Adaptive neurofuzzy ANFIS modeling of laser surface treatments

This paper introduces a new ANFIS adaptive neurofuzzy inference model for laser surface heat treatments based on the Green’s function. Due to its high versatility, efficiency and low simulation time, this model is suitable not only for the analysis and design of control systems, but also for the development of an expert real time supervision system that would allow detecting and preventing any failure during the treatment

Computational kinematics of multibody systems: Two formulations for a modular approach based on natural coordinates

Multibody systems can be divided into an ordered set of kinematically determined modules, known as structural groups, in order to compute their kinematics more efficiently. In this work a procedure for the kinematic analysis of any kind of structural group is introduced, and two different methods for their solution in natural coordinates are presented: the time derivative (TD) and the third-order tensor (3OT) approaches. Moreover, the newly derived methods are compared in terms of efficiency with a global formulation, consisting in solving the kinematics of the multibody system as a whole using dense and sparse solvers. Two scalable case studies have been considered: a 2D four-bar linkage and a 3D slider-crank mechanism with an increasing number of constraint equations. The results show that the TD approach performs better in all cases with speed ups in a range of 27 to 61 times faster in 2D, and of 2.3 to 3.7 times faster in 3D with respect to the global sparse solution

Computational structural analysis of planar multibody systems with lower and higher kinematic pairs

Kinematic and dynamic modeling of multibody systems requires an initial stage of topological recognition or structural analysis, in which the analyst must identify the model coordinates and a sufficient number of constraint equations to relate them. This initial phase could be solved quickly, safely and automatically, determining the kinematic structure of the multibody system; that is, dividing it into a set of kinematic chains called structural groups. Furthermore, structural groups are widely used for structural synthesis and so, the analysis and design of multibody systems can be integrated into the same software package. On the basis of known graph-analytical methods for structural analysis, a computational method that determines the kinematic structure of a multibody system from its adjacency matrix is developed and evaluated. This method allows the choosing of any type of coordinates (relative, natural or reference point) and the kinematic and dynamic formulations most appropriate for solving the problem. The algorithm has been applied to a large number of mechanical systems of different complexity, offering the same kinematic structure as was obtained through the application of graph-analytical methods

Simulating the anchor lifting maneuver of ships using contact detection techniques and continuous contact force models

Designing the geometry of a ship’s hull to guarantee a correct anchor maneuver is not an easy task. The engineer responsible for the design has to make sure that the anchor does not jam up during the lifting process and the position adopted by the anchor on the hull is acceptable when it is completely stowed. Some years ago, the design process was based on wooden scale models of the hull, anchor and chain links, which are expensive, their building process is time consuming and they do not offer the required precision. As a result of this research, a computational tool to simulate the anchor maneuver of generic ships given by CAD models was developed, and it is proving to be very helpful for the naval engineers. In this work, all the theory developed to simulate anchor maneuvers is thoroughly described, taking into account both the behavior of the anchor and the chain. To consider the contact forces between all the elements involved in the maneuver, a general contact algorithm for rigid bodies of arbitrary shapes and a particular contact algorithm for the chain links have been developed. In addition to the contact problem, aspects like the dynamic formulation of the equations of motion or the static equilibrium position problem are also covered in this work. To test the theory, a simulation of the anchor lifting maneuver of a ship is included as a case study.The support of the Spanish Ministry of Economy and Competitiveness (MINECO) under Project DPI2016-81005-P, the Galician Government through Grant ED431B2016/031, and the postdoctoral research contract Juan de la Cierva No. JCI-2012-12376 is greatly acknowledged

Direct Sensitivity Analysis of Multibody Systems With Holonomic and Nonholonomic Constraints via an Index-3 Augmented Lagrangian Formulation With Projections

This is a post-peer-review, pre-copyedit version of an article published in Nonlinear Dynamics. The final authenticated version is available online at: http://dx.doi.org/10.1007/s11071-018-4306-y[Abstract] Optimizing the dynamic response of mechanical systems is often a necessary step during the early stages of product development cycle. This is a complex problem that requires to carry out the sensitivity analysis of the system dynamics equations if gradient-based optimization tools are used. These dynamics equations are often expressed as a highly nonlinear system of Ordinary Differential Equations (ODEs) or Differential-Algebraic Equations (DAEs), if a dependent set of generalized coordinates with its corresponding kinematic constraints is used to describe the motion. Two main techniques are currently available to perform the sensitivity analysis of a multibody system, namely the direct differentiation and the adjoint variable methods. In this paper, we derive the equations that correspond to the direct sensitivity analysis of the index-3 augmented Lagrangian formulation with velocity and acceleration projections. Mechanical systems with both holonomic and nonholonomic constraints are considered. The evaluation of the system sensitivities requires the solution of a Tangent Linear Model (TLM) that corresponds to the Newton-Raphson iterative solution of the dynamics at configuration level, plus two additional nonlinear systems of equations for the velocity and acceleration projections. The method was validated in the sensitivity analysis of a set of examples, including a five-bar linkage with spring elements, which had been used in the literature as benchmark problem for similar multibody dynamics formulations, a point-mass system subjected to nonholonomic constraints, and a full-scale vehicle model.Ministerio de Economía y Competitividad (MINECO); DPI2016-81005-PXunta de Galicia; ED431B2016/03

Projection methods for large-scale T-Sylvester equations

The matrix Sylvester equation for congruence, or T-Sylvester equation, has recently attracted considerable attention as a consequence of its close relation to palindromic eigenvalue problems. The theory concerning T-Sylvester equations is rather well understood and there are stable and e cient numerical algorithms which solve these equations for small- to medium-sized matrices. However, developing numerical algorithms for solving large-scale T-Sylvester equations still remains an open problem. In this paper, we present several projection algorithms based on di erent Krylov spaces for solving this problem when the right-hand side of the T-Sylvester equation is a low-rank matrix. The new algorithms have been extensively tested, and the reported numerical results show that they work very well in practice, o ering a clear guidance on which algorithm is the most convenient in each situation.This work has been supported by Ministerio de Economía y Competitividad of Spain through grant MTM2012-32542.Publicad

Behaviour of Augmented Lagrangian and Hamiltonian Methods for Multibody Dynamics in the Proximity of Singular Configurations

This is a post-peer-review, pre-copyedit version of an article published in Nonlinear Dynamics. The final authenticated version is available online at: http://dx.doi.org/10.1007/s11071-016-2774-5.[Abstract] Augmented Lagrangian methods represent an efficient way to carry out the forward-dynamics simulation of mechanical systems. These algorithms introduce the constraint forces in the dynamic equations of the system through a set of multipliers. While most of these formalisms were obtained using Lagrange's equations as starting point, a number of them have been derived from Hamilton's canonical equations. Besides being efficient, they are generally considered to be robust, which makes them especially suitable for the simulation of systems with discontinuities and impacts. In this work, we have focused on the simulation of mechanical assemblies that undergo singular configurations. First, some sources of numerical difficulties in the proximity of singular configurations were identified and discussed. Afterwards, several augmented Lagrangian and Hamiltonian formulations were compared in terms of their robustness during the forward-dynamics simulation of two benchmark problems. Newton-Raphson iterative schemes were developed for these formulations with the Newmark formula as numerical integrator. These outperformed fixed point iteration approaches in terms of robustness and efficiency. The effect of the formulation parameters on simulation performance was also assessed

On the effect of linear algebra implementations in real-time multibody system dynamics

[Abstract] This paper compares the efficiency of multibody system (MBS) dynamic simulation codes that rely on different implementations of linear algebra operations. The dynamics of an N-loop four-bar mechanism has been solved with an index-3 augmented Lagrangian formulation combined with the trapezoidal rule as numerical integrator. Different implementations for this method, both dense and sparse, have been developed, using a number of linear algebra software libraries (including sparse linear equation solvers) and optimized sparse matrix computation strategies. Numerical experiments have been performed in order to measure their performance, as a function of problem size and matrix filling. Results show that optimal implementations can increase the simulation efficiency in a factor of 2–3, compared with our starting classical implementations, and in some topics they disagree with widespread beliefs in MBS dynamics. Finally, advices are provided to select the implementation which delivers the best performance for a certain MBS dynamic simulation

A theoretical study on the mechanism of the base-promoted decomposition of N-chloro,N-methylethanolamine

The first step of the base-promoted decomposition of N-chloro,N-methylethanolamine in aqueous solution (CH3N(Cl)CH2CH2OH + HO- →imine + Cl- + H2O (+ CH2O)→amine + aldehyde) is investigated at the MP2/6-31++G(d,p) computing level. Solvation is included by using both a microsolvated model, in which two explicit water molecules simulate the specific solvent effects, and a hybrid cluster-continuum model, by applying a polarized continuum on the previous results, to account for the bulk effect of the solvent. Four alternative pathways (bimolecular fragmentation, Hofmann, Zaitsev and intramolecular eliminations) are possible for the rate-limiting step of this base-promoted decomposition. These reactive processes are bimolecular asynchronous concerted reactions. The common feature of the four pathways is the proton transfer to HO- being more advanced than all other molecular events, whereas imine formation is delayed. Non-reactive cyclic arrangements involving one of the explicit water molecules are found at transition structures of Hofmann and Zaitsev eliminations, such water molecule acting both as H+ donor and acceptor. Although MP2 calculations misjudge the absolute activation Gibbs free energy values, this computational level adequately predicts the enhancement in the decomposition rate due to the presence of the -OH grou

Effect of Ionizing Radiation on Human Myeloperoxidase: Reaction With Hydrated Electrons

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] Myeloperoxidase (MPO) is a myeloid-lineage restricted enzyme largely expressed in the azurophilic granules of neutrophils. It catalyses the formation of reactive oxygen species, mainly hypochlorous acid, contributing to anti-pathogenic defense. Disorders in the production or regulation of MPO may lead to a variety of health conditions, mainly of inflammatory origin, including autoimmune inflammation. We have studied the effect of ionizing radiation on the activity of MPO, as measured by the capacity retained by the enzyme to produce hypochlorous acid as reactive oxygen species after exposure to successive doses of solvated electrons, the strongest possible one-e− reducing agent in water. Chlorination activity was still present after a very high irradiation dose, indicating that radiation damage does not take place at the active site, hindered in the core of MPO structure. Decay kinetics show a dependence on the wavelength, supporting that the process must occur at peripheral functional groups situated on external and readily accessible locations of the enzyme. These results are relevant to understand the mechanism of resistance of our innate anti-pathogenic defense system and also to get insight into potential strategies to regulate MPO levels as a therapeutic target in autoimmune diseases.This work was supported by: the Spanish Ministerio de Ciencia y Tecnología (CTQ2004-00534/BQU), the European Commission through the Access to Large-Scale Scientific Facilities Program (ref 41365), and the regional government of the Xunta de Galicia (Project GPC ED431B 2020/52)Xunta de Galicia; ED431B 2020/5