Runway friction testing is performed in order to enhance the safety of aircraft operation on runways. Preventative maintenance friction surveys are performed to determine if there is any deterioration of the frictional resistance on the surface over a period of time and to determine if there is a need for corrective maintenance. In addition operational performance friction surveys are performed to determine frictional properties of a pavement surface in order to provide corrective action information in maintaining safe take-off or landing performance limits. A major issue encountered in both types of friction evaluation on runways is the standardization of the friction measurements from different Continuous Friction Measuring Equipment (CFME). The International Friction Index (IFI) has been formulated to address the above issue and determine the friction condition of a given runway is a standardized format. The ASTM recommended standard procedure to compute the IFI of a runway surface employs two distinct parameters to express the IFI; F60 is the friction value adjusted to a slip speed of 60 km/h and correlated to the standard Dynamic Friction Tester (DFT) measurement. And Sp is the speed constant which is governed by the mean profile depth of that surface. The primary objective of this thesis is to investigate the reliability of the current ASTM procedure to standardize runway friction measurements in terms of IFI. Based on the ASTM standard procedure, two equipment specific calibration constants (A and B) are assigned for each CFME during calibration. Then, in subsequent testing those calibrations constants can be used to adjust the equipment measurements to reliable IFI values. Just as much as A and B are presumed to be characteristic of any given CFME, they are also expected to be independent of the operational speed. The main objective of the annual NASA Runway Friction Workshop held in Wallops Island, Virginia, is to calibrate commonly used CFMEs such that all calibrated equipment would provide a standard reading (i.e. IFI) on a particular surface. During validation of the existing ASTM procedure using the NASA Runway Friction Workshop data it was observed that the single value-based IFI predictions of the calibrated CFMEs were inaccurate resulting in low correlations with DFT measured values. Therefore, a landing pilot should not be left to make a safe decision with such an uncertain single standard friction value because the actual standard friction value could very well be much less than this value. Hence a modified procedure was formulated to treat the calibration constants A and B as normally distributed random variables even for the same CFME. The new procedure can be used to predict the IFI (F60) of a given runway surface within a desired confidence interval. Since the modified procedure predicts a range of IFI for a given runway surface within two bounds, a landing pilot's decision would be made easier based on his/her experience on critical IFI values. However, even the validation of the modified procedure presented some difficulties since the DFT measurements on a few validated surfaces plotted completely outside the range of F60 predicted by the modified method. Furthermore, although the ASTM standard stipulates the IFI (F60) predictions to be independent of the testing speed, data from the NASA Runway Friction Workshop indicates a significant difference in the predictions from the two testing speeds of 65 km/hr and 95 km/hr, with the results from the 65 km/hr tests yielding better correlations with the corresponding DFT measurements. The above anomaly could be attributed to the significantly different FR60 values obtained when the 65 km/hr data (FR65) and 95 km/hr data (FR95) are adjusted to a slip speed of 60 km/hr. Extended analytical investigations revealed that the expected testing speed independency of the FR60 for a particular CFME cannot be supported by the ASTM defined general linear relationship between Sp and the mean profile depth which probably has been formulated to satisfy a multitude of CFMEs operating on a number of selected test surfaces. This very reason can also be attributed to the above mentioned outliers observed during the validation of the modified procedure.

This dissertation is compiled of the findings of several phases of a detailed research study that was aimed at investigating the Skid Resistance phenomenon. In the first phase of the dissertation research a study was performed to evaluate the different factors that influence frictional measurements obtained using the Dynamic Friction Tester (DFT). A temperature calibration factor that would account for temperature effects on DFT readings and IFI computations was developed. In addition, other variables that also affect the friction measurements obtained using the DFT are identified. In the next phase of the dissertation research the effect of pavement roughness on the Skid Resistance was investigated. The variation of the normal load and its nonlinear relation to SN was used to explain lower SN values measured on relatively rougher surfaces. The feasibility of using the International Roughness Index (IRI) and the Dynamic Load Coefficient (DLC) as predictors of the reduction in SN due to pavement roughness was also investigated. In the final phase of the dissertation research an in-depth investigation was carried out to better understand the principles underlying the concept of the International Friction Index (IFI), and specifically the role played by the Speed Constant ( Sp) parameter in the IFI computations. The parameter Sp dictates the speed variation of the wet friction measurements taken on a given pavement surface. The results of the current investigation suggest the revision of the procedure for computation of the Sp parameter to incorporate device specific properties. Furthermore, the incorporation of vehicle characteristics in the Sp parameter computations would help address a well known deficiency of the IFI, which is the inconsistent FR60 (predicted friction at 60 km/h) obtained from the friction values measured at two different slip speeds on the same surface. This study also showed that the modification of the Sp parameter reduces significantly the slip speed dependency of the device calibration parameters A and B. Finally, a modified IFI procedure that incorporates device specific slip conditions is presented. The modified IFI procedure showed consistently better predictive capability than the conventional ASTM procedure on all the different devices considered in this study.

Pavement roughness has been found to have an effect on the coefficient of friction measured with the Locked-Wheel Skid Tester (LWT) with measured friction decreasing as the long wave roughness of the pavement increases. However, the current pavement friction standardization model adopted by the American Society for Testing and Materials (ASTM), to compute the International Friction Index (IFI), does not account for this effect. In other words, it had been previously assumed that the IFI's speed constant (SP), which defines the gradient of the pavement friction versus speed relationship, is an invariant for any pavement with a given mean profile depth (MPD), regardless of its roughness. This study was conducted to quantify the effect of pavement roughness on the IFI's speed constant. The first phase of this study consisted of theoretical modeling of the LWT using a two-degree of freedom vibration system. The model parameters were calibrated to match the measured natural frequencies of the LWT. The calibrated model was able to predict the normal load variation during actual LWT tests to a reasonable accuracy. Furthermore, by assuming a previously developed skid number (SN) versus normal load relationship, even the friction profile of the LWT during an actual test was predicted reasonably accurately. Because the skid number (SN) versus normal load relationship had been developed previously using rigorous protocol, a new method that is more practical and convenient was prescribed in this work. This study concluded that higher pavement long-wave roughness decreases the value of the SP compared to a pavement with identical MPD but lower roughness. Finally, the magnitude of the loss of friction was found to be governed by the non-linear skid number versus normal load characteristics of a pavement.

In this thesis, control schemes for the self-excited induction generator are developed with Matlab/Simulink. Self-excited induction generator is considered as a constant voltage-constant frequency supply for an isolated load. A wind turbine is assumed to be the variable-speed drive of the induction generator. Control schemes aim to ensure a constant voltage-constant frequency operation of the induction generator in case of the variations in the wind speed and/or the load. From the general model of the self-excited induction generator, the characteristics of the system and the dynamic responses of the system in case of any disturbance are examined. Next, the control strategies are developed both for the squirrel-cage rotor induction generator and for the wound-rotor induction generator. Two control loops are necessary for constant voltage-constant frequency operation of a variable speed induction generator, one for the voltage regulation and the other for the frequency regulation. After developing the control loops, constant voltage-constant frequency operation of the self-excited induction generator is simulated with a cage type saturation adaptive induction generator, a fixed capacitor with thyristor controlled reactor (TCR) used for frequency regulation and switched external resistors connected to the stator terminals used for voltage regulation.

Este trabalho apresenta a análise teórica e experimental do gerador assíncrono de dupla alimentação, denominado GEADA ao longo deste trabalho, operando em regime permanente com velocidade não fixa, mas com freqüência da armadura constante. Compreende o escopo do trabalho a análise teórica a partir do circuito equivalente do gerador, a análise teórica e experimental da curva de magnetização do GEADA operando em freqüência do rotor variável, uma proposta de adaptação da curva de capacidade aplicada na operação dos geradores síncronos para o GEADA e a sua análise considerando-o como máquina síncrona a partir dos seus terminais, os ensaios normalizados e complementares necessários para o levantamento dos parâmetros para este circuito equivalente e ensaios do GEADA operando com carga para verificação de seu desempenho Os resultados obtidos permitem um melhor entendimento desse sistema de geração, de suas condições de operação e utilização em sistemas de geração de velocidade não fixa como, por exemplo, sistemas eólicos e hidrelétricos. / The study presents the theoretical and experimental analysis of the double fed asynchronous generator, called GEADA, operating in steady state with non-fixed speed but with constant armature frequency. It comprehends the theoretical analysis based on the equivalent circuit of this generator, the theoretical and experimental analysis of the curve of magnetization of the GEADA operating with variable rotor frequency. A proposal of adaptation of the capability curve applied in the operation of the synchronous generators for the GEADA is also presented, its analysis considering it as a synchronous machine from its terminals, the standard and complementary tests necessary for the calculation of the parameters for the equivalent circuit and the tests with the GEADA operating under on-load conditions to verify its performance. The achieved results allow a better understanding of this generation system, its operational conditions and applicability to the power generation systems based on variable speed, such as wind and hydroelectric power plants.

Este trabalho apresenta a análise teórica e experimental do gerador assíncrono de dupla alimentação, denominado GEADA ao longo deste trabalho, operando em regime permanente com velocidade não fixa, mas com freqüência da armadura constante. Compreende o escopo do trabalho a análise teórica a partir do circuito equivalente do gerador, a análise teórica e experimental da curva de magnetização do GEADA operando em freqüência do rotor variável, uma proposta de adaptação da curva de capacidade aplicada na operação dos geradores síncronos para o GEADA e a sua análise considerando-o como máquina síncrona a partir dos seus terminais, os ensaios normalizados e complementares necessários para o levantamento dos parâmetros para este circuito equivalente e ensaios do GEADA operando com carga para verificação de seu desempenho Os resultados obtidos permitem um melhor entendimento desse sistema de geração, de suas condições de operação e utilização em sistemas de geração de velocidade não fixa como, por exemplo, sistemas eólicos e hidrelétricos. / The study presents the theoretical and experimental analysis of the double fed asynchronous generator, called GEADA, operating in steady state with non-fixed speed but with constant armature frequency. It comprehends the theoretical analysis based on the equivalent circuit of this generator, the theoretical and experimental analysis of the curve of magnetization of the GEADA operating with variable rotor frequency. A proposal of adaptation of the capability curve applied in the operation of the synchronous generators for the GEADA is also presented, its analysis considering it as a synchronous machine from its terminals, the standard and complementary tests necessary for the calculation of the parameters for the equivalent circuit and the tests with the GEADA operating under on-load conditions to verify its performance. The achieved results allow a better understanding of this generation system, its operational conditions and applicability to the power generation systems based on variable speed, such as wind and hydroelectric power plants.

Este trabalho apresenta a análise teórica e experimental do gerador assíncrono de dupla alimentação, denominado GEADA ao longo deste trabalho, operando em regime permanente com velocidade não fixa, mas com freqüência da armadura constante. Compreende o escopo do trabalho a análise teórica a partir do circuito equivalente do gerador, a análise teórica e experimental da curva de magnetização do GEADA operando em freqüência do rotor variável, uma proposta de adaptação da curva de capacidade aplicada na operação dos geradores síncronos para o GEADA e a sua análise considerando-o como máquina síncrona a partir dos seus terminais, os ensaios normalizados e complementares necessários para o levantamento dos parâmetros para este circuito equivalente e ensaios do GEADA operando com carga para verificação de seu desempenho Os resultados obtidos permitem um melhor entendimento desse sistema de geração, de suas condições de operação e utilização em sistemas de geração de velocidade não fixa como, por exemplo, sistemas eólicos e hidrelétricos. / The study presents the theoretical and experimental analysis of the double fed asynchronous generator, called GEADA, operating in steady state with non-fixed speed but with constant armature frequency. It comprehends the theoretical analysis based on the equivalent circuit of this generator, the theoretical and experimental analysis of the curve of magnetization of the GEADA operating with variable rotor frequency. A proposal of adaptation of the capability curve applied in the operation of the synchronous generators for the GEADA is also presented, its analysis considering it as a synchronous machine from its terminals, the standard and complementary tests necessary for the calculation of the parameters for the equivalent circuit and the tests with the GEADA operating under on-load conditions to verify its performance. The achieved results allow a better understanding of this generation system, its operational conditions and applicability to the power generation systems based on variable speed, such as wind and hydroelectric power plants.