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Micro power generators (MPGs) can harvest electrical power from ambient energy resources in natural environments to operate small-scale electronic devices. Such systems exploit structural vibrations due to cross-flow instabilities through fluid–structure interactions (FSI). Due to attractive features of piezoelectric transducers, we utilize them for vibration-to-electricity conversion in this work. We develop strongly coupled FSI-based computational models to handle large-amplitude structural motions in which unsteady forces exerted by fluid flows on structures, their dynamical responses, and harvested power are directly computed. Our mathematical model for incompressible flows over moving bodies relies on arbitrary Lagrangian–Eulerian (ALE) formulation. Our in-house FSI solver primarily works using radial basis interpolation technique for grid morphing. Using broad ranges of fluidic, structural, and electrical parameters, we investigate the power generation performance of two types of MPGs, working through vortex-induced vibrations of a circular cylinder and a fluttering NACA-0012 airfoil, under different excitation conditions. Optimum values of load resistance are found to maximize the harvested power. Furthermore, our findings support the linear analysis, which provides insights into the possible instabilities in the electro-mechanical system. Another salient feature of this research work is the inclusion of cubic nonlinear stiffness in the energy harvesting models. [ABSTRACT FROM AUTHOR]

Using immersed boundary methods, we perform numerical simulations for flow over an elliptical airfoil oscillating at a reduced frequency of 6.283 over a range of Strouhal number with Reynolds number 500. We quantify the response of this nonlinear system through time-histories of aerodynamic lift and thrust force coefficients, their Fourier spectra, phase maps, Poincáre sections, and higher-order spectral analysis. When the oscillation amplitude increases, this nonlinear system undergoes bifurcations, thus eventually achieving chaotic solutions. The aerodynamic response moves quasi-periodically through to chaos. We also relate these behavioral changes in the response of the system to the wake transitions. We also present cross-bispectrum between the lift and thrust coefficients, and auto-trispectrum for the lift coefficient to study cubic coupling among various frequency components. We find the strongest quadratic and cubic coupling between the excitation frequency components. We also observe the cubic coupling among various frequency components responsible for generating new harmonics in the spectra of the lift force at higher Strouhal numbers. [ABSTRACT FROM AUTHOR]

We perform numerical simulations using immersed boundary method for flow over a single and two fish in tandem performing traveling wave like motion for a range of Strouhal numbers. We investigate the hydrodynamic performance of single- and tandem-fish configurations using unsteady profiles of lateral side-force and drag coefficients, their time-averaged values, and wake behind these bodies. We present the spectra of hydrodynamic forces and find that the nature of these forces for a single fish resembles to those of stationary/oscillating bluff bodies and oscillating airfoils. For tandem cases, we vary the phase speed of undulatory motion of the rear fish while keeping the free-stream velocity constant. We show that hydrodynamic forces of the upstream and rear fish contain harmonics which are produced by nonlinear interaction of the oscillation frequencies of both fish. We find that the wake and time-averaged drag of the upstream fish remain almost independent of the undulating frequency of the rear fish at a certain Strouhal number. We also relate this observation with the absence of oscillation frequency of the rear fish in the Fourier spectra of hydrodynamic forces of the upstream fish. For the complete range of parameters, it is inferred that swimming in a tandem configuration seems more beneficial for the upstream fish. It happens due to wake-splitting effect of the rear fish that causes an enhancement of pressure in its wake. For the rear fish, it gains an advantage of drafting under certain conditions and its performance deteriorates at Strouhal numbers greater than 0.40. [ABSTRACT FROM AUTHOR]

The nonlinearity and time-dependent nature of hydroelastic slamming along with violent fluid–structure interactions (FSIs) and evolution of free surfaces present great challenges to the numerical modeling. The inherent physical mechanisms of such a violent FSI involved with structural vibrations have not been well investigated so far. In this work, an adaptive element–particle coupling approach is extended to reveal the underlying mechanisms of hydroelastic slamming, which leverages the advantages of grid-based method in accurately modeling structural deformations and fluid flows with small deformations as well as particle method in effectively capturing moving interfaces. After well validating with experimental results, we focus on investigating the flow physics and hydrodynamic loads along with structural hydroelastic performances including wedge kinematics and dynamic responses. It is demonstrated that the plate deformation has minimal influence on the maximum hydrodynamic load in normal slamming, whereas it has significant effects in oblique slamming. Both rolling free surfaces and waves around the plate ends may affect the distribution of hydrodynamic loads on the elastic structure. For kinematics and dynamic responses of the structure under slamming loads, different configurations of deformation and stages of motion are identified. With increasing deadrise angle, the structural deformation becomes more pronounced and later gets smaller for a large structural flexibility. However, it may decrease in a direct manner with an increase in the deadrise angle when a smaller plate flexibility is adopted. Further, the important phenomenon of structural vibration is studied with typical influencing factors analyzed. A novel empirical formulation is proposed to predict vibrational characteristics of the wedge during hydroelastic slamming processes. This relation is unified and applicable for a broad of scenarios from normal to oblique slamming. [ABSTRACT FROM AUTHOR]

Hydroelastic fluid-structure interaction (FSI) problems usually involve nonlinear free surface flows, large structure deformations and changing interfaces, which present great challenges for numerical modeling. To deal with violent FSIs, the authors proposed a multi-resolution smoothed particle element method (M-SPEM), which adaptively simulates local fluid regions with an improved smoothed particle hydrodynamics (SPH) method and models other solid/fluid regions with a smoothed finite element method (S-FEM). Both computational accuracy in local fluid domain and entire efficiency can be improved by M-SPEM compared with the conventional partitioned FSI solvers based on SPH-FEM coupling schemes. In this work, an improved M-SPEM is developed and extended to simulate the complex hydroelastic FSI problems with structural deformations considered in the numerical model. To solve the accuracy reduction problem in the multi-resolution simulations, we developed a velocity and position correction technique for the generated fluid and virtual particles. The computational results demonstrated that the new correction technique can effectively improve the computational accuracy of M-SPEM while the corrected schemes produce results very close to the reference ones. The positions of the generated particles should also be appropriately optimized during the element-particle conversion process. With both accuracy and efficiency improved, the improved M-SPEM is proven to be suitable to deal with some challenging hydroelastic FSI problems. • An improved M-SPEM approach is developed to model hydroelastic FSI problems. • The velocity and position correction technique is proposed to improve the computational accuracy. • The improved M-SPEM can greatly save computational cost compared to the general FEM-SPH coupling approaches. • The multi-resolution interfaces between elements and particles are handled by splitting ghost particles. • The M-SPEM is very effective for modeling challenging FSI problems involved with large structural deformations. [ABSTRACT FROM AUTHOR]