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 ∼4900 to ∼15,000, and its corresponding reduced velocities, based on the natural frequency in still water, vary up to ∼7. 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 (m * ζ ) is 0.09472. The results for the bare pipe cylinder in this experimental setup are in good agreement with other measurements found in the literature.
This paper presents the model testing of an 8.23m boat with hard chine planning hull generated waves at the Kilim recreational park. Wake is considered one of the main causes of riverbank erosion due to the energy carried by waves hitting the riverbank. Initially, ship particulars were measured from actual boats to generate a hull form using MAXSURF software. A lines plan was then generated to fabricate the model using fibreglass. Experiments were conducted in the National Hydraulic Research Institute of Malaysia (NAHRIM) at various speeds at a constant operating draft. The wave patterns generated by the modelled boats at different speeds were recorded for analysis. Wave attenuation for deep water conditions was studied and it was found that the wave exponent, n ranged from -0.36 to -0.75 for all depth Froude number (Fnh) condition. Wave decay analysis was used to estimate wave height for defined water depth. For 11 people with an average mass of 65 kg on board, the produced wave height was greater than the permissible wave wake height of 75 mm. The generated energy exceeded 60 Joules/m for nearly all measured speeds. A boat speed of less than 5 knots was suggested for boats loaded with the maximum passenger limit of 11 people. Other recommendations were made to minimize the wave wake height produced by the modelled boat.
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.
This paper presents an active vibration control strategy in order to prevent resonance occurrence in marine offshore vertical riser pipe. Experimental data collected by previous research are used as an input -output data for system identification. Both Least Squares (LS) and Recursive Least Squares (RLS) methods are employed to model the dynamic response of the riser pipe at a particular speed. An auto-tuned PID controller algorithm is developed and implemented for suppression of the riser pipe's vibration. The research revealed the superiority of RLS in modeling the system with the lowest mean squared error of 0.0062. Later, the transfer function obtained by RLS identification technique was utilized within Matlab SIMULINK environment for development of the PID active vibration controller (PID -A VC) using Iterative Learning Algorithm (ILA). The iterative learning PID -AVe controller's capability in suppressing the vortex induced vibration for marineriser and its robustness was tested, verified and proven.
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.
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