2021-01

Journal of University of Duhok (Issue : 2) (Volume : 23)

Weirs are discharge measurement structures have different geometrical shapes. The performances of the modified triangular plan form weirs were studied under free-flow condition. Three groups of weirs were tested experimentally. The first group has a flat top; the second has one slope and the third has two slopes. Each group has three vertex angles (60o , 90o and 120o ) with constant height. The hydraulic performances of weirs are based on the ability to pass the discharge for certain head flow and on the value of the coefficient of discharge. The values of discharge and the coefficient were compared with earlier studies being carried on conventional normal weir, broad crest, triangular plan-form and different labyrinth weirs. All the groups show better performance than conventional shaped and broad weir. The magnification of the actual discharge to the discharge of broad crested weir is more than one and the best one is the first in the third group, while the vertex angle is (60o ) for the second and third group and (120o ) for the first. The performance of the third group is better than rectangular labyrinth weirs, and it is compatible with the triangular labyrinth. The discharge coefficient decreases with the increase of relative value of the head to the height of weir except for the first group. Equations for predicting coefficient of discharge are proposed within the limitations of this test.

2016-07

ZANCO Journal of Pure and Applied Sciences (Issue : 27) (Volume : 2)

The aim of the present investigation is to study the effects of side slope, bed slope and bed roughness on the flow over free overfalls in trapezoidal channels. Three models of trapezoidal free overfall channels have been built and tested in a laboratory flume; each model had four different bed slopes. For each slope, the bed was roughened using artificial strip roughness elements with eight different roughness patterns. The experimental testing program included ninety-six series of experiments for different ranges of Froude number. Experimental results of all models showed that the variation of (𝑸𝒎𝟏.𝟓/√𝒈𝒃𝟓) with (𝒎𝒚𝒃/𝒃) for different bed slopes and various roughness patterns is simple power equation. It was also observed that values of (𝑸𝒎𝟏.𝟓/√𝒈𝒃𝟓) increase with the increase of (𝒎𝒚𝒃/𝒃) values. The correlation between (𝒎𝒚𝒃/𝒃) with (𝒎𝒚𝒄/𝒃) was found to be linear for different bed slopes and roughness patterns. The ratio (𝒚𝒃/𝒚𝒄) decreases with the increase of bed slope (S). An empirical expression was obtained for the variation of (𝑸𝒎𝟏.𝟓/√𝒈𝒃𝟓) with (𝒎𝒚𝒃/𝒃) and (S/n) for the free overfalls with rough beds

2016-05

Journal of University of Zakho (Issue : 1) (Volume : 4)

Sills under sluice gates is used in hydraulic structures; their effect on the head generated upstream gates for certain rate of flow is related to the height and length of sill. A study is held in laboratory flume on four different prismatic sill heights and one model without sill by changing the gate opening four times for each model. Statistical analyses on the dimensionless physical quantities are done. A positive effect of sill on the performance of flow is noted by increasing the flow rate up to 25% for some models. The coefficient of discharge decreases with increase of relative sill height to the head upstream and increases with three other dimensionless parameters. The relative sill height to the gate opening shows the highest correlation factor with the discharge coefficient and its positive effect on the flow phenomena is 55.4%. Within the experimental measures limitations, a linear equation for predicting the discharge coefficient is proposed with Adj. R2 0.923 .

2016-04

Arabian Journal for Science and Engineering (Issue : 10) (Volume : 41)

The aim of the present investigation is to studythe effect of both side and bed slopes on the flow over freeoverfalls in trapezoidal channels, three models of trapezoidal free overfall channels have been built and tested in a labo￾ratory flume. These models had 0.1 m bed width and 3.7 mlength with different values of side slope (m = 0.268, 0.577, and 1). Each model had four different bed slopes (S =0, 0.0033, 0.01, and 0.02). A total of twelve series of the experiments were tested for different ranges of Froude number.Experimental results of all models showed that the variation of (Qm1.5/gb5) with (myb/b) for different values of side slope and different bed slopes is a simple power equation.It was observed that the values of (Qm1.5/gb5) increase with the increase in (myb/b) values. The correlation between(myb/b) with (myc/b) is found to be linear for different bed slopes. The ratio (yb/yc) decreases with the increase of slope(S) with an average value of 0.729 for subcritical and super￾critical flow on smooth beds of different slopes. An empirical expression is obtained for the variation of (Qm1.5/ gb5) with (myb/b), and (S). The results of the present study have been compared with theoretical and experimental results ob￾tained by other investigators showing well agreements.

2015-05

University of Zakho (Issue : 1) (Volume : 3)

The aim of this research is to investigate the effect of surface roughness on the performance of weir and gate. An experimental study in a laboratory flume is carried out to study flow over and under cylindrical weir gate in combined structure as flow measurement device. Four models having different diameters were tested in a laboratory flume. In each model, the surface was roughed four times. The results of the test show logical negative effect of the increase of surface roughness on the performance. The performance of the combined structure improved with decrease ratio of roughness to the upstream head (Ks/H) and with the increase of the total head to the diameter of the weir (H/d). Empirical relations were obtained to estimate the variation of discharge coefficient (Cd) in terms of some dimensionless parameters. Within the limitations of the present experimental work an equation to predict the discharge is proposed with R2 of 0.936. Finely the contribution of the gate increases relative to the weir when the surface roughness increases.

2014-06

Research Journal of Applied Sciences, Engineering and Technology (Issue : 24) (Volume : 7)

The aim of this study is to investigate the effects of surface roughness sizes on the discharge coefficient for a broad crested weirs. For this purpose, three models having different lengths of broad crested weirs were tested in a horizontal flume. In each model, the surface was roughed four times. Experimental results of all models showed that the logical negative effect of roughness increased on the discharge (Q) for different values of length. The performance of broad crested weir improved with decrease ratio of roughness to the weir height (Ks/P) and with the increase of the total Head to the Length (H/L). An empirical equation was obtained to estimate the variation of discharge coefficient Cd in terms total head to length ratio, with total head to roughness ratio.