Scholarly Publications - Mechanical Engineering

Permanent URI for this collectionhttps://hdl.handle.net/11693/115626

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Open Access
3D Force field spectroscopy
(Springer, Cham, 2015) Baykara, Mehmet Z.; Schwarz, U. D.; Morita, S.; Giessibl, F. J.; Meyer, E.; Wiesendanger, R.
With recent advances in instrumentation and experimental methodology, noncontact atomic force microscopy is now being frequently used to measure the atomic-scale interactions acting between a sharp probe tip and surfaces of interest as a function of three spatial dimensions, via the method of three-dimensional atomic force microscopy (3D-AFM). In this chapter, we discuss the different data collection and processing approaches taken towards this goal while highlighting the associated advantages and disadvantages in terms of correct interpretation of results. Additionally, common sources of artifacts in 3D-AFM measurements, including thermal drift, piezo nonlinearities, and tip-related issues such as asymmetry and elasticity are considered. Finally, the combination of 3D-AFM with simultaneous scanning tunneling microscopy (STM) is illustrated on surface-oxidized Cu(100). We conclude the chapter by an outlook regarding the future development of the 3D-AFM method.
Open Access
A 3D game theoretical framework for the evaluation of unmanned aircraft systems airspace integration concepts
(Elsevier, 2021-10-23) Albaba, Berat Mert; Musavi, Negin; Yıldız, Yıldıray
Predicting the outcomes of integrating Unmanned Aerial System (UAS) into the National Airspace System (NAS) is a complex problem, which is required to be addressed by simulation studies before allowing the routine access of UAS into the NAS. This paper focuses on providing a 3-dimensional (3D) simulation framework using a game-theoretical methodology to evaluate integration concepts using scenarios where manned and unmanned air vehicles co-exist. In the proposed method, the human pilot interactive decision-making process is incorporated into airspace models which can fill the gap in the literature where the pilot behavior is generally assumed to be known a priori. The proposed human pilot behavior is modeled using a dynamic level-k reasoning concept and approximate reinforcement learning. The level-k reasoning concept is a notion in game theory and is based on the assumption that humans have various levels of decision making. In the conventional “static” approach, each agent makes assumptions about his or her opponents and chooses his or her actions accordingly. On the other hand, in the dynamic level-k reasoning, agents can update their beliefs about their opponents and revise their level-k rule. In this study, Neural Fitted Q Iteration, which is an approximate reinforcement learning method, is used to model time-extended decisions of pilots with 3D maneuvers. An analysis of UAS integration is conducted using an Example 3D scenario in the presence of manned aircraft and fully autonomous UAS equipped with sense and avoid algorithms.
Open Access
3D modeling of on-chip acoustophoretic particle manipulation in a polymer microfluidic device
(Chemical and Biological Microsystems Society, 2016) Çaǧatay, E.; Özer, M. B.; Çetin, Barbaros
This study focuses on understanding of the sensitivities of the acoustophoretic process on uncertainties/errors in the geometric properties of the chip material and the piezoelectric actuators. The sensitivity of the acoustophoretic process is investigated both numerically and experimentally. For the numerical simulations a three dimensional finite element model is used. In the experimental analysis, a microfluidic chip with two stations is used. The first station has the accurate geometric values of the design and the second station has the introduced error in a geometric parameter so that the effect of this error can be demonstrated on the same chip and the channel.
Open Access
3D printed microfluidic reactor for high throuhput chitosan nanoparticle synthesis
(Chemical and Biological Microsystems Society, 2016) Aşık, M. D.; Çetin, Barbaros; Kaplan, M.; Erdem, Yegan; Saǧlam, N.
The major bottleneck for the commercialization of nanoparticle related technologies is the mass production of the nanoparticles. One approach to overcome this bottleneck is use of microfluidic devices. In this paper, a 3D printed, high throughput micro-reactor that is capable of synthesizing both chitosan and chitosan coated iron oxide nanoparticles is presented.
Open Access
A compliant, force-controlled active tail for miniature robots
(IEEE, 2024-05-13) Raheem, Haider; Ozbek, Doga; Uğur, Mustafa; Özcan, Onur
Climbing up the slopes and scaling the obstacles are challenging tasks for miniature robots. By taking inspiration from nature, this paper investigates the use of a tail, like a lizard to aid the climbing capabilities of our miniature robot. We present the design of an active soft tail controlled by the force feedback from a 3D-printed, custom, soft force sensor. This paper also investigates the benefit of using an active tail controlled by force to climb slopes and obstacles. Increasing the slope that the miniature robot attempts to scale increases the need for the force applied by the tail to avoid the pitch-back movement of the robot. We can observe a positive correlation between the force applied by the tail and the slope of the surface. The experiments were conducted until the maximum degree of incline of slope that the robot could climb without any adhesive feet, i.e., 20 degrees. Additionally, this paper proves that the tail also improves the tail obstacle scaling capability of the robot. The maximum heights of the obstacle that the robot scales with and without the tail are 19 mm and 9 mm respectively.
Open Access
A computational design framework for lubrication interfaces with active micro-textures
(The American Society of Mechanical Engineers, 2024-08-27) Pekol, Sena; Kılınç, Özge; Temizer, İlker
The major goal of the present study is to develop a computational design framework for the active control of hydrodynamically lubricated interfaces. The framework ultimately delivers an electrode distribution on an elastomeric substrate such that a voltage-controlled texture may be induced on its surface. This enables the setup to attain a desired time-dependent macroscopic lubrication response. The computational framework is based on a numerically efficient two-stage design approach. In the first stage, a topology optimization framework is introduced for determining a microscopic texture and the uniform modulation of its amplitude. The objective is to attain the targeted fluid flux or frictional traction signals based on the homogenization-based macroscopic response of the texture. As a minor goal, a novel unit cell geometry optimization feature will be developed which will enable working in a design space that is as unrestricted as possible. The obtained designs are then transferred to the second stage where the electrode distribution on a soft substrate is determined along with the voltage variation that delivers the desired amplitude variation. The first stage operates in a two-dimensional setting based on the Reynolds equation whereas the second stage operates in a three-dimensional setting based on an electroelasticity formulation. The two stages are heuristically coupled by transferring the texture topology to the electrode distribution through a projection step. The viability of such an active lubrication interface design approach is demonstrated through numerous examples that methodically investigate the central features of the overall computational framework.
Open Access
A novel constitutive model for surface elasticity at finite strains suitable across compressibility spectrum
(Elsevier Masson, 2023-03-24) Javili, Ali; Dörtdivanlioğlu, Berkin
The surface elasticity theory of Gurtin–Murdoch has proven to be remarkably successful in predicting the behavior of materials at the nano scale, which can be attributed to the fact that the surface-to-volume ratio increases as the problem dimension decreases. On the other hand, surface tension can deform soft elastic solids even at the macro scale resulting e.g. in elastocapillary instabilities in soft filaments reminiscent of Plateau–Rayleigh instabilities in fluids. Due to the increasing number of applications involving nanoscale structures and soft solids such as gels, the surface elasticity theory has experienced a prolific growth in the past two decades. Despite the large body of literature on the subject, the constitutive models of surface elasticity theory at large deformations are not suitable to capture the surface behavior from fully compressible to nearly incompressible elasticity, especially from a computational perspective. A physically meaningful and proper decomposition of the surface free energy density in terms of area-preserving and area-varying contributions remains yet to be established. We show that an immediate and intuitive generalization of the small-deformation surface constitutive models does not pass the simple extension test at large deformations and results in unphysical behavior at lower Poisson’s ratios. Thus, the first contribution of the manuscript is to introduce a novel decomposed surface free energy density that recovers surface elasticity across the compressibility spectrum. The second objective of this paper is to formulate an axisymmetric counterpart of the elastocapillary theory methodically derived from its three-dimensional format based on meaningful measures relevant to the proposed surface elasticity model. Various aspects of the problem are elucidated and discussed through numerical examples using the finite element method enhanced with surface elasticity.
Open Access
A numerical algorithm to model wall slip and cavitation in two-dimensional hydrodynamically lubricated contacts
(Elsevier Ltd, 2023-03-23) Çam, Mert Yusuf; Giacopini, M.; Dini, D.; Biancofiore, Luca
Hydrodynamic lubrication takes a fundamental role in mechanical systems to reduce energy losses and prevent mechanical breakdown. The analytic instrument usually adopted to describe hydrodynamic lubrication is the Reynolds equation, which in its simplest statement for monophase lubricants and with assuming no fluid slip at the walls, is a linear equation in the hydrodynamic pressure. However, this classical linear Reynolds equation cannot reflect all the lubricant characteristics in engineered surfaces (e.g. superhydro(oleo)phobic surfaces and textured surfaces). In these cases, the effect of two critical factors, such as wall slip and cavitation, need to be considered, introducing non-linearities in the system. In order to tackle this issue, a modified two-dimensional Reynolds equation is introduced, able to capture both the cavitation presence, via a complementary mass-conserving model, and wall slippage, starting from the multi-linearity description introduced by Ma et al. (2007). In addition, an alternative model for the slippage at the wall is proposed by modifying the multi-linearity wall slip model to improve accuracy and computational cost. In this new model, the possible slip directions are limited to three, separated by equal angles, with the slip occurring only along the first direction, and the other directions, then, used to iteratively adjust the direction of slippage, until a suitable convergence criterion is satisfied. The proposed mathematical model is validated versus results available in literature with tests performed on (i) journal bearings, (ii) slider bearings, (iii) squeeze dampers, and (iv) surface textured bearings. By conducting these tests, the proposed alternative wall slip model is proved to be up to one order of magnitude more computational efficient than the original multi-linearity wall slip model.
Open Access
A robust human-autonomy collaboration framework with experimental validation
(Institute of Electrical and Electronics Engineers, 2024-09-24) Uzun, M. Yusuf; İnanç, Emirhan; Yıldız, Yıldıray
In this letter, we introduce a robust human-autonomy collaboration framework focusing on flight control applications. The objective is to optimize performance by always keeping the human operator in control of the vehicle while compensating for human limitations. A significant aspect of this framework is its robustness to human intent estimation errors. This is achieved by precisely modulating the automation assistance to prevent undesired interference with the human operator. We provide human-in-the-loop experimental results, demonstrating significant performance improvements when intent estimation is accurate. Experiments also validate that the pilots maintain vehicle control even when the estimation is faulty.
Open Access
A self-adjusting and modular supervisory control algorithm for planar dexterous manipulation
(Elsevier, 2023-04) Ristevski, Stefan; Çakmakçı, Melih
Many applications require precise handling and manipulation of delicate objects. In some cases, the object must be transported to a new location following a strict travel path including time-related constraints. This paper presents a self-adjusting modular control algorithm for dexterous manipulation of planar objects using multiple manipulators with precise path and timing deliveries. The popular caging approach is simple, and usually effective when manipulating objects with multiple devices but can fail following complex paths with orientation adjustments under time-critical tracking requirements. The proposed approach exploits the dynamics of the object in real-time using tracking control and allocates the force that needs to be applied by each manipulator based on their current position around the object to maximize their capability to push in the direction of the contact angle. The new algorithm is self-adjusting and modular; It can adjust its force allocation according to configuration changes during operation, and manipulators execute the same algorithm regardless of their number. The advantages of the new approach are successfully demonstrated both with simulations and testbed experiments, including orientation tracking, which is not typically featured with the caging approach. Conditions to check when the new algorithm is most effective are also analyzed. The closed-loop stability and performance of the new algorithm are also studied and necessary conditions are identified.
Open Access
A study on the effect of structural compliance placing in soft contact/collision properties of multirotor micro aerial vehicles
(Wiley-VCH Verlag GmbH & Co. KGaA, 2024-10-14) Abazari, Amirali; Bakır, Alihan; Sertpoyraz, Altar; Özcan, Onur
Adding compliance (softness) has been introduced as an effective way to improve the physical collision resilience characteristics of multirotor micro aerial vehicles(MAVs). This article answers the question “Where is the best place to apply compliance in a multirotor MAV to make it more collision-resilient?” by analyzing the output data of more than 1200 drone collision tests through two sets of accelerated and nonaccelerated collision experiments for four main conﬁgurations of micro-quadcopters each possessing a unique softness layout of physical frame. It is shown that while applying compliance to the protective propeller guards (bumpers) of a micro-quadcopter provides a more elastic collision, it does not improve its energy-dissipation (impact damping) characteristics. On the other hand, enhancing the inner frame of the micro-quadcopter with a softer structure results in higher rates of impact energy damping during the collision sand an increase in the impact time, which results in lower impact accelerations the MAV experiences during the crush. A mathematical model is developed representing the contact/collision interactions as nonlinear viscoelastic forces. Comparing the results of the simulations to the experiments suggests that this model can effectively mimic the impact behavior of contacting/colliding MAVs with different structural stiffness and damping.
Open Access
A versatile implicit computational framework for continuum-kinematics-inspired peridynamics
(Springer, 2023-11-13) Firooz, S.; Javili, Ali; Steinmann, P.
Continuum-kinematics-inspired peridynamics (CPD) has been recently proposed as a novel reformulation of peridynamics that is characterized by one-, two- and three-neighbor interactions. CPD is geometrically exact and thermodynamically consistent and does not suffer from zero-energy modes, displacement oscillations or material interpenetration. In this manuscript, for the first time, we develop a computational framework furnished with automatic differentiation for the implementation of CPD. Thereby, otherwise tedious analytical differentiation is automatized by employing hyper-dual numbers (HDN). This differentiation method does not suffer from round-off errors, subtractive cancellation errors or truncation errors and is thereby highly stable with superb accuracy being insensitive to perturbation values. The computational framework provided here is compact and model-independent, thus once the framework is implemented, any other material model can be incorporated via modifying the potential energy solely. Finally, to illustrate the versatility of our proposed framework, various potential energies are considered and the corresponding material response is examined for different scenarios.
Open Access
Ablation-cooled material removal at high speed with femtosecond pulse bursts
(OSA, 2015) Kerse, Can; Kalaycıoğlu, Hamit; Elahi, Parviz; Akçaalan, Önder; Yavaş, S.; Aşık, M. D.; Kesim, Deniz Koray; Yavuz, Koray; Çetin, Barbaros; İlday, Fatih Ömer
We report exploitation of ablation cooling, a concept well-known in rocket design, to remove materials, including metals, silicon, hard and soft tissue. Exciting possibilities include ablation using sub-microjoule pulses with efficiencies of 100-mJ pulses.
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Ablation-cooled material removal with ultrafast bursts of pulses
(Nature Publishing Group, 2016) Kerse C.; Kalaycıoğlu, H.; Elahi, P.; Çetin B.; Kesim, D. K.; Akçaalan, Ö.; Yavaş S.; Aşık, M. D.; Öktem B.; Hoogland H.; Holzwarth, R.; Ilday, F. Ö.
The use of femtosecond laser pulses allows precise and thermal-damage-free removal of material (ablation) with wide-ranging scientific, medical and industrial applications. However, its potential is limited by the low speeds at which material can be removed and the complexity of the associated laser technology. The complexity of the laser design arises from the need to overcome the high pulse energy threshold for efficient ablation. However, the use of more powerful lasers to increase the ablation rate results in unwanted effects such as shielding, saturation and collateral damage from heat accumulation at higher laser powers. Here we circumvent this limitation by exploiting ablation cooling, in analogy to a technique routinely used in aerospace engineering. We apply ultrafast successions (bursts) of laser pulses to ablate the target material before the residual heat deposited by previous pulses diffuses away from the processing region. Proof-of-principle experiments on various substrates demonstrate that extremely high repetition rates, which make ablation cooling possible, reduce the laser pulse energies needed for ablation and increase the efficiency of the removal process by an order of magnitude over previously used laser parameters. We also demonstrate the removal of brain tissue at two cubic millimetres per minute and dentine at three cubic millimetres per minute without any thermal damage to the bulk.
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Accelerated 3D CFD modeling of multichannel flat grooved heat pipes
(Elsevier, 2024-10-01) Gökçe, Gökay; Çetin, Barbaros; Dursunkaya, Zafer
Flat grooved heat pipes (HPs) have become essential in advanced thermal management solutions across various engineering applications. Modeling these devices, especially multichannel flat grooved HPs, involves significant challenges due to complex phenomena such as phase-change heat transfer and free-surface flow, requiring substantial computational resources, time and expertise. These constraints often limit the full exploration and optimization of HPs’ potential in diverse applications. To address this gap, an accelerated 3D computational fluid dynamics (CFD) modeling approach is presented in this study. This novel method begins with a detailed 3D modeling of a single groove, developed using kinetic theory and facilitated by CFD software. The results from this model are then applied as boundary conditions to simulate the entire HP in a multichannel configuration. The importance of this methodology is further highlighted by the alignment of simulation results with experimental observations. The approach significantly enhances computational efficiency by reducing the number of iterations by 10% and computational time by 80%, resulting in a five-fold speed-up. The methodology enables accelerated, comprehensive modeling of multichannel variations and delivers critical insights for optimizing the design of multichannel flat grooved HPs for various engineering applications.
Open Access
Accelerated solution methodology for 3D hydrodynamic and thermal modeling of grooved heat pipes with complex geometries
(Springer, 2024-08-31) Gökçe, Gökay; Çetin, Barbaros; Dursunkaya, Zafer
Heat pipes play a crucial role in industrial thermal management owing to their exceptional heat-carrying capacity, minimal thermal resistance and reliable performance. However, designing and optimizing heat pipes becomes intricate especially when dealing with multi-phase heat transfer encompassing complex phenomena like phase-change processes (i.e., evaporation, condensation and free surface flow). Grooved heat pipes, characterized by complex groove shapes, introduce an additional layer of complexity necessitating physically based mathematical models and skin friction correlations that may not always be readily available or may yield inferior results. To address these limitations, an innovative computational methodology is integrated into a commercial CFD program (Fluent®) using the Python® programming language. This approach allowed for comprehensive computation of the 3D fluid flow field and heat transfer phenomena within grooved heat pipes. Notably, the methodology incorporates data fitting procedures for boundary conditions leading to a substantial acceleration of the computation process and a reduction in solution times. This investigation represents a substantial advancement in addressing the challenges of multi-phase heat transfer phenomena while providing a compelling solution to the limitations of previous modeling methodologies for grooved heat pipes. Furthermore, the proposed methodology exhibits versatility, extending beyond its initial scope to encompass complex geometries like omega-shaped grooves and various physical scenarios involving phase-change phenomena and free-surface flow. Due to its comprehensive insights and adaptable framework, developed methodology serves as a valuable tool for analyzing heat pipes with multiple grooves addressing a significant gap in the literature.
Open Access
Accommodating new flights into an existing airline flight schedule
(Elsevier, 2019) Şafak, Özge; Atamtürk, A.; Aktürk, M. Selim
We present two novel approaches to alter a flight network for introducing new flights while maximizing airline’s profit. A key feature of the first approach is to adjust the aircraft cruise speed to compensate for the block times of the new flights, trading off flying time and fuel burn. In the second approach, we introduce aircraft swapping as an additional mechanism to provide a greater flexibility in reducing the incremental fuel cost and adjusting the capacity. The nonlinear fuel-burn function and the binary aircraft swap and assignment decisions complicate the optimization problem significantly. We propose strong mixed-integer conic quadratic formulations to overcome the computational difficulties. The reformulations enable solving instances with 300 flights from a major U.S. airline optimally within reasonable compute times.
Open Access
Adaptive control allocation for constrained systems
(Elsevier, 2020-06) Tohidi, Seyed Shahabaldin; Yıldız, Yıldıray; Kolmanovsky, I.
This paper proposes an adaptive control allocation approach for uncertain over-actuated systems with actuator saturation. The proposed control allocation method does not require uncertainty estimation or persistency of excitation. Actuator constraints are respected by employing the projection algorithm. The stability analysis is provided for two different cases: when ideal adaptive parameters are inside and when they are outside of the projection boundary which is chosen consistently with the actuator saturation limits. Simulation results for the Aerodata Model in Research Environment (ADMIRE), which is used as an example of an over-actuated aircraft system with actuator saturation, demonstrate the effectiveness of the proposed method.
Open Access
Adaptive control allocation for over-actuated systems with actuator saturation
(Elsevier B.V., 2017) Tohidi, Seyed Shahabaldin; Yıldız, Yıldıray; Kolmanovsky, Ilya
This paper proposes an adaptive control allocation approach for over-actuated systems with actuator saturation. The methodology can tolerate actuator loss of effectiveness without utilizing the control input matrix estimation, eliminating the need for persistence of excitation. Closed loop reference model adaptive controller is used for identifying adaptive parameters, which provides improved performance without introducing undesired oscillations. The modular design of the proposed control allocation method improves the flexibility to develop the outer loop controller and the control allocation strategy separately. The ADMIRE model is used as an over-actuated system, to demonstrate the effectiveness of the proposed method using simulation results.
Open Access
Adaptive control design for nonlinear systems via successive approximations
(ASME, 2017) Babaei, N.; Salamcı, M. U.; Karakurt, Ahmet Hakan
The paper presents an approach to the Model Reference Adaptive Control (MRAC) design for nonlinear dynamical systems. A nonlinear reference system is considered such that its response is designed to be stable via Successive Approximation Approach (SAA). Having designed the stable reference model through the SAA, MRAC is then formulated for nonlinear plant dynamics with a new adaptation rule to guarantee the convergence of the nonlinear plant response to that of the response of the nonlinear reference model. The proposed design methodology is illustrated with examples for different case studies.