Active vibration control of transverse vibrating segmented marine riser

Vortex induced vibration (VIV) could be regarded as a fluid-structure interaction vibration type where the bluff structure vibrates due to fluid flowing around the body. The separation of boundary layer has created vortex layer that staggers the structure in cross-flow direction. VIV suppression work has attracted numerous researchers to build a passive device that could reduce the vibration. However, such device requires an intricate design which incurs high expense and indirectly contributes to higher chance of VIV occurrence due to the additional mass to the system. This research proposed a method to overcome those shortcomings by introducing an active flow control concept to the system. Since the vibration originates from unhindered flowing fluid, the approach is to avoid the development of the vortex by attaching a single control rod to the system as an actuator. The actuator injects momentum to the boundary layer thus preventing the VIV phenomenon. Both simulation and experimental works were implemented in this study. The input-output data of the system were measured directly from the experimental rig. For system identification, three methods were employed which were least square (LS), recursive least square (RLS) and differential evolutionary (DE) algorithms. It was found that the DE methods were stable, had considerably lower mean squared error (MSE) and the transfer function itself represented the natural frequency of the system. The study was continued by tuning the proportionalintegral- derivative (PID) based controllers to the simulated system plant in offline mode. The PID based controllers were tuned using heuristic and Ziegler-Nichols (ZN) methods. The best performance was recorded. However, it was observed that once the disturbance of the system changed, the performance of the PID tuned using heuristic and ZN were deteriorated. To overcome this drawback, adaptive tuning algorithms were introduced, namely ZN-Fuzzy-PID and ZN-Fuzzy-Iterative Learning Algorithm-PID (ZN-Fuzzy-ILA-PID) based controllers. In simulation, it was found that the ZN-Fuzzy-ILA-PD controller outperformed other controllers with 57.82 dB of attenuation level. In experimental works, dynamic response comparison was made between the bare pipe, fixed single and double control rods. It was observed that the fixed single and double control rods could not effectively attenuate the system, but amplified the vibration instead. Further experimental work was conducted by varying the rotating speed of the actuator at various disturbances. The result shows that at 100 % actuator rotating speed with 33 Hz disturbance flow to the system, the vibration was successfully reduced with attenuation level of 20.71 dB. However, by changing the disturbance, the actuator performance was reduced. Therefore, the controller was adaptively tuned using the fuzzy and iterative learning (ILA) schemes. It was observed that the maximum vibration attenuation was achieved by ZN-Fuzzy-ILA-PD controller with 13.8 dB of attenuation level at changing disturbance. Overall results show that by adopting the single rotating control rod, the vibration of VIV could be successfully attenuated

Synthesis of Hybrid Fuzzy Logic Law for Stable Control of Magnetic Levitation System

In this paper, we present a method to design a hybrid fuzzy logic controller (FLC) for a magnetic levitation system (MLS) based on the linear feedforward control method combined with FLC. MLS has many applications in industry, transportation, but the system is strongly nonlinear and unstable at equilibrium. The fast response linear control law ensures that the ball is kept at the desired point, but does not remain stable at that point in the presence of noise or deviation from the desired position. The controller that combines linear feedforward control and FLC is designed to ensure ball stability and increase the system's fast-response when deviating from equilibrium and improve control quality. Simulation results in the presence of noise show that the proposed control law has a fast and stable effect on external noise. The advantages of the proposed controller are shown through the comparison results with conventional PID and FLC control laws

Aeronautical Engineering: A special bibliography with indexes, supplement 74

This special bibliography lists 295 reports, articles, and other documents introduced into the NASA scientific and technical information system in August 1976

FUNDAMENTAL STUDY AND DEVELOPMENT OF TUNED ACTIVE FLOW CONTROL ACTUATORS

A novel, multi-level, flow-control actuator was developed using piezoceramic materials. Several actuators were fabricated in various shapes and sizes to produce a variety of effects for flow control applications. The actuators were studied in a quiescent-air bench test to understand the vibrations produced by various actuator shapes. The actuator flow-control effect was studied experimentally with flat-plate and cavity configurations, and was studied numerically using moving boundary conditions and dynamic meshing. The disturbances produced by the actuator couple with the cavity flow field producing increased cavity tones, increased vorticity, and sustainment of large-scale vorticity downstream of the cavity. The combined actuation result, from perturbations upstream of the cavity to increased vorticity downstream of the cavity, is the novel multi-level actuator developed and studied in this research. The largest actuator was experimentally tested in boundary layers with free-stream Mach numbers from 0.1 to 0.5 and Reynolds numbers, based on momentum thickness, from approximately 800 to 3600. Actuator effects were measured using high-frequency-response pressure instrumentation in the floor downstream of the actuator. The actuator produced disturbances with amplitudes at least 30 dB above the noise floor and frequencies nine-times the actuator driving frequency. The disturbances created by the actuator coupled with the boundary layer flow and were observable up to 62 kHz. A time-dependent effect from changing actuation frequency was observed on the stability of the flow. A compact, multi-actuator pack was designed to study multi-level flow control using experimental tests of a two-dimensional cavity flow at Mach numbers of 0.1, 0.2, and 0.3. Actuator operation did not produce amplified cavity oscillations at all Rossiter tones in the experiments. However, significant flow coupling occurred when the actuator driving frequency matched a Rossiter tone and a fundamental cavity acoustic tone. The cavity amplifications were stronger when the distance between the actuator and the cavity leading edge was increased. The numerical simulations showed that the actuator produced cavity flow amplifications at the first Rossiter tone about 8 dB higher amplitude than without actuation

Large Eddy Simulation of the Pulsating, Non-Reacting Flow in Combustion Chambers

In the present work a numerical investigation of the pulsating, non-reacting flow in a combustion chamber, and a coupled system of burner plenum and combustion chamber is presented. The results are compared with an analytical model and experimental data. The numerical simulations provide the damping ratio, an important input, for the analytical model, which was developed to predict the stability limits of technical combustion systems

Aeronautical Engineering: A continuing bibliography, supplement 120

This bibliography contains abstracts for 297 reports, articles, and other documents introduced into the NASA scientific and technical information system in February 1980

Aeronautical engineering: A continuing bibliography, supplement 122

This bibliography lists 303 reports, articles, and other documents introduced into the NASA scientific and technical information system in April 1980

Aeronautical Engineering: A continuing bibliography with indexes, supplement 137, July 1981

This bibliography lists 483 reports, articles, and other documents introduced into the NASA scientific and technical information system in June 1981