Enhanced isogeometric analysis of fracturing in solid and porous media

EXtended Finite Element Method (XFEM) decouples the crack path from the discretisation, a major advantage compared to interface elements for simulating arbitrary fracturing. Also, avoiding the costly option of remeshing, XFEM enables propagating discontinuities to be modelled on the original mesh layout. XFEM, however, has been replaced by other techniques, such as meshless methods, to provide higher-order continuity across element boundaries. This is required to remove stress jumps at element boundaries, to improve stress estimates particularly in the presence of a discontinuity, and to locally satisfy mass conservation of the fluid part needed at element boundaries of a porous medium. With the advent of IsoGeometric Analysis (IGA), spline bases have been proposed to provide C^\mathbbm{p}-continuity (\mathbbm{p}>0) across element boundaries, which also have been incorporated in XFEM, so-called eXtended IsoGeometric Analysis (XIGA), to replace the underlying $C^0$-continuity of the Lagrangian interpolations. Within the realm of Linear Elastic Fracture Mechanics (LEFM), XIGA has been well addressed, but not so far cohesive zone models. The interelement sharing of control points in splines removes the Kronecker-Delta property available for Lagrange interpolation underlying the customary finite element method. These features complicate elementwise enrichment of individual control points, as well as the compatibility enforcement. The latter is of utmost importance as a possible source of error, which has not been well addressed for XIGA despite the full investigation carried out in the original contribution combining IGA and XFEM. Shifting technique can localise the effect of the Heaviside function, although, unlike XFEM, it stretches to the blending elements. This is similar to the effect of blending technique to enforce compatibility in XFEM. An XIGA formulation is proposed for Non-Uniform Rational B-splines (NURBS) to account for small strain and geometrically nonlinear cohesive fractures. Compatibility enforcement is realised of shifting and blending techniques perpendicular and parallel to the discontinuity, respectively. The latter enables removing the undesired effect of the discontinuity ahead of the crack tip, which is absent in recent XIGA contributions. To provide a standard finite element data structure B{\'e}zier extraction is utilised. In a further development, XIGA is augmented with the Local Maximum Entropy (LME), a meshless technique with superior features to elevate the accuracy of the enhanced section, which is coined X-IGALME. The results indicate a guaranteed stability of the solution for X-IGALME, where XIGA and XFEM fail. Unlike elementwise approaches, the singularity-free characteristic of X-IGALME facilitates a single prescription for enrichment in any condition, including void level set. Finally, XIGA for a progressively fracturing porous medium is investigated, representing a successful fracture simulation in fluid saturated porous media using a 2PDOF (two pressure degrees of freedom) model

The Role of Urban Morphology Design on Enhancing Physical Activities and Public Health

Along with environmental pollutions, urban planning has been connected to public health. The research indicates that the quality of built environments plays an important role in reducing mental disorders and overall health. The structure and shape of the city are considered as one of the factors influencing happiness and health in urban communities and the type of the daily activities of citizens. The aim of this study was to promote physical activity in the main structure of the city via urban design in a way that the main form and morphology of the city can encourage citizens to move around and have physical activity within the city. Functional, physical, cultural- social, and perceptual-visual features are regarded as the most important and effective criteria in increasing physical activities in urban spaces based on literature review. The environmental quality of urban spaces and their role in the physical activities of citizens in urban spaces were assessed by using the questionnaire tool and analytical network process (ANP) of structural equation modeling. Further, the space syntax method was utilized to evaluate the role of the spatial integration of urban spaces on improving physical activities. Based on the results, the consideration of functional diversity, spatial flexibility and integration, security, and the aesthetic and visual quality of urban spaces plays an important role in improving the physical health of citizens in urban spaces. Further, more physical activities, including motivation for walking and consequently, the sense of public health and happiness, were observed in the streets having higher linkage and space syntax indexes with their surrounding texture

A computational approach to financial option pricing using Quasi Monte Carlo methods via variance reduction techniques

Journal articleIn this paper, we consider two types of pricing option in financial markets using quasi Monte Carlo algorithm with variance reduction procedures. We evaluate Asian-style and European-style options pricing based on Black-Scholes model. Finally, some numerical results presented

Matrix balancing and robust Monte Carlo algorithm for evaluating dominant eigenpair

Matrix balancing may effect the stability of algorithms in matrix computations and the accuracy of computed solutions. In this paper, we first introduce an algorithm for matrix balancing. Then, using Monte Carlo method we propose a robust algorithm to evaluate dominant eigenpair of a given matrix. Finally, several randomly generated examples are presented to show the efficiency of the new method

Quasi Monte Carlo algorithm for computing smallest and largest generalised eigenvalues

The problem of obtaining the smallest and the largest generalised eigenvalues using quasi Monte Carlo algorithm is considered. We first study the results of Dimov and others using three algorithms based on the power method combined with Monte Carlo and quasi Monte Carlo methods for evaluating extremal eigenvalue of real matrices. We present a quasi Monte Carlo algorithm for computing both the smallest and the largest generalised eigenvalues using Sobol, Halton sequences and the rand function in Matlab. We finally compare the efficiency of three employed generators in our algorithm for different pencils. References Alexandrov V. N., Efficient parallel Monte Carlo Methods for Matrix Computation, Mathematics and computers in Simulation, Elsevier 47 (1998) 113--122, doi:10.1016/S0378-4754(98)00097-4 Chi H., Mascagni M. and Warnock T., On the optimal Halton sequence, Mathematics and Computers in Simulation, 70 (2005) 9--21, doi:10.1016/j.matcom.2005.03.004 Dimov I., Monte Carlo methods for applied scientists, World Scientific Publishing Co., 2008. Dimov I., Alexandrov V. and Karaivanova A., Implementation of Monte Carlo Algorithms for Eigenvalue Problem Using MPI, Recent Advances in Parallel Virtual Machine and Message Passing Interface, Springer, 1998. Fathi Vajargah B. and Mehrdoust F., New Monte Carlo algorithm for obtaining three dominant eigenvalues, Int. J. Appl. Math. 22 (2009), no. 4, 553--559. Kressner D., Numerical Methods for General and Structured Eigenvalue Problems, Springer--Verlag Berlin Heidelberg, 2005. Lemieux C., Monte Carlo and Quasi Monte Carlo Sampling, Springer Science, 2009. Mascagni M. and A. Karaivanova, A Parallel Quasi Monte Carlo Method for Computing Extremal Eigenvalues, Monte Carlo and Quasi Monte Carlo Methods, Springer, 12 (2002) 369--380. Sobol I. M., On quasi Monte Carlo integrations, Mathematics and Computers in Simulation, 47 (1998) 103--112. doi:10.1016/S0378-4754(98)00096-2 Sobol I. M., Quasi Monte Carlo methods, Progress in Nuclear Energy, 24 (1990) 55--61

The effect of Iranian snake, Naja naja oxiana venom on the blood glucose concentration and some biochemical parameters of experimental diabetic rats

Diabetes is a chronic disease resulting from impaired insulin production and function; leading to hyperglycaemia and long-term complications. The treatment for Type I diabetes treatment involves insulin injections while Type II diabetes treatments include drugs such as metformin and sulfonylureas, along with lifestyle changes. These medicines can be expensive and may have adverse effects. Therefore, the search for new therapeutic agents continues. Venoms from various animals yield numerous pharmacologically active compounds. In this study, we investigated the effects of the venom from an Iranian snake, Naja naja oxiana, on blood glucose concentration and certain serum biochemical parameters in male rats with induced diabetes.Diabetes was induced in male rats using either a single injection of streptozotocin (STZ) alone (55 mg/kg i. p.) or STZ (65 mg/kg i. p.) preceded by nicotinamide (230/kg i. p.) administered 15 min earlier. The diabetic rats produced by either method received a single injection of either vehicle or venom (0.2 or 0.4 mg/kg i. p.). In the STZ rats, this was done 13 days after diabetes induction, while in the STZ-nicotinamide rats, venom was injected 3 days after diabetes induction.The venom from Naja naja oxiana significantly reduced blood glucose levels in male rats with diabetes induced by either method. Additionally, the venom decreased serum cholesterol and triglycerides concentrations. However, the venom had no effect on the blood glucose levels of healthy male rats. Pretreatment with the venom did not prevent the induction of diabetes by STZ. These findings suggest that Naja naja oxiana venom exhibits an anti-diabetic effect and could be a potential candidate for effectively controlling diabetes

Modeling the merging capacity for two streams of product returns in remanufacturing systems

International audienceWe consider a remanufacturing system with two streams of returned products and different variability levels (high and low). The arrival of returns with high variability is modeled with a hyperexponential renewal process and that of returns with low variability is modeled with a Poisson process. The reman-ufacturing facility can process the returned products in two ways. For the first way, each type of returns is remanufactured by a dedicated capacity. For the second way, returns from two different markets are remanufactured by a merged capacity. Analytical queueing models with the time value of money consideration are proposed for the admission decision, which decides on the acceptance or not of returned products based on quality and processing time. The proposed modeling determines the admission decision threshold value in order to maximize the total expected profit of the remanufacturing system. Our analysis also allows to study the interaction between the overall utilization and the arrival process variability. The results show the impact of the model parameters on the admission decision value and the total expected discounted profit. Also, the total expected discounted profit under the separated and merged capacities are compared

Application of Response Surface Methodology to Optimize Malachite Green Removal by Cl-nZVI Nanocomposites

Disposal of effluents containing dyes into natural ecosystems pose serious threats to both the environment and its aquatic life. Malachite green (MG) is a basic dye that has extensive industrial applications, especially in aquaculture, throughout the world. This study reports on the application of the central composite design (CCD) under the response surface methodology (RSM) for the optimization of MG adsorption from aqueous solutions using the clinoptilolite nano-zerovalence iron (Cl-nZVI) nanocomposites. The sorbent structures produced are characterized by means of scanning electron micrograph (SEM), energy-dispersive X-ray spectroscopy (EDS), and vibrating sample magnetometer (VSM). The effects of different parameters including pH, initial MG concentration, and sorbent dosage on the removal efficiency (R) of MG were studied to find the optimum operating conditions. For this purpose, a total of 20 sets of experiments were designed by the Design Expert.7.0 software and the values of removal efficiency were used as input response to the software. The optimum pH, initial MG concentration, and sorbent dosage were found to be 5.6, 49.21 mg.L-1, and 1.43 g.L-1, respectively. A high MG removal efficiency (57.90%) was obtained with optimal process parameters. Moreover, a desirability value of 0.963 was obtained for the optimization process