A wind turbine tower is a tube, not a post.<\/p>\n
It carries the machine on top by keeping its own wall in tension and compression, and that wall is thinner in proportion than the skin of a drinks can.<\/p>\n
Thin walls do not snap.<\/p>\n
They buckle, which means a dent forms on the compressed side and the whole section folds through it in a fraction<\/strong> of a second.<\/p>\n That is what happened in Iowa.<\/p>\n Rows of steel towers<\/strong> went over in one afternoon, and the tornado that did it was still being measured<\/strong> as it passed.<\/p>\n A turbine is built for a direction.<\/p>\n The rotor turns to face the wind, the blades feather to spill it, and every load path in the tower assumes the push arrives from one side at a time.<\/p>\n A tornado removes that assumption.<\/p>\n The flow rotates, so the direction of the push swings through a full circle<\/strong> in seconds and the tower is loaded from angles it never saw in testing.<\/p>\n There is also lift.<\/p>\n Air inside a tornado moves upward as well as around, which adds a vertical component<\/strong> to a structure designed almost entirely for sideways force<\/strong>.<\/p>\n The machines were not experimental.<\/p>\n The damaged sites ran two megawatt units from a Danish manufacturer, a workhorse design installed by the thousand across the American Midwest.<\/p>\n The rotor is the giveaway.<\/p>\n Blades on that model sweep a circle about 361 feet<\/strong> across, which is an enormous amount of surface for a moving air mass to catch hold of.<\/p>\n The towers went down in a line.<\/p>\n Survey crews found the flattened machines strung along a corridor of seven to eight<\/strong> miles, which traces the damage path rather than a series of unrelated failures.<\/p>\n Design wind speed is the reference point.<\/p>\n Machines of this class are built to ride out gusts near 120 miles per hour, and the engineer who refined the damage scale puts the toppling threshold at 140.<\/p>\n Nothing about the sites was unusual.<\/p>\n Two of them sit in Adair County on ordinary farm ground, in a state that ranks second in the country for installed wind capacity<\/strong>.<\/p>\n The official rating came from damage.<\/p>\n Surveyors put the tornado at the fourth step of the intensity scale with winds around 185 miles<\/strong> per hour, which is the standard method and a conservative one.<\/p>\n A radar truck happened to be there.<\/p>\n A mobile Doppler unit scanning every seven seconds recorded between 308 and 318 miles<\/strong> per hour at roughly one hundred feet above the ground.<\/p>\n That reading is not the whole tornado.<\/p>\n The peak sat in a narrow band on one side of the circulation and lasted under a second at any given point, which is long enough to start a buckle.<\/p>\n The storm was on the ground for 48 minutes.<\/p>\n It ran 42 miles from beginning to end and grew to nearly a mile wide at its broadest, which is how it managed to cross more than one wind farm.<\/p>\n The turbines reported too, briefly.<\/p>\n Sensors on several machines logged winds above 100 miles per hour and then stopped transmitting<\/strong>, so that figure marks where the instruments quit rather than where the wind stopped.<\/p>\n Six is one company’s share.<\/p>\n The same tornado also took down four more turbines at a third site in the next county, owned by a completely different operator.<\/p>\n The real total is ten.<\/p>\n Ten machines across three wind farms<\/strong> in two counties, which is a larger event<\/strong> than the figure most coverage settled on.<\/p>\n The engineering account is harder to check.<\/p>\n A journal study of these failures exists and the paper<\/a> sits behind a paywall, so nobody quoting its conclusions in public has shown the working.<\/p>\n The field evidence points one way.<\/p>\n The forensic engineer who walked the site said the blades came apart first and the tower held longer, which is the same order seen when one blade<\/a> fails on a calm day<\/strong>.<\/p>\n The operator called it unprecedented.<\/p>\n That word is doing real work, because the company has run wind farms since 2004 and had lost exactly one turbine to a tornado before this.<\/p>\n The denominator matters.<\/p>\n Six losses came out of a fleet of more than 3,400 turbines<\/strong> across 34 counties, and the operator<\/a> keeps that number public.<\/p>\n The failures are becoming useful.<\/p>\n Damage surveyors are adding turbines to the intensity scale as a formal indicator, because a folded tower says more about the wind than a blade<\/a> that simply stops turning.<\/p>\n None of it changes the design.<\/p>\n A tower built to survive a direct tornado hit would cost far more than the losses it prevents, so the economics point at rebuilding instead.<\/p>\n Which leaves the honest reading.<\/p>\n Six steel towers<\/strong> folded because a rotating wind found a thin wall, and the machines that did not fold were a mile away<\/strong>.<\/p>\n","protected":false},"excerpt":{"rendered":" A wind turbine tower is a tube, not a post. It carries the machine on top by keeping its own wall in tension and compression, and that wall is thinner in proportion than the skin of a drinks can. Thin walls do not snap. They buckle, which means a dent forms on the compressed side … Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":2372,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[9],"tags":[],"class_list":["post-2274","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-wind-power"],"_links":{"self":[{"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/posts\/2274","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/comments?post=2274"}],"version-history":[{"count":3,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/posts\/2274\/revisions"}],"predecessor-version":[{"id":2374,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/posts\/2274\/revisions\/2374"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/media\/2372"}],"wp:attachment":[{"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/media?parent=2274"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/categories?post=2274"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ecoportal.net\/uk\/wp-json\/wp\/v2\/tags?post=2274"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}Why a tornado is not simply faster wind<\/h2>\n
What was standing on that ground<\/h2>\n
The numbers the storm left behind<\/h2>\n
The count that keeps getting left out<\/h2>\n
What six towers out of thousands means<\/h2>\n