Effect Of Incidence Angle Research Articles

Capability of a potential-flow solver to analyze articulated multibody offshore modules

Within the EU-funded Space@Sea project, a standardized floating solution for offshore space was developed, and modularity was one of the key elements. Computational tools used to design and analyze such modules must be validated. The objective here was to critically examine the capability of a potential-flow solver to predict wave-induced motions and loads on offshore systems consisting of such articulated modules, as this kind of solver is often used to assess the safety and effectiveness of articulated multibody offshore structures. A frequency-domain analysis considered only the hydrodynamic interactions between two floating modules, by locking the motions of interacting structures. A time-domain analysis treated also the mechanical coupling effects between the two articulated floating modules. Comparative computations from a RANS-based solver and experimental model measurements were available to validate the results. Although the agreement was reasonable between numerical predictions and experimental measurements for the floating modules in wave frequencies far away from their natural frequencies, deviations were observed in waves at frequencies in the neighborhood of the module’s natural frequencies. Generally, the agreement between numerically predicted and experimentally measured hinge forces was favorable. The effects of incident wave angles on hinge forces revealed that numerically predicted hinge forces at all incident wave heading angles compared favorably to measurements. An accurate evaluation of wave-induced motions and loads on articulated floating structures was possible only by accounting also for nonlinearities associated with the connecting joints.

Topology optimization combined with a genetic algorithm to design structured materials for underwater broadband acoustic absorption

This paper applies topology optimization in combination with a genetic algorithm to design a coating structure for sound absorption in underwater applications. The coating is designed with a high broadband acoustic absorption of 0.94 ranging from 1 to 10 kHz by optimizing the cavity topology and the dimensions of the embedded steel scatterers. This study demonstrates the application process of the topology optimization with a genetic algorithm method and the optimization results of the optimization process stages. The absorption mechanism of the topology design is analyzed. The effects of different cavity compositions, steel scatterers, design ideas, material parameters, and acoustic incident angles on the sound absorption coefficients are investigated. These acoustic structures and the method provide more ideas for the design of coating structures for underwater sound absorption.

An Infrared Ultra-Broadband Absorber Based on MIM Structure

We designed an infrared ultra-broadband metal–insulator–metal (MIM)-based absorber which is composed of a top layer with four different chromium (Cr) nano-rings, an intermediate media of aluminum trioxide (Al2O3), and a bottom layer of tungsten (W). By using the finite-difference time-domain (FDTD), the absorption performance of the absorber was studied theoretically. The results indicate that the average absorption of the absorber can reach 94.84% in the wavelength range of 800–3000 nm. The analysis of the electric and magnetic field indicates that the ultra-broadband absorption rate results from the effect of local surface plasmon resonance (LSPR). After that, the effect of structural parameters, metal and dielectric materials on the absorptivity of the absorber was also discussed. Finally, the effect of incidence angle on absorption was investigated. It was found that it is not sensitive to incidence angle; even when incidence angle is 30°, average absorptivity can reach 90%. The absorber is easy to manufacture and simple in structure, and can be applied in infrared detection and optical imaging.

Evaluation of light transmittance performance of light-transmitting concrete with optical fibre

• Synergistic effects of fibre diameter, fibre spacing and light incidence angle were studied. • LTC specimens were tested for its compressive strength and light transmittance. • The effect of fibre diameter is more significant than fibre spacing. • ANOVA was carried out for compressive strength and light transmittance analysis. • Lower compressive strength may not due to gaps between fibre–matrix interface. Light incidence angle is an important parameter to Light-transmitting Concrete (LTC), especially when it is used for building materials exposed to sunlight. Yet, there is a lack of deeper understanding on the performance of LTC when light incidence is encountered with different angles. This study covers the synergistic effect of light incidence angle, fibre spacing, and fibre diameter on the light transmittance of LTC. Optical fibres with different diameters and spacings are incorporated into the LTC specimen. Light transmittance is measured using a light meter, where the test is conducted in a tight enclosed wooden board. The results show that, as the fibre diameter becomes larger in the LTC, the light transmittance increases. The highest transmittance of 1.613 % was found for LTC with a fibre diameter of 2 mm. In contrast, the light transmittance decreases with the increase in fibre spacing and light incidence angle. It was found that LTC with a 2 mm fibre diameter shows a significant difference with other fibre diameters even at the light incidence angle of 30°. Besides, the effect of fibre diameter on light transmittance was found to be more significant as compared to fibre spacing.

Research on heat transfer augment of the helical half-pipe jacket by jet longitudinal vortex generator

In order to evaluate the comprehensive performance of enhanced heat transfer by jet more reasonably, considering the increase of additional power consumption caused by jet, the thermal coefficient ratio (TCR) was proposed as the evaluation index to analyze the effect of comprehensive enhanced heat transfer. In this study, the jet vortex generator (JVG) is applied to the half-pipe jacket for obtaining further heat transfer enhancement. The structural parameters of the half-pipe jacket is kept constant. The effect of the jet incidence angle (α) and the ratio of jet flow rate to mainstream flow rate (ε) on the heat transfer augment has been investigated by numerical simulation. The results showed that the jet action changed the original secondary vortex structure and enhanced the convective heat transfer capacity of the fluid in the helical half-pipe jacket. In the flow region near the jet, a pair of common-flow-down (CFD) longitudinal vortices were generated in the cross section of the half-pipe jacket. With the development of the mainstream, the vortex gradually evolved into a common-flow-up (CFU) vortex. With the increase of ε, heat transfer convective heat transfer capacity was enhanced. Moreover the flow resistance was increased. The local Nusselt number (Nulocal) of the heated wall could be enhanced by up to 2.3 times in the investigated range when compared to the corresponding value of the single half-pipe jacket. Within the range of ε=0.5-2 and α=45°-60°, the jet with α=50° had the best comprehensive enhanced heat transfer performance. The TCR was between 0.91 and 1.19.

Influence of incidence angle effects on the performance of bifacial photovoltaic modules considering rear-side reflection

Improving the accuracy of performance evaluation of bifacial photovoltaic (PV) devices is critical to the development of bifacial PV technology. The incidence angle effect (IAE) is one of the characteristics related to the power generation of PV modules. Due to the ability of bifacial PV modules to collect light from double sides, the IAE evaluation should involve the effects of both the front and rear sides of PV simultaneously. This work aims to investigate the IAE of bifacial PV modules considering both front-side beam irradiation and rear-side reflection. The rear-side reflection makes the IAE of bifacial PV modules more complicated than that of monofacial PV modules. The rear-side IAE of bifacial PV modules was defined, and a corresponding mathematical model was derived theoretically in this work. A simulation model based on the view-factor method was developed to investigate the performance of bifacial PV modules under various incidence angles, whose validity was verified by indoor measurements. Furthermore, the results show that rear-side IAE is more suitable to be investigated with the simulation, and it is sensitive to the surrounding and installation conditions. The proposed method is applicable in evaluating and predicting the performance of bifacial PV modules related to IAE under different installation conditions.

Development and application of a profile loss model considering the low-Re effect in low-pressure turbine

Abstract To improve the prediction accuracy of profile loss at low Reynolds number, a typical low-pressure turbine cascade T106D-EIZ was selected to numerically investigate the effect of Reynolds number on turbine cascade flow. A detailed analysis of profile loss was performed and a profile loss model considering the low-Re effect was developed. Results showed that the incidence angle has a great effect on the inlet and outlet Mach number at low Reynolds number, and the variation of inlet and outlet Mach number further affects the blade profile loss. A correction factor was introduced to consider the effect of incidence angle and Mach number on the profile loss. The profile loss coefficient and stalling incidence angle were both extended to lower Reynolds number based on the numerical results. A Smart Through Flow Analysis Program (STFAP) was developed using the finite volume method to solve the circumferentially averaged Euler equations of S2 surface. Aerodynamic performance of E3 5-stage low-pressure turbine was predicted by STFAP coupled with low-Re profile loss model. Compared with K-O model, the prediction accuracy of efficiency of low-pressure turbine last stage is improved by nearly 1.1 percentage points when the 5-stage low-pressure turbine is in a low Reynolds number state.

Development and application of a profile loss model considering the low-Re effect in low-pressure turbine

Abstract To improve the prediction accuracy of profile loss at low Reynolds number, a typical low-pressure turbine cascade T106D-EIZ was selected to numerically investigate the effect of Reynolds number on turbine cascade flow. A detailed analysis of profile loss was performed and a profile loss model considering the low-Re effect was developed. Results showed that the incidence angle has a great effect on the inlet and outlet Mach number at low Reynolds number, and the variation of inlet and outlet Mach number further affects the blade profile loss. A correction factor was introduced to consider the effect of incidence angle and Mach number on the profile loss. The profile loss coefficient and stalling incidence angle were both extended to lower Reynolds number based on the numerical results. A Smart Through Flow Analysis Program (STFAP) was developed using the finite volume method to solve the circumferentially averaged Euler equations of S2 surface. Aerodynamic performance of E3 5-stage low-pressure turbine was predicted by STFAP coupled with low-Re profile loss model. Compared with K-O model, the prediction accuracy of efficiency of low-pressure turbine last stage is improved by nearly 1.1 percentage points when the 5-stage low-pressure turbine is in a low Reynolds number state.

Low-frequency waterborne sound insulation by an acoustic metascreen with a metal chiral structure

Low sound speed or low-density materials can be used as soft acoustic boundaries in water, potentially as low-frequency underwater sound insulation. This study uses a chiral structure to construct an acoustic metascreen with deep subwavelength thickness. The results show that the transmission coefficient of the metascreen decreases noticeably in the low-frequency range when adjusting the chiral structure. The displacement pattern and the effective acoustic impedance are used to investigate the sound insulation mechanism. Low sound speed and effective acoustic impedance are found in the anisotropic chiral structure, and an extensive range of quasi-longitudinal wave phase velocities from 116.70 m/s to 3935.48 m/s can be obtained by adjusting the structural parameters without changing the filling rate. Finally, the effect of the oblique incidence angle on the sound insulation of the metascreen is investigated.

Absorption enhancement in terahertz region by cross-shaped grating

Cross-shaped silicon-doped arrays are proposed for ultra-broadband absorber in the terahertz region, which consists of periodic Si/SiO2 microstructure. The cross-shaped silicon-doped absorber has a maximum absorption of over 99.9% and a relative bandwidth for absorption over 95% is 147% (0.96–6.24 THz). In this work, the absorber has better absorption bandwidth, center frequency, and relative bandwidth ratio than the various reference absorbers. The physical mechanism of the structure to achieve broadband absorption is explained by studying the electric field distribution. Furthermore, the ultra-broadband absorption characteristics of the absorber is demonstrated well by impedance matching theory. Finally, the effects of polarization angle, incident angle, angular rotation, and structural parameters on the absorption performance of the target structure are analyzed in detail, demonstrating that the structure has properties such as polarization-independent, wide-angle absorption and good process tolerance.

Numerical Investigation of a Gear-Shaped Triple-Band Perfect Terahertz Metamaterial Absorber as Biochemical Sensor

In this work, a triple-band perfect metamaterial absorber (MA) in the terahertz (THz) regime is demonstrated for different biochemical sensing applications. The metasurface’s unit cell is made up of a distinct metallic gear-shaped core with eight identical teeth and two concentric circular rings (CCRs) on the top layer. Finite-difference time-domain (FDTD) method-based software is utilized for modeling and numerical analysis, and a genetic algorithm (GA) is employed to optimize some geometric parameters of the absorber. The proposed MA shows almost 100% absorption in the frequency range from 0.5 to 4.5 THz. The MA becomes almost insensitive to polarization angle when the number of gear tooth has been increased. Resonance frequencies can be tweaked by adjusting the top layer’s geometric parameters while maintaining the absorption constant. The influence of different metals and forms in the top layer, such as solid and hollow circular metallic cores, on absorption spectra is also illustrated in this article. The modeled MA can detect glucose, ethanol, oils, and cancer cells (BCCs) by changing the resonance frequency and peak absorption of the spectra due to the variation in refractive index (RI) of the sample. When detecting ethanol, the absorber achieves a maximum sensitivity and figure of merit (FOM) of 56.67 THz/RIU and 358.7 RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> , respectively. In addition, the effects of incident angle of light and bending of MA on absorption are analyzed in this study. With this unique feasible design, structural tunability, and high sensitivity, the proposed absorber exhibits good promise in detecting biochemicals in the THz region.

Effects of crosswinds and tip configurations on the initial phase of wingtip vortex evolution

Wingtip vortex is the initial phase of aircraft wake flow that jeopardizes flight safety. Previous studies have focused on the effect of incidence angle on tip vortex flow; thus, investigations on tip vortex in the roll-up stage under crosswind conditions are limited. In the present study, two NACA0012 wings with different tip shapes (round and square) were numerically analyzed to explore the effects of wingtip configurations on tip vortex. In addition, the effects of crosswinds on wingtip vortex evolution were also investigated. It was found that sharp edges of the square wingtip generated a multi-vortex system, resulting in a larger turbulent wake vortex core radius. The lift and vortex strength of the square wingtip were 23% higher and only 12% stronger than those of the round wingtip, respectively. Furthermore, crosswinds changed both the pressure distribution and the vortex structure. Crosswinds made the flow field unstable; hence, upwind lower edge vortices of the square wingtip burst earlier and merged faster. Consequently, the tightness of the upwind vortex of the square wingtip increased, and the corresponding vortex strength was enhanced. The downwind vortex of the square wingtip was weakened by 2.7% under a crosswind velocity of 4 m/s, whereas the downwind tip vortex of the round wingtip was strengthened under the same conditions.

A novel broadband double-ring holed element metasurface absorber to suppress EMI from PCB heatsinks

In this study, a new Broadband Double Ring Hole Element (BDHE) meta-surface absorber is studied to suppress EMI from PCB heatsink for 1-12 GHz covering L, S, C, and X bands. The proposed metamaterial-structure consists of resistances and 8 ring resonators, four of which are inner and four are outer that are configured to provide an absorbing effect. For broadband, numerical simulations show that an average of 65% absorption value is obtained between 4-12 GHz. It is determined that this value reached 69.84% by increasing the used resistance values (R = 150?). This value may be significant to reduce the EMI values to which PCB circuit elements are exposed. Also, when the incidence angle effect is examined, the absorption values of 90% at 10.1 GHz and 98% at 11 GHz for ?=15° can also be recommended for narrowband applications. On the other hand, for R = 50 ?, this value is 82% and 89%, respectively, in the 3-4 GHz and 9.9-11.5 GHz ranges. It can also be stated that the average E-field from the heatsink can be decreased with the location of the proposed metamaterial relative to the base and increased metamaterial dimensions. Finally, in the near-field region, the distance between metamaterial and the heatsink has no appreciable effect on the E-field.

Hydroelastic Response to Oblique Wave Incidence on a Floating Plate with a Submerged Perforated Base

A hydroelastic model is developed of a floating flexible structure in the presence of a submerged perforated base connected with mooring lines under oblique wave action. Using the velocity decomposition method, the analytical solution of the referred model is obtained in finite water depth. The convergence of the analytical solution for different oblique wave incidences is examined, and the present results of deflection amplitude are compared with experimental datasets and the numerical results available in the literature. The effects of oblique wave incidence, along with various design parameters on the reflection, transmission, and dissipation coefficients, as well as structural displacements, are analysed through hydroelastic analysis. Further, the effect of oblique incidence angle on the free oscillation hydroelastic waves in two wave modes is investigated by deriving the free motion velocity potential in a wave basin.

Torsional effect of the single-bay masonry building considering seismic wave incident angle

Single-bay masonry building is the main structure form of rural houses in Southwest China. In the investigation of earthquake damage in Lushan earthquake, it is found that this type of structure has serious torsional damage. In this paper, the torsional effect was verified with 1/6 scale model while the torsional responses of some actual size models were simulated by self-compiled program. Under the coupling action of translation and torsion, the effects of seismic wave incident angle and structural geometric dimension on the torsional response of structure were analyzed. The results showed that the incident angle of seismic wave and the structural irregularity were the important reasons which caused the torsional failure of the structure. When the incident angle of the seismic wave was about 60°, the torsional response of the structure was the strongest. Besides, in order to reduce the influence of torsional effect, the eccentricity ratio should be smaller than 6%, and the number of storey should better be three or less.

Combined effects of particle shape, incident angle and porosity on momentum and heat transfer between spheroids and fluids

• PR-DNS is used to study momentum and heat transfer of porous spheroids under laminar flow . • Effects of particle shape , incident angle, porosity and Reynolds number are quantified. • Novel correlations of Cd and Nu for porous spheroids under laminar flow are established. Particle-resolved direct numerical simulations are carried out to investigate the distribution of drag coefficient ( Cd ) and average Nusselt number ( Nu ) of a porous spheroid in a fluid under different Reynolds number (20≤ Re ≤200), particle shape (aspect ratio, 0.5≤ Ar ≤2.5), incident angle (0°≤ θ ≤90°) and porosity (0.57≤ ε ≤0.94). Through the analysis on the numerical simulation results from 525 study cases, it is found that Cd increases first and then decreases with the increase of Ar for prolate spheroids and this trend is opposite for oblate spheroids. For both prolate and oblate spheroids, it is found that Nu decreases first and then increases with the increase of Ar. Under higher Reynolds number (100≤ Re ≤200), the effect of ε on Cd and Nu is noticeable. On the contrary, the effect of ε is almost negligible at low Reynolds number (20≤ Re <100). Numerical results also show that when Ar <1, Cd decreases considerably and Nu decreases slightly with the increase of θ , and this variation trend is opposite when Ar >1. Finally, based on the numerical database, new predictive correlations of Cd and Nu for irregular porous particles in a fluid are established and the accuracy is assured by comparing the prediction results and the numerical data. These correlations can be used to improve the macroscopic multiphase models such as two-fluid model and coupled computational fluid dynamics and discrete element method.

Vortex-induced vibration of flexible riser transporting high-speed spiral flow in deep-sea mining

According to Hamilton's principle and a mechanical decomposition model proposed for high-speed spiral flow, vibration governing equations of flexible riser transporting high-speed spiral flow are developed for vortex-induced vibration (VIV) analysis for lifting pipe system in deep-sea mining. The classic van der Pol oscillator is used to simulate the dynamic characteristics of VIV. The governing equations are then discretized and solved by the finite element method and the Runge-Kuta method. Furthermore, dynamic characteristics of VIV of the flexible riser transporting straight flow and spiral flow are investigated and the effects of the spiral flow incidence velocity and angle controlled by the jet device on VIV responses are evaluated. Also, the VIV dynamics considering different damping ratios are examined. The results show that the rotational angular velocity of the spiral flow would amplify the mean deflection of the in-line (IL) direction, and the incidence velocity has a significant nonlinear effect on the dominant frequency of the riser, which would induce the high-order dominant vibration modes when the incidence velocity is large sufficiently. However, the incidence angle has relatively less effects on the VIV responses of flexible riser. Moreover, the locked interval of VIV is less influenced by damping ratio below 0.1.

Sub-diffraction focusing by a meta spiral zone plate

The sub-diffraction focus has been widely studied because of its wide application in the fields of optical lithography and super-resolution imaging. The methods based on the traditional refractive elements to achieve sub-diffraction focal spots face the problem of large volume, large mass and difficult alignment. Although diffractive optical elements can achieve the combination of multiple phase modulation functions, the polarization modulation cannot be achieved by such elements. As a planar element to achieve integrated modulation of phase and polarization, the metasurface has the potential to further miniaturize the sub-diffraction focusing system and eliminate alignment errors. In this article, we demonstrate the meta spiral zone plate, which converts the incident linearly polarized beam to an azimuthally polarized beam and focuses the latter into a sub-diffraction solid spot. The meta spiral zone plate with a diameter of 600 μm and a numerical aperture of 0.8 working at the wavelength 405 nm is designed and verified experimentally. The simulated full width at half maximum (FWHM) and measured FWHM of the focus spot are 0.6λ and 0.65λ. The simulated and measured efficiencies are 37.69% and 15.18%, respectively. Meanwhile, the effects of the incident beam's incident angle and polarization orientation on the focal spot are also investigated. Our proposal eliminates the alignment errors in the traditional methods and further simplifies the optical systems realizing sub-diffraction focusing, which may have great potential applications in super-resolution focusing and optical manipulation.

Fragmentation prevention for Kevlar fiber pipe reinforced honeycomb cabin

The ship protection tank is the key structure to defend the warship against fragment attack. The side cabin can prevent the high-speed fragment from hitting deeply, and has the functions of cooling, absorbing heat and extinguishing fire. The research shows that the fiber-filled foam lightweight structure has good cavity inhibition effect. In this paper, Kevlar pipe reinforced honeycomb cabin was designed, and the mechanism of Kevlar reinforced honeycomb tank against fragment attack was studied by armor piercing test and numerical simulation. The fragment penetration process and damage mode of Kevlar reinforced honeycomb structure under high-speed impact were systematically analyzed and model verified. Compared with the hollow aluminum foam structure, Kevlar reinforced honeycomb structure is found that can effectively enhance the ability of the side cabin structure to resist fragment impact. Moreover, the effects of core layer height, panel thickness, fragment velocity, incident angle and installation of sandwich structure on preventing fragment penetration were further systematically discussed. The conclusions will provide reference for the design of fiber-filled foam side cabin structure.

Hydrodynamic characteristics and wake structure of flow over a round-ended cylinder at a low Reynolds number

Hydrodynamic characteristics and wake structures of the flow over a round-ended cylinder are invaluable for the design of associated cylindrical structures such as bridge piers and submerged floating tunnels. This paper reports the results of a numerical investigation into the flow past a round-ended cylinder and the associated hydrodynamic forces as well as the evolution of vortex structure and boundary layer separation. The effect of incidence angle α, ranging from 0° to 90°, is examined at a low Reynolds number of 100 based on the projected length. Both the drag and lift forces are sensitive to the incidence angle. When 0° &amp;lt; α &amp;lt; 90°, boundary layers asymmetrically separate from two sides of the cylinder, giving rise to a time-mean pressure difference that is not perpendicular to the incoming flow direction. There are two directly related results, one is the non-zero time-mean lift coefficient, and the other is the occurrence of a secondary frequency of drag coefficient, the same as that of lift coefficient. The most forward separation point of the upper boundary layer and the maximum size difference of vortices generated from two sides contribute to the maximum time-mean lift coefficient occurring at α = 45°. The vortex formation length is shortened with increasing α, resulting in the augment of the fluctuation amplitudes of fluid forces. The enlargement of drag force is mainly attributed to the broadened wake width with the increase in α.