A Design Concept and Kinematic Model for a Soft Aquatic Robot with Complex Bio-mimicking Motion

Fish mortality assessments for turbine passages are currently performed by live-animal testing with up to a hundred thousand fish per year in Germany. A propelled sensor device could act as a fish surrogate. In this context, the study presented here investigates the state of the art via a thorough literature review on propulsion systems for aquatic robots. An evaluation of propulsion performance, weight, size and complexity of the motion achievable allows for the selection of an optimal concept for such a fish mimicking device carrying the sensors. In the second step, the design of a bioinspired soft robotic fish driven by an unconventional drive system is described. It is based on piezoceramic actuators, which allow for motion with five degrees of freedom (DOF) and the creation of complex bio-mimicking body motions. A kinematic model for the motion’s characteristics is developed, to achieve accurate position feedback with the use of strain gauges. Optical measurements validate the complex deformation of the body and deliver the basis for the calibration of the kinematic model. Finally, it can be shown, that the calibrated model presented allows the tracking of the deformation of the entire body with an accuracy of 0.1 mm.

Analysis of propulsion performance of wave-propelled mechanism based on fluid-rigid body coupled model

Wave-propelled mechanisms are applied to propel unmanned marine vehicles such as Wave Glider and wave-powered boats, which can convert wave energy directly into propulsion. In this paper, a fluid-rigid body coupled dynamic model is utilized to investigate the propulsion performance of the wave-propelled mechanism. Firstly, the coupled dynamic model of the wave-propelled mechanism is developed based on relative motion principle by combining rigid body dynamics model and CFD method. Then, the motion responses of wave-propelled mechanism are calculated. The relationship between the propulsion force, heave and pitch motion of hydrofoil are analyzed by using phase diagrams and the actual operation conditions of propulsion mechanism are obtained. Besides, the effects of restoring spring stiffness and wave heights on the propulsion performance are also investigated, and the vortex evolution is illustrated at different moments of movement and different restoring stiffness. These works can be helpful for the design and optimization of different kinds of wave-propelled vehicles.

Propulsion performances study for a chemical tank

The design of a propulsion system for each ship must take into consideration a large number of factors. Some important factors that will lead to obtaining an efficient propulsion system are: the integration of a large number of elements in a functional space, selection of suitable components, the efficiency assessment taking into account functional safety and comfort criteria for crew and passengers. Considering the factors listed above, the analysis and design of the propulsion system for a chemical tank was performed. To choose the optimal components, the propulsion performance for this ship was analysed using 4 different engines. The operation of the propeller behind the ship has an effect on both the structure of the ship and the navigation conditions of the crew on board. Ttherefore, in the last part of the paper will be presented the effect of the operation of the propeller chosen for the chemical tank. In this sense, the surface forces induced by the propeller that appear in the stern vault will also be a center of interest in this work.

Multi-mode adaptive-pitch propeller and its application prospects for ships with variable running conditions

Object and purpose of research. This paper describes multi-mode adaptive-pitch propeller and its hydrodynamics. Based on the calculation data, the study demonstrates that this kind of propeller might be quite promising in terms of propulsion performance for the ships with variable running conditions, like patrol vessels that switch between patrol and chase running mode. More-over, multi-mode adaptive pitch propellers may work as two-positional CPPs commonly regarded as general-use propellers. These results might be useful in design of ships for various applications. Materials and methods. Experimental data on hydrodynamic parameters of multi-mode adaptive pitch propeller and design calculation results for a virtual triple-shaft patrol vessel. Main results. The results of this study could be useful in propeller selection for given ship design. Conclusion. It is shown that, as compared to FPPs, multi-mode adaptive pitch propellers are more efficient in terms of propulsion performance.

Validating propulsion system optimization procedure for a carrier vessel

Object and purpose of research. This research was intended to validate supercomputer-based optimization procedure for propulsion systems of carrier ships, with a case study of hull shape and propeller optimization for a Project 1594 vessel. Materials and methods. The optimization proceeds in Russian software package pSeven. The computation core is Siemens Star CCM+ software. Three-dimensional parametric model of the propeller is generated in KSRC-developed BladePlus software, whereas three-dimensional parametric model of the hull is generated in Siemens NX software package. Hydrodynamic parameters of the propulsion system are obtained as per CFD methods. Viscous flow parameters are obtained through control volume-based solution of unsteady Reynolds equations (URANS) closed by biparametric semi-empirical turbulence model. Main results. The study yielded a new bow shape offering lower wave-making resistance for the same overall dimensions. It also yielded a new shape of propeller offering higher efficiency than the initial one taking into account the limitations for available shaft torque. Design hydrodynamic parameters have been confirmed by the model test data obtained at KSRC Deepwater Test Tank. Propulsion performance calculation has shown a growth in the achievable speed of the optimized propulsion system in different running conditions. Conclusion. The optimization studies intended to improve propulsion efficiency of Project 1594 ships yielded new shapes for hull and propeller. The solution thus obtained features high propeller efficiency and low wave-making resistance of the hull. Numerical simulation results have been confirmed with experimental data.

Hydrodynamic Analysis of Self-Propulsion Performance of Wave-Driven Catamaran

The wave-driven catamaran is a small surface vehicle driven by ocean waves. It consists of a hull and hydrofoils, and has a multi-body dynamic structure. The process of moving from static state to autonomous navigation driven by ocean waves is called “self-propulsion”, and reflects the ability of the wave-driven catamaran to absorb oceanic wave energy. Considering the importance of the design of the wave-driven catamaran, its self-propulsion performance should be comprehensively analysed. However, the wave-driven catamaran’s multi-body dynamic structure, unpredictable dynamic and kinematic responses driven by waves make it difficult to analyse its self-propulsion performance. In this paper, firstly, a multi-body dynamic model is established for wave-driven catamaran. Secondly, a two-phase numerical flow field containing water and air is established. Thirdly, a numerical simulation method for the self-propulsion process of the wave-driven catamaran is proposed by combining the multi-body dynamic model with a numerical flow field. Through numerical simulation, the hydrodynamic response, including the thrust of the hydrofoils, the resistance of the hull and the sailing velocity of the wave-driven catamaran are identified and comprehensively analysed. Lastly, the accuracy of the numerical simulation results is verified through a self-propulsion test in a towing tank. In contrast with previous research, this method combines multi-body dynamics with computational fluid dynamics (CFD) to avoid errors caused by artificially setting the motion mode of the catamaran, and calculates the real velocity of the catamaran.

Study on impulse and ablation of aluminum irradiated by millimeter spot of short pulse laser

Aluminum is a high performance working medium for laser ablation micro propulsion. In order to study the propulsion performance and ablation of aluminum under millimeter light spot irradiation, a short pulse Nd: YAG laser with wavelength of 1064nm and pulse width of 8NS was used to irradiate aluminum target in atmosphere. The impulse, the impulse coupling coefficient and the ablation morphology of the aluminum target produced by 6 kinds of millimeter-level light spots are measured. The experimental results show that when the spot diameter reaches 6-7mm, the increasing trend of impulse and impulse coupling coefficient of aluminum target with the increase of laser energy slows down; A large number of ablation products began to accumulate on the surface of the target pit.

Effects of Nonlinearity of Restoring Springs on Propulsion Performance of Wave Glider

Wave glider is an unmanned surface vehicle which can directly convert wave energy into forward propulsion and fulfill long-term marine monitoring. Previous study suggested that the wave motion and stiffness of restoring springs mounted on the hydrofoil are main factors affecting the propulsion performance of wave glider. In this paper, the dynamic responses and nonlinear characteristics of underwater propulsion mechanism considering the nonlinear stiffness of restoring springs are investigated based on a fluid-rigid body coupled model. Firstly, the models of propulsion mechanism with different kind of restoring spring are proposed, and the linear and nonlinear characteristics of restoring spring are considered. Then, a fluid-rigid body coupled model of wave glider is developed by coupling the rigid body dynamics model and hydrodynamic model. Dynamic responses are simulated by numerical analysis method and the nonlinear characteristics with different restoring springs are illustrated by time/frequency domain motion response and phase diagram analysis. The effects of wave excitation frequency and wave heights on the propulsion performance of wave glider are analyzed. The results show that, multi-frequency responses occurred in propulsion system. And the study suggests that the nonlinear restoring spring on the hydrofoil can be suitable for different sea condition and better propulsion performance can obtained than linear stiffness spring, which provides a reference for developing propulsion mechanism with high performance in complex marine environment.

Analysis of influence of guide vane wrap angle and blade number on propulsive performance of a water jet propulsor

In this paper, the propulsion performance of a screw mixed-flow jet propulsion pump is studied systematically. The optimum thrust performance is achieved by changing the geometrical dimensions of the guide vanes. Under the condition of keeping other parameters unchanged, the operating conditions of the pump can be effectively adjusted by changing the number of guide vanes and wrap angle. The focus of this paper is on the presentation and demonstration of a strategy that takes the number of guide vanes and wraps angle as the main research object and its propulsion efficiency as the main reference index to analyze the advantages and disadvantages of each working condition in detail. The CFD numerical simulation technology has been used for numerical calculation. The simulation results are compared with the experimental results, and the numerical calculation results are in good agreement with the experimental values. The results show that the kinetic energy of the propulsion pump increases with the number of guide vane blades and the angle of wrap angle. The increase of guide angle and the number of blades will reduce the overall propulsion efficiency of the propeller. Finally, a mathematical model of propeller efficiency with the number of guide vane blades and the angle coefficient of guide vanes is established.