{"id":7358,"date":"2019-12-16T12:08:00","date_gmt":"2019-12-16T11:08:00","guid":{"rendered":"https:\/\/www.vtei.cz\/?p=7358"},"modified":"2024-07-17T09:37:13","modified_gmt":"2024-07-17T08:37:13","slug":"mereni-malych-prutoku-pomoci-mernych-prelivu","status":"publish","type":"post","link":"https:\/\/www.vtei.cz\/en\/2019\/12\/mereni-malych-prutoku-pomoci-mernych-prelivu\/","title":{"rendered":"Measurement of low flow rates using measuring weir"},"content":{"rendered":"

This article is available in Czech only. For translation or more information on this topic, please contact author.<\/h4>\n

Souhrn<\/h2>\n

P\u0159\u00edsp\u011bvek prezentuje v\u00fdsledky hydraulick\u00e9ho fyzik\u00e1ln\u00edho v\u00fdzkumu m\u011brn\u00fdch p\u0159eliv\u016f pro m\u011b\u0159en\u00ed mal\u00fdch, resp. minim\u00e1ln\u00edch pr\u016ftok\u016f. V\u00fdzkum se zam\u011b\u0159il na ur\u010den\u00ed sou\u010dinitel\u016f p\u0159epadu pro n\u00edzk\u00e9 p\u0159epadov\u00e9 v\u00fd\u0161ky. V\u00a0p\u0159\u00edsp\u011bvku jsou uvedeny v\u00fdsledky m\u011b\u0159en\u00ed pro troj\u00faheln\u00edkov\u00fd, obd\u00e9ln\u00edkov\u00fd a\u00a0kruhov\u00fd ostrohrann\u00fd p\u0159eliv. Nam\u011b\u0159en\u00e1 data jsou porovn\u00e1v\u00e1na se vztahy podle jednotliv\u00fdch autor\u016f a\u00a0je ur\u010dena vhodnost jejich pou\u017eit\u00ed pro oblast n\u00edzk\u00fdch p\u0159epadov\u00fdch v\u00fd\u0161ek. V\u00a0r\u00e1mci m\u011b\u0159en\u00ed byly tak\u00e9 provedeny pokusy s\u00a0polokruhovou p\u0159elivnou hranou. P\u0159i laboratorn\u00edm testov\u00e1n\u00ed byly zkoum\u00e1ny rozd\u00edln\u00e9 um\u00edst\u011bn\u00ed p\u0159elivu v\u016f\u010di proudu a\u00a0jejich vliv na v\u00fdsledky m\u011b\u0159en\u00ed.<\/p>\n

\u00davod<\/h2>\n

Pro kontinu\u00e1ln\u00ed m\u011b\u0159en\u00ed minim\u00e1ln\u00edch pr\u016ftok\u016f na mal\u00fdch vodn\u00edch toc\u00edch lze pou\u017e\u00edt m\u011brn\u00e9 p\u0159elivy, kter\u00e9 dok\u00e1\u017eou s\u00a0velkou p\u0159esnost\u00ed m\u011b\u0159it \u0161irok\u00fd rozsah pr\u016ftok\u016f (obr. 1<\/em>). Vlastn\u00ed m\u011b\u0159en\u00ed je realizov\u00e1no nep\u0159\u00edmo pomoc\u00ed m\u011b\u0159en\u00ed polohy hladiny nad m\u011brn\u00fdm p\u0159elivem (pomoc\u00ed tlakov\u00e9 sondy \u010di ultrazvukov\u00e9ho hladinom\u011bru) a\u00a0znalosti vztahu mezi v\u00fd\u0161kou p\u0159epadov\u00e9ho paprsku a\u00a0odpov\u00eddaj\u00edc\u00ed hodnot\u011b pr\u016ftoku. Vzhledem k\u00a0\u010dast\u00fdm such\u00fdm period\u00e1m a\u00a0ke st\u00e1le v\u011bt\u0161\u00edmu tlaku na monitoring minim\u00e1ln\u00edch z\u016fstatkov\u00fdch pr\u016ftok\u016f je p\u0159esnost m\u011b\u0159en\u00ed minim\u00e1ln\u00edch pr\u016ftok\u016f na mal\u00fdch vodn\u00edch toc\u00edch aktu\u00e1ln\u00edm t\u00e9matem. Minim\u00e1ln\u00ed \u010di mal\u00fd pr\u016ftok lze pro n\u00e1mi zkoumanou oblast definovat v\u00a0rozsahu jednotek litr\u016f za vte\u0159inu.<\/p>\n\"\"<\/a>\n

Obr. 1. M\u011brn\u00fd p\u0159eliv osazen\u00fd v\u00a0ter\u00e9nu
\nFig. 1. Measuring weir situated in the stream<\/h6>\n

P\u0159i m\u011b\u0159en\u00ed mal\u00fdch, resp. minim\u00e1ln\u00edch pr\u016ftok\u016f ov\u0161em nast\u00e1v\u00e1 cel\u00e1 \u0159ada obt\u00ed\u017e\u00ed a\u00a0probl\u00e9m\u016f. N\u00edzk\u00e9 pr\u016ftoky p\u0159epadaj\u00ed p\u0159es p\u0159eliv s\u00a0malou p\u0159epadovou v\u00fd\u0161kou, p\u0159i kter\u00e9 ji\u017e nen\u00ed hodnota sou\u010dinitele p\u0159epadu v\u00a0rozsahu platnosti pou\u017e\u00edvan\u00fdch vzorc\u016f. D\u00e1le doch\u00e1z\u00ed k\u00a0probl\u00e9m\u016fm se zan\u00e1\u0161en\u00edm p\u0159eliv\u016f pl\u00e1v\u00edm, kter\u00e9 m\u016f\u017ee do zna\u010dn\u00e9 m\u00edry zkreslit m\u011b\u0159en\u00e9 pr\u016ftoky.<\/p>\n

V\u00a0r\u00e1mci laboratorn\u00edho testov\u00e1n\u00ed byly ov\u011b\u0159ov\u00e1ny hodnoty p\u0159epadov\u00e9ho sou\u010dinitele pro r\u016fzn\u00e9 ostrohrann\u00e9 m\u011brn\u00e9 p\u0159elivy a\u00a0pro n\u00edzk\u00e9 p\u0159epadov\u00e9 v\u00fd\u0161ky. Nam\u011b\u0159en\u00e1 data byla porovn\u00e1na s\u00a0hodnotami podle rozli\u0161n\u00fdch autor\u016f a\u00a0byla ov\u011b\u0159ena vhodnost jejich pou\u017eit\u00ed pro n\u00edzk\u00e9 p\u0159epadov\u00e9 v\u00fd\u0161ky. D\u00e1le byla testov\u00e1na kruhov\u00e1 p\u0159elivn\u00e1 hrana a\u00a0jej\u00ed vliv na kapacitu a\u00a0chov\u00e1n\u00ed p\u0159epadov\u00e9ho paprsku. V\u00a0r\u00e1mci laboratorn\u00edho testov\u00e1n\u00ed byly zkoum\u00e1ny rozd\u00edln\u00e9 um\u00edst\u011bn\u00ed p\u0159elivu v\u016f\u010di proudu. M\u011brn\u00e9 p\u0159elivy byly vyrobeny metodou 3D tisku, kter\u00e1 zaji\u0161\u0165ovala variabilitu a\u00a0p\u0159esnost p\u0159i v\u00fdrob\u011b r\u016fzn\u00fdch tvar\u016f p\u0159eliv\u016f.<\/p>\n\"\"<\/a>\n

Metodika experiment\u016f<\/h2>\n

Ve\u0161ker\u00e9 laboratorn\u00ed experimenty prob\u00edhaly v mal\u00e9 vodohospod\u00e1\u0159sk\u00e9 hale V\u00fdzkumn\u00e9ho \u00fastavu vodohospod\u00e1\u0159sk\u00e9ho T. G. Masaryka, v. v. i., v pevn\u00e9m hydraulick\u00e9m \u017elabu \u0161\u00ed\u0159ky 500 mm. Dod\u00e1vka vody byla zaji\u0161t\u011bna pomoc\u00ed \u010derpac\u00ed stanice, kter\u00e1 \u010derpala vodu z doln\u00ed n\u00e1dr\u017ee do vysoko polo\u017een\u00e9 n\u00e1dr\u017ee, je\u017e zaji\u0161\u0165ovala st\u00e1lou tla\u010dnou v\u00fd\u0161ku pomoc\u00ed p\u0159elivu s dlouhou p\u0159elivnou hranou. Z t\u00e9to n\u00e1dr\u017ee byla potrub\u00edm p\u0159ivedena voda do \u017elabu. Pr\u016ftok byl nastaven na z\u00e1klad\u011b velikosti otev\u0159en\u00ed \u0161oup\u011bte na p\u0159\u00edvodn\u00edm potrub\u00ed. P\u0159ed vlastn\u00edm vtokem do \u017elabu byl instalov\u00e1n Thomson\u016fv m\u011brn\u00fd p\u0159eliv. Voda na konci \u017elabu byla odvedena odpadn\u00edm potrub\u00edm do doln\u00ed n\u00e1dr\u017ee.<\/p>\n

Testovan\u00fd m\u011brn\u00fd p\u0159eliv byl p\u0159i ka\u017ed\u00e9m m\u011b\u0159en\u00ed um\u00edst\u011bn ve st\u0159edu \u017elabu ve v\u00fd\u0161ce 40 cm nade dnem \u017elabu (obr. 2<\/em>). Testovan\u00fd p\u0159eliv byl um\u00edst\u011bn cca 3,5 metru od n\u00e1toku do \u017elabu. Na n\u00e1toku do \u017elabu byl um\u00edst\u011bn tlumi\u010d p\u0159it\u00e9kaj\u00edc\u00ed vody, kter\u00fd zaji\u0161\u0165oval jej\u00ed uklidn\u011bn\u00ed a\u00a0rovnom\u011brn\u00fd n\u00e1tok do \u017elabu. Tlumi\u010d byl tvo\u0159en dv\u011bma ocelov\u00fdmi ro\u0161ty, mezi nimi\u017e bylo um\u00edst\u011bno kamenivo. Testovan\u00e9 p\u0159elivy m\u011bly \u0161\u00ed\u0159ku 10\u201330 cm a\u00a0v\u00fd\u0161ku 5\u201315 cm. Rozsah m\u011b\u0159en\u00fdch pr\u016ftok\u016f byl od 0,2 l\/s\u00a0do 20\u00a0l\/s.<\/p>\n\"\"<\/a>\n

Obr. 2. Um\u00edst\u011bn\u00ed p\u0159elivu ve \u017elabu
\nFig. 2. Measuring weir situated in the laboratory flume<\/h6>\n

Typick\u00fd pr\u016fb\u011bh pokusu lze charakterizovat n\u00e1sledovn\u011b, ve \u017elabu je nainstalovan\u00fd p\u0159\u00edslu\u0161n\u00fd m\u011brn\u00fd p\u0159eliv (nen\u00ed ovlivn\u011bn doln\u00ed vodou), na Thomsonov\u011b p\u0159elivu je nastaven po\u017eadovan\u00fd pr\u016ftok a\u00a0poloha hladiny p\u0159ed m\u011brn\u00fdm p\u0159elivem se nem\u011bn\u00ed (stav je ust\u00e1len\u00fd). V\u00a0t\u00e9to chv\u00edli je mo\u017en\u00e9 ode\u010d\u00edst polohu hladiny p\u0159ed m\u011brn\u00fdm p\u0159elivem pomoc\u00ed hrotov\u00fdch m\u011b\u0159\u00edtek. Prvn\u00ed hrotov\u00e9 m\u011b\u0159\u00edtko je um\u00edst\u011bno ve sklen\u011bn\u00e9m v\u00e1lci spojen\u00e9m dnov\u00fdm odb\u011brem se \u017elabem, dnov\u00fd odb\u011br se nach\u00e1z\u00ed 45 cm p\u0159ed m\u011brn\u00fdm p\u0159elivem, tj. vzd\u00e1lenost 3\u00b7hp,max<\/sub> protiproudn\u011b p\u0159ed m\u011brn\u00fdm p\u0159elivem. Druh\u00e9 hrotov\u00e9 m\u011b\u0159\u00edtko m\u011b\u0159\u00ed v\u00fd\u0161ku hladiny ve stejn\u00e9m m\u00edst\u011b a\u00a0je um\u00edst\u011bn\u00e9 na posuvn\u00e9m nosn\u00edku na vrcholu \u017elabu.<\/p>\n

Pr\u016ftoky do cca 7 l\/s\u00a0byly m\u011b\u0159eny pomoc\u00ed kalibrovan\u00e9 m\u011brn\u00e9 n\u00e1doby. M\u011brn\u00e9 n\u00e1doba m\u011bla tvar kv\u00e1dru o\u00a0rozm\u011brech 0,4 m\u00a0\u00d7 0,5 m\u00a0\u00d7 0,3 m, hladina v\u00a0n\u00e1dob\u011b byla m\u011b\u0159ena pomoc\u00ed osazen\u00e9ho hrotov\u00e9ho m\u011b\u0159\u00edtka. M\u011brn\u00e1 n\u00e1doba byla opat\u0159ena koly, tak\u017ee s\u00a0n\u00ed bylo mo\u017en\u00e9 jednodu\u0161e a\u00a0rychle manipulovat. M\u011b\u0159en\u00ed pr\u016ftoku prob\u00edhalo n\u00e1sledovn\u011b\u00a0\u2013 pod p\u0159epadov\u00fd paprsek pod m\u011brn\u00fdm p\u0159elivem byla nasunuta m\u011brn\u00e1 n\u00e1doba, v\u00a0tento okam\u017eik bylo zapo\u010dato m\u011b\u0159en\u00ed \u010dasu pomoc\u00ed stopek, jakmile do\u0161lo k\u00a0napln\u011bn\u00ed m\u011brn\u00e9 n\u00e1doby, do\u0161lo k\u00a0odsunut\u00ed m\u011brn\u00e9 n\u00e1doby a\u00a0zastaven\u00ed stopek, tento postup byl obvykle dvakr\u00e1t opakov\u00e1n pro ka\u017ed\u00fd pokus. Typick\u00e1 doba odb\u011bru byla 120\u20137 s. Nejistotu m\u011b\u0159en\u00ed pr\u016ftoku lze odhadnout pomoc\u00ed um\u011ble zaveden\u00e9 chyby m\u011b\u0159en\u00ed \u010dasu o\u00a0velikosti 0,2 s. V\u00a0mezn\u00edm p\u0159\u00edpad\u011b, kdy je pr\u016ftok roven cca 7 l\/s, je doba pln\u011bn\u00ed m\u011brn\u00e9 n\u00e1doby 7,1 s, pokud zavedeme um\u011blou chybu \u00b1 0,2 s,\u00a0zm\u011bn\u00ed se hodnota m\u011b\u0159en\u00e9ho pr\u016ftoku o\u00a0\u00b1 3 %. Pro n\u00edzk\u00e9 pr\u016ftoky s\u00a0dlouhou dobou odb\u011bru je velikost chyby v\u00a0\u0159\u00e1dech desetin procenta. Pr\u016ftoky v\u011bt\u0161\u00ed ne\u017e 7 l\/s\u00a0byly m\u011b\u0159eny pomoc\u00ed kalibrovan\u00e9ho m\u011brn\u00e9ho Thomsonova p\u0159elivu um\u00edst\u011bn\u00e9ho p\u0159ed vtokem do \u017elabu. Lze p\u0159edpokl\u00e1dat obdobnou p\u0159esnost m\u011b\u0159en\u00ed pr\u016ftoku jako pomoc\u00ed m\u011brn\u00e9 n\u00e1doby.<\/p>\n

Ostrohrann\u00e9 m\u011brn\u00e9 p\u0159elivy<\/h2>\n

V\u00a0r\u00e1mci laboratorn\u00edho m\u011b\u0159en\u00ed byly testov\u00e1ny t\u0159i ostrohrann\u00e9 p\u0159elivy pro m\u011b\u0159en\u00ed mal\u00fdch pr\u016ftok\u016f (troj\u00faheln\u00edkov\u00fd, obd\u00e9ln\u00edkov\u00fd a\u00a0kruhov\u00fd p\u0159eliv). P\u0159elivn\u00e1 hrana testovan\u00fdch p\u0159eliv\u016f byla konstruov\u00e1na n\u00e1sledovn\u011b\u00a0\u2013 \u0161\u00ed\u0159ka p\u0159elivn\u00e9 hrany byla 1 mm a\u00a0pot\u00e9 byla zkosena pod \u00fahlem 45\u00b0 pro zaji\u0161t\u011bn\u00ed voln\u00e9ho p\u0159epadov\u00e9ho paprsku. Proveden\u00ed p\u0159elivn\u00e9 hrany je ve shod\u011b s\u00a0normou \u010cSN ISO 1438 [1]. Testovan\u00e9 geometrie p\u0159eliv\u016f a\u00a0nam\u011b\u0159en\u00e9 konsum\u010dn\u00ed k\u0159ivky jsou zobrazeny na obr. 3<\/em> a\u00a04<\/em>. Nam\u011b\u0159en\u00e9 hodnoty byly konfrontov\u00e1ny s\u00a0hodnoty predikovan\u00fdmi jednotliv\u00fdmi vzorci a\u00a0d\u00e1le bylo zkoum\u00e1no chov\u00e1n\u00ed jednotliv\u00fdch p\u0159eliv\u016f p\u0159i minim\u00e1ln\u00edch p\u0159epadov\u00fdch v\u00fd\u0161k\u00e1ch.<\/p>\n\"\"<\/a>\n

Obr. 3. Rozm\u011bry testovan\u00fdch m\u011brn\u00fdch p\u0159eliv\u016f
\nFig. 3. Tested weir dimensions<\/h6>\n

Pro ka\u017ed\u00fd m\u011brn\u00fd p\u0159eliv byla ur\u010dena hodnota p\u0159epadov\u00e9 v\u00fd\u0161ky, pod kterou ji\u017e doch\u00e1z\u00ed k\u00a0\u201ep\u0159ilnut\u00ed\u201c p\u0159epadov\u00e9ho paprsku na vlastn\u00ed konstrukci m\u011brn\u00e9ho p\u0159elivu. Tato v\u00fd\u0161ka p\u0159edstavuje limitn\u00ed minim\u00e1ln\u00ed v\u00fd\u0161ku pro vlastn\u00ed m\u011b\u0159en\u00ed pr\u016ftoku pomoc\u00ed m\u011brn\u00e9ho p\u0159elivu. U\u00a0obd\u00e9ln\u00edkov\u00e9ho p\u0159elivu doch\u00e1z\u00ed k\u00a0p\u0159ilnut\u00ed p\u0159i v\u00fd\u0161ce p\u0159epadov\u00e9ho paprsku cca 10 mm, u\u00a0troj\u00faheln\u00edkov\u00e9ho p\u0159elivu p\u0159i v\u00fd\u0161ce cca\u00a015\u00a0mm a\u00a0u\u00a0kruhov\u00e9ho p\u0159elivu p\u0159i v\u00fd\u0161ce cca 20 mm.<\/p>\n\"\"<\/a>\n

Obr. 4. Konsum\u010dn\u00ed k\u0159ivky ostrohrann\u00fdch p\u0159eliv\u016f z obr. <\/em>3 prolo\u017een\u00e9 vztahy vybran\u00fdch autor\u016f
\nFig. 4. Sharp-crest weir discharge curves from fig. 3<\/em> with formulas from selected authors<\/h6>\n

Troj\u00faheln\u00edkov\u00fd p\u0159eliv (Thomson\u016fv)<\/h2>\n

Troj\u00faheln\u00edkov\u00fd p\u0159eliv s vrcholov\u00fdm \u00fahlem o velikosti 90\u00b0, t\u00e9\u017e naz\u00fdv\u00e1n \u201eThomson\u016fv\u201c p\u0159eliv, je vhodn\u00fd na lokality s velk\u00fdm rozsahem m\u011b\u0159en\u00fdch pr\u016ftok\u016f. Troj\u00faheln\u00edkov\u00fd p\u0159eliv dok\u00e1\u017ee p\u0159esn\u011b m\u011b\u0159it mal\u00e9 i velk\u00e9 pr\u016ftoky, jeho nev\u00fdhodou je snadn\u00e9 zanesen\u00ed pr\u016fto\u010dn\u00e9ho profilu p\u0159i minim\u00e1ln\u00edch p\u0159epadov\u00fdch v\u00fd\u0161k\u00e1ch. Pr\u016ftok troj\u00faheln\u00edkov\u00fdm rovnoramenn\u00fdm p\u0159elivem lze obecn\u011b vypo\u010d\u00edtat n\u00e1sledovn\u011b [2]:<\/p>\n\"\"<\/a>\n

Pro troj\u00faheln\u00edkov\u00fd pravo\u00fahl\u00fd p\u0159eliv b\u00fdv\u00e1 nej\u010dast\u011bji ud\u00e1v\u00e1na Thomsonova rovnice [3]:<\/p>\n\"\"<\/a>\n

Havl\u00edk [4] pro tento vztah ud\u00e1v\u00e1 meze platnosti 0,05 m < h < 0,18 m a\u00a0z\u00e1rove\u0148 B\/h \u2265 8 a\u00a0s\/h \u2265 3.<\/p>\n

D\u00e1le je tak\u00e9 uv\u00e1d\u011bna rovnice podle Kinga [5]:<\/p>\n\"\"<\/a>\n

Ji\u010d\u00ednsk\u00fd a\u00a0\u0160eflov\u00e1 [2] navrhli na z\u00e1klad\u011b porovn\u00e1n\u00ed \u0159ady vztah\u016f vztah pro v\u00fdpo\u010det:<\/p>\n\"\"<\/a>\n

Porovn\u00e1n\u00ed v\u00fdsledk\u016f m\u011b\u0159en\u00ed na troj\u00faheln\u00edkov\u00e9m p\u0159elivu s\u00a0vrcholov\u00fdm \u00fahlem 90\u00b0 s\u00a0hodnotami stanoven\u00fdmi podle v\u00fd\u0161e uveden\u00fdch vzorc\u016f je zobrazeno na obr. 5<\/em>. Porovn\u00e1n\u00ed je provedeno pomoc\u00ed R<\/em>rel<\/sub>\u00a0\u2013 relativn\u00edho rozd\u00edlu m\u011b\u0159en\u00e9ho pr\u016ftoku a\u00a0hodnotou pr\u016ftoku stanoven\u00e9ho podle v\u00fd\u0161e uveden\u00fdch rovnic. Z\u00a0porovn\u00e1n\u00ed je patrn\u00e9, \u017ee nejv\u011bt\u0161\u00edch relativn\u00edch rozd\u00edl\u016f je dosahov\u00e1no p\u0159i mal\u00fdch pr\u016ftoc\u00edch, resp. mal\u00fdch p\u0159epadov\u00fdch v\u00fd\u0161k\u00e1ch. P\u0159i vy\u0161\u0161\u00edch pr\u016ftoc\u00edch jsou ji\u017e chyby zanedbateln\u00e9, nebo\u0165 se ji\u017e v\u00fd\u0161ka p\u0159epadov\u00e9ho paprsku dost\u00e1v\u00e1 do platn\u00fdch hodnot pou\u017eitelnosti vzorc\u016f pro v\u00fdpo\u010det p\u0159epadov\u00e9ho sou\u010dinitele.<\/p>\n\"\"<\/a>\n

Obr. 5. Porovn\u00e1n\u00ed relativn\u00edch rozd\u00edl\u016f pr\u016ftok\u016f pro troj\u00faheln\u00edkov\u00fd ostrohrann\u00fd m\u011brn\u00fd p\u0159eliv
\nFig. 5. Relative flow errors comparison of triangle sharp-crested weir<\/h6>\n

 <\/p>\n\"\"<\/a>\n

Porovn\u00e1n\u00ed nam\u011b\u0159en\u00fdch sou\u010dinitel\u016f p\u0159epadu a\u00a0hodnot sou\u010dinitel\u016f p\u0159epadu vypo\u010dten\u00fdch z\u00a0v\u00fd\u0161e uveden\u00fdch vztah\u016f je zobrazeno na obr. 6<\/em>. Pro troj\u00faheln\u00edkov\u00fd p\u0159eliv a\u00a0mal\u00e9 p\u0159epadov\u00e9 v\u00fd\u0161ky se jev\u00ed jako optim\u00e1ln\u00ed pou\u017eit\u00ed rovnice podle Ji\u010d\u00ednsk\u00e9ho a\u00a0\u0160eflov\u00e9 (4) nebo podle Thomsona (2). Naopak podle m\u011b\u0159en\u00ed nelze doporu\u010dit vztah podle Kinga (3).<\/p>\n\"\"<\/a>\n

Obr. 6. Porovn\u00e1n\u00ed p\u0159epadov\u00fdch sou\u010dinitel\u016f pro troj\u00faheln\u00edkov\u00fd p\u0159eliv
\nFig. 6. Comparison of the overfall weir coefficients (triangle weir)<\/h6>\n

Obd\u00e9ln\u00edkov\u00fd p\u0159eliv<\/h2>\n

V\u00a0r\u00e1mci pokus\u016f byly pou\u017eity obd\u00e9ln\u00edkov\u00e9 p\u0159elivy s\u00a0kontrakc\u00ed, \u0161\u00ed\u0159ky p\u0159eliv\u016f byly 15\u201330 cm a\u00a0v\u00fd\u0161ky 8\u201312,5 cm. Obd\u00e9ln\u00edkov\u00e9 p\u0159elivy lze s\u00a0v\u00fdhodou pou\u017e\u00edt na vodn\u00ed toky, jeliko\u017e maj\u00ed dostate\u010dnou kapacitu a\u00a0nezp\u016fsob\u00ed p\u0159\u00edli\u0161 velk\u00e9 vzdut\u00ed hladiny p\u0159ed m\u011brn\u00fdm p\u0159elivem. Pro v\u00fdpo\u010det pr\u016ftoku lez pou\u017e\u00edt rovnici p\u0159epadu:<\/p>\n\"\"<\/a>\n

Porovn\u00e1n\u00ed v\u00fdsledk\u016f m\u011b\u0159en\u00ed na obd\u00e9ln\u00edkov\u00fdch p\u0159elivech s\u00a0hodnotami stanoven\u00fdmi podle v\u00fd\u0161e uveden\u00fdch vzorc\u016f je zobrazeno na obr. 7 <\/em>a\u00a08<\/em>. Porovn\u00e1n\u00ed je provedeno pomoc\u00ed R<\/em>rel<\/sub> (5). Z\u00a0grafu je patrn\u00e1 pom\u011brn\u011b dobr\u00e1 shoda se vztahem podle Rehbocka (9), vztah podle Zschiedricha (8) naopak nelze doporu\u010dit. \u010casto uv\u00e1d\u011bn\u00fd H\u00e9glyho vztah (7) dosahuje relativn\u00edch rozd\u00edl\u016f R<\/em>rel<\/sub> des\u00edtek a\u017e stovek procent a\u00a0nelze ho pro n\u00edzk\u00e9 p\u0159epadov\u00e9 v\u00fd\u0161ky doporu\u010dit. Porovn\u00e1n\u00ed nam\u011b\u0159en\u00fdch sou\u010dinitel\u016f p\u0159epadu a\u00a0hodnot sou\u010dinitel\u016f p\u0159epadu vypo\u010dten\u00fdch z\u00a0v\u00fd\u0161e uveden\u00fdch vztah\u016f je zobrazeno na obr. 8<\/em>. Z\u00a0porovn\u00e1n\u00ed jsou patrn\u00e9 v\u00fd\u0161e uveden\u00e9 z\u00e1v\u011bry o\u00a0vhodnosti pou\u017eit\u00ed vztah\u016f podle jednotliv\u00fdch autor\u016f.<\/p>\n\"\"<\/a>\n

Obr. 7. Porovn\u00e1n\u00ed relativn\u00edch rozd\u00edl\u016f pr\u016ftok\u016f pro obd\u00e9ln\u00edkov\u00fd ostrohrann\u00fd m\u011brn\u00fd p\u0159eliv
\nFig. 7. Relative flow errors comparison of rectangular sharp-crested weir<\/h6>\n\"\"<\/a>\n
Obr. 8. Porovn\u00e1n\u00ed p\u0159epadov\u00fdch sou\u010dinitel\u016f pro obd\u00e9ln\u00edkov\u00fd p\u0159eliv
\nFig. 8. Comparison of the overfall weir coefficients (rectangular weir)<\/h6>\n

Hodnota sou\u010dinitele z\u00fa\u017een\u00ed \u03be<\/em> byla uva\u017eov\u00e1na 1. Sou\u010dinitel p\u0159epadu m<\/em> lze ur\u010dit podle H\u00e9glyho vztahu [6]:<\/p>\n\"\"<\/a>\n

Sou\u010dinitel p\u0159epadu lze d\u00e1le ur\u010dit nap\u0159\u00edklad pomoc\u00ed vztahu podle Zschiedricha [2]:<\/p>\n\"\"<\/a>\n

P\u0159\u00edpadn\u011b lze ur\u010dit p\u0159epadov\u00fd sou\u010dinitel \u03bc<\/em> podle Rehbocka [7]:<\/p>\n\"\"<\/a>\n

Kruhov\u00fd p\u0159eliv<\/h2>\n

V r\u00e1mci pokus\u016f byly pou\u017eity kruhov\u00e9 p\u0159elivy o polom\u011bru 10 a\u017e 30 cm. Kruhov\u00e9 p\u0159elivy p\u0159edstavuj\u00ed kompromis mezi troj\u00faheln\u00edkov\u00fdm a obd\u00e9ln\u00edkov\u00fdm p\u0159elivem, d\u00e1vaj\u00ed pom\u011brn\u011b p\u0159esn\u00e9 hodnoty pr\u016ftoku i p\u0159i mal\u00fdch p\u0159epadov\u00fdch v\u00fd\u0161k\u00e1ch a z\u00e1rove\u0148 maj\u00ed pom\u011brn\u011b velkou maxim\u00e1ln\u00ed kapacitu v porovn\u00e1n\u00ed se stejn\u011b vysok\u00fdm troj\u00faheln\u00edkov\u00fdm p\u0159elivem. Pro v\u00fdpo\u010det pr\u016ftoku kruhov\u00fdm p\u0159elivem lze pou\u017e\u00edt vztah odvozen\u00fd Stausem [8]:<\/p>\n\"\"<\/a>\n\"\"<\/a>\n

 <\/p>\n\n\n\n
kde<\/td>\nq<\/em><\/td>\nje<\/td>\npr\u016ftok p\u0159i pr\u016fm\u011bru kruhu 1 dm v\u00a0z\u00e1vislosti na pom\u011bru hp<\/sub>\/D.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Porovn\u00e1n\u00ed v\u00fdsledk\u016f m\u011b\u0159en\u00ed na kruhov\u00fdch p\u0159elivech s\u00a0hodnotami stanoven\u00fdmi podle v\u00fd\u0161e uveden\u00e9ho vzorce je zobrazeno na obr. 9<\/em> a\u00a011<\/em>. Na obr. 9<\/em> je zobrazeno porovn\u00e1n\u00ed relativn\u00edch rozd\u00edl\u016f pr\u016ftok\u016f R<\/em>rel<\/sub> (5) se vztahem podle Stause. Z\u00a0grafu je patrn\u00e9, \u017ee pro n\u00edzk\u00e9 hodnoty p\u0159epadov\u00fdch v\u00fd\u0161ek je relativn\u00ed rozd\u00edl nejv\u011bt\u0161\u00ed\u00a0\u2013 cca 4 % a\u00a0pot\u00e9 se plynule sni\u017euje na cca 2 %. Porovn\u00e1n\u00ed nam\u011b\u0159en\u00fdch p\u0159epadov\u00fdch sou\u010dinitel\u016f je zobrazeno na obr. 11<\/em>, nam\u011b\u0159en\u00e9 sou\u010dinitele se li\u0161\u00ed od hodnot ur\u010den\u00fdch vztahem (11). Nam\u011b\u0159en\u00e1 data byla prolo\u017eena n\u00e1sleduj\u00edc\u00ed funkc\u00ed (byla vy\u0159azena data, kdy byl pr\u016ftok v\u011bt\u0161\u00ed ne\u017e 7 l\/s, tj. stavy, kdy pr\u016ftok nebyl m\u011b\u0159en kalibrovanou n\u00e1dobou):<\/p>\n\"\"<\/a>\n

Vztah je ov\u011b\u0159en pro p\u0159elivy o\u00a0pr\u016fm\u011bru 10 a\u017e 30 cm s\u00a0ostrou hranou definovanou na za\u010d\u00e1tku kapitoly a\u00a0minim\u00e1ln\u00ed p\u0159epadovou v\u00fd\u0161kou 2 cm.<\/p>\n

Na obr. 10<\/em> je zobrazen vliv um\u011ble zanesen\u00e9 chyby p\u0159i m\u011b\u0159en\u00ed pr\u016ftoku kalibrovanou m\u011brnou n\u00e1dobou definovanou v\u00fd\u0161e v\u00a0kapitole metodika experiment\u016f. Pro p\u0159eliv o\u00a0pr\u016fm\u011bru 20 cm byly zm\u011bn\u011bny doby pln\u011bn\u00ed m\u011brn\u00e9 n\u00e1doby o\u00a0\u00b1 0,2\u00a0s a\u00a0n\u00e1sledn\u011b byly ur\u010deny tomu odpov\u00eddaj\u00edc\u00ed pr\u016ftoky a\u00a0p\u0159epadov\u00e9 sou\u010dinitele.<\/p>\n\"\"<\/a>\n

Obr. 9. Porovn\u00e1n\u00ed relativn\u00edch rozd\u00edl\u016f pr\u016ftok\u016f pro kruhov\u00fd ostrohrann\u00fd m\u011brn\u00fd p\u0159eliv
\nFig. 9. Relative flow errors comparison of circular sharp-crested weir<\/h6>\n\"\"<\/a>\n
Obr. 10. Z\u00e1vislost hodnoty p\u0159epadov\u00e9ho sou\u010dinitele na p\u0159esnosti m\u011b\u0159en\u00ed pr\u016ftoku
\nFig. 10. Dependency of the overfall weir coefficients on the flow measuring<\/h6>\n\"\"<\/a>\n
Obr. 11. Porovn\u00e1n\u00ed p\u0159epadov\u00fdch sou\u010dinitel\u016f pro kruhov\u00fd p\u0159eliv
\nFig. 11. Comparison of the overfall weir coefficients (circular weir)<\/h6>\n

Chyby p\u0159i m\u011b\u0159en\u00ed pr\u016ftok\u016f mohou z\u00e1sadn\u011b ovliv\u0148ovat v\u00fdsledky m\u011b\u0159en\u00ed a\u017e p\u0159i pr\u016ftoku vy\u0161\u0161\u00edm ne\u017e cca 7 l\/s, velikost t\u00e9to chyby byla redukov\u00e1na opakov\u00e1n\u00edm m\u011b\u0159en\u00ed pr\u016ftoku kalibrovanou n\u00e1dobou.<\/p>\n

M\u011brn\u00e9 p\u0159elivy s\u00a0kruhovou p\u0159elivnou hranou<\/h2>\n

Velk\u00fdm probl\u00e9mem, kter\u00fd nast\u00e1v\u00e1 zejm\u00e9na v\u00a0podzimn\u00edch m\u011bs\u00edc\u00edch, je ulp\u00edv\u00e1n\u00ed list\u016f na p\u0159elivn\u00e9 hran\u011b m\u011brn\u00fdch p\u0159eliv\u016f. Polokruhov\u00e1 p\u0159elivn\u00e1 hrana je l\u00e9pe, v\u016f\u010di ostr\u00e9 hran\u011b, hydraulicky tvarovan\u00e1 a\u00a0list\u00ed by na n\u00ed nemuselo ulp\u00edvat v\u00a0takov\u00e9 m\u00ed\u0159e a\u00a0zkreslovat nam\u011b\u0159en\u00e1 data. V\u00a0r\u00e1mci v\u00fdzkumu byly proto testov\u00e1ny m\u011brn\u00e9 p\u0159elivy s\u00a0kruhovou p\u0159elivnou hranou (obd\u00e9ln\u00edkov\u00fd (b = 15 cm a\u00a0h\u00a0=\u00a08 cm) a\u00a0kruhov\u00fd (D = 20 cm)). P\u0159elivn\u00e1 hrana byla tvo\u0159ena p\u016flkruhem o\u00a0polom\u011bru 2,5 mm, tj. tlou\u0161\u0165ka konstrukce p\u0159elivu byla celkem 5 mm, na vrcholu t\u00e9to konstrukce byla um\u00edst\u011bna polokruhov\u00e1 p\u0159elivn\u00e1 hrana o\u00a0polom\u011bru 2,5 mm.<\/p>\n\"\"<\/a>\n

Obr. 12. Porovn\u00e1n\u00ed konsum\u010dn\u00edch k\u0159ivek ostrohrann\u00e9 a\u00a0kruhov\u00e9 p\u0159elivn\u00e9 hrany obd\u00e9ln\u00edkov\u00e9ho a\u00a0kruhov\u00e9ho p\u0159elivu
\nFig. 12. Comparison of the sharp and semi-circle crest weir discharge curves (circle and rectangular weir)<\/h6>\n

Porovn\u00e1n\u00ed nam\u011b\u0159en\u00fdch konsum\u010dn\u00edch k\u0159ivek je zobrazeno na obr. 12<\/em>. Z\u00a0grafu je patrn\u00e1 v\u011bt\u0161\u00ed kapacita m\u011brn\u00e9ho p\u0159elivu s\u00a0polokruhovou hranou oproti ostr\u00e9 p\u0159elivn\u00e9 hran\u011b. Z\u00e1rove\u0148 je zde uveden vztah podle Gonga a\u00a0kol. [9], kte\u0159\u00ed se zab\u00fdvali m\u011brn\u00fdmi obd\u00e9ln\u00edkov\u00fdmi p\u0159elivy s\u00a0polokruhovou p\u0159elivnou hranou. Gong a\u00a0kol. prov\u00e1d\u011bli m\u011b\u0159en\u00ed na v\u011bt\u0161\u00edch obd\u00e9ln\u00edkov\u00fdch p\u0159elivech ne\u017e jsou na\u0161e nam\u011b\u0159en\u00e1 data, proto si nejsp\u00ed\u0161e neodpov\u00eddaj\u00ed nam\u011b\u0159en\u00e1 data s\u00a0jejich odvozen\u00fdm vztahem [9]:<\/p>\n\"\"<\/a>\n

V\u00a0r\u00e1mci pokus\u016f byly tak\u00e9 ur\u010deny p\u0159epadov\u00e9 v\u00fd\u0161ky, p\u0159i nich\u017e ji\u017e doch\u00e1z\u00ed k\u00a0p\u0159ilnut\u00ed paprsku na konstrukci p\u0159elivu a\u00a0jeho neodtr\u017een\u00ed od p\u0159elivn\u00e9 hrany. Pro obd\u00e9ln\u00edkov\u00fd p\u0159eliv je to cca 20 mm a\u00a0pro kruhov\u00fd p\u0159eliv cca 30 mm. Porovn\u00e1n\u00ed nam\u011b\u0159en\u00fdch dat pro kruhovou hranu s\u00a0ostrou p\u0159elivnou hranou pomoc\u00ed relativn\u00edch rozd\u00edl\u016f velikosti pr\u016ftok\u016f je zobrazeno na obr. 13<\/em>. Z\u00a0grafu je patrn\u00e9, \u017ee kruhov\u00e1 p\u0159elivn\u00e1 hrana je o\u00a0cca 10 % kapacitn\u011bj\u0161\u00ed ne\u017e ostr\u00e1 hrana. Porovn\u00e1n\u00ed je provedeno pomoc\u00ed R<\/em>rel,KH<\/sub>:<\/p>\n\"\"<\/a>\n\"\"<\/a>\n

Obr. 13. Porovn\u00e1n\u00ed relativn\u00edch rozd\u00edl\u016f pr\u016ftoku ostrohrann\u00fdch a\u00a0kruhov\u00fdch hran m\u011brn\u00fdch p\u0159eliv\u016f
\nFig. 13. Comparison of the discharge\u00b4s\u00a0relative differences of sharp and semi-circle crests weirs<\/h6>\n

Porovn\u00e1n\u00ed nam\u011b\u0159en\u00fdch sou\u010dinitel\u016f p\u0159epadu pro kruhovou a\u00a0ostrou p\u0159elivnou hranu je zobrazeno na obr. 14<\/em>.<\/p>\n\"\"<\/a>\n

Obr. 14. Porovn\u00e1n\u00ed p\u0159epadov\u00fdch sou\u010dinitel\u016f pro kruhov\u00fd a\u00a0obd\u00e9ln\u00edkov\u00fd p\u0159eliv s\u00a0ostrohrannou nebo kruhovou p\u0159elivnou hranou
\nFig. 14. Comparison of the semi-circle and rectangular overfall weir coefficients with sharp and semi-circle crest<\/h6>\n

Um\u00edst\u011bn\u00ed m\u011brn\u00e9ho p\u0159elivu v\u016f\u010di sm\u011bru nat\u00e9kaj\u00edc\u00edho proudu<\/h2>\n

V\u00a0r\u00e1mci pokus\u016f prov\u00e1d\u011bn\u00fdch ve \u017elabu byly tak\u00e9 realizov\u00e1ny pokusy se z\u00e1m\u011brn\u011b \u201echybn\u011b\u201c um\u00edst\u011bn\u00fdmi p\u0159elivy. Jako spr\u00e1vn\u011b geometricky instalovan\u00fd p\u0159eliv lze definovat takov\u00fd, kter\u00fd je svisl\u00fd a\u00a0p\u016fdorysn\u011b kolm\u00fd na osu koryta. Na vodn\u00edm toku m\u016f\u017ee doj\u00edt ke zm\u011bn\u011b geometrie usazen\u00ed p\u0159elivu nap\u0159\u00edklad p\u0159i vlastn\u00ed chybn\u00e9 instalaci p\u0159elivu. Celkem byly testov\u00e1ny t\u0159i varianty zm\u011bn\u011bn\u00e9ho um\u00edst\u011bn\u00ed p\u0159elivu (viz obr. 15<\/em>)\u00a0\u2013 vertik\u00e1ln\u00ed n\u00e1klon 1 a\u00a02 (po a\u00a0proti proudu, vlastn\u00ed p\u0159eliv byl v\u016f\u010di svisl\u00e9mu p\u0159elivu naklon\u011bn o\u00a0\u00b1 10\u00b0) a\u00a0horizont\u00e1ln\u00ed n\u00e1klon 3 (tj. p\u0159eliv nebyl kolmo v\u016f\u010di ose koryta, \u00fahel mezi osou toku a\u00a0p\u0159elivem byl 65\u00b0). Pokusy byly uskute\u010dn\u011bny na obd\u00e9ln\u00edkov\u00e9m p\u0159elivu \u0161\u00ed\u0159ky 15 cm a\u00a0v\u00fd\u0161ky 8 cm. V\u00fdsledky t\u00e9to citlivostn\u00ed anal\u00fdzy jsou zobrazeny na obr. 16<\/em> pomoc\u00ed relativn\u00ed chyby R<\/em>rel,u<\/sub>, kde Q<\/em>kolm\u00fd<\/sub> je roven pr\u016ftoku p\u0159es geometricky spr\u00e1vn\u011b usazen\u00fd p\u0159eliv a\u00a0Q<\/em>upraven\u00fd<\/sub> je rovn\u00fd pr\u016ftoku p\u0159es geometricky \u201echybn\u011b\u201c um\u00edst\u011bn\u00fd p\u0159eliv:<\/p>\n\"\"<\/a>\n

Z v\u00fdsledk\u016f je patrn\u00e9, \u017ee vertik\u00e1ln\u00ed n\u00e1klon po proudu zp\u016fsob\u00ed chybu cca + 1,5 % v\u016f\u010di kolm\u00e9 variant\u011b p\u0159i stejn\u00e9 p\u0159epadov\u00e9 v\u00fd\u0161ce a obdobn\u011b je pr\u016ftok o 2,5 % men\u0161\u00ed, pokud je p\u0159eliv o 10\u00b0 naklon\u011bn proti sm\u011bru proud\u011bn\u00ed. P\u016fdorysn\u00e9 nato\u010den\u00ed p\u0159elivu v\u016f\u010di ose toku o 25\u00b0 nezp\u016fsobilo m\u011b\u0159itelnou odchylku. Lze konstatovat, \u017ee chybn\u00e9 um\u00edst\u011bn\u00ed p\u0159elivu, definovan\u00e9 v\u00fd\u0161e, nezp\u016fsob\u00ed p\u0159\u00edli\u0161 velkou chybu m\u011b\u0159en\u00ed. Toto tvrzen\u00ed je ov\u0161em ov\u011b\u0159eno pouze pro mal\u00e9 m\u011brn\u00e9 p\u0159elivy a n\u00edzk\u00e9 pr\u016ftoky, v p\u0159\u00edpad\u011b v\u011bt\u0161\u00edch p\u0159\u00edtokov\u00fdch rychlost\u00ed lze o\u010dek\u00e1vat zv\u011bt\u0161en\u00ed chyb m\u011b\u0159en\u00ed pr\u016ftoku.<\/p>\n\"\"<\/a>\n

Obr. 15. Zobrazen\u00ed zm\u011bn\u011bn\u00fdch um\u00edst\u011bn\u00ed p\u0159elivu v\u016f\u010di standardn\u00edmu um\u00edst\u011bn\u00ed (\u0161ed\u00e1\u00a0\u2013 standardn\u00ed um\u00edst\u011bn\u00ed, \u010dern\u00e1\u00a0\u2013 zm\u011bn\u011bn\u00e9 um\u00edst\u011bn\u00ed)
\nFig. 15. Different positions diagrams of the weir against the channel centre line (grey\u00a0\u2013 standard position, black\u00a0\u2013 different position)<\/h6>\n\"\"<\/a>\n
Obr. 16. Porovn\u00e1n\u00ed relativn\u00edch chyb zp\u016fsoben\u00fdch chybn\u00fdm geometrick\u00fdm um\u00edst\u011bn\u00edm m\u011brn\u00e9ho p\u0159elivu v\u00a0toku
\nFig. 16. Relative errors comparison of different positions of the weir against the channel centre line<\/h6>\n

V\u00fdroba m\u011brn\u00fdch p\u0159eliv\u016f<\/h2>\n

M\u011brn\u00e9 p\u0159elivy pro testov\u00e1n\u00ed v\u00a0laboratorn\u00edm \u017elabu a\u00a0v\u00a0ter\u00e9nu byly zhotoveny metodou 3D tisku. Tato metoda umo\u017e\u0148ovala relativn\u011b snadn\u00e9 proveden\u00ed variabiln\u00edch tvar\u016f m\u011brn\u00e9ho p\u0159elivu a\u00a0p\u0159elivn\u00e9 hrany. Trojrozm\u011brn\u00fd model ka\u017ed\u00e9ho p\u0159elivu byl vytvo\u0159en na po\u010d\u00edta\u010di a\u00a0pot\u00e9 vyti\u0161t\u011bn tisk\u00e1rnou. V\u00a0r\u00e1mci pokus\u016f v\u00a0laborato\u0159i byl pou\u017eit materi\u00e1l PLA (kyselina polyml\u00e9\u010dn\u00e1), tento materi\u00e1l je pln\u011b biologicky odbourateln\u00fd, vyr\u00e1b\u00ed se z\u00a0kuku\u0159i\u010dn\u00e9ho \u0161krobu. Jeho v\u00fdhodou je snadn\u00fd a\u00a0rychl\u00fd tisk, nev\u00fdhodou je mal\u00e1 pru\u017enost a\u00a0k\u0159ehkost materi\u00e1lu, kter\u00e1 ho vylu\u010duje pro pou\u017eit\u00ed v\u00a0ter\u00e9nu.<\/p>\n

Pro vyu\u017eit\u00ed v\u00a0ter\u00e9nu se osv\u011bd\u010dil materi\u00e1l PET (polyethylentereftal\u00e1t), kter\u00fd je zn\u00e1m\u00fd d\u00edky plastov\u00fdm lahv\u00edm. Materi\u00e1l je dostate\u010dn\u011b pevn\u00fd a\u00a0z\u00e1rove\u0148 pru\u017en\u00fd a\u00a0odoln\u00fd proti vodn\u00edmu prost\u0159ed\u00ed. V\u00a0r\u00e1mci ter\u00e9nn\u00edho m\u011b\u0159en\u00ed jsou ji\u017e p\u0159elivy z\u00a0PET instalov\u00e1ny dva roky, b\u011bhem tohoto obdob\u00ed nebyly zji\u0161t\u011bny \u017e\u00e1dn\u00e9 materi\u00e1lov\u00e9 nedostatky, kter\u00e9 by nep\u0159\u00edzniv\u011b ovliv\u0148ovaly kvalitu m\u011b\u0159en\u00ed pr\u016ftoku. Velk\u00e1 v\u00fdhoda materi\u00e1lu v\u00a0zimn\u00edch m\u011bs\u00edc\u00edch, p\u0159i poklesu teploty n\u011bkolik stup\u0148\u016f pod nulu je, \u017ee nedoch\u00e1z\u00ed k\u00a0namrz\u00e1n\u00ed vody na vlastn\u00edm p\u0159elivu v\u00a0porovn\u00e1n\u00ed nap\u0159\u00edklad s\u00a0ocelov\u00fdm p\u0159elivem.<\/p>\n

Z\u00e1v\u011br<\/h2>\n

V r\u00e1mci laboratorn\u00edho m\u011b\u0159en\u00ed byly testov\u00e1ny p\u0159elivy s ostrou p\u0159elivnou hranou \u2013 troj\u00faheln\u00edkov\u00fd, obd\u00e9ln\u00edkov\u00fd a kruhov\u00fd. Pro jednotliv\u00e9 p\u0159elivy byly porovn\u00e1ny hodnoty nam\u011b\u0159en\u00fdch p\u0159epadov\u00fdch sou\u010dinitel\u016f s hodnotami podle r\u016fzn\u00fdch autor\u016f p\u0159i minim\u00e1ln\u00edch p\u0159epadov\u00fdch v\u00fd\u0161k\u00e1ch. Pro troj\u00faheln\u00edkov\u00fd p\u0159eliv s vrcholov\u00fdm \u00fahlem 90\u00b0 se jev\u00ed jako optim\u00e1ln\u00ed pou\u017e\u00edvat rovnici podle Ji\u010d\u00ednsk\u00e9ho a\u00a0\u0160eflov\u00e9 (4) nebo podle Thomsona (2). Pro obd\u00e9ln\u00edkov\u00fd p\u0159eliv vych\u00e1z\u00ed nejl\u00e9pe rovnice podle Rehbocka (9). Pro kruhov\u00fd p\u0159eliv byl odvozen vztah podle V\u00daV TGM (12). Pro ka\u017ed\u00fd p\u0159eliv byla ur\u010dena hodnota p\u0159epadov\u00e9 v\u00fd\u0161ky, pod kterou doch\u00e1z\u00ed k\u00a0p\u0159ilnut\u00ed p\u0159epadov\u00e9ho paprsku ke konstrukci p\u0159elivu a\u00a0k\u00a0hysterezi konsum\u010dn\u00ed k\u0159ivky (obd\u00e9ln\u00edkov\u00fd\u00a0\u2013 10 mm, troj\u00faheln\u00edkov\u00fd\u00a0\u2013 15 mm, kruhov\u00fd\u00a0\u2013 20\u00a0mm).<\/p>\n

V\u00a0r\u00e1mci pokus\u016f s\u00a0polokruhovou p\u0159elivnou hranou byly nam\u011b\u0159eny p\u0159epadov\u00e9 sou\u010dinitele pro kruhov\u00fd a\u00a0obd\u00e9ln\u00edkov\u00fd p\u0159eliv. Pro kruhov\u00fd a\u00a0obd\u00e9ln\u00edkov\u00fd p\u0159eliv s\u00a0polokruhovou p\u0159epadovou hranou byly ur\u010deny hodnoty p\u0159epadov\u00e9 v\u00fd\u0161ky, pod kterou ji\u017e doch\u00e1z\u00ed k\u00a0ulp\u00edv\u00e1n\u00ed p\u0159epadov\u00e9ho paprsku na p\u0159elivu\u00a0\u2013 obd\u00e9ln\u00edkov\u00fd p\u0159eliv 20 mm a\u00a0kruhov\u00fd p\u0159eliv 30 mm. Polokruhov\u00e1 p\u0159epadov\u00e1 hrana nezaru\u010duje p\u0159i n\u00edzk\u00fdch p\u0159epadov\u00fdch v\u00fd\u0161k\u00e1ch dokonal\u00e9 odtr\u017een\u00ed v\u00fdtokov\u00e9ho paprsku.<\/p>\n

Soubor pokus\u016f tak\u00e9 obsahoval m\u011b\u0159en\u00ed se z\u00e1m\u011brn\u011b chybn\u011b um\u00edst\u011bn\u00fdmi p\u0159elivy v\u016f\u010di proudu. V\u00fdsledky m\u011b\u0159en\u00ed uk\u00e1zaly, \u017ee pokud je p\u0159eliv naklon\u011bn o\u00a025\u00b0 v\u00a0horizont\u00e1ln\u00ed rovin\u011b, v\u00fdsledky m\u011b\u0159en\u00ed se neli\u0161\u00ed od kolm\u00e9ho um\u00edst\u011bn\u00ed p\u0159elivu. Pokud je p\u0159eliv vertik\u00e1ln\u011b naklon\u011bn o\u00a010\u00b0 proti sm\u011bru proud\u011bn\u00ed, nam\u011b\u0159en\u00e9 pr\u016ftoky jsou o\u00a02,5 % men\u0161\u00ed ne\u017e v\u00a0p\u0159\u00edpad\u011b svisl\u00e9ho um\u00edst\u011bn\u00ed. Pokud je p\u0159eliv vertik\u00e1ln\u011b naklon\u011bn o\u00a010\u00b0 po sm\u011bru proud\u011bn\u00ed, m\u011b\u0159en\u00e9 pr\u016ftoky jsou o\u00a01,5 % v\u011bt\u0161\u00ed ne\u017e v\u00a0p\u0159\u00edpad\u011b svisl\u00e9ho um\u00edst\u011bn\u00ed. Tyto z\u00e1v\u011bry lze ale aplikovat pouze, pokud je rychlost proud\u011bn\u00ed p\u0159ed m\u011brn\u00fdm p\u0159elivem mal\u00e1.<\/p>\n

Pod\u011bkov\u00e1n\u00ed<\/h3>\n

P\u0159\u00edsp\u011bvek vznikl za podpory projektu Z\u00e9ta I\u00a0\u2013 TJ01000343\u00a0\u2013 V\u00fdvoj hydraulicky vhodn\u00e9ho p\u0159elivu pro m\u011b\u0159en\u00ed mal\u00fdch pr\u016ftok\u016f.<\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

P\u0159\u00edsp\u011bvek prezentuje v\u00fdsledky hydraulick\u00e9ho fyzik\u00e1ln\u00edho v\u00fdzkumu m\u011brn\u00fdch p\u0159eliv\u016f pro m\u011b\u0159en\u00ed mal\u00fdch, resp. minim\u00e1ln\u00edch pr\u016ftok\u016f. V\u00fdzkum se zam\u011b\u0159il na ur\u010den\u00ed sou\u010dinitel\u016f p\u0159epadu pro n\u00edzk\u00e9 p\u0159epadov\u00e9 v\u00fd\u0161ky. <\/p>\n","protected":false},"author":8,"featured_media":7234,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[86],"tags":[1767,1766,1764,1765],"coauthors":[1635,868],"class_list":["post-7358","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-hydraulics-hydrology-and-hydrogeology","tag-chyby-mereni","tag-mereni-malych-prutoku","tag-ostrohranne-merne-prelivy","tag-prepadovy-soucinitel"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/7358","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/users\/8"}],"replies":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/comments?post=7358"}],"version-history":[{"count":4,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/7358\/revisions"}],"predecessor-version":[{"id":30554,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/posts\/7358\/revisions\/30554"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/media\/7234"}],"wp:attachment":[{"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/media?parent=7358"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/categories?post=7358"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/tags?post=7358"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.vtei.cz\/en\/wp-json\/wp\/v2\/coauthors?post=7358"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}