Tech Science Press
Not a member yet
3972 research outputs found
Sort by
Adaptive Differentiators via Second Order Sliding Mode for a Fixed Wing Aircraft
Get PDFSafety automation of complex mobile systems is a current topic issue in industry and research laboratories, especially in aeronautics. The dynamic models of these systems are nonlinear, Multi-Input Multi-Output (MIMO) and tightly coupled. The nonlinearity resides in the dynamic equations and also in the aerodynamic coefficients’ variability.
This paper is devoted to developing the piloting law based on the combination of the robust differentiator with a dynamic adaptation of the gains and the robust controller via second order sliding mode, by using an aircraft in virtual simulated environments.
To deal with the design of an autopilot controller, we propose an environment framework based on a Software In the Loop (SIL) methodology and we use Microsoft Flight Simulator (FS-2004) as the environment for plane simulation.
The first order sliding mode control may be an appropriate solution to this piloting problem. However, its implementation generates a chattering phenomenon and a singularity problem. To overcome these problems, a new version of the adaptive differentiators for second order sliding modes is proposed and used for piloting.
For the sliding mode algorithm, higher gains values may be used to improve accuracy; however this leads to an amplification of noise in the estimated signals. A good tradeoff between these two criteria (accuracy, robustness to noise ratio) is difficult to achieve. On the one hand, these values must increase the gains in order to derive a signal sweeping of some frequency ranges. On the other hand, low gains values have to be imposed to reduce noise amplification. So, our goal is to develop a differentiation algorithm in order to have a good compromise between error and robustness to noise ratio. To fit this requirement, a new version of differentiators with a higher order sliding modes and a dynamic adaptation of the gains, is proposed: the first order differentiator for the control of longitudinal speed and the second order differentiator for the control of the Euler angles
A Fast Multipole Accelerated Singular Boundary Method for Potential Problems
Get PDFThe singular boundary method (SBM) is a recently-developed meshless boundary collocation method. This method overcomes the well-known fictitious boundary issue associated with the method of fundamental solutions (MFS) while remaining the merits of the later of being truly meshless, integral-free, and easy-to-program. Similar to the MFS, this method, however, produces dense and unsymmetrical coefficient matrix, which although much smaller in size compared with domain discretization methods, requires O(N2) operations in the iterative solution of the resulting algebraic system of equations. To remedy this bottleneck problem for its application to large-scale problems, this paper makes the first attempt to develop a fast multipole SBM (FM-SBM) formulation for two-dimensional (2D) potential problems. The proposed strategy can solve large-scale problems with several millions boundary discretization nodes on a desktop computer
Scaled Boundary Finite Element Method for Thermoelasticity in Voided Materials
Get PDFThe scaled boundary finite element method (SBFEM) is presented to study thermoelastic problems in materials with voids. The SBFEM combines the main advantages of the finite element method (FEM) and the boundary element method (BEM). In this method, only the boundary is discretized with elements leading to a reduction of spatial dimension by one. It reduces computational efforts in mesh generation and CPU. In contrast to the BEM, no fundamental solution is required, which permits to analyze general boundary value problems, where the conventional BEM cannot be applied due to missing fundamental solution. The computational homogenization technique is applied for thermo-mechanical analyses in voided materials. The evolution of the mechanical and thermal fields at the macroscopic level is resolved through the incorporation of the microstructural response. The microstructural analyses are performed on the representative volume element (RVE), where essential physical geometrical information about the microstructural components is included
Factorial Experiment Design in the Front Velocity Modeling Approach Applied to Chromatographic Separation of Glucose and Fructose
Get PDFThis work deals with a statistical approach to the uncertainty propagation analysis when estimating the kinetic mass transfer parameters used to model a chromatographic column in the Simulated Moving Bed. The chromatographic column modeling was performed using the new front velocity approach. The uncertainty propagation analysis of operational factors intervening in the chromatographic process to estimated parameters was made using the response surface methodology. The application of the factorial experimental design allowed us to establish those operational factors showing a greater influence on continuous chromatography. Besides, the chromatographic regions, where factors cause a greater output variation as well as their respective patterns, were determined. The analysis was applied to the separation of glucose and fructose
Least Squares Stochastic Finite Element Method in Structural Stability Analysis of Steel Skeletal Structures<sup>1</sup>
No full textBasic probabilistic characteristics and reliability indices of critical forces for high steel skeletal towers are numerically modeled by using the Stochastic, perturbation-based Finite Element Method. It is implemented together with the Weighted Least Squares Method and compared with the Monte-Carlo simulation as well as with the semi-analytical Probabilistic FEM. The Finite Element Method solution to the stability problem for a full 3D model of a tower accounts for both first and second order effects known from the engineering codes as the so-called P-delta effect. Two different Gaussian input random variables are adopted here – Young modulus of steel as well as principal structural elements thickness – to compare an influence of the material versus the geometrical uncertainty on the overall structural response. The numerical analysis has been carried out with a combination of the FEM engineering program with symbolic algebra software providing WLSM approximation, probabilistic simulation, integration, as well as for the general order Taylor expansion procedures. The reliability indices related to the stability problem are calculated using both the First and the Second Order Reliability Methods and they showed safety margins for the telecommunication towers
A Finite Wavelet Domain Method for the Rapid Analysis of Transient Dynamic Response in Rods and Beams
Get PDFA computationally efficient numerical method is developed for the prediction of transient response in orthotropic rod and beam structures. The method takes advantage of the outstanding properties of compactly supported Daubechies wavelet scaling functions for the spatial approximation of displacements in a finite domain of the structure, hence is termed Finite Wavelet Domain (FWD) method. The basic principles and advantages of the method are presented and the discretization of the equations of motion is formulated for one-dimensional structures. Numerical results for the simulation of propagating guided waves in rods and strips are presented and compared against traditional finite elements
Modular Model Library for Energy System in Lunar Vehicle
Get PDFFor modeling and simulation of energy system in lunar vehicle, there are many special purpose tools along with their models, such as PSIM, EMTP/ATP, could be used. But the models in these tools lack of flexibility and are not open to the end-user. Models developed in one tool can’t be conveniently used in others because of the barriers among these simulators. Usually these models are expressed in an explicit state-space form and their topology gets lost and future extension and reuse of the model is almost impossible. In order to solve those problems, a flexible and extensible energy system model library for lunar vehicle is constructed in this study, based on the Modelica, by the level progressive modeling strategy. Each model in this library is expressed in equation form. It supports reuse of knowledge on different granularities: physical phenomenon, unit model and system model. It is an interface-friendly, accurate, fast PC-based and easily reusable simulating tool which enables end-user to customize and extend the framework to add new functionality or adapt the simulation behavior as required. It also allows new models to be composed programmatically or graphically to form more complex models by invoking the existing components. A solar battery and storage battery model is simulated and the results agree well with the experimental data. At last, a simple energy system model for lunar vehicle is built and calculated using the library and it shows that the level progressive modeling strategy is effective, the framework of the library is reasonable
Elasto-Plastic MLPG Method for Micromechanical Modeling of Heterogeneous Materials
Get PDFIn this study, a truly meshless method based on the meshless local Petrov-Galerkin method is formulated for analysis of the elastic-plastic behavior of heterogeneous solid materials. The incremental theory of plasticity is employed for modeling the nonlinearity of the material behavior due to plastic strains. The well-known Prandtl-Reuss flow rule of plasticity is used as the constitutive equation of the material. In the presented method, the computational cost is reduced due to elimination of the domain integration from the formulation. As a practical example, the presented elastic-plastic meshless formulation is employed for micromechanical analysis of the unidirectional composite material. A quarter of the fiber surrounded in the matrix in a square array is considered as the Representative Volume Element (RVE). The fully bonded fiber-matrix interface condition is assumed and the continuity of displacement and reciprocity of traction are imposed to the interface. A predictor-corrector numerical integration method is used for the solution of the discretized equations of the problem. The numerical results show excellent agreement with the predictions of the finite element analysis
On the Discrete-Analytical Solution Method of the Problems Related to the Dynamics of Hydro-Elastic Systems Consisting of a Pre-Strained Moving Elastic Plate, Compressible Viscous Fluid and RigidWall
Get PDFThe discrete-analytical solution method is proposed for the solution to problems related to the dynamics of the hydro-elastic system consisting of an axially-moving pre-stressed plate, compressible viscous fluid and rigid wall. The fluid flow caused by the axial movement of the plate and the pre-stresses in the plate are taken into consideration as the initial state of the system under consideration. It is assumed that the additional lineally-located time-harmonic forces act on the plate and these forces cause additional flow field in the fluid and an additional stress-strain state in the plate. The additional stress-strain state in the plate is described by utilizing the equations and relations of the three-dimensional linearized theory of elastic waves in initially stressed elastic bodies. The additional fluid flow field is described with linearized Navier-Stokes equations for compressible viscous fluid. As the fluid flow velocities in the initial state are non-homogeneous, the linearized Navier-Stokes equations have variable coefficients and this situation causes difficulties in obtaining an analytical solution to these equations. The proposed discrete-analytical solution method allows this difficulty to be overcome and for approximate analytical solutions for these types of problems to be obtained. The proposed solution method is examined with respect to concrete problems. Numerical results obtained with the proposed approach are presented and discussed
Conjugate Heat Transfer in Uniformly Heated Enclosure Filled with Micropolar Fluid
Get PDFThis paper investigates numerically the conjugate heat transfer in a concentric enclosure that is formed between two concentric cylinders and filled with micropolar fluid. The wall of inner cylinder is considerably thick, while the wall of outer cylinder is very thin. The inner cylinder is heated from inner side through constant heat flux, whereas the outer cylinder is cooled and maintained at constant temperature. The induced buoyancy driven flow and associated conjugate heat transfer are predicted numerically by solving flow and energy governing equations considering a combination of finite difference and Fourier spectral methods. The study investigates the effect of controlling parameters on both flow and thermal fields, keeping focus on inner wall temperature. The controlling parameters are Rayleigh number Ra, dimensionless thickness of inner wall, inner cylinder fluid thermal conductivity ratio Kr, and material parameters of micropolar fluid (λ, B and D). The study shows that the steady dimensionless mean inner wall temperature ∅ˉI decreases with increase in Kr and Ra, and decrease in the vortex viscosity D. The study also shows that the increase in thickness of inner wall at Kr ˉI. While in case of Kr > 1, for a given value of Ra and D, ∅ˉI assumes maximum value at certain thickness of inner wall. In general, the study demonstrates that, for same geometrical and flow parameters, ∅ˉI is more in case of micropolar fluids as compared to Newtonian fluids