Mechanical Engineering / Makina Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/4129
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Article Citation - WoS: 1Citation - Scopus: 1Analysis and Comparison of the Projectile Impact Response of an Electron Beam Melt-Ti64 Body Centered Cubic Lattice-Cored Sandwich Plate(Springer, 2025) Erten, H.İ.; Çimen, G.; Yıldıztekin, F.M.; Güden, M.Background: One potential application of additively fabricated lattice structures is in the blade containment rings of gas turbine engines. The blade containment rings are expected to be able to absorb the kinetic energy of a released blade (broken blade) in order to protect the engine parts from damaging. Metallic lattice-cored sandwich plates provide a gap (free space) between two face sheets, which helps to arrest the released blade and increases the energy absorption capability of containment rings. Objective: The objective was to investigate numerically the projectile impact response of Body-Centered-Cubic (BCC) Electron-Beam-Melt (EBM) lattice-cored/Ti64 face sheet sandwich plates as compared with that of an equal-mass monolithic EBM-Ti64 plate. Methods: The projectile impact simulations were implemented in LS-DYNA using the previously determined flow stress and damage models and a spherical steel impactor at the velocities ranging from 150 to 500 m s−1. The experimental projectile impact tests on the monolithic plate were performed at two different impact velocities and the results were used to confirm the validity of the used flow stress and damage models for the monolithic plate models. Results: Lower impact stresses were found numerically in the sandwich plate as compared with the monolithic plate at the same impact velocity. The bending and multi-cracking of the struts over a wide area in the sandwich plate increased the energy absorption and resulted in the arrest of the projectile at relatively high velocities. While monolithic plate exhibited a local bent area, resulting in the development of high tensile stresses and the projectile perforations at lower velocities. Conclusions: The numerical impact stresses in the sandwich plate were distributed over a wider area around the projectile, leading to the fracture and bending of many individual struts which significantly increased the resistance to the perforation. Hence, the investigated lattice cell topology and cell, strut, and face sheet sizes and the lattice-cored sandwich plate was shown potentially more successful in stopping the projectiles than the equal-mass monolithic plates. © The Author(s) 2025.Article Citation - WoS: 9Citation - Scopus: 11Experimental Investigation of Spray Characteristics of Ethyl Esters in a Constant Volume Chamber(Springer, 2022) Ulu, Anılcan; Yıldız, Güray; Özkol, Ünver; Rodriguez, Alvaro DiezAbstract: Biodiesels are mainly produced via the utilization of methanol in transesterification, which is the widespread biodiesel production process. The majority of this methanol is currently obtained from fossil resources, i.e. coal and natural gas. However, in contrast with methanol, biomass-based ethanol can also be used to produce biodiesels; this could allow the production line to become fully renewable. This study aimed to investigate the spray characteristics of various ethyl ester type biodiesels derived from sunflower and corn oils in comparison to methyl esters based on the same feedstocks and reference petroleum-based diesel. Spray penetration length (SPL) and spray cone angle (SCA) were experimentally evaluated in a constant volume chamber allowing optical access, under chamber pressures of 0, 5, 10 and 15 bar and injection pressures of 600 and 800 bar. Sauter mean diameter (SMD) values were estimated by using an analytical correlation. Consequently, ethyl esters performed longer SPL (2.8–20%) and narrower SCA (5.1–19%) than diesel under ambient pressures of 5 and 10 bar. Although the SMD values of ethyl esters were 48% higher than diesel on average, their macroscopic spray characteristics were very similar to those of diesel under 15 bar chamber pressure. Moreover, ethyl esters were found to be very similar to methyl esters in terms of spray characteristics. The differences in SPL, SCA and SMD values for both types of biodiesels were lower than 4%. When considering the uncertainty (± 0.84%) and repeatability (±5%) ratios, the difference between the spray characteristics of methyl and ethyl esters was not major.Article Citation - WoS: 8Citation - Scopus: 10Design and Control of Spatial Inverted Pendulum With Two Degrees of Freedom(Springer, 2020) Bayram, Atilla; Kara, FıratThe inverted pendulum systems have inherently unstable dynamics. In order to stabilize the inverted pendulum at upright position, an actuation mechanism should generate fast-reactive motions at the pivot point of the system. This paper addressed the design and control of a spatial inverted pendulum with two degrees of freedom (DOF). The first part of the study consists of designing a novel planar two-DOF (PRRRR) actuation mechanism in order to balance the spatial inverted pendulum. The system is underactuated and has inherently extreme nonlinearity and also the restrictions on the actuators. Then, in the second part, a second-order sliding-mode and a linear quadratic Gaussian (LQG) controller have been proposed to control the pendulum within the equilibrium position. Finally the simulation results evaluated in terms of the robustness, time response and stability show that the second-order sliding-mode controller is more robust and has fast response performances in re-stabilizing the spatial inverted pendulum, while LQG controller is better in terms of keeping the system in equilibrium during the long period of time.Article Citation - WoS: 4Citation - Scopus: 5Analytical Solution of Micro-/Nanoscale Convective Liquid Flows in Tubes and Slits(Springer, 2017) Kalyoncu, Gülce; Barışık, MuratAnalytical solutions examining heat transport in micro-/nanoscale liquid flows were developed. Using the energy equation coupled with fully developed velocity, we solved developing temperature profiles with axial conduction and viscous dissipation terms. A comprehensive literature review provided the published range of velocity slip and temperature jump conditions. While molecular simulations and experiments present constant slip and jump values for a specific liquid/surface couple independent of confinement size, non-dimensional forms of these boundary conditions were found appropriate to calculate non-equilibrium as a function of flow height. Although slip and jump conditions are specific for each liquid/surface couple and hard to obtain, we proposed modeling of the slip and jump as a function of the surface wetting, in order to create a general, easy to measure methodology. We further developed possible correlations to calculate jump using the slip value of the corresponding surface and tested in the results. Fully developed Nu showed strong dependence on slip and jump. Heat transfer stopped when slip and jump coefficients became higher than a certain value. Strong variation of Nu in the thermal development length was observed for low slip and jump cases, while an almost constant Nu in the flow direction was found for high slip and jump coefficients. Variation of temperature profiles was found to dominate the heat transfer through the constant temperature surface while surface and liquid temperatures became equal at heat transfer lengths comparable with confinement sizes for no-dissipation cases. In case of non-negligible heat dissipation, viscous heating dominated the Nu value by enhancing the heating while decreasing the heat removal in cooling cases. Implementation of proposed procedure on a micro-channel convection problem from a micro-fluidics application showed the dominant effect of the model defining the slip and jump relationship. Direct use of kinetic gas theory resulted in an increase of Nu by an increase in non-equilibrium, while models developed from published liquid slip and jump values produced an opposite behavior.Article Citation - WoS: 23Citation - Scopus: 24Law of the Nano-Wall” in Nano-Channel Gas Flows(Springer, 2016) Barışık, Murat; Beşkök, AliMolecular dynamics simulations of force-driven nano-channel gas flows show two distinct flow regions. While the bulk flow region can be determined using kinetic theory, transport in the near-wall region is dominated by gas–wall interactions. This duality enables definition of an inner-layer scaling, (Formula presented.) , based on the molecular dimensions. For gas–wall interactions determined by Lennard–Jones potential, the velocity distribution for (Formula presented.) exhibits a universal behavior as a function of the local Knudsen number and gas–wall interaction parameters, which can be interpreted as the “law of the nano-wall.” Knowing the velocity and density distributions within this region and using the bulk flow velocity profiles from Beskok–Karniadakis model (Beskok and Karniadakis in Microscale Thermophys Eng 3(1):43–77, 1999), we outline a procedure that can correct kinetic-theory-based mass flow rate predictions in the literature for various nano-channel gas flows.