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Fluid-Structure Interaction; Numerical Modelling andExperimental Comparison

Lindgren, Johan LU and Karlsson, Hannes LU (2017) In TVSM-5000 VSM820 20171
Structural Mechanics
Department of Construction Sciences
Abstract
The purpose of this thesis is to investigate the effects of fluid-structure interaction on a submerged oscillating structure. It is to be determined whether it is possible to model such effects with acoustic fluid elements in LS-DYNA using Mat\_Acoustic.
Experiments of an oscillating submerged box were performed and the results were used to compare simulations of the same setups. The setups comprised of 4 different oscillating frequencies and the optional addition of a plate inducing more fluid-structure interaction. From the experiments, an analysis of the rate of decay was performed and a two term exponential model was proposed.

The results showed that added mass is consistently underestimated by 15\% in the FE-model. Furthermore the... (More)
The purpose of this thesis is to investigate the effects of fluid-structure interaction on a submerged oscillating structure. It is to be determined whether it is possible to model such effects with acoustic fluid elements in LS-DYNA using Mat\_Acoustic.
Experiments of an oscillating submerged box were performed and the results were used to compare simulations of the same setups. The setups comprised of 4 different oscillating frequencies and the optional addition of a plate inducing more fluid-structure interaction. From the experiments, an analysis of the rate of decay was performed and a two term exponential model was proposed.

The results showed that added mass is consistently underestimated by 15\% in the FE-model. Furthermore the plate resulted in an increase of added mass for the experiment and the FE-model.

Additionally, convergence studies regarding the required fluid volume to assume infinite depth and fluid mesh sizing were performed and the results were presented as dimensionless quantities. General guidelines on how to use Mat\_Acoustic and maintain stability were presented. Structure shell elements proved to be particularly difficult to model in terms of stability. (Less)
Popular Abstract (Swedish)
Målet med examensarbetet är att undersöka påverkan av fluid-struktur interaktionen för en svängande kropp nedsänkt i vatten. Vidare är det undersökt huruvida det går att modellera denna typ av fenomen med akustiska element i LS-DYNA med Mat\_Acoustic. Experiment med en svängande låda utfördes för att kunna jämföras med simuleringar av samma uppsättning. Experimenten innefattade fyra olika svängningsfrekvenser och en bottenplatta kunde dessutom läggas till för att öka fluid-struktur interaktionen. För experimentdatan utfördes en analys av dämpningen och en exponentialfunktion med två termer föreslogs för att beskriva den.

Resultaten visade att den virtuella massan konsekvent underskattades med 15\% i FE-modellen för det givna fallet.... (More)
Målet med examensarbetet är att undersöka påverkan av fluid-struktur interaktionen för en svängande kropp nedsänkt i vatten. Vidare är det undersökt huruvida det går att modellera denna typ av fenomen med akustiska element i LS-DYNA med Mat\_Acoustic. Experiment med en svängande låda utfördes för att kunna jämföras med simuleringar av samma uppsättning. Experimenten innefattade fyra olika svängningsfrekvenser och en bottenplatta kunde dessutom läggas till för att öka fluid-struktur interaktionen. För experimentdatan utfördes en analys av dämpningen och en exponentialfunktion med två termer föreslogs för att beskriva den.

Resultaten visade att den virtuella massan konsekvent underskattades med 15\% i FE-modellen för det givna fallet. Utöver det visades det även att tillägget av bottenplattan resulterade i en ökning av virtuell massa för både experimentet och FE-modellen.

Konvergensstudier angående den volym som krävs för att antagandet oändligt vattendjup skall vara giltig genomfördes även. Konvergensstudier genomfördes även för storleken av fluidelementen.

Generella riktlinjer för hur Mat_Acoustic bör användas för att bibehålla stabilitet presenteras även. Strukturer modellerade med skalelement visade sig vara speciellt svårmodellerade med hänsyn till stabilitet. (Less)
Please use this url to cite or link to this publication:
author
Lindgren, Johan LU and Karlsson, Hannes LU
supervisor
organization
course
VSM820 20171
year
type
H3 - Professional qualifications (4 Years - )
subject
keywords
Fluid-Structure Interaction FSI LS-DYNA mat_acoustic model
publication/series
TVSM-5000
report number
TVSM-5227
ISSN
0281-6679
language
English
id
8924584
alternative location
http://www.byggmek.lth.se/english/publications/tvsm-5000-masters-dissertations/
date added to LUP
2017-09-11 12:02:50
date last changed
2017-09-11 12:02:50
@misc{8924584,
  abstract     = {The purpose of this thesis is to investigate the effects of fluid-structure interaction on a submerged oscillating structure. It is to be determined whether it is possible to model such effects with acoustic fluid elements in LS-DYNA using Mat\_Acoustic.
Experiments of an oscillating submerged box were performed and the results were used to compare simulations of the same setups. The setups comprised of 4 different oscillating frequencies and the optional addition of a plate inducing more fluid-structure interaction. From the experiments, an analysis of the rate of decay was performed and a two term exponential model was proposed.

The results showed that added mass is consistently underestimated by 15\% in the FE-model. Furthermore the plate resulted in an increase of added mass for the experiment and the FE-model. 

Additionally, convergence studies regarding the required fluid volume to assume infinite depth and fluid mesh sizing were performed and the results were presented as dimensionless quantities. General guidelines on how to use Mat\_Acoustic and maintain stability were presented. Structure shell elements proved to be particularly difficult to model in terms of stability.},
  author       = {Lindgren, Johan and Karlsson, Hannes},
  issn         = {0281-6679},
  keyword      = {Fluid-Structure Interaction FSI LS-DYNA mat_acoustic model},
  language     = {eng},
  note         = {Student Paper},
  series       = {TVSM-5000},
  title        = {Fluid-Structure Interaction; Numerical Modelling andExperimental Comparison},
  year         = {2017},
}