stress and the inversion transformation mechanism are then clarified, and verification of the proposed theoretical model is examined.
3
Habashy, T. M., A. Abubakar, G. Pan et A. Belani. « Source-receiver compression scheme for full-waveform seismic inversion ». GEOPHYSICS 76, no 4 (juillet 2011) : R95—R108. http://dx.doi.org/10.1190/1.3590213.
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We have developed a source-receiver compression approach for reducing the computational time and memory usage of the acoustic and elastic full-waveform inversions. By detecting and quantifying the extent of redundancy in the data, we assembled a reduced set of simultaneous sources and receivers that are weighted sums of the physical sources and receivers used in the survey. Because the numbers of these simultaneous sources and receivers could be significantly less than those of the physical sources and receivers, the computational time and memory usage of any gradient-type inversion method such as steepest descent, nonlinear conjugate gradient, contrast-source inversion, and quasi-Newton methods could be reduced. The scheme is based on decomposing the data into their principal components using a singular-value decomposition approach, and the data reduction is done through the elimination of the small eigenvalues. Consequently, this would suppress the effect of noise in the data. Moreover, taking advantage of the redundancy in the data, this compression scheme effectively stacks the redundant data, resulting in an increased signal-to-noise ratio. For demonstration of the concept, we produced inversion results for the 2D acoustic Marmousi and BP models for surface measurements and an elastic model for crosswell measurements. We found that this approach has the potential to significantly reduce computational time and memory usage of the Gauss-Newton method by 1–2 orders of magnitude.
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Foks, Nathan Leon, Richard Krahenbuhl et Yaoguo Li. « Adaptive sampling of potential-field data : A direct approach to compressive inversion ». GEOPHYSICS 79, no 1 (1 janvier 2014) : IM1—IM9. http://dx.doi.org/10.1190/geo2013-0087.1.
Texte intégralRésumé :
Compressive inversion uses computational algorithms that decrease the time and storage needs of a traditional inverse problem. Most compression approaches focus on the model domain, and very few, other than traditional downsampling focus on the data domain for potential-field applications. To further the compression in the data domain, a direct and practical approach to the adaptive downsampling of potential-field data for large inversion problems has been developed. The approach is formulated to significantly reduce the quantity of data in relatively smooth or quiet regions of the data set, while preserving the signal anomalies that contain the relevant target information. Two major benefits arise from this form of compressive inversion. First, because the approach compresses the problem in the data domain, it can be applied immediately without the addition of, or modification to, existing inversion software. Second, as most industry software use some form of model or sensitivity compression, the addition of this adaptive data sampling creates a complete compressive inversion methodology whereby the reduction of computational cost is achieved simultaneously in the model and data domains. We applied the method to a synthetic magnetic data set and two large field magnetic data sets; however, the method is also applicable to other data types. Our results showed that the relevant model information is maintained after inversion despite using 1%–5% of the data.
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Portniaguine, Oleg, et Michael S. Zhdanov. « 3‐D magnetic inversion with data compression and image focusing ». GEOPHYSICS 67, no 5 (septembre 2002) : 1532–41. http://dx.doi.org/10.1190/1.1512749.
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We develop a method of 3‐D magnetic anomaly inversion based on traditional Tikhonov regularization theory. We use a minimum support stabilizing functional to generate a sharp, focused inverse image. An iterative inversion process is constructed in the space of weighted model parameters that accelerates the convergence and robustness of the method. The weighting functions are selected based on sensitivity analysis. To speed up the computations and to decrease the size of memory required, we use a compression technique based on cubic interpolation. Our method is designed for inversion of total magnetic anomalies, assuming the anomalous field is caused by induced magnetization only. The method is applied to synthetic data for typical models of magnetic anomalies and is tested on real airborne data provided by ExxonMobil Upstream Research Company.
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Pan, Shiyang, Tongchun Li, Guicai Shi, Zhen Cui, Hanjing Zhang et Li Yuan. « The Inversion Analysis and Material Parameter Optimization of a High Earth-Rockfill Dam during Construction Periods ». Applied Sciences 12, no 10 (15 mai 2022) : 4991. http://dx.doi.org/10.3390/app12104991.
Texte intégralRésumé :
Inversion analysis is usually an efficient solution to process the monitoring data of earth-rockfill dams. However, it is still difficult to obtain calculation results that are consistent with monitoring data due to different construction statuses. To deal with this situation and to introduce a new solution to improve calculation accuracy, the general method of inversion analysis based on back-propagation neural networks and the original step-by-step inversion method assuming that the parameters of the constitutive model vary with construction periods are introduced and verified in this work. Then, both methods are applied in the inversion analysis of a high gravelly soil core rock-fill dam during construction periods. Moreover, the relationship between the inversed material parameters and the stress values of the core wall is discussed. The material parameters are further optimized to obtain more accurate displacement values. The results show that the step-by-step inversion method has a higher accuracy in vertical compression values compared with the conventional inversion method, the trend of material parameter K is more significant than other parameters, and the proposed variable parameter constitutive model has an accuracy between the step-by-step and conventional inversion methods. Conclusions can be drawn that the original step-by-step inversion method has more advantages than the conventional method and the variable parameter constitutive model proposed in this paper might be more suitable for the analysis of a high earth-rockfill dam during construction periods.
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Lin, Cherng-Yuan, et Keng-Hung Lin. « Comparison of the Engine Performance of Soybean Oil Biodiesel Emulsions Prepared by Phase Inversion Temperature and Mechanical Homogenization Methods ». Processes 11, no 3 (16 mars 2023) : 907. http://dx.doi.org/10.3390/pr11030907.
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The engine performance and emission characteristics of burning emulsions of soybean oil biodiesel in a compression-ignition diesel engine prepared through the phase inversion temperature method were compared with those of neat soybean oil biodiesel and the emulsion prepared by the mechanical homogenization method. The engine torque was set constantly at 98 N·m with varying engine speeds. The experimental results show that the emulsion prepared by the method of phase inversion temperature had higher O2 and NOx emissions, a higher excess air ratio, a higher exhaust gas temperature, and a higher brake fuel conversion efficiency than the emulsion prepared by the mechanical homogenization method, which had lower CO and CO2 emissions, a lower equivalence ratio, and lower brake-specific fuel consumption. While the neat soybean oil biodiesel was found to have the lowest fuel consumption rate, brake-specific fuel consumption, and CO and CO2 emissions, it had the highest exhaust gas temperature and brake fuel conversion efficiency, NOx and O2 emissions, and excess air ratio among those three fuels. Therefore, the phase inversion temperature method is considered promising for preparing fuel emulsions as an alternative to petro-derived diesel for compression-ignition engines.
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Jiang, Dandan, Zhaofa Zeng, Shuai Zhou, Yanwu Guan, Tao Lin et Pengyu Lu. « Three-Dimensional Magnetic Inversion Based on an Adaptive Quadtree Data Compression ». Applied Sciences 10, no 21 (29 octobre 2020) : 7636. http://dx.doi.org/10.3390/app10217636.
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Three-dimensional magnetic inversion allows the distribution of magnetic parameters to be obtained, and it is an important tool for geological exploration and interpretation. However, because of the redundancy of the data obtained from large-scale investigations or high-density sampling, it is very computationally intensive to use these data for iterative inversion calculations. In this paper, we propose a method for compressing magnetic data by using an adaptive quadtree decomposition method, which divides the two-dimensional data region into four quadrants and progressively subdivides them by recursion until the data in each quadrant meets the regional consistency criterion. The method allows for dense sampling at the abnormal boundaries with large amplitude changes and sparse sampling at regions with small amplitude changes, and achieves the best approximation to the original data with the least amount of data, thus retaining more anomalous information while achieving the purpose of data compression. In addition, assigning values to the data in the quadrants using the averaging method is essentially equivalent to average filtering, which reduces the noise of the magnetic data. Testing the synthetic model and applying the method to mineral exploration a prove that it can effectively compress the magnetic data and greatly improve the computational efficiency.
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Liu, Weiqiang, et Liangyong Yang. « A New Method for Geophysical Induced Polarization Inversion Based on Stochastic Medium Model and Sample-Compressed Artificial Neural Network ». Journal of Physics : Conference Series 2025, no 1 (1 septembre 2021) : 012010. http://dx.doi.org/10.1088/1742-6596/2025/1/012010.
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Abstract Induced polarization (IP) is a near-surface geophysical exploration method. Inverting the electrical properties of the underground medium from surface apparent IP parameters is a highly nonlinear problem. To further improve the accuracy, the artificial neural network (ANN) algorithm is applied to the two-dimensional (2D) IP data inversion for the first time. We firstly produced smooth geo-electric models based on the stochastic medium theory, and obtained the corresponding theoretical responses through forward modelling. Then, we compressed the responses and models through image compression technology. Finally, the above compressed responses and models were used as input and output samples to train an optimal network system for inversion. We tested the algorithm with synthetic examples. The results show that ANN can improve the longitudinal resolution of the inversion results and make the inversion results more focused.
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Abubakar, A., T. M. Habashy, Y. Lin et M. Li. « A model-compression scheme for nonlinear electromagnetic inversions ». GEOPHYSICS 77, no 5 (1 septembre 2012) : E379—E389. http://dx.doi.org/10.1190/geo2011-0494.1.
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We have developed a model-compression scheme for improving the efficiency of the regularized Gauss-Newton inversion algorithm for marine controlled-source electromagnetic applications. In this scheme, the unknown model parameters (the conductivity/resistivity distribution) are represented in terms of a basis such as Fourier and wavelet (Haar and Daubechies). By applying a truncation criterion, the model may then be approximated by a reduced number of basis functions, which is usually much less than the number of the model parameters. Further, because the controlled-source electromagnetic measurements have low resolution, it is sufficient for inversion to only keep the low-spatial-frequency part of the image. This model-compression scheme accelerates the computational time and also reduces the memory usage of the Gauss-Newton method. We are able to significantly reduce the algorithm computational complexity without compromising the quality of the inverted models.
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Xie, Longhao, Qing Zhao, Chunguang Ma, Binbin Liao et Jianjian Huo. « Ü-Net : Deep-Learning Schemes for Ground Penetrating Radar Data Inversion ». Journal of Environmental and Engineering Geophysics 25, no 2 (juin 2020) : 287–92. http://dx.doi.org/10.2113/jeeg19-074.
Texte intégralRésumé :
Electromagnetic (EM) inversion is a quantitative imaging technique that can describe the dielectric constant distribution of a target based on the EM signals scattered from it. In this paper, a novel deep neural network (DNN) based methodology for ground penetrating radar (GPR) data inversion, known as the Ü-net is introduced. The proposed Ü-net consists of three parts: a data compression unit, U-net, and an output unit. The novel inversion approach, based on supervised learning, uses a neural network to generate the dielectric constant distribution from GPR data. The GPR data can be compressed and reshaped the size using data compression unit. The U-net maps the object features to the dielectric constant distribution. The output unit meshes the dielectric constant distribution more finely. A novel feature of the proposed methodology is the application of instance normalization (IN) to the DNN EM inversion method and a comparison of its performance to batch normalization (BN). The validity of this technique is confirmed by numerical simulations. The Mean-Square Error of the test data sets is 0.087. These simulations prove that the instance normalization is suitable for GPR data inversion. The proposed approach is promising for achieving quality dielectric constant images in real-time.
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Yin, Yanchun, Guangyan Liu, Tongbin Zhao, Qinwei Ma, Lu Wang et Yubao Zhang. « Inversion Method of the Young’s Modulus Field and Poisson’s Ratio Field for Rock and Its Test Application ». Materials 15, no 15 (8 août 2022) : 5463. http://dx.doi.org/10.3390/ma15155463.
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As one typical heterogeneous material, the heterogeneity of rock micro parameters has an important effect on its macro mechanical behavior. The study of the heterogeneity of micro parameters is more important to reveal the root cause of deformation and failure. However, as a typical heterogeneous material, the current testing and inversion method is not suitable for micro parameters measurement for the rock. Aiming at obtaining the distribution of micro Young’s modulus and micro Poisson’s ratio of the rock, based on the digital image correlation method (DIC) and finite element method (FEM), this paper proposed a parameter field inversion method, namely the DF-PF inversion method. Its inversion accuracy is verified using numerical simulation and laboratory uniaxial compression test. Considering the influences of heterogeneity, stress state and dimension difference, the average inversion error of Young’s modulus field and Poisson’s ratio field are below 10%, and the proportion of elements with an error of less than 15% accounts for more than 86% in the whole specimen model. Compared with the conventional measuring method, the error of macro Young’s modulus and macro Poisson’s ratio calculated by the DF-PF inversion method is less than 2.8% and 9.07%, respectively. Based on the statistical analysis of Young’s modulus field and Poisson’s ratio field, the parameter homogeneity and quantitative function relation between the micro parameter and the principal strain can also be obtained in laboratory tests. The DF-PF inversion method provides a new effective method of testing Young’s modulus field and Poisson’s ratio field of the rocks under complex stress states.
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Jiang, Huai, Min Han et Hui Chang Zhao. « A New Imaging Method for Circular Trace Scanning SAR with Wide Observation ». Applied Mechanics and Materials 716-717 (décembre 2014) : 1047–50. http://dx.doi.org/10.4028/www.scientific.net/amm.716-717.1047.
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Circular Trace Scanning SAR is a new strip map mode SAR imaging in recent years, its imaging speed is fast with larger scene. This paper first establishes the imaging geometry right, by the four order approximation of the oblique distance model, combined with the series inversion method, and the removal of the coupling terms in the spectrum in the range Doppler domain, finally complete the azimuth compression. The simulation results prove the validity and feasibility of the imaging.
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Kukreja, Navjot, Jan Hückelheim, Mathias Louboutin, John Washbourne, Paul H. J. Kelly et Gerard J. Gorman. « Lossy checkpoint compression in full waveform inversion : a case study with ZFPv0.5.5 and the overthrust model ». Geoscientific Model Development 15, no 9 (12 mai 2022) : 3815–29. http://dx.doi.org/10.5194/gmd-15-3815-2022.
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Abstract. This paper proposes a new method that combines checkpointing methods with error-controlled lossy compression for large-scale high-performance full-waveform inversion (FWI), an inverse problem commonly used in geophysical exploration. This combination can significantly reduce data movement, allowing a reduction in run time as well as peak memory. In the exascale computing era, frequent data transfer (e.g., memory bandwidth, PCIe bandwidth for GPUs, or network) is the performance bottleneck rather than the peak FLOPS of the processing unit. Like many other adjoint-based optimization problems, FWI is costly in terms of the number of floating-point operations, large memory footprint during backpropagation, and data transfer overheads. Past work for adjoint methods has developed checkpointing methods that reduce the peak memory requirements during backpropagation at the cost of additional floating-point computations. Combining this traditional checkpointing with error-controlled lossy compression, we explore the three-way tradeoff between memory, precision, and time to solution. We investigate how approximation errors introduced by lossy compression of the forward solution impact the objective function gradient and final inverted solution. Empirical results from these numerical experiments indicate that high lossy-compression rates (compression factors ranging up to 100) have a relatively minor impact on convergence rates and the quality of the final solution.
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Chen, Chow‐Son. « Mapping plate boundaries using TEM method along the Longitudinal Valley, Taiwan ». GEOPHYSICS 63, no 3 (mai 1998) : 868–79. http://dx.doi.org/10.1190/1.1444397.
Texte intégralRésumé :
The transient electromagnetic (TEM) method was used to map plate boundaries in the Longitudinal Valley (LV), Taiwan. The SIROTEM in‐loop configuration with square transmitting loops 90 to 200 m on a side were used for this survey. More than 350 soundings were conducted in the valley. The field data were inverted by a smooth model inversion, and the soundings resolved more than 300 m beneath the LV. A set of geoelectric maps containing horizontal slices at different depths and vertical profiles from north to south along the LV have been constructed based on these inversion results. Based on the TEM sounding results, one predominant electrical discontinuity can be recognized in the LV that agrees well with the known suture trace on the surface between the Philippine Sea and the Eurasian plates. Moreover, the fact that the sedimentation trend thickened southward in the LV supports the geologic viewpoint that the LV is undergoing severe compression‐closure action; the northern part of the valley seems to have been closed already, whereas the southern part has not.
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Rebetsky, Yu L., et R. S. Alekseev. « The Pattern and Possible Formation Mechanisms of Current Crustal Stress in High Asia ». Russian Geology and Geophysics 63, no 6 (1 juin 2022) : 726–42. http://dx.doi.org/10.2113/rgg20204246.
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Abstract —The pattern of current crustal stress in central and southeastern Asia has been reconstructed from earthquake focal mechanisms by inversion using Rebetsky’s method of cataclastic analysis. The inversion provides constraints on principal stress directions, as well as on relative magnitudes of maximum shear and effective isotropic pressure. The crust of the High Asian mountainous province is subject to horizontal extension or shear in plateaus (East and South Pamir and Tibet) and to horizontal compression or shear in mountain ranges. The relatively high horizontal compression in the ranges is apparently due more to denudation and exhumation than to the pressure from the Indian indentor. Denudation and removal of clastic material from the Himalayan slopes has been a key agent that may compensate for the N–S crust shortening in central Tibet and the W–E stretching in eastern Tibet. The current stress field of High Asia has been mainly controlled by vertical buoyancy forces that arise by thickening of lighter crust and detachment of heavier lithosphere.
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Zhao, Li Jun, Feng Peng Zhang, Xiao Zhi Hu et Bao Zong Huang. « Study on Interlaminar Shear and Damage Behavior of Carbon Fiber Composites with Short Fiber Interleaves : 1. The Comparative Test ». Advanced Materials Research 41-42 (avril 2008) : 335–40. http://dx.doi.org/10.4028/www.scientific.net/amr.41-42.335.
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A special test setup was designed and used in compression shear test of unidirectional carbon fiber composites to study the effect of short fiber interleaves (SFIs) on the interlaminar shear behavior. The comparative tests for two kinds of double-notched compression specimens, with and without SFIs, were carried out to determine the interlaminar shear strength and modulus (ILSS and ILSM) and to examine the failure characteristics. To determine ILSM of the specimens with SFIs an inversion analysis method was proposed based on comparing compression displacement of specimens with and without SFIs. The experimental results show that SFIs makes ILSS decreasing due to lower interface strength, and the complex damage process of SFIs leads to a considerable increase of interlaminar shear compliance.
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Moon, Wooil M. « Born inversion of surface-scattered SAR (synthetic aperture radar) wave field ». Canadian Journal of Physics 69, no 10 (1 octobre 1991) : 1256–60. http://dx.doi.org/10.1139/p91-188.
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A new approach to synthetic aperture radar (SAR) digital image formation, based on inverse scattering theory, is derived as an alternative to the conventional method of imaging surface-scattered wave fields. The conventional image formation technique for high-resolution SAR data utilized azimuth compression using correlation in the range-Doppler domain. More recent approaches in SAR image formation algorithms exploit downward extrapolation of the wave field in the frequency–wavenumber (f–k) domain to perform not only the azimuth compression but also the range curvature correction at the same time, with improved quality of the final image. In this paper, imaging of the SAR wave field is formulated with the Born inversion approach, which includes a range-curvature-correction term that is valid at all ranges of image formation. This new inversion formula is established to exploit f–k domain computation, from which the complex backscattering coefficient, defined by the ratio of the backscattered wave field to the incident wave field, can be accurately estimated from the observed back-scattered wave field.
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Tian, Guan Feng. « Three-Dimension Rheological Model and Parameters Solving for Unsaturated Soil ». Advanced Materials Research 368-373 (octobre 2011) : 2698–701. http://dx.doi.org/10.4028/www.scientific.net/amr.368-373.2698.
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Based on the three-dimension rheological model for unsaturated soil the constitutive equations are deduced by Laplace transformation. Then the time-dependent analytic expressions of vertical strain and lateral total stress in confined compression situation are also obtained. The modified confined rheological test has been carried out to get time-varying data of vertical strain and lateral total stress. Thus all the model parameters in the constitutive model can be calculated by the methods of curve fitting and formula inversion. At last, the method of the parameters solving is proved reasonable by an example.
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Li, Zilong, et Yang Tang. « Mesoscopic Simulation Method for Uniaxial Compression Test of RCC Dam Material Based on DEM ». Mathematical Problems in Engineering 2020 (17 décembre 2020) : 1–13. http://dx.doi.org/10.1155/2020/6686609.
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The roller compacted concrete (RCC) dam has become one of the most competitive dam types due to its fast construction speed, low cost, and strong adaptability. However, the macroscale compaction test can hardly reflect the mesoscopic structure on the RCC’s rolling characteristics. According to the characteristics of RCC dam materials, a numerical discrete element method (DEM) is proposed in this paper, which is used to simulate the irregular shape and proportion of RCC aggregates. Moreover, a mesoscopic parameter inversion method based on the adaptive differential evolution (ADE) algorithm is proposed to enhance the efficiency of model contact parameters determination and overcome the inconvenience and time-consumption of conventional methods. Compared with the physical test, the simulation compression curve has good consistency with the physical test curve, and the proposed method can adequately reflect the physical and mechanical properties of RCC dam materials, which provides a basis for the subsequent research on the properties of RCC dam materials under different filling times.
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Zhou, Jian Jun, Zhan Ling Fu, Guo Bin Zhao et Geng You Han. « Study on the Deep Rock Parameters of Fushun Mining Area ». Advanced Materials Research 255-260 (mai 2011) : 3722–26. http://dx.doi.org/10.4028/www.scientific.net/amr.255-260.3722.
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In order to get the mechanical parameters of deep rock for the Fushun mining area, some mechanical properties tests of rock prepared from the drill core and trial adit were carried out. The complex mechanical parameters of rock mass were proposed by inversion of B-P neural network method with intruding the uniformity design theory. The deep rock parameters were amended and correction factor was proposed by according to geostress test and high confining pressure triaxial compression test.
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Zhou, Jian Jun, Ke Ke Xie, Lei Chen et Zhi Peng Gong. « Parameters of Muzhuping Landslide in the Shuibuya Reservoir ». Applied Mechanics and Materials 90-93 (septembre 2011) : 442–45. http://dx.doi.org/10.4028/www.scientific.net/amm.90-93.442.
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Landslide is common geological hazards to the hydropower reservoir. Reasonable parameters are the key to design and prevent the landslide. After geological exploration, a few laboratory tests (uniaxial compression test, unsaturated permeability test, unsaturated direct-shear test) were conducted for the sliding mass. In order to obtain reasonable strength parameters of sliding mass, basing on the experimental results, some researches (such as engineering analogy, parametric inversion) were performed by using limit equilibrium method. The mechanical parameters of the slope were proposed.
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Pereira Lara, Ana Maria, et Tiago Cavalcanti Rolim. « Analysis of the Shock Wave/Boundary Layer Interaction considering a Compression Corner Model Using the MacCormack Method ». Journal of Engineering 2023 (22 mars 2023) : 1–30. http://dx.doi.org/10.1155/2023/8115465.
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The objective of this paper is to numerically study the shock wave/boundary layer interaction and boundary layer separation. The first stage of this research is the development of methodology, flow simulations, and data analysis. When comparing the plots, it can be seen that the results of the check of the methodology were similar. Following, methodologies were developed and simulations were carried out considering the compression corner model. It was noticed that the shock wave could be identified by the jump on the pressure profile near the leading edge and by analyzing the thermodynamic properties of the plate. An increase in pressure, flow inversion, and boundary layer separation through negative values of the friction coefficient was observed, and negative speed at the wall was observed due to the presence of a plateau on the pressure curves. Flow expansion and further reattachment of the boundary layer were also seen. It is possible to observe type VI shock-shock interference and the triple point T, causing a series of expansion waves to form. Finally, an increase in the Mach number, a decrease in the corner compression angle, and a decrease in the wall temperature interfere and reduce the possibility of separating the boundary layer.
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Sobczyk, Artur, et Jacek Szczygieł. « Paleostress reconstruction of faults recorded in the Niedźwiedzia Cave (Sudetes) : insights into Alpine intraplate tectonic of NE Bohemian Massif ». International Journal of Earth Sciences 110, no 3 (18 février 2021) : 833–47. http://dx.doi.org/10.1007/s00531-021-01994-1.
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AbstractBrittle structures identified within the largest karstic cave of the Sudetes (the Niedźwiedzia Cave) were studied to reconstruct the paleostress driving post-Variscan tectonic activity in the NE Bohemian Massif. Individual fault population datasets, including local strike and dip of fault planes, striations, and Riedel shear, enabled us to discuss the orientation of the principal stresses tensor. The (meso) fault-slip data analysis performed both with Dihedra and an inverse method revealed two possible main opposing compressional regimes: (1) NE–SW compression with the formation of strike-slip (transpressional) faults and (2) WNW–ESE horizontal compression related to fault-block tectonics. The (older) NE-SW compression was most probably associated with the Late Cretaceous–Paleogene pan-regional basin inversion throughout Central Europe, as a reaction to ongoing African-Iberian-European convergence. Second WNW–ESE compression was active as of the Middle Miocene, at the latest, and might represent the Neogene–Quaternary tectonic regime of the NE Bohemian Massif. Exposed fault plane surfaces in a dissolution-collapse marble cave system provided insights into the Meso-Cenozoic tectonic history of the Earth’s uppermost crust in Central Europe, and were also identified as important guiding structures controlling the origin of the Niedźwiedzia Cave and the evolution of subsequent karstic conduits during the Late Cenozoic.
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Guo, Lixia, Song Li, Ling Zhong, Lei Guo et Lunyan Wang. « Inverse Analysis of Concrete Meso-constitutive Model Parameters Considering Aggregate Size Effect ». Science and Engineering of Composite Materials 27, no 1 (17 novembre 2020) : 397–404. http://dx.doi.org/10.1515/secm-2020-0043.
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AbstractThe meso numerical simulation has become an important method to study the characteristics of materials; however, the key to its further application is determining the parameters of meso-constitutive model. Considering that the meso-scale parameters of materials are hard to measure, this paper took into account the aggregate size effect and proposed a meso-parameter identification method by combining random aggregate numerical simulation and genetic algorithm. First, a random aggregate model of concrete was established, and its meso-model parameters were analyzed. The Morris method was used to analyze the sensitivity of meso-component parameters to the macro-responses, and results showed that the elastic modulus of mortar matrix, interface and large aggregates had a great effect on the peak strain and that the elastic modulus, Poisson’s ratio and tensile strength of interface and mortar matrix, as well as the Poisson’s ratio of large aggregates and the elastic modulus of small aggregates all had an effect on the peak stress, among which the interface tensile strength produced the greatest effect. Second, a parametric inversion and optimization function was established. The uniaxial compression numerical simulation test and genetic algorithm were combined to invert the meso-parameters, and results showed that compared with the single-aggregate parameter inversion curve, the multi-aggregate inversion stress-strain curve was much closer to the measured curve. That was because the aggregates of small size had lower elastic modulus, easing the stress concentration at the interface between aggregates and cement stone, and delaying the formation and growth of cracks.
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Bartaschuk, Оleksii, et Vasyl Suyarko. « GEODYNAMICS ». GEODYNAMICS 1(30)2021, no 1(30) (29 juin 2021) : 25–35. http://dx.doi.org/10.23939/jgd2021.01.025.
Texte intégralRésumé :
The second part of the article studies the tectonic conditions and natural mechanisms of tectonic inversion of the Dnieper-Donets Basin and the Western Donets Graben. Method. The research uses the original method of reconstruction of fields of tectonic stresses and deformations. It also makes tectonophysical analysis of geostructures was used. The analytical base of the research consisted of the latest materials of geo-mapping, numerical modeling of deformations of the southern edge of the Eastern European platform and comparison of model and reconstructed stress fields. Results. In the geodynamic environment of the interference of the intraplate submeridional collision compression with the regional strike-slip stress field, the inversion deformations of the rift-like geostructure took place in the uplift-thrust and strike-slip modes. This led to significant horizontal movements of geomass of sedimentary rocks, deformation folding with the formation of three inversion floors - Late Hercynian (Saal-Pfalz), Early Alpine (Laramian) and Late Alpine (Attic). They formed structural ensembles of scaly tectonic covers of transverse displacement of geomass a from axial to onboard zones, folded covers of longitudinal approach from the Donbas Foldbelt and long linear anti- and synforms, the axes of which are oriented orthogonally to the direction of geomass advancement. Together they form the body of the Segment of Tectonic Wedging of geomass, which is distinguished as part of the Cover-Folded System of Tectonic Thrusting of regional scale. A feature of the tectonic framework of the Segment is the curvature of the planes of the main thrusts, which limit it, and smaller plumage thrusts, which control the folded covers of the thrust. It is associated with a change in the extension of the thrusts from the north-west in the territory of the Western Donets Graben to the western direction in the extreme south-east of the Basin. This causes the corresponding bending of the axes of the fracture anti- and synforms. Structural patterns of folding with a tendency to adapt the axes of folds to the extension of thrusts indicate significant horizontal displacements of geomas of the sedimentary stratum, which in conditions of limited geological space cause secondary deformations of linear folded forms. Due to the displacement of geomas from the zones of maximum compression in the axial part of the Graben to the zones of geodynamic shadow - in the direction of the Oryl depression and Graben boards, the West Donets Cover-Folded Tectonic Region was formed within the transition zone. Scientific novelty. The study completed an original kinematic model of tectonic inversion of the Western Donets Graben was completed. The mechanism of inversion, due to which the riftogenic structure is completely destroyed by folded deformations of platform orogeneses, is caused by the pressure of the "tectonic stamp" of the Donbas Foldbelt. Under its influence, a segment of tectonic wedge was formed in the Graben, which was diagnosed with oroclin of transverse extension of the sliding type. The body of the Oroclin is formed by echeloned, rock-articulated ensembles of anticlinal uplift -folds, synclines and scaly plates-covers of pushing. A geodynamic injection band was formed in the foreland of the Tectonic Orocline extension, where folded zones of geomas displacement were formed, which consist of coulisse articulated uplift-anticlines. At the top of the Orocline, at the ends of dynamically conjugate main thrusts, an advanced tectonic compression fan is formed. In the rear of the Oroclin – hinterland are tectonic sutures – the roots of the folding covers of the approach. Practical significance. Development of a structural-kinematic model of tectonic inversion of the Western Donets Graben will allow to improve the geodynamic model of tectonic inversion of the Dnieper-Donets paleorift, on the basis of which regional schemes of tectonic and oil-gas-geological zoning will be adjusted.
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Doroshenko, Volodymyr, et Alexander Yanchenko. « PREREQUISITES FOR THE PRODUCTION OF CONNECTOR ASSEMBLIES OF BUILDING METAL STRUCTURES BY FOUNDRY METHOD ACCORDING TO ONE-TIME PATTERNS ». Modern technology, materials and design in construction 32, no 1 (28 juin 2022) : 14–20. http://dx.doi.org/10.31649/2311-1429-2022-1-14-20.
Texte intégralRésumé :
The article reviews the common elements of prefabricated modular building metal structures with a list of their advantages and assessment of the prospects for the manufacture of their important components of the Lost Foam Casting (LFC) process. Such construction with the use of metal structures must have all the prerequisites to become an impetus and an effective solution in the construction industry, which will contribute to the reconstruction of the country. The fabrication of connector assemblies and bolt brackets for connecting beams and connectors with flexible steel plates for seismically unstable conditions is considered. A number of frame-cell thin-walled cast structures have been patented by the PTIMA Institute of the National Academy of Sciences of Ukraine since 2011 on the basis of patterns made of expanded polystyrene, which are assembled mainly from repeating elements, and which is similar to the modern method of mounting prefabricated building metal structures. We have also gained experience in casting with LFC parts with cast threads, which simplifies the serial production of ball joints and conical tips for tubular elements. When constructing hangars and warehouses with shell vaults, reducing the weight of metal shells with the obligatory preservation of their required strength is an important requirement for the design of such structures. For this purpose, in particular, the method of inversion of flexible hanging nets formed from a flat state by gravity is used for building structures. The article uses the fact that the inverted chain line serves as an ideal outline for arches and domes, as homogeneous arches in the form of such a line undergo only compression deformation, but not bending. The method of physical modeling of the support surface of the momentless vault shell of a complex curved surface by the method of inversion of the sagging heated thermoplastic synthetic film was developed, which turned out to be simpler than the method of inversion of hanging nets.
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Armstrong, M. A., M. Ravasio, W. G. Versteijlen, D. J. Verschuur, A. V. Metrikine et K. N. van Dalen. « Seismic inversion of soil damping and stiffness using multichannel analysis of surface wave measurements in the marine environment ». Geophysical Journal International 221, no 2 (14 février 2020) : 1439–49. http://dx.doi.org/10.1093/gji/ggaa080.
Texte intégralRésumé :
SUMMARY Determination of soil material damping is known to be difficult and uncertain, especially in the offshore environment. Using an advanced inversion methodology based on multichannel spectral analysis, Scholte and Love wave measurements are used to characterize subsea soil from a North Sea site. After normalization, a determinant-based objective function is used in a genetic algorithm optimization to estimate the soil shear modulus. The inverted shear-modulus profile is comparable to previously published results for the same data, although a higher degree of certainty is achieved in the near-surface layers. The half-power bandwidth method is used for extracting the attenuation curve from the measurements and efficient reference data points are chosen based on wavelet compression. The material-damping ratio inversion is performed using a modified stochastic optimization algorithm. Accounting for measurement errors, the material-damping ratio profile is retrieved from the fundamental-mode Scholte wave with a high degree of certainty. Furthermore, a method is proposed for identifying the frequency dependence of the material-damping ratio from in situ measurements. No evidence for frequency dependence is found and the small-strain soil material-damping ratio at this site can be said to be frequency independent for the measured conditions.
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Säglitz, Sylvia A., et Michael R. Gaab. « Investigations using magnetic resonance imaging : is neurovascular compression present in patients with essential hypertension ? » Journal of Neurosurgery 96, no 6 (juin 2002) : 1006–12. http://dx.doi.org/10.3171/jns.2002.96.6.1006.
Texte intégralRésumé :
Object. A possible relationship between neurovascular compression of the rostral ventrolateral medulla oblongata (RVLM) and essential hypertension is investigated using a specifically designed magnetic resonance (MR) imaging method. In conjunction with the ninth and 10th cranial nerves, baroreceptor afferents enter the RVLM, which represents a crucial relay for regulation of autonomic blood pressure. In 1985 Jannetta and coworkers proposed a causal relationship between essential hypertension and intraoperatively observed neurovascular compression of the left RVLM. Methods. Currently, MR imaging is the method of choice for the assessment of neurovascular relationships at the brainstem. By obtaining axial images of a thin-slice turbo inversion-recovery sequence and three-dimensional time-of-flight MR angiograms (fast imaging with steady-state precision), the authors documented the occurrence of neurovascular contacts with the RVLM at the level of the root entry zones (REZs) of the ninth and 10th cranial nerves in 25 patients with essential hypertension, 30 normotensive volunteers, and 10 patients with renal hypertension. Neurovascular contacts with the REZ at the left RVLM were found in 32% of patients with essential hypertension, 37% of normotensive volunteers, and 20% of patients with renal hypertension. In total, neurovascular contacts on either side of the RVLM were documented in 68% of patients with essential hypertension, 53% of normotensive volunteers, and 50% of patients with renal hypertension. Conclusions. The results do not support the theory of neurovascular compression in cases of essential hypertension. Findings of neurovascular contacts on MR images are not indications for decompression surgery. For further clarification, however, prospective MR imaging studies should be considered in young patients with essential hypertension in whom the history of high blood pressure is short.
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Li, Chuang, Heng Zhang et Yunkai Deng. « Focus Improvement of Airborne High-Squint Bistatic SAR Data Using Modified Azimuth NLCS Algorithm Based on Lagrange Inversion Theorem ». Remote Sensing 13, no 10 (13 mai 2021) : 1916. http://dx.doi.org/10.3390/rs13101916.
Texte intégralRésumé :
In this paper, a modified azimuth nonlinear chirp scaling (NLCS) algorithm is derived for high-squint bistatic synthetic aperture radar (BiSAR) imaging to solve its inherent difficult issues, including the large range cell migration (RCM), azimuth-dependent Doppler parameters, and the sensibility of the higher order terms. First, using the Lagrange inversion theorem, an accurate spectrum suitable for processing airborne high-squint BiSAR data is introduced. Different from the spectrum that is based on the method of series reversion (MSR), it is allowed to derive the bistatic stationary phase point while retaining the double square root (DSR) of the slant range history. Based the spectrum, a linear RCM correction is used to remove the most of the linear RCM components and mitigate the range-azimuth coupling, and, then, bulk secondary range compression is implemented to compensate the residual RCM and cross-coupling terms. Following this, a modified azimuth NLCS operation is applied to eliminate the azimuth-dependence of Doppler parameters and equalize the azimuth frequency modulation for azimuth compression. The experimental results, with better focusing performance, prove the high accuracy and effectiveness of the proposed algorithm.
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Smithyman, B. R., R. M. Clowes et E. Bordet. « New geophysical models for subsurface velocity structure in the Nechako–Chilcotin plateau from 2.5-D waveform tomography ». Canadian Journal of Earth Sciences 51, no 4 (avril 2014) : 373–92. http://dx.doi.org/10.1139/cjes-2013-0152.
Texte intégralRésumé :
Seismic inversion is applied to generate physical property models (P-wave velocity and numerical attenuation) for four profiles in the Nechako–Chilcotin plateau region of south-central British Columbia, Canada. A newly developed method that combines three-dimensional (3-D) travel-time inversion and 2.5-dimensional (2.5-D) viscoacoustic full-waveform inversion was applied to generate the geophysical models from vibroseis data acquired along the preexisting crooked roads. These models are useful for the characterization of rock types in terms of their positions and thicknesses, which may be used in conjunction with geological ground truth to infer the extent of lithostratigraphic units in the subsurface. The velocity structures also may be used for future reprocessing of the seismic reflection data to derive improved images based on the better near-surface velocity models. The subsurface geology of the Nechako–Chilcotin plateau region is complex, resulting from multiple stages of tectonic compression and extension, contemporaneous with the deposition of sediments and volcanic material. Several basin structures are identified from the joint interpretation of the waveform tomography velocity models and post-stack time migration images. The combination of these results enables the extrapolation and characterization of geological structures to ∼3 km depth, particularly within the Cenozoic volcanic units that dominate near-surface stratigraphy. Based on the seismic profiles, a fence-diagram geological interpretation that extends to ∼3 km depth illustrates the complex structure of the Jurassic to Neogene stratigraphic sequence.
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Kwon, Ryun-Young, et Angelos Vourlidas. « The density compression ratio of shock fronts associated with coronal mass ejections ». Journal of Space Weather and Space Climate 8 (2018) : A08. http://dx.doi.org/10.1051/swsc/2017045.
Texte intégralRésumé :
We present a new method to extract the three-dimensional electron density profile and density compression ratio of shock fronts associated with coronal mass ejections (CMEs) observed in white light coronagraph images. We demonstrate the method with two examples of fast halo CMEs (∼2000 km s−1) observed on 2011 March 7 and 2014 February 25. Our method uses the ellipsoid model to derive the three-dimensional geometry and kinematics of the fronts. The density profiles of the sheaths are modeled with double-Gaussian functions with four free parameters, and the electrons are distributed within thin shells behind the front. The modeled densities are integrated along the lines of sight to be compared with the observed brightness in COR2-A, and a χ2 approach is used to obtain the optimal parameters for the Gaussian profiles. The upstream densities are obtained from both the inversion of the brightness in a pre-event image and an empirical model. Then the density ratio and Alfvénic Mach number are derived. We find that the density compression peaks around the CME nose, and decreases at larger position angles. The behavior is consistent with a driven shock at the nose and a freely propagating shock wave at the CME flanks. Interestingly, we find that the supercritical region extends over a large area of the shock and lasts longer (several tens of minutes) than past reports. It follows that CME shocks are capable of accelerating energetic particles in the corona over extended spatial and temporal scales and are likely responsible for the wide longitudinal distribution of these particles in the inner heliosphere. Our results also demonstrate the power of multi-viewpoint coronagraphic observations and forward modeling in remotely deriving key shock properties in an otherwise inaccessible regime.
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BARTASHCHUK, Оleksiy. « Collision deformations of the Dnieper-Donets Depression Article 3. Geodynamic model of tectonic inversion ». Geology and Geochemistry of Combustible Minerals 1, no 182 (23 janvier 2020) : 40–51. http://dx.doi.org/10.15407/ggcm2020.01.040.
Texte intégralRésumé :
The article concludes the trilogy on post-strip deformations of the Dnieper-Donets Basin. The results of tectonophysical analysis of collision deformations of the platform cover of the south-eastern part of the Dnieper-Donets Basin are summarized. Using the original method of reconstruction of stress and strain fields and tectonophysical analysis of geostructures, the system organization of inversion structural deformations of the Dnieper-Donets Basin and Donbass was studied. The tectonic inversion of the Dnieper-Donets Basin began in the Late Hercynian epoch in the situation of a general-plate collision under the influence of the inversion rise of the Donbas. Structural and kinematic analysis of deformations shows that the folds in the depression and linear anti- and synforms of the Donets Foldbelt were formed by the natural mechanism of longitudinal bending as a result of collisional warping of horizons in the geodynamic mode of transformation. In the late Mesozoic–Cenozoic inversion continued in the field of right-hand horizontal-shear deformations with a variable compressive component. This mode caused the advancing and pushing of sedimentary geomass from the Donets Foldbelt to the Hercynian neo-autochthonous and syneclise autochthonous of the South-Eastern Dnieper-Donets Basin. Due to the influence of the tectonic stamp of the Donets Foldbelt, the West Donets wedge-shaped segment was formed – the orocline of geomass tectonic wedging. Geodynamic bands of injection and displacement of sedimentary geomass were formed in the front of the invasion and in the axial zone of the orocline, where the main folded zones were formed. In Forland, at the ends of the main thrusts – “tectonic rails” of the wedging, an advanced scaly compression fan was formed. In the hinterland of the orocline, folded suture zones are formed by the roots of the covers of thrusting. The original geodynamic model of tectonic inversion provides for the destruction of the riftogenic structure in the Southeast of the Dnieper-Donets Basin by thrusting echelons of scaly covers and coulisses-articulated upliftt-folding. They compose a segment of the insertion of the geomasses of the Paleozoic cover into the territory of the West Donets Graben from the side of the Donets Foldbelt. The intrusion of the tectonic segment led to the formation of an inversion structure of a regional scale – the West Donets Cover-Folded Region.
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Sakhaei, Seyed Reza, et Ghasem Ghorbani Rostam. « Crustal deformation analysis in Zagros and Makran zones, based on GPS permanent network data ». Contributions to Geophysics and Geodesy 50, no 1 (24 mai 2020) : 61–81. http://dx.doi.org/10.31577/congeo.2020.50.1.4.
Texte intégralRésumé :
We present an analysis of strain based on the evaluation of crustal deformation in Zagros and Makran, which has implications in terms of the dynamics of the study area. We have used data from 17 permanent GPS stations of the Cartographic Centre of Iran spanning the period 2011–2013. The raw observed data were in RINEX format. The elements of strain tensor were calculated by a 2D isoparametric method and the inversion of strain equation. Then the dilatation (extension and compression) and shearing were obtained through the analysis of eigenvalue and eigenvector of tensors. In most cases compression has overcome the extension, which can be expected due to the convergence of the Arabia and Eurasia plates. The compression axis is nearly vertical along the Zagros causing reverse and thrust faults in Zagros. Due to the N–S trending of the Sabzvaran–Jiroft–Kahnuj fault system and to the direction of compression and extension, the system will be of strike–slip mechanism. Sudden changes of shearing can be used to identify the strike–slip faults. As observed in this study, there were sudden changes in shearing of the Rafsanjan and Jiroft–Kahnuj faults. The P/T axis rotates significantly in the Zagros–Makran transition zone. Moreover, the Makran's P/T axis is smaller than the P/T axis of Zagros, which demonstrates that the impact of the Arabian plate, moving towards Iran, is greater than the impact of the Indian subcontinent plate movement. The values of the counter-clockwise rotation rate at stations located east of the Zagros–Makran transition zone are higher than at other stations. Also the velocity vectors at stations were determined while using the software GAMIT/GLOBK.
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Rocher, Muriel, Marc Cushing, Francis Lemeille et Stéphane Baize. « Stress induced by the Mio-Pliocene Alpine collision in northern France ». Bulletin de la Société Géologique de France 176, no 4 (1 juillet 2005) : 319–28. http://dx.doi.org/10.2113/176.4.319.
Texte intégralRésumé :
Abstract In most rocks, tectonic stress induces crystalline deformation, such as mechanical twinning. The inverse analysis of calcite twinning allows reconstruction of both directions and values of the paleostress field. The Etchecopar inverse method using calcite twinning has been improved in this paper, lowering the uncertainties on the calculated stress values. Calcite was sampled in the foreland of the western Alps, along a SE-NW section from the Jura Mountains to the Isle of Wight. The calcite twinning inversion has identified the successive Cenozoic tectonic events, named “Pyrenean” compression, “Oligocene” extension and “Alpine” compression. The distribution of the Mio-Pliocene Alpine orogenic stress was specified. This stress field varies in terms of stress regime, directions and values. The horizontal principal stress trends E-W in southern France, WNW in the centre, and NW in the North, which can be attributed to the Alpine indenter phenomenon. The tectonic stress regime roughly corresponds to a pure compression in the Jura and rapidly evolves to the NW to a strike-slip state of stress, then beyond the Paris basin’s centre to a perpendicular extension. Unlike the Pyrenean or Appalachian foreland stress, the Alpine differential stress does not significantly decrease from the Jura front to the far field (30 to 25 MPa). Moreover, stress values vary from one area to another, low in the Burgundy high, fractured and uprising during this tectonic event, and high in Paris basin centre, poorly fractured and subsiding during this event. Three possible explanations are proposed : variation in crust thickness, crustal buckling during the Mio-Pliocene, and pre-existing fractures.
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Ghalenoei, Emad, Jan Dettmer, Mohammed Y. Ali et Jeong Woo Kim. « Trans-dimensional gravity and magnetic joint inversion for 3-D earth models ». Geophysical Journal International 230, no 1 (25 février 2022) : 363–76. http://dx.doi.org/10.1093/gji/ggac083.
Texte intégralRésumé :
SUMMARY Studying 3-D subsurface structure based on spatial data is an important application for geophysical inversions. However, major limitations exist for conventional regularized inversion when applied to potential-field data. For example, global regularization parameters can mask model features that may be important for interpretation. In addition, 3-D inversions are typically based on data acquired in 2-D at the Earth’s surface. Such data may contain significant spatial error correlations in 2-D due to the choice of spatial sampling, acquisition geometry, ambient noise and model assumptions. These correlations can cause trade-offs with spatial resolution and should be accounted for. However, correlations are often ignored, particularly 2-D correlations in spatial data, such as potential field data recorded on the Earth’s surface. Non-linear Bayesian methods can address these shortcomings and we present a new hierarchical model for 2-D correlated errors. Nonetheless, limitations also exist. For example, non-linear Bayesian estimation requires numerical integration with a considerable computational burden to collect a posterior ensemble of models. For 3-D applications, this cost can be prohibitive. This paper presents a non-linear Bayesian inversion with trans-dimensional (trans-D) partitioning of space by a hierarchy of Voronoi nodes and planes (VP), and trans-D estimation of the data noise covariance matrix. The addition of planes permits the introduction of prior information which reduces non-uniqueness. The covariance matrix estimation uses a trans-D autoregressive (AR) noise model to quantify correlated noise on 2-D potential-field data. We address computational cost by wavelet compression in the forward problem and by basing susceptibility on an empirical relationship with density contrast. The method is applied to simulated data and field data from off-shore Abu Dhabi. With simulated data, we demonstrate that subsurface structures are well-resolved with the trans-D model that applies hierarchical VP partitioning. In addition, the model locally adapts based on data information without requiring regularization. The method is also successful in reducing 2-D error correlation via trans-D AR models in 2-D. From field data, the inversion efficiently resolves basement topography and two distinct salt diapirs with a parsimonious and data-driven parametrization. Results show a considerable reduction in 2-D spatial correlations of field data using the proposed trans-D AR model.
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Mkhitaryan, S. M. « On the Application of the Method of Hypersingular Integral Equations to Solving Problems for an Elastic Plane with a Collinear System of Cracks ». UNIVERSITY NEWS. NORTH-CAUCASIAN REGION. NATURAL SCIENCES SERIES, no 2 (206) (18 juin 2020) : 72–83. http://dx.doi.org/10.18522/1026-2237-2020-2-72-83.
Texte intégralRésumé :
In the present paper, using the method of hypersingular integral equations, based on the formulas of the inversion of the corresponding singular integral equations, the exact quadrature solution of the classical problems of the mechanics of an elastic plane with a collinear system of cracks is constructed. The elastic plane is in a state of antiplane deformation or plane deformation; in case of antiplane deformation, crack edges are symmetrically loaded by tangential forces, while in case of plane deformation, they are again loaded symmetrically but by normal forces. Mixed boundary-value problems for an elastic half-plane equivalent to these problems are formulated. Under plane deformation, the mixed boundary-value problem for an elastic half-plane is discussed as well when the plane boundary is reinforced by two similar and symmetrically located semi-infinite stringers between which a system of an arbitrarily final number of stringers is situated. It is considered that the stringers are absolutely rigid for expansion and compression and absolutely flexible for bending. A particular case of two similar symmetrically located cracks is considered more in detail. In this case, the exact solution to the problem is also constructed by the method of Chebyshev orthogonal polynomials.
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Giampiccolo, Riccardo, Alberto Bernardini, Oliviero Massi et Augusto Sarti. « On the Virtualization of Audio Transducers ». Sensors 23, no 11 (1 juin 2023) : 5258. http://dx.doi.org/10.3390/s23115258.
Texte intégralRésumé :
In audio transduction applications, virtualization can be defined as the task of digitally altering the acoustic behavior of an audio sensor or actuator with the aim of mimicking that of a target transducer. Recently, a digital signal preprocessing method for the virtualization of loudspeakers based on inverse equivalent circuit modeling has been proposed. The method applies Leuciuc’s inversion theorem to obtain the inverse circuital model of the physical actuator, which is then exploited to impose a target behavior through the so called Direct–Inverse–Direct Chain. The inverse model is designed by properly augmenting the direct model with a theoretical two-port circuit element called nullor. Drawing on this promising results, in this manuscript, we aim at describing the virtualization task in a broader sense, including both actuator and sensor virtualizations. We provide ready-to-use schemes and block diagrams which apply to all the possible combinations of input and output variables. We then analyze and formalize different versions of the Direct–Inverse–Direct Chain describing how the method changes when applied to sensors and actuators. Finally, we provide examples of applications considering the virtualization of a capacitive microphone and a nonlinear compression driver.
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YADAV, Abhishek, Suresh KANNAUJIYA, Prashant Kumar CHAMPATI RAY, Rajeev Kumar YADAV et Param Kirti GAUTAM. « Estimation of crustal deformation parameters and strain build-up in Northwest Himalaya using GNSS data measurements ». Contributions to Geophysics and Geodesy 51, no 3 (28 septembre 2021) : 225–43. http://dx.doi.org/10.31577/congeo.2021.51.3.2.
Texte intégralRésumé :
GPS measurements have proved extremely useful in quantifying strain accumulation rate and assessing seismic hazard in a region. Continuous GPS measurements provide estimates of secular motion used to understand the earthquake and other geodynamic processes. GNSS stations extending from the South of India to the Higher Himalayan region have been used to quantify the strain build-up rate in Central India and the Himalayan region to assess the seismic hazard potential in this realm. Velocity solution has been determined after the application of Markov noise estimated from GPS time series data. The recorded GPS data are processed along with the closest International GNSS stations data for estimation of daily basis precise positioning. The baseline method has been used for the estimation of the linear strain rate between the two stations. Whereas the principal strain axes, maximum shear strain, rotation rate, and crustal shortening rate has been calculated through the site velocity using an independent approach; least-square inversion approach-based triangulation method. The strain rate analysis estimated by the triangulation approach exhibits a mean value of extension rate of 26.08 nano-strain/yr towards N131°, the compression rate of –25.38 nano-strain/yr towards N41°, maximum shear strain rate of 51.47 nano-strain/yr, dilation of –37.57 nano-strain/yr and rotation rate of 0.7°/Ma towards anti-clockwise. The computed strain rate from the Baseline method and the Triangulation method reports an extensive compression rate that gradually increases from the Indo-Gangetic Plain in South to Higher Himalaya in North. The slip deficit rate between India and Eurasia Plate in Kumaun Garhwal Himalaya has been computed as 18±1.5 mm/yr based on elastic dislocation theory. Thus, in this study, present-day surface deformation rate and interseismic strain accumulation rate in the Himalayan region and the Central Indian region have been estimated for seismic hazard analysis using continuous GPS measurements.
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Nazarova, Larisa A., et Leonid Nazarov. « Method for weak zones location at the coal-bed – host rock joint relative to the problem of sudden outbursts : theory and laboratory experiment ». Frattura ed Integrità Strutturale 17, no 63 (21 décembre 2022) : 13–25. http://dx.doi.org/10.3221/igf-esis.63.02.
Texte intégralRésumé :
Within the framework of a geomechanical model that describes the deformation of a rock mass during the subhorizontal coal-bed extraction, the mechanism for the formation and implementation of a sudden outburst is substantiated: as working face gets close to the weak zone of coal-bed – host rock joint, areas of tensile stresses arise, which creates the prerequisites for face space spalling and coal loss with methane. The inverse problem of determining the conditions at the horizontal boundaries of a coal-bed is formulated and solved using tomography data (longitudinal wave velocity V distribution) and the empirical dependence of V on the mean normal stress σ. Lab tests results on stepwise compression of parallelepipeds made of artificial geomaterials are presented. Tomography of the specimens was performed by acoustic sounding data, and the distribution of velocities V* was found. Using the pre-established empirical dependence V(σ) for geomaterial, the distribution σ*=V-1(V*) in the specimen was calculated, which served as input data for inverse problem of determining the shear stresses σxy at the “specimen faces – press platens” joints. Lab data inversion confirmed the possibility of identifying weak zones of the boundaries where σxy=0. These zones are associated with probable nucleus of failure and sudden outbursts.
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D’yachkov, Pavel. « Electromechanical Property Calculation of Carbon Nanotubes Using Linear Augmented Cylindrical Wave Method ». Applied Functional Materials 2, no 2 (30 juin 2022) : 35–47. http://dx.doi.org/10.35745/afm2022v02.02.0006.
Texte intégralRésumé :
Deformations of single-walled carbon nanotubes (SWNTs) change their band structure in the nanoelectromechanical systems. In this study, we investigated the response of the electronic structure of chiral and nonchiral SWNTs (8,7), (9,6), (10,5), (7,7), (11,0), (12,0), and (13,0) to twisting and axial tension modes by using the symmetrized linear augmented cylindrical wave technique. We showed that perturbations of the band structures depend on a “family” index p = (n1 − n2)mod 3 (where p = −1, 0 or 1). Twisting the semiconducting (8,7) tubule with p = 1 in the direction of the screw axis is accompanied by the large broadening of minimum gap E11 and narrowing of the second gap E22, while these gaps drastically change in the tubule (10,5) with p = −1. In these tubules, changing the direction of twisting leads to the reversal in direction of the gap shifts. Regardless of the twisting direction, in metallic (7,7) and quasi-metallic (9,6) SWNTs with p = 0, the E11 gap rapidly increases from 0.0 and 0.035 eV to about 1 eV. When twisting the zigzag tubules (13,0) p = 1 and (11,0) p = −1, the gaps E11 equal to about 0.8 eV increase and decrease by several hundredths of eV. On the contrary, the compression and extension of these tubules cause a sharp change in their band structure with approximately a twofold change in the gaps E11 and E22 and inversion in the sequence of the boundary bands. The similar deformation of the armchair nanotube (7,7) has practically no effect on its electronic levels. In the case of zigzag (12,0) p = 0 SWNT, all deformation modes transform the quasi-metallic tubule into the semiconductor.
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Wang, Li, Ruizhao Yang, Zhipeng Sun, Lingda Wang, Jialiang Guo et Ming Chen. « Overpressure : Origin, Prediction, and Its Impact in the Xihu Sag, Eastern China Sea ». Energies 15, no 7 (30 mars 2022) : 2519. http://dx.doi.org/10.3390/en15072519.
Texte intégralRésumé :
The complex relationship between deep overpressure, abnormal porosity, and hydrocarbon generation in the Pinghu Formation is interesting and challenging for hydrocarbon exploration and development in the East China Sea Shelf Basin. It shows three-stage pore pressure evolution based on the characteristics of logs in the west slope of the Xihu Sag. Disequilibrium compaction was identified as the dominant overpressure mechanism in stage II (1.0 < PC < 1.6). The fluid expansion was identified as the predominant mechanism of overpressure generation in stage III (PC > 1.6), and tectonic compression occurs in Well B. Pore pressure was predicated by the Fillippone method based on the combination of raw velocity spectra and high-resolution velocity parameters obtained by seismic inversion. The overpressure at the bottom of the Pinghu Formation is mainly distributed in the F2 and F3 fault blocks. The deep gas reservoir of the Pinghu Formation is controlled by both lithology and pressure. The overpressure distribution area is consistent with the center of hydrocarbon generation. The overpressure distribution illustrated that overpressure was positively correlated with the porosity and permeability of the reservoir. The first porosity and permeability inversion zone of the Pinghu Formation formed because the overpressure caused by under-compaction offsets the pressure of some overlying strata and slows down diagenesis. Due to a large amount of hydrocarbon generation in source rocks, the acidic fluid with high temperature promoted the development of secondary pores, resulting in the second pore permeability inversion zone of the Pinghu Formation. The index of porosity preserving (IPP) is proposed here to quantitatively describe the relationship between overpressure and porosity. The index of porosity preserving in the second stage is 1.16%/10 MPa, and in the third stage is 1.75%/10 MPa. The results can be used to guide the exploration of the deep-basin gas reservoir of the Xihu Sag in the Eastern China Sea Basin.
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Bansal, Rishi, et Mike Matheney. « Wavelet distortion correction due to domain conversion ». GEOPHYSICS 75, no 6 (novembre 2010) : V77—V87. http://dx.doi.org/10.1190/1.3494081.
Texte intégralRésumé :
Converted-wave (PS) data, when converted to PP time, develop time- and location-varying compression of the seismic wavelet due to a variable subsurface [Formula: see text] [Formula: see text]. The time-dependent compression distorts the wavelet in a seismic trace. The lack of a consistent seismic wavelet in a domain-converted PS volume can eventually lead to an erroneous joint PP/PS inversion result. Depth-converted seismic data also have wavelet distortion due to velocity-dependent wavelet stretch. A high value of seismic velocity produces more stretch in a seismic wavelet than a low value. Variable wavelet stretch renders the depth data unsuitable for attribute analysis. A filtering scheme is proposed that corrects for distortion in seismic wavelets due to domain conversions (PS to PP time and time-to-depth) of seismic data in an amplitude-preserving manner. The method uses a Fourier scaling theorem to predict the seismic wavelet in the converted domain and calculates a shaping filter for each time/depth sample that corrects for the distortion in the wavelet. The filter is applied to the domain-converted data using the method of nonstationary filtering. We provide analytical expressions for the squeeze factor [Formula: see text] that is used to predict the wavelet in the converted domain. The squeeze factor [Formula: see text] for PS to PP time conversion is a function of the subsurface [Formula: see text] whereas for PP time-to-depth conversion [Formula: see text] is dependent on subsurface P-wave velocity. After filtering, the squeezed wavelets in domain-converted PS data appear to have resulted from a constant subsurface [Formula: see text], which we denote as [Formula: see text]. Similarly, the filtered depth-converted data appear to have resulted from a constant subsurface P-wave velocity [Formula: see text].
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Moghadas, Davood, et Jasper A. Vrugt. « The Influence of Geostatistical Prior Modeling on the Solution of DCT-Based Bayesian Inversion : A Case Study from Chicken Creek Catchment ». Remote Sensing 11, no 13 (29 juin 2019) : 1549. http://dx.doi.org/10.3390/rs11131549.
Texte intégralRésumé :
Low frequency loop-loop electromagnetic induction (EMI) is a widely-used geophysical measurement method to rapidly measure in situ the apparent electrical conductivity (ECa) of variably-saturated soils. Here, we couple Bayesian inversion of a quasi-two-dimensional electromagnetic (EM) model with image compression via the discrete cosine transform (DCT) for subsurface electrical conductivity (EC) imaging. The subsurface EC distributions are obtained from multi-configuration EMI data measured with a CMD-Explorer sensor along two transects in the Chicken Creek catchment (Brandenburg, Germany). Dipole-dipole electrical resistivity tomography (ERT) data are used to benchmark the inferred EC fields of both transects. We are especially concerned with the impact of the DCT truncation method on the accuracy and reliability of the inversely-estimated EC images. We contrast the results of two different truncation approaches for model parametrization. The first scenario considers an arbitrary selection of the dominant DCT coefficients and their prior distributions (a commonly-used approach), while the second methodology benefits from geostatistical simulation of the EMI data pseudosection. This study demonstrates that DCT truncation based on geostatistical simulations facilitates a robust selection of the dominant DCT coefficients and their prior ranges, resulting in more accurate subsurface EC imaging from multi-configuration EMI data. Results based on geostatistical prior modeling present an excellent agreement between the EMI- and ERT-derived EC fields of the Chicken Creek catchment.
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Jiang, Yang, Yurong Tang, Wen Li, Yong Zeng, Xiaolong Li, Yang Liu et Hong Zhang. « Determination Method of Core Parameters for the Mechanical Classification Simulation of Thin-Skinned Walnuts ». Agriculture 13, no 1 (29 décembre 2022) : 104. http://dx.doi.org/10.3390/agriculture13010104.
Texte intégralRésumé :
Simulation can be used to visualize the mechanical classification of walnuts. It can collect microscopic information about walnuts in the classification roller and guide its optimization design. In this process, simulation parameters are essential factors that ensure the effectiveness of the simulation. In this study, the crucial parameters of thin-skinned walnut particles in classification simulation were determined by combining the discrete element method (DEM) and physical tests. Firstly, the moisture content, shear modulus, stacking angle, and some contact parameters in the shell and kernel were obtained by drying test, compression test, cylinder lifting test, and physical test of contact parameters, respectively. A walnut model was constructed using reverse modeling technology. Then, the ranges of the rest contact parameters were determined using simulation inversion based on the Generic EDEM Material Model database. Second, the parameters significantly influencing the stacking angle were screened via the Plackett–Burman test using contact parameters as factors and stacking angle as the index. The results revealed that the walnut–walnut static friction coefficient, walnut–walnut rolling friction coefficient, and walnut–steel plate static friction coefficient significantly affect the stacking angle. The steepest ascent experiment produced the optimal value intervals of crucial parameters. Besides, a quadratic regression model of important parameters was built using the Box–Behnken test to achieve the optimal parameter combination. The stacking and classification experiments verified that the stacking angle and morphology are mostly similar under calibration parameters without any considerable differences. The relative error was only 0.068%. Notably, the relative error of the average staying time of walnut in the classification roller was 0.671%, and the dimensionless distribution curves of stay time were consistent. This study provides technological support to the simulation analysis of walnut classification and recommends novel methods and references to determine the parameters of other shell materials.
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Tompkins, Michael J., Juan L. Fernández Martínez, David L. Alumbaugh et Tapan Mukerji. « Scalable uncertainty estimation for nonlinear inverse problems using parameter reduction, constraint mapping, and geometric sampling : Marine controlled-source electromagnetic examples ». GEOPHYSICS 76, no 4 (juillet 2011) : F263—F281. http://dx.doi.org/10.1190/1.3581355.
Texte intégralRésumé :
We have developed a new uncertainty estimation method that accounts for nonlinearity inherent in most geophysical problems, allows for the explicit search of model posterior space, is scalable, and maintains computational efficiencies on the order of deterministic inverse solutions. We accomplish this by combining an efficient parameter reduction technique, a parameter constraint mapping routine, a sparse geometric sampling scheme, and an efficient forward solver. In order to reduce our model domain and determine an independent basis, we implement both a typical principal component analysis, which factorizes the model covariance matrix, and an alternative compression method, based on singular-value decomposition, which acts on training models, directly, and is storage efficient. Once we have a reduced base, we map parameter constraints, from our original model domain, to this reduced domain to define a bounded geometric region of feasible model space. We utilize an optimal scheme to sample this reduced model space that uses Smolyak sparse grids and minimizes the number of forward solves by finding the sparsest sampling required to produce convergent uncertainty measures. The result is an ensemble of equivalent models, consistent with our inverse solution structure, which is used to infer inverse uncertainty. We tested our method with a 1D synthetic example, a comparison with a published Metropolis-Hastings sampling example, and an extension to 2D problems using a field data inversion.
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ROSTAM, Ghasem Ghorbani. « Determination of the stress field in the Kopeh Dagh and Eastern Iran regions ». Contributions to Geophysics and Geodesy 52, no 1 (3 avril 2022) : 95–112. http://dx.doi.org/10.31577/congeo.2022.52.1.4.
Texte intégralRésumé :
The land of Iran is situated in a compression zone with a high seismicity rate due to the convergence of Arabian and Eurasian plates. In this study, the stress field of two provinces of Kopeh Dagh and Eastern Iran, which are located in the east and northeast of Iran, has been studied and compared. These two provinces are different in terms of seismicity patterns so that Kopeh Dagh is much more active than Eastern Iran. To achieve this goal, the iterative joint inversion method for stress and fault orientations developed by Vavryčuk (2014) has been used. The average direction of the maximum principal stress (σ1) and the maximum horizontal stress (SHmax) in the study area are estimated to be N30.1°E and N12.1°E, respectively. These directions are in agreement with the convergence of the Arabian plate and the Eurasian plate. The value of the optimal friction coefficient was determined for both regions and it was found that this coefficient is lower in Kopeh Dagh than in Eastern Iran. This indicates a potential relationship of the fault friction with the activity pattern and seismicity of in the region.
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ROSTAM, Ghasem Ghorbani. « Determination of the stress field in the Kopeh Dagh and Eastern Iran regions ». Contributions to Geophysics and Geodesy 52, no 1 (3 avril 2022) : 95–112. http://dx.doi.org/10.31577/congeo.2022.52.1.4.
Texte intégralRésumé :
The land of Iran is situated in a compression zone with a high seismicity rate due to the convergence of Arabian and Eurasian plates. In this study, the stress field of two provinces of Kopeh Dagh and Eastern Iran, which are located in the east and northeast of Iran, has been studied and compared. These two provinces are different in terms of seismicity patterns so that Kopeh Dagh is much more active than Eastern Iran. To achieve this goal, the iterative joint inversion method for stress and fault orientations developed by Vavryčuk (2014) has been used. The average direction of the maximum principal stress (σ1) and the maximum horizontal stress (SHmax) in the study area are estimated to be N30.1°E and N12.1°E, respectively. These directions are in agreement with the convergence of the Arabian plate and the Eurasian plate. The value of the optimal friction coefficient was determined for both regions and it was found that this coefficient is lower in Kopeh Dagh than in Eastern Iran. This indicates a potential relationship of the fault friction with the activity pattern and seismicity of in the region.
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Wang, Xiaoxing, Lixin Zhang, Yu Zhao et Huijian Li. « A New Uniaxial Tensile Model for Foam Metal/Epoxy Interpenetrated Phase Composites ». Polymers 15, no 4 (6 février 2023) : 812. http://dx.doi.org/10.3390/polym15040812.
Texte intégralRésumé :
Foam metal/epoxy interpenetrating phase composite is a new type of composite material with interpenetrating continuity in composition, which exhibits different intrinsic relationships under different stress states in tension and compression, and it is necessary to study the intrinsic relationships in the tensile state in depth. A mesoscopic damage-based tensile intrinsic model is developed, and the elasto-plastic tensile intrinsic equations of the representative volume element are derived based on small deformation theory and total strain theory, as well as the assumptions of equal stress and equal strain. The tensile strengths of nickel–iron foam/epoxy interpenetrated phase composites in three different sizes and their constituent phases were measured, and it was shown in the results that the composite of three-dimensional network interpenetration with high-strength foam metal and epoxy resin formed a weak surface inside the material, and did not significantly improve the tensile strength of the composites. The tensile instantonal equations and damage instantonal equations of nickel–iron foam/epoxy interpenetrated phase composites were predicted by the method of inversion, and the applicability and high accuracy of the tensile intrinsic model were verified in comparison with the measured results.
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Ladak, Sameer, Sheri Molnar et Samantha Palmer. « Multi-method site characterization to verify the hard rock (Site Class A) assumption at 25 seismograph stations across Eastern Canada ». Earthquake Spectra 37, no 1_suppl (9 avril 2021) : 1487–515. http://dx.doi.org/10.1177/87552930211001076.
Texte intégralRésumé :
Site characterization is a crucial component in assessing seismic hazard, typically involving in situ shear-wave velocity ( VS) depth profiling, and measurement of site amplification including site period. Noninvasive methods are ideal for soil sites and become challenging in terms of field logistics and interpretation in more complex geologic settings including rock sites. Multiple noninvasive active- and passive-seismic techniques are applied at 25 seismograph stations across Eastern Canada. It is typically assumed that these stations are installed on hard rock. We investigate which site characterization methods are suitable at rock sites as well as confirm the hard rock assumption by providing VS profiles. Active-source compression-wave refraction and surface wave array techniques consistently provide velocity measurements at rock sites; passive-source array testing is less consistent but it is our most suitable method in constraining the rock VS. Bayesian inversion of Rayleigh wave dispersion curves provides quantitative uncertainty in the rock VS. We succeed in estimating rock VS at 16 stations, with constrained rock VS estimates at 7 stations that are consistent with previous estimates for Precambrian and Paleozoic rock types. The National Building Code of Canada uses solely the time-averaged shear-wave velocity of the upper 30 m ( VS30) to classify rock sites. We determine a mean VS30 of ∼ 1600 m/s for 16 Eastern Canada stations; the hard rock assumption is correct (>1500 m/s) but not as hard as often assumed (∼2000 m/s). Mean variability in VS30 is ∼400 m/s and can lead to softer rock classifications, in particular, for Paleozoic rock types with lower average rock VS near the hard/soft rock boundary. Microtremor and earthquake horizontal-to-vertical spectral ratios are obtained and provide site period classifications as an alternative to VS30.