This paper presents a hydrodynamics study that examines the comparison and collaboration of two swimming modes relevant to the universality of dolphins. This study utilizes a three-dimensional virtual swimmer model resembling a dolphin, which comprises a body and/or caudal fin (BCF) module, as well as a medium and/or paired fin (MPF) module, each equipped with predetermined kinematics. The manipulation of the dolphin to simulate various swimming modes is achieved through the application of overlapping grids in conjunction with the parallel hole cutting technique. The findings demonstrate that the swimming velocity and thrust attained through the single BCF mode consistently surpass those achieved through the single MPF mode and collaborative mode. Interestingly, the involvement of the MPF mode does not necessarily contribute to performance enhancement. Nevertheless, it is encouraging to note that adjusting the phase difference between the two modes can partially mitigate the limitations associated with the MPF mode. To further investigate the potential advantages of dual-mode collaboration, we conducted experiments by increasing the MPF frequency while keeping the BCF frequency constant, thus introducing the concept of frequency ratio (β). In comparison to the single BCF mode, the collaborative mode with a high β exhibits superior swimming velocity and thrust. Although its efficiency experiences a slight decrease, it tends to stabilize. The corresponding flow structure indirectly verifies the favorable impact of collaboration.

Based on the concept of same structure but different laws, we propose two driving modes, maneuvering and cruising, using multiple tentacles of cephalopods as biomimetic prototypes. These two modes are distinguished by transient or continuous kinematic laws and can achieve self-steering behaviors with different features. The computational evolution process between this underwater robot and the flow field is solved on the OpenFOAM platform. We nest the secondary developed solver with dynamic overlapping mesh technology and integrate multiple functional modules. The numerical results show that for the maneuvering mode, the robot achieves rapid turning by collectively generating high-intensity pressure and vorticity fields during the upstroke of tentacles. This mode is suitable for application scenarios that require real-time direction adjustment, such as obstacle avoidance and emergency response. For the cruising mode, the robot relies on continuous asymmetric swing of their tentacles to generate stable yaw moment, and the navigation trajectory presents a fan-shaped pattern with serrated edges. This mode is suitable for purposeful application scenarios such as anti-interference stability and advance prediction.

This study conducts a numerical investigation of the self-propelled performance of a bio-inspired squid robot equipped with four rigid tentacles, exploring three sets of collaborative modes. Leveraging the open-source platform OpenFOAM, we develop a self-propulsion module incorporating the dynamic overset grid technique to manipulate the complex motion of rigid tentacles. The driving system of a single tentacle is simplified into a two-link mechanism, where the phase difference between the links effectively emulates the oscillatory pattern of fish-like locomotion. The interaction of four tentacles gives rise to three distinct driving modes: reverse, homologous, and interlace modes. The results indicate that the homologous mode follows the hydrodynamic characteristics of fish-like waves, the interlace mode can cause the robot to deviate from the initial path, and the reverse mode outperforms the other two modes, exhibiting a higher ultimate cruising speed. Regardless of the propulsion process, the cruising performance of the robot is significantly influenced by the maximum amplitude angle θmax. An increase in θmax also contributes to an elevation in the instantaneous longitudinal force coefficient CFx, with the most pronounced impact observed in the homologous mode. The disparity among the three modes is also evident in the periodic pressure variation and flow field evolution patterns. The vortex distribution during steady-state moments systematically reveals the collaborative effects among the tentacles in different modes on the self-propulsion performance.