Vibration damping in boats : passive damping by magnetic actuators
Creators: name: Wang, HanChuan
Publisher: name: University of British Columbia
Year: 2021

description: The rolling motion experienced by boats may cause discomforts in passengers and unwanted movements in the cargo. This motion is mainly attributed to the oscillations of waves. The repeated movements of the boat caused by waves can be viewed as a vibration problem, specifically base excitation. Currently, there are a few solutions on the market, and they are generally classified into active or passive systems. Active systems require some form of power to operate, while passive systems do not. Gyroscopes and active fin stabilization are the most common options for active systems. Gyroscopes can weigh up to 30% of boat mass to provide stabilizing forces against high amplitude waves. Thus, these gyroscopes tend to require a lot of power to operate, ranging from 600 to 5000 Watts per gyroscope. Larger boats will require multiple gyroscopes for optimal damping. Active fin stabilization is a rudder-like device attached to the hull. These fins are angled against the flow of water, inducing an upward force. The angle is determined based on the flow rate and the amplitude of waves. An accelerometer is usually used to detect the roll experienced before a computer proceeds to make necessary adjustments. The downside of these fins is the modification to the hull, and the large drag created. While passive systems do not require a power supply to function, they are less effective than active systems and require modifications to the hull of the boat. The purpose of this thesis is to introduce a novel passive actuator that can reduce the low frequency and high amplitude vibrations from waves. This actuator induces a vibration that is out of phase of the waves, thereby cancelling the motion experienced by the boat. To find the most responsive method that applies an opposing force, three different damping systems using mass, liquid, and magnetic spring have been theorized. Among the three systems, the magnetic spring system has been determined to be the most effective through a cantilever vibration test. Therefore, a magnetic spring actuator is prototyped and used in the experiments. For the actuator to be effective, an opposing force has to be applied on the edge of the boat. Thus, the prototype actuators are designed to be as wide as the boats used for experimentation. To test the efficacy of the actuators, multiple tests have been conducted with varying conditions. Firstly, a wave generator was built using an electric motor that rotates an off-centered mass. However, due to the limitations of the motor, only high-frequency waves with low amplitude are generated. Therefore, a water jet wave generator is later acquired and used for experimentation. Next, the actuator is tested using a smaller model boat and a larger constructed boat, weighing 0.88 kg and 2 kg, respectively. A data logger is used to record the G-force experienced by the boats. Since a boat can experience both vertical and roll motion by the waves; the data collected will be inaccurate. To prevent sway affecting the data, the boats are fixed to a position to only allow free rolling. Results collected have shown significant damping capability by the actuator. While the actuator has achieved significant results, further design optimization should be conducted to improve effectiveness.