TRANSIENT MULTI-DOF VIBRATION TESTING: ANALYTICAL AND EXPERIMENTAL DATA

The HYDRA facility is a very large 6-Degrees-of-Freedom (DoF) hydraulic shaker located in the European Space Research and Technology Centre of ESA in The Netherlands. It has been recently used as test platform to perform a number of innovative, 6-DoF experimental vibration runs with the aim of assessing more flight-representative ways to dynamically qualify a spacecraft, hence reducing the level of conservatism. This paper focuses on the methodology behind the definition of the injected profiles computed by launcher/spacecraft coupled loads analysis, the performance achieved by HYDRA and its state-of-the-art MIMO control system, how the experimental data compare to the simulation ones, and aims also at defining success criteria for 6-DoF transient testing.

Methodology for Calculating Floating Offshore Wind Foundation Internal Loads Using Bladed and a Finite Element Analysis Software

In the recent years, the floating offshore wind industry has developed quickly and most authors are now converging towards the need of a coupled loads analysis using aero-hydro-servo-elastic software on time domain simulations for floating foundations design. Different hydrodynamic theories still exist and their application depends on the floating platform characteristics. The Morison equation and the boundary element method (BEM, not to be confused with the Blade Element Momentum theory) theory approaches are often used in combination on the same platform model, sometimes applied to different elements of the same structure depending on their shape. When using the potential flow theory approach calculating internal distributed loads and later on transferring them to stress for hull design purposes is still a challenge due to the large ammount of load cases needed and the complexity of the structure. Furthermore, accounting for platform flexibility is also difficult in most codes using BEM theory due to the same reasons. Different approaches have been proposed by different authors, and currently there is not a single best industry practice for this. This paper presents a method for accounting for platform flexibility when using BEM theory. A range of methods for the load to stress transfer are also presented and the advantages and disadvantages between them are discussed. The choice of one or another method will depend heavily on the platform structure, and different methods might be used and combined for the same platform depending on the shape of the different elements within it. The different methods presented here involve performing coupled loads analysis using the aero-elastic software Bladed and multiple bodies to represent the floating platform in order to obtain internal loads at different points in the structure, as well as allowing for platform flexiblity modelling. Bladed can model multiple hydrodynamic bodies including the hydrodynamic effects between (e.g. coupled terms in the radiation force). The approach used in the current study is based on a platform modelled with the hydrodynamic loading distributed over independent sections, but originally computed from a single body BEM calculation. This simplification offers significant gains in computational efficiency and is expected to be valid for many types of floating structure, whist still allowing for some platform flexiblity to be modelled. The simulation resultant time series can later on be postprocessed to obtain distributed pressure forces on the platform wetted surface and transfer those onto a Finite Element code. Different options are presented here on how to perform this last step for both extreme and fatigue analysis of the hull structure. A couple of examples are shown using the OC3 spar and OC4 semisubmersible, focusing on a subsection of the structures to demonstrate the methodology.

Development of a finite element human vibration model for use in spacecraft coupled loads analysis

Finite element human vibration models were developed and implemented for use in human-tended spacecraft-coupled loads analysis, an analytical process used to predict low-frequency spacecraft loads which occur during dynamic phases of flight of such as launch, ascent, or ascent aborts. Human vibration may also affect stress predictions for spacecraft systems which the crew interacts with, such as crew seats and crew impact attenuation systems. These human vibration models are three-dimensional, distributed-mass representations of 1st-percentile female, 50th-percentile male, and 99th-percentile male American crew members and provide a relatively simple linear and low-load representation of the nonlinear dynamic response of a seated human. The most significant features of these finite element models are anthropometrically based geometric human mass distribution, soft tissue vibration attributes, and skeleton and joint stiffness.