Sinusoidal Case Research Articles

Manipulation of a turbulent boundary layer using sinusoidal riblets

We investigate experimentally the effects of micro-grooves on the development of a zero pressure gradient turbulent boundary layer at two different values of the friction Reynolds number. We consider both the well-known streamwise aligned riblets as well as wavy riblets, characterized by a sinusoidal pattern in the mean flow direction. Previous investigations by the authors showed that sinusoidal riblets yield larger values of drag reduction with respect to the streamwise aligned ones. We perform new particle image velocimetry experiments on wall-parallel planes to get insights into the effect of the sinusoidal shape on the near-wall organisation of the boundary layer and the structures responsible for the friction drag reduction and the turbulence generation. Conditional averages, aimed at identifying the topology of the low-speed streaks in the turbulent boundary layer, reveal that the flow is highly susceptible to wall manipulation. This is particularly evident in the cases that are associated with greater values of drag reduction. The results suggest a fragmentation and/or weakening of the streaks in the sinusoidal cases, that is triggered by the larger values of the wall-normal vorticity found at the streaks’ edges. The results are also confirmed by applying the variable interval spatial averaging events eduction technique. The turbulent kinetic energy budget also shows that the sinusoidal geometry significantly attenuates the turbulence production, hence supporting the idea of the manipulation of the turbulence regeneration cycle.

Evaluation of viscous damper on the vibration transmission to the piping system and the support structure exposed to sinusoidal vibration in vertical, horizontal, and lateral directions.

Viscous dampers have been shown to be a potential solution to addressing piping vibration problems. The primary objective of this study is to confirm the ability of viscous dampers in addressing piping vibration problem in a piping system at different supporting structural stiffness. The piping systems were fabricated and arranged horizontally, vertically, and axially with respect to the direction of the input vibration force. Input force was applied to the piping system using an electromagnetic shaker. A sinusoidal vertical vibration at a 5 Hz frequency (21 mm/s RMS) was applied at one end of the piping system. The use of viscous damper was varied from no viscous damper to one, two and three dampers. Results showed that having three viscous dampers installed caused the piping vibration at point P2 showed the maximum reduction in vibration of up to 80% for three axes, respectively. For the case of structural vibration, the measurement results showed that point S1 experienced the highest vibration exposure before the installation of the viscous dampers, in all axes. With the three viscous dampers installed, the maximum vibration reduction for the sinusoidal vibration test case at point S1 were 86% and 91% for the x- and z-axes, respectively. In conclusion, viscous dampers able to reduce both the piping and structural vibration in multiple axes. This study also highlights the importance of positioning dampers in reducing piping vibration and vibration transmitted to the structure, with reduction up to 90% amplitude for sinusoidal input and 80% for random input.

Spatial displacement tracking of vibrating structure using multiple feature points assisted binocular visual reconstruction

Current vision-based displacement measurement methods have limitations of requiring manual target and parameter adjustment, along with significant user involvement to achieve the desired results. This paper proposes an advanced and comprehensive vision system based on ZED cameras for full-field three-dimensional (3D) vibration displacement measurement of civil structures. Compared to existing binocular systems consisting of multiple monoculars, ZED binoculars offer greater flexibility on instrument setup and data acquisition. A novel keypoint detection and matching algorithm based on deep learning is used to achieve target-free measurement, which is capable of capturing feature points with high precision. The performance of the proposed vision-based approach is evaluated through experimental studies on a six-story scaled frame structure. Statistical analysis of the comparative results in sinusoidal cases demonstrates that the displacement responses obtained from the proposed vision-based approach show consistent results in compliance with displacement sensor measurements. System identification of the target structure is achieved through a seismic case and the error analysis is also concluded in detail.

2-D Analytical Model for Computing Eddy-Current Loss in Nonlinear Thick Steel Laminations

In this article, we propose an analytical method to compute the eddy-current loss in nonlinear thick steel laminations (3–12 mm) by considering the return path of the eddy currents. Initially, a 2-D finite-element (FE) model is applied to segregate losses measured from toroidal material samples into hysteresis and eddy-current loss components to use them as reference. Afterward, a 2-D analytical time-domain model is proposed for the eddy currents based on the solution of the 2-D field problem. The time-domain model is then used to derive a simple frequency-domain eddy-current loss formulation for the sinusoidal flux density case with the inclusion of a skin-effect correction factor, which accounts for the nonlinearity of the material. Highly accurate results are obtained from the proposed model compared to FE reference results with a mean relative error of 5.1% in the nonlinear region.

Aerodynamic Forces on a Bluff Cylinder in Sinusoidal Streamwise Winds with Different Angles of Attack

In the present study, multiple-fan active control wind tunnel tests are conducted to investigate the aerodynamic forces on a 5:1 rectangular cylinder in sinusoidal streamwise winds with different angles of attack (AoA). The effects of the frequency, amplitude, and AoA of the sinusoidal flow on the statistical parameters, spectral characteristics, and spanwise distributions of drag, lift, and moment coefficients are analyzed. Results show that each force has two components: the one induced by the approaching velocity oscillation and the one induced by wake vortex-shedding—this is quite different from that in the smooth flows, where the fluctuating forces are totally due to wake vortex-shedding. For each force, changes of the two components and their relationship with the frequency, amplitude, and AoA are presented. The drag fluctuations are generally dominated by the approaching velocity oscillations, whereas the lift and moment are more sensitive to wake vortex-shedding. Therefore, the drag force has better spanwise correlations than the lift and moment forces. Meanwhile, at a non-zero AoA, the inflow amplitude has different effects on the vortex-shedding-induced component as that at a zero AoA. The differences of spanwise distributions between the sinusoidal flow cases and the smooth flow cases are analyzed.

Performance analysis of three‐phase five‐leg transformers under DC bias using a new frequency‐dependent reluctance‐based model

This paper presents a reluctance-based model considering the frequency-dependent loss nature of the windings for the analysis of three-phase five-leg transformers under grid voltages with direct current (DC) bias. This is very important especially for proper determination of their harmonic current distortion and maximum loading capability (MLC) under DC-biased grid voltage conditions. To figure out the developed model's validity under sinusoidal and DC-biased grid voltage cases, it is comparatively analyzed with the model based on 2D finite element method (FEM). Thus, for the considered transformer type operated under DC bias, the excitation current's harmonic pollution, losses, and reactive power demand parameters are analyzed by using the developed model. Additionally, by regarding these performance parameters, the DC susceptibilities of the considered-type transformer and the single-phase shell-type transformer are comparatively evaluated. Finally, for the studied grid voltage conditions, the effects of two important design considerations as (i) magnetic core material selection and (ii) legs’ cross-sectional area sizing on the MLC are investigated. It is concluded from these investigations that under saturation conditions, the transformers, which have the core material with higher permeability or lower reluctance, draw higher excitation current, and have lower MLC ratio when compared to ones having the core material with lower permeability or higher reluctance. However, for unsaturated transformers, which work under DC bias, the case is the opposite to that in saturation conditions. On the other hand, under DC bias conditions, the effect of cross-sectional area sizing on the MLC ratio is much more for the transformer with high permeable magnetic core material with regards to ones with low permeable magnetic core material.

Time Evolution of Partial Discharges in a Dielectric Subjected to the DC Periodic Voltage

Partial discharge (PD) detection can be considered one of the most useful tools for assessing the insulation conditions of the power apparatus in high-voltage systems. Under AC conditions, this analysis is widely employed in online and offline tests, such as type tests or commissioning, and can be carried out by applying the phase-resolved PD (PRPD) method, since the patterns can give information about the defect classification. Under DC voltages, the classic pattern recognition method cannot be performed, and the measurements show complexities related to the nature of the phenomena. For this reason, to date, a standard for PD measurements under DC does not exist. In previous papers, a new method for PD detection under DC stress voltages has been proposed by the authors. It is based on the application of a direct current periodic (DCP) waveform useful in obtaining PRPD patterns. The dependence of partial discharge inception voltage (PDIV) and PD repetition rate (PDRR) on the δ shape parameter of the DCP for different materials, as well as the capability to recognize different discharge phenomena, provided valid indications on the behavior of PD in the transition from AC to DC. The aim of this paper is to evaluate the time dependence of PD occurring in a dielectric by applying the DCP waveform. In our previous studies, the investigations were focused on the PD behavior under different values of the DC voltage periodic part. In another work, the DCP waveform with both positive and negative polarity was applied to several dielectric materials. In the proposed work, instead, the DCP waveform is applied for a long time in order to observe its effect on the PD behavior for 72 h. In this way, due to the space charge accumulation phenomenon, the aging effect, also due to the space charge accumulation phenomenon, is evaluated. The methodological approach was to acquire PRPD patterns over time and evaluate their trends in comparison with the sinusoidal case. The experimental results show that, with a DCP waveform having δ = 0.6, the aging effect similar to that provided by pure DC stress is observed, while the acquired PRPD patterns are easily interpretated, as in the AC case.

Wave resonant scattering mechanism of sinusoidal seabed elucidated by Mathieu Instability theorem

In this article, we shed light on unresolved issues on the physics of the problem, and clarify the effects of slope and other related parameters controlling the wave scattering phase shifting by sinusoidal seabed based on Mathieu Instability theorem. As a starting point, 3D water wave scattering by arbitrarily-varying sea bottom is governed by 2D wave potential and wavenumber coupling equation using Fredholm's Alternative Theorem. Seabed undulating effects are split into different components, including wavenumber and bottom slope and curvature effects. Sinusoidal ripples are used to demonstrate these different seabed undulating effects. The presented model predictions agree very well with lab data. Furthermore, a method with quantitative formulations is constructed and proposed to elucidate the resonance mechanism of wave scattering by sinusoidal seabed using Mathieu instability theorem. General stability chart is generated in a relevant parametric plane to detect the unstable conditions. Quantitively formulations of resonance conditions are presented to predict peak shifting features that beyond the Bragg's perdition. As demonstrated in this work, slope effect is contributed to peak shifting and the calculation formula of the shifting distance is given, though the shifting in single sinusoidal case is small, it is more obvious in double sinusoidal cases.

Influence of the trap potential waveform on surface oscillation and breakup of a levitated charged drop

A charged droplet can be electrodynamically levitated in air using a quadrupole trap by typically applying a sinusoidal electric field. When a charged drop is levitated, it exhibits surface oscillations simultaneously building charge density due to continuous evaporation and subsequently undergoes breakup due to Rayleigh instability. In this work, we examined large-amplitude surface oscillations of a sub-Rayleigh charged drop and its subsequent breakup, levitated by various applied signals such as sine, square, and ramp waveforms at various imposed frequencies, using high-speed imaging (recorded at 100 000–130 000 frames per second). It is observed that the drop surface oscillates in a sphere–prolate–sphere–oblate mode and seldom in a sphere–prolate-sphere mode depending on the intricate interplay of various forces due to charge(q), the intensity of the applied field (Λ), and the shift of the droplet from the geometric center of the trap (zshift). The Fast Fourier Transformation analysis shows that the droplet oscillates with the forced frequency irrespective of the type of the applied waveform. While in the sinusoidal case, the nonlinearities are significant, in the square and ramp potentials, there is an admittance of all the harmonic frequencies of the applied potential. Interestingly, the breakup characteristics of a critically charged droplet are found to be unaffected by the type of the applied waveform. The experimental observations are validated with an analytical theory as well as with the Boundary Integral simulations in the potential flow limit, and the results are found to be in a reasonable agreement.

Cauer-Equivalent Circuit for Inductors Considering Hysteresis Magnetic Properties for SPICE Simulation

This article presents a new method to synthesize the Cauer-equivalent circuit for inductors that can represent the hysteresis, eddy current, anomalous core losses, dc and ac winding losses as well as inductance. Only the measurement of inductor loss under the sinusoidal excitation is required to synthesize the SPICE loss model. The proposed circuit model can be used to evaluate the loss under arbitrary voltage/current excitations. In the proposed approach, the measured loss is subdivided into the ac and hysteresis losses. Then, the Cauer-equivalent circuit for SPICE simulation is synthesized from the loss model. It is shown that the losses evaluated by the proposed model are in good agreement with the measured results under the condition of the sinusoidal and triangular cases with and without dc bias current.

Heating and cooling conditions effects on the kinetic of phase change of PCM embedded in metal foam

Phase change materials (PCM) are attractive candidates for energy storage. They can store large quantities of energy in small volumes at nearly constant temperatures. Despite their advantage, their thermal conductivity is very low with a high-volume change during the melting and solidification process. One way to increase their poor thermal conductivity is to embed them into open cell metallic foams. In this paper, a numerical study is conducted on the effect of the heating and cooling conditions on phase change kinetics of paraffin embedded in a metal foam. Constant heating and sinusoidal heating are similarly investigated. For the constant heat flux, a step function ranging from +1800 W/m2 to −1800 W/m2 is considered, while for the variable heat flux, a sinusoidal function having a similar area as step function is considered at one wall of the container to provide heating and cooling of the PCM/Metal foam composite. A new mathematical model based on the Brinkmann-Forchheimer-extended Darcy equation and the local thermal non-equilibrium model (LTNE) is proposed by applying a two-energy equation. The paraffin phase change is modeled using the enthalpy-porosity method. The numerical results are validated by comparing them with the experimental data. The results showed that at the time of melting it has reduced with sinusoidal heating. The results also showed that the heat losses on the boundary have a greater effect in a sinusoidal heat flux case than in constant heat flux case and this effect is more important on the solidification than on the melting process of the paraffin.

Demodulating AM Square Signals via a Digital Timer for Sensor Applications

This article evaluates theoretically and experimentally the performance of a timer-based demodulator applied to low-frequency amplitude-modulated (AM) square signals coming from sensor circuits. The demodulator extracts the amplitude of the AM square signal by measuring the period of a reference triangular signal that is altered by the AM signal itself, as already suggested in a previous article but for AM sinusoidal signals. The demodulation and digitization are carried out simultaneously via a digital timer and without requiring a rectifier, a mixer, a low-pass filter, or an analog-to-digital converter, thus resulting in a simple and low-cost design solution. Unlike the sinusoidal case, this article proposes to infer the amplitude of the AM square signal by measuring the bias of the period measurement with respect to the ideal (known) value. Experimental results show a nonlinearity error lower than 0.03% full-scale span and a resolution of 13.3 bits.

A relativistic one dimensional band model with position dependent mass

In this note a one-dimensional band model is proposed based on a periodic Dirac comb having a periodic mass distribution m(x). The mass function is represented as a Hermitian, non-local separable operator. Two specific cases–a constant mass model and a sinusoidal mass model–are examined. The lowest electron and positron bands for the constant mass case are similar to those for the standard relativistic Kronig-Penney model, suggesting that non-locality has little influence. The results for the sinusoidal case are consistent with the expectation that at low wavenumber an electron “feels” it has an average constant mass, but at high wave number, the particle “sees” the periodic mass variation and the band is distorted.

Semiclassical optimization of entrainment stability and phase coherence in weakly forced quantum limit-cycle oscillators.

Optimal entrainment of a quantum nonlinear oscillator to a periodically modulated weak harmonic drive is studied in the semiclassical regime. By using the semiclassical phase-reduction theory recently developed for quantum nonlinear oscillators [Y. Kato, N. Yamamoto, and H. Nakao, Phys. Rev. Res. 1, 033012 (2019)10.1103/PhysRevResearch.1.033012], two types of optimization problems, one for the stability and the other for the phase coherence of the entrained state, are considered. The optimal waveforms of the periodic amplitude modulation can be derived by applying the classical optimization methods to the semiclassical phase equation that approximately describes the quantum limit-cycle dynamics. Using a quantum van der Pol oscillator with squeezing and Kerr effects as an example, the performance of optimization is numerically analyzed. It is shown that the optimized waveform for the entrainment stability yields faster entrainment to the driving signal than the case with a simple sinusoidal waveform, while that for the phase coherence yields little improvement from the sinusoidal case. These results are explained from the properties of the phase sensitivity function.

Phase shifting method for non-sinusoidal interference fringes with phase shift error

When applying phase shifting interferometry to practical phase measurement, the wave may become non-sinusoidal, and could include some phase shift errors. Prior phase shift algorithms are primarily used for sinusoidal cases, and can cause system errors when used for these non-sinusoidal interference. We propose two phase recovery methods for non-sinusoidal interference fringes: specifically, a least-squares-based fitting algorithm that eliminates system errors using a sufficient number of measured images, and a Fourier transform-based method that effectively suppresses system errors using a lower (or insufficient) number of images. Simulation and experimental results verify the efficacy of the proposed methods.

Numerical investigation of cold flow over regular and wavy V-gutters

In this paper, the numerical study of cold flow over two types of regular and wavy V-gutter flame holders has been presented. The edges of the V-gutter, which are smooth in the regular case, are shaped in a sinusoidal form with different phase angles on upper and lower edges. The three-dimensional numerical analysis has been performed using the finite volume method and the renormalization group k–ɛ model has been used for turbulence modeling. The results were compared and validated by an existing experimental work based on the particle image velocimetry method. This study provided the fluid flow structure behind the V-gutter, the dimensions of the recirculation region, the behavior of vortex shedding phenomenon, and the static pressure distribution in the wake area. According to the results, the recirculation length for the sinusoidal case with 90 ° of the phase difference is the largest compared with the other cases, which increases the mass flow rate of the fresh unburnt mixture into the recirculation region and improves flame stability. The results also show that the 90 ° wavy V-gutter case has the lowest pressure drop in the wake region, which reduces the drag coefficient against the main flow. The values of the Strouhal number are approximately the same and equal to 0.27 for both cases (the regular and the 90 ° cases). Therefore, it is concluded that the 90 ° wavy V-gutter shows better performance than the regular V-gutter in flame stabilization.

Comparative analysis of toxic components in different medicinal parts of Gynura japonica and its toxicity assessment on mice

BackgroundThe roots of Gynura japonica are used as traditional medicine for treating blood stasis or traumatic injury even though hundreds of hepatic sinusoidal obstruction syndrome cases have been reported after consumption of the roots, which contain large amounts of hepatotoxic pyrrolizidine alkaloids (HPAs). However, no information is available about the toxic compounds in the aerial parts of G. japonica, which are also used as herbal medicines and even vegetables in several areas. Thus, the toxic chemicals in the aerial parts of G. japonica, i.e., HPAs, must be urgently identified. PurposeIn this study, we aimed to 1) identify the toxic compounds in different medicinal parts and 2) examine the hepatotoxicity of G. japonica. Study designA total of 35 batches of the roots and aerial parts of G. japonica were collected from different sources and analyzed for HPAs. The hepatotoxicity of different extracts (i.e., total extracts [TE] and total alkaloids [TA]) and a single compound (i.e., senecionine) was evaluated on mice. MethodsQualitative analysis of HPAs was performed using an ultra-performance liquid chromatography (UPLC)-mass spectrometry (MS)-parent ion scan approach, whereas a quantitative assay was performed by a UPLC-MS-selected ion monitoring approach. Male C57BL mice were orally administered the different extracts or the single compound at dosages equivalent to 50 mg HPAs/kg body weight. The sera and the livers were collected at 48 h after treatment and used to evaluate the hepatotoxicity through serum clinical biomarkers assay, liver histology, and bile acid profiling. ResultsA total of 21 HPAs were identified in the roots and the aerial parts. The roots contained higher levels of HPAs (4.90 mg/g) than did the aerial parts (2.21 mg/g). TE and TA induced similar acute liver injuries, but senecionine was considerably more toxic than these extracts. Mice treated with TE showed significantly impaired bile acid homeostasis in the sera and the livers. ConclusionThe roots and aerial parts of G. japonica contained large amounts of HPAs, including senecionine, which were responsible for the hepatotoxicity of G. japonica. Bile acid homeostasis was uniquely impaired after exposure to the plant. Therefore, neither the roots nor the aerial parts of G. japonica should be consumed as medicines or vegetables.

RGSE-Based SPICE Model of Ferrite Core Losses

A SPICE model for estimating and simulating core losses of a ferrite magnetic device is presented. The approach is based on a proposed revised generalized Steinmetz equation (RGSE) and requires only the use of the Steinmetz coefficients and core geometry data. The letter presents a RGSE-based SPICE simulation strategy that can both estimate and simulate the effect of the core losses on the circuit. Primary advantages of RGSE approach are that it does not require switching frequency data and is applicable to arbitrary excitation and not just sinusoidal excitation as the Steinmetz equation approximation does. RGSE model is also insensitive to dc bias, this is an improvement over the earlier model. Comparison of previously reported measured and calculated core loss values with the simulation results of the presented SPICE RGSE model shows excellent agreement in the sinusoidal case and good agreement in the rectangular pulse case.

Heat transfer on topographically structured surfaces for power law fluids

The three-dimensional power law fluid flow through rough microchannels has been studied numerically to determine the effects of the topographic structures on the thermal and hydrodynamic characteristics of the system. Rectangular, triangular and sinusoidal element shapes have been considered in order to investigate the effects of roughness height, width, pitch and channel separation on the pressure drop and heat transfer. Uniform wall heat flux boundary condition has been applied for all the peripheral walls.The results indicate that the global heat transfer performance can be improved or reduced by the roughness elements at the expense of pressure head when compared with the smooth channels. The maximum heat transfer performance has been obtained for triangular roughness shapes with the relative roughness height of 0.333. In most cases heat performance is smaller than unity. It is also revealed that for the sinusoidal and triangular cases by decreasing the relative roughness width, heat transfer performance is improved. Furthermore, the effects of the roughness features and the channel separation are intensified in power-law fluids. For dilatant fluids with a power-law index equal to n = 1.25, channel separation ratio reduction causes a steep rise in normalized friction factor up to 140.8 in the rectangular case. By increasing the relative roughness pitch of the cases with rectangular elements and the power-law index of n = 0.75, a reasonable heat transfer performance enhancement has been observed.

Approximate output regulation of non-minimum phase hypersonic flight vehicle

To circumvent the non-minimum phase behavior in a hypersonic flight vehicle, an asymptotic flight tracking controller is investigated in this work. When the elevator is the only control surface available for the altitude dynamics, the hypersonic vehicle model exhibits unstable zero dynamics, preventing the application of standard inversion-based control techniques. The standard output regulation theory is utilized to design a nonlinear controller, achieving asymptotic tracking of velocity and altitude in a sinusoidal maneuver case with longitudinal acceleration and deceleration. Moreover, a three-layer neural network-based approximation method is presented to solve the center manifold equation for the output regulation problem. Finally, numerical simulations in MATLAB/Simulation Environment illustrate that the proposed controller is effective in providing favorable tracking performance and resisting unstable zero dynamics.