Imperial College London

Dr Elnaz Naghibi

Faculty of EngineeringDepartment of Aeronautics

Teaching Fellow
 
 
 
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Contact

 

+44 (0)20 7594 3024e.naghibi

 
 
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Location

 

139City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

9 results found

Sadati H, Naghib E, Shiva A, Michael B, Renson L, Howard M, Rucker C, Althoefer K, Nanayakkara DPT, Zschaler S, Bergeles C, Hauser H, Walker Iet al., 2021, TMTDyn: A Matlab package for modeling and control of hybrid rigid–continuum robots based on discretized lumped system and reduced-order models, International Journal of Robotics Research, Vol: 40, Pages: 296-347, ISSN: 0278-3649

A reliable, accurate, and yet simple dynamic model is important to analyzing, designing, and controlling hybrid rigid–continuum robots. Such models should be fast, as simple as possible, and user-friendly to be widely accepted by the ever-growing robotics research community. In this study, we introduce two new modeling methods for continuum manipulators: a general reduced-order model (ROM) and a discretized model with absolute states and Euler–Bernoulli beam segments (EBA). In addition, a new formulation is presented for a recently introduced discretized model based on Euler–Bernoulli beam segments and relative states (EBR). We implement these models in a Matlab software package, named TMTDyn, to develop a modeling tool for hybrid rigid–continuum systems. The package features a new high-level language (HLL) text-based interface, a CAD-file import module, automatic formation of the system equation of motion (EOM) for different modeling and control tasks, implementing Matlab C-mex functionality for improved performance, and modules for static and linear modal analysis of a hybrid system. The underlying theory and software package are validated for modeling experimental results for (i) dynamics of a continuum appendage, and (ii) general deformation of a fabric sleeve worn by a rigid link pendulum. A comparison shows higher simulation accuracy (8–14% normalized error) and numerical robustness of the ROM model for a system with a small number of states, and computational efficiency of the EBA model with near real-time performances that makes it suitable for large systems. The challenges and necessary modules to further automate the design and analysis of hybrid systems with a large number of states are briefly discussed.

Journal article

Naghibi SE, Karabasov SA, Jalali MA, Sadati SMHet al., 2019, Fast spectral solutions of the double-gyre problem in a turbulent flow regime, Applied Mathematical Modelling, Vol: 66, Pages: 745-767, ISSN: 0307-904X

Several semi-analytical models are considered for a double-gyre problem in a turbulent flow regime for which a reference fully numerical eddy-resolving solution is obtained. The semi-analytical models correspond to solving the depth-averaged Navier–Stokes equations using the spectral Galerkin approach. The robustness of the linear and Smagorinsky eddy-viscosity models for turbulent diffusion approximation is investigated. To capture essential properties of the double-gyre configuration, such as the integral kinetic energy, the integral angular momentum, and the jet mean-flow distribution, an improved semi-analytical model is suggested that is inspired by the idea of scale decomposition between the jet and the surrounding flow.

Journal article

Chintagunta A, Naghibi SE, Karabasov SA, 2018, Flux-corrected dispersion-improved CABARET schemes for linear and nonlinear wave propagation problems, Computers and Fluids, Vol: 169, Pages: 111-128, ISSN: 0045-7930

The new two-time-level dispersion improved CABARET scheme is developed as an upgrade of the original CABARET for improved wave propagation modelling in multiple dimensions and for nonlinear conservation laws including gas dynamics. The new upgrade retains many attractive features of the original CABARET scheme such as shock-capturing and low dissipation. It is simple for implementation in the existing CABARET codes and leads to a greater accuracy for solving linear wave propagation problems. A non-linear version of the dispersion-improved CABARET scheme is introduced to efficiently deal with contact discontinuities and shocks. The properties of the new linear and nonlinear CABARET schemes are analysed for numerical dissipation and dispersion error based on Von Neumann analysis and Pirrozolli's method. Numerical examples for one-dimensional and two-dimensional linear advection, the one-dimensional inviscid Burger's equation, and the isothermal gas dynamics problems in one and two dimensions are presented.

Journal article

Sadati SMH, Naghibi SE, Walker ID, Althoefer K, Nanayakkara Tet al., 2017, Control Space Reduction and Real-Time Accurate Modeling of Continuum Manipulators Using Ritz and Ritz–Galerkin Methods, IEEE Robotics and Automation Letters, Vol: 3, Pages: 328-335, ISSN: 2377-3766

To address the challenges with real-time accurate modeling of multisegment continuum manipulators in the presence of significant external and body loads, we introduce a novel series solution for variable-curvature Cosserat rod static and Lagrangian dynamic methods. By combining a modified Lagrange polynomial series solution, based on experimental observations, with Ritz and Ritz-Galerkin methods, the infinite modeling state space of a continuum manipulator is minimized to geometrical position of a handful of physical points (in our case two). As a result, a unified easy to implement vector formalism is proposed for the nonlinear impedance and configuration control. We showed that by considering the mechanical effects of highly elastic axial deformation, the model accuracy is increased up to 6%. The proposed model predicts experimental results with 6%-8% (4-6 mm) mean error for the Ritz-Galerkin method in static cases and 16%-20% (12-14 mm) mean error for the Ritz method in dynamic cases, in planar and general three-dimensional motions. Comparing to five different models in the literature, our approximate solution is shown to be more accurate with the smallest possible number of modeling states and suitable for real-time modeling, observation, and control applications.

Journal article

Sadati SMH, Naghibi SE, Shiva A, Noh Y, Gupta A, Walker ID, Althoefer K, Nanayakkara Tet al., 2017, A geometry deformation model for braided continuum manipulators, Frontiers Robotics AI, Vol: 4

Continuum manipulators have gained significant attention in the robotic community due to their high dexterity, deformability, and reachability. Modeling of such manipulators has been shown to be very complex and challenging. Despite many research attempts, a general and comprehensive modeling method is yet to be established. In this paper, for the first time, we introduce the bending effect in the model of a braided extensile pneumatic actuator with both stiff and bendable threads. Then, the effect of the manipulator cross-section deformation on the constant curvature and variable curvature models is investigated using simple analytical results from a novel geometry deformation method and is compared to experimental results. We achieve 38% mean reference error simulation accuracy using our constant curvature model for a braided continuum manipulator in presence of body load and 10% using our variable curvature model in presence of extensive external loads. With proper model assumptions and taking to account the cross-section deformation, a 7-13% increase in the simulation mean error accuracy is achieved compared to a fixed cross-section model. The presented models can be used for the exact modeling and design optimization of compound continuum manipulators by providing an analytical tool for the sensitivity analysis of the manipulator performance. Our main aim is the application in minimal invasive manipulation with limited workspaces and manipulators with regional tunable stiffness in their cross section.

Journal article

Naghibi SE, Jalali MA, Karabasov SA, Alam MRet al., 2017, Excitation of the Earth's Chandler wobble by a turbulent oceanic double-gyre, Geophysical Journal International, Vol: 209, Pages: 509-516, ISSN: 0956-540X

We develop a layer-averaged, multiple-scale spectral ocean model and show how an oceanic double-gyre can communicate with the Earth's Chandler wobble. The overall transfers of energy and angular momentum from the double-gyre to the Chandler wobble are used to calibrate the turbulence parameters of the layer-averaged model. Our model is tested against a multilayer quasi-geostrophic ocean model in turbulent regime, and base states used in parameter identification are obtained from mesoscale eddy resolving numerical simulations. The Chandler wobble excitation function obtained from the model predicts a small role of North Atlantic ocean region on the wobble dynamics as compared to all oceans, in agreement with the existing observations.

Journal article

Chintagunta A, Markesteijn A, Naghibi SE, Karabasov Set al., 2017, Dispersion improved CABARET for computational aeroacoustics

Conference paper

Naghibi SE, Mahzoon M, 2016, Nonlinear vibrations and chaos in rectangular functionally graded plates with thermo-mechanical coupling, International Journal of Acoustics and Vibrations, Vol: 21, Pages: 308-316, ISSN: 1027-5851

We analyze the nonlinear dynamics of a simply supported, rectangular, and functionally graded plate in terms of a newly derived coupled system of thermo-elasticity and energy equations, which is then expanded here in derivations and explored for chaotic responses through a parameter study in the state space.1 The plate properties vary linearly in thickness. Three-dimensional stress-strain relations are considered in general case and nonlinear strain-displacement relations are deployed to account for the plate's large deflection. A lateral harmonic force is applied on the plate, and there is a heat generation source within it and the surfaces are exposed to free convection. By integrating over the thickness, four new thermal parameters are introduced, which together with the midplane displacements constitute a system of seven partial differential equations. These equations are changed into ordinary differential equations in time using Galerkin's approximation and solved by using the 4th order Runge-Kutta method. Finally, a parameter study is performed and the appropriate conditions resulting in chaotic solutions are determined by using numerical features such as the Lyapunov exponent and power spectrum.

Journal article

Sadati SMH, Naghibi SE, Naraghi M, 2015, An Automatic Algorithm to Derive Linear Vector Form of Lagrangian Equation of Motion with Collision and Constraint, Procedia Computer Science, Vol: 76, Pages: 217-222

The use of complex systems with switching behavior and control design such as multitask walking and flying robots which need different Equation of Motion (EOM) for their states has become more popular recently. Having a reliable, exact and easy to drive dynamic model is important for their analysis, design, path planning and control. While the Newton and Lagrange approaches are being used widely to derive robot dynamics, they are not fully optimized for numerical modelling of systems with switching behaviors. TMT method which is a linear vector form for Lagrange EOM has recently been used, but not generally intruded and investigated, to simplify the EOM derivation and improve the numerical simulation efficiency of robotic system models. Here a systematic approach to derive EOM of different rigid body robot systems with impact using TMT method is presented. An automatic algorithm and a code based on that is developed in Matlab language to derive different systems' EOM. The algorithm needs simple geometric inputs for joints, actuator inputs, external loadings and constraints; and can be used for modelling both serial and parallel mechanism with external collision. The application of this approach and algorithm inputs is shown for three sample systems: a biped walker with upper body, a flapping flyer and a Clemens joint.

Journal article

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