Wind excitation structure design and evaluation for a vibration pump

Abstract

A wind excitation structure was designed, built, tested and experimentally evaluated. This excitation structure was used to drive a vibration pump. The vibration pump excluded any rotating parts. The design entailed that wind forces excited the natural frequency of the rotational mode of this structure (Original system). The response was then used to transfer dynamic fluctuating forces to a vibration pump coupled to the structure (Modified system). The excitation structure was designed so that the natural frequency of the rotational bending mode must coincide with wind-induced frequencies (vortex-shedding related) for lift and drag forces respectively, in order to create resonance conditions. The dynamic properties of the vibration pump were chosen to allow tuning of the vibration pump to act as a vibration absorber for this resonance. Mathematical models were formulated in order to describe the response and natural frequencies of the Original and Modified systems. This entailed the formulation of the differential equations of motion for these systems. Other mathematical models were developed for characterisation of the torsional dynamic mount properties of the Original system, and also the equivalent vertical properties of the vibration pump. These models were implemented in different computer programs in a Matlab environment for simulation purposes. Two other computer simulation programs were used in a Solidworks and Ansys environment respectively. Natural frequencies at corresponding mode shapes for the excitation structure were modelled with Finite Element Analysis (FEA) in a Solidworks environment. Computational Fluid Dynamics (CFO) for air flow was simulated in an Ansys environment. Typical wind velocities were measured and used for computation of wind excitation forces. The characterisation of certain parameters at the Original system was done to examine the accuracy of some of these parameters used, and also at the predictions made by FEA. These parameters and some others, including the vertical dynamic properties of the vibration pump, were experimentally characterised and used in computer simulations. The predicted natural frequencies, responses and dynamic forces of the Original and Modified systems were experimentally evaluated. Wind excitation tests were done in the laboratory to evaluate the presence of resonance for different wind velocities. Water was pumped by the vibration pump with dynamic forces transmitted from the excitation structure to drive the pump. Wind forces predicted by CFO were used to roughly determine a feasible estimated height of a similar excitation structure for field applications, in order to replace a typical conventional wind pump with rotating parts.