I am a postdoctoral researcher at Max Planck Institute for Intelligent Systems, Haptic Intelligence Department directed by Dr. Katherine J. Kuchenbecker. I received my Ph.D. degree in Mechanical Engineering from Koc University (Istanbul, Turkey) in 2018, under the supervision of Dr. Ipek Basdogan. I received my M.Sc. degree in Computational Mechanics from Technical University of Munich in 2013, where I completed my thesis at BMW Group under the supervision of Prof. Dr. Fabian Duddeck. I earned my B.Sc. degree in Mechanical Engineering from Middle East Technical University (Ankara, Turkey) in 2011.
My research focuses on computational modeling of contact mechanics between the finger and surfaces providing haptic feedback via electrovibration and/or mechanical vibrations. I aim to develop simulation tools that will enable deeper understanding of contact phenomenon in surface haptics applications and circumventing a portion of costly experimental procedures. Such tools can be used for optimal design of intelligent systems delivering various realistic haptic experiences on today’s electronic devices such as smartphones or tablet computers.
Development of surface haptic technologies has lately drawn significant attention, in parallel with the growing use of modern electronic devices involving touchscreens. Different haptic scenarios provide active tactile feedback by controlling natural physical phenomena such as contact, friction, and vibrations. However, these system...
Serhat, G., Anamagh, M. R., Bediz, B., Basdogan, I.
Computers & Structures, 239, pages: 106294, October 2020 (article)
Efficient modeling and optimization techniques are required to overcome the high design complexity and computational costs concerning the engineering of composite structures. In this paper, a modeling framework for the dynamic analysis of doubly curved composite panels is developed. Lamination parameters are used to characterize the stiffness properties of the laminate, and the responses are calculated through the two-dimensional spectral-Tchebychev method. The proposed framework combines the computational efficiency advantages of both lamination parameters formulation and spectral-Tchebychev method which is extended for dynamic analysis of curved composite laminates. Compared to the finite element method, the developed model significantly decreases the computation duration, thereby leading to analysis speed-ups up to 40 folds. In the case studies, fundamental frequency contours for the doubly curved composite panels are obtained in lamination parameters space for the first time. The results show that, unlike flat or singly curved laminates, the maximum frequency design points for doubly curved panels can be inside the feasible region of lamination parameters requiring multiple layer angles. The fundamental mode shapes for the maximum frequency designs are also computed to investigate the influence of panel curvatures on the vibration patterns, which can exhibit mode switching phenomenon.
Composite Structures, 242(112183), June 2020 (article)
This paper describes an efficient framework for the design and optimization of the variable-stiffness composite plates. Equations of motion are solved using a Tchebychev polynomials-based spectral modeling approach that is extended for the classical laminated plate theory. This approach provides highly significant analysis speed-ups with respect to the conventional finite element method. The proposed framework builds on a variable-stiffness laminate design methodology that utilizes lamination parameters for representing the stiffness properties compactly and master node variables for modeling the stiffness variation through distance-based interpolation. The current study improves the existing method by optimizing the locations of the master nodes in addition to their lamination parameter values. The optimization process is promoted by the computationally efficient spectral-Tchebychev solution method. Case studies are performed for maximizing the fundamental frequencies of the plates with different boundary conditions and aspect ratios. The results show that significant improvements can be rapidly achieved compared to optimal constant-stiffness designs by utilizing the developed framework. In addition, the optimization of master node locations resulted in additional improvements in the optimal response values highlighting the importance of including the node positions within the design variables.
Applied Mathematical Modelling, 76, pages: 883–899, December 2019 (article)
Dynamic properties of the plate structures can be enhanced by introducing discontinuities of different kinds such as using surface-bonded discrete patches or spatially varying the stiffness and mass properties of the plate. Fast and reliable design of such complex structures requires efficient and accurate modeling tools. In this study, a novel semi-analytical model is developed for the dynamic analysis of plates having discrete and/or continuous non-uniformities. Two-dimensional Heaviside unit step functions are utilized to represent the discontinuities. Different from existing numerical methods based on Heaviside functions, a numerical technique is proposed for modeling the discontinuities that are not necessarily aligned with the plate axes. The governing equations are derived using Hamilton's principle and Rayleigh–Ritz method is used for determining the modal variables. The surface-bonded patches are used to demonstrate discrete non-uniformities where variable-stiffness laminates are selected to represent continuous non-uniform structures. Natural frequencies and mode shapes obtained using the proposed method are validated with finite element analyses and the existing results from the literature. The results show that the developed model performs accurately and efficiently.
Materials & Design, 180(107904), October 2019 (article)
Laminated composite plates are extensively used in various industries due to their high stiffness-to-weight ratio and directional properties that allow optimization of the stiffness characteristics for specific applications. In multi-objective optimization problems, optimal designs for individual performance metrics may be conflicting, necessitating knowledge on the design requirements for different metrics and potential trade-offs. In this paper, a multi-objective design methodology for laminated composite plates with dynamic and load-carrying requirements is presented. Lamination parameters are used to characterize laminate stiffness matrices in a compact form resulting in a convex design space. Single and multi-objective optimization studies are carried out to determine the optimal stiffness properties. For improving the dynamic performance, maximization of the fundamental frequency metric is aimed. For enhancing the load-carrying capability, buckling load and equivalent stiffness metrics are maximized. Conforming and conflicting behavior of multiple objective functions for different plate geometries, boundary conditions and load cases are presented by determining Pareto-optimal solutions. The results provide a valuable insight for multi-objective optimization of laminated composite plates and show that presented methodology can be used in the design of such structures for improving the dynamic and load-carrying performance.
Work-in-progress paper (2 pages) presented at the IEEE World Haptics Conference (WHC), Tokyo, Japan, July 2019 (misc)
In this study, we develop a high-fidelity finite element (FE) analysis framework that enables multiphysics simulation of the human finger in contact with a surface that is providing tactile feedback. We aim to elucidate a variety of physical interactions that can occur at finger-surface interfaces, including contact, friction, vibration, and electrovibration. We also develop novel FE-based methods that will allow prediction of nonconventional features such as real finger-surface contact area and finger stickiness. We envision using the developed computational tools for efficient design and optimization of haptic devices by replacing expensive and lengthy experimental procedures with high-fidelity simulation.
AIAA Journal, 57(7):3052–3065, July 2019 (article)
Variable-stiffness laminates have lately drawn attention because they offer potential for additional structural performance improvements. In the optimization studies, laminate stiffness properties can be described efficiently by using lamination parameters, which is a well-established formulation for constant-stiffness laminates. However, ensuring manufacturability in the design of variable-stiffness laminates with lamination parameters is difficult. In this paper, a novel method for the design of variable-stiffness composite panels using lamination parameters is proposed. The method constrains the design space by controlling the magnitude and direction of change for the lamination parameters, and subsequently leads to a smooth change in the fiber angles. The method is used to maximize the fundamental frequencies of several panels as example cases. The solutions are calculated for various panel geometries and boundary conditions using the developed finite element analysis software. After finding optimal lamination parameter distributions, corresponding discrete fiber angles and fiber paths are retrieved, and the minimum radii of curvature are calculated. The results demonstrate that the proposed design method provides manufacturable smooth fiber paths while using the compact stiffness formulation feature of lamination parameters.
Laminated composite panels are extensively used in various industries due to their high stiﬀness-to-weight ratio and directional properties that allow optimization of stiﬀness characteristics for speciﬁc applications. With the recent improvements in the manufacturing techniques, the technology trend has been shifting towards the development of nonconventional composites. This work aims to develop new methods for the design and optimization of nonconventional laminated composites. Lamination parameters method is used to characterize laminate stiﬀness matrices in a compact form. An optimization framework based on ﬁnite element analysis was developed to calculate the solutions for diﬀerent panel geometries, boundary conditions and load cases. The ﬁrst part of the work addresses the multi-objective optimization of composite laminates to maximize dynamic and load-carrying performances simultaneously. Conforming and conﬂicting behaviors of multiple objective functions are investigated by determining Pareto-optimal solutions, which provide a valuable insight for multi-objective optimization problems. In the second part, design of curved laminated panels for optimal dynamic response is studied in detail. Firstly, the designs yielding maximum fundamental frequency values are computed. Next, optimal designs minimizing equivalent radiated power are obtained for the panels under harmonic pressure excitation, and their eﬀective frequency bands are shown. The relationship between these two design sets is investigated to study the eﬀectiveness of the frequency maximization technique. In the last part, a new method based on lamination parameters is proposed for the design of variable-stiﬀness composite panels. The results demonstrate that the proposed method provides manufacturable designs with smooth ﬁber paths that outperform the constant-stiﬀness laminates, while utilizing the advantages of lamination parameters formulation.
Composites Part B: Engineering, 147, pages: 135–146, August 2018 (article)
In this paper, dynamic response of composite panels is investigated using lamination parameters as design variables. Finite element analyses are performed to observe the individual and combined effects of different panel aspect ratios, curvatures and boundary conditions on the dynamic responses. Fundamental frequency contours for curved panels are obtained in lamination parameters domain and optimal points yielding maximum values are found. Subsequently, forced dynamic analyses are carried out to calculate equivalent radiated power (ERP) for the panels under harmonic pressure excitation. ERP contours at the maximum fundamental frequency are presented. Optimal lamination parameters providing minimum ERP are determined for different excitation frequencies and their effective frequency bands are shown. The relationship between the designs optimized for maximum fundamental frequency and minimum ERP responses is investigated to study the effectiveness of the frequency maximization technique. The results demonstrate the potential of using lamination parameters technique in the design of curved composite panels for optimal dynamic response and provide valuable insight on the effect of various design parameters.
Journal of Intelligent Material Systems and Structures, 29(10):2192–2205, March 2018 (article)
Laminated composite panels are extensively used in various engineering applications. Piezoelectric transducers can be integrated into such composite structures for a variety of vibration control and energy harvesting applications. Analyzing the structural dynamics of such electromechanical systems requires precise modeling tools which properly consider the coupling between the piezoelectric elements and the laminates. Although previous analytical models in the literature cover vibration analysis of laminated composite plates with fully covered piezoelectric layers, they do not provide a formulation for modeling the piezoelectric patches that partially cover the plate surface. In this study, a methodology for vibration analysis of laminated composite plates with surface-bonded piezo-patches is developed. Rayleigh–Ritz method is used for solving the modal analysis and obtaining the frequency response functions. The developed model includes mass and stiffness contribution of the piezo-patches as well as the two-way electromechanical coupling effect. Moreover, an accelerated method is developed for reducing the computation time of the modal analysis solution. For validations, system-level finite element simulations are performed in ANSYS software. The results show that the developed analytical model can be utilized for accurate and efficient analysis and design of laminated composite plates with surface-bonded piezo-patches.
In Proceedings of International Congress and Exposition of Noise Control Engineering (INTER-NOISE), Hamburg, Germany, August 2016 (inproceedings)
In this paper, a comparison of preliminary design methodologies for optimization of stiffened, fiber-reinforced composite fuselages for vibro-acoustic requirements is presented. Fuselage stiffness properties are modelled using lamination parameters and their effect on the vibro-acoustic performance is investigated using two different approaches. First method, only considers the structural model in order to explore the effect of design variables on fuselage vibrations. The simplified estimation of the acoustic behavior without considering fluid-structure interaction brings certain advantages such as reduced modelling effort and computational cost. In this case, the performance metric is chosen as equivalent radiated power (ERP) which is a well-known criterion in the prediction of structure-born noise. Second method, utilizes coupled vibro-acoustic models to predict the sound pressure levels (SPL) inside the fuselage. ERP is calculated both for bay panels and fuselage section and then compared with the SPL results. The response surfaces of each metric are determined as a function of lamination parameters and their overall difference is quantified. ERP approach proves its merit provided that a sufficiently accurate model is used. The results demonstrate the importance of the simplifications made in the modelling and the selection of analysis approach in vibro-acoustic design of fuselages.
In Proceedings of the ASMO UK International Conference on Numerical Optimisation Methods for Engineering Design, pages: 160–168, Munich, Germany, July 2016 (inproceedings)
Eigenfrequency optimization of laminated composite panels is a common engineering problem. This process mostly involves designing stiffness properties of the structure. Optimal results can differ significantly depending on the values of the model parameters and the metrics used for the optimization. Building the know-how on this matter is crucial for choosing the appropriate design methodologies as well as validation and justification of prospective results. In this paper, effects of aspect ratio and boundary conditions on eigenfrequency optimization of composite panels by altering stiffness properties are investigated. Lamination parameters are chosen as design variables which are used in the modeling of stiffness tensors. This technique enables representation of overall stiffness characteristics and provides a convex design space. Fundamental frequency and difference between fundamental and second natural frequencies are maximized as design objectives. Optimization studies incorporating different models and responses are performed. Optimal lamination parameters and response values are provided for each case and the effects of model parameters on the solutions are quantified. The results indicate that trends of the optima change for different aspect ratio ranges and boundary conditions. Moreover, convergence occurs beyond certain critical values of the model parameters which may cause an optimization study to be redundant.
In Proceedings of AIAA/ISSMO Multidisciplinary Analysis and Optimization Conference, Washington, USA, June 2016 (inproceedings)
In this paper, a preliminary design methodology for optimization of stiffened, fiber-reinforced composite fuselages for combined mechanical and vibro-acoustic requirements is presented. Laminate stiffness distributions are represented using the method called lamination parameters which is known to provide a convex solution space. Single-objective and multi-objective optimization studies are carried out in order to find optimal stiffness distributions. Performance metrics for acoustical behavior are chosen as maximum fundamental frequency and minimum equivalent radiated power. The mechanical performance metric is chosen as the maximum stiffness. The results show that the presented methodology works effectively and it can be used to improve load-carrying and acoustical performances simultaneously.
Our goal is to understand the principles of Perception, Action and Learning in autonomous systems that successfully interact with complex environments and to use this understanding to design future systems