University of Plymouth PEARL https://pearl.plymouth.ac.uk Faculty of Science and Engineering School of Engineering, Computing and Mathematics 2019-08-19 Wolf Rock lighthouse: past developments and future survivability under wave loading Raby, A http://hdl.handle.net/10026.1/14777 10.1098/rsta.2019.0027 Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences Royal Society, The All content in PEARL is protected by copyright law. Author manuscripts are made available in accordance with publisher policies. Please cite only the published version using the details provided on the item record or document. In the absence of an open licence (e.g. Creative Commons), permissions for further reuse of content should be sought from the publisher or author. Submitted to Phil. Trans. R. Soc. A - Issue Wolf Rock lighthouse: past developments and future survivability under wave loading Journal: Philosophical Transactions A Manuscript ID RSTA-2019-0027.R1 Article Type:ForResearch Review Only Date Submitted by the n/a Author: Complete List of Authors: Raby, Alison; University of Plymouth, School of Marine Science and EngineeringFaculty of Science and Environment Antonini, Alessandro; Technische Universiteit Delft Pappas, Athanasios; University College London Dassanayake, Darshana; University of Plymouth Faculty of Science and Engineering, School of Engineering Brownjohn, James; University of Exeter College of Engineering Mathematics and Physical Sciences, D'Ayala, Dina; University College London, Issue Code (this should have already been entered but HERITAGE please contact the Editorial Office if it is not present): Subject: Civil engineering < ENGINEERING AND TECHNOLOGY Lighthouses, Wave loading, Modal testing, Wave statistics, Structural Keywords: response http://mc.manuscriptcentral.com/issue-ptrsa Page 1 of 29 Submitted to Phil. Trans. R. Soc. A - Issue 1 2 3 Author-supplied statements 4 5 6 Relevant information will appear here if provided. 7 8 Ethics 9 10 Does your article include research that required ethical approval or permits?: 11 This article does not present research with ethical considerations 12 13 Statement (if applicable): 14 CUST_IF_YES_ETHICS :No data available. 15 16 17 Data 18 19 It is a condition of publication that data, code and materials supporting your paper are made publicly 20 available. Does your paper present new data?: 21 Yes For Review Only 22 23 Statement (if applicable): 24 25 Data will be made available through the data repositories of the contributing universities at 26 Plymouth, Exeter and UCL. 27 28 Conflict of interest 29 30 I/We declare we have no competing interests 31 32 Statement (if applicable): 33 CUST_STATE_CONFLICT :No data available. 34 35 36 Authors’ contributions 37 38 This paper has multiple authors and our individual contributions were as below 39 40 Statement (if applicable): 41 Alison Raby - lead author, early Wolf Rock developments, helideck design history, paper editing. 42 Alessandro Antonini - wave loading, modal testing and analysis 43 44 Athanasios Pappas - FE/DE modelling 45 Datshana Dassanayake - water level estimations 46 James Brownjohn - modal test and field data analysis 47 Dina D'Ayala - early lighthouse development and FE/DE modelling 48 49 50 51 52 53 54 55 56 57 58 59 60 http://mc.manuscriptcentral.com/issue-ptrsa Submitted to Phil. Trans. R. Soc. A - Issue Page 2 of 29 1 2 3 4 Phil. Trans. R. Soc. A. 5 doi:10.1098/not yet assigned 6 7 8 9 10 11 12 Wolf Rock lighthouse: past developments and future 13 14 survivability under wave loading 15 1 2 3 1 16 A.C. Raby* , A. Antonini , A. Pappas , D.T. Dassanayake , J.M.W. 4 3 17 Brownjohn , D. D’Ayala 18 1School of Engineering, University of Plymouth, Drake Circus, Plymouth, PL4 8AA, UK 19 2Department of Hydraulics Engineering, Delft University of Technology, 2628 CN Delft, Netherlands 20 3Civil, Environmental and Geomatic Engineering, UCL, Gower Street, London WC1E 6BT, UK 21 4College of Engineering,For Mathematics Review and Physical Sciences, Only University of Exeter, Exeter, EX4 4QF, UK 22 23 Keywords: lighthouses, wave loading, modal testing, wave statistics, structural response 24 25 26 27 28 29 Summary 30 31 Lighthouses situated on exposed rocky outcrops warn mariners of the dangers that lurk beneath the waves. 32 They were first constructed when approaches to wave loading and structural response were relatively 33 unsophisticated, essentially learning from previous failures. Here, we chart the evolution of lighthouses on the 34 Wolf Rock, situated between Land’s End and the Isles of Scilly in the UK. The first empirical approaches are 35 described, followed by design aspects of the present tower, informed by innovations developed on other 36 37 rocky outcrops. We focus on a particular development associated with the automation of lighthouses: the 38 helideck platform. The design concept is described and the structure then scrutinised for future survivability, 39 using the latest structural modelling techniques of the entire lighthouse and helideck. Model validation data 40 was obtained through a complex logistical field operation and experimental modal analysis. Extreme wave 41 loading for the model required the identification of the 250 year return period wave using a Bayesian method 42 with informative prior distributions, for two different scenarios (2017 and 2067). The structural models predict 43 responses of the helideck to wave loading which is characterised by differential displacements of 0.093 m 44 (2017) and 0.115 m (2067) with associated high tension forces and plastic strain. 45 46 47 1. Introduction 48 49 50 Eight miles off the most south-westerly point of the UK, halfway between Land’s End and the Isles of Scilly, 51 lies the Wolf Rock lighthouse. Only the lighthouse itself is visible at high tide, with no sign of the treacherous 52 rock that it marks. The surface-piercing rock is steep-sided and surrounded by water depths of around 60 m. 53 From a wave transformation point of view, this means that waves have the potential to reach the tower with 54 little of their energy being dissipated by breaking onto the rocks. The lighthouse therefore has the potential to 55 experience the largest wave impacts of any of the twenty rock lighthouses around the UK. These lighthouses 56 are still essential forms of navigation, even in the era of GPS, as the UK and Irish General Lighthouse 57 Authorities (GLAs) do not regard such satellite systems as failsafe. 58 59 60 *Author for correspondence ([email protected]). †Present address: Department, Institution, Address, City, Code, Country http://mc.manuscriptcentral.com/issue-ptrsa Page 3 of 29 Submitted to Phil. Trans. R. Soc. A - Issue 2 1 2 3 4 5 For many years, lighthouses were permanently manned by lighthouse keepers, though in recent times they 6 have become fully automated. Still, engineering crews stay for up to two weeks at a time, depending on 7 maintenance requirements. Some of the anecdotal accounts from a previous lighthouse keeper stationed on 8 Wolf Rock over a nine year period are recorded in the Editorial of this Special Issue. While the accounts are 9 10 fairly alarming in nature, none of the structural vibrations arising from wave impacts have until now been 11 quantified, except at the less-exposed Eddystone where maximum displacements were modest [1]. However, 12 the towers of Wolf Rock, Longships, Bishop Rock, Les Hanois, Dubh Artach and Fastnet (see Fig. 1) face much 13 worse wave climates and so have been investigated in the STORMLAMP project, funded by the UK 14 Engineering and Physical Sciences Research Council. The UK and Irish GLAs need to know the condition of 15 these assets and whether they will remain operational into the future in the light of climate change, with the 16 increase in sea level and the possibility of increased storminess. Lessons learned from this project will be 17 applicable to other rock lighthouses internationally. Also, methods of monitoring remote structures are 18 19 relevant for other situations, and the hydrodynamic and structural modelling of wave impacts on the 20 lighthouses has relevance for a host of coastal and offshore structures. 21 For Review Only 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 Figure 1. Map of the British Isles indicating the locations of the seven lighthouses investigated in the 42 STORMLAMP project. 43 44 This paper presents the adaptation of the earliest beacons and the lighthouse on the Wolf Rock, over a period 45 of nearly 200 years. It particularly charts the latest chapter of its story, with results from on-going monitoring 46 and modelling that is shedding light on the current and future stability of the lighthouse. The paper is 47 48 organised as follows: Section 2 presents the chronological developments of structures on the rock over the past 49 two centuries; Section 3 describes the field modal testing and experimental modal analysis of the current 50 lighthouse, providing valuable information on the structural behaviour to validate the structural models; 51 Section 4 presents the Bayesian method to predict wave loading that will be applied to the structural model 52 for current and future scenarios; Section 5 provides details of the structural model with particular focus on the 53 helideck behaviour under the wave loading; and Section 6 concludes with a discussion. 54 55 56 2. Engineering developments at Wolf Rock 57 58 59 60 Phil. Trans. R. Soc. A. http://mc.manuscriptcentral.com/issue-ptrsa Submitted to Phil. Trans. R. Soc. A - Issue Page 4 of 29 3 1 2 3 4 5 6 Initial beacons 7 8 At high tide the Wolf Rock is completely covered. This presented a severe hazard to mariners; indeed three 9 Elder Brethren of Trinity House were drowned close to the spot during a visit [2].