نوع مقاله : مقاله پژوهشی
نویسندگان
گروه مهندسی آب، دانشکده کشاورزی، دانشگاه بوعلیسینا، همدان، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Roughness coefficient is an effective factor on water velocity and discharge in drain pipes. Roughness coefficient in experimental box model with dimensions of 100×41×56cm was evaluated with two pipes of smooth and corrugated in a diameter of 63 and 56mm by three series of independent tests. The first set was done on pipes with mineral envelop, the second set on pipes with synthetic materials and the third one on pipes without envelop. The mean values of "n" Manning’s in the smooth pipe with synthetic and mineral envelope and non-envelop materials were measured 0.0106, 0.0111, 0.011, and for the corrugated pipe 0.0088, 0.009, 0.0091. The mean values of "n" Ganguillete-Kutter’s in the smooth pipe with synthetic and mineral envelop and non-envelop materials were obtained 0.0048, 0.0048, 0.0048, and for the corrugated pipe 0.0041, 0.0042, 0.0042. The "n" values from the Reynolds-Darcy Weissbach combination formula in the smooth pipe with synthetic and mineral envelop and non-envelop materials were calculated to be 0.0050, 0.0050, 0.0049 and for the corrugated pipe 0.0048, 0.0048, 0.0049. Two evaluation indexes (R2 and RMSE Error Value) indicated a better result for n value obtained by Ganguillet-Kutter formula. The flow inside the drainage pipes is a turbulent and spatially variable which is affected by the small flows entering the pipe through holes. This flow pattern, while disrupting the uniform distribution of the transverse velocity of the flow, caused flow inhibition and increased Manning's roughness coefficient in the first 30 cm due to the flow rate and low flow speed compared to the second 30 cm. The negligible difference between "n" Manning’s with "n" Ganguillete-Kutter’s is not important and applying 0.011 for Manning coefficient in smooth pipe and 0.009 for corrugating pipe with envelop is satisfactory.
کلیدواژهها [English]
Experimental Study of roughness coefficient in smooth and corrugated drainage pipes with envelop and non-envelope
EXTENDED ABSTRACT
The roughness coefficient is effective parameter in the drainage pipes that constant coefficients, under full flow conditions an error in calculating could result. Therefore, knowing the from of experimental roughness coefficients are usually is needed different conditions type of pipes and under half depth or lower flows. The roughness coefficient can be determined from the Darcy-Weissbach and Manning formula. The roughness coefficient of two types of smooth and corrugated pipes using the physical model in three states: mineral envelop, artificial (plastic mesh) produced domestically, and non-envelop according to U.S.B.R. has been studied in a sandy soil. The objective of this research is to determined roughness coefficient from Manning, Ganguillet-Cutter and combination Reynolds&Darcy-Weissbach formulas in drainage pipes.
The required soil was a combination of sandy and clay soil. In this research, an experimental box model was used. The roughness coefficient was determined by independent tests in the two smooth pipe with a diameter of 63 and corrugated with a diameter 56mm. The first set was for pipes with envelop of mineral, second test included synthetic materials and third test pipes without envelop. For mineral envelop is used d60 of Particle Size Distribution curve according to U.S.B.R standard. For artificial materials, plastic with 2mm mesh was used based on the criterion of . pipe of drainage length was 100cm, which installed with a slope of 2%. The discharge of drain pipe was measured in different time steps. To compare the results, were used factors R2 and RMSE.
With roughness coefficient of the pipe increases, to reduce the flow velocity and discharge rate in the pipe. The smooth or corrugated of pipe and the hydraulic conditions inside the pipe with the greatest effect have on the roughness coefficient. Value of 'n' Manning’s in the first 30cm of the smooth pipe with artificial, mineral envelop and non-envelop was 0.0111, 0.0113, 0.0112, and for the corrugated pipe obtained 0.0090, 0.0091, 0.0094. The same changes at the first of 30cm from the Ganguillet-Cutter relationship and the Reynolds-Darcy-Weissbach relationship were also established. So that 'n' Ganguillet-Cutter’s was obtained for the smooth pipe in synthetic envelop, mineral and non-envelop, 0.0048 and for the corrugated pipe 0.0042, 0.0042 and 0.0043, respectively. The roughness coefficient, from the Reynolds-Darcy Weissbach combination formula in the smooth pipe with synthetic envelop, mineral and non-envelop was calculated 0.0050, 0.0050, 0.0049 and for the corrugated pipe 0.0048, 0.0048, 0.0049. The resulting roughness coefficient values for the second 30 cm of the pipe have the same conditions as the first 30cm of the pipe. In total, the average 'n' Manning’s for the first and second 30cm of the smooth pipe with synthetic envelop, mineral, and non-envelop was 0.0106, 0.0111, 0.011 and for the corrugated pipe 0.0088, 0.009, 0.0091. Also, the average 'n' Manning’s from the Ganguillet-Cutter relationship for both lengths of smooth pipe with artificial envelop, mineral, non-envelop is 0.0048, 0.0048, 0.0048 and for corrugated pipe 0.0041, 0.0042, 0.0042 obtained. The average 'n' Manning’s from the combined Reynolds-Darcy-Weissbach relationship for the length of first and second of the smooth pipe with artificial envelop, mineral, non-envelop 0.005, 0.005, 0.0049 and for the corrugated one 0.0048, 0.0048, 0.0049 was obtained. The lack of clear difference in the roughness difference between two smooth and corrugated pipes can be seen in the small diameter of the pipes, low roughness, the short height of the waves in the corrugated pipe, the close distance of the waves to each other, and the shape of the corrugated pipe waves. The Manning theory stated that the flow rate is inversely proportional to the roughness coefficients. From the experiments, it shows smoother surface is having higher roughness coefficient and higher retarding effect on the water flow, lower flow rate is produced. Results showed, R2 and RMSE of the Ganguillet-Cutter than Manning in the smoot pipe are 0.80-0.97 and 0.006-0.007, and corrugated pipe 0.82-0.96 and 0.005 respectively. Also, this factors of the combinate Reynolds&Darcy-Weissbach in the smoot pipe 0.08-0.84 and 0.006-0.007 and corrugated pipe 0.03-0.90 and 0.004 - 0.005 respectively. This study showed in addition to Manning formula providing a roughness coefficient way of estimating, Ganguillet-Cutter can be the accuracy and efficiency of the prediction of the roughness coefficient. Now, corrugated plastic pipe in envelope is first choices. It is much more complicated for corrugated drains. The performance comparison of each of the envelops regarding the roughness value showed that both envelops have an acceptable hydraulic performance.
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