Reza Kamali

A robust adaptive fuzzy sliding mode controller for trajectory tracking of ROVs

This study deals with dynamic modeling and tracking control of a remotely underwater vehicle (ROV) with six degrees of freedom (DOF). The sliding mode scheme for tracking control of an ROV is a powerful approach to compensate structured and unstructured uncertainties. In this study, performance of sliding mode approach modified by robust adaptive fuzzy control algorithm for an ROV is presented. Fuzzy algorithm is used for on-line estimation of external disturbances as well as unknown nonlinear terms of dynamic model of the ROV. A robust control rule is employed to compensate for estimation errors. The boundedness and asymptotic convergence properties of the control algorithm and its semi-global stability are analytically proven using Lyapunov stability theory and Barbalats lemma. Moreover, adaptation laws and robust control terms are derived from Lyapunov stability synthises. The adopted control scheme is implemented in numerical simulations, based on the dynamic parameters of Shiraz University Remotely Operated Vehicle (Ariana I ROV). Simulations show the effectiveness of the adopted controller for trajectory tracking.

Curvature effect on droplet impacting onto hydrophobic and superhydrophobic spheres

ABSTRACT Droplet impact on hydrophobic and superhydrophobic solid surfaces finds numerous applications, while the wide range of the parameters affecting its outcome necessitate a thorough study to reveal the underlying physics. Specific applications are related to the drop impact upon curved surfaces, such as micro-encapsulation in fluidized beds. Three-dimensional numerical simulations by applying Level-Set Method have been performed to investigate the water droplet impact on curved and flat hydrophobic and superhydrophobic substrates. Parameters such as the impact Weber number, the surface curvature and the equilibrium contact angle have been varied in order to assess their effects on the dynamics of the impact process. After providing a strong validation, it is found that impact on spherical surfaces generally presents a higher area of liquid to be in contact with the substrate with respect to the case of flat surfaces, when all other impact conditions are the same.

Numerical simulation of the leaky dielectric microdroplet generation in electric fields

Microdroplet generation has a vast range of applications in the chemical, biomedical, and biological sciences. Several devices are applied to produce microdroplets, such as Co-flow, T-junction and Flow-focusing. The important point in the producing process is controlling the separated fluid volume in these devices. On the other hand, a large number of liquids, especially aqueous one, are influenced by electric or magnetic fields. As a consequence, an electric field could be used in order to affect the separated fluid volume. In this study, effects of an electric field on the microdroplet generation in a Co-flow device are investigated numerically. Furthermore, effects of some electrical properties such as permittivity on the separating process of microdroplets are studied. Leaky dielectric and perfect dielectric models are used in this investigation. According to the results, in the microdroplet generating process, leaky dielectric fluids show different behaviors, when an electric field is applied to the device. In other words, in a constant electric field strength, the volume of generated microdroplets can increase or decrease, in comparison with the condition without the electric field. However, for perfect dielectric fluids, droplet volume always decreases with increasing the electric field strength. In order to validate the numerical method of this study, deformation of a leaky dielectric droplet in an electric field is investigated. Results are compared with Taylor theoretical model.

Molecular dynamics study of electric double layer in nanochannel

The Electric Double Layer for electroosmotic flow of NaCl aqueous solution in nanochannels is studied numerically in this paper using Molecular Dynamics (MD) approach. For an electrolyte solution flowing in 40 nm nanochannel, two different conditions for charge on channel wall are defined; first the charge on the wall is held as equal to the amount that was previously reported by the experiment when charge dissociation on silicon dioxide wall occurs and second the constant surface charge density on the wall is assumed. The MD based numerical results show great agreement with experimental data for zeta potential in the range of 10−2−10−1 M. The MD simulations show that Debye length decreases as NaCl concentration increases. Moreover the electric conductance and velocity profile in nanochannel could be extracted from MD results. Performance of the MD approach as a most promising numerical method to study electrokinetic phenomena in nanoscale devices is then verified.

Effect of temperature-dependency of Newtonian and non-Newtonian fluid properties on the dynamics of droplet impinging on hot surfaces

In the present work, three-dimensional computational fluid dynamics analysis is employed to study the droplet dynamics of Newtonian and non-Newtonian droplets impinging on a hot surface under various impact conditions. The Navier–Stokes equations for unsteady, incompressible, and viscous fluid flow are solved using a control volume method. The volume-of-fluid (VOF) technique is also used to track the free-surface of the liquid. The effect of viscosity, density and surface tension on droplet dynamics is evaluated considering their dependence of temperature. The results indicate that the temperature dependence of the both Newtonian and non-Newtonian physicochemical liquid properties must be considered to obtain better agreement of the numerical results with experimental data. After ensuring the accuracy of the numerical methodology, the internal behavior of the droplets is examined, which is shown that the receding velocity of the non-Newtonian droplet is slower than the Newtonian one.

Effects of Magnetic Particles Entrance Arrangements on Mixing Efficiency of a Magnetic Bead Micromixer

In this study, a computer code is developed to numerically investigate a magnetic bead micromixer under different conditions. The micromixer consists of a microchannel and numerous micro magnetic particles which enter the micromixer by fluid flows and are actuated by an alternating magnetic field normal to the main flow. An important feature of micromixer which is not considered before by researchers is the particle entrance arrangement into the micromixer. This parameter could effectively affect the micromixer efficiency. There are two general micro magnetic particle entrance arrangements in magnetic bead micromixers: determined position entrance and random position entrance. In the case of determined position entrances, micro magnetic particles enter the micromixer at specific positions of entrance cross section. However, in a random position entrance, particles enter the microchannel with no order. In this study mixing efficiencies of identical magnetic bead micromixers which only differ in particle entrance arrangement are numerically investigated and compared. The results reported in this paper illustrate that the prepared computer code can be one of the most powerful and beneficial tools for the magnetic bead micromixer performance analysis. In addition, the results show that some features of the magnetic bead micromixer are strongly affected by the entrance arrangement of the particles.

Three-Dimensional Passive and Active Control Methods of Shock Wave Train Physics in a Duct

In the present work, the physics of a three-dimensional shock train in a convergent-divergent nozzle is numerically investigated. In this regards, the Ansys-Fluent Software with Algebraic Wall-Modeled Large-Eddy Simulation (WMLES) is used. To estimate precision and errors accumulation we used the Smirinov’s method; fine flow structures are obtained via Laplacian of density called shadowgraph and the shock parameter is defined as multiplication of flow Mach number by the normalized pressure gradient, in which shock wave structures are visible distinctly. The results are compared with the experimental data of Weiss et al. [Experiments in Fluids 49(2) (2010) 355–365], in the same conditions including geometry, boundary conditions, etc. The results show that there is good agreement with experimental trends concerning wall pressure and centerline Mach number profiles. Therefore, the focus of the present study is an assessment of various flow control methods to change the shock structures. Consequently, we investigated the effects of passive (bump and cavity) and active (suction and blowing) control methods on the starting point of shock, shock strength, minimum pressure, maximum flow Mach number, etc. All CFD investigations are carried out by High Performance Computing Center (HPCC).

Rigorous study of molecular dynamics of a single dsDNA confined in a nanochannel: Introduction of a critical mobility behaviour.

The essential and effective characteristics of a double-stranded DNA (dsDNA) confined in a nanochannel is revisited by employing the rigorous full numerical approach of Molecular Dynamics (MD). The deformation of dsDNA and wall-biomolecule interaction which is critical in highly confined regime has been precisely imposed in numerical simulations. The numerical approach has been justified against available theoretical outcomes. A new and general expression for DNA electrophoretic mobility versus DNA length is extracted from numerical simulation which is out of reach of experimental methods due to practical shortcomings. The newly derived expression suggests an essential correction in the previously proposed expression for the critical case of small DNA molecules and reveals an astonishingly unbeknown trend of small DNAs mobility. Sub-molecular phenomenon of dsDNA melting under the condition of large external force is also studied. Assuming strong electric field exertion, the MD approach aptly demonstrates the elaborate melting phenomenon for dsDNA in sub-molecular scale.Graphical abstract

Large eddy simulation of the flameless oxidation in the IFRF furnace with varying inlet conditions

In the present study, large eddy simulation methodology is applied to investigate the 3D non-premixed flameless oxidation in the IFRF furnace. In order to serve this purpose, to model the combustion and radiation, the partially stirred reactor and finite volume discrete ordinate model are used, respectively.Moreover, the detailed mechanism of GRI-2.11 is undertaken to represent chemistry reactions. The present simulations agree qualitatively well with published experimental data. Finally, the present study focusses on the assessment of the effects of variations in the fuel vertical injection by adding an inert gas as well as the fuel temperature on combustion behavior. The results revealed that important changes occur in the characteristics of the flameless oxidation process.

Investigation of multiscale fluid flow characteristics based on a hybrid atomistic–continuum method

Abstract A computer program based on a molecular dynamics–continuum hybrid method has been developed in which the Navier–Stokes equations are solved in the continuum region and the molecular dynamics in the atomistic region. The coupling between the atomistic and continuum is constructed through constrained dynamics within an overlap region where both molecular and continuum equations are solved simultaneously. The simulation geometries are solved in three dimensions and an overlap region is introduced in two directions to improve the choice of using the molecular region in smaller areas. The proposed method is used to simulate steady and start-up Couette flow showing quantitative agreement with results from analytical solutions and full molecular dynamics simulations. The prepared algorithm and the computer code are capable of modeling fluid flows in micro and nano-scale geometries.