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By Y. L. Su, R. Stefanko, Y. J. Wang

This chapter describes a new approach to the solution of stress distribution around underground openings utilizing the finite element method and employing stochastically simulated rock properties. It is well-known from extensive laboratory tests that the properties of rocks, e.g., Young's modulus and Poisson's ratio, are not single-valued but form some distribution. If the scatter of test data is attributed to the variability of the rock itself rather than due to an inadequacy in test procedure, then stress solutions have to consider these variations. Utilizing this basic philosophy, the present study was initiated. A long circular opening subjected to plane strain in a hydrostatic stress field was chosen as a specific example to illustrate this approach. The technique adopted in solving stress distributions was based on the finite element method. This method is essentially a generalization of standard structural analysis procedures in which the continuum is idealized as an assemblage of "elements," interconnected at a finite number of nodal points. It is capable therefore of handling different material properties for individual elements in the model, if desired. In this study, each individual element was assumed to be isotropic, homogeneous, and elastic. However, values for Young's modulus and Poisson's ratio were randomly varied from element to element according to an assumed frequency distribution.

Jan 1, 1970

By W. G. Pariseau

Recent advances in rock mass mechanics and computational technology now allow for stability analysis of excavations in "wet" mines where mining-induced changes in rock mass deformation and fluid flow are coupled and time-dependent. All the usual dry mine parameters including the premining stress state and rock mass properties are taken into account, in addition to water pressure and flow in jointed, possibly porous, rock masses. Finite element analyses of shafts and tunnels as circular, elliptical, rectangular and arched-rectangular hole shapes excavated in an initially stressed and pressurized rock mass indicate that the usual guidelines for optimum shape and orientation of single openings apply. Here, optimum means maximizing the minimum wall safety factor, or equivalently, minimizing the peak stress concentration. The results also show that failure originates in elements at the wall and that the minimum safety factor at the wall in the wet case is always less than the dry case regardless of drainage time allowed.

Jan 1, 1995

By M. Cepak, K. Donovan, W. G. Pariseau

This paper examines the difficulties of applying the finite element (FE) method of analysis to quantitative design of cable bolt systems. Cable bolt systems are in general use for ground control in VCR (Vertical Crater Retreat) topes throughout the world. However, despite their widespread use and importance, design of cable bolt systems is highly subjective. Two difficulties with the FE approach are examined: (i) the use of standard elements with a high aspect ratio (slender elements) to represent bolts, and (ii) the influence of cable bolts on hanging wall stability of a VCR study stope. Analysis results indicate that the use of slender elements for bolts is practical in large scale finite element analyses of VCR stopes. There are significant advantages in this approach to the engineering design of cable bolt systems in underground mining.

Jan 1, 1984

By K. C. Viveros, R. R. Ambriz, C. García, F. De Villèle, A. Talha, D. Jaramillo

Cold hole expansion on base metal, weld metal and heat affected zone of 6061-T6 aluminum alloy welds was simulated by means of finite element method. Three dimensional compact test models with a previous fatigue crack length with a relation of ??= a/W = 0.3, were used to analyze the hole expansion process. Considering the local mechanical properties for each zone of the welded joint, the optimal expansion degree (1.64 to 2.46 %) was determined. The residual stress field, through thickness, after the expansion process in all welding zones, were correlated with the crack opening displacement obtained by finite element analysis. It was observed, that compressive residual stress fields for a post-expansion, in different crack lengths, provided a crack closure mechanism for base metal, weld metal and heat affected zone. Contrary, the crack remained open when residual stresses are positive. The results are given as tangential stresses versus distance from the edge of the cold expansion and crack opening displacement as a function of applied load.

Jan 1, 2014

By R. S. Sandhu, S. H. Advani, J. K. Lee, B. L. Aboustit

A comprehensive finite element formulation for thermo-elastic consolidation based on a general variational principle is presented Sample one dimensional problems associated with isothermal consolidation, heat conduct ion, and thermo-elastic consolidation are presented. In addition, evaluations of thermo-elastic consolidation for an underground coal conversion field site are conducted.

Jan 1, 1982

By I. S. Laitinen

Outokumpu Technology has recently introduced new technology in both copper electrorefining and electrowinning. This technology includes, among other things, a new permanent cathode (Outokumpu Permanent Cathode) and new busbar technology (Outokumpu Double Contact System). The new technology has already been tested in commercial scale cells. To get a better understanding of the busbar system a multiphysical simulation model of the electrowinning and electrorefining cells was developed. A mathematical model of electrical conduction and heat transfer in a copper electrolysis cell was developed from partial differential equations. The model was expanded to a cell group including seven electrolysis cells connected electrically in series. The model was solved numerically using the finite element method (FEM). Using the model, different intercell busbar systems were simulated. Typical electrical disturbances, like loose contacts between cathodes and the main busbar and short circuits between electrodes, were included in the simulation. The results of the simulation runs with conclusions are presented in this paper.

Jan 1, 2007

By B. Q. Li, H. C. de Groh, X. Lu

"A fully 3-D, transient finite element model is developed to represent the magnetic damping effects on complex fluid flow, heat transfer and electromagnetic field distributions in a metallic melt. The model development is based on our in-house finite element code for the fluid flow, heat transfer and electromagnetic field calculations. The numerical model is tested against numerical and experimental results for water as reported in literature. Various numerical simulations are carried out for the melt convection and temperature distribution with and without the presence of a transverse magnetic field. Numerical results show that magnetic damping can be effectively applied to stabilize melt flow, reduce turbulence and flow levels in the melt and over a certain threshold value a higher magnetic field resulted in a greater reduction in velocity. Also, for the study of melt flow instability, a long enough running time is needed to ensure the final fluid flow recirculation pattern. Moreover, numerical results suggest that there seems to exist a threshold value of applied magnetic field, above which magnetic damping becomes possible and below which the convection in the melt is actually enhanced.1. INTRODUCTIONThe imposition of a DC magnetic field on a moving, electrically conducting fluid, such as molten metal or semiconductor melt, produces an opposing Lorentz force that results in a reduction of flow velocity in the liquid. This effect has been explored in both the semiconductor and metals industries to control natural convection and/or surface tension induced Marangoni convection as well as thermally induced flow instability during solidification processing of these melts [1-6]. A mathematical model can be of great use in developing both fundamental understanding of the fluid-magnetic field interactions in these magnetically-assisted processing systems and basic guidelines for process design, control and optimization.This paper presents a 3-D mathematical model for magnetically damped fluid flow and heat transfer in a melt cavity, which is useful for interpreting results for unidirectional solidification processes at slow solidification rate, and some preliminary results concerning the magnetic damping effects on the flow instability in the melt. The model development is based on the finite element solution of the Navier-Stokes equations, energy equations and equations for induced electric field. The model is tested against reported results and is then applied to study the fluid flow and thermal distribution in the metallic melt with and without an external magnetic field."

Jan 1, 1999

By A. S. Usmani

The flow associated with the pouring of molten metal into moulds has been modelled on the basis of certain simplifying assumptions. A finite element based Navier-Stokes equation solver has been used to analyse the flow. The velocities obtained from the Navier-Stokes equation solver are used to advect a pseudo-concentration function for modelling the fluid front. A simple problem with a known analytical solution is solved first to test the model. Subsequently, several more examples with varied geometrical configurations are modelled, including one with curved flow boundaries.

Jan 1, 1992

By Youliang He

Twin-roll casting is an integrated casting and rolling process that involves the continuous solidification of a melt and the plastic deformation of the solidified metal between two rotating rolls. Computer modeling is a valuable tool to help engineers understand the metallurgical process during twin-roll casting. However, commercially available software can only model either the fluid flow/heat transfer of the melt or the plastic deformation of the solid, but not both. In this study, an object-oriented finite element program was developed to simulate the steady-state fluid flow, solidification and plastic deformation of an A7,31 magnesium alloy in a horizontal twin-roll caster. The melt, the mush zone and the solid were treated as a generalized Newtonian flow in an Eulerian reference frame and different constitutive equations were employed to describe the material behaviours. The effect of operational parameters on the solidification process was discussed based on the simulation results.

Jan 1, 2010

By S. Behera, K. Dey

This paper presents a methodology for finite element (FE) modelling to analyse the total deformation of rockmass under blast-load, with a focus on predicting backbreak that may occur during surface blasting operations. Backbreak can result from improper use of explosive energy, leading to damage beyond the excavation zone and jeopardizing operational safety and productivity. The paper highlights the impacts of backbreak on bench stability, excavator operation, drilling operation, flyrock generation, and improper fragmentation and boulder formation in surface blasting. However, prior estimation of extent of rock breakage zone can provide an idea to formulate the blast design to control the backbreak. While vibration-based prediction models are commonly used to estimate backbreak, they require physical blasting experimentation. To overcome this limitation, the paper describes the development of a FE model using ANSYS Explicit dynamics, which simulates rock blasting and calculates the total deformation of the rockmass. The rockmass deformation is modelled using Drucker-Prager (D-P) strength model with the Jones-Wilkins-Lee (JWL) equation of state for the explosives. The accuracy of the FE model is evaluated through physical experiments, and the results are compared with the vibration models. The FE model demonstrates close proximity to physical observations as well as vibration model result in predicting backbreak, thereby offering a promising alternative to vibration-based prediction models. The primary objective of the study is to predict the response of the insitu rockmass to explosive blast loading and determine the effective rock breakage zone.

Jan 1, 2024

The paper describes a practical methodology based on numerical modelling for the prediction of progressive failure of underground mine stopes with cable bolt support. A case study of the 40-761 stope at Kidd Creek Mine, Timmins, Ontario is presented. The stope was mined by blasthole open stoping in 1986 as a lead stope within a mining block between 36-1 and 38-2 levels. Initially designed to peak at 38-2 level, the stope back caved upwards approximately 40m towards 36-1 level. Cable bolts were installed above the stope from 36-1 level after caving had begun. The stope eventually stopped to cave when the falling rock mass encountered a sufficiently high cable density. The paper provides details of the geomechanical data and modelling results of the case study. Numerical modelling is carried out using a finite element package known as e-z tools which has, among other things, a special cable/rockbolt simulation capability.

Jan 1, 1994

By F. Fournier Dit Chabert, F. Tancret, J. François Castagné, R. Le Gall

During the repair of turbine blades by a laser cladding process, it is observed that interdendritic cracking occurs in the heat affected zone (HAZ). Auger electron spectroscopy, performed on sample broken at high temperature, reveals interfacial sulfur segregation, which is known to be one of the main causes of microcraking in the HAZ during welding processes. Moreover, thermal gradients generated by the process are responsible for important thermomechanical stresses. In the present work, the finite element code Comsol Multiphysics is used to simulate the laser cladding process in order to determine both the thermal field and, using an elastoplastic law, the stress field inside the component. The originality is that the temperature history calculated in the thermomechanical model is extracted then injected in a segregation model in order to calculate the local segregation behavior. This model can be eventually used to predict the risk of cracking as a function of process parameters and alloy chemistry.

Jan 1, 2006

By A. F. Giamei, F. Landis, M. O. Duffy, R. J. Mador

"The directional solidification of complex advanced gas turbine airfoils must be carried out without the nucleation of undesirable grains and with minimal shrinkage. Such problems are typically eliminated by using a number of mold design and process iterations. A more efficient approach is envisioned where a solidification model is generated and utilized to accelerate process development. Towards this end, the directional solidification (DS) of simple geometrical shapes in a crystal grower apparatus has been simulated with MARC finite element nonlinear thermal analyses.The finite element models of cylindrical (2D) and rectangular (3D) cross-section bars in the DS environment are presented. Temperature dependent properties, the impact of latent heat of fusion and a time-dependent radiation boundary condition constitute the more salient features of the MARC models. Solidification zone thermal behavior is predicted during the withdrawal transient for the specific case of nickel based superalloys grown in ceramic shell molds. Comparisons of analytical results with experiments demonstrate notable prediction accuracy. INTRODUCTIONSingle crystal and uni-directional crystal turbine blades require tightly controlled conditions if metallurgically and mechanically acceptable parts are to be produced. Gated blade geometry and process parameters must be precisely determined if incorrect grain structure, orientation and shrinkage are to be avoided. Since purely experimental development programs designed to evaluate these parameters can be excessively costly and time-consuming, an effort combining engineering analysis and verification by experiment has been initiated at Pratt & Whitney. Comparison of analytical predictions and measured data for geometries simpler than a turbine blade, namely cylindrical and rectangular bars, comprised the initial stage of this effort. Subsequent tasks involve modeling geometries of increasing complexity and ultimately the simulation of the directional solidification of the turbine blade, shown schematically in Figure 1. This paper summarizes the results of the initial stage of the effort."

Jan 1, 1986

By O. E. Wheeler

The term "finite element analysis" is heard and seen in print a great deal these days; a few words on what precisely it is are in order. In the broadest sense, finite element analysis is an application of an idea developed by a nineteenth century mathematician named Rayleigh. His basic idea was to decompose any problem in mathematical physics into a large number of simpler problems, solve the simpler problems, and then put those solutions together to form an approximation to the solution of the original problem. The scheme works nicely because of two features: first, much of the difficulty in solving practical problems of mathematical physics stems from irregularities in the boundaries and the simpler problems can be chosen with regular boundaries and second the smaller problems are solved for small physical areas where simple approximations of the solution do not differ much from the true solution. In the narrower sense, in which we are now interested, finite element analysis is a technique of using imaginary simple structural elements to construct analytical models of real structures. A direct parallel with the Rayleigh approach exists since the "finite elements" have simple boundaries and are restricted to simple behavior within a single element. Although the correspondence between Rayleigh's ideas and finite element analysis is now widely recognized, the computational tool, as it has developed over the last thirty years, comes not from the discipline of physics but rather from that of structural engineering. It is interesting that it came not from the traditional research community, the universities, but instead from working

Jan 1, 1974

By Viswanadham B. V. S., Babu K. V

Wind energy is one of the most economical renewable energy sources. In order to support wind turbines onshore or offshore open-ended monopile foundations are widely used. Unlike conventional structures, wind turbine foundations experience a large magnitude of lateral loads in the order of 20 % to 30% of total vertical loads. The presence of soft clayey layers at shallow depth along the coastal region, offers lesser lateral load resistance to monopile foundations. One option to enhance lateral load capacity is by introducing fins to the outer surface of the monopiles. Studies pertaining to lateral load response of finned piles in clayey soils are very sparse. This paper presents some of the numerical model studies on the lateral load response of monopiles and finned piles in soft and stiff clay. In the present study, three-dimensional finite element analyses were performed on monopiles as well as finned piles. Analyses were performed in clay with different consistency varying from soft to stiff. Pile material is mild steel for all analyses. The pile section modeled as linear elastic material whereas soil was modeled as Mohr – Coulomb constitutive model with non-associated flow rule. Monopiles and finned piles having four and eight fins with different fin sizes and configurations are considered during the analyses. Finned piles advantage over monopiles to resist lateral load is highlighted in the present study. The results have shown that fins are effective to enhance the lateral load carrying capacity of monopiles and also it reduces the bending moment in monopiles for a given design load.

Sep 1, 2022

By D Olivier

De Beers' Finsch Mine is situated in the Northern Cape province, 170 km northwest of Kimberley. The concentrator facility, designed and constructed by Bateman Engineering, was commissioned in 1967 and upgraded in 1979 using diamond liberation and extraction technology available at the time of design. Since then significant advances in diamond processing and technology have been made and these -have been incorporated into the new main treatment plant and recovery plant flowsheets, making diamond liberation and recovery from the Pre-1979 dumps a viable economic option at Finsch."

Jan 1, 2010

By J. -M. Lopez-Cuesta, C. Petter, B. Otazaghine, M. Batistella, R. Sonnier

"Kaolinite is a dioctahedral aluminosilicate widely used as paper filler and coating pigment. At the best of our knowledge, kaolinite is not widely used in polymer industry. Therefore, in this study, the flame retardant effect of kaolinite in ethylene vinyl acetate copolymer (EVA) and polypropylene (PP) were studied and compared with an alumina trihydrate (ATH) and Talc. Cone calorimeter results shows that the weight percentage of ATH in EVA/ATH composites must be at least 50 wt. % in order to reach an improvement in fire retardancy in terms of pHRR. In the case of EVA/kaolinite, even with 35 wt. % the pHRR is largely reduced. Comparing PP/Talc and PP/kaolinite composites at 30 wt. %, both fillers leads to same reduction in pHRR with a slightly better performance for PP/kaolinite composites. In both cases an intumescent behavior of kaolinite composites was observed that could slow the rate of the rising degradation products, allowing radical recombination reactions. Also, it was observed that kaolinite forms a protective layer on the surface of the samples, which could insulate the material. These behaviors (intumescence and formation of a protective barrier) could reduce the transfer of the degradation products to the flame and explain the better performance of kaolinite composites. INTRODUCTION The use of mineral fillers as fire retardants in polymer matrix are well known and widely studied [1]–[10]. Aluminum and magnesium hydroxides (respectively ATH and MDH) are the most widely used inorganic fire retardants. To achieve fire retardancy with these mineral fillers, about 50-60% loading is required which decrease the physical properties of the composites. The fire behavior of composite EVA has been the subject of many studies [4], [7], [9]–[15]. EVA copolymers are commonly used in the cable industry, due to their high ductility, even at high loading rates. In such applications, the flame retardant systems should be introduced into the polymer to improve the fire reaction. Many flame retardant systems have been tested but the most used industrially relates to formulations based on hydrated mineral fillers (aluminum hydroxide and magnesium hydroxide). Their low cost and reduced fumes generation explains their success. However, to obtain good performance with this type of flame retardants, it is necessary to incorporate high levels (up to 65 wt %), which severely impact other properties such as processability and mechanical behavior. The main modes of action of these flame retardants are the dilution of the gas phase, the endothermic decomposition and a barrier effect created by the inorganic oxide residue which may be improved by the incorporation of other components such as montmorillonites, silicas or talcs."

Jan 1, 2015

By Negar Elhami Khorasani, Anthony Tessari, Nan Hua

Fire hazards can cause severe and irrecoverable damage to reinforced concrete (RC) tunnel linings, threatening the serviceability and resilience of transportation networks. This paper first examines the existing methodologies that are used to classify damage to tunnel linings from fire. These approaches are then supplemented with the results of advanced modeling and inputs from industry experts to propose new fire damage/ repair classifications with the associated thresholds. The results of the presented research can be used to guide fire risk assessment as well as the performance-based design of tunnel fire protection.

Jun 13, 2023

"A fire design innovation of the concrete lining of the Ohio River Bridges East End Crossing Tunnel has been developed. As a result from a fire suppression and tunnel ventilation system, the project design Heat Release Rate (HRR) was able to be constrained from 300 MW to about 50 MW. With this reduced HRR, concrete lining without passive fire protection may be acceptable, if the tunnel concrete lining will not result in explosive spalling during the designed fire event. Concrete explosive spalling test was proposed to verify this assumption. Since no standard concrete fire explosive spalling testing procedure exists, a project specific testing procedure was developed and fire tests conducted. From fire test results, it is concluded that the proposed tunnel concrete lining, in conjunction with the proposed fire suppressing and ventilation system, will not experience explosive spalling and does not require a passive fire protection system. INTRODUCTION The Ohio River Bridge East End Crossing Tunnel is part of a Public Private Partnership project, which connects transportation network between Louisville, Kentucky and southern Indiana. Located in Louisville, Kentucky, the twin-tube highway tunnel provides northbound and southbound lanes of the Kentucky approach to a new bridge across the Ohio River. Tunnel lengths are approximately 1,675-ft and 1,685 for the northbound tube and the southbound tube, respectively. Connected by two cross-passages, both tubes have a roadway width of 40-ft, for 3-lane traffic, and a vertical clearance of 26.5-ft.The Tunnel was constructed by drill and blast method with shotcrete and rock dowels as initial ground supports. The final tunnel lining consists of 16 inches cast-in-place concrete lining and 20 inches invert slab, with a waterproofing system around the tunnel perimeter. Two (2) tunnel side drains and one (1) invert drain were provided for each tube. This paper describes the rational in assessing fire design requirements of the tunnel final concrete lining, to answer the question whether a passive fire protection system is needed or not."

Jan 1, 2016

Provide reliable, early-warning fire detection instruments, telemetry, and control systems for noncoal underground mines. Approach Industrial-grade fire detection instruments and signal telemetry equipment were modified for long-term exposure to harsh underground mine conditions, then were installed in four mines to evaluate long-term performance and reliability. How It Works The elapsed time between the onset of a fire and its detection is critical because fires tend to grow in size and intensity with time. Early fire detection and warning permit the initiation of a mine's emergency plan (evacuation, fire fighting, etc.) while the fire is still small, or ideally, while it is still in the incipient stage. Fire detection and warning systems, utilizing sensitive heat, flame, smoke, and gas analyzers, provide the most rapid and reliable indication of a developing fire.

Jan 1, 1987