Stochastic Uncertainty in a Dam-Break Experiment with Varying Gate Speeds

Uncertainties inherent in gate-opening speeds are rarely studied in dam-break flow experiments due to the laborious experimental procedures required. For the stochastic analysis of these mechanisms, this study involved 290 flow tests performed in a dam-break flume via varying gate speeds between 0.20 and 2.50 m/s; four pressure sensors embedded in the flume bed recorded high-frequency bottom pressures. The obtained data were processed to determine the statistical relationships between gate speed and maximum pressure. The correlations between them were found to be particularly significant at the sensors nearest to the gate (Ch1) and farthest from the gate (Ch4), with a Pearson’s coefficient r of 0.671 and −0.524, respectively. The interquartile range (IQR) suggests that the statistical variability of maximum pressure is the largest at Ch1 and smallest at Ch4. When the gate is opened faster, a higher pressure with greater uncertainty occurs near the gate. However, both the pressure magnitude and the uncertainty decrease as the dam-break flow propagates downstream. The maximum pressure appears within long-period surge-pressure phases; however, instances considered as statistical outliers appear within short and impulsive pressure phases. A few unique phenomena, which could cause significant bottom pressure variability, were also identified through visual analyses using high-speed camera images. For example, an explosive water jet increases the vertical acceleration immediately after the gate is lifted, thereby retarding dam-break flow propagation. Owing to the existence of sidewalls, two edge waves were generated, which behaved similarly to ship wakes, causing a strong horizontal mixture of the water flow.

Evaluation of the Hydraulic Performance of a Rear-Parapet Vertical Breakwater under Regular Waves through Hydraulic Experiments

Climate change has resulted in increased intensity and frequency of typhoons and storm surges. Accordingly, attention has been paid to securing the breakwater’s stability to protect the safety of the port. Herein, hydraulic model experiments were conducted to evaluate the hydraulic performance of a vertical breakwater having a rear parapet. For comparison, cases in which the parapet was placed on the seaside, the harborside, and at the center of the breakwater were considered. Regular waves were used for convenient performance analysis. Five wave gauges and nine pressure transducers were installed to secure physical data for hydraulic performance evaluation. Results showed that a rear parapet can reduce the maximum wave force acting on the breakwater. Even though impulsive pressure was generated, it did not affect the stability of the breakwater owing to the phase difference between the maximum wave pressures acting on the caisson and parapet. By decreasing the maximum wave force, the required self-weight that satisfies the safety factor of 1.2 was reduced by up to 82.7%; the maximum bearing pressure was reduced by up to 47.6% compared with that of the parapet located on the seaside. Thus, the rear parapet was found to be more suitable for actual applications.

A new hypothesis that contributes to the formation of cold sludge volcanoes and fluid outlets in tectonic seabed & terrestrial regions; with its helpful interpretation for time fracture sequence of fault segments.

<p>During the co-seismic development of a fault in lithological environments, regions containing cavities may form momentarily or permanently. In the tectonic shift zones, these pressure gaps lead to the formation of irregular new intermediate sediment zones, as infiltrate in to the gap, if the pressure perturbations are large. The semi-fluid sediment material and sea water enter through opening fault sector's surrounding sediments at the far place from dispersing fault energy burst. But pore water infiltration is independent about place of vomited energy burst. In some cases hard material which detached from fault wall or top sediment material, provide isolation lids, as obstacling on 'cell type empty interlaying gaps' at tectonic line. They can collapse again or stay as gap form for a long time with suction force after seismic activities by effects of gravitation or pressure perturbations. For durable gaps, pore water is capable to infiltrate in to the gap with long lasting suction forces.  In these regions, in contrast to gravitational folding or collapse structures, the partial sediment sequence may be drawn and folded into the area of the material with different or close lithological density value. Deformational variety of the displaced materials are related with physical properties of seismic event at opening sector such as friction, displacement parameters (velocity, time), dimensional parameters of gap, and water depth.  The main objective of the paper is to figure out all interference mechanisms about these zones (created by pressure perturbations), which develop rapidly during earthquake fractures (or in some cases fractures generated by impulsive pressure changes such as those created by volcanoes). Fracture of fault segments forms a complex mechanical system associated with bedrock, upper sedimentary sequence, and aquatic environment, depending on the location where they occur, even the atmosphere. Therefore, the displacement may be bi-directional to the lower slit or upward from the seabed during the opening or closing stages of the cavity, depending on the nature with variations of the atmosphere & water-sediment mixture. The strong (pulling or impulsive) pressure perturbation effect associated with permanent cavities caused by rapid breakage pulls the material that may form a sludge volcano or water outlet under deformation and brings the environment to near pressure equilibrium. This simple explanation can help to find real additional effective reason for the different formations of assumed collapse or folding structures created by gravitational movements in geology. The hypothesis after main objective at above mentioned in this article is based on the fact that the emergence of  escapes as squeezed fluid form  of water & sediment from compacted secondary irregularities in the previously broken fault segment will help to understand the next seismic mobility in other tectonic segments by identifying source depth cues through physical and chemical analysis. Geophysical instrumentation and applications are still need further developments of compact reflection line information, because the vertical thin anomalies mentioned in this paper are the most difficult structures for detection.</p>

A Hydraulic Experimental Study of a Movable Barrier on a Revetment to Block Wave Overtopping

This paper presents a design for a movable barrier on the revetment of the Haeundae Marine City in Busan, the Korea. This movable barrier was developed to use as a tourist deck in a normal state and to block wave overtopping in an abnormal state. To carry out the physical experiment in a wave flume, the model structure was reduced to a scale of 1/36 compared to the field structure. The discharge of the wave overtopping, the uplift pressure acting on the under surface of a non-standing barrier, and the wave pressure acting in front of a standing barrier were measured to analyze the hydraulic characteristics of the movable barrier. The results show that the impulsive pressure acts on the movable barrier, although the overtopping discharge is less than the allowable limit. When designing a movable barrier at a full scale, engineers should consider the impulsive pressure to secure the barrier’s stability on the target site.

Richtmyer–Meshkov instability of an unperturbed interface subjected to a diffracted convergent shock

The Richtmyer–Meshkov (RM) instability is numerically investigated on an unperturbed interface subjected to a diffracted convergent shock created by diffracting an initially cylindrical shock over a rigid cylinder. Four gas interfaces are considered with Atwood number ranging from $-0.18$ to 0.67. Results indicate that the diffracted convergent shock increases its strength gradually and reduces its amplitude quickly when it propagates towards the convergence centre. After the strike of the diffracted convergent shock, the initially unperturbed interface deforms with a bulge structure at the centre and two interface steps at both sides, which can be ascribed to the non-uniformity of the pressure distribution behind the diffracted convergent shock. With the decrease of Atwood number, the bulge structure becomes more pronounced. Quantitatively, the interface amplitude experiences a fast but short growing stage and then enters a linear stage. A good collapse of the dimensionless amplitude is found for all cases, which indicates a weak dependence of the growth rate on Atwood number in the deformed shock-induced RM instability. Then the impulsive theory is modified by eliminating the Atwood number and considering the geometry convergence, which well predicts the amplitude growth for the deformed shock-induced RM instability. Finally, the underlying mechanism is decoupled into three parts, and it is found that both the impulsive pressure perturbation and the geometry convergence promote the growth of interface perturbation while the continuous pressure perturbation inhibits the growth. As the Atwood number decreases, the impulsive perturbation plays an increasingly important role, which suggests that the impulsive perturbation dominates the deformed shock-induced RM instability at the linear stage.