Effect Of Gap Distance Research Articles

Effect of Blade Gap Ratio on Turbine Performance in Drag-Based Vertical-Axis Wind Turbines

The aim of this study was to improve the performances of three-bladed vertical-axis wind turbines with gap distance. For this purpose, turbine design conditions such as a gap ratio between the blades and the addition of blades were changed to provide performance increase, and an aerodynamic performance-enhancing performance setup placed in front of the vertical-axis wind turbine was also used. Therefore, in this study, the effects of gap distance and blade addition on wind turbine performance were investigated, especially by keeping the aspect ratio of the vertical-axis wind turbine constant. The investigation of the effects of turbine design parameters, such as the gap distance and additional blade number, on turbine performance was carried out using the ANSYS Fluent program with a numerical analysis method validated with experimental data. The turbine gap ratio, at which the maximum torque coefficient of a three-bladed vertical-axis wind turbine is obtained, was determined to be 40% without performance setup and 30% with performance setup. It was determined that the average torque coefficient value obtained from the turbine with the addition of turbine blades and with the performance setup increased by approximately 66% compared to the torque coefficient value obtained from the three-bladed turbine without the performance setup. It was also determined that the maximum power coefficient obtained from the vertical-axis wind turbine with optimum turbine design parameters with the performance setup increased by approximately 46% compared to the maximum power coefficient obtained from the version of the turbine without the performance setup.

Snap-through dynamics of buckled flexible filaments in a side-by-side configuration

The flow-induced snap-through dynamics of side-by-side buckled flexible filaments in a uniform flow were investigated using the penalty immersed boundary method. We systematically examined the effects of gap distance and bending rigidity on the filament's motion and energy harvesting performance. Four distinct modes were observed as we varied the aforementioned parameters: the dual equilibrium mode, the dual streamwise oscillation mode, the single snap-through oscillation (STO) mode, and the dual STO mode. We analyzed the corresponding wake patterns associated with each of these modes. A phase transition from out-of-phase to in-phase motion was observed at low gap distances and bending rigidities. At lower gap distances, the interaction between two filaments was pronounced, leading to a co-motion of the filaments and enhanced elastic energy. This interaction decreased as the gap distance increased. Filaments in the 2STO mode exhibited significantly higher strain energy compared to the other modes. The elastic energy was concentrated at the rear part of the filaments and increased with higher gap distances and bending rigidities. Considering both energy harvesting efficiency and space utilization rate, a gap distance equal to 1 exhibited the best performance.

Discharge characteristics and development process of potential transfer gap in live-line work

Potential transfer is an essential link in equipotential live-line work (EPLW), which has a potential safety hazard. To ensure the safety of the linemen, this paper conducted experimental research on this process. First, to investigate the discharge characteristics of the potential transfer gap in EPLW, this paper developed a simplified experimental platform to examine the relationship between the transfer voltage and gap distance, as well as the electrode structure, during the potential transfer process. Second, to explore the discharge development process of potential transfer, this paper built a discharge observation experimental platform to observe the discharge process and explore the effects of gap distance and type of the floating electrode on the discharge development process and potential transfer current. The research results are valuable for practical projects and linemen safety.

Breakdown Characteristics of a Long Air Gap Containing a Floating Conductor Under Positive Switching Impulse

Experiments on the breakdown characteristics of a long air gap containing a floating conductor under switching impulse are carried out to address issues in live-line work engineering. The effects of gap distance, floating conductor structure, wavefront time, and high altitude on breakdown voltage are investigated, respectively. The results show that a floating conductor with sharp protrusions reduces the breakdown voltage and produces the lowest breakdown voltage area (LBA). The maximum reduction rate of the breakdown voltage and the position of the LBA vary with the gap distance. The position of the LBA is also related to the floating conductor structure. The results indicate that different floating conductor structures with similar electric field distortions have a similar effect on the breakdown voltage. For the effect of wavefront time on breakdown characteristics, the results show that the breakdown voltage under switching impulse with a long wavefront time is higher than that under a standard switching impulse. For the effect of high altitude, the results show that the LBA at high altitude is different from that at low altitude, and the high-altitude breakdown voltage corrected using the International Electrotechnical Commission (IEC) altitude correction method is not exactly the same as the actual experimental results.

Estimating the seismic pounding force between adjacent buildings and study the effect of gap distance on seismic pounding

Insufficient separation distance between adjacent buildings may lead to their pounding during strong earthquakes causing damage or local failure. Accordingly, most of the design codes specify a minimum separation or gap distance between adjacent buildings to prevent their seismic pounding. Main objectives of this research are studying the seismic pounding between adjacent reinforced concrete (RC) buildings under various ground motions and studying the effect of gap distance on seismic pounding. The studied buildings are modeled as three-dimensional frames to idealize the adjacent buildings. This study considers adjacent frame buildings having the same number of floors as well as frames having a different number of floors. Nonlinear finite element time history analysis is performed using ETABS commercial software. Three different real earthquake records with different characteristics are scaled and used to simulate ground motion. Nonlinear gap element is used to model pounding between buildings at their interface points. The results of the study indicate that, the maximum pounding force was investigated for each of the studied cases. Pounding does not occur between buildings having equal height. Increasing separation distance between buildings reduces the pounding force between them. Separation distance, which is estimated by the Egyptian code, is conservative.

Effect of slurry particles on PVA brush contamination during post-CMP cleaning

PVA (polyvinyl acetal) brush scrubbing is a widely used post-CMP cleaning process due to its low cost and high cleaning efficiency. However, during these processes, the PVA brush gets contaminated with abrasive particles that result in wafer cross-contamination and reduced cleaning efficiency. This study investigated the effects of abrasive types such as silica and ceria, the slurry pH, and the scrubbing process parameters on brush contamination. Ceria slurries showed significantly more contamination of brushes compared to silica slurries. The brush contamination increased with a decrease in pH from 7 to 4 due to increased electrostatic attractive forces between the ceria particles and the brush surfaces, although very low brush contamination was observed by the ceria slurries at pH 10 due to a strong electrostatic repulsion. Conversely, very low brush contamination was observed for the silica slurries at all pH values due to the reduced interaction between the particles and the brush surface (electrostatic repulsion). Furthermore, there was no significant effect of gap distance and brush rotation speed on brush contamination. The abrasive concentration and the contamination process time showed a linear relationship as the contamination was significantly increased by increasing the abrasive concentration in slurry and process time. These results indicate that brush contamination is more sensitive to the abrasive nature and concentration, the slurry pH, and the process time than to other parameters.

Parametric Study and Analysis of Modified Electromagnetic Band Gap in Frequency Notching of Ultra-Wide Band Antenna

This paper presents parametric study of dual band notch ultra wideband (UWB) antenna using modified electromagnetic band gap. The Electromagnetic Band Gap (EBG) comprises of two strip patched and an edge-located via with respect to ground for dual notch band. The study was presented in order to have an improved knowledge of EBG characteristics and its effect on the notching band of a small squared ultra wideband antenna of size 24 by 31 mm2 dual band notch using HFSS software. The antenna operates within the return loss (s11< -10dB) 3.2 to 12.3 GHz. The simulation results show that the notched band between 4.57 – 4.99 GHz and 7.96 – 8.32 GHz corresponding to WLAN and ITU respectively was achieved. The effect of gap distance between the field line and EBG was demonstrated as well and the position of via with respect to the ground as a means for notched band centre frequency tuning. The antenna could be considered a good candidate for any UWB applications that must avoid narrow band interference. The research gives ideas on the best placement position of EBG structure along field line in UWB antenna frequency notching technique.

Statistical analysis of pulsed spark discharges in water: Effects of gap distance, electrode material, and voltage polarity on discharge characteristics

Repetitive discharges in dielectric liquid are involved in many technological applications. The relatively poor reproducibility of such discharges, induced by significant modification of experimental conditions (electrode and liquid), hinders the understanding of their fundamental dynamics and optimizing processes. In this paper, we study the electrical characteristics of multiple discharges run in de-ionized water, at low frequency (3 Hz), using pin-to-plate electrode geometry, under varying conditions of gap distance (50–500 μm), electrode composition (Cu and W), and voltage polarity (amplitude of ±20 kV and pulse width of 500 ns). The voltage and current waveforms of each occurring discharge are recorded and then processed to determine the probability of discharge occurrence, breakdown voltage, discharge current, discharge delay, injected charge, and injected energy. The results show that the highest numbers of occurring discharges are achieved at shortest distance, using the Cu electrode, and negative polarity. The data points comprising the electrical characteristics waveforms (e.g., breakdown voltage) are more or less dispersed, depending on the electrode composition and voltage polarity. Moreover, in negative polarity, a reflected positive pulse of ∼5 kV is observed when discharges do not occur in the first pulse. Considering that these pulses may induce discharges, their characteristics are also provided. Finally, the voltage-current plots show appreciable dependence on discharge conditions, and the data are well fitted by linear profiles with slopes, i.e., resistances, that may reflect the ignition conditions of the discharge.

The Effect of Gap Distance between a Pin and Water Surface on the Inactivation of Escherichia coli Using a Pin-to-Water Plasma.

Atmospheric plasmas have been applied for the inactivation of microorganisms. Industrials demand to investigate the relation of the key reactive species induced by plasmas and the operating parameters including boundary conditions in order to control plasma treatment processes. In this study, we investigated the effect of gap distance between a pin-electrode and water surface on inactivation efficacy. When the gap distance decreased from 5 mm to 1 mm, the reduction of Escherichia coli (E. coli) was increased to more than 4 log CFU/mL. The reactive oxygen species measured optically and spectrophotometrically were influenced by gap distance. The results from electron spin resonance (ESR) analysis showed that the pin-to-water plasma generated hydroxyl radical (OH•) and singlet oxygen (1O2) in the water and superoxide radical (O2−•) served as a precursor of OH•. The inactivation of E. coli was significantly alleviated by sodium azide (1O2 scavenger), indicating that 1O2 contributes the most to bacterial inactivation. These findings provide a potentially effective strategy for bacterial inactivation using a pin-to-water plasma.

The Effect of Gap Distance between a Pin and Water Surface on the Inactivation of Escherichia Coli Using a Pin-to-Water Plasma

The Effect of Gap Distance between a Pin and Water Surface on the Inactivation of Escherichia Coli Using a Pin-to-Water Plasma

Monitoring multi-respiratory indices via a smart nanofibrous mask filter based on a triboelectric nanogenerator

Respiratory parameters, such as respiratory rate ( RR ), inhalation time ( t in ), exhalation time ( t ex ), and their ratio ( IER=t in / t ex ), are of great importance to indicate clinical differences between healthy people and those with respiratory diseases. Herein, we report a respiration monitoring triboelectric nanogenerator (RM-TENG) with nanofibrous membranes, which can be used as a smart, changeable, self-powered mask filter with high filtration efficiency for monitoring multiple respiratory indices (e.g., RR , t in , t ex , IER ). We created a mathematical model to quantitatively analyze the effects of gap distance between two triboelectric layers on the contact area by recording the nanofibers layer's deformation profile with digital image correlation (DIC) tests. The RM-TENG is more sensitive to smaller gap distances between 1 mm and 5 mm because the high specific area of nanofibers can provide a more effective contact area. An RM-TENG built with optimized structure parameters can accurately and consistently detect the above-mentioned respiratory indices with excellent sensing stability for 40 h. The monitored RR and IER have 100% and 93.53% agreement with the real-time RR and IER set on the ventilator, respectively. Furthermore, it has a filtration efficiency of 99 wt% for particle sizes between 0.3 µm and 5 µm. This study introduces a mask filter fabricated with a simple structure with both filtering and sensing capability, which has excellent potential for self-powered health diagnostics. • A TENG sensor for monitoring respiration is fabricated with two nanofiber layers. • A mathematical model is established to calculate the contact area between the two nanofiber layers. • A medical ventilator is used to examine the accuracy and stability of the TENG sensor. • The TENG attached to a commercial mask can monitor multi-respiratory indices. • The TENG is also an air filter with a filtration efficiency of 99 wt% for the particle size of 0.3–5 µm.

Effect of Gap Distance Between Fenestration and Aortic Wall on Target Artery Instability After Fenestrated-Branched Endovascular Aortic Repair

Target artery (TA) instability is the most frequent indication for secondary interventions after fenestrated-branched endovascular aneurysm repair (FB-EVAR) of pararenal aortic aneurysms (PRAAs) and thoracoabdominal aortic aneurysms (TAAAs). The aim of our study was to evaluate the effect of the fenestration gap (FG) distance on target-related outcomes after FB-EVAR.

Mode interpretation of interference effects between tall buildings in tandem and side-by-side arrangement with POD and ICA

In this study, the effect of gap distance on the aerodynamic interference effect of two neighboring buildings has been systematically investigated. Firstly, the variation of aerodynamic features of principal building with different gap distances (from 1.5B to 6B) and wind directions (from 0°to 180°) are analyzed. Then, Proper Orthogonal Decomposition (POD) and Independent Component Analysis (ICA) methods are employed to further unveil the interference mechanism under tandem and side-by-side arrangement. The spatial-spectral feature of surface pressure field, including pressure pattern, modal coefficients and correlation are comprehensively compared to highlight the differences of POD and ICA. The results show that 3B is recognized as the critical gap whose pressure pattern is more similar to the small gap type than the large gap type. Moreover, two new phenomena, “mode competition” and “mode transition”, are respectively captured by POD and ICA in tandem arrangement, and quantitively interpreted by modal load component ratio. For side-by-side arrangement, the variation of channeling effect with gap distance is well reflected by both POD and ICA pressure patterns. Compared with POD, ICA provides a more variety of information on pressure patterns by capturing their variation with gap distance on all four side-surfaces. These conclusions can enhance understanding of fluid–structure interaction mechanism and provide reference for wind-induced responses control measures for interference buildings.

Modeling accident risks in different lane-changing behavioral patterns

Lane-changing is a complicated task and has a high probability of accident occurrence. Although a large body of literature has used vehicle trajectories to microscopically understand and model lane-changing behavior, most of these studies focus on lane-changing decision making and lane changing's impacts on surrounding vehicles, not on traffic safety. The contributing factors to lane-changing risks have not been fully explored from the perspective of microscopic behavior using vehicle trajectory data. This study investigates the contributing factors to accident risks in different lane-changing patterns with taking unobserved heterogeneity into account. A vehicle trajectory dataset, HighD is used and 4842 lane-changing vehicle groups are extracted for analysis. These vehicle groups are divided into sixteen patterns according to the vehicle type, and three major patterns are examined. A lane-changing risk index (LCRI) is proposed to evaluate the risk level of each vehicle group. Two methods are developed and compared for exploring lane-changing risks of the three patterns including (1) establishing the random parameters fractional logit models; and (2) classifying LCRI by k-means algorithm and establishing random parameters ordered logit models with heterogeneity in means and variances. The modeling results show that the latter method performs better and the risk level of the vehicle group is strongly associated with (1) the mean and standard deviation of the gap distance between vehicles; (2) the longitudinal velocities and acceleration of vehicles; and (3) the lane-changing direction and duration. However, different patterns are found to have different contributing variables and effects. The effects of gap distances vary considerably across different vehicle groups and the longitudinal velocity of vehicles are associated with the means of random parameters for gap distance.

Production of aligned electrospun polyvinyl alcohol nanofibers via parallel electrode method

Uniaxially alignment of electrospun nanofibers is one of the main concerns to produce nanofiber yarns. Parallel electrode collectors have been used for this purpose. In this study, the effect of gap distance between parallel electrodes, electrode plate’s width, tip to collector distance (TCD) and charge density (CD) on uniaxial alignment and average diameter of polyvinyl alcohol (PVA) nanofibers in parallel electrode electrospinning is investigated. Scanning electron microscopy analysis is used to measure alignment angles and average diameters of the nanofibers. The results indicate that plate width is an effective parameter on the nanofiber alignment and need be considered with gap distance together. Increasing of gap distance and plate width together, increases the alignment of the nanofibers. Also, decreasing of CD and TCD increases the alignment of the nanofibers. Gap distance and plate width affect the average nanofiber diameter, but there is no obvious relationship.

The effect of photonic crystal fibre structure on the performance of Mach-Zehnder interferometer fibre optic gas sensors

A compact refractive index (RI) sensor, based on the Mach-Zehnder Interferometer (MZI), has been developed and experimentally evaluated for the highly sensitive detection and quantification of gases (Helium, Methane, and Carbon Dioxide). The RI sensor utilizes a variety of fibre types: Single Mode Fibre (SMF), Photonic Crystal Fibre (PCF), and Hollow-Core Photonic Crystal Fibre (HC-PCF). In order to fabricate the MZI sensors, a short length of sensing fibre was positioned between a lead-in and a lead-out single mode fibre (SMF) with an air gap at each interface. Three types of sensors were fabricated using this configuration employing 4 mm stub of: (i) PCF, (ii) 10 µm HC-PCF, and (iii) 20 µm HC-PCF as the sensing elements. The performance of these sensors, for detecting and measuring the quantity of gas present, were compared. The transmission spectrum of MZI sensors are formed by interference between the cladding and core modes. These transmission signals correspond to the frequency components in the sensor’s Fast Fourier Transform (FFT) spectrum. The effect of gap distance on the number and amplitude distribution of the modes was examined in an effort to optimize the design elements. The resulting fiber sensors can measure the RI of a gas-filled cavity and they showed high-sensitivity to helium, methane, and carbon dioxide. The highest RI sensitivity of 3210 nm/RIU was demonstrated in the RI range of 1.0000347-to-1.000449 by a sensor with a 4 mm long sensing stub element of 10 µm HC-PCF. Cyclic tests with the group of gases demonstrated that the measurements are highly repeatable. The measurement response and recovery times for all sensors were determined, and it was concluded that the 20 µm HC-PCF sensor has the fastest response/recovery time and the PCF sensor has the slowest. This research illustrates that the sensors fabricated by the proposed method have potential for improving the ability to detect and quantify pure gases. Additionally, the sensors are highly sensitive to low percentages of CO 2 , making them suitable for greenhouse gas measurement.

Effects of impingement gap and hole arrangement on overall cooling effectiveness for impingement/effusion cooling

The effects of geometrical parameters on overall cooling effectiveness were experimentally investigated on the flat plate with impingement/effusion cooling. Geometrical parameters investigated included two relative positions of impingement and effusion holes (staggered arrangement and overlapped arrangement) and three impingement gap distances (H/D = 2.5, 5 and 7.5). In addition, numerical simulation was employed to predict the effect of gap distance in a wider range. The results indicate that overall cooling effectiveness is significantly improved by adding impingement, while distribution of cooling effectiveness is mainly determined by film cooling and bore cooling. The comparison of cooling effectiveness between staggered and overlapped hole arrangement indicates that the former produces higher value at each blowing ratio and gap distance. At the same blowing ratio, the overall cooling effectiveness decreases as the increase of gap distance for staggered arrangement. For overlapped arrangement, the cooling effectiveness peaks at H/D = 10. Specific scaling principles of overall cooling effectiveness are experimentally validated by three cases with different temperature ratios. After matching mainstream side Reynolds number, Biot number, and the momentum flux ratio, the cooling effectiveness of case with lower temperature ratio agrees well with that of case with higher temperature ratio at each gap distance and hole arrangement.

벽 사이 간격이 원형 실린더 주위 유동의 비대칭성에 미치는 영향

To investigate an effect of gap distance on asymmetric features of the flow past a circular cylinder above a moving wall, the numerical simulations are performed for 0.2≤G/D≤10, where G/D is the ratio of gap distance between the cylinder and the wall. As the G/D decreases, the vortices formed in lower side of cylinder are getting to be suppressed. The asymmetric features of vortical behaviors in the lower and upper sides are hard to be clearly observed from the time histories of the drag and lift coefficients. We examined the temporal trajectories of C<SUB>d (L)</SUB> and C<SUB>d (U)</SUB>, where C<SUB>d (L)</SUB> and C<SUB>d (U)</SUB> denote the drag coefficients acting on the lower and upper side of cylinder respectively. The trajectories disclose three different features of flow regime. The first is alternately unsteady behaviors of unsuppressed upper- and suppressed lower-vortices where C<SUB>d (L)</SUB> is negatively proportional to C<SUB>d (U)</SUB>. The second is phase-shifted unsteady behaviors where a phase difference between C<SUB>d (L)</SUB> and C<SUB>d (U)</SUB> makes quasi-circular trajectories. The last is a steady state where C<SUB>d (L)</SUB> and C<SUB>d (U)</SUB> show a dot.

Ultrahigh thermal rectification based on near-field thermal radiation between dissimilar nanoparticles

The capability of manipulating heat flux at the nanoscale has many promising applications in modern electronics and information processing industries. In this paper, a design to achieve ultrahigh thermal rectification is proposed based on near-field thermal radiation between nanoparticles made of intrinsic silicon and a dissimilar material. A record-high rectification ratio of more than 104 is theoretically demonstrated, and the underlying mechanism lies in the prominent increase of imaginary part of dielectric function of intrinsic silicon induced by thermally excited electrons at high temperatures. Effects of gap distances, materials and configurations of nanoparticles on the rectification ratio are also investigated. This work may pave the way for the design of efficient thermal diodes, thermal transistors, and other thermotronics devices.

Analytical model of squeeze film air damping of perforated plates in the free molecular regime

In this paper, an analytical model of squeeze film damping (SQFD) of perforated plates in the free molecular regime is developed, which is based on: (1) the modification of the perforated energy transfer model (P-ETM) (Li and Hu, J Micromech Microeng 21:025006, 2011) by giving the probability of molecules entering the gap through holes; (2) the application of Sumali’s formula (J Micromech Microeng 17:2231–2240, 2007) to relate to the Monte Carlo model (MC) (Hutcherson and Ye, J Micromech Microeng 14:1726–1733, 2004) quantitatively. The analytical model can model the perforation effect on SQFD of plates of various hole sizes. Compared with experiment data and numerical models, the analytical model is proved to be accurate, easy to operate. The effect of gap distance on SQFD of perforated plate in the free molecular regime is discussed. Due to perforation effect, as gap distance increases, the damping constant of non-perforated plate decreases faster than that of perforated plate of the same size.