Effect of channel slope and roughness on hydraulic jump in open channel flow

An experimental study is conducted on hydraulic jump characteristics for understanding the impact of slope in an open channel flume. Hydraulic jump on different channel characteristics (horizontal smooth & rough and sloping smooth & rough) were analysed. The measured characteristics of hydraulic jump with different channel roughness and different slope were compared. The results showed that the sequent depth ratio (y2/y1 ) increases with the increase in Froude number (Fr1 ) for smooth horizontal bed and horizontal rough bed. It was also observed that with an increase in Fr1 , a decrease in y2/y1 in smooth sloping bed condition and decreases for rough sloping bed. New empirical relationships were also developed with the experimental data and results were found similar with the observed hydraulic characteristics data.

TRANSIENT DAM-BREAK WAVE LOADING ON PIPELINES NEAR SLOPING BED

Extreme events such as tsunamis and floods have caused massive damaging consequences to nearshore infrastructures. This has been more significant recently due to a changing climate. Transmission pipelines are among such infrastructures and need to be protected against potential extreme events. Design of pipelines requires comprehensive understanding of the exerting hydrodynamic forces. Such pipelines are often placed on sloping beds in coastal areas. Therefore, to address the uncertainties and parameters involved in extreme hydrodynamic loading on pipelines near sloping bed, an experimental program was conducted at the hydraulic laboratory in WASEDA University, Tokyo, Japan. This study is a complement of another experimental research conducted by Ghodoosipour et al., 2019a and b to investigate loadings from tsunami-like dam-break waves on pipelines located on flat bed.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/y6nSfe34SAw

Underground Barrier Wall Evaluation for Controlling Saltwater Intrusion in Sloping Unconfined Coastal Aquifers

Barrier walls are considered one of the most effective methods for facilitating the retreat of saltwater intrusion (SWI). This research plans to examine the effect of using barrier walls for controlling of SWI in sloped unconfined aquifers. The sloping unconfined aquifer is considered with three different bed slopes. The SEAWAT model is implemented to simulate the SWI. For model validation, the numerical results of the seawater wedge at steady state were compared with the analytical solution. Increasing the ratio of flow barrier depth (db/d) forced the saltwater interface to move seaward and increased the repulsion ratio (R). With a positive sloping bed, further embedding the barrier wall from 0.2 to 0.7 caused R to increase from 0.3% to 59%, while it increased from 1.8% to 41.7% and from 3.4% to 46.9% in the case of negative and horizontal slopes, respectively. Embedding the barrier wall to a db/d value of more than 0.4 achieved a greater R value in the three bed-sloping cases. Installing the barrier wall near the saltwater side with greater depth contributed to the retreat of the SWI. With a negative bed slope, moving the barrier wall from Xb/Lo = 1.0 toward the saltwater side (Xb/Lo = 0.2) increased R from 7.21% to 68.75%, whereas R increased from 5.3% to 67% for the horizontal sloping bed and from 5.1% to 64% for the positive sloping bed. The numerical results for the Akrotiri coastal aquifer confirm that the embedment of the barrier wall significantly affects the controlling of SWI by increasing the repulsion ratio (R) and decreasing the SWI length ratio (L/La). Cost-benefit analysis is recommended to determine the optimal design of barrier walls for increasing the cost-effectiveness of the application of barrier walls as a countermeasure for controlling and preventing SWI in sloped unconfined aquifers.

An experimental decomposition of nonlinear forces on a surface-piercing column: Stokes-type expansions of the force harmonics

Wave loading on marine structures is the major external force to be considered in the design of such structures. The accurate prediction of the nonlinear high-order components of the wave loading has been an unresolved challenging problem. In this paper, the nonlinear harmonic components of hydrodynamic forces on a bottom-mounted vertical cylinder are investigated experimentally. A large number of experiments were conducted in the Danish Hydraulic Institute shallow water wave basin on the cylinder, both on a flat bed and a sloping bed, as part of a European collaborative research project. High-quality data sets for focused wave groups have been collected for a wide range of wave conditions. The high-order harmonic force components are separated by applying the ‘phase-inversion’ method to the measured force time histories for a crest focused wave group and the same wave group inverted. This separation method is found to work well even for locally violent nearly-breaking waves formed from bidirectional wave pairs. It is also found that the $n$th-harmonic force scales with the $n$th power of the envelope of both the linear undisturbed free-surface elevation and the linear force component in both time variation and amplitude. This allows estimation of the higher-order harmonic shapes and time histories from knowledge of the linear component alone. The experiments also show that the harmonic structure of the wave loading on the cylinder is virtually unaltered by the introduction of a sloping bed, depending only on the local wave properties at the cylinder. Furthermore, our new experimental results reveal that for certain wave cases the linear loading is actually less than 40 % of the total wave loading and the high-order harmonics contribute more than 60 % of the loading. The significance of this striking new result is that it reveals the importance of high-order nonlinear wave loading on offshore structures and means that such loading should be considered in their design.

THE FLOW OVER ASYMMETRICAL RIPPLES: EXPERIMENTAL INVESTIGATION ON THE MORPHODYNAMIC BEHAVIOR

This paper reports on an experimental campaign focused on the generation and evolution of small scale bedforms over a sloping sandy beach. The wave propagation over a sloping bed triggers a flow asymmetry that reflects on the bedform characteristics. Morphodynamic analyses on ripple evolution and migration led to observe that at the equilibrium the ripples have larger offshore flanks and are leant toward the beach. However migration velocity may be onshore or offshore directed. The equilibrium ripple characteristics seem to be well described by Nielsen (1981) ripple predictor.