Gap Distance Research Articles

Vortex-induced vibration of a rotating cylinder with dual splitter plates

To explore suppression method on vortex-induced vibrations (VIVs) response of the rotating cylinders, the VIVs of two-degree-of-freedom rotating cylinders with dual splitter plates at a Reynolds number of 200 and a mass ratio of 2.6 are investigated via numerical simulations. The numerical results show that splitter plates are more effective at suppressing VIV in the cylinders with low rotation rates, and the suppression effect decreases with increasing rotation rate. Three flow patterns are defined [overshoot, merge shedding, and individual shedding], and the distributions of the flow patterns and wake patterns under different rotation rates and gap distances are discussed. The vibration–fluid force–wake interaction is analyzed, and the variation of flow patterns is accompanied by the sudden increase in amplitude and fluid force. In addition, the directional sensitivity of the lift and drag is discussed, the lift is more sensitive to the rotation rate, and the drag is more sensitive to the gap distance.

Enhancing efficiency in capacitive power transfer: exploring gap distance and load robustness

In this paper, the capacitive power transfer (CPT) technology is used as an alternative to inductive power transfer (IPT). CPT relies on electric fields that are not sensitive to the presence of any metals, utilizes metal electrodes for power transfer, and is less bulky compared to IPT. The proposed CPT system utilizes a Class-E resonant inverter with a double-sided inductor-capacitor (LC) matching circuit which operates at an optimum load, with a duty cycle, D=0.5 to gain an output power, W and efficiency, η=84.6%. The proposed CPT system enhances the system’s efficiency as compared to the past research while preserving the zero-voltage switching (ZVS) condition within a wider load range from 50 Ω to 1,316 Ω. This paper also shows that the proposed CPT system is less sensitive to load and coupling variations. Finally, the rate of power dissipated at varied load resistances, has been derived successfully to determine the sensitivity level of the proposed CPT systems toward load variations. These equations are then validated by plotting the efficiency graphs based on load and coupling variations.

Colossal Near-Field Radiative Heat Transfer Mediated by Coupled Polaritons with an Ultrahigh Dynamic Range.

Near-field radiative heat transfer (NFRHT) can exceed the blackbody limit by several orders of magnitude owing to the tunneling evanescent waves. Exploiting this near-field enhancement holds significant potential for emerging technologies. It has been suggested that coupled polaritons can give rise to orders of magnitude enhancement of NFRHT. However, a thorough experimental verification of this phenomenon is still missing. Here this work experimentally shows that NFRHT mediated by coupled polaritons in millimeter-size graphene/SiC/SiO2 composite devices in planar plate configuration can realize about 302.8 ± 35.2-fold enhancement with respect to the blackbody limit at a gap distance of 87 ± 0.8nm. The radiative thermal conductance and effective gap heat transfer coefficient can reach unprecedented values of 0.136 WK-1 and 5440 Wm-2K-1. Additionally, a scattering-type scanning near-field optical measurement, in conjunction with full-wave numerical simulations, provides further evidence for the coupled polaritonic characteristics of the devices. Notably, this work experimentally demonstrates dynamic regulation of NFRHT can be achieved by modulating the bias voltage, leading to an ultrahigh dynamic range of ≈4.115. This work ambiguously elucidates the important role of coupled polaritons in NFRHT, paving the way for the manipulation of nanoscale heat transport, energy conversion, and thermal computing via the strong coupling effect.

Close-Range Coordination to Enhance Constant Distance Spacing Policies in Oversaturated Traffic Systems.

In the pursuit of string stability within CACC (cooperative adaptive cruise control) platoons, prevalent research has favored constant time gap (CTG) spacing policies; namely, vehicle interspacing increases linearly with the speed. Although constant distance gap (CDG) spacing policies have greater potential to enhance traffic capacity, they suffer from notable limitations regarding string stability and diminished safety margins at high velocities. In our previous work, we proposed applying CDG in specific scenarios, such as starting platoons at signalized intersections, where traffic throughput is critical and safety requirements can be met due to relatively low speeds. We demonstrated the substantial potential of CDG to increase the capacity of signalized intersections under oversaturated conditions. However, our study also revealed potential performance drops of CDG in dense traffic networks. To address these issues, we propose close-range coordination between vehicles to (1) limit platoon length, (2) create gaps for merging, and (3) avoid entering intersections when there is a high likelihood of stopping within the intersection area. In this paper, we extend our previous work by implementing these three measures. We successfully evaluate their positive impact on CDG's performance in entire traffic systems through large-scale traffic simulations involving several thousand vehicles, thereby affirming our earlier hypothesis.

Theoretical and experiment optimization research of a frequency up-converted piezoelectric energy harvester based on impact and magnetic force

Harvesting environmental vibrations to power electronic components is an essential approach for addressing the power supply challenge in MEMS. However, conventional vibration energy harvesting systems frequently suffer from limited frequency bandwidth and high-frequency deficiencies. This paper proposes a novel up-frequency structure for piezoelectric vibration energy harvesting (VEH) that relies on both nonlinear magnetic force and piecewise linear force. The proposed VEH’s nonlinear dynamic characteristics are analyzed theoretically, and an experimental prototype machining and vibration test platform are constructed. Theoretical and experimental results are compared and analyzed by conducting basic experiments and key parameter optimization experiments. The research results demonstrate that the proposed VEH can efficiently harvest vibration energy in low-frequency and wide-band environments. Regarding the system parameters, higher vibration acceleration results in increased output voltage and wider working frequency bandwidth. Reducing the gap distance enhances piecewise linear vibration, which broadens the working frequency bandwidth. Furthermore, the proposed VEH’s ability to harvest low-frequency vibrations can be enhanced by reducing the magnet distance, thereby reducing the linear resonance frequency of the system. The findings of this study offer valuable insights for advancing the engineering application of MEMS self-power supply technology.

Trueness of 3D-printed cobalt chromium versus titanium removable partial denture clasps.

The purpose of this in vitro study was to evaluate the trueness of removable partial denture clasps fabricated with titanium (Ti) through the selective laser melting (SLM) technique compared to cobalt-chromium alloys (CoCr). A virtual Aker clasp was designed on a scanned tooth, and SLM printers were used to print 20 claps using cobalt chromium (n = 10) and titanium alloy (n = 10). The deviation between the printed clasps and reference design was measured using the surface matching software (Geomagic control x) at rest, retentive tip, reciprocal tip, retentive shoulder, and reciprocal shoulder. An Independent t-test was used to determine the influence of 3D-printed material on the trueness (a = 0.05). The gap distance in mm between the reference design and printed in titanium showed an average of 0.0001 ±0.0544, 0.0256 ±0.1309, 0.0230 ±0.1028, 0.0701 ±0.1234, and 0.0013 ±0.0735mm in rest, reciprocal arm tip, retentive arm tip, retentive arm shoulder, and reciprocal arm shoulder, respectively. The gap distance in mm between the reference design and printed clasps in CoCr alloy showed an average of 0.0316 ±0.0692, 0.2783 ±0.1678, 0.1446 ±0.1528, 0.0315 ±0.0906, and 0.0419 ±0.1088mm in rest, reciprocal arm tip, retentive arm tip, retentive arm shoulder, and reciprocal arm shoulder, respectively. The difference between titanium and CoCr alloys at each observation site was significant. Clasps fabricated from titanium with SLM printing have the least deviation and better trueness compared to those fabricated from cobalt chromium.

EVALUATION OF ENHANCED SOLAR DESALINATION SYSTEM PROTOTYPE

Solar desalination technology has been one of the effective solutions to tackle the problem of water scarcity. A number of studies have been conducted at our water research group to determine which variable influences the quantity of distilled water produced by an independent solar desalination unit. Aims: This study was aimed to design and optimize a novel solar desalination unit and field-tested using the best variable from the previous studies. Methodology and results: Variables used from the previous studies were evaluated to obtain the best values for each parameter, those are: glass cover inclination, gap distance between water and glass cover, insulation thickness, water depth, and water mass flow rate. Those best values were then implemented in the optimized basin design, delivery mechanisms, evaporation techniques, and heat isolation methods. The optimized design can generate up to 2,778.2 mL/m2/8hrs of distilled water with an efficiency of 23.35% in preliminary test, and was field tested at Batukaras Beach, where it produced up to 902 mL/m2/8hrs with an efficiency of 13.56%. Conclusion, significance and impact study: Meteorological parameters and environmental conditions are important factors that greatly affect the performance and productivity of the desalination unit. The relative humidity is inversely proportional to the volume of distillate water, where the smaller the value, the greater the amount of distillate water that can be produced, and it has significant impact on the productivity of the prototype. The quality of the distillate water produced still needs improvement on the parameters of pH, turbidity, and total coliform.

Reversal of the electric field and the anode fall in DC arcs in air during contact opening

A unified one-dimensional model of an arc plasma in air, between copper electrodes, that includes the change of the gap distance is presented. The occurrence of multiple reversals of the electric field and the anode voltage drop is observed. The evolution of the spatial distribution of the electron and heavy particle temperatures with the gap distance and the opening speed is also studied. The model quantitatively predicts a number of plasma properties under conditions that are relevant to the contact separation in low-voltage switching devices.

Gap distance of UHV substation in areas with an altitude of 5000 m and below

Abstract In view of the increasing energy consumption and power demand, the construction of UHV AC is growing rapidly, and the construction of the project is gradually advancing to higher altitudes. It is urgent to conduct research on typical gap discharge in substations at high altitudes. Combined with the engineering requirements, this paper corrects the test data at an altitude of 0 m according to GB/T 24842 standard through altitude correction and combines the discharge voltage requirements of various typical gaps in substations to obtain the minimum air gap distance in UHV substations at an altitude of 5000 m and below. The calculation results of the two altitude correction methods are compared and analyzed, and the applicability of the two methods is analyzed.

Wind loads on a square high-rise building under aerodynamic interference effects of a short building in close proximity

Although the interference effect of an equally high or higher building has been examined extensively, the interference effect of a short building in close proximity on the wind pressure of a high-rise building has not yet been investigated comprehensively and thoroughly. In view of the fact that a newly built wind-sensitive high-rise building is more likely to be close to neighboring shorter buildings, this research focuses on wind loads of a square high-rise building under the interference effect of a short building in close proximity. Wind pressure on the principal square building model is measured by wind tunnel test for a series of cases of interfering buildings with different heights and gap distances. In addition, computational fluid dynamics simulation is conducted for a few typical cases. Characteristics of wind flow and pressure on the principal building are then discussed in detail for three typical interfering configurations to uncover the mechanism of interference effect of a short building. Although a short interfering building in many cases tends to decrease wind loads on the high-rise building, especially for the dynamic component of wind loads, the interfering effect from a short building could induce damage to cladding structures from the increased tension caused by the asymmetrical wind pressure, channeling effect, and the wind-over-top flow over the short interfering building.

Research on the method of air gap clearance selection for bushing at high-altitude areas

Abstract As an important component of the core equipment of the UHV substation, the operation reliability of the bushing is directly related to the safe operation of the main equipment. There are some technical problems in the development of casing in the Sichuan-Chongqing project, such as technical problems at high altitudes and a lack of relevant experience in the correction of air gap and equipment external insulation altitude. Therefore, there is an urgent need to research the selection of gap distance for UHV AC substation bushing electrical characteristics test in high altitude areas. In this paper, based on the standard meteorological conditions and the rod-plate gap switching impulse discharge test data at an altitude of 4300 m, the minimum gap distance of UHV AC substation bushing withstanding 1800 kV and 1950 kV under different methods is obtained. The results show that by comparing the two calculation methods, the minimum distance calculation method of the true test combined with the gap coefficient method avoids the error of altitude correction, and the minimum gap distance is reduced by 7.84%-14.17% compared with the former. The research content can provide a reference for selecting the dry arc distance of the casing. The next step should be to carry out the discharge characteristic test of the true-size electrode at a high altitude, so as to simulate the field situation more realistically and provide more powerful technical support for the project.

Analysis of gap distance of ultra high voltage AC transmission lines in areas with altitude above 2000m

Abstract Research on long-wave front discharge characteristics of lines and long gaps of substation equipment in high-altitude areas needs to be conducted in a systematic manner immediately in order to guarantee the safety and economy of high-altitude UHV lines with respect to external insulation. However, at present, the gap discharge test of transmission lines is mainly carried out in areas below 2000m above sea level. The actual test is challenging to conduct in the high altitude region, and the test data is incomplete. To further confirm the validity of extrapolation of existing altitude test data to high altitude areas, this paper conducts theoretical analysis based on the real test data under standard meteorological conditions provided by GB/T 24842 standard. The altitude correction methods in IEC 60071-2: 2018 and IEC 60060-1: 2010, the m-coefficient method and g-parameter method, are used to correct the lightning impulse, power frequency, and standard switching impulse of AC transmission line gaps. The discharge voltage in areas below 5000m above 2000m is obtained, and several significant discharge characteristic parameters are obtained. Based on the 50% discharge voltage requirements of various voltage types of 1000kV transmission lines, combined with the discharge voltage curves at multiple altitudes, the minimum air gap distance of transmission lines at the altitude of 2000m-5000m is obtained. The comparative analysis of the correction results of the two methods provides a way of thinking for the next step to carry out the true test of UHV AC transmission line gap discharge in higher elevation regions.

Measurement of wing motion, deformation, and inertial forces of a biomimetic butterfly.

This paper introduces a method for measuring wing motion, deformation, and inertial forces in bio-inspired aircraft research using a camera motion capture system. The method involves placing markers on the wing surface and fitting rigid planes to determine the wing's spatial axis. This allows for describing the wing's rigid motion and obtaining deformation characteristics, such as deflection, twist angle, and gap distance of the forewing and hindwing. An image-based method is proposed for determining wing mass distribution, mass blocks, and mass points for inertial force measurement. The study addresses wing motion, deformation, and inertial force measurement in a real butterfly-like flapping wing vehicle and demonstrates the effectiveness of the approach. The results reveal that inertial forces play a negligible role in the generation of lift peaks and contribute minimal lift during the entire flapping cycle. Furthermore, a transitional phase between downstroke and upstroke is found in flexible wing motion, which has high lift production. This measurement approach offers a rapid and effective solution to experimental challenges in bio-inspired aircraft design and optimization.

Evaluation of Gap Distance of Different Types of Resin-Based Composites on Extracted Permanent Molars: In-Vitro Study

Evaluation of Gap Distance of Different Types of Resin-Based Composites on Extracted Permanent Molars: In-Vitro Study

The contribution of electrode spacing and operating voltage on the time-resolved optical emission spectra of atmospheric-pressure air and Ar DBD plasma

This paper reports the optical characterization of a controlled atmospheric-pressure dielectric barrier discharge (DBD) plasma source in air and Ar environments. In this study, Ar flow rate is held constant at 1 L/min while the operating voltages varied from 6.5 kV to 12.7 kV. Under these conditions, a calibrated commercial compact spectrometer covering the range from 200 to 850 nm was used to record the emission spectra of DBD plasma operating at different voltages, gap distances, and gas types. Using the Boltzmann distribution, we calculated the electron density ( n e ) and excitation temperatures in the plasma of air and Ar DBD at 2 mm gap distance . The emission spectra lines of the hydroxyl radicals (OH), N 2 , and Ar ions are acquired at different operating conditions. According to the findings, the light intensity of Ar DBD is significantly higher than that of air DBD under the same conditions of operation. The intensity of the generated plasma spectrum is also shown to rise with both an increase in the input voltage and a decrease in the gap distance. The measurements also showed that the average temperature of the excited electrons is around 1.1 eV for air DBD and 0.11 eV for Ar DBD, while n e for both is on the order of 10 16 cm − 3 . These results show that as the working voltage increases, the plasma changes from a filamentary state to a homogeneous mode. Knowing the DBD parameters increases its chance to compete with traditional methods in many fields, such as water, polymers, and biomedical treatments.

Assessment of the Aerodynamic and Aeroelastic Performance of Long-Span Twin-Box Bridges Based upon Multidimensional Surrogate Models

Twin-box decks are being extensively used in the design of long-span bridges due to their superior flutter performance. Although the significant role played by the gap distance has been previously addressed in the frame of experimental studies, there is still a lack of understanding about the complex interplay between box geometry, gap distance and the aerodynamic force coefficients and flutter derivatives. In the present work, firstly, a surrogate model is developed, considering three design inputs for the geometry of the deck along with the angle of attack, providing the force coefficients as output. Afterwards, the work is then extended by developing another surrogate model, considering as inputs the reduced velocity and the same geometric variables of the deck, with the outputs being the flutter derivatives. The methodology, comprising the selection of the design domain, the definition of the samples, the CFD-based evaluation of the samples' response and the construction of the surrogate through the application of the neural network-based radial basis method, is reviewed. The surrogate models enable a quantitative description of the impact caused in the force coefficients and the flutter derivatives by modifications in the geometry of the twin-box deck. It has been found that flutter derivatives H1*, H2* and A2* are strongly dependent on the gap distance.

Radiative heat transfer between biaxial hyperbolic film in the far-field and near-field

Thin films demonstrate considerable potential in the realms of radiative heat transfer and play a major role in thermal rectification and energy conversion. Hyperbolic materials can effectively promote radiative heat transfer due to the ability to excite hyperbolic polaritons in a wide range of hyperbolic bands. However, the potential of biaxial hyperbolic film in radiative heat transfer remains insufficiently explored. In this work, the radiative heat transfer between α-phase molybdenum trioxide (α-MoO3) is theoretically investigated, considering separations ranging from 20 nm to 2 μm. When considering radiative heat flux along the [010] direction, the near-field radiative heat flux of α-MoO3 with a thickness of 10 nm is only 8 % less than that of the bulk material and exceeds the blackbody limit by approximately three orders of magnitude at a separation of 20 nm. This phenomenon is attributed to the excitation of hyperbolic polaritons. Conversely, when the gap distance is 1000 nm, the heat flux between films is an order of magnitude lower than that between bulk materials. These findings help study radiative heat transfer between thin films at micro- and nano-scale.

Prediction of Regional Broadband Strong Ground Motions Using a Teleseismic Source Model of the 18 April 2014 Mw 7.3 Papanoa, Mexico, Earthquake

ABSTRACT To estimate predicted ground motion from a teleseismic slip model, we use a low- and high-frequency hybrid method to simulate the regional, strong ground motions observed following the 18 April 2014 moment magnitude (Mw) 7.3 Papanoa, Mexico, earthquake. To generate the regional ground motion at low frequencies (<1 Hz), a teleseismically derived, finite-fault, kinematic model is used to define the earthquake source, taking into account slip-model variations identified with a parameter sampling approach that considers possible errors in the fault geometry, the hypocenter depth, and the rupture velocity. A 3D crustal model is used to calculate the low-frequency ground motions using a finite-element calculation that includes topography and considers variations in the source model to estimate the uncertainty in the calculations. High frequencies (>1 Hz) are added using a 1D full-wave propagation code that estimates uncertainties by considering multiple random distributions of slip with different spatial correlation lengths. The synthetic, broadband (0.05–10.0 Hz) ground motions are obtained by combining the low- and high-frequency portions match filtered at 1 Hz. These synthetic ground motions are compared with the regional observations using velocity records, peak ground acceleration, and medians of the orientation-independent response spectra of the horizontal components (RotD50) calculated at periods of 0.2, 0.3, 0.5, 1.0, 2.0, 3.0, 5.0, 7.5, and 10.0 s. The results indicate that ground motions estimated at these periods using our hybrid approach based primarily on a teleseismically derived source model are comparable to the values observed for the 2014 Papanoa earthquake at regional distances. The approach could be used to estimate strong-motion spectral levels expected for regions with limited local and regional recordings and could also fill in magnitude or distance gaps in ground-motion prediction relations utilized in the assessment of seismic hazard.

Achieving Low Voltage Plasma Discharge in Aqueous Solution Using Lithographically Defined Electrodes and Metal/Dielectric Nanoparticles.

Because of the high dielectric strength of water, it is extremely difficult to discharge plasma in a controllable way in the aqueous phase. By using lithographically defined electrodes and metal/dielectric nanoparticles, we create electric field enhancement that enables plasma discharge in liquid electrolytes at significantly reduced applied voltages. Here, we use high voltage (10-30 kV) nanosecond pulse (20 ns) discharges to generate a transient plasma in the aqueous phase. An electrode geometry with a radius of curvature of approximately 10 μm, a gap distance of 300 μm, and an estimated field strength of 5 × 106 V/cm resulted in a reduction in the plasma discharge threshold from 28 to 23 kV. A second structure had a radius of curvature of around 5 μm and a gap distance of 100 μm had an estimated field strength of 9 × 106 V/cm but did not perform as well as the larger gap electrodes. Adding gold nanoparticles (20 nm diameter) in solution further reduced the threshold for plasma discharge to 17 kV due to the electric field enhancement at the water/gold interface, with an estimated E-field enhancement of 4×. Adding alumina nanoparticles decorated with Pt reduced the plasma discharge threshold to 14 kV. In this scenario, the emergence of a triple point at the juncture of alumina, Pt, and water results in the coexistence of three distinct dielectric constants at a singular location. This leads to a notable concentration of electric field, effectively aiding in the initiation of plasma discharge at a reduced voltage. To gain a more comprehensive and detailed understanding of the electric field enhancement mechanism, we performed rigorous numerical simulations. These simulations provide valuable insights into the intricate interplay between the lithographically defined electrodes, the nanoparticles, and the resulting electric field distribution, enabling us to extract crucial information and optimize the design parameters for enhanced performance.

Freezing of Water Solvation Dynamics in Nanoconfinement by Reverse Micelles at Room Temperature.

Much attention has recently been paid to anomalously low dielectric constants of nanoconfined water between two slabs at room temperature (Fumagalli et al. Science, 2018, 360, 1339). These low values imply that the dipole rotation of the interfacial water on the slab is completely suppressed. Such freezing has so far been observed for water confined between solids. In contrast, it remains unclear whether this holds for water in soft confinement, which is omnipresent naturally and artificially. Here, we address this question using encapsulated reverse micelles with a dye molecule, allowing us to study water sandwiched between the surfactant and dye molecules in solution. Moreover, we examine the solvation related to the dielectric property of water, which is reorientational motion in the hydration layer of the dye molecule, by persistent hole-burning spectroscopy. We first show that the dye molecule is surrounded by water without contact with the surfactant and that the dye molecule has two or three hydration layers on average. We next demonstrate that the solvation dynamics is frozen below the water droplet size of ∼4 nm, whereas they become liquid-like when the RM size is further increased. The average gap distance (∼1.5 nm) for freezing the solvation agrees with the gap distance with no rotational water motions between slabs. Our findings may have biological relevance, providing a new aspect for understanding biological function in cells.