Journal of Fluids and Structures最新文献

Flow-induced structural noise is an important component of hydrodynamic noise of underwater structures. Local resonance metamaterials are considered to have excellent performance and enormous potential in the field of low-frequency vibration and noise control. To verify its potential, the paper derived the underwater band gap of a lateral local resonance (LLR) plate through the plane wave expansion (PWE). Then, utilizing the modal superposition approach and Rayleigh integral technique, the vibro-acoustic response of a LLR plate under a turbulent boundary layer (TBL) excitation is obtained. Finite element certification is also conducted through an uncorrelated wall plane wave technique. Parametric study is conducted to analyse the factors which influence the control effects. The result shows that the plate exhibits excellent suppression performance for flow-induced vibration at band gap frequencies. The band gaps and suppression ranges generated by the underwater metamaterial plate, are dramatically narrowed due to the thick fluid load. The paper provides theoretical guidance for the control of flow-induced structural vibration and the application of acoustic metamaterials.

In this paper, a numerical approach able to evaluate the sound power emitted by a non-cavitating flexible marine propeller blade is proposed. With asymptotic expansions and order of magnitude analysis, two main phenomena are identified: the so-called propulsion and vibroacoustic phenomenon. The propulsion phenomenon is nonlinear and models the lift generation along the blade. It creates a pre-stress and a pre-strain on a deformed configuration on which the blade vibrates and emits sound waves. The vibroacoustic phenomenon is linearized and has no retroaction on the first static phenomenon. This simplified model allows to solve the fully coupled fluid–structure system in order to compute the radiated noise of a pre-stressed blade.

This study experimentally investigates the effectiveness of a control rod in suppressing self-excited acoustic resonance within a range of Reynolds numbers (Re) spanning from $2.1$ × $10^4$ to $1.6$ × $10^5$. The investigation focuses on specific parameters, including diameter ratio ($d/D$) values of 0.1, 0.2, and 0.3; gap ratio ($G/D$) values of 0.05, 0.1, and 0.2; and angular positions ($\theta$) ranging from 0 to 180 degrees. Comparative analyses are conducted between cases featuring the control rod and a reference case (base case) without it. The near-wake flow field is characterized using Particle Image Velocimetry (PIV), and aeroacoustic response measurements are employed to quantify the aeroacoustic noise emission, particularly during self-excited acoustic resonance. Simultaneous measurements of fluctuating lift force and aeroacoustic response measurements, facilitate the quantification of energy transfer from the flow field to the acoustic field during self-excited acoustic resonance. The results reveal that the control rod’s placement significantly impacts the Strouhal periodicity, with outcomes heavily dependent on the rod’s angular orientation. At certain angular positions, the control rod reduces the sound pressure level (SPL) generated during acoustic resonance excitation. However, at different angular positions, the rod exacerbates resonance excitation. This variability is attributed to the control rod’s profound influence on the vortex core formation and the energy transfer mechanism during acoustic resonance.

Magnetic helical swimmers are one type of robots that swim at low Reynolds number environments by rotating around the helix axis. Considering the importance and dramatic increase in the use of robots and microrobots in the near future, optimizing and increasing their efficiency is very important and noteworthy. Propulsion force and translational velocity are among the most important features of the magnetic helical swimmer, which improves the function of the swimmer as each of them increases. In this paper, a new design has been proposed for the magnetic helical swimmer by changing the geometry of the tail region, which has increased the propulsion force and improved its translational velocity. A suitable experimental setup has been designed and built in accordance with the required experiments to evaluate the translational velocity of the proposed swimmer. Using the experimental results, two models have been presented to express the translational velocity and propulsion force of the swimmer in terms of its angular velocity. The results of the experiments show that the propulsion force of the built swimmer is 698.89 % higher than that of the common magnetic helical swimmer with similar dimensions and the same environmental conditions in Newtonian fluid. At the end of the experiments, the motion of the proposed swimmer is simulated in the COMSOL software, and the results of the experiments are used to validate the simulation results. Finally, the effect of parameters such as the helix pitch and the number of turns of the helix on the translational velocity of the swimmer is investigated using the computer simulations.

This study numerically investigates the aerodynamic and aeroelastic characteristics of a square prism (aeroelastic model) and wind field around it in sinusoidal oscillatory flows (SOFs). The reliability of the fluid-solid interaction (FSI) simulation is validated by a free vibration test and wind tunnel tests in smooth flow and SOF. The effects of the amplitude and frequency of SOFs are studied at the mean wind speed of vortex-induced resonance. The results show that increasing the amplitude and frequency of SOFs will amplify the root mean square (RMS) along-wind and across-wind base shear forces of the aeroelastic model but decrease the RMS across-wind displacement at the top of the aeroelastic model. The spectral analysis of the base shear forces indicates that the influence of vortex shedding on the across-wind base shear force is reduced by either increasing the amplitude or increasing the frequency of SOFs. The mean and instantaneous wind fields around the aeroelastic model in SOFs and smooth flow are compared, and the wake characteristics of the aeroelastic model in SOFs are analysed by dynamic mode decomposition. It is observed that when the frequency of SOFs is 1.5 times as large as the fundamental natural frequency of the aeroelastic model, the regular vortex shedding process is substantially affected.

Fluidic circuits are a promising recent development in embodied control of soft robots. These circuits typically make use of highly non-linear soft components to enable complex behaviors given simple inputs, such as constant flow or pressure. This approach greatly simplifies control, as it removes the need for external hardware or software. However, detailed fundamental understanding of the non-linear, coupled fluidic and mechanical behavior of these components is lacking. Such understanding is needed to guide new designs and increase the reliability of increasingly autonomous soft robots. Here, we develop an analytical model that captures the coexistence of a pressure regulation mode and an oscillatory mode in a specific soft hysteretic valve design, that we previously used to achieve reprogrammable activation patterns in soft robots. We develop a model that describes the mechanics, fluidics and dynamics of the system by two coupled non-linear ordinary differential equations. The model shows good agreement with the experimental evidence, as well as correctly predicts the effect of design changes. Specifically, we experimentally show that we can remove the regulation mode at low input flow rates by changing the fluidic response of the valve. Taken together, the present study contributes to better understanding of system-level behavior of fluidic circuits for controlling soft robots. This may contribute to the reliability of soft robots with embodied control in future applications such as autonomous exploration and medical prosthetic devices.

Mesh-based Eulerian and particle-based Lagrangian models are common computational fluid dynamics (CFD) tools for simulating wave-structure interactions. While Eulerian models are efficient in terms of computational time, they are limited in their ability to handle large interface discontinuities between two flows and complex structure motion responses. Conversely, Lagrangian models are suitable for such discontinuities and motion responses but can be computationally expensive. However, there is a lack of comprehensive discussion on the (dis)advantages of hybrid Eulerian-Lagrangian models, which have the potential to achieve both numerical efficiency and flexibility through a combined use of mesh and particles. This paper presents a comparative study of a hybrid Eulerian-Lagrangian Particle-In-Cell (PIC) model and the widely-used OpenFOAM model, applied to a variety of complex wave interactions with floating offshore renewable energy structures in both 2D and fully 3D domains. We found that both models demonstrate good performance in simulating complex floating structures. Additionally, it is the first time that the two models have been compared in parallel on the same computing facility, allowing us to directly show their computational efficiency. The PIC model has the advantage of using staggered grids, which enables it to achieve computational efficiency comparable to the pure mesh-based OpenFOAM. The findings of this study provide researchers and practitioners in the field of computational fluid dynamics with a clear understanding of the performance of the hybrid Eulerian-Lagrangian PIC model and OpenFOAM for simulating complex fluid-structure interaction problems.

Given the current context of changes in aeronautics to reduce emissions, it is also necessary to modernise the computation methods to anticipate future cases where disciplines which are now calculated separately (i.e. manoeuvers and gusts) should be computed at the same time including flexible effects and using a time-domain approach. In this work, a static aeroelasticity formulation is adapted to compute wind gust loads. This static method uses aerodynamic matrices to calculate an effective angle of attack (used to recover the local pressure coefficients) from a structural deformation. The approach has been to define this deformation including unsteady effects influence in order to use the same formulation as the static case. Three gust cases (two unsteady and one quasi-steady) have been tested in a rectangular wing, and the proposed method has been compared to the aeroelastic high-fidelity solution and to an uncorrected version of the Doublet Lattice Method (Nastran Solution 146). The proposed solution benefits from the use of the lookup tables to accurately estimate the peak lift coefficient value (maximum error of 6.7%) at least 2.5 times faster than the Doublet Lattice Method. Nevertheless, using a limited model with only two degrees of freedom prevents the proposed method from capturing complex dynamics coming from highly unsteady gust excitation or from aerodynamic instabilities.

The study of the vibration characteristics of the liquid-filled pipeline has important academic significance and practical value for analyzing the dynamic behavior of the pipeline system, ensuring its stability and improving its reliability. The fluid-structure interaction transfer matrix method (FSITMM) is regarded as an effective method for the study of these vibration characteristics. Nonetheless, there are relatively few studies concerning the theoretical basis, especially stability and orthogonality, of the FSITMM for liquid-filled piping systems. The existing studies cannot adequately address computational failure issues in models based on the FSITMM, cannot determine whether the results are credible, and even more, cannot predict whether the new models will be computationally successful. The weighted orthogonality of the eigenvectors is a necessary condition for the modal synthesis method to determine the transient (or time-domain) response of the pipeline, and the stability is crucial as it guarantees the accuracy of the solution results. In this paper, the weighted orthogonality of the modes of the FSITMM for liquid-filled piping systems is validated, the stability of this transfer matrix is examined, and enhanced by the reduced transfer matrix method. Numerical simulation results demonstrate the ability of stability validation to predict the success of computational results, while weighted orthogonality validation can determine the accuracy of computational results. The results obtained from the fluid-structure interaction model using the approach of this paper are more accurate.

Vortex induced vibrations is a withstanding ubiquitous problem in the marine industry. Although seemingly simple, cylindrical structures in cross-flows originate extremely complex and, at times, chaotic hydrodynamics which are not fully understood nowadays. One of the biggest industries driving economic development that has had to deal which this problem is Offshore Oil & Gas. Key to a safe oil extraction, marine risers have to operate and withstand the erratic process that arises from the fluid–structure interaction of marine risers with vortex induced hydrodynamic forces.

In the following paper we put forward a methodology to assimilate large amounts of data into empirical models. In doing so, we hope to bring attention to the potential that sensors and data collected by them can have in improving predictions of VIV phenomena. Although we leverage a semi-empirical VIV prediction tool (VIVA), the optimization methods used to extract robust hydrodynamic databases for a Steel Catenary Riser (SCR) are not limited to this method. The performance of the extracted databases are systematically cross-validated. To the authors’ best knowledge, an extensive cross-validation of this methodology has not been performed in previous studies.