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In this study, we integrated the manufacturability constraints related to the maximum fiber curvature into our meshless modeling approach developed for variable-stiffness laminates. We used the developed framework to maximize the fundamental frequency of plates. The variable-stiffness designs provided significantly higher frequencies compared to optimum constant-stiffness laminates, although the actual level of improvement depends on the number of layers. Finally, we obtained manufacturable fiber paths considering the allowed fiber curvature, which can also reduce the frequency values.

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Thermal feedback has been proven to enhance user experience in human-machine interactions. Yet state-of-the-art thermal technology has focused on the single finger or palm in static contact, overlooking dynamic and multi-finger interactions. The underlying challenges include incompatible designs of conventional interfaces for providing salient thermal stimuli for such interactions and, thereby, a lack of knowledge on human thermal perception for relevant conditions.

In this paper, we present the ThermoSurf, a new thermal display technology that can deliver temperature patterns on a large interface suitable for dynamic and multi-finger interactions. We also investigate how user exploration affects the perception of the generated temperature distributions. Twenty-three human participants interacted with the device following three exploration conditions: static-single finger, dynamic-single finger, and static-multi finger. In these experiments, the individuals evaluated 15 temperature differences ranging from -7.5 °C to +1.5 °C with an initial temperature of 38 °C. Our results showed that human sensitivity against thermal stimuli is significantly greater for static-single finger contact compared to the other tested conditions. In addition, this interaction type resulted in higher thermal discrimination thresholds than the ones reported in the literature. Our findings offer new perspectives on providing salient and consistent thermal feedback for future tactile interfaces.

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In this paper, we introduced a lightweight wearable silicone finger sheath that can deliver salient and rich vibrotactile cues using electromagnetic actuation. We fabricated the sheath on a ferromagnetic mandrel with a process based on dip molding, a robust fabrication method that is rarely used in soft robotics but is suitable for commercial production. A miniature rare-earth magnet embedded within the silicone layers at the center of the finger pad was driven to vibrate by the application of alternating current to a nearby air-coil.

We experimentally determined the amplitude of the magnetic force and the frequency response function for the displacement amplitude of the magnet perpendicular to the skin. In addition, high-fidelity finite element analyses of the finger wearing the device were performed to investigate the trends observed in the measurements. Moreover, we conducted a psychophysical study to find the detection thresholds at different frequencies. Finally, a cue identification experiment and a demonstration in virtual reality validated the feasibility of this approach to fingertip haptics.

Link to the open-access article

I was honored to be invited by Composite Materials Group of KU Leuven to present at the “Break the Borders” event. Link to the event page

With great pleasure, I would like to announce that I have joined the Department of Mechanical Engineering at KU Leuven as Assistant Professor. I am located at the Bruges Campus, and I am affiliated with both Mecha(tro)nic Systems Dynamics Group and M-Group. I am honored to be a faculty member of such a prestigious university with a centuries-long history.

I was delighted to attend the International Conference on Noise and Vibration Engineering (ISMA2022) held in Leuven, Belgium on 12-14 September. With this third one, I conclude my summer conferences for this year.

Besides enjoying excellent presentations, I had the chance to have many interesting discussions with leading researchers in the field. This event was also a very timely opportunity for me to meet my new colleagues from LMSD at KU Leuven!

Here is a moment from the “Substructuring and coupling” session that I chaired.

It was a great pleasure to participate in the International Conference of Nonlinear solid Mechanics, which took place in Alghero, Italy on 13-16 June. I presented a part of our research on using machine learning as a model reduction technique for contact analysis using finite elements. There were amazing plenary talks, technical sessions, and poster presentations. Still, the best part was engaging in interesting discussions with the top solids mechanics researchers around the world. I have to mention the mood-boosting effect of beautiful Alghero as well!

In the design of sandwich laminates, increasing the proportion of carbon fiber can increase both stiffness and cost, while using more glass fiber has the opposite effect. Thus, in the multi-objective design of these structures, eigenfrequency gaps, buckling load, and cost metrics can be in conflict. This discrepancy requires finding the laminate configuration with the best trade-off. In our study, we addressed this problem using lamination parameters, the spectral Chebyshev method, and genetic algorithms. We determined 2D and 3D Pareto-optimal solutions that correspond to the binary and ternary combinations of the mentioned objectives. The results provide insights into the design requirements for improving the dynamic and load-carrying behavior of sandwich laminates while minimizing the cost.
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I had the pleasure of visiting Sorbonne University to deliver a talk about the design of nonconventional composite structures using lamination parameters. In my talk, I highlighted the advantages and limitations of lamination parameters, summarized my doctoral and postdoctoral studies on this topic, and outlined the major remaining challenges and potential future directions. The presentation was followed by great discussions!

Mixing data from experiments and simulation can be a good recipe in many machine learning applications. We used this approach to develop large-scale tactile sensors in our recent article published in IEEE Transactions on Automation Science and Engineering. In the paper, we introduced a hybrid method that combines simulation data synthesized from an electromechanical finite element model with real measurements collected from a new ERT-based tactile sensor. Our modular pipeline’s results outperform predictions by both a physics-based model and end-to-end learning.
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In collaboration with the researchers from the University of Stuttgart, we addressed this problem in our recent Structures article “A design methodology for fiber layup optimization of filament wound structural components”. In this study, we introduced a novel technique that integrates lamination parameters into the design of filament wound structures. The case studies demonstrated the effectiveness of our approach and the applicability of continuous shell models to analyze structures with internal gaps.
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Our article “Free and Forced Vibration Modes of the Human Fingertip” has recently been published in Applied Sciences. In this study, we developed DigiTip, a detailed three-dimensional finite element model of a representative human fingertip that is based on prior anatomical and biomechanical studies. Using this model, we first performed modal analyses to determine the free vibration modes with associated frequencies up to about 250 Hz. Subsequently, we applied distributed harmonic forces at the fingerprint centroid in three principal directions to predict forced vibration responses through frequency-response analyses. The results illuminate the dynamic behavior of the human fingertip in haptic interactions involving oscillating stimuli, such as textures and vibratory alerts, and they show how the modal information can predict the forced vibration responses of the soft tissue.
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My article “Design of circular composite cylinders for optimal natural frequencies” has recently been published in Materials. This study concerns optimizing the eigenfrequencies of circular composite cylinders using lamination parameters. In the lamination parameter plane, novel response contours are obtained for the first and second natural frequencies as well as their difference. The lamination parameters yielding the maximum response values are determined, and the first two mode shapes are shown for the optimum points. The results demonstrate that the maximum fundamental frequency points of the laminated cylinders mostly lie at the inner lamination parameter domain, unlike the singly curved composite panels. In addition, the second eigenfrequency shows a nonconvex response surface containing multiple local maxima for several cases. Moreover, the frequency difference contours appear as highly irregular, which is unconventional for free vibration responses.
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My article “COMPACT: Concurrent or Ordered Matrix-based Packing Arrangement Computation Technique” has been published in Applied Sciences. The method presented in this study allows the objects to be rotated by arbitrary angles, unlike the right-angled rotation restrictions imposed in many existing packing optimization studies based on raster methods. The raster approximations are obtained through loop-free operations that improve efficiency. Additionally, a novel performance metric is introduced, which favors efficient filling of the available space by maximizing the overall contact within the domain. Moreover, the objective functions are exploited to discard the overlap and overflow constraints and enable the use of unconstrained optimization methods. The results of the case studies demonstrate the effectiveness of the proposed technique.
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I am glad to share that my article “Concurrent lamination and tapering optimization of cantilever composite plates under shear” has been published in Materials. In this study, I focused on simultaneously optimizing layer and taper angles of cantilever composite laminates under shear. Such an approach fully utilizes stiffness tailoring and geometric design to maximize the operational performance of the structure.
Link to the article

I am proud to share that my profile is now on shellbuckling.com, a website featuring developments regarding buckling of shell structures as well as the people who substantially contributed to the field.
Link to my page

I am happy to share that our article “Dynamic analysis of doubly curved composite panels using lamination parameters and spectral-Tchebychev method” has been published in Computers & Structures. In this paper, we built a modeling framework for the dynamic analysis of doubly curved composite panels. The proposed framework combines the computational efficiency advantages of both lamination parameters formulation and spectral-Tchebychev method. Besides the developed methodology, our novel results give insight on the optimal dynamic design of doubly curved shells.
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Our paper “Calibrating a Soft ERT-Based Tactile Sensor with a Multiphysics Model and Sim-to-real Transfer Learning” has been published in the proceedings of 2020 IEEE International Conference on Robotics and Automation (ICRA). In this study we introduced a new method for calibrating soft ERT-based tactile sensors using sim-to-real transfer learning with a finite element multiphysics model. The model is composed of three simple models that together map contact pressure distributions to voltage measurements. We optimized the model parameters to reduce the gap between the simulation and reality. Our results show that the developed calibration technique can be utilized for improving the sensing performance of ERT-based tactile sensors.
Link to the article

EuroHaptics 2020, the primary European meeting for researchers working on haptic perception and technology, took place on September 6-9, in Leiden, Netherlands. Due to COVID-19 pandemic, the conference organizers hybridized an in-person meeting with a virtual event. I found the opportunity to present two work-in-progress (WIP) posters that contain a part of our research that we have been conducting in the Max Planck Institute for Intelligent Systems. The conference was very succesful as it enabled exchange of ideas between researchers of the field and paved the way for potential collaborations.

I am glad to share that our article “Unifying lamination parameters with spectral-Tchebychev method for variable-stiffness composite plate design” has been published in Composite Structures. In this study we developed an effective framework for the analysis and optimization of the variable-stiffness composite plates. We exploited computational advantages of lamination parameter interpolation method and spectral-Tchebyshev technique to obtain a very efficient design tool.
Link to the article

Today, Yasemin Vardar and I visited Fethiye Science High School to speak with the students about possible career paths in engineering and science. Impressed by the excellent questions that have been asked, we are convinced that a very bright generation is approaching!

I am happy to say that our article “Multi-objective optimization of composite plates using lamination parameters” has been published in Materials & Design. In this study we investigated multi-objective optimization of composite plates using lamination parameters. We aimed to provide insight on the conformity/conflict of multiple performance metrics by determining Pareto-optimal solutions for different problem cases.
Link to the article

I presented our work-in-progress poster entitled “High-Fidelity Multiphysics Finite Element Modeling of Finger-Surface Interactions with Tactile Feedback” at World Haptics Conference 2019 held in Tokyo, Japan. The diversity and quality of the studies demonstrated in the conference were absolutely fantastic!