TRANSIENT MULTI-DOF VIBRATION TESTING: ANALYTICAL AND EXPERIMENTAL DATA

2020 ◽  
Vol 63 (1) ◽  
pp. 75-90
Author(s):  
M. Appolloni ◽  
S. Fransen ◽  
H. Fischer ◽  
M. Remedia
Keyword(s):  
Experimental Data ◽  
Degrees Of Freedom ◽  
State Of The Art ◽  
Success Criteria ◽  
Test Platform ◽  
Loads Analysis ◽  
Coupled Loads Analysis ◽  
Definition Of ◽  
6 Degrees Of Freedom ◽  
Coupled Loads

Abstract 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.

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

2018 ◽  
Vol 38 (2) ◽  
pp. 839-851 ◽  
Author(s):  
Nancy J Currie-Gregg ◽  
Kelly Carney
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Joint Stiffness ◽  
Low Frequency ◽  
Nonlinear Dynamic Response ◽  
Vibration Model ◽  
Loads Analysis ◽  
Impact Attenuation ◽  
Coupled Loads Analysis ◽  
Coupled Loads

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.

First Industrial Strength Multi-Axial Robotic Testing Campaign for Composite Material Characterization

2012 ◽  
Author(s):  
John G. Michopoulos ◽  
John C. Hermanson ◽  
Athanasios Iliopoulos
Keyword(s):  
Experimental Data ◽  
Composite Material ◽  
Material Characterization ◽  
Research Laboratory ◽  
Degrees Of Freedom ◽  
Naval Research Laboratory ◽  
Naval Research ◽  
Robotic Testing ◽  
6 Degrees Of Freedom ◽  
Industrial Strength

In this paper we are reporting on the first successful campaign of systematic, automated and massive multiaxial tests for composite material constitutive characterization. The 6 degrees of freedom system developed at the Naval Research Laboratory (NRL) called NRL66.3, was used for this task. This was the in-augural run that served as the validation of the proposed overall constitutive characterization methodology. It involved accomplishing performing 1152 tests in 12 business days reaching a peak throughput of 212 tests per day. We describe the context of the effort in terms of the reasoning and the actual methods behind it. Finally, we present representative experimental data and associated constitutive characterization results for representative loading paths.

scholarly journals Subtitling 3D VR Content with Limited 6DoF: Presentation Modes and Guiding Methods

2021 ◽  
Vol 11 (16) ◽  
pp. 7472
Author(s):  
Mario Montagud ◽  
Cristian Hurtado ◽  
Juan Antonio De Rus ◽  
Sergi Fernández
Keyword(s):  
Degrees Of Freedom ◽  
State Of The Art ◽  
Presentation Mode ◽  
Multimedia Content ◽  
Video Content ◽  
Multimedia Services ◽  
Presentation Modes ◽  
6 Degrees Of Freedom ◽  
First Time ◽  
Access Services

All multimedia services must be accessible. Accessibility for multimedia content is typically provided by means of access services, of which subtitling is likely the most widespread approach. To date, numerous recommendations and solutions for subtitling classical 2D audiovisual services have been proposed. Similarly, recent efforts have been devoted to devising adequate subtitling solutions for VR360 video content. This paper, for the first time, extends the existing approaches to address the challenges remaining for efficiently subtitling 3D Virtual Reality (VR) content by exploring two key requirements: presentation modes and guiding methods. By leveraging insights from earlier work on VR360 content, this paper proposes novel presentation modes and guiding methods, to not only provide the freedom to explore omnidirectional scenes, but also to address the additional specificities of 3D VR compared to VR360 content: depth, 6 Degrees of Freedom (6DoF), and viewing perspectives. The obtained results prove that always-visible subtitles and a novel proposed comic-style presentation mode are significantly more appropriate than state-of-the-art fixed-positioned subtitles, particularly in terms of immersion, ease and comfort of reading, and identification of speakers, when applied to professional pieces of content with limited displacement of speakers and limited 6DoF (i.e., users are not expected to navigate around the virtual environment). Similarly, even in such limited movement scenarios, the results show that the use of indicators (arrows), as a guiding method, is well received. Overall, the paper provides relevant insights and paves the way for efficiently subtitling 3D VR content.

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

2018 ◽  
Author(s):  
Armando Alexandre ◽  
Ricard Buils Urbano ◽  
John Roadnight ◽  
Robert Harries
Keyword(s):  
Finite Element ◽  
Offshore Wind ◽  
Theory Approach ◽  
Floating Platform ◽  
Advantages And Disadvantages ◽  
Hull Structure ◽  
Loads Analysis ◽  
Coupled Loads Analysis ◽  
Coupled Loads ◽  
Bem Theory

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.

Sign in / Sign up

Export Citation Format

Share Document