Impact of deposition borehole geometry on mechanical spalling in nuclear waste repositories

2020 ◽  
Author(s):  
Maria Cristina Saceanu ◽  
Adriana Paluszny ◽  
Robert Zimmerman ◽  
Diego Mas Ivars
Keyword(s):  
Rock Mass ◽  
Elevated Temperatures ◽  
Domain Boundary ◽  
Three Dimensional ◽  
Growth Patterns ◽  
Spent Fuel ◽  
Stress Concentrations ◽  
Pillar Stability ◽  
Growth Step ◽  
Fracture Growth

<p>Predictions of rock spalling around deep-drilled boreholes and tunnels in underground geologic repositories in crystalline rocks remain a significant challenge, due to the heterogeneities present in the rock mass, uncertain stress fields, and the complex thermo-mechanical behaviour of the rock mass at elevated temperatures.</p><p>This study presents a three-dimensional numerical analysis of multiple fracture growth leading to spalling around a deposition borehole. The mechanical spalling due to stress amplification after drilling is simulated using a finite element-based discrete fracture growth simulator. Fractures are grown by computing stress intensity factors at each fracture tip, and the mesh is adapted to accommodate the changing fracture geometries at every growth step. The model is validated using the Äspö Pillar Stability Experiment (APSE), calibrated to simulate the drilling of a borehole in the Forsmark granite, and subjected to a far-field anisotropic triaxial stress, corresponding to the <em>in situ</em> stress model from Forsmark. The deposition tunnel is implicitly simulated by attaching the deposition borehole to a free domain boundary.</p><p>The effect of borehole geometry on the predicted spalling around a typical deposition borehole is studied. The cylindrical borehole is modified at the top to provide an access ramp for the spent fuel canisters, which can effectively improve the repository design by reducing the height of the deposition tunnel. Three cases are investigated, in which the borehole top is cylindrical, conical, and wedge-shaped, respectively. Numerical results show that spalling occurs in all cases, but the borehole geometry affects fracture nucleation and growth patterns. The enlargement of the borehole top induces higher stress concentrations at the borehole-tunnel junction, increasing the severity of spalling at the top of the borehole. The final spalled zone and the fractures-borehole interaction are illustrated for each stress and geometry scenario.</p>

Thermo-mechanical Effects on Fracture Growth and Apertures in Three-Dimensional Subsurface Fractured Rocks 

2021 ◽  
Author(s):  
Adriana Paluszny ◽  
Robin N. Thomas ◽  
M. Cristina Saceanu ◽  
Robert W. Zimmerman
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Three Dimensional ◽  
Growth Patterns ◽  
Three Dimensions ◽  
Interaction Patterns ◽  
Flow Equations ◽  
The Matrix ◽  
Model Equations ◽  
Fracture Growth

<p>A finite-element based, quasi-static growth algorithm models mixed mode concurrent fracture growth in three dimensions, leading to the formation of non-planar arrays and networks. To model the fully coupled THM model, equations describing mechanical deformation as well as heat transfer in the matrix and in the fractures are introduced in the formulation, simultaneously accounting for the effect of fluid flow and stress-strain response. This results in five separate, but two-way coupled model equations: a thermoporoelastic mechanical model; two fluid flow equations, one for the rock matrix and one for the fractures; two heat transfer equations, similarly for both the matrix and fractures. Fractures are represented explicitly as discrete surfaces embedded within a volumetric domain [1]. Growth is computed as a set of vectors that modify the geometry of a fracture by accruing new fracture surfaces in response to brittle deformation. Fracture tip stress intensity factors drive fracture growth. This growth methodology is validated against analytical solutions for fractures under compression and tension [2]. Thermal effects on the apertures and growth patterns will be presented. Isolated fracture geometries are compared with selected experimental results on brittle media. Accurate growth is demonstrated for domains discretised by refined and coarse volumetric meshes. Fracture and volume-based growth rates are shown to modify fracture interaction patterns. Two-dimensional cut-plane views of fracture networks show how fractures would appear on the surface of the studied volume.</p><p><strong>REFERENCES</strong></p><p>[1] N. Thomas, A. Paluszny and R. W. Zimmerman. Growth of three-dimensional fractures, arrays, and networks in brittle rocks under tension and compression. Computers and Geotechnics, 2020. doi: 10.1016/j.compgeo.2020.103447</p><p>[2] Paluszny and R. W. Zimmerman. Numerical fracture growth modeling using smooth surface geometric deformation. Eng. Fract. Mech., 108, 19-36, 2013. doi: 10.1016/j.engfracmech.2013.04.012</p>

Growth Pattern Study of Closed Surface Flaw under Compression

2007 ◽  
Vol 353-358 ◽  
pp. 158-161
Author(s):  
Y.S.H. Guo ◽  
Wei Shen Zhu ◽  
Shu Cai Li ◽  
R.H.C. Wong ◽  
B. Sin
Keyword(s):  
Rock Mass ◽  
Three Dimensional ◽  
Closed Surface ◽  
Growth Patterns ◽  
Surface Flaw ◽  
Mode Iii ◽  
Surface Flaws ◽  
Crack Zone ◽  
Polyester Film ◽  
Brittle Fracture Mechanics

Under extra compressive stress, some phenomena of rock spallings and fractures often exist on rock mass located in sidewalls of underground house and tunnels. It is the reason that the crack growth and coalescence initiation from original flaws (or faults) in rock mass. In the previous studies, many researchers took a flaw as a through flaw (2-dimentional model), but the flaws are not always through the whole rock mass in fact, most of them are only near the surface of rock mass, These are so named as surface flaws. They belong to three dimensional (2-D) flaws. Now, the reports on initiation and growth of 3-D surface flaw are few. So, for the investigation on growth patterns of 3-D surface flaw, a series of samples containing a surface flaw were carried out using frozen casting resin material at about -30°C temperatures. The surface flaw was made of a polyester film was used to model a single closed flaw on rock mass. The experimental results show that the wrapping wing crack (Mode I) initiated at the ends (or tips) of surface flaw first, and then formed a kinking zone (mixed crack zone) at a certain place at the middle of surface flaw region. Some petal cracks (Mode III) and shell-shaped cracks (Mode III) would grow at the middle place of flaw. A big fin crack (Mixed Mode) also emerged in middle of flaw and grown along loading direction. Finally, a team of large cracking curved faces deformed inside the resin specimen; the whole specimen would be splitted off by the initiation and growth of the cracks. The reasons lead to the fracture patterns of 3-D closed surface flaw were provided with brittle fracture mechanics theory in the article, preliminarily.

scholarly journals Detecting the Mechanism behind the Transition from Fixed Two-Dimensional Patterned Sika Deer (Cervus nippon) Dermal Papilla Cells to Three-Dimensional Pattern

2021 ◽  
Vol 22 (9) ◽  
pp. 4715
Author(s):  
Guanning Wei ◽  
Hongmei Sun ◽  
Haijun Wei ◽  
Tao Qin ◽  
Yifeng Yang ◽  
...  
Keyword(s):  
Culture Condition ◽  
Sika Deer ◽  
Three Dimensional ◽  
Cervus Nippon ◽  
Dermal Papilla ◽  
Growth Patterns ◽  
The Self ◽  
Dermal Papilla Cells ◽  
Aggregative Behavior ◽  
Cell Pattern

The hair follicle dermal papilla is critical for hair generation and de novo regeneration. When cultured in vitro, dermal papilla cells from different species demonstrate two distinguishable growth patterns under the conventional culture condition: a self-aggregative three dimensional spheroidal (3D) cell pattern and a two dimensional (2D) monolayer cell pattern, correlating with different hair inducing properties. Whether the loss of self-aggregative behavior relates to species-specific differences or the improper culture condition remains unclear. Can the fixed 2D patterned dermal papilla cells recover the self-aggregative behavior and 3D pattern also remains undetected. Here, we successfully constructed the two growth patterns using sika deer (Cervus nippon) dermal papilla cells and proved it was the culture condition that determined the dermal papilla growth pattern. The two growth patterns could transit mutually as the culture condition was exchanged. The fixed 2D patterned sika deer dermal papilla cells could recover the self-aggregative behavior and transit back to 3D pattern, accompanied by the restoration of hair inducing capability when the culture condition was changed. In addition, the global gene expressions during the transition from 2D pattern to 3D pattern were compared to detect the potential regulating genes and pathways involved in the recovery of 3D pattern and hair inducing capability.

scholarly journals Three-Dimensional Elastodynamic Analysis Employing Partially Discontinuous Boundary Elements

Algorithms ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 129
Author(s):  
Yuan Li ◽  
Ni Zhang ◽  
Yuejiao Gong ◽  
Wentao Mao ◽  
Shiguang Zhang
Keyword(s):  
Side Effect ◽  
Domain Boundary ◽  
Three Dimensional ◽  
Boundary Integral ◽  
Integration Scheme ◽  
Computational Accuracy ◽  
Time Step ◽  
Corner Points ◽  
Discontinuous Elements ◽  
The Time Domain

Compared with continuous elements, discontinuous elements advance in processing the discontinuity of physical variables at corner points and discretized models with complex boundaries. However, the computational accuracy of discontinuous elements is sensitive to the positions of element nodes. To reduce the side effect of the node position on the results, this paper proposes employing partially discontinuous elements to compute the time-domain boundary integral equation of 3D elastodynamics. Using the partially discontinuous element, the nodes located at the corner points will be shrunk into the element, whereas the nodes at the non-corner points remain unchanged. As such, a discrete model that is continuous on surfaces and discontinuous between adjacent surfaces can be generated. First, we present a numerical integration scheme of the partially discontinuous element. For the singular integral, an improved element subdivision method is proposed to reduce the side effect of the time step on the integral accuracy. Then, the effectiveness of the proposed method is verified by two numerical examples. Meanwhile, we study the influence of the positions of the nodes on the stability and accuracy of the computation results by cases. Finally, the recommended value range of the inward shrink ratio of the element nodes is provided.

Three-Dimensional Atomic Structure of Supported Au Nanoparticles at High Temperature

Nanoscale ◽  
2021 ◽  
Author(s):  
Pei Liu ◽  
Ece Arslan Imran ◽  
Annick De Backer ◽  
Annelies de Wael ◽  
Ivan Lobato ◽  
...  
Keyword(s):  
High Temperature ◽  
Atomic Structure ◽  
Au Nanoparticles ◽  
Elevated Temperatures ◽  
Three Dimensional

Au nanoparticles (NPs) deposited on CeO2 are extensively used as thermal catalysts since the morphology of the NPs is expected to be stable at elevated temperatures. Although it is well...

Effective Convergence Checks for Verifying Finite Element Stresses at Three-Dimensional Stress Concentrations

2018 ◽  
Vol 3 (3) ◽  
Author(s):  
J. R. Beisheim ◽  
G. B. Sinclair ◽  
P. J. Roache
Keyword(s):  
Finite Element ◽  
Error Estimation ◽  
A Posteriori Error Estimates ◽  
Three Dimensional ◽  
Posteriori Error ◽  
Test Problems ◽  
A Posteriori ◽  
Stress Concentrations ◽  
Element Analysis ◽  
A Posteriori Error

Current computational capabilities facilitate the application of finite element analysis (FEA) to three-dimensional geometries to determine peak stresses. The three-dimensional stress concentrations so quantified are useful in practice provided the discretization error attending their determination with finite elements has been sufficiently controlled. Here, we provide some convergence checks and companion a posteriori error estimates that can be used to verify such three-dimensional FEA, and thus enable engineers to control discretization errors. These checks are designed to promote conservative error estimation. They are applied to twelve three-dimensional test problems that have exact solutions for their peak stresses. Error levels in the FEA of these peak stresses are classified in accordance with: 1–5%, satisfactory; 1/5–1%, good; and <1/5%, excellent. The present convergence checks result in 111 error assessments for the test problems. For these 111, errors are assessed as being at the same level as true exact errors on 99 occasions, one level worse for the other 12. Hence, stress error estimation that is largely reasonably accurate (89%), and otherwise modestly conservative (11%).

Three-dimensional stromatolites from Maastrichtian–Danian Yacoraite Formation, Argentina: modelling and assessing hydrodynamic controls on growth patterns

2021 ◽  
pp. 1-17
Author(s):  
Patricio Guillermo Villafañe ◽  
Carlos Cónsole-Gonella ◽  
Paolo Citton ◽  
Ignacio Díaz-Martínez ◽  
Silvina de Valais
Keyword(s):  
Environmental Factors ◽  
Methodological Approach ◽  
Three Dimensional ◽  
Growth Patterns ◽  
External Morphology ◽  
Water Dynamics ◽  
Microbial Composition ◽  
Depositional Processes ◽  
Run Off ◽  
Internal Arrangement

Abstract Stromatolites are biogenic sedimentary structures formed by the interplay of biological (microbial composition) and environmental factors (local hydrodynamic conditions, clastic input and/or water chemistry). Well-preserved, three-dimensional (3D) fossil stromatolites are key to assessing the environmental factors controlling their growth and resulting morphology in space and time. Here, we report the detailed analysis of well-exposed, highly informative stromatolite build-ups from a single stratigraphic horizon within the Maastrichtian–Danian Yacoraite Formation (Argentina). This study focuses on the analysis of depositional processes driving intertidal to shallow subtidal stromatolites. Overall depositional architecture, external morphology and internal arrangement (mega, macro, meso and microstructures) of stromatolite build-ups were analysed and combined with 3D photogrammetric models, allowing us to decipher the links between stromatolite structure and tidal dynamics. Results suggest that external morphology and architecture of elongated and parallel clusters grew under the influence of run-off channels. The internal morphology exhibits columnar structures where the space between columns is interpreted as recharge or discharge channels. This work supports the theory that stromatolites can be used as a high-resolution tool in the assessment of water dynamics, and provides a new methodological approach and data for the dynamic reconstruction of intertidal stromatolite systems through the geological record.

scholarly journals Three-dimensional CFD modeling of thermal behavior of a disc brake and pad for an automobile

2020 ◽  
Vol 15 (4) ◽  
pp. 543-549
Author(s):  
Haydar Kepekci ◽  
Ergin Kosa ◽  
Cüneyt Ezgi ◽  
Ahmet Cihan
Keyword(s):  
Cast Iron ◽  
Friction Coefficient ◽  
Elevated Temperatures ◽  
Gray Cast Iron ◽  
Three Dimensional ◽  
Brake System ◽  
Gray Cast ◽  
Cfd Modeling ◽  
Disc Brake ◽  
Disc Material

Abstract The brake system of an automobile is composed of disc brake and pad which are co-working components in braking and accelerating. In the braking period, due to friction between the surface of the disc and pad, the thermal heat is generated. It should be avoided to reach elevated temperatures in disc and pad. It is focused on different disc materials that are gray cast iron and carbon ceramics, whereas pad is made up of a composite material. In this study, the CFD model of the brake system is analyzed to get a realistic approach in the amount of transferred heat. The amount of produced heat can be affected by some parameters such as velocity and friction coefficient. The results show that surface temperature for carbon-ceramic disc material can change between 290 and 650 K according to the friction coefficient and velocity in transient mode. Also, if the disc material gray cast iron is selected, it can change between 295 and 500 K. It is claimed that the amount of dissipated heat depends on the different heat transfer coefficient of gray cast iron and carbon ceramics.

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