Gap Height Research Articles

A Study on the Detent Torque and Holding Torque of a Micro-Claw Pole Stepper Motor.

The micro-claw pole stepper motor is widely used in the field of camera modules and VR focusing. The influence of torque ripple on positioning accuracy becomes more obvious with a decrease in motor volume. In order to reduce the torque ripple of the micro-claw stepper motor and increase the load capacity of the motor, the torque of the motor is simulated by using finite element software. Firstly, the influences of four parameters, namely air gap, magnet thickness, claw thickness and claw height, on the detent torque and holding torque of the claw permanent magnet stepper motor are obtained through the Taguchi experiment. The Signal-to-noise ratio (SNR) of each factor to the response was calculated and the degree of influence of the four parameters on the detent torque and holding torque of the micro-claw pole permanent magnet stepper motor was determined. Then, the optimal value of each factor to reduce the detent torque and increase the holding torque was obtained through optimization analysis. Finally, experiments were carried out to test the holding torque of the motor, and the accuracy of the results was verified by comparing the test values with the simulation values. According to the analysis of the paper, the response delta of air gap to detent torque is the largest, reaching 5.99, and that to holding torque is 0.73. The response delta of the magnet thickness to the detent torque is 5.87, and the response delta to the holding torque is 1.52. The optimized parameters obtained by optimization analysis reduce the detent torque of the motor by 26.74% and increase the holding torque by 18.35%. It is found that air gap and permanent magnet thickness have the greatest influence on the detent torque and holding torque of a micro-claw permanent magnet stepper motor, followed by claw thickness and claw height. Among them, the air gap has more influence on the detent torque than on the holding torque, and the thickness of the permanent magnet has more influence on the holding torque than on the detent torque.

Performance investigation and design optimization of novel rotating-cylinder sliding vane rotary compressors

Novel rotating-cylinder sliding vane rotary compressors (RC-SVRCs) are promising machines in energy conversion systems due to extremely low friction. However, three-dimensional visual investigations on geometrical optimizations of RC-SVRCs are highly limited. Besides, most flow mechanisms and leakage flow affected by geometric structures have not been fully revealed yet. Therefore, the sliding vane number, gap heights at vane tips and length-to-diameter ratio are numerically studied in this work. The results show that more sliding vanes (4∼12) lead to more uniform flow and temperature fields, lower mass flow rates and outlet temperature, less leakage between rotor and rotating cylinder. The mass flow rate, leakage mL1 between rotor and cylinder and leakage mL2 at vane tip of 8-sliding-vane scheme are 2.944 × 10−2, 9.949 × 10−4 and 3.692 × 10−5 kg·s−1, respectively. Gap height at vane tips has vital effects on flow fields. As the gap increases (0.01∼0.05 mm), mass flow rate and isentropic efficiency are decreased by 12.68% and 18.26%, the outlet temperature, leakage mL1 and mL2 are increased by 91.5 K, 69.60% and 22 times, respectively. High-temperature areas and leakage flow increase with the increase of cylinder length, which is recommended no longer than 0.6 diameters. This work allows making recommendations for designing RC-SVRCs.

Multilayer Masking Technology for Fabricating Airborne CMUTs With Multi-Depth Fluidic Trenches

This paper presents a novel multilayer masking technology for fabricating airborne capacitive micromachined ultrasonic transducers (CMUTs) with multi-depth fluidic trenches, in which a plurality of masking layers for different etch depths are selectively patterned prior to the real etching to keep a planar wafer surface. The multi-depth fluidic trenches are utilized to effectively control the squeeze film within the CMUT gap and tune the fractional bandwidth (FBW) of CMUT. As such, the FBW can be changed over a wide range by only adjusting the trench height. With further lowering the gap height, the FBW can be extremely widened up to 168%. The receive sensitivity has also been significantly improved through the process of local oxidation of silicon to reduce the parasitic capacitance. The proposed multilayer masking technology enables the fabrication of airborne CMUTs with different FBWs and sensitivities on the same wafer and further combine these devices into arrays for high-resolution imaging and photoacoustic or thermoacoustic applications. These devices also provide a low minimum detectable pressure (MDP), as low as 1.37 mPa in the FBW of 13.5% for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8.5~\mu \text{m}$ </tex-math></inline-formula> deep fluidic trenches and 1.52 mPa in the 17.2% FBW for the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$16.2~\mu \text{m}$ </tex-math></inline-formula> trenches. Furthermore, the multilayer masking technology demonstrates the capability of building microelectromechanical systems (MEMS) with multi-depth micro/nanostructures. [2021-0090]

Heat Transfer and Pressure Drop in Single-Phase Flows in Tapered Microchannels

Abstract This paper presents a comparison of heat transfer and pressure drop during single-phase flows inside diverging, converging, and uniform microgaps using distilled water as the working fluid. The microgaps were created with a plain 10 mm × 10 mm heated copper surface and a polysulfone cover that was either uniform or tapered with an angle of 3.4 deg, and average gap heights of 400 and 800 μm. Experiments were conducted with single-phase water flow with an inlet temperature of 30 °C for flow rates varying from 57 to 498 mL/min and heat flux from 27 to 153 W/cm2 depending on the flowrate and microgap configuration. The uniform configuration resulted in the lowest pressure drop due to the less constricted flow. A slight decrease of pressure drop with heat flux was observed due to temperature dependent properties. The best heat transfer performance was obtained with the converging configuration, which was especially significant at low flow rates and shorter average gap. This behavior could be explained by an increase in the heat transfer coefficient due to flow acceleration in the converging gaps, which compensates for the decrease in temperature difference between the fluid and the surface along the flow length. Overall, the converging microgaps have better performance than uniform or diverging ones for single-phase flows, and this effect is more pronounced at lower flow rates, where the fluid experiences higher temperature changes.

Theoretical and experimental investigation on the seismic performance of a novel variable-damping viscous fluid damper

This paper presents a novel three-stage variable-damping-coefficient viscous fluid damper (VCVFD) and investigates its effectiveness in mitigating the seismic structural response. The concept and design of the displacement-dependent VCVFD were based on the equations for one-dimensional viscous flow in the damper orifice. A series of performance tests on VCVFDs were conducted to investigate the mechanical behaviour of the dampers with different design parameters under various loading conditions. The damping force increases more significantly than in the conventional viscous fluid damper (VFD) when the operating displacement is larger, and the expected effect of variable damping is achieved. A smaller gap height is more beneficial to energy dissipation in the VCVFD. Moreover, the hysteresis loop of the VCVFD was consistent with the theoretical results. To validate the effectiveness of the VCVFD in structural control, shaking table tests of two-storey steel frames equipped with VCVFDs under different seismic intensities were conducted. VCVFD can slightly increase the natural frequencies of the steel frame and significantly increase the structural damping ratio. The effectiveness of the VCVFD in mitigating the structural acceleration under low earthquake intensities was not prominent, but as the earthquake intensity increased, the acceleration amplification factor decreased. The added damping contributed by VCVFDs can significantly reduce the displacement response. It is concluded that with reasonable damping structural design, the VCVFD can achieve an almost similar mitigation effect as VFD in low-intensity earthquakes, whereas the VCVFD can provide higher damping under high-intensity earthquakes.

Experimental investigation and discrete element modeling for particle-scale powder spreading dynamics in powder-bed-fusion-based additive manufacturing

Experiments and discrete element method simulation are combined to systematically reveal the particle-scale powder spreading dynamics based on the actual situation in additive manufacturing. To the best of our knowledge, this is the first report that introduces experimental calibration of powder layer height and line-contact triangular blade in the simulation. The results show that contributions of powder bed to the packing density fluctuations originate from the combined effect of gap height, particle jamming, and scraping effect. Due to the presence of force arches, long-duration jamming events with duration more than 5 times the normalized survival time, are necessary for the formation of empty patch. Instantaneous scraping effects lead to particle collisions and elastic deformation, which enhances the sensitivity of particle bursts after the blade. Overall, this study establishes a practical solution to optimize the particle packing state and provides support for subsequent modeling of laser-material interaction and melt pool dynamics.

Numerical investigation on the generation mechanism of aero-heating of rudder shaft from three-dimensional flow separation and vortices

The hypersonic flow past a controlled rudder mounted at a gap to the aircraft fuselage is numerically investigated by solving three-dimensional (3D) Reynolds-averaged Navier–Stokes equations. This paper aims to explain the mechanism of production of extreme thermal environment faced by a rudder shaft from the view of physics of flow in the mounting gap. Simulations are conducted at Mach number of 10, and the gap ratio h/δ varies from 0 to 1.42, where h denotes the gap height and δ represents the thickness of the incoming turbulent boundary layer. Topological theory is utilized to identify the separation types. The formation of vortices is traced by extracting volume streamlines in the 3D space. The results indicate that the types of 3D separation appear in the gap shifts from the coexistence of horseshoe-type and tornado-type separations to only horseshoe-type separation that persists with the increase of h/δ. It is found that high heat flux is generated by the high-momentum fluid transported toward the surface by the horseshoe vortices. The tornado-type vortex prevents the incoming flow from arriving at the rudder shaft, which avoids the generation of high heat flux at the center of the rudder shaft. The rate of local heat transfer increases with h/δ as a result of the shrink and disappearance of the tornado-type vortices, which means that the region of low-speed backflow in front of the rudder is reduced and vanished. This study contributes to a clearer understanding of the flow physics in the complex disturbance area.

Experimental Study of the Fire Dynamics in a Semi-enclosure Formed by Photovoltaic (PV) Installations on Flat Roof Constructions

Flame spread experiments upon a BROOF(t4) compliant flat roof mock-up located below a vertical barrier were carried out for variations in gap height, inclination, subjacent insulation material, and the barrier type (stainless-steel board or photovoltaic (PV) module). A binary flame spread scenario was identified, where re-radiation from the flame facilitated self-sustained flame spread if the gap height to the horizontal panel was below 10 cm for the stainless-steel board and 11 cm for PV modules. These were defined as the critical gap heights. Inclination of the PV modules increased the critical gap height and caused a 25% faster flame spread rate (FSR) than the FSR below horizontal modules with the same gap height at the location of ignition. The faster FSR for inclined modules caused a 40% reduction of the maximum temperature measured at a depth of 70 mm in the insulation materials (242°C). Based on temperatures measured in the insulation materials, the 60 mm polyisocyanurate (PIR) insulation performed slightly better than the 50 mm mineral wool insulation. However, it is expected that the mineral wool would outperform the PIR insulation if tested with the same thickness, as it insulates significantly better at high temperatures. Finally, no sustained flame spread was observed on the back side polymer sheet of the PV modules, but one of the three PV module brands produced burning droplets. Based on the experiments, it can be concluded that the current standards are inadequate as the introduction of a PV system on a compliant roof construction enables flame spread.

Factors influencing the outcome after surgical reconstruction of OTA type B and C tibial plateau fractures: how crucial is the restoration of articular congruity?

IntroductionOnly few and inconsistent data about the impact of articular congruity and tolerable residual intraarticular steps and gaps of the joint surface after tibial plateau fractures exist. Therefore, aim of this study was to investigate the correlation between OTA type B and C tibial plateau fracture outcomes and postoperative articular congruity using computed tomography (CT) data.Materials and methodsFifty-five patients with a mean age of 45.5 ± 12.5 years and treated for 27 type B and 28 C tibial plateau fractures with pre- and postsurgical CT data were included. Primary outcome measure was the correlation of postoperative intraarticular step and gap sizes, articular comminution area, the postoperative medial proximal tibial angle (MPTA), and the Lysholm and IKDC score. Receiver-operating characteristic (ROC) curves were used to determine threshold values for step and gap heights according to the following outcome scores: IKDC > 70; Lysholm > 80. Secondary outcome measures were the correlation of fracture severity, the number of complications and surgical revisions and the outcome scores, as well as the Tegner activity score before injury and at final follow-up.ResultsAfter a mean follow-up of 42.4 ± 18.9 months, the mean Lysholm score was 80.7 ± 13.3, and the mean IKDC score was 62.7 ± 17.6. The median Tegner activity score was 5 before the injury and 4 at final follow-up (p < 0.05). The intraarticular step height, gap size, comminution area and MPTA deviation were significantly negatively correlated with the IKDC and Lysholm scores. The cutoff values for step height were 2.6 and 2.9 mm. The gap size threshold was 6.6 mm. In total, an average of 0.5 ± 0.8 (range 0–3) complications occurred, and on average, 0.5 ± 1.1 (range 0–7) surgical revisions had to be performed. The number of complications and surgical revisions also had negative impacts on the outcome. Neither fracture severity nor BMI or patient’s age was significantly correlated with the IKDC or Lysholm score.ConclusionsTibial plateau fractures are severe injuries, which lead to a subsequent reduced level of patient activity. Precise reconstruction of the articular surface with regard to intraarticular step and gap size, residual comminution area and joint angle is decisive for the final outcome. Complications and surgical revisions also worsen it.Level of evidenceIII.

Effects of Operating Conditions on Evaporation Rate and Wall Shear Stress Development in a Micro-gap Heat Sink with Internal Micro-Fins

Evaporation in the micro-gap heat sink has a very high heat transfer coefficient. As a result, it is significant for high heat flux management. Heat transfer rate can be enhanced further by including internal micro-fins. However, the pressure drop penalty due to the small gap height and fin surfaces is a major concern. Wall shear stress development is responsible for pressure drop. This paper investigates the effects of operating conditions, e.g., wall heat flux, pumping power, and inlet void fraction, on evaporation rate and wall shear stress development in a micro-gap heat sink with internal micro-fins of rectangular and triangular profiles, while the cross-sectional area (21.8 mm2) is kept constant. R-134a is considered as coolant. Results show that the evaporation rate from per unit volume increases with the increment of wall heat flux and decreases with the enhancement of pumping power. However, after a threshold value of the pumping power (2×10-4 W), the decrement rate falls. Again, the wall shear stress rises with the increasing wall heat flux and pumping power while reduces for escalating inlet void fraction.

The supporting capacity of ferrofluids bearing: From the liquid ring to droplet

In this paper, a simple ferrofluids (FFs) bearing, which consists of a rotor, a stator embedded with a cylinder magnet, and FFs is proposed. By controlling the volume of FFs, two types of liquid structures of the ring and droplet shapes are formed on the stator surface. Models of the bearing for the static supporting force are established and validated by experiments. The multicycle loading-unloading of the FFs bearings as well as the dynamic supporting force are performed. Results show that the static supporting force of the bearings can be predicted approximately by the theoretical model. Multicycle loading-unloading tests indicate that force values with excellent repeated accuracy can be achieved only within a limited range of oscillation in gap height. Compared with the FFs droplet bearing, the rotation speed manifests more significant impact on the dynamic supporting force of the ring structured bearing. Such design presents a new thought for micro-electro-mechanicalsystem (MEMS) that requires precisionsupporting or frictionless bearing.

Analysis of pressure wave signal generation in MPT: An integrated model and numerical simulation approach

Mud pulse telemetry (MPT) is one of the essential means to ensure a high transmission rate of downhole data. Continuous-wave mud pulse has a high transmission rate, strong stability, and outstanding adaptability, the most widely used downhole data transmission mode. One factor that restricts the high transmission rate of downhole data is the quality of the pressure wave generation signal. However, there is a lack of complete mathematical modeling research methods. Based on CFD theory, a numerical model of the integration of pulse generator and upstream and downstream pipelines was established for the first time, as well as the corresponding grid division process, which was to simulate the pressure wave generation and propagation process under drilling conditions, and the sensitivity analysis of parameters was carried out. The results show that the pressure drop curve derived from the thin-wall throttling theory is not the actual pressure wave, so the optimization results have a particular theoretical error. In fact, with the periodic change of the flow area, the upstream and downstream synchronously generate compression waves and expansion waves, which propagate and gradually decay. The amplitude of pressure wave increases with the increase of displacement and density but decreases sharply with the increase of gap height. Meanwhile, the amplitude does not change with the frequency and viscosity, but it aggravates the propagation attenuation of the pressure wave. Moreover, it is observed that the pressure wave is not a perfect sine wave in the case of sinusoidal rotor rotation, which needs further study. The research results of this paper provide a technical means for the optimization of downhole pressure wave generation, transmission, and noise reduction and help improve the transmission rate of downhole data.

Numerical Study on Particle Transport and Placement Behaviors of Ultralow Density Particles in Fracture-Vuggy Reservoirs

Summary A solid/liquid two-phase flow numerical model based on the computational fluid dynamics-discrete element method (CFD-DEM) model was established to study the transport and settlement law of ultralow-density (ULD) particles during the waterdrive channel adjustment of the Tahe carbonate fractured-vuggy reservoir. The mass, momentum, and turbulence equations of the fluid phase were established in Euler coordinates, whereas the particle motion equations were established based on Newton’s second law. The interaction between the ULD particles was described using a soft sphere model, and the water and particle phases were bidirectionally coupled. Meanwhile, virtual experiments were conducted to calibrate the contact parameters of the particles, and parallel plate experiments were performed to validate the model. Using numerical simulations of particle transport behavior in fractures, the process and characteristics of particle transport and placement in fractures are demonstrated, which can be described by the settlement profile angle and equilibrium gap height. According to parameterized simulations, the change law of the settlement profile angle and equilibrium gap height with different parameters such as particle size, pump displacement, and fracture width are demonstrated, which is helpful for the prediction of migration and accumulation of ULD particles in fracture-vuggy reservoirs.

Investigation of the vortex instability in a two-dimensional inkjet print-zone using numerical analysis

At specific operating conditions, especially at large print gap heights, the airflow in the print gap of inkjet printers can become unstable and misplace the satellite droplets on the paper. Two-dimensional numerical analyses are performed to shed light into the dynamics of the vortex in the print-zone and determine the range of flow regimes at different conditions. This will provide a refined understanding of the two-dimensional mode of oscillation while characterizing the upper bound at which the base flow meets the conditions for a uniform print.

Multi-objective optimization of a CSP-based dish Stirling field layout using Genetic Algorithm and TOPSIS method: Case studies in Ouarzazate and Madrid

CSP systems have experienced significant growth with great ability to supply clean and eco-friendly electrical power. In this paper, multi-objective optimization is carried out to design the most energy and cost-effective Solar Dish Stirling (SDS) power plant. Meteorological data from two different sites have been considered to simulate the technical and economical performances of 10 MW SDS power plant. Two main energy and economic conflicting objective functions were considered with the ultimate goal to maximize of the annual Capacity Factor and minimize the Total Cost of Site Improvements simultaneously. Several parameters such as the separation distance between collectors, ground slope, slot gap height and width have been parametrically assessed to find out effects on the Capacity Factor and the Total Cost of Site Improvements. First, a third-order multiple non-linear surrogate model was constructed. The model validity was demonstrated by the R-square values which were found to be 0.995 and 0.9964 for Ouarzazate and Madrid, respectively. Then, multi-objective optimization using Elitist Non-Dominated Sorting Genetic Algorithm (NSGA-II) has been applied to address the trade-off between the two objective functions. The obtained Pareto Front was identified accordingly and final optimal solution was determined using Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) decision-making method. Final optimal solution corresponded to Capacity Factor (CF) values of 22.99% and 12.91% and a Total Cost of Site Improvements (TCSI) of 2.69 M$ and 2.60 M$, for Ouarzazate and Madrid, respectively.

Validation of a coupled multibody and TEHL simulation by a piston/cylinder component test rig

A tribological highly stressed contact in the actuating system of axial piston machines is located between the control piston and the control chamber. This paper presents a new type of component test rig for measuring the frictional force and the gap heights between piston and cylinder. For this purpose, the original system is reduced to the actuator system, whereby the real kinematics and the loading forces are maintained. The axial movement of the control piston and the pressure in the control chamber can be configured individually. The measurement results of different parameter variations are compared with the results of the simulation. The simulation based on a coupled multibody and TEHL simulation with a transient, three-dimensional, thermal elastohydrodynamic contact calculation.

Development of Psi Factors for Thermal Bypass Due to Insulation Gaps in Low-Slope Roofing Assemblies

In commercial roofs, the presence or formation of gaps could be due to improper installation, thermal expansion, and dimensional changes in the insulation boards. The heat loss from these gaps could lead to higher thermal transmittance in the roof assembly. The current research study conducted around 70 experiments to investigate the effect of gap height, gap width and gap offset on the thermal transmittance of the roofing assembly. The measured data showed that in a staggered insulation layout with a joint offset of 610 mm (24 in), formation of 6.4 mm (1/4 in) to 12.7 mm (1/2 in) gaps at the insulation joints could contribute to an average decrease of 2% to 9% in the effective R-value of the roof assembly. As the insulation thermal resistance increases or becomes thicker, the thermal losses in the roof assembly increase. Generalized gap impact curves were developed to provide the relation between gap parameters (i.e., gap widths and height) and the thermal performance of the roof assembly. The experimental data were further analyzed using the psi factor approach of linear thermal bridging generating thermal transmittance data to support the calculation of thermal bypass from gaps in the thermal roof design.

Epoxy Molding Compound Filler Clogging Simulation During Integrated Circuit Encapsulation Process

As IC components become denser and smaller in a package, more problems emerge. In the mold filling process, because epoxy molding compound (EMC) contains approximately 80 wt.&#x0025; silica fillers, the fillers may clog at the gate of gap if the gap height between the component and the substrate is too small. This clogging will cause a popcorn effect due to the high resin content in the gap. In order to determine the EMC filling process in the mold cavity and the relation between the gap height and the filler size, we simulate the EMC filling process and the EMC filler concentration distribution in the mold cavity using mold flow analysis software and then use computational fluid dynamics-discrete element method (CFD-DEM) coupling method to simulate the EMC filler motion to determine the relationship between gap height and filler size and the factors that affect filler clogging. Based on the mold flow analysis results, the filler concentration was higher at the gate of gap than in other regions, and the filler concentration at the gate of gap for the 30-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> gap-height model was higher than that for the 50-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> gap-height model. Based on the DEM-CFD coupling results, particles with a single diameter larger than one-half of the gap height caused particle clogging the gate of gap, and particles with a mean particle size larger than one-third of the gap height caused particle clogging the gate of gap.

Fabry-Perot interferometric calibration of van der Waals material-based nanomechanical resonators.

One of the challenges in integrating nanomechanical resonators made from van der Waals materials in optoelectromechanical technologies is characterizing their dynamic properties from vibrational displacement. Multiple calibration schemes using optical interferometry have tackled this challenge. However, these techniques are limited only to optically thin resonators with an optimal vacuum gap height and substrate for interferometric detection. Here, we address this limitation by implementing a modeling-based approach via multilayer thin-film interference for in situ, non-invasive determination of the resonator thickness, gap height, and motional amplitude. This method is demonstrated on niobium diselenide drumheads that are electromotively driven in their linear regime of motion. The laser scanning confocal configuration enables a resolution of hundreds of picometers in motional amplitude for circular and elliptical devices. The measured thickness and spacer height, determined to be in the order of tens and hundreds of nanometers, respectively, are in excellent agreement with profilometric measurements. Moreover, the transduction factor estimated from our method agrees with the result of other studies that resolved Brownian motion. This characterization method, which applies to both flexural and acoustic wave nanomechanical resonators, is robust because of its scalability to thickness and gap height, and any form of reflecting substrate.

Определение давления при течении жидкости в плоском клиновидном слое с учетом сил инерции

The Reynolds equations are solved with account for inertial forces in a plane wedge-shaped layer using the Slezkin-Targ method. The analytical expressions determining the dimensionless longitudinal velocity, hydrodynamic pressure, and total pressure force as functions of the lubricating Reynolds number and dimensionless parameter of the problem are obtained. A new method for solving the Reynolds equations is proposed accounting for inertial forces and avoiding averaging the inertial terms with respect to the gap height. The numerical analysis of the proposed method shows that in the first and second approximations, the deviations for the total hydrodynamic pressure force in a plane wedge-shaped layer differ little from each other in the considered range of the lubricating Reynolds number for varying dimensionless parameter of the problem, but exceed the deviation obtained using the Slezkin-Targ method. The coincidence of the first approximation with the second one gives ground to believe that the proposed method is more accurate for calculating the total hydrodynamic pressure force in the fluid flow occurring in a plane wedge-shaped layer.