Nonlinear Research Papers - Academia.edu (original) (raw)

The interaction among structures, their foundations and the soil medium below the foundations alter the actual behaviour of the structure considerably than what is obtained from the consideration of the structure alone. Thus, a reasonably... more

The interaction among structures, their foundations and the soil medium below the foundations alter the actual behaviour of the structure considerably than what is obtained from the consideration of the structure alone. Thus, a reasonably accurate model for the soil-foundation-structure interaction system with computational validity, efficiency and accuracy is needed in improved design of important structures. The present study makes an attempt to gather the possible alternative models available in the literature for this purpose. Emphasis has been given on the physical modeling of the soil media, since it appears that the modeling of the structure is rather straightforward. The strengths and limitations of the models described in a single paper may be of help to the civil engineers to choose a suitable one for their study and design.

Cette these est principalement consacree a l'association des methodes de points interieurs et des techniques de l'optimisation DC et DCA pour resoudre les problemes d'optimisation non convexes de grande taille. La these... more

Cette these est principalement consacree a l'association des methodes de points interieurs et des techniques de l'optimisation DC et DCA pour resoudre les problemes d'optimisation non convexes de grande taille. La these comporte trois parties : la premiere partie est consacree aux techniques d'optimisations locales et s'articule autour des methodes de points interieurs et de la programmation DC. Nous y developpons deux algorithmes. Apres une presentation non exhaustive de la programmation DC, des methodes de points interieurs et des proprietes essentielles de la classe des matrices quasi-definies au chapitre un, nous presentons au chapitre deux un nouvel algorithme base sur une reformulation des conditions d'optimalite de Karush-Kuhn-Tucker. Le troisieme chapitre est consacre a l'integration des techniques d'optimisation DC dans un schema de points interieurs, c'est l'algorithme IPDCA. La seconde partie de la these est consacree aux solutions ...

In this study, we re-examine the PPP hypothesis in the light of the new developments in the unit root testing literature. The recent theoretical findings have pointed out that the real exchange rate series exhibit asymmetric nonlinear... more

In this study, we re-examine the PPP hypothesis in the light of the new developments in the unit root testing literature. The recent theoretical findings have pointed out that the real exchange rate series exhibit asymmetric nonlinear behavior. A unit root test applied to analyze the PPP hypothesis therefore, should also take into account this asymmetry inherent in the real exchange rate. Different unit root tests that consider the presence of these data features have been developed in the time series literature. However, a true attempt to test the PPP hypothesis should take a panel data approach. To this end, we propose a nonlinear heterogeneous panel unit root test where the alternative hypothesis allows for symmetric or asymmetric exponential smooth transition autoregressive nonlinearity and provide its finite sample properties. We apply our test to the real exchange rates of the 15 European Union countries against the US dollar. While the results of the linear and symmetric nonlinear heterogeneous panel unit root tests are against the PPP hypothesis, the asymmetric nonlinear heterogeneous panel test that we propose gives support for the PPP hypothesis as expected. Therefore, the conclusions drawn from the linear panel unit root tests or the nonlinear panel unit root tests that do not take asymmetry into account might be misleading.

The upwind finite volume element method based on straight triangular prism partition is put forward for the nonlinear convection-diffusion problems. Some techniques, such as calculus of variations, commutating operator and prior... more

The upwind finite volume element method based on straight triangular prism partition is put forward for the nonlinear convection-diffusion problems. Some techniques, such as calculus of variations, commutating operator and prior estimates, are adopted. Optimal order error estimate in L 2 is derived to determine the error in approximate solution. Numerical experiment shows that the method is effective for avoiding numerical diffusion and nonphysical oscillations and reducing work time.

In this paper a nonlinear dynamic PDE formulation for a pipe string suspended from a pipelay vessel to the seabed in a pipelay operation is developed. This model extends a three-dimensional beam model capable of undergoing finite... more

In this paper a nonlinear dynamic PDE formulation for a pipe string suspended from a pipelay vessel to the seabed in a pipelay operation is developed. This model extends a three-dimensional beam model capable of undergoing finite extension, shearing, twist and bending, to apply for marine applications by adding the effects of restoring forces, hydrodynamic drag and seabed interaction. The model is validated against the natural catenary equation and the FEM code RIFLEX. The model is extended to include the pipelay vessel dynamics by applying a potential theory formulation of a surface vessel, suited for dynamic positioning and low speed maneuvering, as a boundary condition for the PDE. This system is found to be input-output passive and stable. Pipeline installation applications where the presented model is suited are e.g., analysis and simulation of the installation operation, operability analysis, hardware-in-the-loop (HIL) testing for vessel control systems, and automation of the pipelay operation.

A generalized minimum variance control law is derived for the control of nonlinear, possibly time-varying, multi-variable systems. The solution for the tracking and feedback/feedforward control law was obtained in the time-domain using a... more

A generalized minimum variance control law is derived for the control of nonlinear, possibly time-varying, multi-variable systems. The solution for the tracking and feedback/feedforward control law was obtained in the time-domain using a nonlinear operator representation of the process. The cost index involves both error and control signal costing terms and is normally quadratic but may also involve nonlinear functions. The feedback controller obtained is simple to implement and includes an internal model of the process. The tracking controller can include future reference change information, providing a predictive control capability. In one form the compensator might be considered a nonlinear version of the Smith Predictor that has feedforward action.

Background Nonlinear relationships are common in the environmental discipline. Spreadsheet packages such as Microsoft Excel come with an add-on for nonlinear regression, but parameter uncertainty estimates are not yet available. The... more

Background Nonlinear relationships are common in the environmental discipline. Spreadsheet packages such as Microsoft Excel come with an add-on for nonlinear regression, but parameter uncertainty estimates are not yet available. The purpose of this paper is to use Monte Carlo and bootstrap methods to estimate nonlinear parameter uncertainties with a Microsoft Excel spreadsheet. As an example, uncertainties of two parameters (α and n) for a soil water retention curve are estimated. Results The fitted parameters generally do not follow a normal distribution. Except for the upper limit of α using the bootstrap method, the lower and upper limits of α and n obtained by these two methods are slightly greater than those obtained using the SigmaPlot software which linearlizes the nonlinear model. Conclusions Since the linearization method is based on the assumption of normal distribution of parameter values, the Monte Carlo and bootstrap methods may be preferred to the linearization method.

Financial instruments are known to exhibit abrupt and dramatic changes in behaviour. This paper investigates the relative efficacy of two-regime threshold autoregressive (TAR) models and smooth threshold autoregressive (STAR) models,... more

Financial instruments are known to exhibit abrupt and dramatic changes in behaviour. This paper investigates the relative efficacy of two-regime threshold autoregressive (TAR) models and smooth threshold autoregressive (STAR) models, applied successfully to econometric dynamics, in the finance domain. The nature of this class of models is explored in relation to the conventional linear modeling approach, with reference to simulated data and real stock return indices.

The interaction among structures, their foundations and the soil medium below the foundations alter the actual behaviour of the structure considerably than what is obtained from the consideration of the structure alone. Thus, a reasonably... more

The interaction among structures, their foundations and the soil medium below the foundations alter the actual behaviour of the structure considerably than what is obtained from the consideration of the structure alone. Thus, a reasonably accurate model for the soil-foundation-structure interaction system with computational validity, efficiency and accuracy is needed in improved design of important structures. The present study makes an attempt to gather the possible alternative models available in the literature for this purpose. Emphasis has been given on the physical modeling of the soil media, since it appears that the modeling of the structure is rather straightforward. The strengths and limitations of the models described in a single paper may be of help to the civil engineers to choose a suitable one for their study and design.

In this study, the effect of foundation soil stiffness on the seismic performance of integral bridges (IBs) is investigated. For this purpose, nonlinear structural models of a two-span IB with four different foundation soil stiffness... more

In this study, the effect of foundation soil stiffness on the seismic performance of integral bridges (IBs) is investigated. For this purpose, nonlinear structural models of a two-span IB with four different foundation soil stiffness types (loose, medium, medium-dense and dense sands) are built. In the nonlinear structural models, nonlinear soil-structure interaction including free-field effects is considered. Then, the nonlinear time history analyses of the IB models are conducted using a set of ground motions with various intensities. The analyses results reveal that foundation soil stiffness has significant effects on the seismic performance of IBs, particularly under large-intensity earthquakes. Stiffer foundation soils are found to produce smaller maximum absolute displacement in the deck of IBs, especially in the case of large-intensity earthquakes. This is mainly due to the larger foundation flexibility in the case of soft soil conditions producing larger deck displacements. For the bearings, however, because of their large flexibility, the difference between the bearing displacements for various foundation soil stiffness conditions is negligible. Furthermore, for IBs built on soft soil conditions, the pier columns and steel H piles are observed to experience less damage (better performance) in the case of a potential earthquake.

A study of an existing B-pillar was conducted to examine the changes required to increase the lateral load carrying capability by a factor of ten. A finite element optimization package was used to adjust the geometric and material... more

A study of an existing B-pillar was conducted to examine the changes required to increase the lateral load carrying capability by a factor of ten. A finite element optimization package was used to adjust the geometric and material characteristics simultaneously while minimizing weight. The results show that the weight and cost necessary for the ten-fold improvement in lateral load carrying capability were very low. Further, the results illustrate how structural design optimization with finite element modeling can be effectively utilized to create cost effective elements for use in an integrated occupant protection system.

Nonlinear power-type failure envelopes of the form τ = (a + bσ ) n have been examined in this paper. It is shown that equations for which 0 < n < 1/2 are legitimate failure envelopes provided that 'a' is greater than some function of 'b'... more

Nonlinear power-type failure envelopes of the form τ = (a + bσ ) n have been examined in this paper. It is shown that equations for which 0 < n < 1/2 are legitimate failure envelopes provided that 'a' is greater than some function of 'b' contrary to earlier assertions. The principal stress σ 1 -σ 3 relations corresponding to these laws have been derived explicitly for the quadratic law (n = 1/ 2) and implicitly for n =1/3, 2/3, 3/4. For other 'n' values a numerical algorithm for deducing the principal stress relations has been given. The procedure for evaluating the parameters 'a' and 'b' from triaxial test data for a specified 'n' value is presented in detail and it parallels Baker's earlier effort. Almost all previous studies on non-linearity have concentrated on its effect on the factors of safety of slopes. This study provides a numerical method for evaluating the earth pressures on smooth retaining walls, under plane strain conditions, for the case n  1/2. When n = 1/2 closed-form equations, that are non-existent in the literature, have been derived for both the earth pressures and the slip surfaces in two-dimensional plane strain active and passive stress states. A new explicit formula is presented for the depth of tension cracks in plastic soils for n = 1/2 while new implicit formulas are developed for n =1/3, 2/3, 3/4. The assumed value of this depth has a profound influence on the calculated factor of safety of a slope. Existing Rankine, Bell and Coulomb formulas over-estimate the passive resistance of geomaterial and this study shows that the use of a non-linear law predicts more realistic reduced values of passive resistance. Therefore, the factor of safety of two or more hitherto applied to passive resistance in the design of embedded walls can now be reduced to a lower value. A computer program in QBASIC 4.5 has been included for automatically determining the best 'n' value that matches the triaxial test data together with the associated 'a' and 'b' and also for doing the rest of the calculations rapidly. As a consequence, a best-fit non-linear power-type envelope can now be fitted effortlessly to the Hoek-Brown criterion. ________________________________________________________________________________________ has been the nonlinear equation of choice for analyzing the stability of rock masses and has been used by numerous investigators for analyzing stability of rock slopes . Considerable difficulty is encountered when Hoek-Brown equation is used directly in strength-reduction finite element type of slope stability analysis ) hence it has been common to obtain its M-C equivalent. This approximation can have dire consequences on the calculated factors of safety . shows that the power-type failure envelope τ = (a + bσ ) n provides an excellent fit to the transformation of the Hoek-Brown criterion to the σ-τ plane and describes the procedure for determining the coefficients 'a' and 'b' . The routine for doing the latter was coded using Mathematica software that is not easily accessible.

The use of finite element modeling design tools provides the ability to evaluate vehicle structural characteristics relatively inexpensively and expeditiously. The application of FEM early in the conceptual design phase to evaluate safety... more

The use of finite element modeling design tools provides the ability to evaluate vehicle structural characteristics relatively inexpensively and expeditiously. The application of FEM early in the conceptual design phase to evaluate safety risks and identify problem areas prior to design restrictions being imposed provides an important mechanism by which to reduce overall life cycle costs. The development of crashworthiness envelopes is described, wherein a library of crash configurations, representative obstacles and fleet vehicles are used with the finite element model of a subject vehicle to determine occupant response measures of the range of crash conditions, occupant sizes, seating positions. Illustration of the crashworthiness envelopes is presented.

Based on a non-linear stability model, analytical solutions are derived for simply supported beam-column elements with bi-symmetric I sections under combined bending and axial forces. An unique compact closed-form is used for some... more

Based on a non-linear stability model, analytical solutions are derived for simply supported beam-column elements with bi-symmetric I sections under combined bending and axial forces. An unique compact closed-form is used for some representative load cases needed in design. It includes first-order bending distribution, load height level, pre-buckling deflection effects and presence of axial loads. The proposed solutions are validated by recourse to non-linear FEM software where shell elements are used in mesh process. The agreement of the proposed solutions with bifurcations observed on non-linear equilibrium paths is good. It is proved that classical linear stability solutions underestimate the real resistance of such element in lateral buckling stability especially for I section with large flanges. Numerical study of incidence of axial forces on lateral buckling resistance of redundant beams is carried out. When axial displacements of a beam are prevented important tension axial forces are generated in the beam. This results in important reduction of displacements and for some sections, the beam behaviour becomes non-linear without any bifurcation. r

A persistent challenge in the design of composite materials is the ability to fabricate materials that simultaneously display high stiffness and high loss factors for the creation of structural elements capable of passively suppressing... more

A persistent challenge in the design of composite materials is the ability to fabricate materials that simultaneously display high stiffness and high loss factors for the creation of structural elements capable of passively suppressing vibro-acoustic energy. Relevant recent research has shown that it is possible to produce composite materials whose macroscopic mechanical stiffness and loss properties surpass those of conventional composites through the addition of trace amounts of materials displaying negative stiffness (NS) induced by phase transformation [R. S. Lakes, et al., Nature, 410, pp. 565-567, (2001)]. The present work investigates the ability to elicit NS behavior without employing physical phenomena such as inherent nonlinear material behavior (e.g., phase change or plastic deformation) or dynamic effects, but rather the controlled buckling of small-scale structural elements, metamaterials, embedded in a continuous viscoelastic matrix. To illustrate the effect of these buckled elements, a nonlinear hierarchical multiscale material model is derived which estimates the macroscopic stiffness and loss of a composite material containing pre-strained microscale structured inclusions. The nonlinear multiscale model is then utilized in a set-based hierarchical design approach to explore the design space over a wide range of inclusion v geometries. Finally, prototype NS inclusions are fabricated using an additive manufacturing technique and tested to determine quasi-static inclusion stiffness which is compared with analytical predictions.

It has been shown recently that, if the formulations for attacking structural analysis problems are carried on by starting from the minimum energy principle, than the equilibrium problems become optimization problems instead of root... more

It has been shown recently that, if the formulations for attacking structural analysis problems are carried on by starting from the minimum energy principle, than the equilibrium problems become optimization problems instead of root finding problems. Then a technique is developed by combining this formulation together with meta-heuristic algorithms. The emerging method, called "Total Potential Optimization using Meta-heuristic Algorithms" (TPO/MA), is shown to be fortunately able to handle linear and nonlinear structural analysis problems with no special measures and in a black-box manner. The formulation for this new method is given in different forms in what follows, with emphasis on using Ant Colony Optimization (ACO) as the meta-heuristic algorithm chosen to be applied as the technique to optimize the total potential of the system. The study made it possible the emergence of a new way of solving optimization problems with continuous variables by ACO which can be called as Ant Colony Optimization with Increasing Digits (ACO/ID).

Cylindrical compression spring behavior has been described in the literature using an efficient analytical model. Conical compression spring behavior has a linear phase but can also have a nonlinear phase. The rate of the linear phase can... more

Cylindrical compression spring behavior has been described in the literature using an efficient analytical model. Conical compression spring behavior has a linear phase but can also have a nonlinear phase. The rate of the linear phase can easily be calculated but no analytical model exists to describe the nonlinear phase precisely. This nonlinear phase can only be determined by a discretizing algorithm. The present paper presents analytical continuous expressions of length as a function of load and load as a function of length for a constant pitch conical compression spring in the nonlinear phase. Whal’s basic cylindrical compression assumptions are adopted for these new models (Wahl, A. M., 1963, Mechanical Springs, Mc Graw-Hill, New York). The method leading to the analytical expression involves separating free and solid/ground coils, and integrating elementary deflections along the whole spring. The inverse process to obtain the spring load from its length is assimilated to solve...

Computational models are increasingly being used for the dynamic analysis of structures with nonlinear or uncertain behavior, such as cables in stayed bridges, which nowadays are progressively more used as an alternative for long span and... more

Computational models are increasingly being used for the dynamic analysis of structures with nonlinear or uncertain behavior, such as cables in stayed bridges, which nowadays are progressively more used as an alternative for long span and slim structures. In this work, a 3D nonlinear model is described to evaluate the wind dynamic effects on cables for this type of bridges under different scenarios, but also for health monitoring and structural simulation to guarantee performance, evaluate load capacity and estimate life prediction. Fatigue is one of the most relevant and complex failure causes in highway bridges, particularly on the anchorage elements of the cables in stayed bridges; where dampers may be used to minimize the dynamic behavior of the structure and reduce fatigue damage. With this nonlinear simulation model, different damper locations and configurations are evaluated to find the optimal position. A feasibility function is used as a weighting function to take into account the damper's size and design. Analysis is particularly focused for a real cable stayed bridge in the state of Veracruz in México.

The use of finite element modeling design tools provides the ability to evaluate vehicle structural characteristics relatively inexpensively and expeditiously. The.application of FEM early in the conceptual design phase to evaluate safety... more

The use of finite element modeling design tools provides the ability to evaluate vehicle structural characteristics relatively inexpensively and expeditiously. The.application of FEM early in the conceptual design phase to evaluate safety risks and identify problem areas prior to design restrictions being imposed provides an important mechanism by which to reduce overall life cycle costs. The development of crashworthiness envelopes is described, wherein a library of crash configurations, representative obstacles and fleet vehicles are used with the finite element model of a subject vehicle to determine occupant response measures of the range of crash conditions, occupant sizes, seating positions. Illustration of the crashworthiness envelopes is presented.

We documented that the mapping of the fractal dimension of the backscattered Ground Penetrating Radar traces (Fractal Dimension Mapping, FDM) accomplished over heterogeneous agricultural fields gives statistically sound combined... more

We documented that the mapping of the fractal dimension of the backscattered Ground Penetrating Radar traces (Fractal Dimension Mapping, FDM) accomplished over heterogeneous agricultural fields gives statistically sound combined information about the spatial distribution of Andosol' dielectric permittivity, volumetric and gravimetric water content, bulk density, and mechanical resistance under seven different management systems. The roughness of the recorded traces was measured in terms of a single number H , the Hurst exponent, which integrates the competitive effects of volumetric water content, pore topology and mechanical resistance in space and time. We showed the suitability to combine the GPR traces fractal analysis with routine geostatistics (kriging) in order to map the spatial variation of soil properties by nondestructive techniques and to quantify precisely the differences under contrasting tillage systems. Three experimental plots with zero tillage and 33, 66 and 100% of crop residues imprinted the highest roughness to GPR wiggle traces (mean H R/S =0.15), significantly different to Andosol under conventional tillage (H R/S =0.47).

An organization has to make the right decisions in time depending on demand information to enhance the commercial competitive advantage in a constantly fluctuating business environment. Therefore, estimating the demand quantity for the... more

An organization has to make the right decisions in time depending on demand information to enhance the commercial competitive advantage in a constantly fluctuating business environment. Therefore, estimating the demand quantity for the next period most likely appears to be crucial. Manufacturing companies consider forecasting a crucial process for effectively guiding several activities, and research has devoted particular attention to this issue. The objective of the paper is to propose a new forecasting mechanism which is modeled by integrating Fuzzy Delhi Method (FDM) with Artificial Neural Network (ANN) techniques to manage the demand with incomplete information. Artificial neural networks has been applied as it is capable to model complex, nonlinear processes without having to assume the form of the relationship between input and output variables. The effectiveness of the proposed approach to the demand forecasting issue is demonstrated for a 20/25 MVA Distribution Transformer from Energypac Engineering Limited, a leading power engineering company of Bangladesh.

We survey some of the rich history of control over the past century with a focus on the major milestones in adaptive systems. We review classic methods and examples in adaptive linear systems for both control and... more

We survey some of the rich history of control over the past century with a focus on the major milestones in adaptive systems. We review classic methods and examples in adaptive linear systems for both control and observation/identification. The focus is on linear plants to facilitate understanding, but we also provide the tools necessary for many classes of nonlinear systems. We discuss practical issues encountered in making these systems stable and robust with respect to additive and multiplicative uncertainties. We discuss various perspectives on adaptive systems and their role in various fields. Finally, we present some of the ongoing research and expose problems in the field of adaptive control.

This paper describes the design of an adaptive controller based on model reference adaptive PID control (MRAPIDC) to stabilize a two-tank process when large variations of parameters and external disturbances affect the closed-loop system.... more

This paper describes the design of an adaptive controller based on model reference adaptive PID control (MRAPIDC) to stabilize a two-tank process when large variations of parameters and external disturbances affect the closed-loop system. To achieve that, an innovative structure of the adaptive PID controller is defined, an additional PI is designed to make sure that the reference model produces stable output signals and three adaptive gains are included to guarantee stability and robustness of the closed-loop system. Then, the performance of the model reference adaptive PID controller on the behaviour of the closed-loop system is compared to a PI controller designed on MATLAB when both closed-loop systems are under various conditions. The results demonstrate that the MRAPIDC performs significantly better than the conventional PI controller. Keywords: Adaptive Linearization MIT MRAPIDC Nonlinear Parameters Stability This is an open access article under the CC BY-SA license. 1. INTRODUCTION Adaptive control of uncertain processes has become more and more important in industry. Adaptive controllers differ from ordinary ones, because their parameters are variable, and there is a mechanism for adjusting these parameters online based on signals in the system [1]. The design of an adaptive PI controller to stabilize a mass damper-spring system under parameters' uncertainties was proposed in [2]. The designed adaptive PI controller adjusts to parameters' variations, and the output of the process follows the set points, regardless of the values of the parameters. But it does not guarantee stability when external disturbances and large variations of parameters occur. In [3], the design of a PID controller on MATLAB to maintain the level of liquid constant in a coupled-tank system (CTS) was proposed. The control parameters were found using the trial and error methodology and the results were analysed in MATLAB/Simulink environments. Proportional (P), proportional integral (PI), proportional derivative (PD) and proportional integral derivative (PID) controllers were applied on the process and their performances were compared to select the most suitable control solution. The PID controller showed superior results, but it did not guarantee stability to disturbances and variations of plant parameters. Adaptive controllers, as opposed to conventional constant gain controllers (PID controllers), are very effective in handling situations where the variations of parameters and environmental changes are very frequent with the application of model reference adaptive control scheme in a first order system [4].

In this work, it is shown that dc voltages may be measured via a capacitive interface, provided that the capacitance between the measurement system and the dc voltage source being measured is nonlinearized. This nonlinearization is... more

In this work, it is shown that dc voltages may be measured via a capacitive interface, provided that the capacitance between the measurement system and the dc voltage source being measured is nonlinearized. This nonlinearization is achieved by the addition of a nonlinear capacitor in series with the coupling capacitance. Two types of nonlinear capacitor are used-multilayer ceramics and varicap diodes. Currently available multilayer ceramics have a larger value than desired but prove the concept, while the small capacitance of the varicap diode allows measurement on real wires. Results show that over a low voltage range (−8 V to +8 V), the voltage on a conductor can be measured if the coupling capacitance between source and electrode is larger than 20 pF, which equates to an electrode length of 5 cm when wire compliant with MIL-W-81044-22 is used. Detection is performed by momentarily applying a voltage at a node within the measurement system, then measuring the time it takes for this voltage to decay to a threshold level-the capacitive nonlinearity causes this time delay to be dependent upon the dc input voltage whose value is being measured.

Terrestrial heat flow is considered an important parameter in studying the regional geotectonic and geodynamic evolutionary history of any region. However, its distribution is still very uneven. There is hardly any information available... more

Terrestrial heat flow is considered an important parameter in studying the regional geotectonic and geodynamic evolutionary history of any region. However, its distribution is still very uneven. There is hardly any information available for many geodynamically important areas. In the present study, we provide a methodology to predict the surface heat flow in areas, where detailed seismic information such as depth to the lithosphere-asthenosphere boundary (LAB) and crustal structure is known. The tool was first tested in several geotectonic blocks around the world and then used to predict the surface heat flow for the 2001 Bhuj earthquake region of Kachchh, India, which has been seismically active since historical times and where aftershock activity is still continuing nine years after the 2001 main event. Surface heat flow for this region is estimated to be about 61.3 mW m-2. Beneath this region, heat flow input from the mantle as well as the temperatures at the Moho are quite high at around 44 mW m-2 and 630 °C, respectively, possibly due to thermal restructuring of the underlying crust and mantle lithosphere. In absence of conventional data, the proposed tool may be used to estimate a first order heat flow in continental regions for geotectonic studies, as it is also unaffected by the subsurface climatic perturbations that percolate even up to 2000 m depth.

The main point of this paper is to identify the key features and load transfer mechanisms controlling friction fatigue of piles under cyclic loading. Numerical modeling makes use of an advanced elastoplastic state dependent constitutive... more

The main point of this paper is to identify the key features and load transfer mechanisms controlling friction fatigue of piles under cyclic loading. Numerical modeling makes use of an advanced elastoplastic state dependent constitutive model, the ECP model, also known as Hujeux's model. Therefore, the cyclic loading simulations allowed the identification of three levels of friction degradation, depending on the amplitude of the previous maximum load cycle. Furthermore, the analysis also offers useful insights regarding the modification of the pile static resistance once it has been cyclically loaded. All analyses are carried out considering nondisplacement piles in Toyoura sand.

In this study we analyzed the Newtonian equation with memory. One physical model possessing memory effect is analyzed in detail. The fractional generalization of this model is investigated and the exact solutions within Caputo and... more

In this study we analyzed the Newtonian equation with memory. One physical model possessing memory effect is analyzed in detail. The fractional generalization of this model is investigated and the exact solutions within Caputo and Riemann-Liouville fractional derivatives are reported.

A semi-active control method for a seismically excited nonlinear benchmark building equipped with a magnetorheological (MR) damper is presented and evaluated. A linear quadratic Gaussian (LQG) controller is designed to estimate the... more

A semi-active control method for a seismically excited nonlinear benchmark building equipped with a magnetorheological (MR) damper is presented and evaluated. A linear quadratic Gaussian (LQG) controller is designed to estimate the optimal control force. The required voltage for the MR damper to produce the control force estimated by LQG controller is calculated by a neural network predictive control algorithm (NNPC). The LQG controller and the NNPC are linked to control the structure. The coupled LQG and NNPC system are then used to train a semi-active neuro-controller designated as SANC, which produces the necessary control voltage that actuates the MR damper. The effectiveness of the NNPC and SANC is illustrated and verified using simulated response of a 3-story full-scale, nonlinear, seismically excited, benchmark building excited by several historical earthquake records. The semi-active system using the NNPC algorithm is compared with the performances of passive as well as active and clipped optimal control (COC) systems, which are based on the same nominal controller as is used in the NNPC algorithm. The results demonstrate that the SANC algorithm is quite effective in seismic response reduction for wide range of motions from moderate to severe seismic events, compared with the passive systems and performs better than active and COC systems. of the reactive velocity and the issued voltage as described in Equations (2)-(5). The damper velocity is the same as the relative velocity of the floors the damper is connected to. This neural network model is denoted as NNMR ( ) and is trained ( ) using input-output data generated analytically using the simulated MR model based on Equations (2)-(5). The NNMR calculates the damper forces based on the current and few previous histories of measured velocity, voltage signals, and damper forces.

The design of cylindrical metal silos and tanks is often controlled by considerations of buckling under axial compression. Whilst the effects of geometric imperfections on the buckling strength have been extensively explored, few studies... more

The design of cylindrical metal silos and tanks is often controlled by considerations of buckling under axial compression. Whilst the effects of geometric imperfections on the buckling strength have been extensively explored, few studies have explored the effects of defects in the boundary conditions and the effects of residual stresses have received even less attention. This paper investigates the initiation and development of imperfections caused by local differential settlement at the supported base and their effect on the elastic buckling of a thin cylindrical shell under axial compression. The shells were treated as initially perfect with perfect support, but developing geometric imperfections and residual stresses as a consequence of local displacement at the supported edge and with residual stresses consistent with the induced geometric imperfections. The results raise interesting questions concerning the criteria of failure and appropriate tolerance measurements for constructed cylindrical shells.

One of the central trends in the optimization community over the past several years has been the steady improvement of general-purpose solvers. A logical next step in this evolution is to combine mixed integer linear programming, global... more

One of the central trends in the optimization community over the past several years has been the steady improvement of general-purpose solvers. A logical next step in this evolution is to combine mixed integer linear programming, global optimization, and constraint programming in a single system. Recent research in the area of integrated problem solving suggests that the right combination of different technologies can simplify modeling and speed up computation substantially. In this paper we address this goal by presenting a general purpose solver, SIMPL, that achieves low-level integration of solution techniques with a high-level modeling language. We apply SIMPL to production planning, product configuration, and machine scheduling problems on which customized integrated methods have shown significant computational advantage. We find that SIMPL can allow the user to obtain the same or greater advantage by writing concise models for a general-purpose solver. We also solve pooling, distillation, and heat exchanger network design problems to demonstrate how global optimization fits into SIMPL's framework.

Received Mar 31, 2020 Revised Jun 20, 2020 Accepted Jul 6, 2020 This paper describes the design of an adaptive controller based on model reference adaptive PID control (MRAPIDC) to stabilize a two-tank process when large variations of... more

Received Mar 31, 2020 Revised Jun 20, 2020 Accepted Jul 6, 2020 This paper describes the design of an adaptive controller based on model reference adaptive PID control (MRAPIDC) to stabilize a two-tank process when large variations of parameters and external disturbances affect the closed-loop system. To achieve that, an innovative structure of the adaptive PID controller is defined, an additional PI is designed to make sure that the reference model produces stable output signals and three adaptive gains are included to guarantee stability and robustness of the closed-loop system. Then, the performance of the model reference adaptive PID controller on the behaviour of the closed-loop system is compared to a PI controller designed on MATLAB when both closed-loop systems are under various conditions. The results demonstrate that the MRAPIDC performs significantly better than the conventional PI controller.

The field of chaotic synchronization has grown considerably since its advent in 1990. Several subdisciplines and ''cottage industries'' have emerged that have taken on bona fide lives of their own. Our purpose in this paper is to collect... more

The field of chaotic synchronization has grown considerably since its advent in 1990. Several subdisciplines and ''cottage industries'' have emerged that have taken on bona fide lives of their own. Our purpose in this paper is to collect results from these various areas in a review article format with a tutorial emphasis. Fundamentals of chaotic synchronization are reviewed first with emphases on the geometry of synchronization and stability criteria. Several widely used coupling configurations are examined and, when available, experimental demonstrations of their success ͑generally with chaotic circuit systems͒ are described. Particular focus is given to the recent notion of synchronous substitution-a method to synchronize chaotic systems using a larger class of scalar chaotic coupling signals than previously thought possible. Connections between this technique and well-known control theory results are also outlined. Extensions of the technique are presented that allow so-called hyperchaotic systems ͑systems with more than one positive Lyapunov exponent͒ to be synchronized. Several proposals for ''secure'' communication schemes have been advanced; major ones are reviewed and their strengths and weaknesses are touched upon. Arrays of coupled chaotic systems have received a great deal of attention lately and have spawned a host of interesting and, in some cases, counterintuitive phenomena including bursting above synchronization thresholds, destabilizing transitions as coupling increases ͑short-wavelength bifurcations͒, and riddled basins. In addition, a general mathematical framework for analyzing the stability of arrays with arbitrary coupling configurations is outlined. Finally, the topic of generalized synchronization is discussed, along with data analysis techniques that can be used to decide whether two systems satisfy the mathematical requirements of generalized synchronization. © 1997 American Institute of Physics. ͓S1054-1500͑97͒02904-2͔

Chatter is an instability condition in machining processes characterized by nonlinear behavior, such as the presence of limit cycles, jump phenomenon, subcritical Hopf and period doubling bifurcations. Although the use of nonlinear... more

Chatter is an instability condition in machining processes characterized by nonlinear behavior, such as the presence of limit cycles, jump phenomenon, subcritical Hopf and period doubling bifurcations. Although the use of nonlinear techniques has provided a better understanding of chatter, neither a unifying model nor an exact solution has yet been developed due to the intricacy of the problem. This work proposes a weakly nonlinear model with square and cubic terms in both structural stiffness and regenerative terms, to represent self-excited vibrations in machining. An approximate solution is derived by using the method of multiple scales. In addition, a qualitative analysis of the effect of the nonlinear parameters on the stability of the system is performed. The structural cubic term gives a better representation of the nonlinear behavior, whereas the square term represents a distant attractor in the stability chart. Instability due to subcritical Hopf bifurcations is established in terms of the eigenvalues of the model in normal form. An important contribution of this analysis is the representation of hysteresis in terms of new lobes within the conventional stability limits, useful in restoring stability. This analysis leads to a further understanding of the nonlinear behavior of regenerative chatter.

In this paper we present a complex network model based on a heterogeneous preferential attachment scheme to quantify the structure of porous soils. Under this perspective pores are represented by nodes and the space for the flow of fluids... more

In this paper we present a complex network model based on a heterogeneous preferential attachment scheme to quantify the structure of porous soils. Under this perspective pores are represented by nodes and the space for the flow of fluids between them is represented by links. Pore properties such as position and size are described by fixed states in a metric space, while an affinity function is introduced to bias the attachment probabilities of links according to these properties. We perform an analytical study of the degree distributions in the soil model and show that under reasonable conditions all the model variants yield a multiscaling behavior in the connectivity degrees, leaving a empirically testable signature of heterogeneity in the topology of pore networks. We also show that the power-law scaling in the degree distribution is a robust trait of the soil model and analyze the influence of the parameters on the scaling exponents. We perform a numerical analysis of the soil model for a combination of parameters corresponding to empirical samples with different properties, and show that the simulation results exhibit a good agreement with the analytical predictions.

In real time environment most of the industrial processes are posses 'n' number of inputs and outputs. Due to intrinsically nonlinear nature and interactions existing among the loops, it is very complicated to design a control strategy... more

In real time environment most of the industrial processes are posses 'n' number of inputs and outputs. Due to intrinsically nonlinear nature and interactions existing among the loops, it is very complicated to design a control strategy for multivariable processes. Tuning of Conventional PID controller for multivariable process is too difficult. This paper utilizes the concept of IMC to determine parameters multivariable PID controller. A case study was included to describe the effectiveness of proposed method.

The response of an electrochemical reacting system to potential perturbations during electrochemical impedance spectrum measurement is investigated using numerical simulation. Electrochemical metal dissolution via an adsorbed intermediate... more

The response of an electrochemical reacting system to potential perturbations during electrochemical impedance spectrum measurement is investigated using numerical simulation. Electrochemical metal dissolution via an adsorbed intermediate species is analyzed and it is shown that applying the potential perturbation causes the average surface coverage to drift. For high frequency perturbations, the final value of the average surface coverage depends mainly on the kinetic parameters and the amplitude of the applied perturbation. Acquiring the data during the first few cycles of perturbations leads to an incorrect calculation of the impedance, particularly for large amplitude perturbations. Repeating the experiments will not identify this drift, while Kramers–Kronig Transform (KKT) can successfully detect this problem. The correct experimental methodology to overcome this effect and obtain the impedance spectra is also described. Another reaction with two adsorbed intermediates is also investigated and it is shown that in certain cases, the violations of linearity criteria can also be detected by KKT. The results illustrate the importance of validating the impedance data with KKT before further analysis.► EIS response of reaction via adsorbed intermediates analyzed. Numerical simulation. ► Surface coverage drifts during measurement. Analytical solution confirms results. ► Correct experimental strategy to overcome the drift effect identified. ► Kramers–Kronig Transforms identify the drift and in certain cases, nonlinearities.

The complexity in the tsunami phenomenon makes the available warning systems not much effective in the practical situations. The problem arises due to the time lapsed in the data transfer, processing and modeling. The modeling and... more

The complexity in the tsunami phenomenon makes the available warning systems not much effective in the practical situations. The problem arises due to the time lapsed in the data transfer, processing and modeling. The modeling and simulation needs the input fault geometry and mechanism of the earthquake. The estimation of these parameters and other aprior information increases the utilized time for making any warning. Here, the wavelet analysis is used to identify the tsunamigenesis of an earthquake. The frequency content of the seismogram in time scale domain is examined using wavelet transform. The energy content in high frequencies is calculated and gives a threshold for tsunami warnings. Only first few minutes of the seismograms of the earthquake events are used for quick estimation. The results for the earthquake events of Andaman Sumatra region and other historic events are promising.

The purpose of this paper is to present a new perspective of the linear-nonlinear thinking style and its critical role in knowledge management education. Previous works in this field identified linear thinking as being rational, logic and... more

The purpose of this paper is to present a new perspective of the linear-nonlinear thinking style and its critical role in knowledge management education. Previous works in this field identified linear thinking as being rational, logic and analytic, and nonlinear thinking as ...