A smooth polynomial shaped command for sloshing suppression of a suspended liquid container

A smooth polynomial shaped command with an adjustable command time length is proposed for eliminating the residual vibrations of a multi-mode system. The ability of eliminating jerks and vibrational modes, regardless of their number, offers the most advantage of the proposed command. A numerical simulation is conducted to test the command’s effectiveness by eliminating the residual sloshing oscillations of a liquid-filled container conveyed by an overhead crane in a rest-to-rest manoeuvre. The governing equations of the liquid free-surface level are derived by modelling the sloshing dynamics by a series of mass–spring–damper harmonics. The proposed model accounts for the coupling between the pendulum dynamics and the sloshing equivalent mechanical model. The command’s robustness to the system parameters’ uncertainties, liquid depth and cable length, are investigated as well. The ability of adjusting the command length and retaining higher sloshing modes in command-designing are also outlined.

Liquid Sloshing Suppression for Three-Phase Separators Installed on Floating Production Unit

In this study, a computational fluid dynamics model based on the volume of fluid (VOF) method is developed to simulate the dynamic sloshing response to external excitations. The modal analysis model based on the linear potential theory is established to predict natural sloshing frequencies and the corresponding mode shapes in three-phase separators. In addition, the effects of separator location, length-to-diameter ratio, oil/water level, porosity, and spacing of perforated baffles on the sloshing response are evaluated quantitatively. Furthermore, comprehensive approaches are proposed to mitigate the sloshing, like enhancing viscous damping effect, reducing the intensity of external excitation sources, and keeping away from the resonant frequencies. Finally, a practical application is carried out to display the optimal design of a three-phase separator. The results show that three-phase separators should be located as close as possible to the center of rotation (COR) of the floating production units (FPU). The length-to-diameter ratio is recommended to be no greater than three. Once the fluids can be separated to reach their respective interfaces, the liquid level should be increased as high as possible, whereas the water level should be lowered as far as possible. There is an almost inversely linear relationship between the antisloshing performance of a perforated baffle and its porosity. The antisloshing performance is attenuated rapidly when the spacing distance of a pair of baffles exceeds a specific range. This research extends the existing scope of sloshing suppression approaches and provides useful guidance in the design of FPU-based three-phase separators.

Integrated Trajectory Planning and Sloshing Suppression for Three-Dimensional Motion of Liquid Container Transfer Robot Arm

For liquid transfer system in three-dimensional space, the use of multijoint robot arm provides much flexibility. To realize quick point-to-point motion with minimal sloshing in such system, we propose an integrated framework of trajectory planning and sloshing suppression. The robot motion is decomposed into translational motion of the robot wrist and rotational motion of the robot hand to ensure the upright orientation of the liquid container. The trajectory planning for the translational motion is based on cubic spline optimization with free via points that produces smooth trajectory in joint space while it still allows obstacle avoidance in task space. Input shaping technique is applied in the task space to suppress the motion induced sloshing, which is modeled as spherical pendulum with moving support. It has been found through simulations and experiments that the proposed approach is effective in generating quick motion with low amount of sloshing.

Sloshing Suppression Method for a Rectangular Pool Using Immersed Blocks and Baffle Plates

There is a possibility that water in a spent fuel storage pool may overflow due to sloshing during long-period earthquakes. Therefore, this paper presents two sloshing suppression methods for a rectangular pool to reduce the volume of overflow water. Vibration tests were carried out to evaluate the volume of overflow water. The 1/20-scale model pool is used. First method is applying immersed blocks on the bottom of the rectangular pool. The volume of the water over the sidewall should be the maximum when the 1st sloshing mode is excited, and this behavior has significant influence on the volume of overflow water. The immersed blocks suppress the 1st sloshing mode, thereby reducing the over flow water. Vibration test were conducted by changing the following conditions: height of blocks, open area ratio, block position in the excitation direction, and number of opening sections. Changing of the natural frequencies and the amplification ratios are confirmed by the sinusoidal sweep test. In random wave excitation tests, the volume of overflow water from the pool with the best configuration blocks is lower than about 60% of that from the regular pool. Second method is applying horizontal baffle plates on the sidewall of rectangular pool. Horizontal baffle plate is a well-known sloshing suppression method. However, there is a little information about the relationship between installation condition of baffle plate and volume of overflow water Vibration test were conducted by changing the following conditions: installation height level, overhang length of baffle plate. In random wave excitation tests, the volume of overflow water from the pool with the best installation condition baffle plate is lower than 40% of that from the regular pool.

Passive Control of Liquid Sloshing in Floating Roof Tank With Multi Dynamic Absorber

A multi dynamic absorber for suppressing liquid sloshing in a floating roof tank is presented. As well known, many seismic damages on floating roof tanks by the sloshing of their contained liquid due to long periodic components of earthquake motion were reported. Since the natural period of sloshing varies according to the height of liquid surface, robustness for parameters such as natural period is required for the sloshing suppression device to obtain a good suppression performance. From this point of view, we developed a multi dynamic absorber instead of the single dynamic absorber which is sensitive to the parameter variance. A multi degree of freedom mechanical model for sloshing of the contained liquid and the presented multi dynamic absorber which sets up on the floating roof of the tank is derived to design the optimal tuning for parameters of the multi dynamic absorber and to evaluate the sloshing suppression performance. Numerical simulations for an actual size floating roof tank were conducted to examine the performance of the present device. As the result the effect of the presented multi dynamic absorber was effective to suppress the sloshing response of the floating roof and to be robust for the natural period variance.