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Prediction of Interfacial Cracking due to Differential Drying Shrinkage of Concrete in Precast Shell Pier Cap
Get PDFIn a precast shell pier cap, cracking at the interface between the precast shell and the cast-in-place concrete may happen due to differences between the drying shrinkage of the inner and the outer concrete. The objective of this study is to establish a prediction method for interfacial cracking that will consider the real mechanism of differential drying shrinkage and creep. The main parameters used in the analysis were determined from experiments for a concrete mix that is applied to the manufacturing of pier caps. The variation of internal relative humidity over time was first calculated based on the nonlinear moisture diffusion; cracking analysis then followed. Prediction of the initiation of interface cracks and the increase of their width over time was performed. It was found that additional reinforcement across the interface is very effective at reducing crack width
An Experimental Study on Enhancing Cooling Rates of Low Thermal Conductivity Fluids Using Liquid Metals
Get PDFIn a previous numerical study (Al Omari, Int. Communication in Heat and Mass Transfer, 2011) the heat transfer enhancement between two immiscible liquids with clear disparity in thermal conductivity such as water and a liquid metal (attained by co- flowing them in a direct contact manner alongside each other in mini channel) was demonstrated. The present work includes preliminary experimental results that support those numerical findings. Two immiscible liquids (hot water and liquid gallium) are allowed experimentally to exchange heat (under noflow conditions) in a stationary metallic cup where they are put in direct contact. The experimental results confirm the significant heat exchange enhancement. The superior thermal conductivity of the used liquid metal as compared with the water is the reason behind the observed enhancement in heat transfer. For the same residence time and the same contact surface area between the two liquids, however, the experiments show a slightly slower rate in the heat transfer between the two liquids compared to the case of the channel flow considered in the numerical simulations. This discrepancy is justified on the basis of the additional enhancements brought about by the forced convectional effects in the case of the channel flow (which are absent in the experiments where conduction and natural convection prevail)
Hydrodynamics and Heat Transfer in Two and Three-dimensional Minichannels
Get PDFOur study deals with the characterization of the flow and related heat transfer in a smooth, circular minichannel. A duct with a sudden (sharp-edged) contraction is also considered. Prediction of the pressure loss coefficient in this case is obtained via the commercial code CFX 5.7.1. This code is based on the finite volume method for the solution of the Navier-Stokes and offers several turbulences models (in this study we use the shear stress turbulence model - SST). The numerical results are compared with experimental results obtained for a configuration similar to those considered in the numerical study. The numerical algorithm is also validated by comparison with [Reynaud, Debray, Franc, and Maitre (2005); Guo, Wang, Yu, Fang, Chongfang, and Zhuo (2010)]. A good agreement is obtained with the exception of the transition zone between laminar and turbulent regime. In the case of duct sudden contraction, the numerical results show that the abrupt contraction coefficient Kc decreases with the Reynolds number, and it is much higher than that of conventional tubes in laminar flow when the diameter D is less than 1mm
Evaluation of some of the existing models for droplet and spray/wall interactions
Get PDFIn this study, a critical summary of existing spray/wall interaction models is given in synergy with a review of available experimental data. In particular, special attention is devoted to the limitations, difficulties and complexities of the most used approaches in the literatures. An attempt is also made to indicate the bottlenecks and criticalities which typically arise when investigators try to extend results obtained for isolated droplets to the more complex dynamics produced by spray impacts
Mixed Convection Investigation in an Opened Partitioned Heated Cavity
Get PDFMixed convection in a rectangular partitioned cavity equipped with two heated partitions at a constant temperature, TC, is investigated numerically. The right vertical wall is featured by two openings (C1 and C2) for admission of cooled air along the horizontal direction, while the lower wall has a single outlet opening (C3) along the vertical axis. The left vertical wall is assumed to be isothermal at temperature TC, while the other walls are cooled to a temperature TF C. The results show that the flow and heat transfer depend significantly on Reynolds number, Re, and block height, B. Correlation laws for the dimensionless heat evacuated trough the opening, Qf, as a function of, Re, and, B, are expressly derived
A mapping method for shock waves using ALE formulation
No full textTo simulate accurately a pressure wave propagation problem, a fine mesh is required in order to capture peak pressures accurately. This may require a very large size problem with several millions of elements. To reduce CPU time and prevent high mesh distortion, a two-dimensional problem for blast ignition and pressure propagation is performed first on a fixed Eulerian mesh. When the pressure wave gets closer to the structure, a three dimensional ALE simulation follows, where the fluid mesh and structure mesh at the fluid structure interface are coincident. The three dimensional problem is performed after mapping history variables from the two-dimensional to the three dimensional mesh. In this paper an ALE multi-material formulation is used for both explosive and air materials, and a classical Lagrangian formulation for the structure. The method has been implemented successfully in LSDYNA code and validated with different applications. To validate the method, this technique is used for pressure wave propagation, due to explosive detonation, and its interaction with the structure. The numerical solution, in term of maximum displacement, is compared to experimental data performed at Aeronautical and Maritime Research Laboratory at DSTO, Australia. Good correlation has been observed between numerical results and experimental data
A New Well Profile for Extended Reach Drilling (ERD)
No full textWell profile design is one of the critical technologies in extended reach drilling (ERD), because an optimum well profile is an effective means for reducing the torque, drag and cost. This paper proposes a new well profile based on an inverse proportional function, and the new profile design method is analyzed in detail. The new well profile is also compared with other existing well profiles in many aspects such as the hook load, the maximum well curvature, the well length, the torque and so on. The results show that the well profile design based on an inverse proportional curve is superior to the existing well profiles used for drilling extended-reach wells, in several aspects such as the maximum well curvature, drag, torque and well length. It is expected that the use of this new well profile may play an important role in the design of extended-reach drilling wells in the future
On the Solution of Burgers-Huxley and Huxley Equation UsingWavelet Collocation Method
No full textIn this paper, Haar wavelet method is applied to compute the numerical solutions of non-linear partial differential equations like Huxley and Burgers- Huxley equation. The approximate solutions of the Huxley and Burgers-Huxley equations are compared with the exact solutions. The present scheme is very simple, effective and convenient with small computational overhead
A <i>GL</i>(<i>n</i>,R) Differential Algebraic Equation Method for Numerical Differentiation of Noisy Signal
No full textWe show that the problem "real-time numerical differentiation" of a given noisy signal in time, by supplementing a compensated controller in the second-order robust exact differentiator, the tracking differentiator or the continuous hybrid differentiator, can be viewed as a set of differential algebraic equations (DAEs) to enhance a precise tracking of the given noisy signal. Thus, we are able to solve the highly ill-posed problem of numerical differentiation of noisy signal by using the Lie-group differential algebraic differentiators (LGDADs) based on the Lie-group GL(n,R), whose accuracy and tracking performance are better than before. The "index-two" differentiators (ITDs), which do not need any parameter in the governing equations, can efficiently depress the chattering, and also improve the dynamical performance under noise. The tracking results obtained by the LGDADs and the ITDs are quite promising
Wavelet solution of a class of two-dimensional nonlinear boundary value problems
No full textBy combining techniques of boundary extension and Coiflet-type wavelet expansion, an approximation scheme for a function defined on a two-dimensional bounded space is proposed. In this wavelet approximation, each expansion coefficient can be directly obtained by a single-point sampling of the function. And the boundary values and derivatives of the bounded function can be embedded in the modified wavelet basis. Based on this approximation scheme, a modified wavelet Galerkin method is developed for solving two-dimensional nonlinear boundary value problems, in which the interpolating property makes the solution of such strong nonlinear problems very effective and accurate. As an example, we have applied the proposed method to the solution of two-dimensional Bratu-like equations. Results demonstrate an excellent numerical accuracy, a 2.5-order convergence rate for the present wavelet method, and a very good capability in dealing with the nonlinear boundary value problems with multiple solution branches. Interestingly, unlike most existing methods, numerical errors of the present solutions are not sensitive to the nonlinear intensity of the two-dimensional equations