Rijit davranış gösteren esnek bitkilerin akıma karşı oluşturduğu direncin belirlenmesi

Bu çalışmada farklı dizilimlerde yerleştirilen çok saplı esnek bitkilerin akıma karşı dik durarak rijit davranış göstermesi durumunda oluşturacağı pürüzlülük katsayılarının elde edilmesi amaçlanmıştır. Dört farklı konfigürasyonda gerçekleştirilen 166 deneyde 7 farklı noktada akım derinliği ölçülmüş, debi elde edilmiş ve bitkilerden ötürü kaynaklanan yük kaybı hesaplanmıştır. Chézy katsayısı , Darcy-Weisbach sürtünme katsayısı ve Manning katsayısı ’in, Reynolds sayısının 10000 değerinden küçük ve büyük olması durumunda tek bir fonksiyonla ifade edilemeyeceği görülmüş ve veriler iki gruba ayrılarak incelenmiştir. Pürüzlülük katsayısını verecek boyutsuz parametreler Froude sayısı , Reynolds sayısı , bağıl pürüzlülük , yaklaşım akımı enerji çizgisi eğimi ve bitki yoğunluğu olarak belirlenmiştir. Pürüzlülük katsayılarının belirlenmesi için doğrusal olmayan regresyon modeli ile en uygun denklemler elde edilmiştir. Reynolds sayısının 10000’den küçük olması durumunda pürüzlülük katsayıları için; f=f{h/hv}, n={Fr,h/hv,k} ve C={Fr, Sf} olduğu; Reynolds sayısının 10000’den büyük olması durumunda f={h/hv,k}, n={Fr,h/hv,k} ve C={Fr, Re, h/hv, Sf, k} olduğu görülmüştür. Ayrıca beklendiği gibi düşük Reynolds sayılarında bitkilerin varlığının, diğer parametrelerden bağımsız olarak akıma karşı gösterilen direnci arttırdığı sonucuna varılmaktadır. Bu denklemlerdeki farklı katsayıların akım doğrultusundaki bitki yüzey alanı ve bitki yoğunluğu gibi faktörlerden etkilendiği düşünülmektedir.

Anahtar Kelimeler:

Bitki, Esnek, Batık olmayan, Akıma karşı direnç, Pürüzlülük katsayıları

Determination of flexible vegetation resistance against the flow with rigid behavior

In this study, it is aimed to obtain roughness coefficients of flexible multi-stemmed vegetation standing upright against flow with rigid behavior. Flow depths and discharges are measured; head losses causing from vegetation are calculated at 7 different points in 166 experiments for four different configurations. It is seen that Chézy coefficient , Darcy-Weisbach friction coefficient and Manning coefficient cannot be expressed with a single function for all Reynolds number. Therefore, the data are analyzed for the two different cases of Reynolds number lower and greater than 10000. Dimensionless parameters for the roughness coefficients are determined as Froude number , Reynolds number , the relative roughness , approach flow energy line slope , and vegetation density . The most suitable equations for estimating roughness coefficients are obtained by non-linear regression models. It is evaluated that for the Reynolds number lower than 10000 the roughness coefficients are defined as f=f{h/hv}, n={Fr,h/hv,k} and C={Fr, Sf} , and for the Reynolds number greater than 10000 they are given as f={h/hv,k}, n={Fr,h/hv,k} and C={Fr, Re, h/hv, Sf, k}. Also, for relatively low Reynolds numbers, the presence of plants caused an increase in resistance against the flow independently of other parameters as expected. It is observed that the regression equation coefficients could be influenced by factors such as surface area plant in the flow direction and plant density.

Keywords:

Vegetation, Flexible, Emergent, Resistance to flow, Roughness coefficients,

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