Dynamic Lift Research Articles

Dynamic plunger lift model for deliquification of shale gas wells

Abstract This paper presents first principles model for operation of a plunger lift system in natural gas wells. The model consists of pressure and flow dynamics of fluids in annulus and the central tubing sections of the well, and dynamics of plunger fall and rise in the tubing. System dynamics switch on shutting or opening the production valve, and with autonomous events related to plunger motion. A nonlinear hybrid model is realized with nine states, switching though six stages (modes) of operation. This is the first instance of modeling complex system of plunger lift using a standard hybrid system model (HSM) framework. The resulting model is used to present insight into plunger lift operation, including an efficient simulation of multiple plunger cycles and analysis of effect of uncertainties on the well behavior.

Hydrodynamic Characteristics of a Hydrofoil-assisted Amphibious Vehicle

For amphibious vehicles that are utilized in military services, high-speed ship-to-shore movement is an important requirement for enhancement of the operational capability in tactical environments. At high speeds, such a vehicle begins to sink at the stern, causing the bow to rise out of the water. Moreover, excessive trim has a deleterious effect on forward field of vision and powering performance. In this study, a hydrofoil was considered as a trim-control device to decrease the significant bow rise without compromising the performance. Experiments were conducted in a towing tank to investigate the running attitude and powering performance of a box-shaped amphibious vehicle at high speeds. Results for the hydrodynamic features show that a fixed hydrofoil under the stern of the vehicle successfully achieved an improved trim. It was also found that the interaction between the waterjet and hydrofoil can enhance the dynamic lift of the hydrofoil.

The uncertainties of residual diagnosis of atmospheric diabatic heating from ERA40 and NCEP reanalysis over Tibetan Plateau

The Tibetan Plateau (TP), a giant elevated landscape, plays a key role in modulating the Asian summer monsoon via dynamic, thermodynamic, and mechanical lifting mechanisms. The spatial and temporal distribution of atmospheric diabatic heating (DH) is vitally important to understand the coupling of energy and moisture between the land surface and the atmosphere over TP. In this study, the residual diagnosis of DH from ERA40 and NCEP reanalysis, in combination with the precipitation and latent heating (LH) results from Tropical Rainfall Measuring Mission Precipitation Radar (TRMM PR) are investigated to reveal the uncertainties in DH over TP. Significant discrepancies of column integrated DH (CDH) between ERA40 and NCEP are found in the southern slope area of TP in summer. The CDH from ERA40 is much stronger than NCEP at high altitudes on the southern slope of TP. The area with strong ERA40 atmospheric heating extends from lower altitudes to higher altitudes exceeding 4000 m isohypse. However, in the heating diagnosis of NCEP, strong atmospheric heating is only located at altitudes lower than 4000 m isohypse. These differences are evident in DH at both the ground layer and 400–500 hPa layer, revealing a significant contribution from LH because sensible heating (SH) peaks at near-surface atmosphere and LH peaks at low to middle atmosphere. As an indicator of LH, the precipitation in southern TP estimated by ERA40 is strong (>10 mm/d) in the 25°–30°N area from April to October. The precipitation observations from TRMM PR and the diagnosis from NCEP diagnosis do not agree about this phenomenon. Instead, the precipitation detected by TRMM PR is mainly located in the area to the south of 25°N. The spatial pattern of overestimated precipitation by ERA40 mostly matches the DH overestimation. Based on the vertical cross-section of DH and the atmospheric circulation along 92.5°E, strong positive ERA40 DH (>4 K/d) over the high altitudes of southern TP (~25°–30°N) extends from surface to high troposphere (~300 hPa) vertically in summer. This fact indicates there is strong latent heating released from deep convective rains in those areas which makes a contribution to DH that is comparable with SH. The associated NCEP DH in the same area can reach only the low troposphere (~700 hPa) and the maximum heating generally is located in the near-surface atmosphere. This conclusion implies that in NCEP diagnosis, only shallow and weak rains can occur in this area and the surface SH dominates DH here. Even at the south edge of main body of TP (to north of 30°N), ERA40 DH in summer can be as high as 6–9 K/d and extend from the surface to ~350 hPa isobaric surface, while the associated NCEP DH is only less than 4 K/d. The diagnosis of vertical velocity and horizontal divergence at the 200 hPa layer from ERA40 is also stronger that from NCEP. The mean vertical profiles of ERA40 DH in summer show positive heating through the surface to 200 hPa and maximum value at 700 (500) hPa on the south (southwest) slope of TP. The shape agrees well with that of the TRMM LH profile, but the value of ERA40 DH is about 2–3 times that of TRMM LH. The NCEP DH profiles show a different shape with peaks at the near-surface layer indicating more contribution from surface SH than from LH, but its amplitude is relatively closer to TRMM LH. We hypothesize that the uncertainties of the vertical structure of precipitation and the associated LH in the southern slope area of TP are the main obstacles preventing us from understanding the real mechanisms of TP-atmosphere interaction.

Elastic Deformation on Trailing edge of a Heaving Elastic Airfoil in a Separation Region and Its Dynamic Lift

Elastic Deformation on Trailing edge of a Heaving Elastic Airfoil in a Separation Region and Its Dynamic Lift

Simulated Supercells in Nontornadic and Tornadic VORTEX2 Environments

Abstract The composite near-storm environments of nontornadic and tornadic supercells sampled during the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2) both appear to be generally favorable for supercells and tornadoes. It has not been clear whether small differences between the two environments (e.g., more streamwise horizontal vorticity in the lowest few hundred meters above the ground in the tornadic composite) are actually determinative of storms’ tornadic potential. From the VORTEX2 composite environments, simulations of a nontornadic and a tornadic supercell are used to investigate storm-scale differences that ultimately favor tornadogenesis or tornadogenesis failure. Both environments produce strong supercells with robust midlevel mesocyclones and hook echoes, though the tornadic supercell has a more intense low-level updraft and develops a tornado-like vortex exceeding the EF3 wind speed threshold. In contrast, the nontornadic supercell only produces shallow vortices, which never reach the EF0 wind speed threshold. Even though the nontornadic supercell readily produces subtornadic surface vortices, these vortices fail to be stretched by the low-level updraft. This is due to a disorganized low-level mesocyclone caused by predominately crosswise vorticity in the lowest few hundred meters above ground level within the nontornadic environment. In contrast, the tornadic supercell ingests predominately streamwise horizontal vorticity, which promotes a strong low-level mesocyclone with enhanced dynamic lifting and stretching of surface vertical vorticity. These results support the idea that larger streamwise vorticity leads to a more intense low-level mesocyclone, whereas predominately crosswise vorticity yields a less favorable configuration of the low-level mesocyclone for tornadogenesis.

Diurnal Variations of the Land–Sea Breeze and Its Related Precipitation over South China

Abstract Convection-permitting numerical experiments using the Weather Research and Forecasting (WRF) Model are performed to examine the diurnal cycles of land and sea breeze and its related precipitation over the south China coastal region during the mei-yu season. The focus of the analyses is a 10-day simulation initialized with the average of the 0000 UTC gridded global analyses during the 2007–09 mei-yu seasons (11 May–24 June) with diurnally varying cyclic lateral boundary conditions. Despite differences in the rainfall intensity and locations, the simulation verified well against averages of 3-yr ground-based radar, surface, and CMORPH observations and successfully simulated the diurnal variation and propagation of rainfall associated with the land and sea breeze over the south China coastal region. The nocturnal offshore rainfall in this region is found to be induced by the convergence line between the prevailing low-level monsoonal wind and the land breeze. Inhomogeneity of rainfall intensity can be found along the coastline, with heavier rainfall occurring in the region with coastal orography. In the night, the mountain–plain solenoid produced by the coastal terrain can combine with the land breeze to enhance offshore convergence. In the daytime, rainfall propagates inland with the inland penetration of the sea breeze, which can be slowed by the coastal mountains. The cold pool dynamics also plays an essential role in the inland penetration of precipitation and the sea breeze. Dynamic lifting produced by the sea-breeze front is strong enough to produce precipitation, while the intensity of precipitation can be dramatically increased with the latent heating effect.

A Biologically-Assisted Curved Muscle Model of the Lumbar Spine

Biomechanically-assisted models have been developed to estimate spine tissue loads in vivo and used to assess the potential risk of injuries in workers. However, most biomechanical models represented trunk muscles as straight-lines vectors acting between a muscle origin and insertion. Even though straight-line muscles behaved reasonably well in simple dynamic occupational tasks, this assumption could be problematic in complex multidimensional dynamic tasks that include highly asymmetric or extreme bending postures. Previous efforts at developing curved muscle models were not empirically validated or tested under dynamic loading conditions. Hence, the accuracy of spine tissue load estimations of such models has not been well documented. In this study, a curved muscle representation was developed and validated to overcome this concern. The objective of this study was to investigate the model fidelity of a biologically-assisted curved muscle model during complex dynamic lifting tasks. Twelve subjects (7 males and 5 females) participated in this study. Subjects performed dynamic lifting tasks as a function of load weight, load origin, and load height to simulate complex lifting activities from extreme and highly dynamic postures. The moment matching measures were calculated to evaluate how well model estimated the spinal moment of L5/S1 compared to measured spinal moments in terms of correlation (R2) and average absolute error (AAE). The model demonstrated good repeatability and very good model fidelity between various experimental conditions. The mean and standard deviations of multi-planar R2 were 0.85 (0.07), with 78% of all trials (411/528) having R2 > 0.8. For the multi-planar normalized AAE (%), mean and standard deviations were 12.1% (3.9), with 80% of all trials (425/528) having AAE < 15%. The results of this study indicated that curved muscle representation in the biologically-assisted model was an empirically reasonable approach to estimate accurate spine tissue loads of the lumbar spine during complex occupational circumstances.

The effects of task execution variables on the musculature activation strategy of the lower trunk during squat lifting

The main objective of this study was to investigate the innervation behavior of lower trunk musculature to determine the muscular activation strategy during free dynamic squat lifting. This may clarify how lower trunk musculature activation compliments task execution variables to control motion during labor and industrial lifting tasks. In total, 12 healthy men volunteered to perform symmetric squat lifting of boxes of various masses (4, 8 and 12 kg) at slow and fast speeds. Eight-channel electromyography was performed on two pairs of abdominal (rectus abdominis and external oblique) and lower back muscles (iliocostalis lumborum and multifidus). Movement patterns were extracted using a 3D-linked segment model and a Vicon system. The results indicated that there were significant increases (all p-values < 0.05) in the mean muscle activation of the right and left multifidus and iliocostalis lumborum with increases in the lift speed and box weight. Furthermore, the results indicated that there were significant decreases (all p-values < 0.05) in the time required for the peak activation of the right and left multifidus, iliocostalis lumborum and external oblique with increases in the lift speed and box weight. Finally, the lower trunk musculature activation strategy was revealed to be compatible with different task execution variables, controlling motion in a manner that compensated for the effects of task execution variables. The findings of this study may effectively be applied to ergonomics, particularly to symmetric squat lifting.

A biologically-assisted curved muscle model of the lumbar spine: Model validation

BackgroundBiomechanical models have been developed to predict spinal loads in vivo to assess potential risk of injury in workplaces. Most models represent trunk muscles with straight-lines. Even though straight-line muscles behave reasonably well in simple exertions, they could be less reliable during complex dynamic exertions. A curved muscle representation was developed to overcome this issue. However, most curved muscle models have not been validated during dynamic exertions. Thus, the objective of this study was to investigate the fidelity of a curved muscle model during complex dynamic lifting tasks, and to investigate the changes in spine tissue loads. MethodsTwelve subjects (7 males and 5 females) participated in this study. Subjects performed lifting tasks as a function of load weight, load origin, and load height to simulate complex exertions. Moment matching measures were recorded to evaluate how well the model predicted spinal moments compared to measured spinal moments from T12/L1 to L5/S1 levels. FindingsThe biologically-assisted curved muscle model demonstrated better model performance than the straight-line muscle model between various experimental conditions. In general, the curved muscle model predicted at least 80% of the variability in spinal moments, and less than 15% of average absolute error across levels. The model predicted that the compression and anterior–posterior shear load significantly increased as trunk flexion increased, whereas the lateral shear load significantly increased as trunk twisted more asymmetric during lifting tasks. InterpretationA curved muscle representation in a biologically-assisted model is an empirically reasonable approach to accurately predict spinal moments and spinal tissue loads of the lumbar spine.

In a dynamic lifting task, the relationship between cross-sectional abdominal muscle thickness and the corresponding muscle activity is affected by the combined use of a weightlifting belt and the Valsalva maneuver

It has been shown that under isometric conditions, as the activity of the abdominal muscles increases, the thicknesses of the muscles also increase. The purpose of this experiment was to determine whether change in muscle thickness could be used as a measure of muscle activity during a deadlift as well as determining the effect of a weightlifting belt and/or the Valsalva maneuver on the muscle thicknesses. The Transversus Abdominis (TrA) and Internal Obliques (IO) muscles were analyzed at rest and during a deadlift. Muscle thickness was measured using ultrasound imaging and muscle activity was simultaneously recorded using electromyography. Each subject performed deadlift under normal conditions, while performing the Valsalva maneuver, while wearing a weightlifting belt and while both utilizing the belt and the Valsalva maneuver. There was no relationship between change in muscle thickness and muscle activity for both the TrA and IO (R2<0.13 for all conditions). However it was found that the Valsalva maneuver increased abdominal muscle thickness whereas the belt limited muscle expansion; each with an increase in activity. These results indicate that ultrasound cannot be used to measure muscle activity for a deadlift and that the belt affects how the IO and TrA function together.

Dynamics of tropical–extratropical interactions and extreme precipitation events in Saudi Arabia in autumn, winter and spring

AbstractExtreme precipitation in the arid Middle East can cause flash floods with dramatic societal impacts. This study investigates the synoptic‐scale dynamics of three extreme precipitation events that occurred in Saudi Arabia in autumn, winter and spring. Using ERA‐Interim reanalysis, soundings and observational precipitation data, we study precipitation characteristics, the synoptic circulations, moisture transport pathways and forcing mechanisms for upward motion. All three cases involved strong tropical–extratropical interactions whereby midlatitude forcing instigated an incursion of tropical moisture over the Arabian Peninsula that fuelled the heavy rainfall. In each case, a midlatitude upper‐level trough, associated with anticyclonic Rossby wave breaking, intruded into the subtropics. The phase relationship between this trough and the tropical low‐level circulation was consistent with wave amplification through baroclinic growth. Eulerian and Lagrangian analyses reveal moisture transport from nearby and remote tropical regions, leading to above‐normal tropospheric moisture content over Saudi Arabia. The autumn case (November 2009) showed a transient midlatitude upper‐level trough that interacted with the climatological Red Sea Trough near the surface, being an ‘Active Red Sea Trough’ event. The winter case (January 2005) resembled tropical plume‐like characteristics and demonstrated the coupling of a midlatitude cyclone and the equatorial low‐pressure zone over Africa, an intensified subtropical jet stream, and pronounced moisture fluxes at middle and upper levels. The spring case (April–May 2013) involved a quasi‐stationary cut‐off low and persistent advection of low‐level moist air masses, partly from the south Indian Ocean through cross‐equatorial flow. The forcing of ascent was associated with low‐level moisture convergence and decreased static stability (autumn case), dynamical lifting (winter case), strong surface sensible heating (spring case), and orographic lifting (all cases), favouring the build‐up and release of potential instability. We discuss the three cases from a seasonal perspective and present a synthesis of their common key synoptic features.

Cumulus over the Tibetan Plateau in the Summer Based on CloudSat–CALIPSO Data

Abstract Cumulus (Cu) can transport heat and water vapor from the boundary layer to the free atmosphere, leading to the redistribution of heat and moist energy in the lower atmosphere. This paper uses the fine-resolution CloudSat–CALIPSO product to characterize Cu over the Tibetan Plateau (TP). It is found that Cu is one of the dominant cloud types over the TP in the northern summer. The Cu event frequency, defined as Cu occurring within 50-km segments, is 54% over the TP in the summer, which is much larger over the TP than in its surrounding regions. The surface wind vector converging at the central TP and the topographic forcing provide the necessary moisture and dynamical lifting of convection over the TP. The structure of the atmospheric moist static energy shows that the thermodynamical environment over the northern TP can be characterized as having weak instability, a shallow layer of instability, and lower altitudes for the level of free convection. The diurnal variation of Cu with frequency peaks during the daytime confirms the surface thermodynamic control on Cu formation over the TP. This study offers insights into how surface heat is transported to the free troposphere over the TP and provides an observational test of climate models in simulating shallow convection over the TP.

Analysis of tunnel hydrodynamic characteristics for planing trimaran by model tests and numerical simulations

The planing trimaran hull has unique hydrodynamic performance due to the tunnel region. In this paper, results of experimental and numerical studies for the planing trimaran hull are presented to analyze the hydrodynamic characteristics of tunnel and its effect on the hull body. Model tests were carried out for volume based Froude number ranging from 0.90 to 5.87. Resistance, sinkage and trim angle obtained by towing tank show that the planing trimaran has poor resistance performance at the hump region, while it operates quite well in the planing mode. A three dimensional computational fluid dynamic (CFD) code based on the Finite Volume Method (FVM) was used to simulate the forward motion of the hull body with two degrees of freedom (heave and pitch) when Froude number is above 3.16. Calculated results were validated with the experimental data and showed good agreement. Wave profile, dynamic lift, longitudinal center of pressure and flow vectors in the tunnel region at various Froude numbers were provided to explain the hydrodynamic and aerodynamic mechanism of this region. At last, models with different tunnel height and beam were calculated to study the influence of tunnel configuration on hull behaviors and hydrodynamic performance.

Development and validation of a three dimensional dynamic biomechanical lifting model for lower back evaluation for careful box placement

One of the major causes to low back injury is the box lifting activity, thus for many years biomechanics has been utilized by designers for ergonomic evaluations of the box lifting activity which includes the placement of the box. More recently these ergonomic investigations have focused on the careful placement of the box. The AnyBody (AB) biomechanical models and optimization within the AB software system in conjunction with motion capture has been shown to obtain adequate estimates of joint reaction forces of the body. To date there has not been a dynamic 3D box lifting model developed and validated for carefully placing a box using the AB modeling system and motion capture. Thus the focus of this paper is on the development, verification and validation of a box lifting full body model for lower back evaluations for a dynamic lifting activity for carefully placing a box on a shelf.

Improvement of Full-Load Performance of an Automotive Engine Using Adaptive Valve Lift and Timing Mechanism

This paper describes an improvement of full-load performance of an internal combustion engine using Adaptive Valve Lift And Timing Mechanism (AVLT). AVLT enables engine power improvement by increasing valve timing and lift at high engine speed and load operating regions. It utilizes engine fluids pressure difference with respect to engine speed to actuate the AVLT mechanism which will make the valve lift higher and longer duration at higher engine speed and loads. Since engine speed and load can be linearly correlated to these pressures, a mechanical sliding arm valve actuation mechanism is constructed based on their transient behavior. Therefore, a continuously dynamic valve lift profile with respect to engine speed can be achieved to increase brake power of the engine. Dynamics analysis performed using MSC Adam software showed that tappet translation increased by 32% from 9.09 mm to 12.01 mm by varying translational skate position between 0o and 10o. The results from this simulation are then set as intake valve profile in Lotus Engineering software simulation. With AVLT, brake power at speed between 5000 and 6500 rpm increased between 2% to 7%. Maximum torque improvement was realized at 7000 rpm while BSFC was reduced by up to 2% at 7000 rpm. The increased in brake power and torque are direct results from volumetric efficiency linear improvement between 1.5 and 6% at speed range of 5000 to 7000 rpm.

Hydrodynamics of the interceptor on a 2-D flat plate by CFD and experiments

AbstractNowadays, the use of interceptor by both partial and total dynamic lift crafts is quite common. In this article, a lot of evidence is given regarding the effectiveness of interceptor. The interceptor, when placed at the stern region, changes the pressure distribution around the craft. Its presence affects drag force, lifting force and the position of pressure's center leading to a new trim. This study focuses on hydrodynamic effects of interceptors on a 2-D flat plate based on both computational fluid dynamic (CFD) and experimental approaches. The Reynolds average Navier-Stokes (RANS) equations are used to model the flow around a fixed flat plate with an interceptor at different heights and attack angles. Based on finite volume method and SIMPLE algorithm which uses static structures, this model can be analyzed and the RANS results can be compared with the experimental data obtained in the current channel of the laboratory of waves and current of COPPE/UFRJ (LOC in Portuguese acronym). According to the results, the increase of pressure at the end of the flat plate was proportional to the interceptor height. In addition, the existence of interceptors can significantly increase the lift force coefficient at high angles of attack also proportional to the interceptor height. The presence of interceptor at the end of the flat plate increased both the lift coefficient and the drag coefficient but hydrodynamic drag did not grow as fast as the lift coefficient did. The lift coefficient increased much more. Furthermore, the results showed that the interceptor effectiveness is proportional to the boundary layer thickness at the end of the flat plate. As the interceptor was inside the boundary layer alterations of flow speed led to changes in boundary layer thickness, directly affecting interceptor's efficiency. Optimum choice of interceptor height had a great effect on its efficiency, and in choosing it the flow speed and length of the boat must be taken into consideration.

Numerical simulation of an intense precipitation event over Rudraprayag in the central Himalayas during 13–14 September 2012

A recent heavy precipitation event on 13 September 2012 and the associated landslide on 14 September 2012 is one of the most severe calamities that occurred over the Rudraprayag region in Uttarakhand, India. This heavy precipitation event is also emblematic of the natural hazards occuring in the Himalayan region. Study objectives are to present dynamical fields associated with this event, and understand the processes related to the severe storm event, using the Weather Research and Forecasting (WRF ver 3.4) model. A triple-nested WRF model is configured over the Uttarakhand region centered over Ukhimath (30∘30′N; 79 ∘15′E), where the heavy precipitation event is reported. Model simulation of the intense storm on 13 September 2012 is with parameterized and then with explicit convection are examined for the 3 km grid spacing domain. The event was better simulated without the consideration of convection parameterization for the innermost domain. The role of steep orography forcings is notable in rapid dynamical lifting as revealed by the positive vorticity and high reflectivity values and the intensification of the monsoonal storm. Incursion of moist air, in the lower levels, converges at the foothills of the mountains and rise along the orography to form the updraft zone of the storm. Such rapid unstable ascent leads to deep convection and increases the condensation rate of the water vapour forming clouds at a swift rate. This culminates into high intensity precipitation which leads to high amount of surface runoff over regions of susceptible geomorphology causing the landslide. Even for this intense and potentially unsual rainfall event, the processes involved appear to be the ‘classic’ enhanced convective activity by orographic lifting of the moist air, as an important driver of the event.

Dynamic Lift on an Artificial Static Armor Layer During Highly Unsteady Open Channel Flow

The dynamic lift acting on a 100 mm × 100 mm section of a static armor layer during unsteady flow is directly measured in a series of physical experiments. The static armor layer is represented by an artificial streambed mold, made from an actual gravel bed. Data from a total of 190 experiments are presented, undertaken in identical conditions. Results show that during rapid discharge increases, the dynamic lift on the streambed repeatedly exhibits three clear peaks. The magnitude of the observed lift depends on the following hydrograph characteristics: (1) the initial flow depth; (2) the ramping duration and therefore the ramping rate; and (3) the total discharge increase. An adjusted unsteadiness parameter combines those three hydrograph characteristics for rapid discharge increases. Direct correlations between the unsteadiness parameter and the measured dynamic lift during unsteady flow are presented. In addition, the armor layer porosity showed a major impact on the observed effects. It is shown that increasing bed porosity leads to decreasing dynamic lift.

Apportionment of lumbar L2–S1 rotation across individual motion segments during a dynamic lifting task

Segmental apportionment of lumbar (L2–S1) rotation is a critical input parameter for musculoskeletal models and a candidate metric for clinical assessment of spinal health, but such data are sparse. This paper aims to quantify the time-variant and load-dependent characteristics of intervertebral contributions to L2–S1 extension during a dynamic lifting task. Eleven healthy participants lifted multiple weights (4.5, 9.1, and 13.6kg) from a trunk-flexed to an upright position while being imaged by a dynamic stereo X-ray system at 30frames/s. Vertebral (L2–S1) motion was tracked using a previously validated volumetric model-based tracking method that employs 3D bone models reconstructed from subject-specific CT images to obtain high-accuracy (≤0.26°, 0.2mm) 3D vertebral kinematics. Individual intervertebral motions as percentages of the total L2–S1 extension were computed at each % increment of the motion to show the segmental apportionment. Results showed L3–L4 (25.8±2.2%) and L4–L5 (31±3.1%) together contributed a larger share (∼60% combined) compared to L2–L3 (21.7±3.7%) and L5–S1 (22.6±4.7%); L4–L5 consistently provided the largest contribution of the measured segments. Relative changes over time in L3–L4 (6±12.5%) and L4–L5 (0.5±10.2%) contribution were minimal; in contrast, L2–L3 (18±20.1%) contribution increased while L5–S1 (−33±22.9%) contribution decreased in a somewhat complementary fashion as motion progressed. No significant effect of the magnitude of load lifted on individual segmental contribution patterns was detected. The current study updated the knowledge regarding apportionment of lumbar (L2–S1) motion among individual segments, serving both as input into musculoskeletal models and as potential biomechanical markers of low back disorders.

Coupled Aeroelastic Prediction of the Effects of Leading-Edge Slat on Rotor Performance

A coupled computational fluid dynamics and computational structural dynamics methodology is developed to analyze the effects of a leading-edge slat on rotor performance. The multielement intermesh connectivity was handled by implicit hole cutting overset implementation. The three-dimensional coupled computational fluid dynamics/computational structural dynamics model is extensively validated against a UH-60 flight-test condition: C9017. The solver is then used to successfully demonstrate the effectiveness of a leading-edge slat in mitigating (or eliminating) dynamic lift and moment stall on a modified UH-60A blade with a 40%-span slatted airfoil section. This results in a reduction of torsional structural loads (up to 73%) and pitch link loads (up to 62%) as compared to the baseline C9017 values. A dynamically moving slat strategy, actuating between slat positions S-1 and S-6 with 1 per revolution harmonic, is considered for stall mitigation. Further, it is shown that using slats with up to 10% higher thrust beyond the limit imposed by McHugh’s stall boundary (C9017) can be achieved. Stall mitigation due to the slat results in a reduction of torsional load up to 54% and a reduction of pitch link load up to 32% as compared to the baseline C9017 flight-test values, even for an increase in thrust of 10%.