Theses supervised by Doç. Dr. Selahattin Çağlar Başlamışlı
11 theses · Hacettepe University
Mobility improvement of wheeled military vehicles using preview controlled active ride height system
The aim of this thesis is to increase the mobility capabilities of wheeled military vehicles by designing a preview control strategy with Model Predictive Controller (MPC). Mobility capabilities of a military vehicle such as trench and obstacle crossing in the off-road are base design criteria that limit the design. The study is basically divided into three parts. The target of the first part is to create a vehicle and create a co-simulation environment where MATLAB and ADAMS can run together. In the second part, the level of achievable improvement in vehicle's operational abilities is investigated. Developing a controller and optimizing vehicle ride height and position for better mobility operations are the main objectives of this part. The actuating system for the vehicle is its own hydropneumatic suspensions. All wheels are assumed to be independent and have height-adjustable springs/dampers. Many vehicles can adjust ride height passively according to off-road conditions. However, this passive adjustment can restrict mobility skills of the vehicle. In this thesis, measured road data is used to improve the controller performance and create an obstacle crossing algorithm. At the end of the first two parts of the study, comparison with simulations for different land operation scenarios is given for both uncontrolled and controlled system. By this, scenario-based results are compared, and improvement levels are determined.
Development of a roller bearing model for multibody simulations:Bearing vibration transfer path analysis
Mechanical systems are major sources of sound radiations and vibrations, even in their good operating conditions. The vibro-acoustic transfer functions of mechanical systems are crucial in Noise Vibration Harshness (NVH) analysis. Rotating machines are among common applications in mechanical engineering. Every mechanical component in rotating machines affect the total vibration transfer path. For this reason, for an accurate NVH modelling of the system, the detailed modelling of each component is required. With the advancements in commercial multibody simulation software and computational capacity of the modern computers, it is possible to model and simulate complex multibody systems. Rolling bearings are considered as the key elements in motion and vibration transmission. They are utilized to carry shaft and transmit the motion. Therefore, rolling bearings need to be modelled accurately by considering their varying dynamic characteristics. A number of studies have proposed and investigated various bearing dynamic models to estimate their dynamical behavior. Although available models have widely being used in industry and academia, their accuracy in estimation of bearing vibrations and vibration transfer path is still doubtful. In this regard, modelling and implementation of the rolling bearing contact mechanism plays major role in bearing vibration transfer path function. Rolling bearing contacts are usually considered as Hertz contact in the literature. In contrast, the recent investigations show the importance of the Elastohydrodynamic (EHD) contacts in dynamic modelling of mechanical parts. The EHD contacts can be simulated and analyzed using Reynolds and Computational Fluid Dynamics (CFD). Within the objectives of the current study, three rolling bearing dynamic models based on three various contact models using, Hertz, Reynolds, and CFD are developed. For this purpose, bearing contacts are considered as Kelvin-Voigt spring-dampers, and extended to a total rolling bearing model in a Multibody Simulation (MBS) environment. Then, their dynamic properties and transfer paths are investigated and compared numerically in the time and frequency domain. The numerical results illustrate and highlight the differences and limitations of the above mentioned bearing contact modelling methods in the context of the total bearing model.
Development of a roller bearing model for multibody simulations:Bearing vibration transfer path analysis
Mechanical systems are major sources of sound radiations and vibrations, even in their good operating conditions. The vibro-acoustic transfer functions of mechanical systems are crucial in Noise Vibration Harshness (NVH) analysis. Rotating machines are among common applications in mechanical engineering. Every mechanical component in rotating machines affect the total vibration transfer path. For this reason, for an accurate NVH modelling of the system, the detailed modelling of each component is required. With the advancements in commercial multibody simulation software and computational capacity of the modern computers, it is possible to model and simulate complex multibody systems. Rolling bearings are considered as the key elements in motion and vibration transmission. They are utilized to carry shaft and transmit the motion. Therefore, rolling bearings need to be modelled accurately by considering their varying dynamic characteristics. A number of studies have proposed and investigated various bearing dynamic models to estimate their dynamical behavior. Although available models have widely being used in industry and academia, their accuracy in estimation of bearing vibrations and vibration transfer path is still doubtful. In this regard, modelling and implementation of the rolling bearing contact mechanism plays major role in bearing vibration transfer path function. Rolling bearing contacts are usually considered as Hertz contact in the literature. In contrast, the recent investigations show the importance of the Elastohydrodynamic (EHD) contacts in dynamic modelling of mechanical parts. The EHD contacts can be simulated and analyzed using Reynolds and Computational Fluid Dynamics (CFD). Within the objectives of the current study, three rolling bearing dynamic models based on three various contact models using, Hertz, Reynolds, and CFD are developed. For this purpose, bearing contacts are considered as Kelvin-Voigt spring-dampers, and extended to a total rolling bearing model in a Multibody Simulation (MBS) environment. Then, their dynamic properties and transfer paths are investigated and compared numerically in the time and frequency domain. The numerical results illustrate and highlight the differences and limitations of the above mentioned bearing contact modelling methods in the context of the total bearing model.
İç içe geçmiş silindirik, yüksek basınç altında çalışabilen, yüksek sızdırmazlığa sahip titanyum tüpün, elektron ışın kaynağı yöntemi kullanılarak deneysel kaynak parametre karakterizasyon çalışması ile elde edilmesi
Dünya genelinde ülkeler açısından savunma sanayi sektörü, sürekli ve değişen diplomatik dengelerden ötürü büyük önem arz etmekte olup; bu sektörün önemi günden güne artmaktadır. Ülkelerin savunma sanayi sektöründe önem verdikleri sistemlerden biri de hava savunma füzeleridir. Bu bağlamda, bu tez çalışması kapsamında kızılötesi arayıcı başlığa sahip hava savunma füze sistemlerinde kullanılan arayıcı başlık soğutma performans ihtiyacını karşılamak amacıyla görev yapacak sistemin ana bileşenlerinden biri olan basınçlı tüpün tasarımı ve geliştirme aşamalarından bahsedilmiştir. Bu tasarım geliştirme çalışmalarının en kritik aşamalarıdan biri olan elektron ışın kaynağı prosesi ve proses parametreleri irdelenmiştir. Elektron ışın kaynağı kulllanılarak, deney tabanlı yaklaşımla, tüp malzemesine yönelik kaynak parametre çalışma yapılmış olup; parametreler belirlenirken maksimum kaynak performansı açısından bir tasarım yaklaşımı geliştirilmiştir. Kaynak parametre çalışması, tahribatlı ve tahribatsız kaynak muayeneleri ile desteklenmiş olup, elde edilen sistemin patlama ve sızdırmazlık performansı incelenmiştir. Elde edilen basınçlı tüpün patlama performansı açısından emniyet gereksinimini sağladığı ve 20 yıl kontrollü depo koşullarında saklandığı takdirde, sızdırmazlığının kabul edilebilir seviyelerde olduğu yapılan deneylerle ispatlanmıştır. Bu deneyler kapsamında deney düzenekleri tasarlanmış olup, ileride bu kapsamda yapılacak çalışmalarda test alt yapısının hazır olması büyük önem arz etmektedir. Sonuç olarak bu çalışma ile, patlama basıncı 900 bar'dan fazla, He sızdırmazlık değeri den daha az (20 yıl görev ömrü sonunda 1 bardan az basınç kaybı) ağırlığı 500 gr'dan az olan, içerisinde yaklaşık 90 ml gaz depolayabilen, titanyum gövde malzemeli ve elektron ışın kaynak yöntemi ile kapalı bir hacme dönüştürülen, iç içe geçmiş çift silindirik yapıda bir basınçlı tüp elde edilmiştir.
An electrification solution for Istanbul metrobus line
In the present case, Istanbul Metrobus Line is operated by Metrobus vehicle with internal combustion engines. This situation is not suitable and sustainable in terms of operating cost and environment pollution. If this line was operated with electric vehicles, it would have lower operation costs and would reduce harmful effects to the environment. As an alternative solution, in this thesis, economically and technically the most suitable electric vehicle solution is determined according to the requirement obtained by driving cycle, environmental conditions, passenger occupancy rates and characteristic of the vehicle. In July 2018, in order to determine the characteristic of the vehicle, a coast down test was performed with an 18 meter articulated Metrobus. Additionally, to create the driving cycle; position, velocity, acceleration and time data were acquired from a Metrobus in service with IMU and GPS. Passenger flow data were generated from data that were obtained from the bus operator company. So as to find out HVAC system requirement of the Metrobus, weather data of Istanbul is obtained from Turkish State Meteorological Service and with the solar position data calculated heat loads of the vehicle were determined according to ASHRAE Standard. According these data, all system requirements are obtained. First of all, according to power requirements of the 18-m articulated bus, the traction system is selected and a suitable gearbox ratio for that traction system is determined to fulfill the system requirements. Secondly, the most important sub-system for passenger comfort, HVAC, is selected in compliance with the weather data. Thirdly, charger and batteries of different chemistry are selected for different lines. Finally, two types of fleets with different charging strategies are designed. At the end of the study, fleets that have different batteries and different charging strategies are compared with each other and with current diesel Metrobus fleet. For the comparison cost of all components are obtained and total cost of ownership of these three fleets are calculated. The most suitable electrification solution is obtained according to these calculations.
Model predictive controller implementation to a multicopter for stability augmentations
Nowadays, multi-rotor systems are widely used in military, civil and academic applications thanks to their cheap, simple and suitable structures for use in different areas such as surveillance and load carrying. On the other hand, thanks to processor and sensor technologies' progress, modern and high computation power-requiring control methods, such as model predictive controller, have become applicable even on these small systems. This thesis study aims to improve the stability and performance of a multi-rotor system with a model predictive controller. The thesis study can be summarized in six main processes. During the study, firstly, a system model consistent with system identification was obtained. Subsequently, this model was verified with flight tests. In the second part, a simulation model was established using MATLAB-Simulink software and, a model predictive controller was designed with "MPC Designer". This controller has been tested in the simulation environment and compared with the reference PID controller. After satisfactory performance results were obtained, C code was generated with "Embedded Coder", it was added to the existing autopilot software, and software in the loop tests were completed. After this step, the generated code was implemented on the Jetson NANO board and the hardware in the loop tests were started. After accomplishing sufficient performance in these tests, flight tests were started. Finally, the system was tested in a real application and compared with the reference controller. Keywords: Model Predictive Control, System Identification, Multirotor, Quadcopter, Software in the Loop, Hardware in the Loop
Model predictive controller implementation to a multicopter for stability augmentations
Nowadays, multi-rotor systems are widely used in military, civil and academic applications thanks to their cheap, simple and suitable structures for use in different areas such as surveillance and load carrying. On the other hand, thanks to processor and sensor technologies' progress, modern and high computation power-requiring control methods, such as model predictive controller, have become applicable even on these small systems. This thesis study aims to improve the stability and performance of a multi-rotor system with a model predictive controller. The thesis study can be summarized in six main processes. During the study, firstly, a system model consistent with system identification was obtained. Subsequently, this model was verified with flight tests. In the second part, a simulation model was established using MATLAB-Simulink software and, a model predictive controller was designed with "MPC Designer". This controller has been tested in the simulation environment and compared with the reference PID controller. After satisfactory performance results were obtained, C code was generated with "Embedded Coder", it was added to the existing autopilot software, and software in the loop tests were completed. After this step, the generated code was implemented on the Jetson NANO board and the hardware in the loop tests were started. After accomplishing sufficient performance in these tests, flight tests were started. Finally, the system was tested in a real application and compared with the reference controller. Keywords: Model Predictive Control, System Identification, Multirotor, Quadcopter, Software in the Loop, Hardware in the Loop
Yaw dynamics control of three wheeled hybrid vehicle by torque vectoring
In this thesis, the lateral dynamics of the three-wheeled hybrid vehicle were evaluated. Mechanical components and moving parts such as the vehicle chassis, suspensions, steering system, and tires are modeled on Adams/Car software. On the other hand, powertrain components such as ICE, electric motors, generators, transmissions, batteries, and controllers such as Energy Management System, Speed Controller and Direct Yaw Controller are modeled in MATLAB/Simulink software. The energy management system is designed according to the maximum SoC strategy and the direct yaw controller with torque vectoring and active braking is designed according to the LQR control strategy. Then, detailed system analyses were performed with the co-simulation technique. The effects of speed, acceleration, battery level, friction coefficient and torque transfer resulting from mode change on lateral dynamics have been investigated and the performance of the yaw controller has been observed against these effects.
Yaw dynamics control of three wheeled hybrid vehicle by torque vectoring
In this thesis, the lateral dynamics of the three-wheeled hybrid vehicle were evaluated. Mechanical components and moving parts such as the vehicle chassis, suspensions, steering system, and tires are modeled on Adams/Car software. On the other hand, powertrain components such as ICE, electric motors, generators, transmissions, batteries, and controllers such as Energy Management System, Speed Controller and Direct Yaw Controller are modeled in MATLAB/Simulink software. The energy management system is designed according to the maximum SoC strategy and the direct yaw controller with torque vectoring and active braking is designed according to the LQR control strategy. Then, detailed system analyses were performed with the co-simulation technique. The effects of speed, acceleration, battery level, friction coefficient and torque transfer resulting from mode change on lateral dynamics have been investigated and the performance of the yaw controller has been observed against these effects.
Robust data-driven fixed-order H∞ controller synthesis using convex optimization
The main objective of this thesis study is to develop fixed-order (low-order) structured controller design methods for frequency domain non-parametric uncertain systems using convex optimization. The majority of the available controller synthesis methods are based on the mathematical model of the system dynamics. The performance of these model based control methods entirely relies on the accuracy of the model. Model uncertainty, due to unmodeled system dynamics, nonlinearities and operating point changes, are almost inevitable and may cause controller performance degradation due to the fact that there is always a trade-off between performance of the closed loop system and robustness. Therefore, model based methods may impede desired high performance requirements of today's industrial complex dynamical systems. In this thesis, a novel robust data-driven fixed-order H1 controller design method based on convex optimization is proposed for linear single input single output systems. Linear time-invariant systems represented by non-parametric frequency domain data and linearly parameterized controllers are considered. The proposed approach renders the need for a mathematical model of the controlled plant unnecessary. First, a semi-definite convex optimization algorithm, which is based on the concept of the Chebyshev center of a set of points, is proposed to simultaneoi usly compute a minimal uncertainty bound and corresponding nominal model from the experimental data. Thanks to this algorithm, multiple measurements can be considered in the robust control design method instead of one set of measurement with minimal uncertainty bound. Then, a new sufficient robust performance condition is derived using Nyquist stability theorem and synthesis methods on the Nyquist plot. Low-order controllers such as lead-lag compensators and proportional integral derivative (PID) controller are much desired in today's industrial process due to their engineering advantages. Therefore, a convex optimization method is developed which optimizes the coefficients of the fixed-order controllers while guaranteeing internal stability and robustness. Furthermore, the proposed method allows formulating closed-loop model matching objective and control input constraints by convex functions. An extension of the one degree of freedom controller design algorithm is proposed to synthesise two degree of freedom controllers for reference tracking of the non-parametric systems. The presented theoretical design approaches are experimentally verified on position control of an electromechanical actuation systems of an air vehicle.
Handling analysis of tracked and wheeled military vehicles
The aim of this thesis is to create a simulation environment that can model non-linear dynamics of tracked vehicles and wheeled vehicles including track-ground and tire-ground relations. Firstly, three different tracked vehicles and two different wheeled vehicles have been modelled in MATLAB SIMULINK environment. The tracked vehicles are six, eight and ten road wheel vehicles, while wheeled vehicles are Ackermann steered and skid steered 6x6 wheeled vehicles. The dynamic models of tracked and wheeled vehicles differentiate in terms only tire and track; all the parameters of the hulls of the vehicles are the same. For traction force calculation, the flexible pad formula has been used for tracked vehicles and has been adopted to wheeled vehicles. Also, stability definitions that are available in the literature for linear and simple vehicle models have been implemented for all vehicles and, the transitions between neutral steer to understeer or neutral steer to oversteer behaviors have been represented for created non-linear vehicle models. After the analysis it has been concluded that, for tracked vehicles, as the number of the road wheels increases the agility of the vehicle increases. Moreover, with this thesis parameter set, skid steering vehicles show oversteering behaviors whereas Ackermann steering vehicle shows understeering behaviors. In addition to these, adopted flexible pad formula for wheeled vehicles performs coherent responses with the literature and reveals expected results.