Search

Biomimetic robotic fish are a novel approach to studying quiet, highly agile, and efficient underwater propulsion systems, attracting significant interest from experts in robotics and engineering. These versatile robots showcase their ability to operate effectively in various water conditions. Nevertheless, the comprehension of the swimming mechanics and the evolution of the flow field of flexible robots in counterflow regions is still unknown. This paper presents a framework for the self-propulsion of robotic fish that imitates biological characteristics. The method utilizes computational fluid dynamics to analyze the hydrodynamic efficiency of the organisms at different frequencies of tail movement, under both still and opposing flow circumstances. Moreover, this study clarifies the mechanisms that explain how changes in the aquatic environment affect the speed and efficiency of propulsion. It also examines the most effective swimming tactics for places with counterflow. The results suggest that the propulsion effectiveness of robotic fish in counterflow locations does not consistently correspond to various tail-beat frequencies. By utilizing vorticity maps, a comparative analysis can identify situations when counterflow zones improve the efficiency of propulsion. [ABSTRACT FROM AUTHOR]

The effect of the seabed on the hydrodynamics of three-dimensional autonomous underwater vehicles (AUVs) varies according to the physical conditions of the place where AUVs interact with the environmental conditions. This study examines the hydrodynamics of an AUV resembling a torpedo model while taking the influence of the seabed surface as a function of the dimensionless distances (G/D) between the torpedo and the seabed. Reynolds numbers, varying from 1 × 104 to 8 × 104, were considered. These Reynolds numbers were associated with various seabed distances falling within 0.25 ≤ G/D ≤ 1.5. To perform the simulations, governing equations were utilized and incorporated with the k–ω SST turbulence model. It has been observed that when AUVs or torpedo models operate in close proximity to the seabed surface, several key hydrodynamic parameters and flow characteristics are affected. These include the pressure coefficient (Cp), drag coefficient (CD), overall flow structures, maneuverability, and performance of the torpedo model. As the AUV or torpedo model approaches the seabed surface, the symmetrical flow pattern deteriorates. This deterioration is associated with changes in vortical flow structures under the influence of seabed surfaces. Additionally, the intensity of the shear stress (τ) near the seabed surface gradually increases as the AUV or torpedo model gets closer to it. In summary, the proximity of AUVs or torpedo models to the seabed surface causes disruptions in the flow patterns, increased shear stress, and alterations in key hydrodynamic parameters, ultimately affecting the system's performance and behavior. [ABSTRACT FROM AUTHOR]

Driven by the demands of ocean exploration, an increasing number of manta ray-inspired robots have been designed and manufactured, primarily utilizing flexible skeletons combined with motor-driven mechanisms. However, the mechanical analysis of these designs remains underdeveloped, often relying on simplistic imitation of biological prototypes and typically neglecting the vertical motion induced by pectoral fin flapping. This paper presents a fluid–structure interaction analysis framework that couples rigid body motion with elastic deformation using flexible multibody dynamics and the vortex particle method. An implicit iterative algorithm with Aitken relaxation is employed to address added-mass instability, and the framework has been validated against experimental data. An analysis of a representative manta-bot model shows that self-induced vertical undulations reduce the thrust coefficient by approximately 40% compared to fixed vertical degrees of freedom, while slightly improving overall propulsive efficiency. The study also highlights the critical role of mass distribution in manta-bots, noting that excessive focus on complex pectoral fin movements and large fin mass can significantly reduce thrust by increasing vertical displacement, ultimately proving counterproductive. [ABSTRACT FROM AUTHOR]

The propulsion system is the core component of unmanned underwater vehicles. The flapping propulsion method of marine animals' flippers, which allows for flexibility, low noise, and high energy utilization at low speeds, can provide a new perspective for the development of new propulsion technology. In this study, a new experimental flapping propulsion apparatus that can be installed in both directions has been constructed. The guide rail slider mechanism can achieve the retention of force in the direction of movement, thereby decoupling thrust, lift, and torque. Subsequently, the motion parameters of frequency–amplitude related to the thrust and lift of a bionic flapping-foil are scrutinized. A response surface connecting propulsion efficiency and these motion parameters is formulated. The highest efficiency of the flapping-foil propulsion is achieved at a frequency of 2 Hz and an amplitude of 40°. Furthermore, the impact of the installation mode and the aspect ratio of the flapping-foil is examined. The reverse installation of the swing yields a higher thrust than the forward swing. As the chord length remains constant and the span length increases, the propulsive efficiency gradually improves. When the chord length is extended to a certain degree, the propulsion efficiency exhibits a parabolic pattern, increasing initially and then diminishing. This investigation offers a novel perspective for the bionic design within the domain of underwater propulsion. This research provides valuable theoretical guidance for bionic design in the underwater propulsion field. [ABSTRACT FROM AUTHOR]

The operation of marine vessels with high efficiency provides a great contribution within the scope of the International Maritime Organization and the sustainable development goals. In terms of the propulsion system, selecting the appropriate propeller is critical to effectively use the engine power installed in marine vessels because the biggest energy losses during transmission occur on the propeller and ship hull. Increasing propeller efficiencies above a certain level is quite a challenge by simply changing the number of blades, pitch, or propeller type. Therefore, various energy-saving device applications, such as propeller boss cap fins (PBCFs), are performed on the ship propeller. The effects of National Advisory Committee for Aeronautics 4415 profile PBCFs which have a different position and pitch angle integrated into the E698 model propeller have been investigated to describe efficiency, vortex, and pressure distributions based on the KRISO very large crude carrier 2 designed hull in this study. The E698 model propeller has been created by the 3D software and the validation has been performed by the computational fluid dynamic solver software based on the reference values of the propeller. The effect of four PBCF applications which have different pitches and positions on the model propeller has been revealed in terms of the efficiency, pressure distributions, and vortexes. Although P45-R45 and P45-R90 PBCF applications are quite close to the E698 propeller in terms of efficiency, no significant efficiency increase has been observed. In addition, the efficiency has decreased considerably in P90-R45 and P90-R90 applications. PBCFs application with P45-R90 has provided superiority to the base model in terms of pressure distributions and vortex formation. However, any improvement has not been achieved in the remaining three designs. Therefore, PBCF applications should be applied quite elaborately based on propeller types. [ABSTRACT FROM AUTHOR]

Biomimetic robotic fish are a novel approach to studying quiet, highly agile, and efficient underwater propulsion systems, attracting significant interest from experts in robotics and engineering. These versatile robots showcase their ability to operate effectively in various water conditions. Nevertheless, the comprehension of the swimming mechanics and the evolution of the flow field of flexible robots in counterflow regions is still unknown. This paper presents a framework for the self-propulsion of robotic fish that imitates biological characteristics. The method utilizes computational fluid dynamics to analyze the hydrodynamic efficiency of the organisms at different frequencies of tail movement, under both still and opposing flow circumstances. Moreover, this study clarifies the mechanisms that explain how changes in the aquatic environment affect the speed and efficiency of propulsion. It also examines the most effective swimming tactics for places with counterflow. The results suggest that the propulsion effectiveness of robotic fish in counterflow locations does not consistently correspond to various tail-beat frequencies. By utilizing vorticity maps, a comparative analysis can identify situations when counterflow zones improve the efficiency of propulsion.

Driven by the demands of ocean exploration, an increasing number of manta ray-inspired robots have been designed and manufactured, primarily utilizing flexible skeletons combined with motor-driven mechanisms. However, the mechanical analysis of these designs remains underdeveloped, often relying on simplistic imitation of biological prototypes and typically neglecting the vertical motion induced by pectoral fin flapping. This paper presents a fluid–structure interaction analysis framework that couples rigid body motion with elastic deformation using flexible multibody dynamics and the vortex particle method. An implicit iterative algorithm with Aitken relaxation is employed to address added-mass instability, and the framework has been validated against experimental data. An analysis of a representative manta-bot model shows that self-induced vertical undulations reduce the thrust coefficient by approximately 40% compared to fixed vertical degrees of freedom, while slightly improving overall propulsive efficiency. The study also highlights the critical role of mass distribution in manta-bots, noting that excessive focus on complex pectoral fin movements and large fin mass can significantly reduce thrust by increasing vertical displacement, ultimately proving counterproductive.

The propulsion system is the core component of unmanned underwater vehicles. The flapping propulsion method of marine animals’ flippers, which allows for flexibility, low noise, and high energy utilization at low speeds, can provide a new perspective for the development of new propulsion technology. In this study, a new experimental flapping propulsion apparatus that can be installed in both directions has been constructed. The guide rail slider mechanism can achieve the retention of force in the direction of movement, thereby decoupling thrust, lift, and torque. Subsequently, the motion parameters of frequency–amplitude related to the thrust and lift of a bionic flapping-foil are scrutinized. A response surface connecting propulsion efficiency and these motion parameters is formulated. The highest efficiency of the flapping-foil propulsion is achieved at a frequency of 2 Hz and an amplitude of 40°. Furthermore, the impact of the installation mode and the aspect ratio of the flapping-foil is examined. The reverse installation of the swing yields a higher thrust than the forward swing. As the chord length remains constant and the span length increases, the propulsive efficiency gradually improves. When the chord length is extended to a certain degree, the propulsion efficiency exhibits a parabolic pattern, increasing initially and then diminishing. This investigation offers a novel perspective for the bionic design within the domain of underwater propulsion. This research provides valuable theoretical guidance for bionic design in the underwater propulsion field.

The cruising velocity of animals, or robotic vehicles, that use flapping wings or fins to propel themselves is not constant but oscillates around a mean value with an amplitude usually much smaller than the mean, and a frequency that typically doubles the flapping frequency. Quantifying the effect that these velocity fluctuations may have on the propulsion of a flapping and oscillating airfoil is of great relevance to properly modeling the self-propelled performance of these animals or robotic vehicles. This is the objective of the present work, where the force and moment that an oscillating stream exerts on a two-dimensional pitching and heaving airfoil are obtained analytically using the vortical impulse theory in the linear potential flow limit. The thrust force of the flapping airfoil in a pulsating stream in this limit is obtained here for the first time. The lift force and moment derived here contain new terms in relation to the pioneering work by Greenberg (1947), which are shown quantitatively unimportant. The theoretical results obtained here are compared with existing computational data for flapping foils immersed in a stream with velocity oscillating sinusoidally about a mean value. [ABSTRACT FROM AUTHOR]

This study considers the aircraft configuration impacts of a liquid-hydrogen fuel-cell electric propulsion system when integrated into a single-aisle, transport-class aircraft having comparable performance capability of a Boeing 737-800. This study demonstrates that, given estimated developments in future components and subsystem technologies for a 2050 entry into service date, the design of an aircraft with a liquid-hydrogen fuel-cell-based propulsion system can be feasibly achieved while still meeting mission-level performance characteristics consistent with modern commercial aircraft throughout the anticipated lifetime of the aircraft. Key technologies that enable this are the purposeful integration of fuel cell thermal management, independent inlet compression to pressurize the air input to the fuel cells, and leveraging distributed electric propulsion advantages. Exploration into the impact of fuel cell power loss due to degradation is also presented. The results show a promising configuration of a liquid-hydrogen fuel-cell-based commercial aircraft to serve as a feasible replacement of narrow-body transport aircraft to help meet climate goals set for the aviation industry. [ABSTRACT FROM AUTHOR]

This paper demonstrates an integrated approach to the sizing and analysis of all-electric, hybrid-electric, and turboelectric variants of a lift-plus-cruise urban air mobility vertical takeoff and landing concept using the Parametric Energy-based Aircraft Configuration Evaluator. In lieu of assuming a point mass performance model, the aircraft is trimmed explicitly for nominal and off-nominal flight conditions for sizing propulsion system components and evaluating mission energy usage. In lieu of using historical tail volume ratio guidelines for stabilizer sizing, an explicit dynamic stability analysis is incorporated to determine the stabilizer size that achieves specified bare airframe handling qualities targets. The effects of varying battery specific energy, C-rate, wing loading, hover disk loading, mission range, and cruise speed on the sizing of the three propulsion architectures are explored. A comparison of the weight breakdown of the three propulsion variants when sized to the same maximum takeoff mass is presented. The sensitivity of the sizing results to the requirement of full vs reduced payload capability at high, hot hover conditions is also assessed. In addition to being insightful, the presented results reinforce the need to incorporate more physics-based analyses, additional stability and control considerations, and configuration optimization studies, which form natural avenues for follow-on work. [ABSTRACT FROM AUTHOR]

This paper demonstrates parametric definition and sizing of all-electric and hybrid-electric variants of a dual-purpose ducted fan lift-plus-cruise aircraft configuration. The dual roles include passenger transportation for urban air mobility as well as transportation of supplies and personnel for military applications. The impact of battery technology on the characteristics of the sized all-electric and hybrid-electric variants is analyzed. For the latter, turboshaft engines are incorporated to satisfy cruise power requirements and offset peak power requirements during vertical flight, at the expense of additional propulsion system weight. The net impact of this penalty is investigated as a function of battery technology and range. The aircraft is sized and analyzed using the Parametric Energy-based Aircraft Configuration Evaluator, a sizing framework utilizing a parametric geometry definition and resizing rule set for the aircraft, strip-theory-based aeropropulsive models, energy-based mission performance analysis, and a combination of empirical and physics-based mass properties analyses. [ABSTRACT FROM AUTHOR]

Copyright of Aeronautical Science Bulletins / Repüléstudományi Közlemények is the property of National University of Public Service and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The exergy analysis has already proved to be of interest for aerospace applications, with the possibility to analyze new types of configurations. It is of particular interest when a pertinent thrust/drag breakdown is not possible and when significant thermal exchanges take place in the control volume. In addition, this method allows to link the different contributions of the exergy terms to physical phenomena in the flow, improving the understanding of the sources of losses degrading the performance of the system under study. The applications and results obtained in a fixed frame of reference have thus motivated the improvement and extension of the exergy balance to more complex flows. This paper aims at presenting an extension of the exergy balance to rotating frames of reference for the analysis of rotating components of the propulsion system (e.g. propeller, turbomachine or helicopter rotor blades). The newly developed theoretical development is summarized, and an application to a numerical simulation of a propeller is presented. Results are discussed in terms of both physical interpretation and numerical accuracy. [ABSTRACT FROM AUTHOR]

In the present research, a 2D simulation of tandem flapping foil following an elliptical trajectory, i.e., altered from a simple flapping trajectory is performed. The purpose of the research is to evaluate the influence of the trajectory motion of the tandem flapping foil on hydrodynamics characteristics and propulsive efficiency. The study is carried out with tandem foil configurations as in such position, both the foils are subjected to the same flow, which allows the flapping foil to enhance the propulsive efficiencies with proper selection of foil position as well as the foil trajectory. The 2D simulation is carried out with NACA 0012 at Re = 1173 by varying Strouhal number (St) between 0.2 and 0.5. The results show that an elliptical motion trajectory pattern and interfoil spacing of 1cm-2cm (where cm is the mean chord length) between the foils would enhance the propulsive efficiency whereas an unfavorable spacing between the foils causes unfavorable wake interaction, which reduces propulsive efficiency as compared to solo flapping foil. When the results of the current numerical investigation of elliptical trajectory are compared to the results of simple trajectory tandem flapping, the current study shows a significant increase in propulsive efficiency. This study gives new insights in the development of biomimetic propulsors, as it strives to improve propulsive efficiency through the usage of wake vortex. [ABSTRACT FROM AUTHOR]

The application of tandem flapping foil propulsors to conventional aerial and underwater vehicles plays the most important role in the exploration of aerial and marine environments. The hydrodynamic study of fish schooling or birds’ flock when swimming/flying in fluid media and the application toward the development of tandem flapping wing robots is gaining more importance in the field of bioinspired vehicles. The advantages of tandem flapping wing configuration are improved thrust performance, maneuvering, and less energy input as the downstream foils consume less power compared to the single flapping foil. In this study, the thrust of two flapping foils arranged in the tandem mode subjected to pitching motion with different pitching amplitudes (AD), Strouhal numbers (StD), streamwise distance (S/c), and phase lag $\ ({\rm{\varphi)\ }}$ of foils is studied numerically using the reynolds-averaged navier-stokes equation (RANSE)-based computational fluid dynamics solver. This novel study mainly investigates the effects of Strouhal number and the dimensionless pitching amplitude on the thrust and efficiency of tandem foils. It is observed that the tandem foils generate higher efficiency at StD = 0.2. At this condition, the effects of streamwise distance and phase lag of tandem foils are also investigated. When ${\rm{\varphi \ }}$ is constant and S/c changes from 0.109 to 1, the efficiency of the upstream foil decreases and the efficiency of downstream foil increases. When S/c is constant and ${\rm{\ \varphi \ }}$ changes from 0° to 180°, the efficiency of the upstream foil increases and the efficiency of the downstream foil decreases with an increase in phase lag. When ${\rm{\ \varphi }}$ is 90°, the total efficiency of the two foils gets the maximum value. In general, when S/c is 1 and ${\rm{\varphi }}$ is 90°, the tandem flapping foils get the maximum propulsive efficiency. For achieving this condition, pitching amplitude, frequency, and increased phase lag between the two foils play a significant role compared to the streamwise distance (S/c) between the tandem foils. [ABSTRACT FROM AUTHOR]

Boundary-layer ingestion (BLI) is a propulsor-airframe integration technology that promises substantial fuel consumption benefits for future civil aircraft. This paper discusses an experimental study, conducted within the European Union-funded Horizon 2020 CENTRELINE project, on the aerodynamic performance of an aircraft with a BLI propulsor integrated at the aft-fuselage section (known as the Propulsive Fuselage Concept). The low-speed wind-tunnel experiments were carried out at Reynolds and Mach numbers of 460,000 and 0.12, whereas the Reynolds and Mach numbers are 40,000,000 and 0.82 at full-flight scale. Aerodynamic loads measurements show that the BLI propulsor affects the longitudinal and lateral-directional equilibrium of the aircraft in off-cruise conditions. Moreover, velocity and total pressure measurements characterize the flowfield around the BLI propulsor in cruise and off-cruise conditions. The analysis of the momentum and power fluxes in the flowfield shows that, while around 20% of the total aircraft drag is due to the fuselage body, only less than 5% of the total aircraft drag power is dissipated in the fuselage wake. Furthermore, the BLI propulsor recovers around 50% the axial kinetic energy flux in the fuselage boundary layer (the so-called wake-filling effect), suggesting an increased propulsive efficiency. [ABSTRACT FROM AUTHOR]

In order to maximize the propulsion efficiency of flapping hydrofoil, a new method is proposed in this paper. The effects of heave amplitude, pitch amplitude, and the phase difference between heave and surge on propulsion performance were analyzed by numerical calculation, and it was found that three motion parameters had interactive effects on flapping hydrofoil propulsion performance. BP neural network was used to fit the three motion parameters and propulsion performance. Using this function model, the optimal motion parameters can be obtained under certain thrust. In this study, the optimization matching under certain thrust was carried out by using this method, and the propulsion efficiency was improved by 7.73%. [ABSTRACT FROM AUTHOR]

In this work, we have performed numerical simulations of the flapping motion of a rectangular wing in a three-dimensional flow field using the discrete vortex method (DVM). The DVM method is computationally more convenient because it does not require the generation of a grid for the flow field at each time step as in other conventional simulation methods. In addition to the rigid wing case, the aerodynamic characteristics of a deformable wing are also investigated. The deformable wing is studied in various configurations, such as bending, twisting, and bending-twisting coupling (BTC), to provide a comprehensive analysis of its performance. In this study, we have introduced a novel aerodynamic technique in wing twisting. Unlike traditional wing rotation about a fixed root axis, our approach involves rotating the wing about a dynamically adjusted point located at the root of the leading edge. This novel approach was found to be effective in increase in the requisite aerodynamic force. The BTC wing represents reflects a sophisticated aerodynamic approach that optimally coordinates both twisting and bending deformations of the wing, resulting in a substantial improvement in its overall aerodynamic efficiency. The investigation of all four modes involves a detailed analysis of the flow mechanisms and vortex dynamics, which play a crucial role in influencing the aerodynamic forces, namely lift and thrust. The study aims to understand how these flow patterns change under different operating conditions and how these changes impact the generation of lift and thrust. The lift, thrust, and propulsive efficiency of all four modes are compared to provide a detailed understanding of their aerodynamic characteristics. The bent wing showed minimal improvements in lift and thrust compared to the rigid wing. In contrast, the twisted wing showed greater improvements in both lift and thrust. The BTC wing proves to be the most efficient method to improve aerodynamic performance during flapping. The parametric dependence of kinematic parameters such as asymmetric ratio (downstroke speed to upstroke speed), aspect ratio and reduced frequency on the aerodynamic performance was also investigated. [ABSTRACT FROM AUTHOR]

Because of their potential to reduce aircraft emissions, counter-rotating open rotors (CRORs) have seen a renewed interest in applications, from civil aviation to urban air mobility. However, there are concerns surrounding their acoustic emissions. In the work presented, the authors investigated the noise sources for a range of CROR configurations for a general aviation class aircraft. Numerical models are used to compute the aerodynamic and aeroacoustic performance of these configurations. Further dissection of the various CROR noise sources is then carried out in order to better understand their contribution to CROR noise, and to direct the design of future low-noise CRORs. Noise reductions were observed when the rotor-rotor spacing was increased. Increased contraction of the wake requires the need for increased clipping to reduce the tip vortex interaction source. Noise reductions were also observed in the case of asynchronous rotational speeds. However, this was accompanied by a reduction in propulsive efficiency. Analysis of the CROR in nonaxial flight demonstrated the need to evaluate noise-reducing strategies at off-design conditions. Although the analysis proved the ability to reduce various CROR noise sources, it highlighted that tradeoffs with aerodynamic performance is necessary. [ABSTRACT FROM AUTHOR]

This work presents the effect of wingtip-mounted propellers on the aircraft drag polar, identified from in-flight measurements. In previous wind-tunnel experiments, significant reductions in drag and an increase in propulsive efficiency through interaction between induced flow by the wingtip-mounted propellers and the flowfield of the wing itself have been claimed. So far, however, these effects have never been verified in actual flight. That gap is closed here by presenting the results of in-flight measurements. A 33.3% scaled version of the manned, electric e-Genius aircraft has been fitted with a wingtip propulsion system and an elaborate measurement system, which allows quantifying the aforementioned effects. The drag polar is deduced through weighted least-squares parameter estimation for different settings and configurations of the wingtip propellers. The findings are compared to results from previous wind-tunnel experiments. The paper further discusses secondary effects that were observed during the flight tests and their influence on the general potential of wingtip propulsion. [ABSTRACT FROM AUTHOR]

This study describes the aerodynamic efficiency of a forebody–inlet configuration and computational investigation of a drone system, capable of sustainable supersonic cruising at Mach 1.60. Because the whole drone configuration is formed around the induction system and the design is highly interrelated to the flow structure of forebody and inlet efficiency, analysis of this section and understanding its flow pattern is necessary before any progress in design phases. The compression surface is designed analytically using oblique shock patterns, which results in a low drag forebody. To study the concept, two inlet–forebody geometries are considered for Computational Fluid Dynamic simulation using ANSYS Fluent code. The supersonic and subsonic performance, effects of angle of attack, sideslip, and duct geometries on the propulsive efficiency of the concept are studied by solving the three-dimensional Navier–Stokes equations in structured cell domains. Comparing the results with the available data from other sources indicates that the aerodynamic efficiency of the concept is acceptable at supersonic and transonic regimes. [ABSTRACT FROM AUTHOR]

The aim of this paper is to develop a software, namely HPS-MOP, based on the multi-level and multi-point hydrodynamic optimization of hull-propeller systems during early-stage ship design. An efficient multi-objective evolutionary algorithm is used as the optimization technique to minimize the effective power and maximize the propulsive efficiency with considering some design constraints. Michell's integral and lifting line theory are, respectively, employed for the hydrodynamic analysis of hulls and propellers in the first-level optimization. At the second level, the boundary element method is applied as a strong tool to predict the hydrodynamic performance of hulls and propellers. The ship added resistance in head waves is estimated using a fast and satisfactory semi-empirical formula. The effectiveness of the approach is illustrated by comparing the optimized results with initial ones in the optimization of series 60 hull form with DTMB P4118 single propeller and S175 hull form with KP505 twin-propeller as the original models. [ABSTRACT FROM AUTHOR]

In order to maximize the propulsion efficiency of flapping hydrofoil, a new method is proposed in this paper. The effects of heave amplitude, pitch amplitude, and the phase difference between heave and surge on propulsion performance were analyzed by numerical calculation, and it was found that three motion parameters had interactive effects on flapping hydrofoil propulsion performance. BP neural network was used to fit the three motion parameters and propulsion performance. Using this function model, the optimal motion parameters can be obtained under certain thrust. In this study, the optimization matching under certain thrust was carried out by using this method, and the propulsion efficiency was improved by 7.73%.

Throughout their lives, squids are both predators and prey for a multitude of animals, many of which are at the top of ocean food webs, making them an integral component of the trophic structure of marine ecosystems. The escape jet, which is produced by the rapid expulsion of water from the mantle cavity through a funnel, is central to a cephalopod's ability to avoid predation throughout its life. Although squid undergo morphological and behavioral changes and experience remarkably different Reynolds number regimes throughout their development, little is known about the dynamics and propulsive efficiency of escape jets throughout ontogeny. We examine the hydrodynamics and kinematics of escape jets in squid throughout ontogeny using 2D/3D velocimetry and high-speed videography. All life stages of squid produced two escape jet patterns: (1) ‘escape jet I’ characterized by short rapid pulses resulting in vortex ring formation and (2) ‘escape jet II’ characterized by long high-volume jets, often with a leading-edge vortex ring. Paralarvae exhibited higher propulsive efficiency than adult squid during escape jet ejection, and propulsive efficiency was higher for escape jet I than escape jet II in juveniles and adults. These results indicate that although squid undergo major ecological transitions and morphology changes from paralarvae to adults, all life stages demonstrate flexibility in escape jet responses and produce escape jets of surprisingly high propulsive efficiency. This article has an associated First Person interview with the first author of the paper.

The objectives of this paper are to numerically investigate the performance of a composite propeller through bidirectional FSI algorithm combining CFD and FEM, and to improve its propulsive efficiency by a pre-deformated method. Numerical results are presented for the composite propeller which has been modeled by unidirectionally stacking with glass-fiber reinforced composites. The propulsive efficiency of the composite and rigid propellers with different advance coefficients J has been compared. The results show that the efficiency of the composite propeller is obviously higher than that of the rigid propeller when J≤0.8, which is attributed to the decrease of pitch angle caused by the bend-twist coupling effects. But for the design condition J=0.851 and the cases with J 0.851, the efficiency of the composite propeller is significantly lower than that of the rigid propeller, which is because the angle of attack αcomposite is deviated from the optimal angle of attack αdesign more than that for the rigid case αrigid. Based on the optimization by the proposed pre-deformated method, the efficiency improvement of the composite propeller at the conditions with J≥0.851 could be obtained, and the composite material used in this work can meet the strength requirement of the designed propellers. [ABSTRACT FROM AUTHOR]

In the nature, the fish can control the wave propagation on the caudal fin using the sarcomere at the leading edge of the caudal fin. The control methods can be classified into three modes: Active Heave and Active Pitch (AHAP),Passive Heave and Active Pitch (PHAP), Active Heave and Passive Pitch (AHPP). Which mode can produce the largest thrust? Which mode can develop the most efficient swimming performance? So far, the research on these issues still cannot be found in the article. In this paper, we have studied the self-propulsion of the flexible plates driven by these three modes. It is expected that results can shed new light on understanding the locomotion mechanism of the fish and give a new idea for the design and control of the robot fish. The vibration of the flexible plate in the high velocity flow maybe unstable, and the velocity threshold of the flow are depending on the stiffness of the plate. The motion of the plate driven by AHAP is the most unstable, while AHPP is the most stable driving mode. The thrust on the flexible plate is mainly affected by the resonance effect, and the thrust in AHAP mode and AHPP mode are larger than that in PHAP mode. The propulsive efficiency is affected by both the resonance effect and the phase dynamics in the oscillator model. The phase dynamics is the dominant factor, and the resonance effect is the secondary factor. • The plate is driven by three modes: AHAP, PHAP and AHPP. • AHPP is the most stable driving way. • AHPP is the most efficient driving modes for moderate stiffness. • PHAP is the most efficient driving modes as stiffness is large enough or small enough. • For improve the propulsive efficiency, the phase dynamics in the oscillator model is the dominant factor, and the resonance effect is secondary factor. [ABSTRACT FROM AUTHOR]

SUMMARY: Biological fish can create high forward swimming speed due to change of thrust/drag area of pectoral fins between power stroke and recovery stroke in rowing mode. In this paper, we proposed a novel type of folding pectoral fins for the fish robot, which provides a simple approach in generating effective thrust only through one degree of freedom of fin actuator. Its structure consists of two elemental fin panels for each pectoral fin that connects to a hinge base through the flexible joints. The Morison force model is adopted to discover the relationship of the dynamic interaction between fin panels and surrounding fluid. An experimental platform for the robot motion using the pectoral fin with different flexible joints was built to validate the proposed design. The results express that the performance of swimming velocity and turning radius of the robot are enhanced effectively. The forward swimming velocity can reach 0.231 m/s (0.58 BL/s) at the frequency near 0.75 Hz. By comparison, we found an accord between the proposed dynamic model and the experimental behavior of the robot. The attained results can be used to design controllers and optimize performances of the robot propelled by the folding pectoral fins. [ABSTRACT FROM AUTHOR]

Improving propulsion efficiency holds the promise of enabling the robotic fish to work for a long time with a limited battery in its small body. In this paper, for the swimming of a bionic robotic fish, we present a virtual musculoskeletal control method from the bionic model of the joint driven by agonist muscle and antagonist muscle. A closed-loop method composed of two loops is proposed as a rule of thumb for the speed control of the robotic fish. The outer loop adjusts the swimming speed using the speed deviation; the inner loop regulates the stiffness according to the virtual muscle spindle feedback to fit the water environment. Compared with the proportion control, the evaluation results show that the virtual musculoskeletal methodology increases the efficiency by 3.4% in the steady flow and 7% in the Karman-vortex flow. This algorithm provides a new idea for the joint-space control of the bionic robots that need to reduce the energy consumption of movements.

Natural flight has consistently been the wellspring of many creative minds, yet recreating the propulsive systems of natural flyers is quite hard and challenging. Regarding propulsive systems design, biomimetics offers a wide variety of solutions that can be applied at low Reynolds numbers, achieving high performance and maneuverability systems. The main goal of the current work is to computationally investigate the thrust-power intricacies while operating at different Reynolds numbers, reduced frequencies, nondimensional amplitudes, and mean angles of attack of the oscillatory motion of a NACA0012 airfoil. Simulations are performed utilizing a RANS (Reynolds Averaged Navier-Stokes) approach for a Reynolds number between 8.5×103 and 3.4×104, reduced frequencies within 1 and 5, and Strouhal numbers from 0.1 to 0.4. The influence of the mean angle-of-attack is also studied in the range of 0∘ to 10∘. The outcomes show ideal operational conditions for the diverse Reynolds numbers, and results regarding thrust-power correlations and the influence of the mean angle-of-attack on the aerodynamic coefficients and the propulsive efficiency are widely explored.

This paper researched into the harmonic and anharmonic underwater flapping foil propulsion systems to improve the efficiency of these bioinspired propulsors. The angle of attack, the pitching angle, the heaving amplitude, and the phase difference are parametrically investigated in this paper. A rigid two-dimensional NACA (National Advisory Committee for Aeronautics) 0012 airfoil is modeled with the aid of a commercial computational fluid dynamics software, FINE™/Marine. Unsteady Reynolds Average Navier-Stokes (URANS) equation is solved together with dynamic mesh to simulate the foil motion. The investigation first verifies the reliability of the developed modeling method against the benchmark data. Then, the systematic investigation is conducted and identifies that the heaving amplitude is most influential factor for the propulsion efficiency. Secondly, phase difference also has a significant influence on efficiency, but this effect is related to the reference working condition, which needs further study. Then, the pitching amplitude has little effect on the maximum efficiency value of flapping foil, while it will affect its optimal speed range. When the heaving amplitude ratio reaches 3 and the corresponding maximum angle of attack is about 9°, the maximum efficiency can reach 87%. The effect of anharmonic motion on the efficiency is very small and varies with the St number, but in summary, it can maintain the peak efficiency over a wider range of operations. In addition, the force and flow field characteristics of different efficiency points are compared and analyzed to distinguish their corresponding relationship with the propulsion efficiency.

The present study deals with the local optimization of the stern area and of the propulsive efficiency of a battery-driven, fast catamaran vessel. The adopted approach considers a parametric model for the catamaran’s innovative transom stern and a QCM (Quasi-Continuous Method) body-force model for the effect of the fitted propellers. Hydrodynamic calculations were performed by the CFD code FreSCO+, which also enabled a deep analysis of the incurring unique propulsive phenomena. Numerical results of achieved high propulsive efficiency were verified by model experiments at the Hamburgische Schiffbau Versuchsanstalt (HSVA), proving the feasibility of the concept.

Aquatic and terrestrial animals have different swimming performances and mechanical efficiencies based on their different swimming methods. To explore propulsion in swimming frogs, this study calculated mechanical efficiencies based on data describing aquatic and terrestrial webbed-foot shapes and swimming patterns. First, a simplified frog model and dynamic equation were established, and hydrodynamic forces on the foot were computed according to computational fluid dynamic calculations. Then, a two-link mechanism was used to stand in for the diverse and complicated hind legs found in different frog species, in order to simplify the input work calculation. Joint torques were derived based on the virtual work principle to compute the efficiency of foot propulsion. Finally, two feet and swimming patterns were combined to compute propulsive efficiency. The aquatic frog demonstrated a propulsive efficiency (43.11%) between those of drag-based and lift-based propulsions, while the terrestrial frog efficiency (29.58%) fell within the range of drag-based propulsion. The results illustrate the main factor of swimming patterns for swimming performance and efficiency.

In the present study, a three-dimensional numerical squid model was generated from a computed tomography images of a longfin inshore squid to investigate fluid flow characteristics around the squid. The three-dimensional squid model obtained from a 3D-printer was utilized in digital particle image velocimetry (DPIV) measurements to acquire velocity contours in the region of interest. Once the three-dimensional numerical squid model was validated with DPIV results, drag force and coefficient, required jet velocity to reach desired swimming velocity for the squid and propulsion efficiencies were calculated for different nozzle diameters. Besides, velocity and pressure contour plots showed the variation of velocity over the squid body and flow separation zone near the head of the squid model, respectively. The study revealed that viscous drag was nearly two times larger than the pressure drag for the squid’s Reynolds numbers of 442500, 949900 and 1510400. It was also found that the propulsion efficiency increases by 20% when the nozzle diameter of a squid was enlarged from 1 cm to 2 cm.

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Natural flight has always been the source of imagination for Mankind, but reproducing the propulsive systems used by animals that can improve the versatility and response at low Reynolds number is indeed quite complex. The main objective of the present work is the computational study of the influence of the Reynolds number, frequency, and amplitude of the oscillatory movement of a NACA0012 airfoil in the aerodynamic performance. The thrust and power coefficients are obtained which together are used to calculate the propulsive efficiency. The simulations were performed using ANSYS Fluent with a RANS approach for Reynolds numbers between 8500 and 34,000, reduced frequencies between 1 and 5, and Strouhal numbers from 0.1 to 0.4. The aerodynamic parameters were thoroughly explored as well as their interaction, concluding that when the Reynolds number is increased, the optimal propulsive efficiency occurs for higher nondimensional amplitudes and lower reduced frequencies, agreeing in some ways with the phenomena observed in the animal kingdom.

A mono tiltrotor (MTR) design which combines concepts of a tiltrotor and coaxial rotor is presented. The aerodynamic modeling of the MTR based on blade element momentum theory (BEMT) is conducted, and the method is fully validated with previous experimental data. An automated optimization approach integrating BEMT modeling and optimization algorithms is developed. Parameters such as inter-rotor spacing, blade twist, taper ratio and aspect ratio are chosen as design variables. Single-objective (in hovering or in cruising state) optimizations and multi-objective (both in hovering and cruising states) optimizations are studied at preset design points; i.e., hovering trim and cruising trim. Two single-objective optimizations result in different sets of parameter selections according to the different design objectives. The multi-objective optimization is applied to obtain an identical and compromised selection of design parameters. An optimal point is chosen from the Pareto front of the multi-objective optimization. The optimized design has a better performance in terms of the figure of merit (FM) and propulsive efficiency, which are improved by 7.3% for FM and 13.4% for propulsive efficiency from the prototype, respectively. Further aerodynamic analysis confirmed that the optimized rotor has a much more uniform load distribution along the blade span, and therefore a better aerodynamic performance in both hovering and cruising states is achieved.