Advances in Structural Mechanics Modeled with FEM

It is well known that many structural and physical problems cannot be solved by analytical approaches. These problems require the development of numerical methods to get approximate but accurate solutions. The minite element method (FEM) represents one of the most typical methodologies that can be used to achieve this aim, due to its simple implementation, easy adaptability, and very good accuracy. For these reasons, the FEM is a widespread technique which is employed in many engineering fields, such as civil, mechanical, and aerospace engineering. The large-scale deployment of powerful computers and the consequent recent improvement of the computational resources have provided the tools to develop numerical approaches that are able to solve more complex structural systems characterized by peculiar mechanical configurations. Laminated or multi-phase composites, structures made of innovative materials, and nanostructures are just some examples of applications that are commonly and accurately solved by the FEM. Analogously, the same numerical approaches can be employed to validate the results of experimental tests. The main aim of this Special Issue is to collect numerical investigations focused on the use of the finite element metho

Applications of Finite Element Modeling for Mechanical and Mechatronic Systems

Modern engineering practice requires advanced numerical modeling because, among other things, it reduces the costs associated with prototyping or predicting the occurrence of potentially dangerous situations during operation in certain defined conditions. Thus far, different methods have been used to implement the real structure into the numerical version. The most popular uses have been variations of the finite element method (FEM). The aim of this Special Issue has been to familiarize the reader with the latest applications of the FEM for the modeling and analysis of diverse mechanical problems. Authors are encouraged to provide a concise description of the specific application or a potential application of the Special Issue

SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES

Crack propagation in thin shell structures due to cutting is conveniently simulated using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell elements are usually preferred for the discretization in the presence of complex material behavior and degradation phenomena such as delamination, since they allow for a correct representation of the thickness geometry. However, in solid-shell elements the small thickness leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new selective mass scaling technique is proposed to increase the time-step size without affecting accuracy. New ”directional” cohesive interface elements are used in conjunction with selective mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile shells

Numerical well testing of coalbed methane (CBM) reservoir

Numerical experiments and field applications proved that there exist percolation non-linearity and fluid multi-variability in low permeability CBM reservoirs. The percolation of fluid needs to overcome threshold pressure gradient, and klinkenberg effects will restrict the gas permeability. In addition, production enhancement and ultimate recovery improvement have given multi-branch horizontal wells the advantage over the vertical wells in many CBM marginal reservoirs. Moreover, Enhance Coalbed Methane (ECBM) recovery through injection of gases has been publicly proven, and can increase gas resources, however, its application in some actual field failed to address the good history matching. In this thesis, the numerical simulation and well testing problems encountered in the reservoir exploration and production are investigated. Firstly, a new dual porosity, single permeability model was developed, which reflects the high velocity non-Darcy flow that considers the threshold pressure, gas slippage and matrix shrinkage effects. It is solved using the fully implicit numerical method, a computer programme called COAFOR has been developed for this purpose. Secondly, an advanced non-analytical coupled CBM model is developed for predicting the flux in the CBM reservoir and single or multi-branch wellbore simultaneously. Thirdly, a coupled compositional triple porosity horizontal wellbore model for CBM reservoir considering the gas slippage and threshold pressure gradient effects is proposed with a newly developed permeability model. The simulator, called TRIPLE-COAL, was developed for this model. Finally, the new models developed in this thesis are validated by applying them into Heshun block, Yanchun South block and Zhijin block respectively. The history matching results checked the reasonability and accuracy of the models built in this thesis. The coupled multi-branch horizontal triple porosity model shows better matching result in Zhijin block than the coupled multi-branch horizontal dual porosity model in Yanchuan South block

Advances in Unconventional Oil and Gas

This book focuses on the latest progress in unconventional oil and gas (such as coalbed methane, shale gas, tight gas, heavy oil, hydrate, etc.) exploration and development, including reservoir characterization, gas origin and storage, accumulation geology, hydrocarbon generation evolution, fracturing technology, enhanced oil recovery, etc. Some new methods are proposed to improve the gas extraction in coal seams, characterize the relative permeability of reservoirs, improve the heat control effect of hydrate-bearing sediment, improve the development efficiency of heavy oil, increase fracturing effectiveness in tight reservoirs, etc

Tracing back the source of contamination

From the time a contaminant is detected in an observation well, the question of where and when the contaminant was introduced in the aquifer needs an answer. Many techniques have been proposed to answer this question, but virtually all of them assume that the aquifer and its dynamics are perfectly known. This work discusses a new approach for the simultaneous identification of the contaminant source location and the spatial variability of hydraulic conductivity in an aquifer which has been validated on synthetic and laboratory experiments and which is in the process of being validated on a real aquifer