Front Slope Research Articles

Fully Nonlinear Potential Flow Simulations of Wave Shoaling Over Slopes: Spilling Breaker Model and Integral Wave Properties

A spilling breaker model (SBM) is implemented in an existing two-dimensional (2D) numerical wave tank (NWT), based on fully nonlinear potential flow (FNPF) theory and the boundary element method (BEM), in which an absorbing surface pressure is specified over the crest of impending breaking waves (detected based on a maximum front slope criterion) to simulate the power dissipated during breaking. The latter is calibrated to match that of a hydraulic jump of parameters identical to local wave properties (height, celerity, $$\ldots $$ ). Although this model is not aimed at being fully physical in the surfzone, it allows more accurately simulating properties of fully nonlinear shoaling waves than standard empirical absorbing beaches (AB). After assessing the convergence with the discretization of 2D-NWT results for strongly nonlinear shoaling waves, simulations are first validated based on laboratory experiments for non-breaking and breaking waves, shoaling up a mild slope; a good agreement is found between both. The NWT is then used to compute fully nonlinear local (height, celerity, asymmetry) and integral (mean-water-level, radiation stress) properties of periodic waves shoaling over mild slopes. Discrepancies with standard results of wave theories are discussed in light of fully nonlinear effects modeled in the NWT. While only periodic waves are considered here, the SBM could be applied to shoaling irregular waves, for which the breaking point location will constantly vary, which would be advantageous compared to an AB fixed in space. For such cases, besides its more physical energy absorption, the SBM would allow better preventing wave overturning that may occur far from shore due to nonlinear wave–wave interactions and otherwise interrupt the FNPF–NWT simulations.

Experiment on wave overtopping of a vertical seawall on coral reefs in large wave flume

Coral reefs are widely distributed in the South China Sea, and its topography is different from the gentle slope of the coastal continental shelf, which has a great impact on wave propagation and deformation. At the same time, reefs are located in a harsh marine environment, so these factors having a profound effect on the stability of the backfilled sand island and the effective operation of other ancillary facilities. Seawall is an important protective structure in the protection works of reefs, and the wave overtopping of seawall plays a decisive role in the engineering safety of reefs. At present, there are few studies on the wave overtopping of reefs around the world, and the existing formula for calculating wave overtopping discharges over seawall on gentle slope terrain is not applicable to reefs terrain, so detailed research on wave overtopping of a vertical seawall on coral reefs is needed. A series of experiments are carried out in the Large Wave Flume (LWF) of Tianjin Research Institute of Water Transport Engineering (TIWTE), which is 456 m long, 12 m deep and 5 m wide. The maximum wave height generated by LWF is 3.5 m, and the wave period range is from 2 to 10 s. The model layout includes 3 parts: Deep-water zone, steep slope zone and platform zone. The depth of the deep-water zone is 5 m. The front slope is divided into 3 sections with slope 1:1, 1:4 and 1:15. The steep slope toe is 330 m away from the wave generator. The strongly non-linear physical process of wave transmission and breaking can be reproduced by this physical model. Based on Froude similarity criterion and a 1:15 scale model, the propagation and deformation process of regular waves on reef-top with seawall is analyzed. The effects of wave height, wave period, water depth and the distance between seawall and reef-edge on the mean overtopping discharge are studied. The results show that the mean overtopping discharge increases significantly with increasing of wave height and period, while it decreases with decreasing of water depth. However, the mean overtopping discharge is not the monotone function with distance. Mostly the mean overtopping discharge decreases with increasing distance. When wave period is longer than 13.56 s, the mean overtopping discharge decreases firstly, then increases a little, finally decreases with increasing distance. The dimensionless mean wave overtopping discharge increases as the wave steepness decreases for given wave height. The dimensionless mean wave overtopping discharge is found to be functions of relative freeboard height, the dimensionless mean wave overtopping discharge decreases as relative freeboard height increases for given wave conditions. On the basis of the experimental data, a formula considering the effects of wave height, wave period, water depth and the distance between seawall and reef-edge on the wave overtopping, is presented to estimate the mean wave overtopping discharge of a vertical seawall on coral reefs.

Construction Control Method and Application of Hydropower Project Based on Permanent and Temporary Monitoring

According to the permanent and temporary monitoring results, the warning boundary method and the mathematical physical model method are used for early warning and forecasting, and the construction measures are dynamically adjusted to form a construction control method based on safety monitoring technology. The application of the method which combines permanent monitoring with temporary monitoring on the front slope of the tail water outlet of the left bank, the upstream side wall of the 7#∼8# machine on the right bank, and the downstream abutment of the 9#∼10# unit section of Wudongde Hydropower Station, shows that it can fully grasp the stability of surrounding rock during construction period of slope and underground caverns. Through the early warning and forecasting, the mechanism of deformation is analyzed, the construction measures are adjusted in time, and the effect of the measures is evaluated, which plays an important role in ensuring the safety of the construction period.

Simultaneous application of two laser-induced fluorescence approaches for film thickness measurements in annular gas-liquid flows

This paper is devoted to the simultaneous application of two spatiotemporally resolved optical techniques capable of liquid film thickness measurements, namely Planar Laser-Induced Fluorescence (PLIF) and Brightness-Based Laser-Induced Fluorescence (BBLIF), to co-current downward annular gas-liquid flows. A single laser sheet is used to excite the liquid film, which has been seeded with a fluorescent dye, along a longitudinal/vertical plane normal to the pipe wall. Two cameras, one for each technique, are placed at different angles to the plane of the laser sheet in order to recover, independently by the two techniques, the shape of the gas-liquid interface along this section. The effect of the angle between the laser sheet and the PLIF camera axis is also investigated. In film regions where the gas-liquid interface is smooth and flat, the conventional approach used for interpreting PLIF data is affected by total internal reflection of the fluorescent light at the free surface, or “mirror effect”, which leads to an overestimation of the film thickness that increases as the angle between the laser sheet and the camera axis is decreased. Nonetheless, local features such as light intensity maxima or minima are often located within the fluorescent signals that correctly identify the true interface, which in these conditions also coincides well with the BBLIF film-thickness measurement. When a correction for the mirror effect based on simple flat-film optical calculations is applied, this leads to PLIF results that correspond well to the true film thickness. Interestingly, it is further found that interfacial three-dimensionality, and in particular azimuthal/circumferential non-uniformity, can lead to underestimation of film thickness by PLIF that in some cases counteracts the overestimation due to the mirror effect. Smaller angles between the laser sheet and camera axis make PLIF less susceptible to this error. In regions where the film surface is rough, including on the surface of disturbance waves, the mirror effect is suppressed. The BBLIF measurement, on the other hand, is affected by loss of signal sensitivity or saturation in thick film regions, as well as distortions at complex or multiple interfaces in agitated flow regions with significant wave activity. Direct comparisons between PLIF and BBLIF measurement data confirm that local overestimations of the film thickness by the latter occur in film regions with higher interfacial curvature, especially at the front slopes of waves and around gas bubbles entrained in the liquid even in smooth films, while underestimations occur in regions with multiple interfaces and inside bubbles although it is often the case that features such as bubbles can be identified and corrected for in simple flows with smooth interfaces. Correction procedures are developed to compensate distortions caused by both methods that make these techniques more accurate for standalone employment. In highly complex, three-dimensional flows, the simultaneous application of both techniques is highly recommended to attain the most reliable information.

Piecewise loading bed for reversible adsorption of VOCs on silica gels

Abstract The vacuum swing adsorption (VSA) with silica gel (SG) is proved to be a promising method for the recovery of volatile organic compounds (VOCs). The adsorption mechanisms of o-xylene on silica gels with different pore size have been revealed through the mathematic modeling of adsorption isotherms. The analysis of adsorption kinetics indicates that SG with micropore shows a steep concentration front and a long breakthrough time due to the strong adsorption force field, negligible transfer resistance and compressive effect of favorable isotherm. However, the reversible capillary condensation and mass transfer resistance cause a dispersed front and a short breakthrough time for mesoporous SG. The fast desorption rate makes mesoporous SG more energy-efficient compared with SG with micropore. Accordingly, to further improve the front slope and utilization of mesoporous SG in the adsorption process, a small amount of SG with micropore was loaded in the end of the fixed bed. The breakthrough time of the piecewise loading bed increased by 55.8% at the same loading volume with single mesoporous SG. The energy consumption was observed to exhibit an obviously decrease from 1.819 kWh/m3 to 1.295 kWh/m3, which proved that the piecewise loading method could recover VOCs in a more energy-saving way.

Stability of Rubble Mound Breakwaters—A Study of the Notional Permeability Factor, Based on Physical Model Tests

The Van der Meer formulae for quarry rock armor stability are commonly used in breakwater design. The formulae describe the stability as a function of the wave characteristics, number of waves, front slope angle and rock material properties. The latter includes a so-called notional permeability factor characterizing the permeability of the structure. Based on armor stability model tests with three armor layer compositions, Van der Meer determined three values of the notional permeability. Based on numerical model results he added for a typical layer composition one more value. Based on physical model tests, the present paper provides notional permeability factors for seven layer compositions of which two correspond to the compositions tested by Van der Meer. The results of these two layer compositions are within the scatter of the results by Van der Meer. To help determination of the notional permeability for non-tested layer compositions, a simple empirical formula is presented.

Giant sublacustrine landslide in the Cretaceous Songliao Basin, NE China

AbstractMass failure deposits in lacustrine settings are some of the most understudied facies associations in the ancient or modern rock record. We integrated seismic data and well logs to investigate the external morphology, internal architecture and deformation and reservoir distribution of the sublacustrine landslides in the Cretaceous Nengjiang Formation of the Songliao Basin (SLB). A large‐scale sublacustrine landslide, named the Qi‐Jia sublacustrine landslide (QJSL), has been identified in the Nengjiang Formation of the SLB. The QJSL is currently the largest known sublacustrine landslide in the world. This landslide covers an area that exceeds 300 km2, with an estimated volume of 30 km3. Seismic imaging and mapping reveal that the QJSL can be recognized by several distinguishing seismic characteristics: discontinuous and internal chaotic seismic facies, compressional structures in the downslope region, irregular top and basal surfaces and erosional grooves in basal shear surfaces. The QJSL is 20–200 m thick, and is composed of a succession of fine‐grained deposits. Sandy layers are present but sparse and thinner than 16 m, and form reservoirs of the petroleum discoveries in this area. Our analyses show that the mechanism that triggered the collapse of the QJSL is attributed to rapid deposition and deltaic progradation. This study demonstrates that sand‐rich sublacustrine landslides formed at delta front slope can serve as conventional reservoirs in the lake centre, and provide a new target for subaqueous hydrocarbon exploration and development.

A low-cost fiber based displacement sensor for industrial applications

In this paper, a low-cost fiber optic displacement sensor (FODS) using a bundle of plastic optical fiber (POF) as a probe is developed and presented. The sensor consists of a high power light emitting diode (LED) as light source, a probe with multiple receiving plastic optical fiber and a photodiode detector. The sensor is characterized at millimeter distance and the sensor output is analyzed from 0 mm to 13 mm displacement. The sensitivity of the sensor is found to be 5.38 mV/mm over 2.6 mm sensing range. The sensor is very useful for close distance target since it is highly sensitive at the front slope. The low development cost, high degree of sensitivity and simplicity of the design make it suitable for wide range of industrial applications.

A semi-empirical formula for calculating the breaking depth of plunging waves

ABSTRACT A new semi-empirical formula for calculating the breaking depth of plunging breakers is proposed in this study. The shallow water equation is used as the governing equation, and the wave front slope, which is one of the key parameters that governs the breaking criterion, is obtained from it analytically. The analytical formula was then modified based on both physical considerations and historical laboratory data. The accuracy of the resulting semi-empirical formula was examined using two sets of new laboratory data – including laboratory experiments performed by the authors – in order to verify its applicability. The results indicate that the proposed new formula is more accurate than existing formulas.

Features of formation of wave front slopes on the telescope aperture at different vertical profiles of optical atmospheric turbulence

Features of formation of wave front slopes on the telescope aperture at different vertical profiles of optical atmospheric turbulence

Holocene environmental changes in Red River delta, Vietnam as inferred from the stable carbon isotopes and C/N ratios

The present study applied stable carbon isotopes, C/N ratios, and sedimentological indicators to reconstruct environmental changes during Holocene and to test the hypothesis that $$\updelta ^{13}\hbox {C}$$ and C/N ratios are accurate proxies of sea level change in the Red River delta (RRD), Vietnam. A 36 m long sediment core was mechanically drilled in the wave-dominated region of the RRD. The covariation of lithological characteristics, sediment grain-size distribution and geochemical proxies (LOI, TOC, C/N, $$\updelta ^{13}\hbox {C}$$ ) suggested that the sediment core could be divided into six depositional environments, consisting of sub- and inter-tidal flats (formed before 8860 cal. year BP), shelf-prodelta, delta front slope (formed from 8860 to 2290 cal. year BP), delta front platform, tidal flat, and flood plain (from 2290 to 0 cal. year BP). Covariation of $$\updelta ^{13}\hbox {C}$$ and C/N ratios in the sediment core allowed for tracing the origin of sedimentary organic carbon, which shifted from the dominance of mangroves and C3 plants at the sub- and inter-tidal flats to marine phytoplankton at the shelf-prodelta and delta front slope. The sedimentary sources of the delta front platform, tidal flat and flood plain were a mixture of phytoplankton and C3 plants, with the later source being dominant.

Hydraulic Stability of the Armor Layer of Overtopped Breakwaters

Mound breakwaters with significant overtopping rates in depth-limited conditions are common in practice due to social concern about the visual impact of coastal structures and sea level rise due to climatic change. For overtopped mound breakwaters, the highest waves pass over the crest producing armor damage, not only to the front slope, but also to the crest and the rear slope. To guarantee the breakwater stability, it is necessary to limit the armor damage in the three parts of the structure: Front slope, crest, and rear slope. This paper describes the hydraulic stability of the armor layer of medium and low-crested structures in wave breaking conditions. Small-scale physical model tests were carried out with different relative crest freeboards and three armor units: Rocks, cubes, and Cubipods. The armor damage progression in the front slope, crest, and rear slope was analyzed using the Virtual Net method to consider the heterogeneous packing and porosity evolution along the armor slope. A comparison is provided between the hydraulic stability of the different armors and their relationship with the measured overtopping volumes.

Germination responses to abiotic stress shape species distributions on coastal dunes

Plant species occupy distinct zones on coastal dunes, but the mechanisms limiting their distributions have not been fully explained. We combined field surveys of plant distributions and abiotic conditions with controlled germination experiments to assess the contribution of germination requirements to plant zonation. Species presence and abiotic conditions were measured in ten transects across the barrier dune at Waquoit Bay, Massachusetts. Germinating seeds of six species were exposed to four fully crossed treatments: pre-treatment (soaked in fresh water, soaked in salt water, or not soaked), temperature (low, moderate, or high), soil salinity (none, moderate, or high), and light (full light, shade, dark). Species distributions in the field were affected by both distance from the shore and presence of dominant shrubs. Germination tolerance of soil salinity reflected species zonation: species found on the front slope of the dune tolerated salinity, while germination of other species was limited by salinity alone or by salinity in combination with high temperature. Shrubs reduced soil surface temperature and decreased light, but these conditions had limited effects on germination. These results indicate that limitations to germination can contribute to explaining species distributions on coastal dunes.

Liquid level sensor using two fiber bundles

The two-tier detection of liquid level using two fiber bundles as sensor has been successfully demonstrated. Each fiber bundle is paired with a reflector displacement device (RDD) to detect liquid level in accordance with its detection area. Based on displacement sensor, the working principle of system is by utilizing hydrostatic pressure to shift the reflector attached to the membrane. Detection of liquid level is done through changes of reflected light intensity from the reflector that goes into each sensor probe. The results show that the sensor can be applied to the front slope or back slope area. Working area and resolution of sensors working on the front slope area are 0–130 cm and 1 cm, meanwhile for the back slope area are 0–50 cm and 0.1 cm.

Numerical Research on the Mixture Mechanism of Polluted and Fresh Air at the Staggered Tunnel Portals

In longitudinal ventilation, circulating air is formed in portals for closely spaced twin tunnels, which causes mixing between the polluted air exhausted from one tunnel and the fresh air flow of another tunnel, thus leading to the rising costs of ventilation system construction and operation. In this study, for the closely spaced tunnel with staggered inlet and outlet, the computational fluid dynamics (CFD) numerical simulation method was adopted to reveal flow characteristics of the circulating air as well as variation rules of the circulating air mixing ratio φc with tunnel structure and operation parameters. Results show that both reducing inlet air velocity and increasing outlet air velocity and lateral distance can reduce the impact of the negative-pressure zone at the tunnel entrance on the jet flow structure at the tunnel exit, thus weakening the circulating air. When the inlet is placed behind or aligned with the outlet (staggered distance ∆l ≤ 0), φc will increase linearly along with the increase of staggered distance; when the inlet is placed before the outlet (∆l > 0), φc will first increase and then decrease with the increase of staggered distance. An expression to predict circulating air mixing ratio was created by sections. The predictions show a good correlation with the measurements and indicate that the front slope gradient of the tunnel portal is also one of the factors affecting the circulating air mixing ratio.

Numerical Simulation of Wave Breaking Over a Submerged Step with SPH Method

Wave breaking over a submerged step with a steep front slope and a wide horizontal platform is studied by smoothed particle hydrodynamic (SPH) method. By adding a momentum source term and a velocity attenuation term into the governing equation, a nonreflective wave maker system is introduced in the numerical model. A suitable circuit channel is specifically designed for the present SPH model to avoid the nonphysical rise of the mean water level on the horizontal platform of the submerged step. The predicted free surface elevations and the spatial distributions of wave height and wave setup over the submerged step are validated using the corresponding experimental data. In addition, the vertical distributions of wave-induced current over the submerged step are also investigated at both low and high tides.

Reflex erection in the rat: reciprocal interplay between hemodynamic and somatic events

BackgroundPenile erection is a complex reflex under spinal control and modulated by the brain. The hemodynamic events under autonomic control and the perineal muscles somatic activity are interconnected during the reflex erection at the spinal level, however if the afferent feedback on the corpus cavernosum pressure during an erection affects the somatic activity (perineal muscles contractions) and vice versa is not known. This study was aimed to test this hypothesis using a rat model.MethodsIntracavernous pressure (ICP) and bulbocavernosus (BC) muscle EMG were recorded during reflex erections elicited with dorsal penile nerve (DNP) electrical stimulation in anaesthetized acutely spinalized SD rats with surgically (bilateral cavernous nerve section, CnX, n = 8) and pharmacologically (trimetaphan infusion, TMPh, n = 8) abolished pressor response, or with surgically (bilateral section of the motor branch of the pudendal nerve, PnX, n = 7) and pharmacologically (1 mg/kg d-tubocurarine, n = 8) blocked perineal muscles contractions, or with interrupted afferent input from the penis (bilateral crush of the dorsal penile nerve, DPnX, n = 7). Control rats (n = 8) received no intervention.ResultsModerate positive correlations were found between net parameters of pressor and somatic activity during DNP-stimulation induced reflex erection in spinal rats, particularly the speed of pressor response development was positively correlated to EMG parameters. No changes of EMG activity were found in CnX rats, while the decrease of BC EMG in TMPh-treated males can be attributed to direct inhibitory action of TMPh on neuromuscular transmission. Pressor response latency was increased and ICP front slope decreased in dTK and PnX rats, indicating that perineal muscles contraction augment pressor response. DPN crush had little effect on ICP and EMG.ConclusionAfferent input on the level of intracavernous pressure and the perineal muscles activity has minimal impact on, correspondingly, the somatic and the autonomic components of the reflex erection in spinal males, once the reflex has been initiated.

Techniques of Creating Optical Effects of Three-dimensional construction, plane composition and constructs at the Gardens of Versailles

This research goes beyond previously existing research in classifying the visual effects techniques employed at the Gardens of Versailles; the research is based on new on-site confirmation of the effects, and it also details some newly discovered visual effects techniques. The following three points have been made clear. First, looking west from the terrace above the Latona Fountain, the three vanishing points of the lines of perspective of the Latona flower beds, the Royal Way (the Green Carpet), and the Grand Canal, respectively, appear to gradually climb higher and higher, due to the difference between the slope of the land and the slope of the surface of the water, and this evokes an impressive soaring sensation. Second, the two pieces of land at the front slope downwards, and the Grand Canal is flat, but the illusion of an intersecting slope causes the surface of the water of the Grand Canal to appear to be facing forwards and rising up, in an extremely striking visual effect. Third, we can assume that Le Nôtre composed these effects deliberately.

An Artificial Neural Network for Prediction of Front Slope Recession in Berm Breakwater

An Artificial Neural Network for Prediction of Front Slope Recession in Berm Breakwater

Calving relation for tidewater glaciers based on detailed stress field analysis

Abstract. Ocean-terminating glaciers in Arctic regions have undergone rapid dynamic changes in recent years, which have been related to a dramatic increase in calving rates. Iceberg calving is a dynamical process strongly influenced by the geometry at the terminus of tidewater glaciers. We investigate the effect of varying water level, calving front slope and basal sliding on the state of stress and flow regime for an idealized grounded ocean-terminating glacier and scale these results with ice thickness and velocity. Results show that water depth and calving front slope strongly affect the stress state while the effect from spatially uniform variations in basal sliding is much smaller. An increased relative water level or a reclining calving front slope strongly decrease the stresses and velocities in the vicinity of the terminus and hence have a stabilizing effect on the calving front. We find that surface stress magnitude and distribution for simple geometries are determined solely by the water depth relative to ice thickness. Based on this scaled relationship for the stress peak at the surface, and assuming a critical stress for damage initiation, we propose a simple and new parametrization for calving rates for grounded tidewater glaciers that is calibrated with observations.