Geomorfologia e estrutura superficial da paisagem de zonas costeiras rochosas: um estudo de caso na Ilha do Cardoso (Litoral Sul de São Paulo)

Com o intuito de contribuir para o conhecimento da geomorfologia litorânea de zonas costeiras rochosas, o presente estudo objetivou caracterizar a estrutura superficial da paisagem das escarpas litorâneas da Ilha do Cardoso (litoral sul de São Paulo). A metodologia consistiu na integração entre trabalhos, mapeamentos e descrições geológicas e geomorfológicas macroscópicas de campo, análises laboratoriais (petrografia) de amostras das unidades litológicas locais e análises de imagens aéreas e orbitais. Com relação a registros da estrutura superficial ligados predominantemente a configurações geomorfológicas e de níveis de base locais distintos das atuais, foram delimitados seis níveis de aplainamento em meio as serranias da Ilha, correlacionados com a geomorfologia litorânea descrita em estudos anteriores. Com relação a registros da estrutura superficial com maiores contribuições de processos atuais e subatuais, foram identificados e caracterizados feições morfológicas de detalhe e depósitos de blocos rochosos de fundos de vales fluviais serranos e de escarpas serranas sob influência direta do mar (costões rochosos). Efetuou-se a caracterização granulométrica, textural e litológica dos referidos registros, bem como ponderou-se sua contextualização na compartimentação da paisagem e na caracterização morfométrica, morfodinâmica, litológica e climática das Serranias da Ilha do Cardoso. Elencou-se que a diversidade da estrutura superficial rochosa local teria contribuição de nove distintos padrões de combinações entre depósitos, formas de relevo, unidades litológicas e processos exógenos, parte deles com sua génese tendo influência de variações climáticas inter-anuais locais e consequentes modificações sazonais na drenagem e escoamento superficial, e uma segunda parte ligada a distintas combinações entre as variações espaciais da caracterização mineralógica das unidades litológicas e dos fatores morfodinâmicos predominantes presentes na linha de costa da Ilha (segmentos expostos a processos lagunares versus segmentos expostos a processos de mar aberto). Geomorphology and surface structure of rocky coastal zones: study case on the Cardoso Island (south coast of São Paulo State, Brazil) A B S T R A C TIn order to contribute to the knowledge of coastal geomorphology of rocky coastal areas, the present study aimed to characterize the surface structure of the coastal escarpments of Ilha do Cardoso (south coast of São Paulo). The methodology consisted of integrating macroscopic geological and geomorphological mapping and field descriptions, characterizing patterns of precipitation and breaking waves in the area, laboratory analysis (petrography) of samples from local lithological units and analysis of aerial and orbital images. There were characterized nine distinct patterns of combinations between deposits, forms of detailed relief, lithological units and exogenous processes. The occurrences of such patterns of surface structure were contextualized amid the characterization of geomorphological compartmentation, precipitation patterns, the prevailing conditions of agitation of the waters surrounding the island, and the mapping and petrographic characterization of local lithological units. Thus, it was pointed out that the genesis of the island's surface structure patterns would have a contribution of overlaps between local inter-annual climatic variations and consequent seasonal changes in drainage and surface runoff, and to different combinations between the spatial variations of the mineralogical characterization of the lithological units and the predominant morphodynamic conditions present on the island (segments exposed predominantly to lagoon processes versus segments exposed to open sea processes versus segments exposed to fluvial action and runoff). The different lithological units of local hard rocks linked to different petrographic characterizations when exposed to the same morphodynamic conditions linked to the action of coastal waters result in features of detail relief and deposits quite different from each other in terms of degree of preservation and inclinations of the rocky platforms, as well as the dimensions and degrees of roundness of the rock fragments deposits. It was interpreted that such heterogeneities would have a contribution of different successibility of the different compositions and mineralogical arrangements of each local hard rock lithological units to the weathering patterns linked to each of the three sets of predominant morphodynamic processes operating in this coastal segmentKeywords: planning levels, coastal rocky cliffs, valley floor deposits, coastal geomorphology, rocky coasts

CFD SIMULATION OF MOTION RESPONSES OF A TRIMARAN IN REGULAR HEAD WAVES

CFD has proved to be an effective method in solving unsteady Reynolds–Averaged Navier-Stokes (RANS) equations for analysing ships in free surface viscous flow. The research reported in this paper is intended to develop a better understanding of the parameters influencing high-speed trimaran motions responses. Variations of gridding system and time step have been investigated and reliability analysis was performed in solving the RANS equations. Different turbulence models were investigated, and the SST Menter K Omega turbulence model proved a more accurate model than Realizable K-epsilon model. In order to validate the CFD method, the results of the motions response of a high- speed trimaran are compared against a set of experimental and numerical results from a 1.6 m trimaran model tested in various head seas conditions. The results suggest that CFD offers a reliable method for predicting pitch and heave motions of trimarans in regular head waves when compared to traditional low speed strip theory methods. Unlike strip theory, the effect of breaking waves, hull shape above waterline and green seas are considered in CFD application. A wave resonance phenomenon was observed and wave deformation as a result of wave-current-wind interaction in CFD was identified as the main source of discrepancy. The results from this work form the basis for future analysis of trimaran motions in oblique seas for developing a better understanding of the parameters influencing the seakeeping response, as well as passenger comfort.

Numerical simulation of wave interaction with a pair of fixed large tandem cylinders subjected to regular non-breaking waves

This paper presents the application of a two-phase Computational Fluid Dynamics (CFD) model to carry out a detailed investigation of nonlinear wave field surrounding a pair of columns placed in the tandem arrangement in the direction of wave propagation and corresponding harmonics. The numerical analysis is conducted using the Unsteady Reynolds-Averaged Navier-Stokes/VOF model based on the OpenFOAM framework combined with the olaFlow toolbox for wave generation and absorption. For the simulations, the truncated cylinders are assumed vertical and surface piercing with a circular cross-section subjected to regular, non-breaking fifth-order Stokes waves propagating with moderate steepness in deep water. Primarily, the numerical model is validated with experimental data for a single cylinder. Future, the given simulations are conducted for different centre-to-centre distances between the tandem large cylinders. The results show the evolution of a strong wave diffraction pattern and consequently, high wave amplification harmonics around cylinders are apparent.

Regression methods for evaluation of the underwater noise levels in the Slovenian Sea

Anthropogenic underwater noise pollution of seas and oceans caused by shipping can have negative effects on marine animals. The aim of this study was to evaluate quantitatively how much the underwater noise levels in the Slovenian Sea were influenced by anthropogenic pressures and meteorological parameters in the period from 2015 until 2018. For this purpose, correlation method and least squares multiple linear regression analysis were used. The results of this study show that the correlation of underwater noise levels with the dredging activity is significant but low, while correlation with the ship densities is insignificant, which could be due to reduced sound wave propagation in the shallow sea levels. Correlation of the underwater noise levels with the wind speed was significant but low to medium, which could be explained by the breaking waves generated by the wind that produced sound.

Electromagnetic Scattering Analysis of the Sea Surface with Single Breaking Waves

A new electromagnetic (EM) scattering model of the sea surface with single breaking waves is proposed based on the high-frequency method in this paper. At first, realistic breaking wave sequences are obtained by solving the fluid equations which are simplified. Then, the rough sea surface is established using the linear filtering method. A new wave model is obtained by combining breaking waves with rough sea surface using a 3D coordinate transformation. Finally, the EM scattering features of the sea surface with breaking waves are studied by using shooting and bouncing rays and the physical theory of diffraction (SBR-PTD). It is found that the structure that is similar to a dihedral corner reflector between the breaking wave and rough sea surface exhibits multiple scattering, which leads to the sea-spike phenomenon that the scattering result of horizontal (HH) polarization is larger than that of vertical (VV) polarization, especially at low-grazing-angle (LGA) incidents with upwind. The sea-spike phenomenon is also closely related to the location of strong scattering.

Focused Plunging Breaking Waves Impact on Pile Group in Finite Water Depth

Accuracy estimation of wave loading on cylinders in a pile group under different impact scenarios is essential for both the structural safety and cost of coastal and offshore structures. Differing from the interaction of waves with a single cylinder, less attention has been paid to pile groups under different arrangements. Numerical simulations of interactions between plunging breaking waves and pile group in finite water depth are performed using the two-phase flow model in REEF3D, an open-source computational fluid dynamics program to investigate the wave loads and flow kinematics characteristics. The Reynolds-averaged Navier-Stokes equation with the two equation k − ω turbulence model is adopted to resolve the numerical wave tank. The model is validated by comparing the numerical wave forces and free surface elevation with measurements from experiments. The computational results show fairly good agreement with experimental data. Four cases are simulated with different relative distances, numbers of cylinders and arrangements. Results show that the wave forces on cylinders in the pile group are effected by the relative distance between cylinders. The staggered arrangement has a significant influence on the wave forces on the first and second cylinder. The interaction inside a pile group mostly happens between the neighboring cylinders.

Numerical Modeling of Failure Mechanisms in Articulated Concrete Block Mattress as a Sustainable Coastal Protection Structure

Shoreline protection remains a global priority. Typically, coastal areas are protected by armoring them with hard, non-native, and non-sustainable materials such as limestone. To increase the execution speed and environmental friendliness and reduce the weight of individual concrete blocks and reinforcements, concrete blocks can be designed and implemented as Articulated Concrete Block Mattress (ACB Mat). These structures act as an integral part and can be used as a revetment on the breakwater body or shoreline protection. Physical models are one of the key tools for estimating and investigating the phenomena in coastal structures. However, it does have limitations and obstacles; consequently, in this study, numerical modeling of waves on these structures has been utilized to simulate wave propagation on the breakwater, via Flow-3D software with VOF. Among the factors affecting the instability of ACB Mat are breaking waves as well as the shaking of the revetment and the displacement of the armor due to the uplift force resulting from the failure. The most important purpose of the present study is to investigate the ability of numerical Flow-3D model to simulate hydrodynamic parameters in coastal revetment. The run-up values of the waves on the concrete block armoring will multiply with increasing break parameter (0.5<ξm−1,0<3.3) due to the existence of plunging waves until it (Ru2%Hm0=1.6) reaches maximum. Hence, by increasing the breaker parameter and changing breaking waves (ξm−1,0>3.3) type to collapsing waves/surging waves, the trend of relative wave run-up changes on concrete block revetment increases gradually. By increasing the breaker index (surf similarity parameter) in the case of plunging waves (0.5<ξm−1,0<3.3), the low values on the relative wave run-down are greatly reduced. Additionally, in the transition region, the change of breaking waves from plunging waves to collapsing/surging (3.3<ξm−1,0<5.0), the relative run-down process occurs with less intensity.

Ocean bubbles under high wind conditions. Part 1: Bubble distribution and development

The bubbles generated by breaking waves are of considerable scientific interest due to their influence on air-sea gas transfer, aerosol production, and upper ocean optics and acoustics. However, a detailed understanding of the processes creating deeper bubble plumes (extending 2–10 metres below the ocean surface) and their significance for air-sea gas exchange is still lacking. Here, we present bubble measurements from the HiWinGS expedition in the North Atlantic in 2013, collected during several storms with wind speeds of 10–27 m s−1. A suite of instruments was used to measure bubbles from a self-orienting free-floating spar buoy: a specialised bubble camera, acoustical resonators, and an upward-pointing sonar. The focus in this paper is on bubble void fractions and plume structure. The results are consistent with the presence of a heterogeneous shallow bubble layer occupying the top 1–2 m of the ocean which is regularly replenished by breaking waves, and deeper plumes which are only formed from the shallow layer at the convergence zones of Langmuir circulation. These advection events are not directly connected to surface breaking. The void fraction distributions at 2 m depth show a sharp cut-off at a void fraction of 10−4.5 even in the highest winds, implying the existence of mechanisms limiting the void fractions close to the surface. Below wind speeds of 16 m s−1 or RHw = 2 × 106, the probability distribution of void fraction at 2 m depth is very similar in all conditions, but increases significantly above either threshold. Void fractions are significantly different during periods of rising and falling winds, but there is no distinction with wave age. There is a complex near-surface flow structure due to Langmuir circulation, Stokes drift, and wind-induced current shear which influences the spatial distribution of bubbles within the top few metres. We do not see evidence for slow bubble dissolution as bubbles are carried downwards, implying that collapse is the more likely termination process. We conclude that the shallow and deeper bubble layers need to be studied simultaneously to link them to the 3D flow patterns in the top few metres of the ocean. Many open questions remain about the extent to which deep bubble plumes contribute to air-sea gas transfer. A companion paper (Czerski, 2021) addresses the observed bubble size distributions and the processes responsible for them.