Numerical Study of Bamboo Breakwater for Wave Reduction

Flood inundation and shoreline erosion have long occurred in Sayung, Demak area, the northern coast of Central Java Province, Indonesia. The people of Sayung planted mangroves to reduce the flood inundation and shoreline erosion in that area. They built the bamboo array to protect the juvenile mangroves from incoming waves. The bamboo acts as a breakwater and is considered an environmentally friendly permeable structure to reduce wave energy and stimulate sedimentation. This paper discusses three bamboo arrays’ effectiveness in wave reduction using Numerical Wave Tank (NWT). The interaction of regular waves with a permeable structure comprising a single row of vertical circular poles was conducted based on the Smoothed Particle Hydrodynamics (SPH) method. The effect of different waves and structural dimensions on the permeable structure was investigated based on the structure’s transmission coefficient (Kt) performance. The investigations have revealed that structures with the combination of Vertical-Horizontal formation (VH) attenuate more wave energy than Vertical Only (VO) and the combination of Vertical-Diagonal formation (VD). As the wave steepness increases, the transmission coefficient decreases. Likewise, the transmission coefficient (Kt) is decreasing when the wave height is increasing. On the other hand, the transmission coefficient (Kt) increases as the wave period increases. As the structure spacing ratio between end-to-end and center-to-center spacing (e/S) rises, the transmission coefficient (Kt) also increases. The diameter (D) has a slight effect on the transmission coefficient (Kt). However, the center-to-center spacing (S) has a more significant impact than the diameter on the transmission coefficient, affecting an inclination on the transmission coefficient (Kt) when center-to-center spacing (S) goes up.

Study on frequency selective/absorption/reflection multilayer composite flexible electromagnetic interference shielding fabric

Three kinds of electromagnetic functional materials, frequency selective surface, carbonyl iron coated absorbing fabric and conductive woven fabric, were laminated to filter, absorb and reflect electromagnetic waves. Through equivalent circuit analysis, the frequency selection characteristics and the correlation between the shape and size of the periodic structure of cross-shaped and Jerusalem-shaped frequency selective surfaces were studied. It is found that frequency selective surfaces can reduce the transmission coefficient of carbonyl iron coated fabric at the resonance point, so that the working frequency band of the composite shielding material can be controlled and adjusted. The stacking order has no effect on the frequency selective surface/frequency selective surface double-layer materials, but influence the transmission coefficient of composite materials with frequency selective surface superimposed carbonyl iron coated fabric and/or conductive woven fabric. Among all samples, the transmission coefficient of Jerusalem-shaped/carbonyl iron coated fabric-3/conductive woven fabric has the most strong shielding effect, which is up to −51.72 dB at 10.48 GHz. It is proved that using flexible fabric as the matrix and compounding materials with different electromagnetic functions is an effective method to realize high efficiency and adjustable electromagnetic shielding ability.

Electromagnetic response from composite carbon-containing structures with technological inhomogeneities at EHF

The results of studies of the electromagnetic response from composite structures made of a carbon-containing polymer with the inclusion of spherical pores in the bulk of the material and with pyramidal corrugation on the surface of the material are presented. The results of modeling the frequency dependences of the transmission, reflection and absorption coefficients in the EHF range are shown. Samples of composite carbon-containing structures with technological inhomogeneities have been fabricated by 3D printing. Measurements of the electromagnetic response from experimental samples were carried out in the frequency range from 100 to 1000 GHz. At frequencies up to 250 GHz, the inclusion of air pores in the polymer volume reduces the transmission coefficient, practically does not affect the reflection, and increases the absorption. Pyramid corrugated material absorbs more than 99% of radiation in the frequency range from 200 to 635 GHz.

Properties of vehicle support suspensions

The processes of damping of vibrations of sprung masses with polyurethane foam support cushions in the frequency range of vibrations with an optimal transfer function are investigated. The amplitude-phase-frequency characteristics of the masses are determined during vibrations with the subsequent presentation of transient processes, according to which the damping time of the vibrations of the sprung masses is determined. The used support cushions made of polyurethane foam reduce the minimum damping time of vibrations of the sprung masses on 1520 %, they are more wear-resistant and have greater damping properties than rubber support cushions. Keywords: spectral density, exposure frequency, transmission coefficient, deformation coefficient, vibration damping time, polyurethane foam. [email protected]

Measurement of the photon detection efficiency of silicon photomultipliers for the new detector cluster of the Cherenkov gamma-ray telescope TAIGA-IACT equipped with UV filters

This study was devoted to measurements of the UV-range photon detection efficiency (PDE) of OnSemi MicroFJ SiPM detectors use together with custom UV filters and of the transmission coefficient of these filters at 277 nm. The final goal of these measurements was to determine feasibility of the filters for the new detector cluster of the TAIGA-IACT telescope. PicoQuant PLS-270 UV source emitting pulses at 277 nm was calibrated. The obtained dependences of the registered radiation power on the distance between the emission source and the reference detector are well approximated by the inverse square function, hence no significant scattering or absorption influenced the PDE measurements. The dependences of the number of detected photons on the distance between the source and the detector were obtained. These dependencies are also well approximated by the inverse square function. The PDE of SiPM MicroFJ-60035 detector was measured at the level of 10.0 ± 0.7%. The transmission coefficients of the considered set of filters at the wavelength of 277 nm were also obtained. The SL 240-300 filter has a sufficiently high transmission coefficient and it is advisable to use it as a bandpass ultraviolet filter in the new detector cluster of the TAIGA-IACT telescope; the SL 290-590 filter absorbs ultraviolet light quite well and is applicable in the visible range.