Monopile Foundation Stiffness Estimation of an Instrumented Offshore Wind Turbine through Model Updating

<table class="table-group" id="tab6"><tr><td><table class="table"><tr><td class="thead-hr" colspan="7"><hr/></td></tr><tr class="thead"><td class="align_center" colspan="2" rowspan="3"> </td><td class="align_center" rowspan="3">Identified <svg height="9.4556pt" id="M76" style="vertical-align:-0.2063894pt" version="1.1" viewbox="-0.0498162 -9.24921 8.42472 9.4556" width="8.42472pt" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"><g transform="matrix(.013,0,0,-0.013,1.683,-.222)"><path d="M470 619L451 641C422 610 391 595 348 595C316 595 288 601 248 612C197 628 172 633 138 633C97 633 43 615 0 555L19 532C54 562 86 578 130 578C166 578 189 571 222 562C267 549 301 540 337 540C381 540 434 557 470 619Z"></path></g><g transform="matrix(.013,0,0,-0.013,0,0)"><path d="M615 290C615 392 563 448 529 448C511 448 491 441 484 434L483 425C518 400 546 349 546 273C546 158 504 46 417 46C381 46 356 77 356 142C356 184 380 293 392 334L387 340L307 323C305 288 296 228 287 188C265 94 221 52 180 52C144 52 112 89 112 171C112 278 164 372 241 430L226 454C106 394 23 288 23 155C23 40 79 -12 139 -12C184 -12 245 32 285 85C292 31 322 -12 376 -12C423 -12 470 18 501 45C570 104 615 184 615 290Z"></path></g></svg></td><td class="align_center" colspan="4"><i>PISA foundation finite element</i></td></tr><tr class="thead"><td class="align_center" colspan="2"><i>Flexible blade (FE-FB)</i></td><td class="align_center" colspan="2"><i>Rigid blade (FE-RB)</i></td></tr><tr class="thead"><td class="align_center"><span style="width: 8.42472ptpx;"><svg height="9.4556pt" id="M77" style="vertical-align:-0.2063894pt" version="1.1" viewbox="-0.0498162 -9.24921 8.42472 9.4556" width="8.42472pt" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"><g transform="matrix(.013,0,0,-0.013,1.683,-.222)"><path d="M470 619L451 641C422 610 391 595 348 595C316 595 288 601 248 612C197 628 172 633 138 633C97 633 43 615 0 555L19 532C54 562 86 578 130 578C166 578 189 571 222 562C267 549 301 540 337 540C381 540 434 557 470 619Z"></path></g><g transform="matrix(.013,0,0,-0.013,0,0)"><path d="M615 290C615 392 563 448 529 448C511 448 491 441 484 434L483 425C518 400 546 349 546 273C546 158 504 46 417 46C381 46 356 77 356 142C356 184 380 293 392 334L387 340L307 323C305 288 296 228 287 188C265 94 221 52 180 52C144 52 112 89 112 171C112 278 164 372 241 430L226 454C106 394 23 288 23 155C23 40 79 -12 139 -12C184 -12 245 32 285 85C292 31 322 -12 376 -12C423 -12 470 18 501 45C570 104 615 184 615 290Z"></path></g></svg></span></td><td class="align_center">MAC</td><td class="align_center"><span style="width: 8.42472ptpx;"><svg height="9.4556pt" id="M78" style="vertical-align:-0.2063894pt" version="1.1" viewbox="-0.0498162 -9.24921 8.42472 9.4556" width="8.42472pt" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"><g transform="matrix(.013,0,0,-0.013,1.683,-.222)"><path d="M470 619L451 641C422 610 391 595 348 595C316 595 288 601 248 612C197 628 172 633 138 633C97 633 43 615 0 555L19 532C54 562 86 578 130 578C166 578 189 571 222 562C267 549 301 540 337 540C381 540 434 557 470 619Z"></path></g><g transform="matrix(.013,0,0,-0.013,0,0)"><path d="M615 290C615 392 563 448 529 448C511 448 491 441 484 434L483 425C518 400 546 349 546 273C546 158 504 46 417 46C381 46 356 77 356 142C356 184 380 293 392 334L387 340L307 323C305 288 296 228 287 188C265 94 221 52 180 52C144 52 112 89 112 171C112 278 164 372 241 430L226 454C106 394 23 288 23 155C23 40 79 -12 139 -12C184 -12 245 32 285 85C292 31 322 -12 376 -12C423 -12 470 18 501 45C570 104 615 184 615 290Z"></path></g></svg></span></td><td class="align_center">MAC</td></tr><tr><td class="thead-hr" colspan="7"><hr/></td></tr><tr><td class="align_left" rowspan="2"><i>1</i><sup><i>st</i></sup><i> tower</i></td><td class="align_center">Fore-aft</td><td class="align_center">0.99</td><td class="align_center">0.99</td><td class="align_center">0.98</td><td class="align_center">0.99</td><td class="align_center">0.39</td></tr><tr><td class="align_center">Side-side</td><td class="align_center">1.00</td><td class="align_center">1.00</td><td class="align_center">1.00</td><td class="align_center">1.00</td><td class="align_center">0.56</td></tr><tr><td class="align_left" colspan="7"><hr/></td></tr><tr><td class="align_left" rowspan="2"><i>2</i><sup><i>nd</i></sup><i> tower</i></td><td class="align_center">Fore-aft</td><td class="align_center">4.08</td><td class="align_center">4.09</td><td class="align_center">0.67</td><td class="align_center">4.08</td><td class="align_center">0.98</td></tr><tr><td class="align_center">Side-side</td><td class="align_center">4.22</td><td class="align_center">4.18</td><td class="align_center">0.68</td><td class="align_center">4.24</td><td class="align_center">0.96</td></tr><tr><td class="align_left" colspan="7"><hr/></td></tr><tr><td class="align_left" rowspan="2"><i>3</i><sup><i>rd</i></sup><i> tower</i></td><td class="align_center">Fore-aft</td><td class="align_center">9.83</td><td class="align_center">10.99</td><td class="align_center">0.90</td><td class="align_center">8.82</td><td class="align_center">0.96</td></tr><tr><td class="align_center">Side-side</td><td class="align_center">11.17</td><td class="align_center">11.35</td><td class="align_center">0.97</td><td class="align_center">11.43</td><td class="align_center">0.96</td></tr><tr class="table-tr"><td colspan="7"><hr class="tbody-hr"/></td></tr></table></td></tr></table>

<div>Tower dominated normalised mode frequencies (Hz) at 09:00 29/08/2017 identified from monitored data using N4SID and predicted using flexible and rigid-bladed variants of the PISA foundation FE model.</div>

Structural Control and Health Monitoring

tab6

Table 6

Table 6: Monopile Foundation Stiffness Estimation of an Instrumented Offshore Wind Turbine through Model Updating 