THE INFLUENCE OF THE SHAPE FACTOR ON THE ROUGHNESS COEFFICIENT

• Main Author: Aisha Uzhelia, Verryn
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/75009
• Institution: Institut Teknologi Bandung

An open channel with a uniform channel geometry sets a roughness value and becomes difficult when the channel comprises different materials. In paying the roughness value n, it is necessary to pay attention to the factors that affect the value of n. One of these factors is the size and shape of the channel, but there is no objective evidence that the size and shape of the channel is an essential factor affecting the value of n. Each section shape has a different form factor, and an understanding of the effect of the other form factors on channel roughness values can help in comparing and selecting the appropriate section for a particular purpose. Thus, understanding the relationship between form factor and roughness value is essential in planning the hydraulic analysis of channels. The influence of the cross-section/channel shape is not considered. It is only seen from the base channel and the material in the channel. The research was conducted with experiments in the laboratory with open channel sections. There were 180 scenarios with four different types of areas, namely 90º, 60º, 45º and 35º sections, and with three types of channel roughness, namely Glass open channel (channels without roughness), Bottom Roughness (roughness on the channel bottom), Wall & Bottom Roughness (roughness on the wall and channel bottom). From the experimental results, it was found that each cross-section with an average n value that was different from the roughness value n at a cross-section of 90º and with the roughness on the channel walls and the channel bottom had the highest n roughness value with a roughness value of 0.024 and with the lowest roughness value on the cross-section 35º where the cross-section is not given any roughness with a roughness value of 0.010. They also get the shape factor value of each cross section with the shape factor percent results for Glass open channel with a cross-section of 90º the shape factor value is 100%, 60º the shape factor value is 92%, 45º the shape factor value is 85% and 35º the shape factor value is 77%, for Bottom Roughness with a cross-section of 90º the value of the shape factor is 100%, 60º the value of the shape factor is 86%, 45º the value of the shape factor is 85% and 35º the value of the shape factor is 76%, for Wall & Bottom Roughness with a cross-section of 90º the value of the shape factor is 100%, 60º the value of the shape factor is 97 %, form factor value 45º 79% and form factor value 35º 72%. From the above results, we obtain the regression equation for the three types of roughness with the following equation y = -0.0004x2 - 0.0016x + 0.013 (Glass open channel), y = 0.0007x2 - 0.0043x + 0.0204 (Bottom Roughness), y = -0.0022x2 - 0.0018x + 0.0239 (Wall & Bottom Roughness). So it can be concluded from this study that changing the cross-section's shape (shape factor) can affect the channel roughness coefficient value.