scholarly journals Effect of Overburden Height on Hydraulic Fracturing of Concrete-Lined Pressure Tunnels Excavated in Intact Rock: A Numerical Study

Fluids ◽  
2019 ◽  
Vol 4 (2) ◽  
pp. 112 ◽  
Author(s):  
Moses Karakouzian ◽  
Mohammad Nazari-Sharabian ◽  
Mehrdad Karami
Keyword(s):  
Finite Element ◽  
Steady State ◽  
Hydraulic Fracturing ◽  
Numerical Study ◽  
Transient State ◽  
Friction Angle ◽  
Intact Rock ◽  
Steady State Condition ◽  
Pressure Tunnel ◽  
The Impact

This study investigated the impact of overburden height on the hydraulic fracturing of a concrete-lined pressure tunnel, excavated in intact rock, under steady-state and transient-state conditions. Moreover, the Norwegian design criterion that only suggests increasing the overburden height as a countermeasure against hydraulic fracturing was evaluated. The Mohr–Coulomb failure criterion was implemented to investigate failure in the rock elements adjacent to the lining. A pressure tunnel with an inner diameter of 3.6 m was modeled in Abaqus Finite Element Analysis (FEA), using the finite element method (FEM). It was assumed that transient pressures occur inside the tunnel due to control gate closure in a hydroelectric power plant, downstream of the tunnel, in three different closure modes: fast (14 s), normal (18 s), and slow (26 s). For steady-state conditions, the results indicated that resistance to the fracturing of the rock increased with increasing the rock friction angle, as well as the overburden height. However, the influence of the friction angle on the resistance to rock fracture was much larger than that of the overburden height. For transient-state conditions, the results showed that, in fast, normal, and slow control gate closure modes, the required overburden heights to failure were respectively 1.07, 0.8, and 0.67 times the static head of water in the tunnel under a steady-state condition. It was concluded that increasing the height of overburden should not be the absolute solution to prevent hydraulic fracturing in pressure tunnels.

Thermo-structural analysis of a honeycomb-type volumetric absorber for concentrated solar power applications

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Masoud Behzad ◽  
Benjamin Herrmann ◽  
Williams R. Calderón-Muñoz ◽  
José M. Cardemil ◽  
Rodrigo Barraza
Keyword(s):  
Heat Transfer ◽  
Thermal Stress ◽  
Steady State ◽  
Discrete Model ◽  
Continuum Model ◽  
Transient State ◽  
Operating Conditions ◽  
Steady State Condition ◽  
Content Type ◽  
The Continuum

Purpose Volumetric air receivers experience high thermal stress as a consequence of the intense radiation flux they are exposed to when used for heat and/or power generation. This study aims to propose a proper design that is required for the absorber and its holder to ensure efficient heat transfer between the fluid and solid phases and to avoid system failure due to thermal stress. Design/methodology/approach The design and modeling processes are applied to both the absorber and its holder. A multi-channel explicit geometry design and a discrete model is applied to the absorber to investigate the conjugate heat transfer and thermo-mechanical stress levels present in the steady-state condition. The discrete model is used to calibrate the initial state of the continuum model that is then used to investigate the transient operating states representing cloud-passing events. Findings The steady-state results constitute promising findings for operating the system at the desired airflow temperature of 700°C. In addition, we identified regions with high temperatures and high-stress values. Furthermore, the transient state model is capable of capturing the heat transfer and fluid dynamics phenomena, allowing the boundaries to be checked under normal operating conditions. Originality/value Thermal stress analysis of the absorber and the steady/transient-state thermal analysis of the absorber/holder were conducted. Steady-state heat transfer in the explicit model was used to calibrate the initial steady-state of the continuum model.

scholarly journals Finite Element Analysis Of Airfield Flexible Pavement

2014 ◽  
Vol 60 (3) ◽  
pp. 323-334 ◽  
Author(s):  
G. Leonardi
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
3D Model ◽  
Numerical Study ◽  
Permanent Deformation ◽  
Flexible Pavement ◽  
Finite Element Code ◽  
Element Analysis ◽  
Pavement Response ◽  
The Impact

Abstract The paper presents a numerical study of an aircraft wheel impacting on a flexible landing surface. The proposed 3D model simulates the behaviour of flexible runway pavement during the landing phase. This model was implemented in a finite element code in order to investigate the impact of repeated cycles of loads on pavement response. In the model, a multi-layer pavement structure was considered. In addition, the asphalt layer (HMA) was assumed to follow a viscoelastoplastic behaviour. The results demonstrate the capability of the model in predicting the permanent deformation distribution in the asphalt layer.

Numerical study of ultimate bearing capacity of rectangular footing on layered sand

2020 ◽  
Vol 1 (101) ◽  
pp. 15-26
Author(s):  
V. Panwar ◽  
R.K. Dutta
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Bearing Capacity ◽  
Numerical Study ◽  
Friction Angle ◽  
Ultimate Bearing Capacity ◽  
Loose Sand ◽  
Sand Layer ◽  
Element Analysis ◽  
Dense Sand

Purpose: The purpose of this study is to investigate the ultimate bearing capacity of the rectangular footing resting over layered sand using finite element method. Design/methodology/approach: Finite element analysis was used to investigate the dimensionless ultimate bearing capacity of the rectangular footing resting on a limited thickness of upper dense sand layer overlying limitless thickness of lower loose sand layer. The friction angle of the upper dense sand layer was varied from 41° to 46° whereas for the lower loose sand layer it was varied from 31° to 36°. Findings: The results reveal that the dimensionless ultimate bearing capacity was found to increase up to an H/W ratio of about 1.75 beyond which the increase was marginal. The results further reveal that the dimensionless ultimate bearing capacity was the maximum for the upper dense and lower loose sand friction angles of 46° and 36°, while it was the lowest for the upper dense and lower loose sands corresponding to the friction angle of 41° and 31°. For H/W = 0.5 and 2, the dimensionless bearing capacity decreases with the increase in the L/W ratio from 0.5 to 6 beyond which the dimensionless ultimate bearing capacity remains constant for all combinations of parameters. The results were presented in nondimensional manner and compared with the previous studies available in literature. Research limitations/implications: The analysis is performed using a ABAQUS 2017 software. The limitation of this study is that only finite element analysis is performed without conducting any experiments in the laboratory. Further the study is conducted only for the vertical loading. Practical implications: This proposed numerical study can be used to predict the ultimate bearing capacity of the rectangular footing resting on layered sand. Originality/value: The present study gives idea about the ultimate bearing capacity of rectangular footing when placed on layered sand (dense sand over loose sand) as well as the effect of thickness of top dense sand layer on the ultimate bearing capacity. The findings could be used to calculate the ultimate bearing capacity of the rectangular footing on layered sand.

Effect of Relative Height of Planting Denture on Interdental Food Impaction: A Numerical Study

2013 ◽  
Vol 444-445 ◽  
pp. 1454-1459
Author(s):  
Ai Ke Qiao ◽  
Zhan Zhu Zhang ◽  
Yu Lin Fu ◽  
De Sheng Yang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Boundary Conditions ◽  
Computational Modeling ◽  
Modeling And Simulation ◽  
Numerical Study ◽  
Food Impaction ◽  
Relative Height ◽  
Computational Modeling And Simulation ◽  
The Impact

The study about the impact of implant denture on getting stuck between the teeth is rarely reported. Computational modeling and simulation was performed in this study in order to investigate the effect of planting denture on interdental food impaction. Four groups of experiment were designed; Simplified teeth models were established and meshed; loads were applied to the models and boundary conditions were constrained in the state of teeth chewing. Finite element method was employed to analyze the deformation of teeth and impacted object. When the force exerting on the impacted object is in the range of 0-5.5N, the distance between denture and tooth after planting denture is less than that between the normal teeth. The deformation is the minimum when the denture is lower than tooth. When the force exerting on the impacted object is in the range of 0-5.5N, interdental food impaction is easier to occur after planting denture, and Interdental food impaction may be more likely prevented when denture is lower than tooth.

A New Sensor Diagnostic Technique Applied to a Micro Gas Turbine Rig

2012 ◽  
Author(s):  
Andrea Tipa ◽  
Alessandro Sorce ◽  
Matteo Pascenti ◽  
Alberto Traverso
Keyword(s):  
Steady State ◽  
Statistical Model ◽  
Gas Turbine ◽  
Measurement Errors ◽  
Combined Cycle ◽  
Model Approximation ◽  
Operating Life ◽  
Steady State Condition ◽  
Micro Gas Turbine ◽  
The Impact

This paper describes the development and testing of a new algorithm to identify faulty sensors, based on a statistical model using quantitative statistical process history. Two different mathematical models were used and the results were analyzed to highlight the impact of model approximation and random error. Furthermore, a case study was developed based on a real micro gas turbine facility, located at the University of Genoa. The diagnostic sensor algorithm aims at early detection of measurement errors such as drift, bias, and accuracy degradation (increase of noise). The process description is assured by a database containing the measurements selected under steady state condition and without faults during the operating life of the plant. Using an invertible statistical model and a combinatorial approach, the algorithm is able to identify sensor fault. This algorithm could be applied to plants in which historical data are available and quasi steady state conditions are common (e.g. Nuclear, Coal Fired, Combined Cycle).

COMPUTATIONAL STUDY OF INTERFACE EFFECT ON IMPACT LOAD SPREADING IN SiC MULTI-LAYERED TARGETS

2005 ◽  
Vol 02 (03) ◽  
pp. 341-373 ◽  
Author(s):  
S. K. DWIVEDI ◽  
J. L. DING ◽  
Y. M. GUPTA
Keyword(s):  
Finite Element ◽  
Steady State ◽  
Friction Coefficient ◽  
Upper Bound ◽  
Wave Speed ◽  
Lateral Load ◽  
Interface Strength ◽  
Crack Speed ◽  
Shear Wave Speed ◽  
The Impact

The effect of finite strength interface with friction on lateral load spreading and phenomena of interface crack initiation and propagation in bonded multi-layered targets under high velocity impact are presented through axisymmetric finite element simulations. The finite element code DYNA2D, developed at the Lawrence Livermore National Laboratory, was augmented with a phenomenological damage model for the silicon carbide ( SiC ) ceramic and contact/cohesive interface model. Simulations were carried out for four target configurations under varying interface strength (Tm), critical strain energy release rate (Gc), and inter-layer friction coefficient (μL). It is shown that the high wave speed SiC remains a potential material for enhanced load spreading if the confinement is ensured to reduce/delay its damage. The load spreading also increases with the increase in μL that comes into play after the interface failure. However, the μL of unity or more needed to approach the upper bound of load spreading found in the perfectly bonded target layers is not practical. It is shown that the resilience of the multi-layered targets depends on Tm as well as the Gc. But, the lateral load spreading depends dominantly on Tm and reaches the upper bound with its increase. It is further shown that the interface cracks initiate and propagate in shear, mode II. The crack speed is invariably the maximum at initiation and is of the order of the longitudinal wave speed of materials on either side. The maximum initiation speed of 11.29Cs and 7.79Cs are predicted at the SiC -aluminum and steel- SiC interfaces for the frictionless case, where Cs is the shear wave speed of the more compliant aluminum or steel. The crack speed reduces monotonously after initiation, but it remains in the intersonic region for more than 150 ns. Whether the propagating crack tip attains the steady state speed depends on the available driving energy. The steady state crack speed of 0.86Cs to 1.21Cs is predicted only at the steel- SiC interface at 2 mm depth from the impact surface, lasts for more than 3 μs, is shown to be independent of the interface strength upto 300 MPa, and is also independent of the friction coefficient.

A Preliminary Numerical Study of the Slurry Wire Sawing Process

2012 ◽  
Author(s):  
Chunhui Chung
Keyword(s):  
Steady State ◽  
Numerical Study ◽  
Semiconductor Wafer ◽  
Steady State Condition ◽  
Local Loads ◽  
Wire Tension ◽  
Wire Saw ◽  
Simulation Results ◽  
The Wire ◽  
Sawing Process

Slurry wire saw has been utilized to slice the brittle semiconductor wafer substrates for over 20 years. However, the complicated slicing process limits the further studies and advances of this exclusive slicing tool for big wafers. In this study, a numerical model of the slurry wire sawing process was developed based on the mechanism of brittle indentation cracks. The simulation results illustrate how the factors such as wire speed, wire tension, and feed rate of the ingot affect the slicing conditions including the bow angles of the wire and the local normal loads on both the workpiece and the wire. In addition, the results show that the steady-state condition would be reached via overshooting or non-overshooting approach based on the slicing parameters. A higher wire speed is suggested to reduce the bow angles and local loads during slicing process. However, the limitation of the wire speed depends on the material of the wire and the specification of the wire saw machine.

Experimental and numerical study of reinforced concrete beams with steel fibers subjected to impact loading

2017 ◽  
Vol 27 (7) ◽  
pp. 1058-1083 ◽  
Author(s):  
Liu Jin ◽  
Renbo Zhang ◽  
Guoqin Dou ◽  
Jiandong Xu ◽  
Xiuli Du
Keyword(s):  
Finite Element ◽  
Reinforced Concrete ◽  
Impact Loading ◽  
Impact Force ◽  
Numerical Study ◽  
Reaction Force ◽  
Fiber Reinforced Concrete ◽  
Steel Fibers ◽  
Reinforced Concrete Beams ◽  
The Impact

As a kind of impact resistant material, steel fiber reinforced concrete (SFRC) has a good ductility and energy dissipation capacity by improving the tensile strength and impact toughness. To explore the dynamic mechanical behavior of SFRC beams subjected to impact loading, 12 simply-supported SFRC beams with different stirrup ratios (0%, 0.253% and 0.502%) and different volume fractions of steel fibers (0%, 1%, 2% and 3%) were tested with free-falling drop-weights impacting at the mid-span of specimens. The failure patterns were observed and videoed, and simultaneously, the time histories of the impact force, the reaction force, and the mid-span deflection were recorded. Moreover, the influences of stirrup ratio and volume fraction of steel fibers on the impact resistant behavior of the SFRC beams were preliminarily analyzed and discussed. The results indicate that the impact resistant performance of SFRC beams, such as crack pattern, ductility, energy consumption capacity, and deformation recovery capacity can be improved by the addition of steel fibers and stirrups. The required static capacity of these beams were calculated based on the analysis of reaction force vs. displacement loop and impact force vs. displacement loop as well as absorbed energy ratio. For further understanding the experimental results, finite element simulation of SFRC beams subjected to impact loading were carried out. The rationality and accuracy of the finite element model was illustrated by the good agreement between the test observations and the numerical results.

Performance of a Turboshaft Engine for Helicopter Applications Operating at Variable Shaft Speed

2012 ◽  
Author(s):  
Gianluigi Alberto Misté ◽  
Ernesto Benini
Keyword(s):  
Steady State ◽  
Engine Performance ◽  
Engine Fuel ◽  
Main Rotor ◽  
Steady State Condition ◽  
Power Turbine ◽  
Steady State Model ◽  
Optimization Routine ◽  
Turboshaft Engine ◽  
The Impact

An off-design steady state model of a generic turboshaft engine has been implemented to assess the influence of variable free power turbine (FPT) rotational speed on overall engine performance, with particular emphasis on helicopter applications. To this purpose, three off-design flight conditions were simulated and engine performance obtained with different FTP rotational speeds were compared. In this way, the impact on engine performance of a particular speed requested from the main helicopter rotor could be evaluated. Furthermore, an optimization routine was developed to find the optimal FPT speed which minimizes the engine specific fuel consumption (SFC) for each off-design steady state condition. The usual running line obtained with constant design FPT speed is compared with the optimized one. The results of the simulations are presented and discussed in detail. As a final simulation, the main rotor speed Ω required to minimize the engine fuel mass flow was estimated taking into account the different requirements of the main rotor and the turboshaft engine.

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