Parametric and nonparametric regression models in study of the length of hydraulic jump after a multi-segment sharp-crested V-notch weir

A multi-segment sharp-crested V-notch weir (SCVW) was used both theoretically and experimentally in this study to evaluate the length of the hydraulic jump at the downstream of the weir. For this aim, a SCVW with three triangular segments at different tail-water depths (tailgate angles), and ten different discharges at a steady flow condition were investigated. Then, the most effective parameters on the length of the hydraulic jump are defined and several parametric and nonparametric regression models, namely multi-linear regression (MLR), additive non-linear regression (ANLR), multiplicative non-linear regression (MNLR), and generalized regression neural network (GRNN) models are compared with two semi-empirical regression models from the literature. The results indicate that the GRNN model is the best model among the selected models. These results are also linked to the nature of the hydraulic jump and the turbulent behavior of the phenomenon, which masks the experimental results with outliers.

Numerical Investigation of Shock Wave Diffraction over a Sphere Placed in a Shock Tube

For evaluating the motion of a solid body in a gaseous medium, one has to know the drag constant of the body. It is therefore not surprising that this subject was extensively investigated in the past. While accurate knowledge is available for the drag coefficient of a sphere in a steady flow condition, the case where the flow is time dependent is still under investigation. In the present work the drag coefficient of a sphere placed in a shock tube is evaluated numerically. For checking the validity of the used flow model and its numerical solution, the present numerical results are compared with available experimental findings. The good agreement between present simulations and experimental findings allows usage of the present scheme in nonstationary flows.

CFD Simulation of Heat Transfer of Pulsating Gas in a Pipe

Numerical Simulation of pulsating flow in a pulse combustor tailpipe was performed using computational fluid dynamics (CFD) method. The flow in the pipe was characterized by periodic pulsating. The influence of this pulsating includes incomplete flow development and high level of convective heat transfer rate, and both were considered and investigated by the CFD model. Compared with the steady flow condition, results showed that the heat transfer coefficient and Nusselt number were 2.35 times higher.

Study on hydraulic resistance of erodible bed at the Chiyoda experimental flume

The authors made erodible bed experiments under steady flow condition at the Chiyoda Experimental Flume, a large-scale facility constructed on the floodplain of the Tokachi River, and observed sand waves on the bed of the flume. In this study, the characteristics of the sand waves are examined along the longitudinal survey lines and confirmed to be dunes. Next, the authors estimated Manning's roughness coefficients from the observed hydraulic values and assumed that the rise of the coefficients attributed to the sand wave development. Finally, vertical flow distribution on the sand waves are examined, and observed velocity distribution on the crest of waves found to be explained by the logarithmic distribution theory.

Study on Phreatic Line of Reservoir Slope under the Rainfall and Reservoir Level Fluctuation

The determination of the phreatic line under the action of rainfall and reservoir water level fluctuation together is of great importance for reservoir slope stability analysis. However, there are no unified Formulas for the calculation of phreatic line. Homogeneous reservoir slope seepage model with inclined impermeable bed is built. Then, a conceptual model is set up based on the basic principle of seepage theory, and the approximate analytic solutions of phreatic line are derived with the Boussinesq Differential Equation of unsteady infiltration and initial value calculated in steady flow condition. And the simplified Formula, which is convenient for engineering application, is obtained by Polynomial Fitting Method.

Experimental Study of a Radial Turbine Using Floating Nozzle for Wave Energy Conversion

The objective of this study is to propose a new radial flow turbine for wave energy conversion and to clarify its performance by model testing under steady flow condition. The proposed radial turbine has a rotor blade row for unidirectional airflow and two guide vane rows. The guide vane rows are named ‘floating nozzle’ in the study. The guide vane rows slide in an axial direction and work as nozzle in the turbine alternately for bi-directional airflow, so as to rectify bidirectional airflow and to make uni-directional airflow. The radial flow turbine with a diameter of 500mm has been manufactured and investigated experimentally under steady flow condition generated by a wind tunnel using a piston/cylinder system with a diameter of 1.4m. As a result, it has been found in the study that the peak efficiency of the proposed radial turbine is approximately 57% and the rotational speed of this turbine is considerably lower that that of Wells turbine. Further, the effect of nozzle setting angle on the turbine performance was investigated and clarified in the study.

Scaled Experiments Evaluating Pulse Jet Mixing of Slurries

Pulse jet mixing (PJM) tests with noncohesive solids in Newtonian liquid were conducted at three geometric scales to support the design of mixing systems for the Hanford Waste Treatment and Immobilization Plant. The test data will be used to develop mixing models. The models predict the cloud height (the height to which solids will be lifted by the PJM action) and the critical suspension velocity (the minimum velocity needed to ensure all solids have been lifted from the floor), two parameters measured during the tests. From the cloud height estimate, the concentration of solids near the vessel floor and the minimum velocity predicted to lift solids can be calculated. The test objective was to observe the influence of vertically downward-directed jets on noncohesive solids in a series of scaled tanks with several bottom shapes. The test tanks and bottom shapes included small- and large-scale tanks with elliptical bottoms, a mid-scale tank with a spherical bottom, and a large-scale tank with a flanged and dished bottom. During testing, the downward-directed jets were operated in either a steady flow condition or a pulsed (periodic) flow condition. The mobilization of the solids resulting from the jets was evaluated based on: the motion/agitation of the particulate on the tank floor and the elevation the solids reach within the tank; the height the solids material reaches in the tank is referred to as the cloud height (HC).