Mixed FE-SP method for nonlinear structure-water interactions with freak waves

This paper develops a mixed finite element – smoothing particle method for violent water-structure interactions involving freak waves and separation between structure and water. The structure undergoes a large rigid motion of 6 DOF with a small elastic deformation, so that its elastic displacement relative to the rigid motion can be represented in a mode summation based on FE analysis. The water is assumed inviscid - incompressible and its motion governed by nonlinear N-S equation. On the coupling interface where no FS separation happens, the equilibrium and consistence conditions are required. The numerical iteration process is suggested to solve the nonlinear FSI equations, and validation examples are shown a good agreement with available experiment results

Geometrical shape influence on energy harvesting performance of oscillating airfoil

In recent years, as an alternative to conventional turbomachinery, flapping foils or oscillating airfoils are under increasingly active investigation to extract energy from wind/water. Their potentials for the generation of electric power are studied here computationally using a two-dimensional unsteady Navier-Stokes solver. In this study, the effect of geometrical shape variation on energy harvesting performance of oscillating airfoil have been investigated. A selective range of parameters have been investigated for symmetrical airfoils (NACA0012, NACA0015, and NACA0018), including the airfoil geometrical parameters: thickness distribution and trailing edge shapes (sharp, blunt and round); fundamental kinematics parameters, i.e. frequency oscillation (f^*=0.10-0.20) at fixed heaving and pitching amplitudes, and the effect of fluid physics (laminar flow at Re = 1100 and turbulent flow at Re = 5x105) are considered. For the turbulent simulations, the highly resolve numerical simulations (y+ ? 1) are performed at high pitch angles using the k-? SST turbulence model, which is found to model the flow separation effectively. The power-extraction efficiency has been used as the performance comparison metric to map the performance into the parametric space considered in this study. The peak efficiency for laminar case has occurred at frequency, f^*=0.14 meanwhile for turbulent case, high efficiency has occurred at frequency, f^*=0.18 and ?_0=76.3°. Less than 2% differences in power efficiency has been observed on the study of the effect of thickness distribution at low Reynolds number, while about 10 to 16% difference has been found for high Reynolds number by comparing NACA0018 and NACA0012 airfoils. Both laminar and turbulent flows show that sharp edge gives the most optimum efficiency performance, with the highest efficiency for laminar is 33.3% while for turbulent is 44.5%. Keywords – oscillating airfoil; energy harvesting; laminar and turbulent flow field<br/

Free surface flow and wave impact at complex solid structures

Hydrodynamic wave loading at structures is a complex phenomenon to quantify. The design of structures to resist wave loading has been historically and predominantly achieved through empirical and experimental observations. This is due to the challenging understanding and quantification of wave impact energy transfer processes with air entrainment at solid structures. This paper investigates wave loading on such structures with effects of air entrapment. Specifically, it focuses on predicting the multi-modal oscillatory wave impact pressure signals which result from transient waves impinging upon a solid wall. A large dataset of compressible (and incompressible) numerical modelling scenarios have been generated to investigate these processes. The modelling simulation data are verified through a grid scaling analysis and validated against previous studies. Air bubble entrapment oscillatory pressure response trends are observed in the compressible simulation during wave impact. A frequency domain analysis of the impact pressure response is undertaken. The numerical modelling results are found in good agreement with theoretical and experimental observation data. These findings provide good confidence on the robustness of our numerical model foundations particularly for investigating the air bubbles formation, their mechanics and adjusted resonance frequency modes at impact with solid wall

A novel reverse hinge spoiler for flight loads control

This paper presents the reverse hinge spoiler, a novel spoiler concept, for flight load control. The reverse hinge spoiler is a control surface mounted on the upper surface of the wing. Unlike conventional hinged spoilers that are hinged at their front and rotate forward toward the leading edge of the wing, the proposed spoiler concept is hinged at its rear and rotates backward toward the trailing edge of the wing. The aerodynamic performance of the proposed spoiler is compared and contrasted with that of a conventional hinged spoiler for different flight conditions and hinge locations using the two-dimensional Reynolds-Averaged Navier–Stokes (RANS) with the k-omega SST turbulence model-based computational fluid dynamic solver. The results show that the proposed spoiler results in a larger increase in drag and a sharper reduction in the lift for a wide range of spoiler angles and flight conditions. Reversing the spoiler is found to cause a higher adverse pressure gradient in front of the spoiler compared to a conventional spoiler, as it ‘traps’ more flow, thereby increasing drag and reducing lift

Exploiting Cloud Computing for Algorithm Development

We consider the application of cloud computing to the process of algorithm development. We introduce a case study focusing on the development of a novel algorithm in computational electromagnetics, illustrating several challenging areas for algorithm developers where cloud-based architectures can deliver enhanced productivity and potentially save costs. The development, verification and tuning of our algorithm have all been assisted by cloud-based technologies. Our preliminary results both demonstrate the potential of the algorithm to solve the problems accurately, and of cloud-based architectures to accelerate the development and verification process. We propose that cloud-based architectures will in the future play a greater role in the development of algorithms; saving costs by improving hardware utilisation, and reducing turnaround time

An investigation on the effect of active vibration isolator on to a structure for low stiffness support

In certain vibration isolation applications, there is a need to achieve a particular low or high supporting stiffness. A method that can provide these particulars supporting stiffness is by using active vibration isolation. The isolation units have to be connected to the supported structure and the effect of the isolation unit on the structure is observed. This paper investigates the effect of a supporting system which is the active vibration isolator on to the beam frequency. It is found that a low stiffness support can be achieved using negative feedback gain and thus affects the beam frequency

Large eddy simulation of flow past stationary and oscillating square cylinders

Flow past stationary and oscillating square cylinders at Reynolds number 22,000 are studied using immersed boundary method (IBM) in large eddy simulation (LES), as the IBM is able to seamlessly simulate arbitrarily-moving bodies at an excellent efficiency. The square cylinders are forced to oscillate in a prescribed sinusoidal motion at reduced velocity 7.7, which corresponds to the resonance point. Two amplitude ratios $A/D$ = 0.05 and 0.1 based on cylinder height $D$ are studied. The accuracy of the current solver with the immersed boundary method is rigorously assessed against the reference data. To understand the effect of osculation motion on the flow and turbulence, aerodynamics of the oscillating cylinder is compared with that of the stationary cylinder. It is found that the oscillation motion reduces the spanwise correlation of flow field and triggers earlier reattachment on the side faces. Consequently, more chaotic surface pressure is generated downstream the reattachment point, and a smaller correlation is observed between upper and lower surface pressures. This helps to fully understand the interaction of turbulence and the flow-induced motion of a structure

Freestream turbulence effects on the aerodynamics of an oscillating square cylinder at the resonant frequency

Flow past a bluff body in freestream turbulence can substantially change the flow behaviour compared to that in smooth inflow. This paper presents the study of wake flow and aerodynamics of an oscillating square cylinder at the resonant frequency in freestream turbulence, with the integral length not greater than the cylinder side and the turbulence intensity not greater than 10\%. Large eddy simulations (LES) in the Cartesian grid using the Immersed Boundary Method (IBM) technique embedded in a FVM solver, together with an efficient synthetic turbulent inflow generator implemented in an in-house parallel FORTRAN code (Chen et al, 2020, Journal of Fluids and Structures 2020) are used for the study. The results are compared with those for smooth inflow, and relevant data published in the literature. The key findings are: the freestream turbulence conditions evidently reduces the local turbulent scales and fluctuations in the shear layer compared to in smooth flow, as small scale freestream turbulence breaks down cylinder-generated larger scale eddies and weakens them; but does not evidently affect the vortex shedding frequency, or the length of the recirculation region behind the cylinder. This suggests negligible change of drag coefficient compared to in smooth inflow. Moreover, this is because the vortex shedding is dominated by the forced oscillation at the resonance frequency, and the turbulence intensity is small