Adaptive Time Stepping, Linearization and a Posteriori Error Control for Multiphase Flow with Wells

We present in this paper a-posteriori error estimators for multiphase flow with singular well sources. The estimators are fully and locally computable, distinguish the various error components, and target the singular effects of wells. On the basis of these estimators we design an adaptive fully-implicit solver that yields optimal nonlinear iterations and efficient time-stepping, while maintaining the accuracy of the solution. A key point is that the singular nature of the solution in the near-well region is explicitly captured and efficiently estimated using the adequate norms. Numerical experiments illustrate the efficiency of our estimates and the performance of the adaptive algorithm.

Gradient Nonlocal Enhanced Microprestress-Solidification Theory and Its Finite Element Implementation

Time-dependent responses of cracked concrete structures are complex, due to the intertwined effects between creep, shrinkage, and cracking. There still lacks an effective numerical model to accurately predict their nonlinear long-term deflections. To this end, a computational framework is constructed, of which the aforementioned intertwined effects are properly treated. The model inherits merits of gradient-enhanced damage (GED) model and microprestress-solidification (MPS) theory. By incorporating higher order deformation gradient, the proposed GED-MPS model circumvents damage localization and mesh-sensitive problems encountered in classical continuum damage theory. Moreover, the model reflects creep and shrinkage of concrete with respect to underlying moisture transport and heat transfer. Residing on the Kelvin chain model, rate-type creep formulation works fully compatible with the gradient nonlocal damage model. 1-D illustration of the model reveals that the model could regularize mesh-sensitivity of nonlinear concrete creep affected by cracking. Furthermore, the model depicts long-term deflections and cracking evolutions of simply-supported reinforced concrete beams in an agreed manner. It is noteworthy that the gradient nonlocal enhanced microprestress-solidification theory is implemented in the general finite element software Abaqus/Standard with the implicit solver, which renders the model suitable for large-scale creep-sensitive structures.

Asymmetric Vibrations and Chaos in Spherical Caps under Uniform Time-varying Pressure Fields

This paper presents a study on nonlinear asymmetric vibrations in shallow spherical caps under pressure loading. The Novozhilov’s nonlinear shell theory is used for modelling the structural strains. A reduced-order model is developed through the Rayleigh-Ritz method and Lagrange equations. The equations of motion are numerically integrated using an implicit solver. The bifurcation scenario is addressed by varying the external excitation frequency. The occurrence of asymmetric vibrations related to quasi-periodic and chaotic motion is shown through the analysis of time histories, spectra, Poincaré maps, and phase planes.

Investigation of Model Configuration Parameters for Stick-Slip Modeling

Stick-slip vibrations modeling is an important topic within drillstring dynamics. Thus, a number of mathematical models has been suggested to describe behavior of drillstrings under torsional. Most of the models take similar approach with regard to, for instance, drillstring discretization, definition of external forces and velocity-weakening effect. Commonly, research papers focus on the models’ core — mathematical expressions that describe stick-slip oscillations and inherent to it negative damping. The results are usually presented in terms of downhole rotational velocity or displacement and reaction forces at various surface rotational velocities and applied external forces. However, little attention is paid to discussion and justification of selected model configuration, which includes definition of the following 1) total simulation time, time step, number of masses/elements, etc., 2) initial conditions and boundary conditions, and 3) numerical solver to obtain solution in time. This paper reviews commonly used configurations for stick-slip vibrations modeling and discusses selection criteria provided in the references. It also presents case studies to evaluate effect of the above-mentioned configuration properties on simulations outcome. A simple in-house 1DOF torsional dynamics model was used for that purpose, where one explicit and one implicit numerical solvers were applied to obtain solution in time. Three case studies are presented, which compare performance of two numerical solvers with respect to convergence and stability. The results from the case studies show, for example, that applied explicit numerical solver (Central Difference Method) introduces numerical damping, while implicit solver (Newton-Raphson Method) does not. Central Difference Method provides convergence when initial force is applied, while damping function has to be defined in case of Newmark-Raphson method to obtain convergence. Stability of the explicit numerical solver is determined by the time step, while selected implicit solver is unconditionally stable. A reasonably small time step has to be selected though to improve the accuracy of the results. Presented literature review and outcome from the case studies can be used by researchers within this area to select suitable configuration parameters for their models and critically evaluate the outputs. In addition, presented results have application in automated drilling where configuration parameters and calibration factors are updated in real time by control algorithms for continuous modeling of drillstring state with regard to stickslip. Understanding the effects of mentioned properties on system dynamics helps to select suitable combination of operational parameters to stabilize the drillstring.

Aerodynamic Performance of the Inboard Elevon on a Blendedwing- Body Aircraf

The objectives of this research are to examine the effects of trailing edge modifications of the inboard elevon of a blended-wing-body (BWB) aircraft, the goal being to try and reduce the hinge moment of the inboard elevon through selective aerodynamic design. A computational model was built for 60⁰ and 70⁰ beveled trailing edge modifications, as well as no modification. The inboard elevon was deflected positive 5⁰ and negative 5⁰. The numerical solutions were obtained using an implicit solver and inviscid model. The results of this research showed that, through the use of a beveled trailing edge on the inboard elevon, a maximum of 112% reduction in the hinge moment could be achieved for the negative deflection case and a maximum of 88% reduction in the hinge moment for the positive deflection case. The results showed that there was a significant improvement in the hinge moments, with less that a 2% average change in the overall aerodynamic performance of the BWB for the inviscid models.

Aerodynamic Performance of the Inboard Elevon on a Blendedwing- Body Aircraf

The objectives of this research are to examine the effects of trailing edge modifications of the inboard elevon of a blended-wing-body (BWB) aircraft, the goal being to try and reduce the hinge moment of the inboard elevon through selective aerodynamic design. A computational model was built for 60⁰ and 70⁰ beveled trailing edge modifications, as well as no modification. The inboard elevon was deflected positive 5⁰ and negative 5⁰. The numerical solutions were obtained using an implicit solver and inviscid model. The results of this research showed that, through the use of a beveled trailing edge on the inboard elevon, a maximum of 112% reduction in the hinge moment could be achieved for the negative deflection case and a maximum of 88% reduction in the hinge moment for the positive deflection case. The results showed that there was a significant improvement in the hinge moments, with less that a 2% average change in the overall aerodynamic performance of the BWB for the inviscid models.

Thermo-mechanical and metallurgical model of leaf spring industrial quenching process

This study is a numerical analysis of the industrial quenching process for leaf springs developed by the CAVEO company. The leaf chosen for this study is of a parabolic profile made of EN-51CrV4 steel (AISI 6150). The aim of this study is to set up a numerical model to predict thermal, metallurgical, and mechanical behavior of a leaf spring from exit of the heating furnace to exit of the quenching bath going through a cambering operation. This study would therefore allow the company to switch from a development scheme based on experiments using physical prototypes tested on the production line to a new scheme based on virtual prototypes using numerical simulation. The development of the numerical model using the finite element method is carried out using the ABAQUS/Implicit solver coupled with two user subroutines Phase and UMAT. The first one have been developed to compute microstructure evolution and the second one to define the constitutive law taking into account phase transformations. This model helps us to follow the spatio-temporal evolutions of temperature and microstructure in the leaf, as well as the variation of the leaf deflection during the process. The proposed numerical model is supported by an experimental protocol based on infrared thermographic images, Rockwell-C hardness measurements, metallographic observations, and deflection measurements. Indeed, the results of the proposed thermo-mechanical and metallurgical model are closed to experimental results.