Research on the sloshing characteristics of the ship tank with baffles under rolling motion based on smoothed particle hydrodynamics method

The water entry of structures is a complex gas–liquid flow. This paper studies the asymmetrical flow characteristics of a curved hull section entering water through numerical and experimental methods. The free-falling test from drop heights of 250–900 mm and inclination angles from 0° to 20° is carried out. Compared to a smooth hull section (cutting the bottom appendage), the experimental results observe some special asymmetrical flow phenomena (i.e., flow separation, jet impact, bubble flows, and bubble expansion). The physical mechanisms behind these flows are explained through combing the free surface flow and pressure distribution obtained by the numerical method. The effects of the inclination angle and impact velocities on these flow phenomena are further discussed, and they increase the degree of flow separation, bubble volume, and fragmentation. The load characteristics before and after cavity formation are analyzed based on a volume-of-fluid method. The high pressure caused by bubble closure can produce an instantaneous impulse pressure that even be 34% larger than the conventional impact pressure and is worth noting. This study clarifies some complex asymmetrical impact flow characteristics of curved hull sections and thus reveals the evolution mechanism of gas–liquid flows for complex geometries during oblique water entry.

Cavity flow characteristics of a curved hull section impacting a free surface with inclined postures

Xie,

Jiang,

Liu

et al. 2024

Study on water entry into shallow-water current using smoothed particle hydrodynamics method

Zhao,

Yang,

Ming

et al. 2024

Water entry is a typical problem in shipbuilding and ocean engineering. When the ship entering shallow-water current, the combined effects of current and water bottom will complicate the fluid field and further affect the hydrodynamic responses of the ship. In this paper, a two-dimensional bow section entering shallow-water current is studied by smoothed particle hydrodynamics method and the accuracy of the method is first validated. Then, the flows around the hull in shallow and deep water are compared. It is found that the shallow water will produce a more significant effect of flow around the hull, resulting in an increasing in the diffusion velocity of the vortex structure and the related flow-induced forces. The asymmetry of free surface is more obvious in shallow water. Furthermore, the water entries into current and into still water under different water depths are simulated, respectively. When entering shallow-water current, several asymmetrical stagnation-point regions will be induced, which intensify the variation and asymmetric distribution of velocity in the fluid around the hull. Due to the bottom effect in shallow water, the pressure on the hull's lower part increases and two obvious pressure peaks will be caused. The influence of water depth on the pressure gradually disappears as the gauging point gets higher. Accordingly, the vertical force under shallow water also has two peaks and is higher than that under deep water. Moreover, when entering shallow-water current, there will be a greater decrease in vertical velocity than entering still water.

Transient resonance of sloshing liquid with time-varying mass

Zhang,

Li,

Xie

et al. 2024

This study examines the sloshing of liquid with time-varying mass in a tank. A set of innovative experiments is carried out involving a shaking table supporting a water tank equipped with a drain pipe. Physical evidence of transient resonance is observed for the first time. Transient resonance occurs under specific excitation conditions when the instantaneous average water level (AWL) approaches a critical depth. During transient resonance, the oscillatory amplitude of the free-surface elevation increases sharply and then decreases in an envelope pattern. A bifurcation of the frequency band is first found in the Morlet-wavelet time–frequency spectrum, coinciding with the appearance of the maximum oscillatory amplitude. How the excitation conditions, drainage rate, and initial water depth affect transient resonance is recognized. Two mathematical models—one based on linear modal theory and the other based on nonlinear asymptotic theory and the Bateman–Luke variational principle—are derived to replicate the physical observations, by which application scopes of both models have been greatly broadened. The linear solution fails to predict the key feature of transient resonance, namely, the asymmetric envelopes of the oscillatory component about the AWL. By contrast, the nonlinear asymptotic solution captures this asymmetric feature accurately, and predicts both the steady and maximum oscillatory amplitudes well. The nonlinear solution is decomposed into terms of order 1/3, 2/3, and 1 using an asymptotic series for component analyses. A special nonlinear jump behavior is observed. The effects of draining and filling on transient resonance are compared.