Slot Height Research Articles

Minimally invasive mini-hemilaminectomy-corpectomy in cadaveric dogs: evaluation of the accuracy and safety of a three-dimensionally printed patient-specific surgical guide

BackgroundAs the frequency of spine surgery increases in the veterinary field, many studies have been conducted on minimally invasive spine surgery (MISS). Although many studies have been conducted on the thoracolumbar spine about MISS in animals, several problems and limitations have emerged regarding this method. Therefore, we developed a three-dimensional (3D) printed patient-specific surgical guide (3DPSSG) using 3D printing technology to overcome these problems. We aimed to evaluate the accuracy and safety of the 3DPSSG in minimally invasive mini-hemilaminectomy-corpectomy (MI-MHC).MI-MHC using 3DPSSG and an endoscopic system was performed at L1–L2 in 15 cadaveric dogs. The procedure of fixing the surgical guide to the vertebral body through screws and the surgical procedure using the guide were performed by two surgeons with different experiences. Postoperative computed tomography was used to measure planned and postoperative screw trajectories (angle, protruding from the far cortex) and to create 3D rendering images of vertebrae to evaluate the direction of bone window formation, corpectomy slot length, depth, and height ratio.ResultsThe two groups which performed by two surgeons with different experiences did not differ in terms of screw angle deviation and length of the screw protruded from the far cortex. The corpectomy slot-length ratio was not different between the two groups; however, the slot-depth and height ratios were different.ConclusionsNo differences were detected in screw trajectory and corpectomy slot-length ratio between the two groups. The 3DPSSG for MI-MHC is classified as accurate and safe; therefore, it can be an alternative to the conventional technique in dogs.

Drag reduction in wall-bounded turbulence by synthetic jet sheets

A turbulent drag-reduction method employing synthetic jet sheets in a turbulent channel flow is investigated by direct numerical simulations. The jet sheets are wall-parallel and produced by periodic blowing and suction from pairs of thin slots aligned with the main streamwise flow. By varying the slot height and the jet-sheet angle with respect to the spanwise direction, drag-reduction margins between $10\,\%$ and $30\,\%$ are obtained for jet-sheet angles between $45 ^{\circ }$ and $75 ^{\circ }$ , while a drag increase of almost 100 % is computed when the jet sheets are spanwise-oriented. When global skin-friction drag reduction occurs, the wall-shear stress near the jet-sheet exits increases during suction and decreases during blowing, while the velocity fluctuations weaken during suction and intensify during blowing. The global drag-reduction effect is produced by a finite counter flow induced by the nonlinear interaction between the jet-sheet flow and the main flow, although the turbulent intensity and Reynolds shear stresses increase. The power spent to generate the jet sheets is computed by modelling numerically the actuator underneath the channel flow as a piston oscillating sinusoidally along the spanwise direction in a round-shaped cavity from which the fluid is released into the channel through the cavity exits. A power balance leads to the computation of the efficiency of the actuator system, quantifying the portion of the piston power that is lost as internal power fluxes and heat transfer through the cavity walls. For the tested configurations, the power consumed by the piston to generate the jet sheets is larger than the power saved thanks to the drag reduction.

Experimental investigation of static pressure characteristics in a slotted short pin array

ABSTRACT A common heat exchange method used for most new designs is the use of heat sinks such as short pin fins. This experimental study investigated the static pressure characteristics developed in a short pin fin. Different fin array arrangements, fin longitudinal and transverse spacing ratios and individual slot heights in the fin were investigated. It was found that the row removed arrangement has superior flow efficiency, but to enhance heat transfer the staggered array is a better choice; the greater the fin spacing and slot height in each fin are, the less the pressure loss was experienced in the array.

Numerical Assessment of the Impact of Sand Control Techniques on Production in a Vertical Well

This study considers a vertical well producing initially without sand control technique in sandstone reservoir in the Niger Delta region. The study uses the data and information of two wells and applied PROSPER to numerically quantify the impact of the extra flow restriction caused by the gravel pack and slotted liner systems respectively. Well model was constructed and several simulations runs performed on key influencing production parameters (production rates, superficial velocities, skin development, pressure losses) and sand control design variables (gravel pack length, gravel pack permeability, slot height and slot width). The study involved two different sand control for two wells (Well X1 and Well X2) which were similarly completed and subjected to the same reservoir and operational conditions. The influence of sand control parameters on the vertical lift performance and inflow performance characteristics of the wells were analyzed at varying first node pressure (500psig – 1400psig). The solution node was set at bottom hole to enable proper diagnosis of the influence of the sand control options on the VLP/IPR relationships. At base case scenario, the gravel pack oil and gas production rates were 8010.0STB/day (ORAT) and 6.008MSCF/day (GRAT) at a flowing bottomhole pressure of 4231.38Psig while the slotted liner was 8010.0STB/day (ORAT) and 6.008MSCF/day (GRAT) at a flowing bottomhole pressure of 4231.38Psig at a flowing bottomhole pressure of 4231.38Psig of 3902.46Psig. The resulting skin due to sand control were 0.0070375 and 0.18 respectively. Result shows that Slotted Liners provides better sand control than gravel packs but causes more pressure drop in the system due to sand control method. Furthermore, Gravel pack permeability and length and slot dimensions have most remarkable influence on the pressure drop due to sand control and can play a crucial role in the choice and design of any gravel pack system and slotted liners respectively. It’s advisable or better that Gravel pack permeability should not exceed 500000md for optimal performance as a sand control device. The work recommends the use of higher slot width to slot height for more efficient production using slotted liners while smaller gravel permeability could be preferred for better sand control with gravel pack systems.

Numerical investigations of the slot blowing technique on the hypersonic vehicle for drag reduction

In this paper, the slot blowing flow-control technique is numerically studied for the hypersonic vehicle, aiming for skin friction drag reduction. Firstly, the influence patterns of the slot blowing parameters on friction drag reduction are analyzed based on a flat-plate boundary layer flow. It is concluded that there is an optimal blowing Mach number to optimize the drag reduction effect with other parameters unchanged, while as the increase of blowing pressure ratio, the skin friction drag reduction effect first increases and then remains almost invariant. On this basis, a slot blowing methodology is designed for a typical lifting-body hypersonic vehicle with a 10 mm slot installed on the middle of the windward side. Under the typical freestream condition of Mach 15 and 60 km altitude, numerical results indicate that the slot blowing with the blowing maximum Mach number 2 and blowing pressure ratio 1 could achieve a remarkable control effect of increasing the lift-drag ratio by about 10.55%. After that, the parametric study of slot blowing for the lifting-body vehicle reveals that when the slot height is increased from 10 mm to 20 mm, the lift-to-drag ratio rises slightly after paying the price of doubling the blowing mass flow rate, which indicates that increasing the slot height does not obtain a more efficient result. As for the effect of the slot position along the streamwise, moving the slot position forward could receive a higher total drag reduction rate with less blowing mass flow rate while also leads to a slight decrease of lift. Thus, the practical application of the slot blowing technique needs to consider the variations of the drag and lift comprehensively.

Experimental Study on Cooling Efficiency of Hypersonic Optical Window

The cooling effectiveness of optical window influences the imaging quality of hypersonic vehicles. This study focuses on the supersonic film cooling efficiency on the optical window of a blunt cone in hypersonic flow. The experiments were conducted in a gun tunnel equipped with a Mach 8 nozzle providing a total pressure and temperature of 9 MPa and 900 K respectively. Three tangential 2D nozzles with different combinations of slot heights and Mach numbers were designed to detect the film cooling length under different injection pressures. The heat flux on window surface was measured by Thin Film Gauges and the flow field was monitored by schlieren technique. When the jet pressure matched the mainstream, the window was completely cooled, and the minimum mass flow rate was achieved when the slot height was 5mm and the jet Mach number was 2.5. If the pressure ratio of jet continues to increase, the heat flux density could be furtherly reduced, but the cooling efficiency of unit coolant mass flow decreased significantly. The data correlation results showed that the cooling efficiency presented a nonlinear relationship of second order polynomial with (x/Sh)λ-0.8 , and the effective cooling length of film was positively correlated with the cooling mass flow ratio (λ) and slot height of the nozzle. Besides, the increase of jet pressure resulted in thickening the mixing layer, which enhanced the heat insulation effect and reduced the heat flux as a result.

Design Optimization of a 4-Poled 1500 rpm 25 kVA SG to Obtain the Desired Magnetic Flux Density Distributions by using RSM

In this study design optimization for 4-poled 1500 rpm 25 kVA synchronous generator (SG) is performed. The aim is to determine the optimum factor levels for the design parameters namely slot opening width (Bs0), height, and width to keep the responses namely ‘pole-body flux density’ and ‘air-gap flux density’ distributions in a desired range. The target values are determined as 1.75 Tesla and 0.9 Tesla for the ‘pole-body flux density’ and ‘air-gap flux density’ respectively. For this purpose, Response Surface Methodology (RSM) is used for optimization. Numerical simulations are performed in the Maxwell environment and the optimization by RSM is performed by Minitab statistical package. Desired goals were achieved and optimum factor levels were determined with RSM. Then the results of RSM are compared by Genetic Algorithm (GA), Particle Swarm Optimization algorithm (PSO), and Modified Social Group Optimization (MSGO) algorithm. These methods are evaluated together in terms of advantages and disadvantages. The comparisons indicate that using RSM provides acceptable results without performing coding effort and also provides users to understand the relations visually between the factors and the responses by the aid of ‘Minitab Response Optimizer Module’.

Towards a better air assisted flare design for low flow conditions: Analysis of radial slot and flow effects

Numerical investigation of flow field characteristics of air injected through an inclined radial slot into a crossflowing stream has been studied for gas flaring applications. CFD is used to simulate turbulent mixing between the inclined slot jet and the crossflowing stream. The slot injection angle with respect to the crossflow, the slot jet velocity, and the slot height were varied in this study. Velocity profiles obtained from the simulations were compared to measured profiles. Simulation results showed that the centerline upflow axial velocities increased with decreasing injection angle and increasing slot height. Results also showed that decreasing injection angle increased the horizontal penetration of the jet flow into the crossflow stream.

Improved Rotor Bar Shape in High-Voltage Large-Power Induction Motors to Eliminate Hotspot and Avoid Broken Bars

Due to the complex harmonic field effects and frequent starting, broken rotor bars (BRB) caused by hotspots at the rotor slot openings are the most common fault in high-voltage and large-power induction motors (IMs) applied to the auxiliary systems of the power plant. This article proposes an improved rotor bar shape of large-power and high-voltage IMs to eliminate the hotspot and avoid the BRB. With the presented rotor bar shape, the skin effect caused by the high-frequency harmonic fields can be weakened effectively. The optimal design of the presented rotor slot shape, the width and height of the slot opening, as well as the air-gap length are also performed by finite-element analysis to achieve the best operating performance of IMs. A 6-kV 1600-kW IM was remanufactured according to the optimal design and applied to the circulator pump in a thermal power plant. The test results showed that the stator winding temperature of the IM was reduced from 80.7 to 62.1 °C; meanwhile, the surface temperature of the motor cooler was also reduced obviously.

Compliance with the ISO 27020:2019 norm of a sample of currently available preadjusted Orthodontic bracket systems. Are the actual dimensions as expected?

BackgroundDetermine the exact slot dimension of a sample of a MBT prescription stainless steel conventional brackets from different manufacturers to compare the actual values with the nominal ones declared by the manufacturers and to verify the compliance with tolerance limits given by the ISO 27020:2019. Different batches from each manufacturer were evaluated to determine whether or not they are different in size. In addition, the geometry of the slot walls was assessed.Methods360 stainless steel preadjusted orthodontic brackets of 12 different manufacturers were assessed. All brackets had a nominal slot size of 0.022 by 0.028 inches, belonged to the right upper central incisor, and were fabricated with the metal injection molding technique (MIM). For each manufacturer, three different manufacturing batches were evaluated. Brackets were coded using a single-blind design.ResultsAll bracket systems in the study group except one displayed a statistically significant difference with the nominal declared value, although only four of the systems did not comply with the tolerance limits established by the ISO 27020:2019. In most of the systems, the slot height was oversized when compared to the nominal one. A significant interbatch variability was found in most of the evaluated systems. Most of the brackets walls were divergent.ConclusionsThe dimensional accuracy of commercially available metal brackets is not guaranteed. The respect for the norm should be enforced as well as the quality controls along the manufacturing process since orthodontic brackets are a precision medical device.

Multiobjective Design Optimization of Stator for Synchronous Generator Using Bat Algorithm and Analysis of Magnetic Flux Density Distribution

— In this study, we aimed to optimize 3000 kVA synchronous generator (SG) stator design to obtain the desired magnetic flux density distribution and efficiency. We used Maxwell simulations for experiments on some design parameters of stator (slot height and teeth width). Then second-order regression models are calculated that represent the relations between the factors (design parameters) and the measured performance criteria (called as the responses: stator-teeth flux density, stator-yoke flux density, and efficiency). These regression models are used at the multiobjective optimization phase. Bat algorithm (BA) is used for performing the multiobjective optimization. By combining Maxwell with regression modeling and BA, the efficiency of the SG is increased to 96.84% from 96.5% with a more acceptable magnetic flux density (between 1.65 and 1.70 T ranges). The stator-teeth flux density and stator-yoke flux density are calculated as 1.9 T and 2.07 T for the current SG, whereas these values are reduced to 1.647 and 1,634 T, respectively, for the optimized SG. Results of this study show how the numerical simulation can be successfully combined with the BA to improve the efficiency of the SG by providing the desired magnetic flux density distribution.

Hydraulic design criteria of the modified meander C-type fishway using the combined experimental and CFD models

Fishways' structure has been developed to mitigate the harmful effects of human-made structures such as dams and weirs on the migratory fish process as an essential part of the environmental cycle. In this study, a Modified Meander C-type Fishway (MMCF) was designed and analyzed based on a fish species movement capability. The proposed fishways' structural design follows the key features of the vertical slot fishways (VSF) structure and consists of eleven successive cylindrical pools connected through vertical slots. In the present study, physical and computational fluid dynamics were used to investigate the flow characteristics inside the cylindrical pools with designed radius (R) and vertical slots as the system's connectors. Different geometry scenarios were applied to the model, such as the slots' various dimensionless opening ratios (s/R = 0.1, 0.2, 0.3) with varying bed slope scenarios (5%, 10%, and 20%). The obtained results illustrated the dimensionless hydraulic design diagrams based on the dimensionless discharge parameter (Q⁎) as a critical parameter for designing and operating the fishways. Horizontal and vertical flow velocity distribution graphs were presented, which could be used to estimate a potential low-velocity field for each specific fish species. As a geometrical improvement scenario, the pool's average-depth parameter (d) was increased for each scenario using the designed vertical baffles adjusted at the pools' opening gate with different vertical slot's height scenarios (hb/R = 0, 0.1, 0.2). Studying the radial and tangential fluctuations of the turbulent flow inside the proposed fishway demonstrated the structure's performance to make a more stable swimming path for the fishes toward the upstream movement.

Study on flow and heat transfer of liquid metal in a new top-slotted microchannel heat sink

In order to overcome the disadvantage of large pump power required to maintain flow with the large flow resistance caused by high viscosity and high density of liquid metal in microchannel heat sink, a new top-slotted microchannel is designed in this paper. The flow and heat transfer performance of microchannel heat sink with different slot heights was studied by numerical simulation. The results show that the lowest pump power of 0.00157W is obtained when the slot height is 0.8mm without affecting the cooling performance of the microchannel heat sink, which is 16.5% lower than that of the traditional channel.

Steady tangential control jet for improving the effectiveness of a rudder under one-engine inoperative condition

The aim of the research is to numerically investigate the use of a steady tangential control jet (CJ) at the hinge of the vertical stabilizer as an active flow control (AFC) technique to improve the effectiveness of a rudder on a subsonic aircraft during one-engine inoperative (OEI) condition by keeping the flow attached to the control surface. The goals are in two folds: firstly to investigate the effects of CJ parameters, specifically the jet-to-freestream velocity ratio (rV ) and the jet slot height ratio (rH ), on the vertical stabilizer performance, and secondly to find the optimum CJ condition that yields the improved and optimal performance. In this regard, the optimal condition of the CJ is prescribed as the condition that gives the maximum side force to drag ratio under the requirements that the required minimum trim side force can be achieved and there is an improvement in control surface margin for yawing motion. The investigation is carried out through computational fluid dynamics (CFD) using the Spalart-Allmaras turbulent model. Under the optimal CJ condition, its implementation can provide the required minimum rudder side force coefficient (Cy, trim ) of 1.19 at a rudder drag coefficient (Cd ) of 0.0013, a decrease in drag coefficient of 95% over the baseline case of plain flap without CJ. In addition, there is an improvement in rudder margin with the maximum side force coefficient increase by 42%, and the corresponding drag force coefficient decrease by 25% for the aircraft to yaw in a direction of the still-active engine.

Influence Analysis of Structural Parameters on the Performance of 120° Phase Belts Toroidal Winding Solid Rotor Induction Motor

120° phase belt toroidal winding solid rotor induction motor (120°PBTWSRIM) has advantages of simple structure, short end winding, and high overload capacity, thus it has good development prospects. To study the influence of different structural parameters on 120°PBTWSRIM performance, the 2D finite element model is established, and the electromagnetic characteristics are analyzed. The influence of six structure parameters on the average output torque, power factor, and torque ripple are analyzed, which are slot opening width, slot opening height, slot width, slot height, slot radius, and copper layer thickness. It is found that copper layer thickness has a significant effect on the performance of 120°PBTWSRIM. When the copper layer thickness is 0.5 mm, locked average output torque is increased to 2.784 Nm, locked power factor is increased by 64.6%, and locked torque ripple is reduced by 79.7%. Finally, a prototype of 120°PBTWSRIM is built and experimented, the correctness of performance influence analysis is verified by the comparison of results of the simulation and the experiment.

Dimensional variability of orthodontic slots and archwires: an analysis of torque expression and clinical implications

BackgroundThe loss of third-order information in pre-adjusted brackets due to torsional play is a problem in clinical orthodontics. The aim of this study was to evaluate the impact of slot height, archwire height, width and edge bevel’s radius on the torsional play for three brackets/archwire systems.MethodsNinety brackets with a 0.022 × 0.028 in. slot with McLaughlin-Bennett-Trevisi prescription from three different manufacturers were selected, and the slot’s height and depth were measured using a profile projector. Sixty stainless-steel rectangular archwires from three different manufacturers were sectioned and observed with a SEM to measure their height, width, and radius of edge bevel. The recorded data were used to calculate the theoretical torsional play between different slot−archwire combinations. One-way ANOVA was used to compare the measurements within different bracket types and among different manufacturers.ResultsSlot height was usually oversized. Archwire’s height was usually undersized, but oversized wires were also observed. The radius edge bevel was the most variable parameter. A certain degree of torsional play is always present that differs from one bracket type to another of the same producer and that can even be doubled from one manufacturer to another.ConclusionsDue to production tolerance, differences between the nominal values and the real dimensions of any components of a slot/archwire system are common. This results in a torsional play that limits torque expression. The archwire’s edge bevel plays an important role in torque expression, and clearer information should be provided by the manufacturers regarding this aspect.

Cavity collapse near slot geometries

Abstract

Stability and transition on a Coandă cylinder

An experimental stability and transition investigation of a centrifugally unstable wall jet blown from a slot over a circular Coandă cylinder was conducted using flow visualization and particle image velocimetry. Clear and unambiguous observations of spontaneously generated stationary streamwise structures, never observed previously, were analyzed using standard image processing techniques. These structures ultimately exhibited a secondary time-dependent wavy instability that was followed by transition to turbulence. A modified Görtler number, based on the slot height, was used as a basis for comparison to linear stability theory and was directly related to the Reynolds number via geometric scaling. Direct observation of the vortices allowed the identification of an upper limit to the critical Görtler number of 6.3 that bracketed the value of 3.5 from the linear stability theory. The vortical shear layer grew exponentially along the azimuth and was characterized by a Reynolds number dependent growth rate parameter. Extrapolation of the growth rate parameter to zero furnished a critical Görtler number of 3.1 ± 1.25 (95% CI) that compared remarkably well with the linear stability theory. The shear layer separation angle did not vary monotonically with the Reynolds number: as the Reynolds number increased, the thicker boundary layer was more susceptible to separation, and thus, the separation angle, relative to the slot, decreased. However, following transition to turbulence at higher Reynolds numbers (≈400), the high-momentum fluid near the wall, resulting from turbulent mixing, produced a subsequent increase in the separation angle.

The effect of slot dimensions and its vertical and horizontal position on the scour around bridge abutments with vertical walls

Scouring is one of the major threats to the stability of bridge abutments constructed over rivers. The present study investigated the usefulness of abutment slots in reducing the scour depth around bridge abutments with vertical walls, experimentally. Nine experiments with no slot and hundred experiments with slots were conducted in clear water conditions. Four subcritical flow conditions (Froude number less than 1) were investigated. For each flow condition, 25 different slot models having different sizes, and vertical and horizontal positions were considered. The results indicated that the slots having heights equivalent to half of the flow depth are more effective in reducing scouring if they are located closer to the bed. Increasing the slot height improves the performance. The best performance is achieved when the slot begins from the water surface and extends below the bed (equal to the scour depth in the model without the slot). Further, the results showed that the greater the distance of the slot is from the abutment nose and closer it is to the channel wall, the more effective the slot would be. Therefore, the most effective slot model is the model in which the slot height equals the distance from the water surface to below the bed, and when it is attached to the channel wall. For different slot models, in different flow conditions, the percentage of reduction of scour depth varies from 20 to 100%.

The Flow Structure in the Narrow Gaps of Compound Channels: The Basic Flow

In the present work, a methodology for the basic flow solution in complex form channels is presented. This methodology, which could be applied to any compound channel, implements an innovative and original solution strategy which solves in a simple way the apparent nonlinearity of the problem. The solution is computed using the finite element method. As an illustration, the methodology was applied to study flows in complex channels consisting of two rectangular channels connected through a rectangular slot. The effects of the slot position (placed either at the bottom or in the centre of the channels) and height on the velocity and wall shear stress distributions and overall friction were investigated. For small slot relative heights, the flow is essentially organized as parallel channel flows with almost no interaction between them and the overall channel friction factor is insensitive to the slot position. For larger gaps, the position of the slot becomes a determinant parameter. The presence of the slot and its relative height influence the entire flow distributions and the overall friction factor. The velocity profiles in the middle of the gap were studied, and their implications on the possibility of the development of hydrodynamic instabilities were considered.