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Thermal performance analysis of an energy pile with triple helix ground heat exchanger
, Article Geothermics ; Volume 104 , 2022 ; 03756505 (ISSN) ; Asgari, B ; Rostami, M ; Sharif University of Technology
Elsevier Ltd
2022
Abstract
A Ground Source Heat Pump (GSHP) is a renewable energy-based HVAC system that extracts or supplies heat from/to the ground via a Ground Heat Exchanger (GHE). One of the most commonly used types of GHE in GSHP systems is the energy pile. In this realm, the GSHP system with a triple helix energy pile has become the focus of attention. To this aim, a comprehensive three-dimensional transient Computational Fluid Dynamics model of the energy pile with triple helix GHE and the surrounding soil is developed. The effect of several parameters, including helix pitch, helix diameter and pipe diameter, on the thermal performance of the system, is investigated. Simulated cases are chosen using the design...
Analyzing transient heat and moisture transport surrounding a heat source in unsaturated porous media using the Green's function
, Article Geothermics ; Volume 81 , 2019 , Pages 224-234 ; 03756505 (ISSN) ; Ghasemi Fare, O ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
Generally, in most areas, groundwater level is deep and heat sources (e.g., energy piles)are embedded in unsaturated soil media. Therefore, in order to accurately analyze the soil response close to heat sources, both heat and moisture transport in unsaturated soil domain should be considered. Thermal loading changes the moisture content in the porous media. In this study, the energy conservation and mass fluid continuity equations derived from hydrothermal analysis of a partially saturated soil medium are considered in cylindrical coordinate system. To make the analytical solution possible, partial differential equations (PDEs)are turned into ordinary differential equations (ODEs), through...
Investigation on the Effect of Liquefaction-Induced Lateral Spreading on a Flexible Pile Group and Mitigation Measures for These Effects by Physical Modeling
, M.Sc. Thesis Sharif University of Technology ; Haeri, Mohesn (Supervisor)
Abstract
Liquefaction-induced lateral spreading is a known cause of severe damages to deep foundations during past earthquakes. Lateral spreading often takes place in gently sloping grounds which consisted of saturated loose cohesionless soil deposits. Several researchers during recent years have been studying the behavior of piles and soil-pile interaction under lateral spreading but there are still many unknowns in this regard. Also with observing catastrophic damages during past earthquakes caused by lateral spreading, developing proper mitigation measures for existing vulnerable piles against this phenomenon is a necessary act. In the present research, the behavior of a 3x3 flexible pile group...
Numerical Study of Ground Vibrations due to Pile Driving and Effect of Trench on Reduction of Amplitude of Vibrations
, M.Sc. Thesis Sharif University of Technology ; Ahmadi, Mohammad Mehdi (Supervisor)
Abstract
Ground vibration during pile driving is one the most important factors that limits usage of this kind of piles. It is of great importance to estimate the level of vibration prior to the beginning of pile driving to avoid structural damage or disturbance of building occupants. In this study, an axisymmetric finite element model that utilises an adaptive meshing algorithm has been introduced, using the commercial code ABAQUS, to simulate the full penetration of a pile from the ground surface to the desired depth by applying successive hammer impacts. The model has been verified by comparing the computed particles velocity with those measured in the field. The results indicate that the peak...
Liquefaction Effects on (a) Individual and Group of Capless Piles and (b) Group of three Piles under Real and Artificial Earthquakes
, M.Sc. Thesis Sharif University of Technology ; Haeri, Mohsen (Supervisor)
Abstract
In the areas where the soil beneath the foundation is made of loose to semi-consolidated sand or noncohesive silts, Buildings and bridges are usually built on the pile foundations. One important issue that must be considered in the design of piles in saturated sandy soils, is liquefaction potential of saturated sandy soil under earthquake loads. During the earthquake, saturated sandy soil faces the sudden loss of shear strength in other word it liquifies . Liquefied Soil acts like a viscous fluid. This behaviour considerably increases the soil deformation and consequently the widespread disruption of soil layers, causes large deformation and applies great amount of forces on the piles...
Effect of Lateral Spreading Due to Liquefaction on Piles, Numerical Simulation with OpenSees
, M.Sc. Thesis Sharif University of Technology ; Haeri, Mohsen (Supervisor)
Abstract
Lateral spreading due to liquefaction and resulting destruction of buildings is important in Iran because of high seismicity and important infrastructure near south and north coasts of Iran. Lateral spreading is vast lateral movement of sloping ground or level ground ending in an opening like river which is caused by earthquake inducedliquefaction. For considering the effects of lateral spreading during design of deep foundations of structures in a susceptible area, one needs to determine the lateral loads on piles under lateral spreading. Present study investigates the behavior of a 3x3 pile group against lateral loads due to lateral spreading with numerical methods using OpenSees software....
Numerical Study of Pile Behavior under Seismic Loading
, M.Sc. Thesis Sharif University of Technology ; Ahmadi, Mohammad Mahdi (Supervisor)
Abstract
Numerous structures which are involved in seismic soil-pile-structure interaction have been destroyed. Considering complexities which exist in soil-pile interaction problems and lack of precise methods without imperfect bases, it is necessary to use numerical methods for analyzing soil-pile interaction problems. In this research, three-dimensional modeling and studying the effect of changing soil and pile parameters on the behavior of pile under earthquake loading is performed using finite difference software, FLAC3D. The soil in this model has a softening behavior. Real earthquake spectrum has been applied into the model as the acceleration time history at the bedrock level. The results of...
Numerical Investigation of the Thermo-mechanical Response of Single Energy Pile and a Group of Energy Piles
, M.Sc. Thesis Sharif University of Technology ; Jafarzadeh, Fardin (Supervisor) ; Ghasemi Fare, Omid (Co-Advisor)
Abstract
Geothermal piles are being used to serve dual purposes: transfer the structural load to the ground and act as heat exchanger elements to harvest and reject heat from and to the ground. Thermal loading can change the mechanical performance and bearing capacity of the geothermal piles during heating and cooling cycles. Therefore the thermo-mechanical responses of the geothermal piles should be comprehensively studied. In this paper the thermo-mechanical performance of a geothermal pile was analyzed using a 3D finite difference model in FLAC. The energy pile tests performed at Lambeth College, London were simulated using the developed numerical model. Comparison of both thermal strain and...
Sandpile Model on Height Parameters
, M.Sc. Thesis Sharif University of Technology ; Moghimi Araghi, Saman (Supervisor)
Abstract
Many statistical systems such as earthquakes, road trafcs, forest fres, neurocortical avalanches etc. exhibit self-organized criticality (SOC). In such systems without tuning extrenal parameters, the system arrives at criticality. During recent decades, a number of models are introduced which show the same charactristics. These models have made a platform to investigate the physics of self-organized criticality. Among them, sandpile models are the best known models. They exhibit critical behaviour such as scaling laws. Also in some of them conformal invariance is checked nummerically.Most of sandpile models deal with slope parameters, that is, the main dynamical parameters are the local...
Simulation of the Self-organized Critical Models on the
Human’s Brain Network
,
M.Sc. Thesis
Sharif University of Technology
;
Moghimi Araghi, Saman
(Supervisor)
Abstract
Self-organized critical phenomena are interesting phenomena which are ubiquitous in nature. Examples include mountain ranges , coastlines and also activities in the hu-man's brain. In these processes, without fine-tuning of any external parameter such as the temperature, the system exhibits critical behavior. In other words, the dynamics of the system, drives it towards an state in which long range correlations in space and scaling behaviors can be seen.The first successful model which could characterize such systems was BTW model, introduced by Bak , Tang and Wiesenfeld in 1987. This model, later named Abelian sandpile model, was very simple and because of this simplicity, a large amount of...
Numerical Analysis of Piles Behavior in Clay under Lateral Load
, M.Sc. Thesis Sharif University of Technology ; Ahmadi, Mohammad Mehdi (Supervisor)
Abstract
There are several factors affecting the behavior and response of a pile under lateral loads. These factors can be divided into two main categories: geometrical factors (e.g. dimensions of the pile, soil, and mesh scheme) and material properties (e.g. shear modulus, bulk modulus, soil elasticity, soil density, and shear strength). Studying the effects and importance of these factors in the final response of the pile (i.e. ultimate forces and displacements) can help design engineers in optimization of their designs. Given the importance of the subject and the possibility of using numerical methods and computer technology to evaluate the behavior of piles, this research attempts to use finite...
Parametric Study of The Piles Behavior under Lateral Load in Clay Soil, Sandy Soil and Soil Layer
, M.Sc. Thesis Sharif University of Technology ; Ahmadi, Mohammad Mehdi (Supervisor)
Abstract
Pile is used to transfer high loads from the structure by bearing on the hard soil layers or through the friction between the soil and the pile. Axial loads and transversal or lateral loads are the main loads apply on the piles. There are several different methods to investigate the pile behavior under lateral load: (1) Limit State method (2) Subgrade Reaction method (3) Elastic method (4) P-Y method (5) Evans and Duncan method (6) Numerical methods. Blum, Brinch Hansen and Broms methods are based on the Limit State method to determine the lateral capacity of pile. Although these methods are simple and the results can find quickly, they failed to calculate the soil resistance under lateral...
Prediction of Scour Depth Around Complex Piers Using Classification Methods
, M.Sc. Thesis Sharif University of Technology ; Ataie-Ashtiani, Behzad (Supervisor) ; Jamali, Mirmosaddegh (Co-Advisor)
Abstract
In this study, existing prediction methods of maximum scour depth around complex piers are studies using available experimental data and a new relationship for scour prediction is presented. Complex pier consists of a column, pile cap and pile group and is frequently used for foundation of bridge piers in hydraulic and marine structures. The results of 52 clear-water scour experiments on 4 CP models are reported which can be valuable to hydraulic design of a CP. The 4 models had different values of pile cap thickness and number of piles inline with the flow and were tested at different pile cap elevations. The duration of experiments ranged from 24 to 120 hours. Then a database of laboratory...
Continuous Transition from Self-organized Criticality to Self-organized Bistability
, M.Sc. Thesis Sharif University of Technology ; Moghimi Araghi, Saman (Supervisor)
Abstract
”Self-organized criticality” is a conceptual term that has helped us describe cer- tain critical behaviors in nature over the past approximately thirty years. In systems exhibiting this characteristic, critical behavior emerges without the need for external parameter adjustments. The necessary mechanism to observe such phenomena is for the critical point to be a dynamical attractor. Based on this, other phenomena have been proposed in which the critical point is not an attractor; instead, a stable cycle forms around it. This mechanism has led to the emergence of a new concept known as ”self- organized bistability.” The primary model proposed for such a phenomenon is based on a sandpile...
Continuous transforming the BTW to the Manna model
, Article Physica A: Statistical Mechanics and its Applications ; Volume 419 , 2015 , Pages 196-202 ; 03784371 (ISSN) ; Moghimi Araghi, S ; Najafi, M. N ; Sharif University of Technology
Abstract
In this paper we define some stochastic perturbations of the BTW model which make it into Manna model. These models have a continuous parameter p, where p = 0 and 1 correspond to the BTW and Manna models respectively. We have investigated the properties of the statistical observables of the waves of avalanches for various values of p. Our data supports the expectation of a crossover in such systems; at large scales Manna model is dominant. Therefore we find strong evidence in favor of the universality classes being distinct. Also it is observed that the BTW fixed point is unstable when Manna-type perturbation is added to the model
Direct evidence for conformal invariance of avalanche frontiers in sandpile models
, Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 79, Issue 3 , Volume 79, Issue 3 , 2009 ; 15393755 (ISSN) ; Moghimi-Araghi, S ; Dashti-Naserabadi, H ; Rouhani, S ; Sharif University of Technology
2009
Abstract
Appreciation of stochastic Loewner evolution (SLEκ), as a powerful tool to check for conformal invariant properties of geometrical features of critical systems has been rising. In this paper we use this method to check conformal invariance in sandpile models. Avalanche frontiers in Abelian sandpile model are numerically shown to be conformally invariant and can be described by SLE with diffusivity κ=2. This value is the same as value obtained for loop-erased random walks. The fractal dimension and Schramm's formula for left passage probability also suggest the same result. We also check the same properties for Zhang's sandpile model. © 2009 The American Physical Society
Controlling cost in sandpile models through local adjustment of drive
, Article Physica A: Statistical Mechanics and its Applications ; Volume 534 , 2019 ; 03784371 (ISSN) ; Moghimi Araghi, S ; Sharif University of Technology
Elsevier B.V
2019
Abstract
In this paper we consider sandpile models and modify the drive mechanisms to control the size of avalanches. The modification to the drive mechanism is local. We have studied the scaling behavior of the BTW and Manna models. We have found that the BTW model is more sensitive to the modification than the Manna model. Furthermore we have assigned a cost function to each avalanche and have found an optimum value for the modification to arrive at the lowest cost © 2019
Non linear response of fixed offshore platforms to seismic excitation including soil-pile-structure interaction
, Article Proceedings of the International Conference on Offshore Mechanics and Arctic Engineering - OMAE, 15 June 2008 through 20 June 2008, Berlin ; Volume 1 , 2008 , Pages 335-345 ; 9780791848234 (ISBN) ; Aghakouchak, A. A ; Aghakouchak, A ; Ocean, Offshore, and Arctic Engineering Division; ASME ; Sharif University of Technology
2008
Abstract
A nonlinear seismic soil-pile-structure interaction (SSPSI) analysis of fixed offshore platforms constructed on pile foundations including both vertical and battered piles is presented. The analysis is carried out in time domain and the effects of soil nonlinearity, discontinuity at pile soil interfaces, energy dissipation through soil radiation damping, formation of soil layers on bed rock, structural material nonlinearity and geometrical nonlinearity are considered. A combination of FEM approach and BNWF approach is used in modeling pile (substructure), platform structure (superstructure) and soil media. Gapping in clay is modeled by a special connector configuration. To find out the...
Thermal Cyclic Effects on the Long-Term Behaviour of Elevated Floating Energy Pile Groups in Saturated Lightly Overconsolidated Clay by Centrifuge Modelling
, Ph.D. Dissertation Sharif University of Technology ; Jafarzadeh, Fardin (Supervisor)
Abstract
There is an increasing interest and use of energy foundations worldwide. Heat transfer from/to energy piles may cause plastic contraction of soft clay with a low overconsolidation ratio (OCR) during heating and cooling. This can influence pile-soil interaction due to thermally induced excess pore water pressure and changes of lateral stress acting on the pile.These thermally induced phenomena cause additional plastic settlement of the soil and pile. The irreversible settlement may cause serviceability or even ultimate limit state problems for floating energy piles whose capacity is mainly derived from shaft resistance. Due to intended operational needs or by accident, cyclic non-symmetrical...
Numerical Investigation of the Effects of Different Parameters on the Mechanical Response of Energy Pile under Cyclic Thermal Loading in Saturated Clay
, M.Sc. Thesis Sharif University of Technology ; Ahmadi, Mohammad Mehdi (Supervisor)
Abstract
Considering the environmental pollution caused by the consumption of fossil fuels, replacing clean and renewable energies instead of fossil fuels has become one of the most critical issues across the world. The use of energy geostructures, especially energy piles, to exchange the heat between the superstructures and the ground is one of the approaches for taking advantage of clean energy. In order to maintain the safety and the serviceability of structures built on energy piles, it is necessary to study the effects of heat exchange between energy piles and the ground on the mechanical behavior of energy piles, as well as the effects of various parameters on the interaction between energy...