Disc Loading Research Articles

How annulus defects can act as initiation sites for herniation

PurposeBoth posture and loading rate are key factors in the herniation process and can determine the mechanism of disc failure. The aim of this study was to test the hypothesis that disruption visible with HR-MRI post-testing corresponds with microstructural features and further elucidate the mechanism by which this disruption weakens the disc. This will enable us to gain new insights into the herniation process.MethodsThirty ovine lumbar spinal segments were subjected to combinations of four loading conditions (0–12° flexion, 0–9° lateral bending, 0–4° axial rotation, 0–1500 N axial compression) for 1000 loading cycles at 2 Hz in a dynamic disc loading simulator. The discs were scanned in an ultra-high field MRI (11.7 T) then examined using brightfield microscopy to examine their microstructure.ResultsFour discs herniated and seven discs suffered nucleus displacement. These discs contained pre-existing defects in the central posterior annulus. Generally, following testing discs contained more posterior annulus disruption, Microstructural investigation revealed there was clear correspondence between HR-MRI and microstructural observations, and that the mid-outer annular-endplate junction had failed in all discs examined in this study.ConclusionsWhile all discs suffered outer annulus damage, only the discs containing pre-existing defects herniated. These pre-existing defects weakened the inner and mid annulus, allowing herniation to occur once the mid and outer annular wall was compromised. We propose this can occur during the degenerative cascade.

Vegetable Oil Based Compressor Oil-optimising of Tribological Characteristics

ABSTRACT This study explored the use of vegetable oil-based polyolester of rapeseed oil as a potential biolubricant for reciprocating air compressor. Rapeseed oil-based pentaerythritol ester (PE) was formulated via ultrasound-assisted transesterification process. Response surface methodology (RSM) based D-optimal design of experiments was used to analyse the tribological parameters, such as disc rotational speed, load and compressor oils on various tribological behaviours, namely, coefficient of friction (COF) and specific wear rate (SWR) using a pin-on-disc tribometer. The least specific wear rate of 1.85 × 10−5 mm3/Nmand COF of 0.0393 was recorded at optimal conditions. The surface morphology analysis of the tested pin using SEM/EDX and tribo-film formation analysis of disc surface using XPS technique disclosed that blended compressor oil (PE75), i.e., 75% by volume of PE and 25% by volume of synthetic compressor oil (SAE30) has numerous capabilities as environmental friendly compressor oil.

A CFD-Based Examination of Rotor-Rotor Separation Effects on Interactional Aerodynamics for eVTOL Aircraft

This study systematically investigates the aerodynamic interactions of a two-rotor system with a front rotor and an aft rotor aligned with the direction of flow. The rotors are 5.5 ftdiameter fixed-pitch rotors operating at approximately 12 lb/ft2 disk loading, representative of large eVTOL aircraft. Fluid flow is simulated using the commercial Navier–Stokes solver, AcuSolve, with a detached eddy simulation (DES) model. Simulations were performed nominally at 40 kt edgewise flight for nine cases corresponding to three values of longitudinal hub–hub separation (2.5R, 3R, 3.5R) and three values of vertical offset (0, 0.25 R, 0.5 R ). Aft rotor performance was compared to an isolated rotor operating in the same conditions in order to quantify the effects of rotor–rotor interaction. For the cases where the aft rotor is closest to the front rotor (2.5R longitudinal offset, zero vertical offset), the aft rotor produced 8.4% less thrust and required 13.4% higher torque than a rotor in isolation. When vertical rotor separation was increased, interactional aerodynamic effects decreased. For a 2.5R longitudinal offset, increasing the vertical offset to 0.5 R decreased the lift deficit to 4.6% and the torque penalty to 6.8%. Increasing the longitudinal offset to 3.5R (while keeping the vertical offset at zero) also reduced interactional aerodynamic effects, but reductions in lift deficit and torque penalty were smaller than those observed with 0.5R vertical offset. Reducing disk loading was found to strengthen interactional aerodynamic effects, with an 11.5% thrust deficit at 6 lb/ft2 compared to 9.0% at 12 lb/ft2. An increase in flight speed also increased interactional aerodynamic penalties from 5.4% thrust deficit at 20 kt to 12.2% at 60 kt. The increased interactional aerodynamic penalties with the reduction in disk loading and increase in flight speed were both attributed to an increase in wake skew angle and the resulting decrease in separation between the aft rotor disk and front rotor wake.

Three-Dimensional Frequency-Domain Green’s Functions of a Finite Fluid-Saturated Soil Layer Underlain by Rigid Bedrock to Interior Loadings

This paper presents the three-dimensional frequency-domain Green’s functions of a saturated poroelastic soil layer with incompressible constituents resting on rigid base due to interior time-harmonic point-, ring-, and disc-loadings with uniform distribution being composed of three effective stress source components and one pore fluid pressure source. The set of Green’s functions can provide complete fundamental solutions for relevant boundary-value problem studies by the method of boundary integral equations. In developing these solutions, the dynamic property of the porous medium is described by Boer’s poroelastic model. Four independent wave equations with definite physical meaning are obtained by introducing four scalar displacement potentials to uncouple the equations of motion of the layer and then resolved by the Fourier–Hankel integral transformations. By imposing the boundary and load interfacial conditions of the layer, the Green’s function solutions of all field variables corresponding to the point-, ring-, and disc-loadings are derived. The obtained solutions are then validated by comparing with the existing special solutions and the finite-element model (FEM) calculation results. Numerical examples with disc loading cases are also performed to examine the effects of the permeability and the thickness of the poroelastic layer on its dynamic characteristic.

Handling qualities of fixed-pitch, variable-speed multicopters for urban air mobility

AbstractOptimisation-based control design techniques are applied to multicopters with variable-RPM rotors. The handling qualities and motor current requirements of a quadcopter, hexacopter and octocopter with equal gross weights (5,360N) and total disk areas (producing a 287N/m$^2$disk loading) are compared in hover. For axes that rely on the rotor thrust (all except yaw), the increased inertia of the larger rotors on the quadcopter increase the current requirement, relative to vehicles with fewer, smaller rotors. Both the quadcopter and hexacopter have maximum current margin requirements (relative to hover) during a step command in longitudinal velocity. In yaw, rotor inertia is irrelevant, as the reaction torque of the motor is the same whether the rotor is accelerating or overcoming drag. This, combined with the octocopter’s greater inertia as well as the fact that it requires 30% less current to drive its motors in hover, results in the octocopter requiring the greatest current margin, relative to hover conditions. To meet handling qualities requirements, the total weight of the motors of the octocopter and hexacopter is comparable at 13.5% weight fraction, but the quadcopter’s motors are heavier, requiring 16% weight fraction. If the longitudinal and lateral axes were flown in ACAH mode, rather than TRC mode, the total motor weight of all configurations would be nearly identical, requiring about 13.5% weight fraction for motors (compared to 7–9% weight fraction from hover torque requirements).

Musculoskeletal biomechanics of patients with or without adjacent segment degeneration after spinal fusion

Study designA retrospective, single center, case-control study was performed.ObjectiveThe present study employed patient-specific biomechanical modeling to find potential biomechanical differences after spinal fusion at L4/5 in patients with and without subsequent development of adjacent segment disease (ASD).MethodsThe study population comprised patients who underwent primary spinal fusion at L4/5 and were either asymptomatic during > 4 years of follow-up (CTRL; n = 18) or underwent revision surgery for ASD at L3/4 (n = 20). Landmarks were annotated on preoperative and follow-up lateral radiographs, and specific musculoskeletal models were created using a custom-built modeling pipeline. Simulated spinal muscle activation and lumbar intervertebral shear loads in unfused segments were analyzed in upright standing and forward flexion. Differences between the pre- and postoperative conditions were computed for each patient.ResultsThe average postoperative muscle activity in the upright standing posture was 88.4% of the preoperative activity in the CTRL group (p < 0.0001), but did not significantly change from pre- to postoperatively in the ASD group (98.0%). The average shear load magnitude at the epifusional joint L3/4 during upright standing increased from pre- to postoperatively in the ASD group (+ 3.9 N, +/− 17.4 (n = 18)), but decreased in the CTRL group (− 4.6 N, +/− 23.3 (n = 20); p < 0.001).ConclusionPatient-specific biomechanical simulation revealed that spinal fusion surgery resulted in greater shear load magnitude and muscle activation and therefore greater forces at the epifusional segment in those with ASD compared with those without ASD. This is a first report of patient-specific disc load and muscle force calculation with predictive merits for ASD.

A Conceptual Design Methodology for e-VTOL Aircraft for Urban Air Mobility

Recent progress of electric systems has raised attention towards hybrid-electric and full-electric aircraft. Nevertheless, the current low battery energy density limits the application of these propulsive architectures to large transport aircraft. In the context of the general aviation category, full-electric aircraft for the so-called Urban Air Mobility scenario are gaining increasing interest. These air taxis, also called e-VTOL, are conceived to exploit vertical take-off and landing capabilities, to carry people from one point to another, typically within the same city. In this paper, a new conceptual design methodology for urban air vehicles is presented and applied to an innovative convertiplane, called TiltOne, based on a box-wing architecture coupled with tilt-wing mechanisms. Several TiltOne configurations have been designed according to the current regulations imposed by European Union Aviation Safety Agency, and sensitivity analyses have been carried out on the varying main design parameters, such as wing loading and propellers’ disk loading, as well as main top-level aircraft requirements. The results provide an overview for today’s operational capabilities of such aircraft and, in addition, depict possible scenarios for a near-future horizon, based on the assumption of increased performance levels for the electric powertrain components. In such scenario, two different concepts of operations are analysed and discussed: the first is based on a given design range, long enough to cover the urban distances; the second is conceived to exploit the capability of flying multiple shorter missions with a single battery charge. The designed TiltOne configurations derived from these different approaches are presented, highlighting their potential capabilities and possible drawbacks.

Great tits do not compensate over time for a radio-tag-induced reduction in escape-flight performance.

The use of biologging and tracking devices is widespread in avian behavioral and ecological studies. Carrying these devices rarely has major behavioral or fitness effects in the wild, yet it may still impact animals in more subtle ways, such as during high power demanding escape maneuvers. Here, we tested whether or not great tits (Parus major) carrying a backpack radio‐tag changed their body mass or flight behavior over time to compensate for the detrimental effect of carrying a tag. We tested 18 great tits, randomly assigned to a control (untagged) or one of two different types of a radio‐tag as used in previous studies in the wild (0.9 g or 1.2 g; ~5% or ~6–7% of body mass, respectively), and determined their upward escape‐flight performance 1, 7, 14, and 28 days after tagging. In between experiments, birds were housed in large free‐flight aviaries. For each escape‐flight, we used high‐speed 3D videography to determine flight paths, escape‐flight speed, wingbeat frequency, and actuator disk loading (ratio between the bird weight and aerodynamic thrust production capacity). Tagged birds flew upward with lower escape‐flight speeds, caused by an increased actuator disk loading. During the 28‐day period, all groups slightly increased their body mass and their in‐flight wingbeat frequency. In addition, during this period, all groups of birds increased their escape‐flight speed, but tagged birds did so at a lower rate than untagged birds. This suggests that birds may increase their escape‐flight performance through skill learning; however, tagged birds still remained slower than controls. Our findings suggest that tagging a songbird can have a prolonged effect on the performance of rapid flight maneuvers. Given the absence of tag effects on reproduction and survival in most songbird radio‐tagging studies, tagged birds in the wild might adjust their risk‐taking behavior to avoid performing rapid flight maneuvers.

Disc Degeneration in Direct Injury or Instability Models Share Common Metabolic Pathways

Introduction: Disc degeneration is the central component involved in numerous common spinal pathologies. Degenerative disc disease affects millions of people every year, yet the mechanisms driving degeneration remain poorly understood. Previous work to date has shown that high levels of intracellular lactate seem to be involved in driving this pathology once thought to be purely mechanical. Here, we present a series of studies utilizing mouse models of mechanical injuring or loading of the intervertebral disc (IVD), with a goal of better defining the role of lactate and lactate transport in degenerative disc disease.&#x0D; Methodology: Four models of disc degeneration were studied: (i) lumbar disc poke, (ii) tail disc poke, (iii) spinal instability, and (iv) sham. Female mice (C57BL/6J, n = 30) were randomly assigned to one group. In group 1, a retroperitoneal approach exposed the IVD of the lumbar spine, and a 27G needle was used to injure the disc. In group 2, the needle was inserted in the tail IVD. In group 3, lumbar instability was induced by resection of bilateral facet joints and supraspinous/interspinous ligaments. In group 4, a sham was used for each. The mice were euthanized at two, four, and eight weeks. IVD was evaluated by histological and immunofluorescence analysis. RNA extraction from disc tissue was analyzed with QPCR.&#x0D; Result: Sham mice did not have significant disc degeneration. In groups 1 and 2, the degenerative process at two, four, and eight weeks was characterized by loss of nucleus pulposus (NP) cells and the gradual increase in matrix components in NP. The distinction between NP and annulus fibroids (AF) or endplate cartilage is lost. There was increased expression of collagen X and MMP13 in the NP, and MCT4 was decreased, while MCT3 was increased. In group 3, disorder of the AF was evident in the first two weeks post surgery, the collapsed disc space and the NP area gradually lessened. The proteoglycan detected in the inner layer of AF and the periphery of NP decreased after eight weeks. There was increase in type X collagen and MMP13 in the inner AF and NP.&#x0D; Conclusion: Our results demonstrate a common molecular pathway whereby discs degenerate after direct injury or becoming unstable. In our model, there was a rapid degeneration of the IVD in mice who exhibit up- and downregulation of several important markers. Importantly, MCT4 was downregulated, while MCT3 was upregulated. While MCT4 was associated with lactate exportation, and its loss resulted in elevated intracellular lactate and disc degradation, MCT3 is rarely expressed and may be acting as a rescue lactate transporter.

Experimental and Analytical Analysis of Rotor-Wing Interaction in Hover for Low Reynolds Number Flow

AbstractHover performance for tiltrotor-like vehicles lacks experimental data and computationally efficient models for single-rotor-wing interactions at low disk loadings and low Reynolds numbers. ...

Analysis of the propellers-airframe interaction of the light transport aircraft

In the design of multi-engine aircraft, one of the important issues is the interaction between the propellers and airframe configuration components, especially in take-off and go-around procedure modes. Modern propeller-driven aircraft concepts in the pulling configuration are characterized by a high disk loading and an increased number of propeller blades used to increase cruising speed and reduce excessive noise. The first problem arising due to high disk loading is the direct impact of forces by operating propellers (thrust, normal force) on fixed-wing stability, especially at angles of attack different from a zero value. The second one involves a high-energy level of the propeller slipstream, having a significant indirect impact on the aircraft’s aerodynamics, stability and controllability. This impact is primarily associated with the interaction of propellers slipstream with other aircraft’s configuration elements. The complexity of taking into account the slipstream-wing interaction and other airframe components stipulated the application of experimental methods to study the problems of propellers – airframe interaction while designing propeller-driven aircraft configurations. This article presents an analysis of the experimental studies results of the operating propellers- airframe interaction for a light twin-engine transport aircraft. The aerodynamic aircraft’s configuration is executed using the conventional pattern of a high-wing and the carrier-on deck type empennage. The high-lift wing device is a fixed-vane doubleslotted flap. The wind-tunnel tests of the model in the cruising, takeoff and landing configurations were carried out in TsAGI lowspeed wind-tunnel T-102. Measurement of forces and moments, acting on the model, was performed by means of an external sixcomponent wind-tunnel balance. Measurement of forces and moments, acting on the propeller, was conducted using strain gauge weighers installed inside the engine nacelles of power plant simulators. The simultaneous combined use of external and internal balances allowed researchers to determine the direct and indirect contribution of operating propellers to the model longitudinal aerodynamic characteristics under variation of loading factor B ranging from 0 to 2.

Ensuring the required law implementation accuracy of the transmission clutches control by regulating the working fluid volume in the hydraulic cylinder compensation chamber

Introduction (problem statement and relevance). Testing the vehicle automatic transmission and shifting gears without interrupting the power flow undesirable dynamic phenomena were revealed. The occurrence of “parasitic” centrifugal pressure in the clutch boosters was observed which resulted in self-activation of the control element, clamping the discs friction linings, which made the hydraulic cylinder emptying and piston removing from the package disks complicated. As a consequence of it there occurred a comfort decrease in the vehicle, and in some cases, the destruction of friction clutches. It was found that the reason for this occurrence was the filling degree instability of the compensation and piston chambers of the hydraulic cylinder clutch, which was not taken into account by the existing calculation and design methods under various initial conditions.The purpose of the study was to improve the implementation accuracy of the required control law of the transmission clutches by purposeful regulating the working fluid volume in the compensation chamber of the hydraulic cylinder clutch.Methodology and research methods. A road test technique was proposed for identifying and reproducing the conditions of the dynamic phenomenon manifestation. The developed mathematical model of the piston stroke made it possible to assess the dependence of the implementation quality of the required clutch control law when individual gears were engaged on the following parameters: the filling degree of the compensation chamber; features of solenoid valves operation; the stiffness of the return spring; the number of clutch friction pairs.Scientific novelty and results. On the experimental research basis of the worked out design and the use of scientifically grounded technical solutions the dynamic effect manifestation of the unbalanced “parasitic” centrifugal pressure rise was excluded.Practical significance. The developed and implemented technical solutions for stabilizing the pressure in the compensation chamber made it possible to ensure the required quality of gear shifting when limiting the dynamic and thermal loading of the friction discs, which made it possible to ensure the required level of dynamic characteristics and comfort ability of the product when shifting gears.

Computational Investigation of Multirotor Interactional Aerodynamics with Hub Lateral and Longitudinal Canting

This study investigates the interactional aerodynamics for laterally and longitudinally canted two-rotor systems with a front rotor and an aft rotor aligned with the flow. The -diameter, three-bladed fixed-pitched rotors are simulated using computational fluid dynamics at a targeted disk loading and 30 kt edgewise freestream. Simulations are performed using the commercial Navier—Stokes solver AcuSolve with a detached eddy simulation model. In addition to an uncanted case, two laterally canted cases (10° advancing sides up and 10° advancing sides down) as well as two longitudinally canted cases (10° inward and 10° outward) are simulated. Aft rotor performance is compared to isolated rotors operating at the same revolutions per minute, speed, and shaft tilt angle in order to quantify the effect of rotor–rotor aerodynamic interaction. For all configurations, the aft rotors experience a lift deficit at the front of the rotor disk, which also results in a nose-down pitching moment relative to an isolated rotor. The lift deficit for the uncanted rotor was around 15%. Lateral canting only slightly increases the lift deficit (to 16–18%) but also produces 28–38% change in roll moments. Change in aft rotor nose-up pitching moments for the uncanted and laterally canted rotors were in the 55–64% range. Longitudinal canting produces larger changes in the magnitude of the lift deficit and pitching moment, but has minimal effect on roll moments. In particular, canting inward results in a lift deficit as high as 21% and a 94% change in pitching moment. Canting outward, on the other hand, reduces the aft rotor lift deficit to 11% and the pitching moment change to 19%. The paper explains the changes in the flowfield and the underlying physics for the different cases in detail.

Efficient Visualization of Large-Scale Oblique Photogrammetry Models in Unreal Engine

Oblique photogrammetry models are indispensable for implementing digital twins of cities. Geographic information system researchers have proposed plenty of methods to load and visualize these city-scaled scenes. However, when the area viewed changes quickly in real-time rendering, current methods still require excessive GPU calculation and memory occupation. In this study, we propose a data organization method in which we merged all quadtrees and used a binary encoding method to encode nodes in a merged tree so that the parent–child relationship between the tree nodes could be calculated using rapid binary operations. After that, we developed a strategy to cancel the loading of redundant nodes based on the parent–child relationship, which helped to reduce the hard disk loading time and the amount of memory occupied in visualization. Moreover, we introduced a parameter to measure the area of the triangle mesh per pixel to achieve unified data scheduling under different production standards. We implemented our method based on Unreal Engine (UE), and three experiments were designed to illustrate the advantages of our methods in index acceleration, frame time, and memory reduction. The results show that our methods can significantly improve visualization fluency and reduce memory usage.

Main Rotor Wake Interference Effects on Tail Rotor Thrust in Crosswind

Reverse pedal operational property in front crosswind flight condition is a potential hazard for accidents involving loss of tail rotor effectiveness (LTE), which is closely related to the main rotor (MR) wake interference on the tail rotor (TR). As understanding of this interaction is vital for the early warning strategy development, the MR wake influence effect on TR thrust and the effect of helicopter yaw stability are examined in this study. For this purpose, the comparison of TR thrust and flow field with wind azimuth and speed in front crosswind environment was performed by experiment and CFD simulation, respectively. Test campaign was performed at a5.5 m×4 mwind tunnel in the China Aerodynamics Research and Development Center using a high-position bottom-blade forward-rotating TR and a counterclockwise rotating MR to address the TR thrust under wind speeds of 8–22 m/s with 50°, 60°, and 70° wind azimuths. The influence of MR disc loading was also contrasted. CFD analysis was used to gain insight into the flow physics responsible for the interference effect. It was conducted with unsteady Reynolds-averaged Navier–Stokes simulations, where the MR using the actuator disk approach and the TR blade rotation was modeled via a sliding mesh method. Results indicated that the MR disc vortex has a remarkable interference effect on the TR aerodynamic performance characteristic and that the effect is sensitive to the wind speed, wind direction, and MR disc loading. The observed yaw instability is considered to be related to the lesser inflow introduced by the MR disc vortex due to the change in the relative position of the disc vortex filament and TR with the wind azimuth. The increase in TR thrust at moderate wind speeds is due to the increase in leading edge dynamic pressure caused by the opposite swirl direction of the disc vortex contrasted to the TR. The MR disc loading affects the TR thrust due to the change of disc vortex strength and position.

Full waveform inversion to estimate the material properties of a layered half-space

Estimations of material properties of layered infinite media have been considered in a variety of problems, including geophysical subsurface imaging, geotechnical site investigations, and nondestructive tests. The full waveform inversion (FWI) approach can be employed because it is versatile when used to estimate the properties of complicated systems. A rigorous formulation of the FWI approach used in conjunction with the thin-layer method, which is accurate and efficient for wave-propagation in a layered medium, is developed to estimate the material parameters of a layered half-space. We measure the vertical displacements of a layered half-space subjected to a harmonic vertical disk load on its surface. The responses are compared with those calculated using the estimated material properties of the considered medium. The estimated responses are obtained using a thin-layer model of the system. The thin-layer model is composed of mid-point integrated finite elements, the thickness of which can be complex, and perfectly matched discrete layers, which are appropriate for the representation of a layered half-space. An objective function, which is defined as the L2-norm of the difference between the measured and estimated responses, is minimized by means of gradient-based optimization. The gradient of the objective function is derived in terms of the derivatives of the eigenvectors and eigenvalues of the thin-layer representation of the considered medium. We then estimate the material properties by solving the optimization problem. The proposed approach is applied to various examples to estimate the profiles of shear-wave velocities of layered half-spaces. We demonstrate that the developed FWI strategy can estimate the material properties of layered half-spaces with satisfactory accuracy.

Lessons Learned While Designing A Next-Generation Firefighting Hel- met: Preliminary Data

In this study, we evaluated the effects of weight and profile (center of gravity location) of three different most widely used firefighting helmets on the head-neck kinematics, positional instability, visual range,and comfort. we compared three different firefighter helmets: a traditional-look (with-brim) helmet (58 oz),a jet-style helmet (62.25 oz), and the jet-style helmet with lighting and communication systems (70.85 oz); all are large.. Since our preliminary investigation showed promising results for the jet-style helmet type, a thorough systematic analysis on a large sample is warranted. Some legitimate concerns that we observed in the preliminary study include: 1) excessive helmet weight caused neck hyper-flexion and imbalanced lateral bending, 2) the CoG of the helmet system lies away from the mid-sagittal plane, and 3) the weight and the displaced CoG poses the threat of an increased risk of cervical spinal disc loading, which can result in disc herniation and degenerated disc.

A BIOMECHANICAL STUDY OF THE EFFECTS OF FLEXION ANGLE ON THE INDUCTION MECHANISM OF CERVICAL SPONDYLOSIS

Lesions in facet joints such as bone hyperplasia and degenerative changes in the intervertebral discs, can compress nerve roots and the spinal cord, leading to cervical spondylosis (CS). Lesions in these parts of the spine are commonly related to abnormal loads caused by bad posture of the cervical spine. This study aimed to understand the potential mechanical effects of load amplitude on cervical spine motion to provide a theoretical basis for the biomechanical causes of CS, and to provide a reference for preventing of the condition. In this study, a finite element model of the normal human cervical spine (C1-C7) was established and validated using an infrared motion capture system to analyze the effects of flexion angle on the stresses experienced by intervertebral discs, the anterior edge of the vertebral body, the pedicle, uncinate and facet joints. Our analysis indicated that the intervertebral disc load increased by at least 70% during the 20∘ to 45∘ flexion of the neck with 121% load increase in the vertebrae. In the intervertebral discs, the stress was largest at C4-C5, and the stress was moderate at C5-C6. These results are consistent with clinical CS prone site research. According to Wolff’s law, when bones are placed under large stresses, hyperplasia can result to allow adaptation to large loads. Increased cervical spine flexion angles caused the proliferation of bone in the above-mentioned parts of the spine and can accelerate accelerating the appearance of CS.

Aerodynamic interaction between propellers of a distributed-propulsion system in forward flight

This article describes an experimental investigation of the aerodynamic interaction that occurs between distributed propellers in forward flight. To this end, three propellers were installed in close proximity in a wind tunnel, and the changes in their performance, flow-field characteristics, and noise production were quantified using internal force sensors, total-pressure probes, particle-image velocimetry (PIV), and microphones recessed in the wind-tunnel wall. At the thrust setting corresponding to maximum efficiency, the efficiency of the middle propeller is found to drop by 1.5% due to the interaction with the adjacent propellers, for a tip clearance equal to 4% of the propeller radius. For a given blade-pitch angle, this performance penalty increases with angle of attack, decreasing thrust setting, or a more upstream propeller position, while being insensitive to the rotation direction and relative blade phase angle. Furthermore, the velocities induced by the adjacent propeller slipstreams lead to local loading variations on the propeller disk of 5% – 10% of the average disk loading. Exploratory noise measurements show that the interaction leads to different tonal noise waveforms of the system when compared to the superposition of isolated propellers. Moreover, the results confirm that an active control of the relative blade phase angles between propellers can effectively modify the directivity pattern of the system.

Application of Particle Swarm Optimization in the Design of an ICT High-Voltage Power Supply with Dummy Primary Winding

The distribution of disk output voltage is a key factor for the design of an insulated core transformer (ICT) high-voltage power supply. The development of an ICT involves the design and optimization of many parameters, which greatly affect the uniformity of disk output voltage. A new ICT structure with dummy primary windings can compensate for the disk output voltage, which aims to improve uniformity. In this work, an optimization method based on a particle swarm optimization (PSO) algorithm was used to optimize the design parameters of an ICT with dummy primary windings. It achieved an optimal uniformity of disk output voltage and load regulation. The design parameters, including the number of secondary winding turns and the compensation capacitance, were optimized based on the finite-element method (FEM) and Simulink circuit simulation. The results show that the maximum non-uniformity of the disk output voltage is reduced from 11.1% to 4.4% from no-load to a full load for a 200 kV/20 mA HUST-ICT prototype. Moreover, the load regulation is greatly reduced from 14.3% to 9.6%. The method improves the stability and reliability of the ICT high voltage power supply and greatly reduces the design time.