Simulating discontinuous phenomena affecting robot motion

The paper deals with simulation of mechanical systems affected by discontinuous phenomena. These phenomena involve impulsive events and/or models whose structure changes depending on the values of some system variables. The models of three kinds of these discontinuities (joint with static friction, collisions with rigid environment, bifurcation behavior near kinematic singularities) are given, and a simulation environment, based on the DAE solver DASSL is presented, that also allows efficient simulation of sample-data systems. Some simulation results achieved with the proposed environment are finally presented.     

Nonlinear transient phenomena in saturated porous media

In this report the transient ‘static’ and ‘dynamic’ response of saturated porous medium is analyzed. The saturated porous medium viewed as a two-phase system whose state is described by the stresses, displacements, velocities and accelerations within each phase. The coupled field and constitutive equations based on mixture's theories are presented, and solved numerically by the use of the finite element method. Time integration is achieved by using an implicit/explicit predictor/multicorrector scheme developed by Hughes and co-workers. The procedure allows for a convenient selection of implicit and explicit elements, and for an implicit/explicit split of the various operators appearing in the differential equations. Accuracy and versatility of the proposed procedure are demonstrated by applying it to obtain solution to various dynamic and pseudo-static, one- and two-dimensional initial value problems.     

Simulating free surface problems using Discrete Least Squares Meshless method

A Discrete Least Squares Meshless (DLSM) method is presented here for the simulation of incompressible free surface flows. The governing equations of the mass and momentum conservations are solved in a Lagrangian form using a pressure projection method. Since there are no particles in the outer region of the free surface, the particle density will drop significantly. Free surfaces are, therefore, resolved by tracking particles with highly reduced density. A fully least squares approach is used in both function approximation and the discretization of the governing differential equations in space. The meshless shape functions are derived using the Moving Least Squares (MLS) method of function approximation. The discretized equations are obtained via a discrete least squares method in which the sum of the squared residuals are minimized with respect to unknown nodal parameters. The method enjoys the advantage of producing symmetric, positive definite matrixes for the cases considered. The method can be viewed as a truly meshless method since it does not need any mesh for both field variable approximation and the construction of system matrices. Two free surface problems namely dam break and evolution of a drop with an initial known velocity are solved to test the accuracy of the proposed method. The results show the ability of the proposed method to solve complex fluid dynamic problems with moving free surface boundaries.     

Diagnostics for functional regression via residual processes

Methods of regression diagnostics for functional regression models are developed which relate a functional response to predictor variables that can be multivariate vectors or random functions. For this purpose, a residual process is defined by subtracting the predicted from the observed response functions. This residual process is expanded into functional principal components (FPC), and the corresponding FPC scores are used as natural proxies for the residuals in functional regression models. For the case of a univariate covariate, a randomization test is proposed based on these scores to examine if the residual process depends on the covariate. If this is the case, it indicates lack of fit of the model. Graphical methods based on the FPC scores of observed and fitted functions can be used to complement more formal tests. The methods are illustrated with data from a recent study of Drosophila fruit flies regarding life-cycle gene expression trajectories as well as functional data from a dose-response experiment for Mediterranean fruit flies (Ceratitis capitata).     

Simulating magnetic positive positioning of cryogenic propellants in a transient acceleration field

A computational simulation of magnetic positive positioning (MP²) is developed to model cryogenic propellant reorientation in reduced gravity. Previous efforts have successfully incorporated an electromagnetic field model into an axisymmetric, two-dimensional, incompressible fluid flow model yielding accurate predictions of fluid motion induced by a magnetic field. To simulate MP², a three-dimensional magnetic field and magnetic force model was developed as a feature of a commercially available fluid flow model which has been well validated. The computational tool was then improved upon to model magnetically induced flows in a transient acceleration field. Simulation predictions obtained with the enhanced model are compared to available reduced gravity experiment data. Evidence is presented and conclusions are drawn that support the continued use of the simulation as viable modeling and predictive tool in the continuing study of MP².     

Simulating the seismic response of embankments via artificial neural networks

Geotechnical earthquake engineering may generally be considered as an “imprecise” scientific area due to the unavoidable uncertainties and the simplifications adopted during the design process of geostructures. Therefore, relatively accurate predictions using advanced soft computing (SC) techniques can be tolerated rather than solving a problem conventionally. Artificial neural networks (ANNs), being one of the most popular SC techniques, have been used in many fields of science and technology, as well as, into an increasing number of earthquake engineering applications on structures and infrastructures. In this work the implementation of ANNs is focused on the simulation of the seismic response of a typical embankment. The dynamic response of the embankment is evaluated utilizing the finite-element method, where the nonlinear behavior of the geo-materials can be taken into account by an equivalent-linear procedure. In the present study, this extremely time-consuming process is replaced by properly trained ANNs.     

Multi-focus images fusion via residual generative adversarial network

Multimedia Tools and Applications - Recently, most existing learning-based fusion methods are not fully end-to-end, which still predict the decision map and recover the fused image by the refined...     

Efficient transfer and concentration of energy between explosive dual bubbles via time-delayed interactions

The dynamics of a high heat flux thermal bubble is constrained by the thermal energy carried on the bubble surface right after the bubble formation because of thermal isolation of vapor. This article proposes a way by assigning time delays between dual bubbles to transfer effectively energy from one bubble into the other, thus, breaks energy limitation that one single bubble can usually carry. Experiment result has demonstrated that the useful work as large as 40% can be transferred from one bubble into the other for the ignition time delay set between 2 and 3 μs in a dual bubble system. At the same time, the total extractable useful work in a dual bubble system is 20% higher than twice that of a single-bubble system with the same input heat energy. This phenomenon opens up a new way to transfer or concentrate energies from distributed energy sources with limit energy density into a much higher one for higher power application.     

Performance monitoring of model-predictive controllers via model residual assessment

Model quality is a main factor that affects the control performance of model-based controllers. In this paper, a new closed-loop model assessment approach is proposed to assess model deficiency from routine closed-loop data. The proposed model quality index is a minimum variance benchmark for the model residuals obtainable from closed-loop data. From the feedback invariant principle the disturbance innovations are shown to be unaffected by the feedback controller. Then it is shown that the disturbance innovations can be estimated from closed loop data by an orthogonal projection of the current output onto the space spanned by past outputs, inputs or setpoints. With the estimated disturbance innovations as the benchmark, a model quality index is developed by using the ratio of a quadratic form of model residuals and that of the estimated disturbance innovations. The effectiveness of the proposed methods is demonstrated by simulations.     

Finite element analysis of transient heat conduction application of the weighted residual process

The transient heat conduction problem can be solved by application of Galerkin's method to space as well as time discretization. The formulation corresponds to the procedure known as finite elements in time and space. A linear time expansion leads to a step by step technique which is convergent, consistent and absolutely stable. Several numerical examples are presented using two-dimensional isoparametric elements.     

Action prediction via deep residual feature learning and weighted loss

Multimedia Tools and Applications - Action prediction based on partially observed videos is challenging as the information provided by partial videos is not discriminative enough for...     

Computing on a free tree via complexity-preserving mappings

The relationship between linear lists and free trees is studied. We examine a number of well-known data structures for computing functions on linear lists and show that they can be canonically transformed into data structures for computing the same functions defined over free trees. This is used to establish new upper bounds on the complexity of several query-answering problems.     

Computing on a free tree via complexity-preserving mappings

The relationship between linear lists and free trees is studied. We examine a number of well-known data structures for computing functions on linear lists and show that they can be canonically transformed into data structures for computing the same functions defined over free trees. This is used to establish new upper bounds on the complexity of several query-answering problems.This work was started when the author was at Brown University, Providence, RI. It was partly supported by NSF Grant MCS 83-03925. A preliminary version of this work has appeared in theProceedings of the 25th Annual IEEE Symposium on Foundations of Computer Science, West Palm Beach, FL, October 1984, pp. 358–368.     

Modeling of redox electrochemical MHD and three-dimensional CFD simulations of transient phenomena in microfluidic cells

Computational fluid dynamics simulations of redox electrochemical magneto-hydrodynamics (MHD) covering a large parameter space have been done to establish the effects of redox species concentration, electrode area, and magnetic field strength and orientation on the limiting current. Simulations of milli-electrode and microelectrode systems show similarities and differences between the two. Potential sweep and potential step simulations using time-accurate solution algorithms enabled accurate capture of transient phenomena which is crucial to the development of lab-on-a-chip flow control applications. Power-law correlations reported in previous experimental investigations of milli-electrodes are found to be less accurate for microelectrodes and nano-electrodes suggesting possible effects of multidimensional diffusion. Further, the orientation of the magnetic field in relation to the electrode surface has a strong influence on the flow field. Interesting and complex flow features are observed in the post-processed still images and animations. This work advances redox MHD simulations by incorporating important aspects in the models that were not considered in previous models. Our simulations based on these new models provide new insight into redox electrochemical MHD.     

A new approach for transient response control via characteristic ratio assignment method

This paper proposes a new direct approach to control the transient response of a LTI system. The characteristic of a repeated-pole system is first studied. It can be shown that the step response of this kind of system has no overshoot. μ-scaled characteristic ratios, β _i = μα _i , i = 1, … n, and τ are introduced, where α _i is the principal characteristic ratio and τ is the generalized time constant. It is shown that two parameters, μ and τ, are used to successfully control the overshoot and the transient time of all minimum phase LTI systems. The result shows that the proposed method is comparable to the method proposed by Bhattacharyya [1], but more luminous and simple in approach.     

Fast and robust face recognition via coding residual map learning based adaptive masking

Robust face recognition (FR) is an active topic in computer vision and biometrics, while face occlusion is one of the most challenging problems for robust FR. Recently, the representation (or coding) based FR schemes with sparse coding coefficients and coding residual have demonstrated good robustness to face occlusion; however, the high complexity of l₁-minimization makes them less useful in practical applications. In this paper we propose a novel coding residual map learning scheme for fast and robust FR based on the fact that occluded pixels usually have higher coding residuals when representing an occluded face image over the non-occluded training samples. A dictionary is learned to code the training samples, and the distribution of coding residuals is computed. Consequently, a residual map is learned to detect the occlusions by adaptive thresholding. Finally the face image is identified by masking the detected occlusion pixels from face representation. Experiments on benchmark databases show that the proposed scheme has much lower time complexity but comparable FR accuracy with other popular approaches.     

A normalized ladder form of the residual energy ratio algorithm for PARCOR estimation via projections

In this paper, we give a square-root normalized ladder algorithm for the residual energy ratio (RER) method of PARCOR coefficient estimation. The derivation uses a Hilbert space projection approach similar to that of Lee and Morf, but requires an additional related Hilbert space and its corresponding projection operators. The resulting partial correlation estimates guarantee a stable synthesis filter. In addition, we show how the algorithm may be cast in a form suitable for implementation by a CORDIC processor. Finally, we show how the normalized covariance form corresponds to an RER formulation where the prediction error energies used are chosen properly.     

Chaos control and synchronization via a novel chatter free sliding mode control strategy

In this paper, we propose a novel chatter free sliding mode control (SMC) strategy for chaos control and synchronization to the nonlinear uncertain chaotic systems. A new sort of dynamical sliding mode surface with both integral and differential operators is introduced to divert the discontinuous sign function switch term into the first derivative of the control input; hence a chatter free control input is obtained for the chaotic systems with uncertainties. Based on the Lyapunov stability theory and SMC technique, stability analysis is performed and a theorem serving as designing the chatter free sliding mode control input is also proposed. In the simulation part, first, the results regarding chaos control and synchronization are given to show that the proposed strategy can control the states of the uncertain chaotic systems to desired states with fast speed. In order to show the advantage of eliminating chatter in control input of our method, we give the simulation results performed by traditional SMC and the method proposed recently. Simulation results indicate that this novel chatter free sliding mode control strategy is very effective to chaos control and synchronization.     

Nonlinear vibration of nanobeam with attached mass at the free end via nonlocal elasticity theory

In the present study, nonlinear free and forced vibration of Euler–Bernoulli nanobeam with attached nanoparticle at the free end is investigated based on nonlocal elasticity theory. The effects of the different nonlocal parameters (γ) and mass ratios (α) as well as effects of fixed-free boundary conditions on the vibrations are determined. To obtain the equation of motion of the system, the Hamilton’s principle is employed. The stretching of neutral axis which introduces cubic nonlinearity is included into the equation for deriving nonlinear equation. And also effects of damping and forcing are included into the equations. The approximate solutions of the equations are derived by using the multiple scale method. Fundamental frequencies, frequency shift and mode shapes for the linear problem are estimated for a nonlocal Euler–Bernoulli nanobeam with an attached nanoparticle and graphically represented the frequency shift and mode shapes. Nonlinear frequencies are derived depending on amplitude and phase modulation. Frequency–response curves are drawn for different nonlocal parameters and different modes.

     

Guaranteeing prescribed performance and contact maintenance via an approximation free robot force/position controller

In this paper, we consider the problem of force/position tracking for a robot with revolute joints in compliant contact with a kinematically known planar surface. A novel controller is designed capable of guaranteeing, for an a priori known nonsingular initial robot condition, (i) certain predefined minimum speed of response, maximum steady state error as well as overshoot concerning the force/position tracking errors, (ii) contact maintenance and (iii) bounded closed loop signals. No information regarding either the robot dynamic model or the force deformation model is required and no approximation structures are utilized to estimate them. As the tracking performance is a priori guaranteed irrespectively of the control gains selection, the only concern is to adopt those values that lead to reasonable input torques. Finally, a comparative simulation study on a 6-DOF robot illustrates the performance of the proposed controller.