14 results
Search Results
Now showing 1 - 10 of 14
Article Citation - WoS: 4Citation - Scopus: 4Multiloop State-Dependent Nonlinear Time-Varying Sliding Mode Control of Unmanned Small-Scale Helicopter(Sage Publications Ltd, 2020) Ozcan, Sinan; Salamci, Metin U.; Nalbantoglu, VolkanTime delays, parameter uncertainties, and disturbances are the fundamental problems that hinder the stability and reduce dramatically the tracking performance of dynamical systems. In this paper, a new state-dependent nonlinear time-varying sliding mode control autopilot structure is proposed to cope with these dynamical and environmental complexities for an unmanned helicopter. The presented technique is based on freezing the nonlinear system equations on each time step and designing a controller using the frozen system model at this time step. The proposed method offers an improved performance in the presence of major disturbances and parameter uncertainties by adapting itself to possible dynamical varieties without a need of trimming the system on different operating conditions. Unlike the existing linear cascade autopilot structure, this study also proposes a nonlinear cascade state-dependent coefficient helicopter autopilot structure consisting of four separate nonlinear sub-systems. The proposed method is tested through the real time and PC-based simulations. To show the performance of the proposed robust method, it is also bench-marked against a linear sliding control control in PC-based simulations.Article Citation - WoS: 7Citation - Scopus: 7A New Strategy for Solving Store Separation Problems Using Openfoam(Sage Publications Ltd, 2022) Abuhanieh, Saleh; Akay, Hasan U.; Bicer, BarisThe ability of OpenFOAM to solve the problem of a store separating from an air vehicle (store separation problem) has been evaluated using a dynamic mesh (Overset/Chimera) technique for an industry-class (transonic and generic) benchmark test case. The major limitations of the standard libraries have been determined. To tackle these challenges, a new strategy has been proposed and implemented using only open-source libraries and tools. The strategy combines porting, modifying, and adapting an overset library from the OpenFOAM fork platform (foam-extend) to the standard OpenFOAM platform (ESI). Furthermore, in order to overcome the well-known weakness of the standard OpenFOAM compressible solvers, the newly adapted overset library was integrated with an open-source, density-based, and coupled solver (HiSA), which uses the OpenFOAM technology. Additionally, a force restrained model was developed to consider the externally applied forces on the store by the store ejectors. The accuracy of the developed strategy has been compared with wind tunnel tests and the solutions of two well-known commercial codes, showing good agreements with them. While the study has focused on simulations with inviscid Euler equations (typical of the test case considered here), the viscosity effect on the solution has also been studied with Navier-Stokes equations and compared with other results in the literature, showing minor differences. To the best of the authors' knowledge, this is the first work which studies and validates the store separation problem in transonic regime with OpenFOAM.Article Citation - WoS: 19Citation - Scopus: 19Interaction Between Assembled 3d Honeycomb Cells Produced From High Density Polyethylene and a Cohesionless Soil(Sage Publications Ltd, 2012) Gurbuz, Ayhan; Mertol, Halit CenanAssembled 3D high-density polyethylene honeycomb cells, providing confinement to arrest spreading of the soil in cells and creating relatively stiff bed that redistributes footing pressure over wider area, were used in the present study to enhance load-carrying capacity and to reduce settlement of base materials under a foundation. The effects of various test parameters including width, height, number of layers of the 3D honeycomb cells, vertical distance between layers of the cells and depth of stress zone of the foundation were studied. The test results indicated that considerable improvement in the load-carrying capacity (congruent to 3.0) and reduction in settlement of the foundation (congruent to 62%) were obtained with the implementation of the single layer of the 3D cells into cohesionless soils. The optimum effective distance between two layers of the 3D cells was 0.142 times the width of foundation, the ratio of effective width of 3D cells to the foundation was about 4.2 and the depth of influence stress zone of the foundation was about two times the width of the foundation.Article Citation - WoS: 7Citation - Scopus: 8Robust and Adaptive Control Design of a Drilling Rig During the Operating Modes(Sage Publications Ltd, 2019) Sadeghi, Amir Nobahar; Arikan, Kutluk Bilge; Ozbek, Mehmet Efe; Baranoglu, BesimOil well drilling towers have different operating modes during a real operation, like drilling, tripping, and reaming. Each mode involves certain external disturbances and uncertainties. In this study, using the nonlinear model for the modes of the operation, robust and/or adaptive control systems are designed based on the models. These control strategies include five types of controllers: cascaded proportional-integral-derivative, active disturbance rejection controller, loop shaping, feedback error learning, and sliding mode controller. The study presents the design process of these controllers and evaluates the performances of the proposed control systems to track the reference signal and reject the uncertain forces including the parametric uncertainties and the external disturbances. This comparison is based on the mathematical performance measures and energy consumption. In addition, three architectures are presented to control the weight on bit during drilling process, and also to maintain a preset constant weight on bit, two control approaches are designed and presented.Article Citation - WoS: 64Citation - Scopus: 74Production and Characterization of Poly (lactic Acid)-Based Biocomposites Filled With Basalt Fiber and Flax Fiber Hybrid(Sage Publications Ltd, 2020) Eselini, Najah; Tirkes, Seha; Akar, Alinda Oyku; Tayfun, UmitPoly (lactic acid) (PLA)-based biocomposites containing flax fiber (FF) and basalt fiber (BF) both separately and together were prepared by melt blending method at the total constant ratio of 30 wt%. Mechanical properties, thermo-mechanical characteristics, thermal stability, flow behaviors, water uptake, and morphology of composites were investigated by tensile, hardness and impact tests, dynamic mechanical analysis (DMA), thermal gravimetric analysis, melt flow index (MFI) test, water absorption, and scanning electron microscopy, respectively. Mechanical test results show that tensile strength, elongation, elastic modulus, and impact strength are extended up to higher values with increase in BF content in hybrid composites. Conversely, the presence of FF displays a negative effect in which these values drop down drastically as the FF concentration increases. On the other hand, slightly higher hardness values are obtained by the addition of FF at higher loadings. DMA analysis reveals that BF inclusion leads glass transition temperature of PLA to one point higher, but hybrid and FF containing composites shift that temperature to lower values. Storage moduli of composites are enhanced with the increase in BF concentration and remarkable decreases are observed for FF-filled composites. Hybrid composites exhibit average MFI values between PLA/FF and PLA/BF composites.Article Citation - WoS: 15Citation - Scopus: 21Tool-Life Modelling of Carbide and Ceramic Cutting Tools Using Multi-Linear Regression Analysis(Sage Publications Ltd, 2006) Amaitik, S. M.; Tasgin, T. T.; Kilic, S. E.This paper presents a study for the development of tool-life models for machining operations by means of a statistical approach called multi-linear regression analysis. The study was applied to a milling process for machining SAE 121 cast iron in a factory without interrupting the mass production. Different cutting tool materials under dry conditions were used in the cutting tests. Several machining experiments were performed and mathematical models for tool life have been postulated by using least-square regression analysis. The analysis was based on a first-order model in which the tool life is expressed as a function of two independent variables; cutting speed and feed rate. Analysis of variance was applied to check the adequacy of the mathematical models and their respective parameters. In order to demonstrate the usefulness of the developed models, tool-life contours have been generated and presented in different plots.Article Citation - WoS: 4Citation - Scopus: 5Numerical Investigation of Store Separation From Cavity Problems at High Speeds(Sage Publications Ltd, 2023) Abuhanieh, Saleh; Akay, Hasan U.In this work, the ability of open-source CFD tools to conduct store separation simulations from cavities is evaluated and validated using a generic test case from the literature. Firstly, the ability and accuracy of these tools for solving cavity flows at high speeds are evaluated. Secondly, their competence in predicting the trajectory of a generic store from a generic deep cavity is checked. Finally, and in order to reduce the associated computational costs, a release-time dependability factor from the recent literature is studied and evaluated. The obtained results using the selected open-source CFD tools matched quite well with the wind tunnel results. Furthermore, the results show that predicting the release-time dependability using a quantified index/factor can be a potential remedy for reducing the computational cost for this type of CFD simulations.Article Citation - WoS: 16Citation - Scopus: 15Macroporous Silicone Biomaterials With Modified Surface Chemistry: Production and Characterization(Sage Publications Ltd, 2012) Gencer, Zeynep A.; Odabas, Sedat; Sasmazel, Hilal T.; Piskin, ErhanPorous and bioactive silicone biomaterials were developed for soft and cartilage tissue repair. A protocol, using compression molding, salt extraction, and supercritical carbon dioxide treatments, was used to obtain disk-shaped materials with specific pore sizes and morphologies by changing the process conditions. Highly open/interconnected macroporous silicone matrices, with an average pore size of 250-300 mu m and porosities in the range of 60%-70%, were obtained by the extracting the NaCl particles. Subsequent treatment with supercritical carbon dioxide slightly decreased the average pore size but increased the porosity to 80%. The supercritical carbon dioxide treatment effectively removed the entrapped salt crystals from the silicone matrix that improved interconnectivity. The compression modulus decreased, while the compression strength was increased using this technique. The surfaces and pores of the silicone materials were modified by silanization to provide primary amine groups for cell attachment, proliferation, migration, and three-dimensional growth of model L929 fibroblast cells.Article Citation - WoS: 1Citation - Scopus: 1Modelling the Positive and Negative Interaction Between Mood and Thermal Sensation in the Built Environment Using a Combined Markov Chain Monte Carlo Algorithm and Morris Method(Sage Publications Ltd, 2025) Ozbey, Mehmet Furkan; Turhan, CihanMood states, categorized into subscales such as Tension (TEN), Anger (ANG), Fatigue (FAT), Vigour (VIG), Confusion (CON), and Depression (DEP), affect occupants' perceptions of thermal environments. This study investigates the influence of these subscales on thermal sensation, exploring both positive and negative effects. Experiments were conducted in a temperate climate zone over an extended period, including both heating and cooling seasons, with 1159 volunteers. The Morris Method was used to assess the impact of psychological parameters (TEN, ANG, FAT, VIG, CON, DEP) on thermal sensation. Markov Chain Monte Carlo (MCMC) simulations, performed via Python code developed by the authors, evaluated the positive and negative impacts of these subscales across 30,000 simulations. Results showed that VIG was the most influential parameter, while CON and FAT had negative effects (feeling cooler) on thermal sensation. These findings emphasize the complex relationship between psychological factors and thermal perception, underlining the importance of mood states in designing environments that enhance thermal comfort. The study offers valuable insights into the interplay of emotional well-being and physiological responses, contributing to environmental psychology and climate-responsive design.Article Citation - WoS: 17Citation - Scopus: 19Physical and Mechanical Performance of Bentonite and Barite Loaded Low Density Polyethylene Composites: Influence of Surface Silanization of Minerals(Sage Publications Ltd, 2020) Elkawash, Hesham; Tirkes, Seha; Hacioglu, Firat; Tayfun, UmitIn this study, two kinds of mineral fillers, bentonite (BNT) and barite (BRT), were incorporated into low density polyethylene (LDPE) by extrusion process. Silane treatment was applied to BRT and BNT surfaces in order to increase their compatibility with LDPE matrix. Surface characteristics of fillers were examined by Fourier transformed infrared spectroscopy (FTIR). LDPE-based composites were prepared at a constant concentration of 10%wt for each additives. Test samples were shaped by injection molding process. Mechanical, thermo-mechanical, water repellency, melt-flow and morphological characterizations of LDPE and its composites were performed by tensile and impact tests, dynamic mechanical analysis (DMA), water absorption test, melt flow index (MFI) measurements and scanning electron microscopy (SEM) technique, respectively. Test results showed that surface treatments led to increase for final properties of composites since they promoted to stronger adhesion between minerals and LDPE matrix compared to untreated ones. Tensile and impact strength values, storage modulus and glass transition temperature of LDPE were improved by inclusion of silane treated minerals. BRT and BNT additions caused no remarkable changes with regard to MFI of LDPE. Additionally, silane modified mineral filled composites exhibited remarkable water resistance behavior. According to SEM analysis of composites, silane treated BNT and BRT containing samples displayed homogeneous dispersions into LDPE phase whereas debondings were observed for untreated BNT and BRT filled composites due to their weak adhesion to polymer matrix.
