scholarly journals Experimental and Numerical Study on Hydromechanical Coupled Deformation Behavior of Beishan Granite considering Permeability Evolution

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-14
Author(s):  
Z. H. Wang ◽  
W. G. Ren ◽  
Y. L. Tan ◽  
Heinz Konietzky
Keyword(s):  
Pressure Difference ◽  
Numerical Study ◽  
Volumetric Strain ◽  
Initial Pressure ◽  
Numerical Code ◽  
Permeability Evolution ◽  
Beishan Granite ◽  
Pore Pressures ◽  
Damaged Zone ◽  
Hlw Repository

Beishan granite is a potential host rock for a high-level radioactive waste (HLW) repository in China. Understanding the hydromechanical (HM) behavior and permeability evolution of Beishan granite is important for the HLW repository safety. Therefore, the granite of Beishan in Gansu province was studied. HM coupled tests are carried out on Beishan granite under different pore pressures. The results show that the initial pressure difference has little influence on permeability measurement before dilatancy starts. However, after onset of dilatancy, the permeability increases with the increasing initial pressure difference. The initial permeability of Beishan granite is about 10−18 m2 under a confining pressure of 20 MPa. In the initial loading phase, the permeability shows a relatively large reduction. Then, the permeability almost keeps constant until dilatancy starts. From dilatancy point to peak stress, permeability increases linearly with volumetric strain. The proposed permeability evolution rule is implemented into a numerical code to perform HM coupled simulations. The simulation results show that the damaged zone first appears at the model boundary and then extends to the inside, forming high volumetric strain areas. And it provides seepage channels for fluid flow. The macroscopic fracture patterns indicate that pore pressure accelerates rock degradation during HM coupling. The obtained results help to understand the damage mechanisms of granite caused by pore pressures and are of great importance for the safety of a HLW repository.

scholarly journals A 3DEC Numerical Analysis of the Interaction Between an Uneven Rock Surface and Shotcrete Lining

2021 ◽  
Author(s):  
Ping Zhang ◽  
Ering Nordlund
Keyword(s):  
Numerical Study ◽  
Support Effect ◽  
Influential Factors ◽  
Numerical Analyses ◽  
Numerical Code ◽  
Rock Surface ◽  
Stress Concentrations ◽  
Circular Tunnel ◽  
Rock Tunnels ◽  
Shotcrete Lining

AbstractRock tunnels excavated using drilling and blasting technique in jointed rock masses often have a very uneven and rough excavation surface. Experience from previous studies shows that the unevenness of a rock surface has a large impact on the support effect of shotcrete lining. However, clear conclusions regarding the effect of 2D and 3D uneven surfaces were not obtained due to limited studies in the literature. The numerical analyses reported in this paper were made to investigate the influence of the surface unevenness of a circular tunnel opening on the support effect of shotcrete using a 3D numerical code (3DEC). The models were first calibrated with the help of observations and measured data obtained from physical model tests. The influential factors were investigated further in this numerical study after calibration had been achieved. The numerical analyses show that, in general, the unevenness of a tunnel surface produces negative support effects due to stress concentrations in recesses (compressive) and at apexes (tensile) after excavation. However, shotcrete sprayed on a doubly waved uneven surface has better support effect compared to shotcrete sprayed on a simply waved tunnel surface. The development of shear strength (specifically frictional strength) on the uneven interface between the shotcrete and the rock contributes to this effect, in the condition where bonding of the shotcrete does not work effectively. The interface is a crucial element when the interaction between the rock and shotcrete is to be simulated. When an entire tunnel surface is covered by shotcrete with high modulus, more failures will occur in the shotcrete especially when rock surface is uneven. Based on the numerical model cases examined, some recommendations on how to incorporate tunnel surface conditions (2D or 3D unevenness) in the design of a shotcrete lining are given.

scholarly journals Detection of Material Degradation of a Composite Cylinder Using Mode Shapes and Convolutional Neural Networks

Materials ◽  
2021 ◽  
Vol 14 (21) ◽  
pp. 6686
Author(s):  
Bartosz Miller ◽  
Leonard Ziemiański
Keyword(s):  
Neural Networks ◽  
Convolutional Neural Networks ◽  
Composite Structures ◽  
Vibration Mode ◽  
Numerical Study ◽  
Mode Shapes ◽  
Zone Size ◽  
Composite Cylinder ◽  
Material Degradation ◽  
Damaged Zone

This paper presents a numerical study of the feasibility of using vibration mode shapes to identify material degradation in composite structures. The considered structure is a multilayer composite cylinder, while the material degradation zone is, for simplicity, considered a square section of the lateral surface of the cylinder. The material degradation zone size and location along the cylinder axis are identified using a deep learning approach (convolutional neural networks, CNNs, are applied) on the basis of previously identified vibration mode shapes. The different numbers and combinations of identified mode shapes used to assess the damaged zone size and location were analyzed in detail. The final selection of mode shapes considered in the identification procedure yielded high accuracy in the identification of the degradation zone.

scholarly journals Numerical Study on the Behavior and Bearing Mechanism of Flat Slabs in Column Loss Events

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Aidin Mohammadi ◽  
Alireza Pachenari ◽  
Behnam Sadeghi
Keyword(s):  
Numerical Study ◽  
Progressive Collapse ◽  
Great Tendency ◽  
Load Bearing ◽  
Collapse Potential ◽  
Flat Slabs ◽  
Collapse Mode ◽  
Damaged Zone ◽  
Initial Load ◽  
Cracking Pattern

This study investigates the behavior and the load-bearing mechanism of a typical flat slab with rectangular panels in several scenarios including the removal of a corner, penultimate, and internal columns. The scenarios are rather similar to those used in the conventional evaluation of the progressive collapse potential; however, application of the uniformly distributed loading over panels adjacent to the removed columns was not limited to twice the value of the initial load. Thus, load-deflection curves were drawn up to the point in which a great number of longitudinal slab bars ruptured. Introducing 5 stages on each curve, finite element outputs on concrete cracking pattern and rebar stress state were presented. A significant increase in the stresses along the diagonals of the slab panels accompanied by bar ruptures around columns adjacent to the removed column proved contribution of an important load-bearing mechanism in addition to the behavior called “quasiframe action.” Consecutive rupture of bars showed formation of a zipper-type collapse mode as well as a great tendency to transfer load share of missing column mainly along shorter direction of slab panels. Moreover, the findings indicated that the slab damaged zone could exceed the panels under uniform overloading.

scholarly journals Numerical Study of Fracture Characteristics of Deep Granite Induced by Blast Stress Wave

2021 ◽  
Vol 2021 ◽  
pp. 1-22
Author(s):  
Zheming Zhu ◽  
Weiting Gao ◽  
Duanying Wan ◽  
Meng Wang ◽  
Yun Shu
Keyword(s):  
Shear Failure ◽  
Numerical Study ◽  
Numerical Models ◽  
Rock Fracture ◽  
Initial Pressure ◽  
3D Models ◽  
In Situ Stress ◽  
Vertical Pressure ◽  
The Difference ◽  
Radial Cracks

To study the characteristics of rock fracture in deep underground under blast loads, some numerical models were established in AUTODYN code. Weibull distribution was used to characterize the inhomogeneity of rock, and a linear equation of state was applied to describe the relation of pressure and volume of granite elements. A new stress initialization method based on explicit dynamic calculation was developed to get an accurate stress distribution near the borehole. Two types of in situ stress conditions were considered. The effect of heterogeneous characteristics of material on blast-induced granite fracture was investigated. The difference between 2D models and 3D models was discussed. Based on the numerical results, it can be concluded that the increase of the magnitude of initial pressure can change the mechanism of shear failure near the borehole and suppress radial cracks propagation. When initial lateral pressure is invariable, with initial vertical pressure rising, radial cracks along the acting direction of vertical pressure will be promoted, and radial cracks in other directions will be prevented. Heterogeneous characteristics of material have an obvious influence on the shear failure zones around the borehole.

Numerical study for wave-induced oscillatory pore pressures and liquefaction around impermeable slope breakwater heads

2018 ◽  
Vol 157 ◽  
pp. 364-375 ◽  
Author(s):  
Chencong Liao ◽  
Dagui Tong ◽  
Dong-Sheng Jeng ◽  
Hongyi Zhao
Keyword(s):  
Numerical Study ◽  
Pore Pressures ◽  
Wave Induced

Numerical Study on Film Foam Flow Characteristics in a Straight Duct

2013 ◽  
Vol 561 ◽  
pp. 472-477 ◽  
Author(s):  
Dong Xing Du ◽  
Fa Hu Zhang ◽  
Dian Cai Geng ◽  
Ying Ge Li
Keyword(s):  
Drag Force ◽  
Pressure Difference ◽  
Numerical Study ◽  
Flow Behavior ◽  
Petroleum Industry ◽  
Flow Characteristics ◽  
Viscous Force ◽  
Ideal Condition ◽  
Surface Evolver ◽  
The Mathematical Model

Straight ducts capture some essential features of the motion of foam in porous media in petroleum industry. In this paper, Surface Evolver was employed to build the mathematical model to study the flow behavior of lamellas in the duct with different models. Numerical results show good agreement with experiments and some important features of lamella flow behavior in straight ducts are obtained. It is concluded that, the physical model with viscous force can adequately describe the flow characteristics of reality foam in the experiment. The actual pressure difference consists of the pressure difference caused by the curvature of the lamellas and the drag force on the boundary wall. Under the ideal condition of without drag force along the wall, the pressure drop for lamella flow in the duct is zero, and the shape and the velocity of the lamellas will maintain constant.

A 2D-PIV Study on Natural Convective Heat Transfer in a Square Enclosure With Partially Active Side Walls

2009 ◽  
Author(s):  
Massimo Paroncini ◽  
Francesco Corvaro ◽  
Alessia Montucchiari
Keyword(s):  
Holographic Interferometry ◽  
Numerical Study ◽  
Numerical Procedure ◽  
Numerical Code ◽  
Number Range ◽  
Square Enclosure ◽  
Nusselt Numbers ◽  
Side Walls ◽  
Dynamic Structures ◽  
Rayleigh Numbers

The present study is an experimental and numerical analysis on the natural convection of air in square enclosures with partially active side walls. The experimental equipment is based on two different systems: an holographic interferometer and a 2D-PIV. The test cell is a square enclosure filled of air with vertical partially active side walls at different temperatures. The hot and cold regions on these sides are located in the middle of the cavity. The remaining vertical walls are made up of glass to allow an optical access to the cavity. The top and bottom surfaces of the enclosure are made up of plexiglas to reduce heat leakages. The experimental study is carried out both through the holographic interferometry, in order to obtain the average Nusselt numbers at different Rayleigh numbers, and through the 2D-PIV, in order to analyse the dynamic behaviour of the phenomenon at the same Rayleigh numbers. The average Nusselt numbers are obtained measuring the temperature distribution in the air layer trough the real-time and double-exposure holographic interferometry; the dynamic structures are the velocity vector distribution, the streamlines and the velocity maps. Finally these experimental data are compared to the results obtained through a numerical study carried out using the finite volume code, Fluent 6.2.3. The aim of this comparison is the validation of the numerical procedure. In this way it is possible to use the numerical code to enlarge the Rayleigh number range.

An Alternative Decomposition of the Strain Gradient Tensor

2001 ◽  
Vol 69 (2) ◽  
pp. 139-141 ◽  
Author(s):  
H. Jiang ◽  
Y. Huang ◽  
T. F. Guo ◽  
K. C. Hwang
Keyword(s):  
Strain Gradient ◽  
Strain Field ◽  
Numerical Study ◽  
Volumetric Strain ◽  
Crack Tip ◽  
Square Root ◽  
Crack Tip Field ◽  
Gradient Tensor ◽  
Classical Plasticity ◽  
Square Root Singularity

An alternative decomposition of the strain gradient tensor is proposed in this paper in order to ensure that the deviatoric strain gradient vanishes for an arbitrary volumetric strain field, which is consistent with the physical picture of plastic deformation. The theory of mechanism-based strain gradient (MSG) plasticity is then modified accordingly based on this new decomposition. The numerical study of the crack-tip field based on the new theory shows that the crack tip in MSG plasticity has the square-root singularity, and the stress level is much higher than the HRR field in classical plasticity.

scholarly journals Leak-Based Method for the Measurement of Air Permeability of Papers

2016 ◽  
Vol 27 (1) ◽  
Author(s):  
Stéphane Colard ◽  
Georges Cholet ◽  
Marlène Testud
Keyword(s):  
Pressure Difference ◽  
Initial Pressure ◽  
Regulatory Compliance ◽  
Air Permeability ◽  
Experimental Investigations ◽  
International Standard ◽  
Alternative Method ◽  
Specific Geometry ◽  
Current Measuring ◽  
Cigarette Paper

SummaryThe air permeability of cigarette paper is currently assessed according to the international standard ISO 2965 by applying a constant pressure difference of 1 kPa between the two faces of a sample and by measuring the corresponding airflow.Lower Ignition Propensity regulations have led tobacco manufacturers to use specific cigarette papers with narrow bands of low air permeability and diffusion capacity to achieve regulatory compliance. The international standard ISO 2965 was revised in 2009 to take into account the specific geometry and characteristics of the bands and to include suitable narrow measuring heads. The consequence was a significant reduction of the measured airflow levels with banded papers and a need for equipment covering specifically low airflow ranges.The well-known pressure-airflow relationship across cigarette paper enables the development of an alternative method to ISO 2965 which does not require direct airflow measurement, and therefore airflow meters which are costly parts of the current measuring devices. The alternative method is based on the measurement of the change of the pressure over time after an initial pressure difference was applied between the two faces of the paper. The consecutive analysis of the pressure difference profile, impacted by the leak across the paper, enables the derivation of the air permeability.The related theoretical aspects were developed for both viscous and inertial airflows, and experimental investigations were conducted with banded and conventional cigarette papers as well as a permeability calibration standard. Results obtained with the proposed method showed good consistency with ISO 2965 measurements and a lower repeatability, demonstrating that a leak-based method could be a simple and reliable alternative.

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