Available Experimental Results (available + experimental_result)

Distribution by Scientific Domains


Selected Abstracts


Non-linear behavior of mass concrete in three-dimensional problems using a smeared crack approach

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2005
H. Mirzabozorg
Abstract A smeared crack approach has been proposed to model the static and dynamic behavior of mass concrete in three-dimensional space. The proposed model simulates the tensile fracture on the mass concrete and contains pre-softening behavior, softening initiation, fracture energy conservation and strain rate effects under dynamic loads. The validity of the proposed model has been checked using the available experimental results under static and dynamic loads. The direct and indirect displacement control algorithms have been employed under incremental increasing static loads. It was found that the proposed model gives excellent results and crack profiles when compared with the available data under static loads. The Koyna Dam in India has been used to verify the dynamic behavior of the proposed model. It was found that the resulting crack profiles were in good agreement with the available experimental results. Finally, the Morrow Point Dam was analyzed, including the dam,reservoir interaction effects, to consider its non-linear seismic behavior. It was found that the resulting crack profiles were in good agreement with the contour of maximum principal stresses and no numerical instability occurred during the analysis. Copyright © 2004 John Wiley & Sons, Ltd. [source]


Damage analysis of laminated composites using a new coupled micro-meso approach

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 7 2010
A. FARROKHABADI
ABSTRACT In this study, the simplicity and strong physical meaning of micromechanics approach and capability of mesomechanics approach for damage analysis of structures with complex loadings are employed to develop a new micro-meso approach. For this purpose, a new micromechanics model is developed to predict the matrix cracking initiation and evolution in laminated composites. These damage initiation and evolution are replaced with the damage criteria and flow rule in the continuum damage approach, respectively. The results of this procedure are used in the FEM damage analyses of laminated composites to predict constitutive response of layered composites. It is shown that, the predicted stress distribution and strain energy in a lamina unit cell are in good agreement with the finite element results. Furthermore, it is shown that the predicted stress,strain behaviours are in good agreement with the available experimental results for various laminates with different lay-ups. [source]


A computerized procedure for long-life fatigue assessment under complex multiaxial loading

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 3 2001
B. Li
A computerized procedure is presented and evaluated for application examples of long-life fatigue analyses of metallic materials under complex multiaxial loading. The method is based on the stress invariants and uses the minimum circumscribed ellipse approach for evaluating the effective shear stress amplitude under complex multiaxial loading. The applicability of the procedure for handling non-proportional loading is examined through typical examples such as combined normal/shear stresses and combined bi-axial normal stresses with complex stress time histories. The effects of phase shift angles, frequency ratios and waveforms on fatigue endurance were re-analysed and compared with available experimental results from the literature. The comparison shows that the presented procedure based on stress invariants is a potential conservative engineering approach, very suitable for fast fatigue evaluation in the integrated computer aided fatigue design. [source]


Thermal effects in partially saturated soils: a constitutive model

INTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2005
Gabriella Bolzon
Abstract The present paper is centred on the assessment of an elastic,plastic model for partially saturated soils, earlier proposed by the authors, for its predictive capability with respect to temperature changes, on the light of available experimental results. The model is cast within a constitutive framework that uses Bishop's stress and suction as main variables governing the volumetric response of the material. Some enhancement to the original temperature-independent formulation is proposed. In particular, functions describing the yield surface and the compressibility modulus are modified to account for the shrinking of the elastic domain and for the increase of irreversible volumetric strain with heating. Some examples illustrate the main features of the present proposal. Comparison with some experimental results is also included. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Combining interface damage and friction in a cohesive-zone model

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2006
Giulio Alfano
Abstract A new method to combine interface damage and friction in a cohesive-zone model is proposed. Starting from the mesomechanical assumption, typically made in a damage-mechanics approach, whereby a representative elementary area of the interface can be additively decomposed into an undamaged and a fully damaged part, the main idea consists of assuming that friction occurs only on the fully damaged part. The gradual increase of the friction effect is then a natural outcome of the gradual increase of the interface damage from the initial undamaged state to the complete decohesion. Suitable kinematic and static hypotheses are made in order to develop the interface model whereas no special assumptions are required on the damage evolution equations and on the friction law. Here, the Crisfield's interface model is used for the damage evolution and a simple Coulomb friction relationship is adopted. Numerical and analytical results for two types of constitutive problem show the effectiveness of the model to capture all the main features of the combined effect of interface damage and friction. A finite-step interface law has then been derived and implemented in a finite-element code via interface elements. The results of the simulations made for a fibre push-out test and a masonry wall loaded in compression and shear are then presented and compared with available experimental results. They show the effectiveness of the proposed model to predict the failure mechanisms and the overall structural response for the analysed problems. Copyright © 2006 John Wiley & Sons, Ltd. [source]


A-scalability and an integrated computational technology and framework for non-linear structural dynamics.

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 15 2003
Part 2: Implementation aspects, parallel performance results
Abstract An integrated framework and computational technology is described that addresses the issues to foster absolute scalability (A-scalability) of the entire transient duration of the simulations of implicit non-linear structural dynamics of large scale practical applications on a large number of parallel processors. Whereas the theoretical developments and parallel formulations were presented in Part 1, the implementation, validation and parallel performance assessments and results are presented here in Part 2 of the paper. Relatively simple numerical examples involving large deformation and elastic and elastoplastic non-linear dynamic behaviour are first presented via the proposed framework for demonstrating the comparative accuracy of methods in comparison to available experimental results and/or results available in the literature. For practical geometrically complex meshes, the A-scalability of non-linear implicit dynamic computations is then illustrated by employing scalable optimal dissipative zero-order displacement and velocity overshoot behaviour time operators which are a subset of the generalized framework in conjunction with numerically scalable spatial domain decomposition methods and scalable graph partitioning techniques. The constant run times of the entire simulation of ,fixed-memory-use-per-processor' scaling of complex finite element mesh geometries is demonstrated for large scale problems and large processor counts on at least 1024 processors. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Variational transition-state theory study of the atmospheric reaction OH + O3 , HO2 + O2

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2007
Li-Ping Ju
We report variational transition-state theory calculations for the OH + O3, HO2 + O2 reaction based on the recently reported double many-body expansion potential energy surface for ground-state HO4 [Chem Phys Lett 2000, 331, 474]. The barrier height of 1.884 kcal mol,1 is comparable to the value of 1.77,2.0 kcal mol,1 suggested by experimental measurements, both much smaller than the value of 2.16,5.11 kcal mol,1 predicted by previous ab initio calculations. The calculated rate constant shows good agreement with available experimental results and a previous theoretical dynamics prediction, thus implying that the previous ab initio calculations will significantly underestimate the rate constant. Variational and tunneling effects are found to be negligible over the temperature range 100,2000 K. The O1O2 bond is shown to be spectator like during the reactive process, which confirms a previous theoretical dynamics prediction. © 2007 Wiley Periodicals, Inc. 39: 148,153, 2007 [source]


Along-channel mathematical modelling for proton exchange membrane fuel cells

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 12 2005
Wenbo Huang
Abstract Proper water and thermal management is essential for obtaining high performance of proton exchange membrane fuel cells (PEMFCs). A steady, two-dimensional water and thermal management model was developed, aiming at considering pressure effects (i.e. the effects of local pressure on the cell performance), pressure drop, open circuit voltage variation with stack temperature, water vapour effects on membrane conductivity, which made the model physically more reasonable and more suitable for various operating conditions. The model could predict the distributions of a series of important parameters along the flow channel, and thus the effects of various operating and design parameters on the fuel cell performance could be investigated easily by numerical trial-and-error method. The modelling results compared well with the available experimental results from the literatures. The results also showed that the humidification of both anode and cathode is crucial for the performance of PEMFCs. The model could be a very useful engineering tool for the optimization of PEMFCs. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Energy analysis in fluidized-bed drying of large wet particles

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2002
S. Syahrul
Abstract Energy analysis of a fluidized-bed drying system is undertaken to optimize the fluidized-bed drying conditions for large wet particles (Group D) using energy models. Three critical factors; the inlet air temperature, the fluidization velocity, and the initial moisture contents of the material (e.g., wheat) are studied to determine their effects on the overall energy efficiency to optimize the fluidized bed drying process. In order to verify the model, different experimental data sets for wheat material taken from the literature are used. The results show that the energy efficiencies of the fluidized-bed dryer decrease with increasing drying time and become the lowest at the end of the drying process. It is observed that the inlet air temperature has an important effect on energy efficiency for the material where the diffusion coefficient depends on both the temperature and the moisture content of the particle. Furthermore, the energy efficiencies showed higher values for particles with high initial moisture content while the effect of gas velocity varied depending on the material properties. A good agreement is achieved between the model predictions and the available experimental results. Copyright © 2002 John Wiley & Sons, Ltd. [source]


Estimation of the ideal solubility (crystal,liquid fugacity ratio) of organic compounds

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2010
Samuel H. Yalkowsky
Abstract Melting point, entropy of melting and heat capacity of melting are required for the calculation of the ideal solubility of a solid solute via the Clausius,Clapyron equation. This article reviews the published approximations of estimating entropy and heat capacity of melting. By comparing the available experimental results to calculated values the authors attempt to identify the best estimation of the ideal solubility and crystal,liquid fugacity ratio for organic compounds. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 1100,1106, 2010 [source]


Theoretical study of the gas-phase decomposition of neutral ,-amino acid ethyl esters.

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 3 2003
Elimination of ethyl picolinate, Part , ethyl 1-methylpipecolinate
Abstract Theoretical studies of the thermolysis in the gas phase of two ,-amino acid ethyl esters, ethyl picolinate and ethyl 1-methylpipecolinate, were carried out using ab initio theoretical methods, at the MP2/6,31G(d) and MP2/6,311+G(2d,p) levels of theory. The reactions studied have two steps: the first corresponds to the formation of a neutral amino acid intermediate via a six-membered cyclic transition state, and the second is the rapid decarboxylation of this intermediate via a five-membered cyclic transition state. The progress of the first step of the reactions was followed by means of the Wiberg bond indices. The results indicate that the transition states have an intermediate character between reactants and products, and the calculated synchronicities show that the reactions are concerted and slightly asynchronous. The bond-breaking processes are more advanced than the bond-forming processes, indicating a bond deficiency in the transition states. The kinetic parameters calculated for both reactions agree very well with the available experimental results. Copyright © 2003 John Wiley & Sons, Ltd. [source]


Anisotropy of spin relaxation of water protons in cartilage and tendon

NMR IN BIOMEDICINE, Issue 3 2010
Konstantin I. Momot
Abstract Transverse spin relaxation rates of water protons in articular cartilage and tendon depend on the orientation of the tissue relative to the applied static magnetic field. This complicates the interpretation of magnetic resonance images of these tissues. At the same time, relaxation data can provide information about their organisation and microstructure. We present a theoretical analysis of the anisotropy of spin relaxation of water protons observed in fully hydrated cartilage. We demonstrate that the anisotropy of transverse relaxation is due almost entirely to intramolecular dipolar coupling modulated by a specific mode of slow molecular motion: the diffusion of water molecules in the hydration shell of a collagen fibre around the fibre, such that the molecular director remains perpendicular to the fibre. The theoretical anisotropy arising from this mechanism follows the ,magic-angle' dependence observed in magnetic-resonance measurements of cartilage and tendon and is in good agreement with the available experimental results. We discuss the implications of the theoretical findings for MRI of ordered collagenous tissues. Copyright © 2009 John Wiley & Sons, Ltd. [source]


Positronium interaction and its Bose-Einstein condensation

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2009
Sadhan K. Adhikari
Abstract We present the actual state of affairs and future perspectives in the study of a quantum system of a collection of positronium (Ps) atoms. The interaction of a Ps atom with other atoms and molecules and specially with another Ps atom is described in some detail as Ps-Ps interaction should play a crucial role in the dynamics of an assembly of Ps atoms. Using a simple model-exchange potential, we could describe the available experimental results of Ps scattering reasonably well. The present scenario of the observation of Ps2 molecule, Ps Bose-Einstein condensate (BEC) and the annihilation laser from a Ps BEC is presented. Possibilities of a Ps BEC formation via laser cooling of Ps atoms and via Ps formation in cavities are considered and difficulties with each procedure discussed (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]