Evaluation of dynamic behaviour of porous media including micro-cracks by ordinary state-based peridynamics

Reliable evaluation of mechanical response in a porous solid might be challenging without any simplified assumptions. Peridynamics (PD) perform very well on a medium including pores owing to its definition, which is valid for entire domain regardless of any existed discontinuities. Accordingly, porosity is defined by randomly removing the PD interactions between the material points. As wave propagation in a solid body can be regarded as an indication of the material properties, wave propagation in porous media under an impact loading is studied first and average wave speeds are compared with the available reference results. A good agreement between the present and the reference results is achieved. Then, micro-cracks are introduced into porous media to investigate their influence on the elastic wave propagation. The micro-cracks are considered in both random and regular patterns by varying the number of cracks and their orientation. As the porosity ratio increases, it is observed that wave propagation speed drops considerably as expected. As for the cases with micro-cracks, the average wave speeds are not influenced significantly in random micro-crack configurations, while regular micro-cracks play a noticeable role in absorbing wave propagation depending on their orientation as well as the number of crack arrays in y-direction.

Measurement of sea wave height by radar sounding with polarizationmodulated signals

Methods for determining the height of sea waves, which are relevant for maritime navigation, have been investigated. The measurement of the height of sea waves by the method of radar sounding by polarization-modulated signals is considered. The energy and spectral characteristics of the radar signal reflected by the sea surface at low angles of incidence are described. An algorithm for calculating the average wave height based on the results of measuring the polarization anisotropy of the specific effective scattering surface of the sea area is considered. The relation of the average frequency of the amplitude fluctuations of the reflected radar signals with the sea waves is given. The spectral characteristics of radar signals reflected by the sea surface when irradiated with polarization-modulated signals are analyzed. The procedure for forming an effective statistical estimate of the average wave height based on the results of spectral measurements is considered. The errors of the generated estimates of the wave height associated with the measurement errors of the polarization anisotropy of the effective scattering surface and the average frequency of the envelope of the amplitude fluctuations caused by the Doppler effect are analyzed. The results of experimental measurements of the spectra of the amplitude fluctuations of the envelope of the reflected signals at different states of the sea surface are presented. The analytical dependence of the polarization anisotropy of the effective sea scattering surface on the irradiation angle relative to the wave propagation direction is given. A comparison of estimates of the height of sea waves obtained from radar sounding and meteorological observation data is carried out.

PENGUKURAN MODULUS YOUNG SENAR PANCING DENGAN METODE ANALISIS FREKUENSI DAWAI

The research has been conducted to determine the Young Modulus value of the fishing line with frequency analysis on a string by using a sound sensor. The fishing line made of Nylon Monofilament and Stainless Steel Nylon Coat. The diameter of the fishing line with each material consisted of 0.25 mm. The fishing line vibration events ware displayed on the graph of the relationship between pressure and time in the Logger pro program. The graph of the relationship between pressure and time was then transformed into an FFT graph of the amplitude relationship to frequency. Then the frequency value which was obtained from the FFT was used to determine the wave velocity value of the fishing line. The average wave velocity value was obtained by graphing the frequency relation to one of each string length. After obtained the average wave velocity value of the fishing line the Modulus Young value can be determined by the equation of the square wave velocity relationship times the mass per length times the cross-sectional area. In this study, the Young Modulus value of Nylon Monofilament fishing line was (1.94±0.09) GPa and the Young Modulus value of the Stainless Steel Nylon Coat fishing line was (45.05±2.05) GPa.

Assessment of Current Influence on the Wind Wave Parameters in the Black Sea based on Numerical Modeling

Currents affect wind waves parameters. The issue of significance of this influence for the Black Sea has not been studied properly. The purpose of this paper is to study the scale, spatial and temporal variability of influence of sea currents on the wave height in the Black Sea. The research was carried out based on simulation using SWAN wave model and an irregular computational grid. Two datasets were used as input data: the NCEP/CFSv2 wind reanalysis and current data taken from the Remote Sensing Department's archive of the Marine Hydrophysical Institute of RAS. It is shown that the average wave height mainly decreases when sea current is considered. These changes are insignificant relative to the average values of wave heights. The greatest negative changes are typical of the western and northeast parts of the Black Sea. Here, the consideration of circulation reduces the average annual wave heights by up to 0.1 m. A slight increase in the average wave height is typical of the southern and southeast parts of the sea as well as the northwest shelf. The positive contribution to the mean annual wave heights is up to 0.02 m. When taken into account, currents change wave parameters at a maximum in winter months and at a minimum in late spring and summer. Currents change the mean monthly wave heights by –0.04…0.06 m in January and February in most parts of the sea. The contribution of currents is close to zero in June and July. The maximum changes in wave height reach 6–10 % of the monthly average.

The Impact of Submerged Breakwaters on Sediment Distribution along Marsh Boundaries

Human encroachment and development on coastlines have led to greater amounts of armoring of shorelines. Breakwaters are a common feature along coastlines, which are used to dampen wave energy and protect shorelines from flash floods or overwash events. Although common, their effects on sediment transport and marsh geomorphology are poorly understood. To address this gap, our study quantifies the effects of breakwaters on sediment transport and marsh evolution under different wave regimes using Delft3D-SWAN, a dynamic geomorphodynamic numerical model. Model configurations used the same numerical domain, but scenarios had different sediments, waves, tides, basin slopes and breakwater distances from the shoreline to explore how waves and tidal currents shape coastal margins. Model results suggested breakwaters were responsible for an average wave damping between 10–50%, proportional to the significant wave height across all modeled scenarios. Shear stress at the beginning of the marsh and the volume of sediment deposited at the end of the simulation (into the marsh behind the breakwater) increased on average between 20–40%, proportional to the slope and distance of the breakwater from the shoreline. Sediment trapping, defined as the ratio between the volume of sediment housed into the salt marsh behind and away from the breakwater, was found to be less than 1 from most model runs. Study results indicated that breakwaters are advantageous for wave breaking to protect shorelines from the wave’s energy, however, they might also be an obstacle for sediment transport, negatively affecting nourishment processes, and, consequently, impeded long-term salt marsh survival. Identifying a balance between waves dampening and shoreline nourishment should be considered in the design and implementation of these structures.

The Average Shape of Large Waves in the Norwegian Sea: Is Non-Linear Physics Important?

Linear wave theory predicts that in a random sea, the shape of the average wave is given by the scaled autocorrelation function — the “NewWave”. However, the gravity wave problem is non-linear. Numerical simulations of waves on deep water have suggested that their average shape can become modified in a number of ways, including the largest wave in a group tending to move to the front of the group through non-linear dispersion. In this paper we examine whether this occurs for waves in the Norwegian Sea. Field data measured from the weather ship Polarfront is analysed for the period 2000 to 2009. We find that, at this location, the effect of non-linearity is small due to the moderate steepness of the sea-states.

Guided Wave Propagation in Detection of Partial Circumferential Debonding in Concrete Structures

The following article presents results of investigating the damage detection in reinforced concrete beams with artificially introduced debonding between the rod and cover, using a non-destructive method based on elastic waves propagation. The primary aim of the research was to analyze the possible use of guided waves in partial circumferential debonding detection. Guided waves were excited and registered in reinforced concrete specimens with varying extents of debonding damage by piezoelectric sensors attached at both ends of the beams. Experimental results in the form of time–domain signals registered for variable extent of debonding were compared, and the relationships relating to the damage size and time of flight and average wave velocity were proposed. The experimental results were compared with theoretical predictions based on dispersion curves traced for the free rod of circular cross-section and rectangular reinforced concrete cross-section. The high agreement of theoretical and experimental data proved that the proposed method, taking advantage of average wave velocity, can be efficiently used for assessing debonding size in reinforced concrete structures. It was shown that the development of damage size in circumferential direction has a completely different impact on wave velocity than development of debonding length. The article contains a continuation of work previously conducted on the detection of delamination in concrete structures. The proposed relationship is the next essential step for developing a diagnostics method for detecting debondings of any size and orientation.

Numerical Simulations of the Hydraulic Performance of a Breakwater-Integrated Overtopping Wave Energy Converter

OBREC is the acronym that stands for Overtopping Breakwater for Energy Conversion. It is a multifunctional device aimed to produce energy from the waves, while keeping the harbour area protected from flooding. In this paper, the inclusions of a berm to reduce wave reflection, the shape of the sloping plate to maximise wave overtopping and the reservoir width and the crown wall shape to maximise wave energy capture while keeping the harbour safety were analysed to optimize the hydraulic and structural performances of the device. Several configurations were numerically investigated by means of a 2DV RANS-VOF code to extend the results already obtained during previous experimental campaigns. The wave reflection coefficient, the average wave overtopping flows and the wave loadings along the structure are computed, compared with existing formulae and discussed with reference to the OBREC prototype installed in the Port of Naples.

The 1D Schrödinger equation with a spacetime white noise: the average wave function

For the 1D Schrödinger equation with a mollified spacetime white noise, we show that the average wave function converges to the Schrödinger equation with an effective potential after an appropriate renormalization.