scholarly journals Thermal Cracking Analysis during Pipe Cooling of Mass Concrete Using Particle Flow Code

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Liang Li ◽  
Xinghong Liu ◽  
Vinh T. N. Dao ◽  
Yonggang Cheng
Keyword(s):  
Thermal Cracking ◽  
Numerical Approach ◽  
Two Dimensions ◽  
Particle Flow ◽  
Particle Flow Code ◽  
Mass Concrete ◽  
Concrete Gravity Dam ◽  
Thermal Cracks ◽  
Thermal Fields ◽  
Good Agreement

Pipe cooling systems are among the potentially effective measures to control the temperature of mass concrete. However, if not properly controlled, thermal cracking in concrete, especially near water pipes, might occur, as experienced in many mass concrete structures. In this paper, a new numerical approach to simulate thermal cracking based on particle flow code is used to shed more light onto the process of thermal crack propagation and the effect of thermal cracks on thermal fields. Key details of the simulation, including the procedure of obtaining thermal and mechanical properties of particles, are presented. Importantly, a heat flow boundary based on an analytical solution is proposed and used in particle flow code in two dimensions to simulate the effect of pipe cooling. The simulation results are in good agreement with the monitored temperature data and observations on cored specimens from a real concrete gravity dam, giving confidence to the appropriateness of the adopted simulation. The simulated results also clearly demonstrate why thermal cracks occur and how they propagate, as well as the influence of such cracks on thermal fields.

scholarly journals Particle Flow Code Simulation of the Characteristics of Crack Evolution in Rock-Like Materials with Bent Cracks

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Zhanguo Ma ◽  
Shixing Cheng ◽  
Peng Gong ◽  
Jun Hu ◽  
Yongheng Chen
Keyword(s):  
Elasticity Modulus ◽  
Gradual Increase ◽  
Simulation Method ◽  
Two Dimensions ◽  
Particle Flow ◽  
Particle Flow Code ◽  
Crack Evolution ◽  
Underground Engineering ◽  
The Stability ◽  
The Impact

The distribution and propagation of rock cracks have a significant impact on geotechnical engineering. Taking rock-like materials with bent cracks as the research object, the particle flow code in two dimensions numerical simulation method was used to study the impact of the bend number on rock-like materials strength and crack evolution. According to the results, when the bend number was 1, 3, and 7, the strength of the specimens gradually increased; the elasticity modulus did not change significantly with the crack bend number. Uniaxial compression generated tensile cracks in all the specimens with bent cracks, but in terms of failure mode, the specimens with 0 bend tended to suffer penetrating failure along the fracture strike, while the specimens with 1, 3, and 7 bend tended to suffer penetrating failure along the diagonal direction. Both the fractal dimension and bend number were positively correlated with strain; with the gradual increase of the stress percentage, the damage variable of the specimens gradually increased at a growing rate. The research results provide a reference for predicting the stability of the underground engineering surrounding rocks containing bent cracks.

PFC/FLAC Coupled Numerical Simulation of Excavation Damage Zone in Deep Schist Tunnel

2012 ◽  
Vol 236-237 ◽  
pp. 622-626 ◽  
Author(s):  
Wei Song ◽  
Ren Hong
Keyword(s):  
Damage Zone ◽  
Particle Flow ◽  
Particle Flow Code ◽  
Lagrangian Analysis ◽  
Excavation Damage Zone ◽  
Tunnel Design ◽  
Simulation Results ◽  
Computational Resources ◽  
Excavation Damage ◽  
Good Agreement

In the present study, a coupled numerical method is used to study EDZ (excavation damage zone) in a deep schist tunnel. Two codes, Fast Lagrangian Analysis of Continua (FLAC) and Particle Flow Code (PFC) are coupled to implement the simulation. The motive to apply the FLAC/PFC coupled approach is to take advantage of each modeling scheme while at the same time minimizing the requirement for computational resources. The coupling is realized through an exchange of displacements, velocities, and forces in each cycling step. Simulation results are found to be in good agreement with in site ultrasonic wave measured EDZ profile. The coupled PFC/FLAC model present more information than each uncoupled model individually, and these simulation results are very important in tunnel design.

Numerical Analysis of Negative Skin Friction for Pile under Surface Loading by Particle Flow Code

2012 ◽  
Vol 166-169 ◽  
pp. 482-486
Author(s):  
Feng Xi Zhou ◽  
Yuan Ming Lai
Keyword(s):  
Numerical Analysis ◽  
Numerical Simulations ◽  
Skin Friction ◽  
Two Dimensions ◽  
Particle Flow ◽  
Particle Flow Code ◽  
Surface Loading ◽  
Negative Skin Friction ◽  
Pile Interaction ◽  
End Bearing Pile

Numerical simulations of soil-pile interaction under surface loading are performed by particle flow code in two dimensions. Considering an end-bearing pile subjected to flexible distribution load, the variety of negative skin friction is studied. Numerical results show that negative skin friction is variation with the increasing of surface loading, and the negative skin friction is decrease when the value is up to ultimate skin friction.

Simulation of small-angle scattering curves by numerical Fourier transformation

2007 ◽  
Vol 40 (1) ◽  
pp. 16-25 ◽  
Author(s):  
Klaus Schmidt-Rohr
Keyword(s):  
Form Factor ◽  
Small Angle ◽  
Fourier Transformation ◽  
Three Dimensional ◽  
Power Laws ◽  
Numerical Approach ◽  
Peak Position ◽  
Two Dimensions ◽  
Correlation Peak ◽  
Scattering Intensity

A simple numerical approach for calculating theq-dependence of the scattering intensity in small-angle X-ray or neutron scattering (SAXS/SANS) is discussed. For a user-defined scattering density on a lattice, the scattering intensityI(q) (qis the modulus of the scattering vector) is calculated by three-dimensional (or two-dimensional) numerical Fourier transformation and spherical summation inqspace, with a simple smoothing algorithm. An exact and simple correction for continuous rather than discrete (lattice-point) scattering density is described. Applications to relatively densely packed particles in solids (e.g.nanocomposites) are shown, where correlation effects make single-particle (pure form-factor) calculations invalid. The algorithm can be applied to particles of any shape that can be defined on the chosen cubic lattice and with any size distribution, while those features pose difficulties to a traditional treatment in terms of form and structure factors. For particles of identical but potentially complex shapes, numerical calculation of the form factor is described. Long parallel rods and platelets of various cross-section shapes are particularly convenient to treat, since the calculation is reduced to two dimensions. The method is used to demonstrate that the scattering intensity from `randomly' parallel-packed long cylinders is not described by simple 1/qand 1/q4power laws, but at cylinder volume fractions of more than ∼25% includes a correlation peak. The simulations highlight that the traditional evaluation of the peak position overestimates the cylinder thickness by a factor of ∼1.5. It is also shown that a mix of various relatively densely packed long boards can produceI(q) ≃ 1/q, usually observed for rod-shaped particles, without a correlation peak.

Establishing and Satisfying Thermal Requirements for Drilled Shaft Concrete Based on Durability Considerations

2021 ◽  
pp. 036119812199635
Author(s):  
Andrew Z. Boeckmann ◽  
Zakaria El-tayash ◽  
J. Erik Loehr
Keyword(s):  
Mechanical Response ◽  
Large Diameter ◽  
Thermal Cracking ◽  
Drilled Shafts ◽  
Maximum Temperature ◽  
Design Parameters ◽  
Mass Concrete ◽  
Temperature Differential ◽  
Thermal Requirements ◽  
Ettringite Formation

Some U.S. transportation agencies have recently applied mass concrete provisions to drilled shafts, imposing limits on maximum temperatures and maximum temperature differentials. On one hand, temperatures commonly observed in large-diameter drilled shafts have been observed to cause delayed ettringite formation (DEF) and thermal cracking in above-ground concrete elements. On the other, the reinforcement and confinement unique to drilled shafts should provide resistance to thermal cracking, and the provisions that have been applied are based on dated practices for above-ground concrete. This paper establishes a rational procedure for design of drilled shafts for durability requirements in response to hydration temperatures, which addresses both DEF and thermal cracking. DEF is addressed through maximum temperature differential limitations that are based on concrete mix design parameters. Thermal cracking is addressed through calculations that explicitly consider the thermo-mechanical response of concrete for predicted temperatures. Results from application of the procedure indicate consideration of DEF and thermal cracking potential for drilled shafts is prudent, but provisions that have been applied to date are overly restrictive in many circumstances, particularly the commonly adopted 35°F maximum temperature differential provision.

Investigation of Recirculating Casing Treatment for Low-Pressure Ratio Mixed-Flow Micro-Compressor

2020 ◽  
Author(s):  
Kewei Xu ◽  
Gecheng Zha
Keyword(s):  
Pressure Ratio ◽  
Numerical Approach ◽  
Efficiency Loss ◽  
Stall Margin ◽  
Design Point ◽  
Casing Treatment ◽  
Final Design ◽  
Upstream Flow ◽  
Total Pressure Ratio ◽  
Good Agreement

Abstract This paper investigates the recirculating casing treatment (RCT) of a low total pressure ratio micro-compressor to achieve stall margin enhancement while minimizing the design point efficiency penalty. Three RCT injection and extraction configurations are studied, including combined slot-duct, ducts only, and slot only. The numerical approach is validated with a tested micro-compressor using RCT. A very good agreement is achieved between the predicted speedlines and the measured results. To minimize the design point efficiency loss, it is observed that the optimal location of extraction and injection is where the recirculated flow rate can be minimized at the design point. To maximize stall margin, extraction location should favor minimizing the tip blockage such as at the location where the tip flow separation of the baseline blade is fully developed. In addition, the slot configuration that generates pre-swirl to the upstream flow is beneficial to improve stall margin due to reduced incidence. The highest stall margin enhancement achieved is 9.49% with the slot geometry that has the extraction at the 62%C chordwise location, but has a design point efficiency loss of 1.9%. Overall, a small efficiency penalty of 0.6% at the design point is achieved for the final design with the stall margin increased by 6.2%.

scholarly journals Modeling temperature profile in mass concrete at early ages of cement hydration

2021 ◽  
Vol 10 (1) ◽  
pp. 64
Author(s):  
Ugwuanyi Donald Chidiebere ◽  
Okafor Fidelis Onyebuchi
Keyword(s):  
Ambient Temperature ◽  
Temperature Profile ◽  
Cement Hydration ◽  
Concrete Block ◽  
Control Measures ◽  
Mass Concrete ◽  
Thermally Induced ◽  
Thermal Cracks ◽  
Concrete Placement ◽  
And Control

Thermally induced cracks due to temperature gradient in mass concrete have adverse effects on its durability and service life. Heat released during the hydration of Portland cement in early age mass concrete can be quite excessive depending on the ambient temperature, cement content of the concrete mix and the size. Finite difference model using Crank Nicholson implicit method was developed based on the two dimensional unsteady state heat conduction. Optimized MATLAB based software was developed for simulation and data visualization. A mass concrete block cast with standard mix ratio and water cement ratio was used to verify the efficacy of the model. Type-K thermocouple and digital thermometer were used to monitor the temperature at time intervals. The temperature profile showed a hotter core and cooler surface except for the initial placement temperature, which exhibited a uniform temperature for all thermocouple locations. Peak temperature values were recorded within the first day of concrete placement. The model successfully predicted the temperature profile of the mass concrete at early ages of cement hydration. With the knowledge of the ambient temperature and the configuration of the mass concrete, the model can reliably predict the temperature profile from which potential for thermal cracks occurrence can be determined to enable suitable proactive preventive and control measures.  

scholarly journals The problem of temperature cracking in concrete gravity dams

Vestnik MGSU ◽  
2020 ◽  
pp. 380-398
Author(s):  
Nikolay A. Aniskin ◽  
Nguyen Trong Chuc
Keyword(s):  
Thermal Stress ◽  
Stress State ◽  
Crack Formation ◽  
Thermal Cracking ◽  
Mass Concrete ◽  
Thermal Stress State ◽  
Research Projects ◽  
Thermal Crack ◽  
Gravity Dams ◽  
Concrete Gravity Dams

Introduction. The concreting of solid structures, such as concrete dams, bridge constructions, foundations of buildings and structures, is accompanied by exothermic heating, caused by cement hydration. Heat, emitted by mass concrete blocks, slowly leaves constructions. A substantial temperature difference frequently arises between the solid concrete centre and its surface. If this temperature difference reaches a critical value, thermal cracking occurs, which destroys structural continuity. Temperature problems and those associated with thermal stress state should be resolved to pre-assess and prevent potential cracking. This problem has enjoyed the attention of specialists, and it has been the subject of numerous research projects. Materials and methods. The overview is based on the information about implemented research projects focused on the thermal cracking of mass concrete dams and its prevention. Computer modeling techniques were applied to develop a mathematical model capable of projecting and assessing the potential cracking of mass concrete. Results. The co-authors have compiled an overview of advanced approaches to the assessment of potential thermal crack formation, contemporary problem-solving methods and selected research findings obtained using the finite element method. The co-authors offer a thermal behaviour/thermal stress state projection methodology for solid concrete, as well as a thermal crack formation assessment methodology. Conclusions. The thermal cracking problem has not been solved yet. The proposed methodology and a projection-oriented numerical model can be used as a reference by civil engineers in the process of designing and constructing concrete gravity dams. It may help to reduce cracking probability caused by heat evolution in cement.

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