Full Text Available
Note: Clicking the button above will open the full text document at the original institutional repository in a new window.
The detection and quantification of wave slamming from full-scale measurements on a polar vessel
Thesis (MEng)--Stellenbosch University, 2020.
Saved in:
| Main Author: | |
|---|---|
| Other Authors: | |
| Format: | Thesis |
| Language: | en_ZA |
| Published: |
Stellenbosch : Stellenbosch University
2020
|
| Subjects: | |
| Tags: |
No Tags, Be the first to tag this record!
|
| _version_ | 1867613883745697792 |
|---|---|
| access_status_str | Open Access |
| author | Bossau, J. C. |
| author2 | Bekker, Annie |
| author_browse | Bekker, Annie Bossau, J. C. |
| author_facet | Bekker, Annie Bossau, J. C. |
| author_sort | Bossau, J. C. |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MEng)--Stellenbosch University, 2020. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/109293 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:43:13.574Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2020 |
| publishDateRange | 2020 |
| publishDateSort | 2020 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/109293 The detection and quantification of wave slamming from full-scale measurements on a polar vessel Bossau, J. C. Bekker, Annie Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. Slamming of ships -- Detections Ships -- Hydrodynamic impact Wavelet analysis Spectrogram UCTD Polar vessels Thesis (MEng)--Stellenbosch University, 2020. ENGLISH ABSTRACT: The SA Agulhas II is a polar supply and research vessel. Her extended transom design predisposes her to stern slamming, which may lead to significant high transient whipping responses. Slamming is a concern for the fatigue life of the vessel and may lead to local damage. Slamming and whipping are investigated through full-scale measurements of ship responses, recorded concurrently with the associated vessel operational parameters and environmental conditions encountered during purposely executed open water manoeuvres. A systematic operational study was conducted accordingly, whereby the relative heading and vessel speed were regulated in consistent wave states. Firstly, slamming events need to be accurately detected from signals measured with an accelerometer array in the vessel hull. The MATLAB findpeaks function, the continuous Morlet wavelet transform and a spectrogram method were implemented. The continuous Morlet wavelet transform and findpeaks method showed the most promising slamming detection capabilities. It was determined that the proposed slamming detection methods require a threshold to identify structurally significant slams and reject slams of smaller magnitude. The peak acceleration amplitude at the time of impact is extracted and the impact site is determined. Typically, more slams are detected at the stern and the peak magnitude of the acceleration measurements is also greatest at the stern. A structural vibration analysis reveals that high velocity levels are potentially a concern for fatigue and may lead to structural damage. Operational modal analysis techniques determined the hull flexure vertical bending response magnitude resulting from wave-induced vibration. The frequency of stern slams is shown to be highest when the vessel is held on station in following and stern-quartering seas and the corresponding acceleration magnitude is largest at the stern under these conditions. It is shown that stern slamming gives rise to higher vibration velocity levels, which indicate that damage is probable for conditions associated with prevalent stern slams of larger magnitude. The frequency and magnitude of slamming incidence detected at the stern can similarly be shown to concur with the associated flexural response, as the first bending mode dominates the response when the ship encounters following and stern-quartering waves during stationary or low-speed operations. The slamming and associated vertical bending mode whipping response is reduced under these conditions as the wave encounter frequency is decreased with increasing vessel speed. Conversely, as the speed increases, more slamming and a greater bending response is observed for head and bow-quartering seas. Consequently, results indicate potential structural damage attributed to stern slamming and whipping, which is exacerbated in following seas when the vessel is stationary. The quantification of wave slamming presented in this thesis therefore warrants a further investigation into the contribution of whipping to fatigue damage in conjunction with a conventional fatigue analysis. AFRIKAANSE OPSOMMING: Die SA Agulhas II is ‘n polêre navorsings- en voorsieningskip. Weens haar verlengede agterdekontwerp is sy geneig tot branderimpakte teen haar agterboeg wat tot beduidende verbygaande transiënte vibrasie lei. Branderimpakte kan lokale skade van die romp veroorsaak, terwyl die daaropvolgende vibrasie gekoppel is aan versnelde vermoeidheid van die struktuur. Branderimpak en die daaropvolgende vibrasie word deur omvattende meting van die dinamiese skeepsrespons ondersoek, saam met die gepaardgaande parameters van omgewingstoestande gedurende doelgerigte oop water maneuvers. ‘n Sistematiese bedryfsstudie is gevolglik uitgevoer waarby die relatiewe gang en skip spoed gereguleer is in gereëlde golf toestande. Eerstens, moet branderimpakte akkuraat uit vessnellingseine vasgestel word wat vir die doel in die skip se romp aangebring is. Die MATLAB findpeaks funksie, die kontinue Morlet golftransformasie en ‘n spektrogram metode is ondersoek om branderimpakte in lang tydseine te identifiseer. Die kontinue Morlet golftransformasie- en findpeaksmetodes het die mees belowende identifikasie van branderimpak gelewer waarneming vermoë gewys. Dit is bewerkstellig dat die voorgestelde metode vir die identifikasie van branderimpakte ‘n drumpel benodig om struktureel betekenisvolle branderimpakte te identifiseer en die minder beduidende impakte te ignoreer. Die piek versnellingsamplitude ten tye van die impak is onttrek en die oreenstemende tyd van impak is bepaal. Die tydstip is gebruik om die posisie van die impak op die skeepsromp vas te stel. Tipies word meer branderimpakte teen die agterboeg ondervind en die piekwaarde van versnellingsmetings is ook die grootste by die agterboeg. ‘n Strukturele vibrasieanalise onthul dat hoë vlakke van snelheid potensiëel gekorreleer is met oortollige vermoedheid van die skip en moontlik tot strukturele skade kan lei. Operasionele modale analise is gebruik om die omvang van die romp se buigingsreaksie te bepaal, wat deur golf-geïnduseerde vibrasie veroorsaak is. Die gereëldheid van impakte teen die agterboeg is die hoogste wanneer die skip stasionêr in navolgende brandertoestande bedryf word. Die korresponderende versnellingsomvang is die grootste by die agterboeg onder hierdie toestande. Dit is bewys dat impakte teen die agterboeg meer beduidende vibrasie snelheid veroorsaak, wat aandui dat skade meer waarskynlik is in toestande met oorwegende branderimpakte teen die agterboeg. Die gereëldheid en omvang van branderimpakte teen die agterboeg val saam met die geassosiëerde buigingsreaksie, omdat die eerste buigmode die skiprespons domineer wanneer volgende golwe gedurende stasionêre of lae spoed operasies die boeg impakteer. Die buigingseffekte neem af in grootte en gereëldheid wanneer die relatiewe spoed tussen die romp en golfblootselling afneem. Gevolglik dui die studie op moontlike strukturele skade toegeskryf aan oortollige vibrasie weens branderimpakte op die agterboeg, veral in navolgende golftoestande wanneer die skip nie beweeg nie. Die kwantifisering van golfimpakte aangebied in hierdie verhandeling regverdig dus verdere ondersoek na die bydrae van impakte tot verswakkende skade in samewerking met ‘n gebruiklike vermoeidheidsanalise. Masters 2020-11-26T14:16:34Z 2021-01-31T19:43:16Z 2020-11-26T14:16:34Z 2021-01-31T19:43:16Z 2020-12 Thesis http://hdl.handle.net/10019.1/109293 en_ZA Stellenbosch University 131 pages application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Slamming of ships -- Detections Ships -- Hydrodynamic impact Wavelet analysis Spectrogram UCTD Polar vessels Bossau, J. C. The detection and quantification of wave slamming from full-scale measurements on a polar vessel |
| title | The detection and quantification of wave slamming from full-scale measurements on a polar vessel |
| title_full | The detection and quantification of wave slamming from full-scale measurements on a polar vessel |
| title_fullStr | The detection and quantification of wave slamming from full-scale measurements on a polar vessel |
| title_full_unstemmed | The detection and quantification of wave slamming from full-scale measurements on a polar vessel |
| title_short | The detection and quantification of wave slamming from full-scale measurements on a polar vessel |
| title_sort | detection and quantification of wave slamming from full scale measurements on a polar vessel |
| topic | Slamming of ships -- Detections Ships -- Hydrodynamic impact Wavelet analysis Spectrogram UCTD Polar vessels |
| url | http://hdl.handle.net/10019.1/109293 |
| work_keys_str_mv | AT bossaujc thedetectionandquantificationofwaveslammingfromfullscalemeasurementsonapolarvessel AT bossaujc detectionandquantificationofwaveslammingfromfullscalemeasurementsonapolarvessel |