Wave loads on offshore wind turbines: Feasibility study using results of wave experiments executed by Electricité de France (EDF)

<p class=MsoNormal style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: justify;mso-hyphenate: none; tab-stops: -24.95pt -12.5pt 0cm 12.5pt 24.95pt 37.45pt 49.9pt 62.4pt 74.9pt 87.35pt 99.85pt 112.3pt 124.8pt 137.3pt 149.75pt 162.25pt 174.7pt 187.2pt 199.7pt 212.15pt 224.65pt 237.1pt 249.6pt 262.1pt 274.55pt 287.05pt 299.5pt 312.0pt 324.5pt 336.95pt 349.45pt 361.9pt 374.4pt 386.9pt 399.35pt 411.85pt 424.3pt 436.8pt 449.3pt"><span style="FONT-SIZE: 11pt; FONT-FAMILY: 'Times New Roman'; LETTER-SPACING: -0.15pt; mso-bidi-font-size: 10.0pt; mso-ansi-language: EN-US">Electricité de France (EDF) has performed an experimental study on the wave loading on a cylindrical pile for offshore wind turbines in shallow water depths. A report with the results of the experimental study has been provided to ECN.</wegspan><wegspan style="FONT-SIZE: 11pt; FONT-FAMILY: 'Times New Roman'; LETTER-SPACING: -0.15pt; mso-bidi-font-size: 10.0pt; mso-ansi-language: EN-US"> <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p></wegspan> <p class=MsoNormal style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: justify; mso-hyphenate: none; tab-stops: -24.95pt -12.5pt 0cm 12.5pt 24.95pt 37.45pt 49.9pt 62.4pt 74.9pt 87.35pt 99.85pt 112.3pt 124.8pt 137.3pt 149.75pt 162.25pt 174.7pt 187.2pt 199.7pt 212.15pt 224.65pt 237.1pt 249.6pt 262.1pt 274.55pt 287.05pt 299.5pt 312.0pt 324.5pt 336.95pt 349.45pt 361.9pt 374.4pt 386.9pt 399.35pt 411.85pt 424.3pt 436.8pt 449.3pt"><span style="FONT-SIZE: 11pt; FONT-FAMILY: 'Times New Roman'; LETTER-SPACING: -0.15pt; mso-bidi-font-size: 10.0pt; mso-ansi-language: EN-US">The aim of the feasibility study is to investigate whether the results of the wave experiment can be used for further research and contribute to the implementation of 6000 MW in the Dutch Exclusive Economic Zone by the year 2020.</wegspan><wegspan style="FONT-SIZE: 11pt; FONT-FAMILY: 'Times New Roman'; LETTER-SPACING: -0.15pt; mso-bidi-font-size: 10.0pt; mso-ansi-language: EN-US"> <o:p></o:p></wegspan> <p class=MsoNormal style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: justify; mso-hyphenate: none; tab-stops: -24.95pt -12.5pt 0cm 12.5pt 24.95pt 37.45pt 49.9pt 62.4pt 74.9pt 87.35pt 99.85pt 112.3pt 124.8pt 137.3pt 149.75pt 162.25pt 174.7pt 187.2pt 199.7pt 212.15pt 224.65pt 237.1pt 249.6pt 262.1pt 274.55pt 287.05pt 299.5pt 312.0pt 324.5pt 336.95pt 349.45pt 361.9pt 374.4pt 386.9pt 399.35pt 411.85pt 424.3pt 436.8pt 449.3pt"><span style="FONT-SIZE: 11pt; FONT-FAMILY: 'Times New Roman'; LETTER-SPACING: -0.15pt; mso-bidi-font-size: 10.0pt; mso-ansi-language: EN-US">The study is divided in three parts:<o:p></o:p></wegspan> <p class=MsoNormal style="MARGIN: 0cm 0cm 0pt 36pt; TEXT-INDENT: -18pt; TEXT-ALIGN: justify; mso-hyphenate: none; tab-stops: -24.95pt -12.5pt 0cm 12.5pt 24.95pt list 36.0pt left 37.45pt 49.9pt 62.4pt 74.9pt 87.35pt 99.85pt 112.3pt 124.8pt 137.3pt 149.75pt 162.25pt 174.7pt 187.2pt 199.7pt 212.15pt 224.65pt 237.1pt 249.6pt 262.1pt 274.55pt 287.05pt 299.5pt 312.0pt 324.5pt 336.95pt 349.45pt 361.9pt 374.4pt 386.9pt 399.35pt 411.85pt 424.3pt 436.8pt 449.3pt; mso-list: l0 level1 lfo1"><wegspan style="FONT-SIZE: 11pt; FONT-FAMILY: Symbol; LETTER-SPACING: -0.15pt; mso-bidi-font-size: 10.0pt; mso-ansi-language: EN-US">·<wegspan style="FONT: 7pt 'Times New Roman'">  </wegspan></wegspan><wegspan style="FONT-SIZE: 11pt; FONT-FAMILY: 'Times New Roman'; LETTER-SPACING: -0.15pt; mso-bidi-font-size: 10.0pt; mso-ansi-language: EN-US"><wegspan style="mso-spacerun: yes"> </wegspan>a literature survey<o:p></o:p></wegspan> <p class=MsoNormal style="MARGIN: 0cm 0cm 0pt 36pt; TEXT-INDENT: -18pt; TEXT-ALIGN: justify; mso-hyphenate: none; tab-stops: -24.95pt -12.5pt 0cm 12.5pt 24.95pt list 36.0pt left 37.45pt 49.9pt 62.4pt 74.9pt 87.35pt 99.85pt 112.3pt 124.8pt 137.3pt 149.75pt 162.25pt 174.7pt 187.2pt 199.7pt 212.15pt 224.65pt 237.1pt 249.6pt 262.1pt 274.55pt 287.05pt 299.5pt 312.0pt 324.5pt 336.95pt 349.45pt 361.9pt 374.4pt 386.9pt 399.35pt 411.85pt 424.3pt 436.8pt 449.3pt; mso-list: l0 level1 lfo1"><wegspan style="FONT-SIZE: 11pt; FONT-FAMILY: Symbol; LETTER-SPACING: -0.15pt; mso-bidi-font-size: 10.0pt; mso-ansi-language: EN-US">·<wegspan style="FONT: 7pt 'Times New Roman'">  </wegspan></wegspan><wegspan style="FONT-SIZE: 11pt; FONT-FAMILY: 'Times New Roman'; LETTER-SPACING: -0.15pt; mso-bidi-font-size: 10.0pt; mso-ansi-language: EN-US"><wegspan style="mso-spacerun: yes"> </wegspan>a visit to the hydraulic laboratory<o:p></o:p></wegspan> <p class=MsoNormal style="MARGIN: 0cm 0cm 0pt 36pt; TEXT-INDENT: -18pt; TEXT-ALIGN: justify; mso-hyphenate: none; tab-stops: -24.95pt -12.5pt 0cm 12.5pt 24.95pt list 36.0pt left 37.45pt 49.9pt 62.4pt 74.9pt 87.35pt 99.85pt 112.3pt 124.8pt 137.3pt 149.75pt 162.25pt 174.7pt 187.2pt 199.7pt 212.15pt 224.65pt 237.1pt 249.6pt 262.1pt 274.55pt 287.05pt 299.5pt 312.0pt 324.5pt 336.95pt 349.45pt 361.9pt 374.4pt 386.9pt 399.35pt 411.85pt 424.3pt 436.8pt 449.3pt; mso-list: l0 level1 lfo1"><wegspan style="FONT-SIZE: 11pt; FONT-FAMILY: Symbol; LETTER-SPACING: -0.15pt; mso-bidi-font-size: 10.0pt; mso-ansi-language: EN-US">·<wegspan style="FONT: 7pt 'Times New Roman'">  </wegspan></wegspan><wegspan style="FONT-SIZE: 11pt; FONT-FAMILY: 'Times New Roman'; LETTER-SPACING: -0.15pt; mso-bidi-font-size: 10.0pt; mso-ansi-language: EN-US"><wegspan style="mso-spacerun: yes"> </wegspan>an analysis of the experimental results</wegspan><wegspan style="FONT-SIZE: 11pt; FONT-FAMILY: 'Times New Roman'; LETTER-SPACING: -0.15pt; mso-bidi-font-size: 10.0pt; mso-ansi-language: EN-US"> <o:p></o:p></wegspan> <p class=MsoNormal style="MARGIN: 0cm 0cm 0pt; TEXT-ALIGN: justify; mso-hyphenate: none; tab-stops: -24.95pt -12.5pt 0cm 12.5pt 24.95pt 37.45pt 49.9pt 62.4pt 74.9pt 87.35pt 99.85pt 112.3pt 124.8pt 137.3pt 149.75pt 162.25pt 174.7pt 187.2pt 199.7pt 212.15pt 224.65pt 237.1pt 249.6pt 262.1pt 274.55pt 287.05pt 299.5pt 312.0pt 324.5pt 336.95pt 349.45pt 361.9pt 374.4pt 386.9pt 399.35pt 411.85pt 424.3pt 436.8pt 449.3pt"><span style="FONT-SIZE: 11pt; FONT-FAMILY: 'Times New Roman'; LETTER-SPACING: -0.15pt; mso-bidi-font-size: 10.0pt; mso-ansi-language: EN-US">The results of the experimental study at EDF are analyzed. The conditions of the wave experiments are compared with conditions in the Dutch Exclusive Economic Zone and correspond well. Wave breaking statistics in the southern North Sea are discussed. Breaking<wegspan style="mso-spacerun: yes"> </wegspan>waves are negligible for water depths greater than 20 m.</wegspan><span style="FONT-SIZE: 11pt; FONT-FAMILY: 'Times New Roman'; LETTER-SPACING: -0.15pt; mso-bidi-font-size: 10.0pt; mso-ansi-language: EN-US"> <o:p></o:p></wegspan> <wegspan style="FONT-SIZE: 11pt; FONT-FAMILY: 'Times New Roman'; LETTER-SPACING: -0.15pt; mso-bidi-font-size: 10.0pt; mso-ansi-language: EN-US; mso-fareast-font-family: 'Times New Roman'; mso-fareast-language: EN-US; mso-bidi-language: AR-SA">EDF also performed a numerical study on the wave loads. The wave loads are calculated according to different wave theories using the Morison equation. EDF compared the measured wave loads with the calculated wave loads. For non-breaking waves, which are expected in Dutch offshore wind farms, the wave loads can be calculated using the stream function wave theory. For breaking waves and post breaking waves the wave loads are underestimated using linear wave theory and stream function theory.</wegspan>