Front Slope Research Articles

An experimental study on the reshaping of berm breakwaters under irregular wave attacks

The main idea concerned with the design of berm breakwaters is to construct a less expensive structure with reshaping berm. An experimental study on the front slope stability of homogeneous berm breakwaters has been carried out in a large number of 2D model tests at Tarbiat Modares University. In this paper, the results of this experimental study are presented conjointly with a formula for estimation of berm recession as the most important parameter for describing the reshaping. This includes the influence of wave height and period, storm duration, berm width and elevation variations on the stability of berm breakwater with different armor stone sizes. A total of 222 tests have been performed to cover the impact of these parameters. According to the present research, one can observe that considering different armor stone sizes, berm width is a significant parameter concerning reshaping of a berm breakwater that has not been covered in previous works, so that as the berm width increases the amount of berm recession decreases. To assess the validity of the present formula, comparisons are made between the estimated berm recessions by this formula and formulae given by other researchers, showing that the estimation procedure foretells berm recession well according to the present data. It is observed that the recession estimated by the present formula has comparatively better correlation with the present experimental data, and also with other experimental results within the range of parameters tested.

On front slope stability of berm breakwaters

The short communication presents application of the conventional Van der Meer stability formula for low-crested breakwaters for the prediction of front slope erosion of statically stable berm breakwaters with relatively high berms. The method is verified (Burcharth, 2008) by comparison with the reshaping of a large Norwegian breakwater exposed to the North Sea waves. As a motivation for applying the Van der Meer formula a discussion of design parameters related to berm breakwater stability formulae is given. Comparisons of front erosion predicted by the use of the Van der Meer formula with model test results including tests presented in Sigurdarson and Van der Meer (2011) are discussed. A proposal is presented for performance of new model tests with the purpose of developing more accurate formulae for the prediction of front slope erosion as a function of front slope, relative berm height, relative berm width, method of armour stone placement, and hydraulic parameters. The formulae should cover the structure range from statically stable berm breakwaters to conventional double layer armoured breakwaters.

Effect of frontal slope on waveform evolution of a depression interfacial solitary wave across a trapezoidal obstacle

Waveform evolution associated with a depression interfacial solitary wave (ISW) over uniform slope or slope-shelf with different front slopes has been observed in many laboratory experiments and field studies since the 1980s, and by numerical modeling in more recent time. However, attention was mainly focused on waveform validation with KdV theory, wave run-up, reflection, energy dissipation and evolution on emergent mild uniform slope, rather on wave evolution and inversion across the plateau of a slope-shelf with steep front slopes, which are common in field conditions. Since it is often difficult to measure the entire process of waveform evolution in the field, laboratory experiments are adopted as an alternative to compliment field observations. This paper presents the results of laboratory experiments on ISW evolution across a submerged trapezoidal obstacle with four different front slopes, ranging from mild to very steep and vertical. Our results indicate that not only the likelihood of internal hydraulic jump, waveform inversion and the strength of internal wave breaking reduced, but more wave energy dissipated as well, as the front slope steepened. Upon using Hilbert–Huang transform to analyse the wave profiles recorded at four probe locations along the wave flume, the variability in the instantaneous characteristic wave period can be detected while an ISW propagated across a trapezoidal obstacle.

Fiber Optic Displacement Sensor Using Multimode Plastic Fiber Probe and Tooth Surface

The principle of operation, experimentation, and performance of a fiber optic displacement sensor on a tooth surface is presented. The performances of this sensor are investigated by correlating the detector output with different probe configurations and various teeth samples with different surface reflectivity properties. With a multimode plastic bundled fiber probe, the sensitivities for the molar, canine, hybrid composite resin, and acrylic surfaces are obtained at 0.9667, 0.775, 0.5109, and 0.25 mV/mm, respectively, with a good linearity of more than 99% based on the analysis of the front slope. With a multimode plastic coupler, the sensitivities for the molar, canine, hybrid composite resin, and acrylic surfaces are obtained at 0.3538, 0.2951, 0.2069, and 0.1579 mV/mm, respectively. This proves that the sensor is capable of discriminating between different teeth surfaces. Such results are useful as guidelines for tooth surface related research, such as tooth surface profiling and measurement of tooth surface roughness.

Nonlinear distortion of optical pulses by self-produced free carriers in short or highly lossy silicon-based waveguides

An explicit analytical solution for the asymmetric attenuation of optical pulses by self-produced free carriers in silicon waveguides is derived. It allows us to quantify the pulse distortion and to calculate explicitly the free-carrier density and the nonlinear phase shifts caused by the Kerr effect and by free-carrier refraction. We show that omitting two-photon absorption (TPA) as a cause of attenuation and accounting only for free-carrier absorption (FCA) as done in the derivation appropriately models the pulse propagation in short or highly lossy silicon-based waveguides such as plasmonic waveguides with particular use for high-energy input pulses. Moreover, this formulation is also aimed at serving as a tool in discussing the role of FCA in its competition with TPA when used for continuum generation or pulse compression in low-loss silicon waveguides. We show that sech-shaped intensity pulses maintain their shape independently of the intensity or pulse width and self-induced FCA may act as an ideal limiter on them. Pulse propagation under self-induced free-carrier absorption exhibits some features of superluminal propagation such as fast or even backward travelling. We find that input pulses need to have a sufficiently steep front slope to be compressible at all and illustrate this with the FCA-induced pulse broadening for Lorentzian-shaped input pulses.

STABILITY OF INTERLOCKING ARMOUR UNITS ON A BREAKWATER CREST

The hydraulic stability of single layer, interlocking armour units on low crested and submerged breakwaters was investigated in 2D hydraulic model tests. Displacements of armour units and rocking were monitored and have been applied as indicators for the armour layer stability on the crest, front and rear slope. The effect of freeboard, packing density and wave steepness on the armour layer stability have been investigated. The stability of interlocking concrete armour units on low crested and submerged structures is qualitatively different from rock armour. About 40% to 50% larger armour units are required on the seaward slope and crest of low crested structures (as compared to conventional high crested breakwaters). About 35% larger armour units are required on the rear slope. Larger armour units are not required on submerged breakwaters if the water depth on the crest exceeds 50% of design wave height.

STABILITY OF HARDLY RESHAPING BERM BREAKWATERS

The present paper deals with stability of berm breakwaters designed to be hardly or sometimes partly reshaping. Burcharth (2008, 2011) showed by comparison to the performance of a prototype berm breakwater that the Van der Meer formulae for stability of conventional rock armour including low crests could predict the deformations of the front slope in terms of the eroded area. The present paper verifies the method by comparison to model test results. It is found that the Van der Meer formula for plunging waves predicts very well the eroded area of the reshaped profile, even if it is applied in the surging wave area. Moreover, a simple method to estimate the erosion area based on recession formulae and the depth of intersection of reshaped and initial profile is presented and is applicable for hardly reshaping to fully reshaping. Even when using the only very simple and inaccurate estimate of the depth of intersection the last method leads to scatter quite similar to the first method when considering hardly and partly reshaping berm breakwaters. The influence of the slope angle is though expected to be more correctly included for hardly reshaping breakwaters using the method for straight non-overtopped slopes when the slope angle is 1:1.5 or flatter.

Plant Species Diversity of Highway Roadsides in Southern New England

Mowed roadsides represent a significant proportion of the grassland habitat in New England, but they receive little attention from naturalists. We sought to test the assumption that mowed roadsides are ecological wastelands dominated by deliberately seeded introduced perennial grass species. Surveys of seven sites in Rhode Island during the summer of 2008 revealed that roadsides are important refugia for grassland plants, including two species and two subspecies believed to be rare in New England. We found 80 grass and forb species, 45% of which are native. We also examined the effects of distance from the road and topography on the relative distributions of annual versus perennial species and of native versus introduced species. Perennial species cover increased with distance from the road at all seven sites, and the number of perennial species increased at five sites. The front slope had the most annual species and the most annual cover at all sites. Perennial species dominated the back slope, swale, and flat areas. Neither distance from the road nor topography had a clear effect on the distribution of native species relative to introduced species. Highway roadsides in southern New England are not an ecological wasteland, but rather are a complex upland grassland habitat reminiscent of the agricultural grasslands which dominated the region in the nineteenth century.

Sequence lithofacies paleogeography and reservoir potential of the Maokou Formation in Sichuan Basin

Abstract Based on multidisciplinary analyses of outcrops, core description and log data, two types of sequence boundary are identified, including a partially exposed unconformity surface and a drowned unconformity surface. The Maokou Formation in the Sichuan Basin is divided into three third-order sequences, each lasting 3.3 Ma on average. In this study, system tracts are used as mapping unit to reconstruct systematically the lithofacies paleogeography map within the sequence framework, and to describe paleogeographic features. The results indicate that the Sichuan Basin is dominated by shallow, open marine carbonate platform deposits during the Middle Permian Maokou stage, in which a range of sedimentary facies developed, such as shallow water open platform, deeper water open platform, platform margin bank, and platform front slope facies. Physical property analysis indicates that shallow calcsparite granular limestone has good reservoir qualities, especially after the reservoir rock is reworked by dolomitization and epigenetic karstification. Thus, dolomite reservoir, paleokarst reservoir and shallow bank reservoir make up the main reservoirs of the Maokou Formation. The study on reservoir distribution patterns within the sequence framework indicates that HST reservoirs are relatively well developed, especially the shallow bank sedimentary regions of SQ2-HST in the western-southwestern Sichuan Basin and the paleokarst development area of SQ3 are the most favorable.

急勾配を有するリーフ地形上の波浪エネルギーによる波浪場評価に関する研究

We investigate wave height change on the coral reef which has steep front slope. Data of both regular and irregular wave experiments were used in order to study characteristics of wave deformation including wave breaking. By using a parameter Hrms/d, properties of energy loss by wave breaking on the reef can be obtained. We modified wave energy balance equation model developed by Tajima and Madsen (2005) in order to estimate wave energy on the coral reef. Calculation results show good agreement with experimental data.

Structure and dynamics of the midshelf front in the New York Bight

The structure and variability of the wintertime midshelf front in the New York Bight is examined using moored observations of currents and hydrography during 2007. The front is located near the 50 m isobath, inshore of the shelf break front and offshore of estuarine outflow plume fronts. It spans the water column and is the boundary between cooler, fresher, and less dense inner shelf water and warmer, saltier, and denser outer shelf water. The mean hydrographic front slopes upward offshore, and there is an associated equatorward along‐shelf 5–10 cm/s surface‐intensified current jet. The mean across‐shelf circulation is offshore near the surface and onshore at depth. The across‐shelf velocity is convergent and strengthens across‐shelf property gradients with a time scale for gradient doubling of approximately 8 days. Tidal analysis of currents and temperatures suggests that tidal shear dispersion is not an important mechanism for midshelf front formation. The frontal structure and location are roughly consistent with the theory of bottom boundary layer advected fronts, suggesting that multiple estuarine outflows are collectively responsible. Pulses of strong offshore wind cause the breakdown of the across‐shelf thermal wind balance, which has been commonly assumed to hold in shelf environments. Observed shear significantly exceeds thermal wind shear at middepths, where observation of low‐gradient Richardson number indicates the importance of vertical mixing. The response of currents to wind fluctuations is asymmetric, whereby the combination of upwelling favorable and offshore winds or downwelling favorable and onshore winds produces a stronger response than winds from the remaining quadrants.

파랑하중에 의한 경사식방파제의 제체와 주변지반의 침하거동

방파제는 태풍 또는 바람 등으로 발생된 파랑으로부터 해안, 항만시설을 보호하고 항내 수역의 정온도 확보를 위한 중요한 구조물이다. 국내에 가장 일반적인 방파제중 하나인 경사식 방파제를 본 연구과제로 선정하였다. 경사식 방파제는 정적조건만을 고려하여 설계되었다. 최근에 파랑작용에 따른 동적파압도 설계에서 고려하고 있다. 하지만 동적파압을 경사식 방파제의 경사면에만 국한하여 적용시키고, 적용된 파압 역시 등가파압으로 가정하였다. 이것은 방파제에 실제로 작용하는 파압분포와 다르다. 따라서 본 연구에서는 방파제경사면에 작용하는 파압을 등가파압이 아닌 실제 작용하는 시간이력파압을 적용하고 파압을 경사방파제의 경사면뿐만 아니라 해저지반에 추가적으로 고려하였다. 이를 반영한 수치해석을 통해 산출된 최대침하량이 현재의 설계법에 의해 산출된 최대침하량과 비교 시 상당한 차이가 있는 것으로 나타났다. A breakwater is a important structure for both calmness of harbor and protection of the port facilities from waves generated from typhoons or wind. This study adopted the rubble mound breakwater, which is one of the most popular type of breakwaters in Korea. Rubble mound breakwater had been designed by considering only static condition previously. Recently, a dynamic wave-load due to waves has been also considered in designing breakwater. In design, the wave-load is assumed as an uniform load which only acts in the front slope of the breakwater. However, the assumption is not applicable in reality. In this study, therefore, a real-time wave-load acting on the breakwater instead of the uniform load is considered, and it is assumed to be acting on the seabed too. Based on the numerical analysis, it is found that there is a significant difference in the maximum settlement compared with the result predicted by the existing design method.

Experimental Investigation of Texture Gradients in Aluminium/Copper Plates Bonded through Explosive Welding Process

In this study, the commercial purity Al/Cu plates were bonded through the explosive welding process. The SEM/EBSD local orientation measurements were conducted to consider the changes in the microstructure and the development of texture gradients for the applied explosive loading. A particular attention was paid to the texture changes across the interface. The detailed local orientation measurements show that the ultra-fine grained layers are formed close to the bonding zone. The layers were characterized by the copper-type rolling texture components. The interface was outlined by a characteristic sharp transition between the two materials. However, in some places, local melted zones were also encountered, mainly in the front slope of the waves.

Paleogeographical restoration and ramp tectonic evidence in Tunisian Tellian domain: Ain El Bey-Bou Awen area

The imbrication’s area in northern Tunisia is the most external segment of Alpine range, where several associated folds types with thrust ramps are recognized within imbricate units beneath Numidian front slope. Their presence help to understand thrusting mechanisms installation through studied area. In fact, this zone was considered as a result of Paleogene gravitary slop (Kujawski (Ann Miner Geol Tunis (24):281, 1969); Caire (Ann Min Geol Tunis 26:87–110, 1973); Rouvier 1977), which is proved to be affected by major deep decollement, given rise to various structures, some are propagation folds, specific of foreland front, limited to this area, and those in more external position: Tunisian Atlas (Creusot et al. (C R Acad Sci Paris 314(Ser II):961–965, 1992); Ouali and Mercier (PII: S0191-8141(97):00048-5, 1997); Ouali 1984; Ahmadi et al. (J Struct Geol 28:721–728, 2006)). Various categories of fold ramps could be identified: frontal folds ramp NE–SW and others as lateral or oblique ramp with NW–SE trend (Aridhi et al. (C R Geosci 343:360–369, 2011)). The relation between various structures has been used as recognition tools of thrusting sequences and to propose a new deformation chronology. Delimited outcropping of these structures between two both parallel faults strikes with regional displacement, leads to interpret these faults as cogenetic tear faults of propagation thrusts; this fault separates two domains with different deformation styles from each other side.

The role of Ca2+, H+, and Cl− ions in generation of variation potential in pumpkin plants

The contributions of Ca2+, H+, and Cl− in generation of variation potentials (VP) in 3- to 4-week-old pumpkin (Cucurbita pepo L., cv. Mozoleevskaya) plants were assessed. During VP generation, transient alkalinization of the medium around the stem was recorded with a potentiometric method. The pH changes were kinetically similar to the electric potential changes and were apparently due to temporal suppression of the plasma-membrane electrogenic H+ pump. These data and the observed inhibition of VP in the stem zone treated locally with a metabolic inhibitor (NaN3) indicate that the VP generation is related to the reversible suppression of the H+-pump. The anion channel blocker (ethacrynic acid) decelerated significantly the front slope of VP and reduced the VP amplitude. A short-term increase in external Cl− concentration around the stem was observed during potential transients representing the VP front slope and the pulses integrated into VP. The removal of Ca2+ from extracellular medium inhibited the VP generation. It is proposed that Ca2+ plays a role in activation of anion channels and in the H+-pump inactivation. The VP generation is probably determined by a complex mechanism, with contributions from passive ion fluxes (Ca2+, Cl−) moving along the electrochemical gradients and from changes in the electrogenic pump activity.

Controls of Short-Term Base-Level Cycle on Macroscopic Heterogeneity of Reservoir: a Case Study of the Major Oil Layer of Liuzan Oilfield in Nanpu Sag

Based on the depositional model and characteristics of fan delta, the short-term base-level cycle of the third submember of the third member of Shahejie Formation （Es33）in North region major oil layer of Liuzan Oilfield of Nanpu Sag is divided into three basic categories applying high-resolution sequence stratigraphy with the reference to core and logging data, namely, deepening-upward asymmetrical type, shallowing-upward asymmetrical type and symmetrical type. Different variation models for macroscopic heterogeneity of reservoir belonging to different categories of short-term base-level cycle were established in this paper; it was further pointed out that the changes of base-level and the ancient landform were major factors controlling the characteristic discrepancy of macroscopic heterogeneity of reservoir. In fan delta plain area, the ancient landform is smooth. Deepening-upward asymmetrical cycle is mainly composed of braided river sand body, and the changes of base-level exert little control on porosity with significant control on permeability. At the delta front slope, the landform becomes steep. Deepening-upward asymmetrical cycle is mainly composed of underwater distributary channel with genetic mechanism of gravity flow. The vertical variations of porosity and permeability inside the cycle are rather complicated. Since the physical properties are mainly manifested as the control on autogenic cycle, they do not directly influence the changes of base level.

Study of Treatment Effect of Front Slope for Deng Cao-Tang Tunnel Outlet

Exampled with the project of front slope for Deng cao-tang tunnel outlet, the front slope is treated with prestressed anchorage cables. The reason of front slope cracking is analyzed. Moreover, the stress distribution of anchorage cables has been monitored so as to obtain the stress distribution in time. The results offer scientific basis with the treatment effect of front slope so that the safety of tunnel construction in ensured. The study has been great theoretical significance and practical value.

On the Transport of Buoyant Coastal Plumes

Abstract The role of discharge conditions and shelf geometry on the transport of coastal plumes is studied with a fully nonlinear, primitive equation hydrodynamic model. The physical setting is an estuarine channel with a small discharge Rossby number. By simulating different discharge magnitudes, buoyant plumes are shown to be succinctly described by a simple coastal front model. Three results emerge from the model analysis. First, the plume transport is given by T = γ0(g′ph2/2f ), where γ0 is a parameter dependent on the ratio of the front and the plume widths, g′p is the plume reduced gravity, h is the plume maximum depth, and f is the Coriolis parameter. Second, this model links the plume transport directly to upstream river conditions with T = γQr, where Qr is the river outflow and γ is a parameter that relates to entrainment, the geometry of the plume front and shelf slope, and the fraction of freshwater carried downshelf. Third, these equations reduce to analytic results previously established for special cases, providing useful formulas to estimate the plume transport from hydrographic and river discharge observations.

Optical Selection of Control Measure of some Rock Slope Along Lan-Cheng-Yu Oil Pipeline

ABSTACT: The K0526 +300 section of Lanzhou-Chengdu-Chongqing (short for Lan-Cheng-Yu) oil pipeline lies in the Sichuan-Shanxi border which has high mountains and deep valleys. Several-meters-high to tens-meter-high inner steep slope was formed by excavation of front slope, and most of the pipe trench and road located at the inner steep slope. “5.12” earthquake in 2008 triggered the unstable rock of K0526 +300 trench section to collapse, and the hazard did not damage the pipeline, but impacting of collapsed body destroyed protection wall outside the road embankment. In addition, the earthquake made rock mass loose, and some unstable rocks are faced with the risk of avalanche at any time, and the operation safety of pipelines was affect seriously. Base on field investigation of the rock slope, comprehensive evaluation of its stability and hazard was given, and two appropriate proposals of control measures were offered furthermore, and then the structure of optimal control method was designed based on structural mechanics theory. It provides a reliable evidence to eliminate the threat of unstable rock and ensure smooth and long-term operation of Lan-Cheng-Yu oil pipeline.

Laboratory experiments on waveform inversion of an internal solitary wave over a slope-shelf

Internal solitary waves (ISWs) have been detected in many parts of the world oceans, particularly over slope-shelf topography, on which signature of waveform inversion has been identified. The effects of these waves on engineering operations and ecological process have also been reported in the literature. This article reports the results of a series of numerical modeling and laboratory experiments on waveform evolution of a depression ISW in a nearly stratified two-layer fluid system, in which specific water depth ratios above the horizontal plateau of the trapezoidal obstacle were arranged to facilitate the occurrence of waveform inversion. Classifications of waveform instability (no instability, shear instability and overturning with breaking) on the slope are confirmed in the present laboratory study. Numerical results for waveform variation are also found in fair agreement with the laboratory measurements for cases without waveform inversion and minor internal breaking. Moreover, laboratory results revealed that the depth ratio of the stratified two-layer fluid above the plateau and the magnitude of the incident ISW were the two most important factors for promoting waveform inversion beyond a turning point, in addition to the requirement of a sufficient distance from the shoulder of the trapezoidal obstacle. These factors also influenced the outcome of the shoaling process, energy dissipation, internal wave breaking and turbulent mixing on the front slope, as well as the likelihood of waveform inversion on the horizontal plateau. Contrary to the common perception, it was also observed, at least from the results of the present laboratory experiments, that not all the incident ISWs of depression would produce waveform inversion on the plateau, where the upper layer was physical greater than the bottom layer, unless moderate incident wave was provided. The outcome might also be attributed to the limited distance from the shoulder onto the plateau in the present laboratory setup. However, once waveform inversion occurred on the plateau, it was found, among others, that: (1) the amplitude of the transmitted leading crest and trough might be as low as 30 and 20%, respectively, to the amplitude of the incident wave in depression; (2) the characteristic wavelength of the transmitted leading trough doubled while that of the crest was asymptotically one-half of the incident wavelength, despite the wide range variation in the depth ratios above the plateau; and (3) the transmitted potential wave energy of the leading crest contained 30% of the incident energy. Based on the results of present laboratory experiments, the range for the non-dimensional parameter α, which indicates the effect of nonlinearity and the promotion of waveform inversion on horizontal plateau, will be proposed.