The problem of converting existing continuous-time (CT) control systems into digital control systems is considered. The objective of this paper is to review, modify and compare three methods to obtain the discrete-time (DT) controller that take the closed-loop behavior into consideration. The first method is the partial compensation for ZOH effect method, it enhances the performance of discretized controllers in order to partially compensate the ZOH effect of the closed-loop digital control system, and to preserve the stability of the closed-loop digital control system. A modified approach is considered to improve the stability of the closed-loop digital system. The second method is the frequency response matching method, it is based on matching the frequency response of the digital control system to that of the continuous system with a minimum weighted mean-square error in the w-domain to obtain the parameters of the DT-controller. The third method is the plant input method, it is an indirect design method, which guarantees a stable control system when the DT-controllers are used to replace the CT-controllers. In this method the stability is assured for any sampling period used in pratice and even for unstable plants.

The problem of converting existing continuous-time (CT) control systems into digital control systems is considered. The objective of this paper is to review, modify and compare three methods to obtain the discrete-time (DT) controller that take the closed-loop behavior into consideration. The first method is the partial compensation for ZOH effect method, it enhances the performance of discretized controllers in order to partially compensate the ZOH effect of the closed-loop digital control system, and to preserve the stability of the closed-loop digital control system. A modified approach is considered to improve the stability of the closed-loop digital system. The second method is the frequency response matching method, it is based on matching the frequency response of the digital control system to that of the continuous system with a minimum weighted mean-square error in the w-domain to obtain the parameters of the DT-controller. The third method is the plant input method, it is an indirect design method, which guarantees a stable control system when the DT-controllers are used to replace the CT-controllers. In this method the stability is assured for any sampling period used in pratice and even for unstable plants.

The problem of converting existing continuous-time (CT) control systems into digital control systems is considered. The objective of this paper is to review, modify and compare three methods to obtain the discrete-time (DT) controller that take the closed-loop behavior into consideration. The first method is the partial compensation for ZOH effect method, it enhances the performance of discretized controllers in order to partially compensate the ZOH effect of the closed-loop digital control system, and to preserve the stability of the closed-loop digital control system. A modified approach is considered to improve the stability of the closed-loop digital system. The second method is the frequency response matching method, it is based on matching the frequency response of the digital control system to that of the continuous system with a minimum weighted mean-square error in the w-domain to obtain the parameters of the DT-controller. The third method is the plant input method, it is an indirect design method, which guarantees a stable control system when the DT-controllers are used to replace the CT-controllers. In this method the stability is assured for any sampling period used in pratice and even for unstable plants.

The dynamic characterization is important in making accurate predictions of the seismic response of the hybrid structures dominated by different damping mechanisms. Different damping characteristics arise from the construction of the tower with different materials: steel for the upper part; reinforced concrete for the lower main part and interaction with supporting soil. The process of modeling damping matrices and experimental verification is challenging because damping cannot be determined via static tests as can mass and stiffness. The assumption of classical damping is not appropriate if the system to be analyzed consists of two or more parts with significantly different levels of damping, such as steel/ concrete mixed structure - supporting soil coupled system. The dynamic response of structures is critically determined by the damping mechanisms, and its value is very important for the design and analysis of vibrating structures. An analytical approach capable of evaluating the equivalent modal damping ratio from structural components is desirable for improving seismic design. Two approaches are considered to define and investigate dynamic characteristics of hybrid tower of cable-stayed bridges: The first approach makes use of a simplified approximation of two lumped masses to investigate the structure irregularity effects including damping of different material, mass ratio, frequency ratio on dynamic characteristics and modal damping; the second approach employs a detailed numerical step-by step integration procedure in which the damping matrices of the upper and the lower substructures are modeled with the Rayleigh damping formulation.