Vehicle handling models are commonly used in the design and analysis of vehicle dynamics. Especially, with the advances in vehicle control systems need for accurate and simple vehicle handling models have increased. These models have parameters, some of which are known or easily obtainable, yet some of which are unknown or difficult to obtain. These parameters are obtained by system identification, which is the study of building model from experimental data. In this thesis, identification of vehicle handling models is based on data obtained from the simulation of complex vehicle dynamics model from ADAMS representing the real vehicle and a general methodology has been developed. Identified vehicle handling models are the linear bicycle model and vehicle roll models with different tire models. Changes of sensitivity of the model outputs to model parameters with steering input frequency have been examined by sensitivity analysis to design the test input. To show that unknown parameters of the model can be identified uniquely, structural identifiability analysis has been performed. Minimizing the difference between the data obtained from the simulation of ADAMS vehicle model and the data obtained from the simulation of simple handling models by mathematical optimization methods, unknown parameters have been estimated and handling models have been identified. Estimation task has been performed using MATLAB Simulink Parameter Estimation Toolbox. By model validation it has been shown that identified handling models represent the vehicle system successfully.

In this thesis large deformation behavior of shell structures under high intensity transient loading conditions is investigated by means of finite element method. For this purpose an explicit finite element program is developed with interactive user interface. The developed program deals with geometric and material nonlinearities which stem from large deformation elastic - plastic behavior. Results of the developed code are compared with the experimental data taken from the literature and simulation results of the commercial finite element program Ls-Dyna. Moreover, sensitivity study is carried out for mesh size, element type and material model parameters. After the comparison and verification of the obtained results, it is concluded that converged and reasonable results are achieved.

In this study, the Element-Free Galerkin (EFG) method has been used for the analysis of plane stress problems. A computer program has been developed by using FORTRAN language. The moving least squares (MLS) approximation has been used in generating shape functions. The results obtained by the EFG method have been compared with analytical solution and the numerical results obtained by MSC. Patran/Nastran. The comparisons show that the mesh free method gives more accurate results than the finite element approximation with less computational effort.

Ethanol is an environmental friendly alternative diesel fuel that has received significant attention both as a possible renewable alternative fuel and as an additive to existing petroleum-based fuels. Beyond simply representing an additional fuel supply, ethanol exhibits several advantages when compared to existing petroleum fuel. The objective of this work is to investigate experimentally the effects of using different blends of specified percentages of ethanol on the engine performance and emissions and to compare it with that of conventional diesel fuel. Tests will be done on the &lsquo / &lsquo / Engine Test Laboratory&rsquo / &rsquo / of the Turkish Tractor Factory (TTF) using a fourcylinder, turbocharged and naturally aspirated, DI diesel engines. Engine performance parameters such as engine speed, torque, power, fuel consumption will be measured. At the same time, the engine emissions including particulate matter, unburned hydrocarbons, carbon monoxide, and NOX will also be recorded.

A nanofluid is the suspension of nanoparticles in a base fluid. Nanofluids are promising for heat transfer enhancement due to their high thermal conductivity. Presently, discrepancy exists in nanofluid thermal conductivity data in the literature, and enhancement mechanisms have not been fully understood yet. In the first part of this study, a literature review of nanofluid thermal conductivity is performed. Experimental studies are discussed through the effects of some parameters such as particle volume fraction, particle size, and temperature on conductivity. Enhancement mechanisms of conductivity are summarized, theoretical models are explained, model predictions are compared with experimental data, and discrepancies are indicated. Nanofluid forced convection research is important for practical application of nanofluids. Recent experiments showed that nanofluid heat transfer enhancement exceeds the associated thermal conductivity enhancement, which might be explained by thermal dispersion, which occurs due to random motion of nanoparticles. In the second part of the study, to examine the validity of a thermal dispersion model, hydrodynamically developed, thermally developing laminar Al2O3/water nanofluid flow inside a circular tube under constant wall temperature and heat flux boundary conditions is analyzed by using finite difference method with Alternating Direction Implicit Scheme. Numerical results are compared with experimental and numerical data in the literature and good agreement is observed especially with experimental data, which indicates the validity of the thermal dispersion model for explaining nanofluid heat transfer. Additionally, a theoretical analysis is performed, which shows that usage of classical correlations for heat transfer analysis of nanofluids is not valid.

Design process of a solid rocket motor with the objective of meeting certain mission requirements can be specified as a search for a best set of design parameters within the overall design constraints. In order to ensure that the best possible design amongst all achievable designs is being achieved, optimization is required during the design process. In this thesis, an optimization tool for internal ballistic design of solid rocket motors was developed. A direct search method Complex algorithm is used in this study. The optimization algorithm changes the grain geometric parameters and nozzle throat diameter within the specified bounds, finally achieving the optimum results. Optimization tool developed in this study involves geometric modeling of the propellant grain, burnback analysis, a 0-dimensional ballistic performance prediction analysis of rocket motor and the mathematical optimization algorithm. The code developed is verified against pretested rocket motor performance.

Low frequency noise caused by vibrating panels can pose problems for vehicles from noise, vibration and harshness (NVH) standpoint. In order to reduce interior noise levels in cars, some structural modifications are required on the car body. Structural modifications studied in this work are stiffeners welded on the walls of enclosed structure to change vibration characteristics. In this thesis, interaction between acoustic domain inside closed structures and their vibrating enclosing boundaries are analyzed. Analysis of vibro-acoustic behavior includes frequency response analysis of structure by Finite Element Method (FEM) and sound pressure level (SPL) prediction of the cabin interior by Boundary Element Method (BEM). The standard parts of the analyses are performed using available CAE (Computer Aided Engineering) software. It is demonstrated that the structural modification technique integrated with the vibro-acoustic model of the system reduces the computational effort considerably. The frequency response functions of a structure for each modification can easily be obtained in a fast and efficient way by using the structural modification technique. Thus, effects of design changes in the structure body on noise levels due to vibration of the structure can be very handily and efficiently studied. In the case studies presented, the effects of various different stiffeners applied on a simple closed structure are studied in detail.

The behavior of structures is totally different when they are exposed to fluctuating loading rather than static one which is a well known phenomenon in engineering called fatigue. When the loading is not static but dynamic, the dynamics of the structure should be taken into account since there is a high possibility to excite the resonance frequencies of the structure especially if the loading frequency has a wide bandwidth. In these cases, the structure&rsquo / s response to the loading will not be linear. Therefore, in the analysis of such situations, frequency domain fatigue analysis techniques are used which take the dynamic properties of the structure into consideration. Vibration fatigue method is also fast, functional and easy to implement. In this thesis, vibration fatigue theory is examined. Throughout the research conducted for this study, the ultimate aim is to find solutions to problems arising from test application for the loadings with nonzero mean value bringing a new perspective to mean stress correction techniques. A new method is developed to generate a modified input loading history with a zero mean value which leads in fatigue damage approximately equivalent to damage induced by input loading with a nonzero mean value. A mathematical procedure is proposed to implement mean stress correction to the output stress power spectral density data and a modified input loading power spectral density data is obtained. Furthermore, this method is improved for multiaxial loading applications. A loading history power spectral density set with zero mean but modified alternating stress, which leads in fatigue damage approximately equivalent to the damage caused by the unprocessed loading set with nonzero mean, is extracted taking all stress components into account using full matrixes. The proposed techniques&rsquo / efficiency is discussed throughout several case studies and fatigue tests.

RHex is an autonomous hexapedal robot capable of locomotion on rough terrain. Up to now, most modelling and simulation efforts on RHex were based on the linear leg assumption. These models disregarded what might be seen as the most characteristic feature of the latest iterations of this robot: the half circular legs. This thesis focuses on developing a more realistic model for this specially shaped compliant leg and studying its effects on the kinematics and dynamics of the resulting platform. One important consequence of the half circular compliant leg is the resulting rolling motion. Due to rolling, the rest length of the leg changes and the leg-ground contact point moves. Another consequence is the varying stiffness of the legs due to the changing rest length. These effect the resulting behaviour of any platform using these legs. In the first part of the thesis we are studying the effects of the half circular leg morphology on the kinematics of RHex using a simple planar model. The rest of the studies within the scope of this thesis focuses on the effect of the half circular compliant legs on the dynamics of a single legged hopping platform with a point mass. The formulation derived in this work is successfully integrated in a readily working but rather simple model of a single legged hopping system. We replace the equations of the straight leg in this model by the equations of the half circular compliant leg. Realistic results are obtained in the simulations and these results are compared to those obtained by the simpler constant stiffness straight leg model. This more realistic leg model brings us the opportunity to further study the effects of this leg morphology, in particular the positive effects of the resulting rolling motion on platform stability.

In this thesis, it is aimed to determine the ballistic limit thicknesses of ST-37 steel plates under oblique impact of bullets having hard steel core (DIN 100Cr6 at 61-62 HRc) by using both experimental and numerical methods. In experimental part, angles of attack of the bullets are changed from 0 to 70 degrees by 10 degrees increments. Bullet velocities are measured for each shot just before the impact and they are found to be between 790-830 m/s. The minimum plate thickness that is not perforated and the maximum plate thickness that is perforated are determined by conducting three shots for each angle of attack - plate thickness combination. After the monolithic case, for some angles, layered plate combinations are also investigated. In the numerical analysis part, Johnson Cook constitutive and failure models are used together with the data obtained from literature. Experiments are simulated numerically by using a commercial non-linear explicit hydrocode software package, ANSYS AUTODYN. Results of the numerical simulations and the experimental findings are presented in tabular and graphical forms and then compared to each other.