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

Slamming impact accelerations analysis on small high speed passenger crafts

Small high speed passenger crafts (HSC) are commonly known for their poor seakeeping qualities. These crafts are frequently exposed to large slamming impacts and these repetitive shocks may pose danger to passengers’ safety and health. In Malaysia, small high speed passenger crafts having lengths between 7 to 9 meters are mainly used to transport tourists between popular island destinations. Evaluation on impact and vibration for this type of craft was conducted by using accelerometers attached to several locations on craft’s deck. The test was conducted at speeds ranged between 20 to 30 knots and the highest peak accelerations were recorded. The highest acceleration record during the sea trial was recorded at 4.22 g and the average acceleration measure is 2.20 g. Apart from this test, evaluation on effectiveness of the current foam seat typically used in this craft were evaluated using Dynamic Response Index (DRI) and results have shown that the seat is less efficient when impact reaches more than 1g at speeds of more than 20 knots. It is concluded that safety measures such as the use of more efficient suspension seat and limiting the operational speed need to be taken into consideration

Challenges and opportunities of marine propulsion with alternative fuels

The increasingly stringent shipping emissions regulations and global decarbonisation movement have prompted the adoption of alternative fuels in the shipping industry. This review presents the performance results and evaluation of alternative fuel engines under low-medium speed operation that has not been considered by existing reviews. This operating regime is typically used in marine propulsion. Relevant articles published by reputable journals were retrieved from scholarly databases and analysed. The evaluated alternative fuels were waste plastic oil (WPO), tyre pyrolysis oil (TPO), biodiesel, ammonia, vegetable oil (VO), and waste lubricant oil (WLO). Neat WPO and TPO demonstrated poorer emissions performances than diesel; alternatively, retarding the fuel injection timing of the WPO engine and blending the TPO with biodiesel had elevated engine performances substantially. As compared to VO degum and blending VO with diesel, VO preheating was a more promising approach to augment engine performance. Ammonia is an attractive candidate owing to its carbon-free chemical composition, but novel technologies are needed to address its terribly high NOx emission. Diesel-like fuel (DLF) derived from WLO produced notably better engine performance than fossil diesel. This review provides insight into liquid alternative fuels performances for low-medium speed engine operation, whose combustion physics is considerably different from high-speed operation. Such understandings are vital to address the current issues regarding marine engine systems, promoting the development of combustion technologies and alternative fuels uptake in marine propulsion

Intelligent Optimization of Force Tracking Parameters for MR Damper Modelling using Firefly Algorithm

Magnetorheological (MR) damper system is commonly used to replace the conventional damper in the suspension system due to its low power consumption, fast time response and simple structure. Since inner loop controller is very important in defining the amount of current supplied to the MR damper system, many existing controllers are found not well-structured in terms of calculating the optimum value of the controller parameter. Poor control design using the conventional method will cause the output current obtained for the MR damper to be unpredictable. To overcome this problem, an intelligent optimization method known as firefly algorithm (FA) was used by this study to optimize the force tracking controller (FTC) parameters as to achieve the exact damping force of MR damper system. The MR damper was first developed using Spencer model and the required voltage input was then provided by the FTC. The controller parameters were tuned using intelligent FA method in order to find the optimum values which would identify the accuracy of the force tracking that followed the MR damping force. The simulation shows that the FTC with FA technique is able to track the desired force better than the heuristic method up to 1.71 % error considering a given desired input force

Experimental study of vortex-induced vibrations of flexibly mounted cylinder in circulating water tunnel

This paper presents the experimental results concerning the vortex-induced vibration phenomena of a flexibly mounted enclosed smooth rigid pipe. The experiment was newly designed and fabricated, utilizing the circulating water tunnel concept. New results on the dynamic response of the vibrating system are shown. The stream flow was generated by using a large displacement volume submersible water tank, controlled through the ABB inverter. The rotation frequency controlled based was implemented in the ABB inverter, and the measurement of stream flow was taken by using a flow rate sensor at the respective pump rotation frequency. The Reynolds number of the experiments ranges from to , and its corresponding reduced velocities, based on the natural frequency in still water, vary up to . The riser modeled pipe was positioned in vertical direction, and it is flexibly mounted at both ends. The system has low mass ratio and damping coefficient, with the values 1.184 and 0.08, respectively. The mass-damping ratio is 0.09472. The results for the bare pipe cylinder in this experimental setup are in good agreementwith othermeasurements found in the literature

System identification of flexibly mounted cylindrical pipe due to vortex induced vibration

This paper presents a system identification for an elastically supported rigid cylinder in one degree of freedom direction undergoes vortex induced vibration (VIV). The cylinder is constrained to oscillate in perpendicular direction with respect to a free stream. The input-output data of the vibrating system are recorded by using accelerometers in capturing the cylinder movement in certain period of time. Both developed Recursive Least Square (RLS) and Adaptive Neuro Fuzzy Inference System (ANFIS) modus are utilized in order to model an offline dynamic system response of the cylinder pipe at a particular speed. The Auto-regressive external input (ARX) model is chosen to represent the model structure of the system and the performances of both modus are compared in term of Mean Squared Error (MSE). Both methods are capable in predicting the system response. However, the research revealed the superiority of ANFIS in modeling the system with the lowest mean squared error of 3.411×10 -10 as compared to RLS

Control and simulation of obstacle avoidance for a quadcopter

The high demand for Unmanned Aerial System (UAS) in today's world increases our community's safety, well-being, and sustainability. However, there are still issues to be solved. One of the problems discussed in this paper is the UAS manoeuvring in the rural area and the ability of the UAS to manoeuvre around buildings or obstacles. This study conceptualizes the control method and motion used to avoid obstacles using a PID controller and a laser scanner embedded to a quadcopter. The distance error experiment measurement shows that the error decreases with distance and expected distance error is about 4mm with a standard deviation of 0.1577mm. The laser scanner distance error and standard deviation experimental measurement applied to Matlab Simulink's avoidance controller program shows that the algorithm can avoid obstacle with a minimum clearance of 0.5m to avoid damage on the quadcopter. The PID controller design can follow a defined path with some noise present in the horizontal position due to the scanner noise and a 5% error in altitude

Evolutionary algorithm for identification of a flexible single-link manipulator system

This study presents an investigation into dynamic modelling of a flexible single-link manipulator system using differential evolutionary technique (DE) and particle swarm optimization technique (PSO). Details of simulation study, Model Selection, optimization and result analysis are given in this study. The input-output data of the system were first acquired through the simulation study using finite element method (FDM) based on Lagrangian approach. A bang-bang torque was applied as an input and the dynamic responses of the system were investigated. Next, an appropriate model structure was chosen and optimized using DE and PSO. One Step Ahead (OSA) prediction, correlation tests and mean squared error (MSE) have been performed for validation and verification of the obtained model in characterizing the manipulator system. Furthermore, an unseen data was used to observe the prediction ability of the model. A comparative assessment of the two models in characterizing the manipulator system is presented in time and frequency domains. Results demonstrate the advantages of DE over PSO in parametric modeling of the flexible manipulator system used in this study

Implementation of swarm algorithm in modeling a flexible beam structure

The application of System Identification techniques for modeling a flexible beam structure are presented in this paper. The flexible beam has been widely applied in various fields engineering and industrial. However, the flexible structure is easily influenced by unwanted vibration which may lead to fatigue, performance reduction and structure damage. Thus, the unwanted vibration must be controlled and reduced. In order to have a good controller performance for vibration suppression, an appropriate model of flexible beam is required. Hence, to obtain a model of the flexible beam structure, Particle Swarm Optimization (PSO) and Artificial Bee Colony (ABC) are implemented in this study as System Identification techniques. The implementation of PSO and ABC requires experimental data input and output retrieved from data acquisition from a well-developed experimental test rig via MATLAB Simulink platform. Results obtained are displayed in graphical plots and numerical values. The predicted model is validated via mean square error (MSE) and correlation tests. To represent the dynamic model of the flexible beam structure, model with minimum MSE value and correlation test within 95 % confidence interval is selected as the best fit model. The result shows that PSO algorithm produces better performance compared to ABC algorithm with a 3rd order predicted model that has lowest MSE value and correlation tests within 95 % confidence interval for the beam system

Vibration control of semi-active suspension system using PID controller with advanced firefly algorithm and particle swarm optimization

Magnetorheological (MR) damper control for semi-active system is one of the areas of interest investigated to improve the ride comfort and stability of vehicle performance. Many types of controllers used to control the semi-active MR damper have recently been investigated by previous researchers. It is found that the improper design of control scheme has led to an unpredictable optimum target force. Therefore, this study aims to investigate an intelligent optimizer called advanced firefly algorithm (AFA) to compute the proportional-integral-derivative (PID) controller for semi-active suspension system. The performance of the PID controller with the AFA tuning was investigated and compared to the original FA technique and other conventional and intelligent optimizers as well as non-PID controller namely as heuristic method, particle swarm optimization (PSO) and Skyhook controller. A MATLAB Simulation environment was used to generate the simulation model of semi-active suspension system complete will all control elements. The study of the controllers has shown a significant improvement as the proposed PID-AFA is capable of reducing the amplitude of the sprung acceleration and body acceleration responses up to 56.5% and 67.1%, respectively compared to PID-HEURISTIC, PID-FA, PID-PSO, Skyhook and passive systems