Dynamic Lift Research Articles

Multi-phase optimisation model predicts manual lifting motions with less reliance on experiment-based posture data

Optimisation-based predictive models are widely-used to explore the lifting strategies. Existing models incorporated empirical subject-specific posture constraints to improve the prediction accuracy. However, over-reliance on these constraints limits the application of predictive models. This paper proposed a multi-phase optimisation method (MPOM) for two-dimensional sagittally symmetric semi-squat lifting prediction, which decomposes the complete lifting task into three phases—the initial posture, the final posture, and the dynamic lifting phase. The first two phases are predicted with force- and stability-related strategies, and the last phase is predicted with a smoothing-related objective. Box-lifting motions of different box initial heights were collected for validation. The results show that MPOM has better or similar accuracy than the traditional single-phase optimisation (SPOM) of minimum muscular utilisation ratio, and MPOM reduces the reliance on experimental data. MPOM offers the opportunity to improve accuracy at the expense of efforts to determine appropriate weightings in the posture prediction phases. Practitioner summary: Lifting optimisation models are useful to predict and explore the human motion strategies. Existing models rely on empirical subject-specific posture constraints, which limit their applications. A multi-phase model for lifting motion prediction was constructed. This model could accurately predict 2D lifting motions with less reliance on these constraints.

Using passive or active back-support exoskeletons during a repetitive lifting task: influence on cardiorespiratory parameters

The objective of this laboratory study was to assess the cardiorespiratory consequences related to the use of different back-support exoskeletons during a repetitive lifting task. Fourteen women and thirteen men performed a dynamic stoop lifting task involving full flexion/extension of the trunk in the sagittal plane. This task was repeated for 5min with a 10kg load to handle. Four conditions were tested: with a passive exoskeleton (P-EXO), with two active exoskeletons (A-EXO1 and A-EXO2), as well as without exoskeleton (FREE). The oxygen consumption rate and cardiac costs were measured continuously. Results showed a significantly lower (p < 0.05) oxygen consumption rate for all exoskeletons as compared to FREE (12.6 ± 2.2ml/kg/min). The values were also significantly lower (p < 0.001) for A-EXO1 (9.1 ± 1.8ml/kg/min) compared to A-EXO2 (11.0 ± 1.8ml/kg/min) and P-EXO (11.8 ± 2.4ml/kg/min). Compared to FREE (59.7 ± 12.9bpm), the cardiac cost was significantly reduced (p < 0.001) only for A-EXO1 (45.1 ± 11.5bpm). Several factors can explain these differences on the cardiorespiratory parameters observed between exoskeletons: the technology used (passive vs active), the torque provided by the assistive device, the weight of the system, but also the level of anthropomorphism (related to the number of joints used by the exoskeleton). Our results also highlighted the lack of interaction between the exoskeleton and sex. Thereby, the three back-support exoskeletons tested appeared to reduce the overall physical workload associated with a repetitive lifting task both for men and women.

Using static postures to estimate spinal loading during dynamic lifts with participant-specific thoracolumbar musculoskeletal models

Static biomechanical simulations are sometimes used to estimate in vivo kinetic demands because they can be solved efficiently, but this ignores any potential inertial effects. To date, comparisons between static and dynamic analyses of spinal demands have been limited to lumbar joint differences in young males performing sagittal lifts. Here we compare static and dynamic vertebral compressive and shear force estimates during axial, lateral, and sagittal lifting tasks across all thoracic and lumbar vertebrae in older men and women. Participant-specific thoracolumbar full-body musculoskeletal models estimated vertebral forces from recorded kinematics both with and without consideration of dynamic effects, at an identified frame of peak vertebral loading. Static analyses under-predicted dynamic compressive and resultant shear forces, by an average of about 16% for all three lifts across the thoracic and lumbar spine but were highly correlated with dynamic forces (average r2 > .95). The study outcomes have the potential to enable standard clinical and occupational estimates using static analyses.

Effects of a Passive Back-Support Exoskeleton on Knee Joint Loading during Simulated Static Sorting and Dynamic Lifting Tasks.

Due to the load shifting mechanism of many back-support exoskeletons (BSEs), this study evaluated possible side effects of using a BSE on knee joint loading. Twenty-nine subjects (25.9 (±4.4) years, 179.0 (±6.5) cm; 73.6 (±9.4) kg) performed simulated static sorting and dynamic lifting tasks, including stoop and squat styles and different trunk rotation postures. Ground reaction force, body posture and the force between the chest and the BSE’s contact interface were recorded using a force plate, two-dimensional gravimetric position sensors, and a built-in force sensor of the BSE, respectively. Using these parameters and the subject’s anthropometry, median and 90th percentile horizontal (HOR50, HOR90) and vertical (VERT50, VERT90) tibiofemoral forces were calculated via a self-developed inverse quasi-static biomechanical model. BSE use had a variable effect on HOR50 dependent on the working task and body posture. Generally, VERT50 increased without significant interaction effects with posture or task. HOR90 and VERT90 were not affected by using the BSE. In conclusion, utilizing the investigated exoskeleton is likely to induce side effects in terms of changed knee joint loading. This may depend on the applied working task and the user’s body posture. The role of these changes in the context of a negative contribution to work-related cumulative knee exposures should be addressed by future research.

Vitamin D Metabolites Are Associated with Physical Performance in Young Healthy Adults.

This study aimed to determine vitamin D metabolites and vitamin D receptor (VDR) single-nucleotide polymorphism (SNP) relationships with physical performance. In 1205 men and 322 women (94.8% White Caucasian, 22.0 ± 2.8 yr) commencing military training, we measured serum vitamin D metabolites (25-hydroxyvitamin D (25(OH)D) and 24,25-dihydroxyvitamin D (24,25(OH) 2 D) by high-performance liquid chromatography tandem mass spectrophotometry and 1,25-dihydroxyvitamin D (1,25(OH) 2 D) by immunoassay), VDR SNPs (rs2228570, rs4516035, and rs7139166 by polymerase chain reaction genotyping), and endurance performance by 2.4-km run, muscle strength by maximal dynamic lift, and muscle power by maximal vertical jump. Serum 25(OH)D was negatively associated with 2.4-km run time and positively associated with muscle power ( β = -12.0 and 90.1), 1,25(OH) 2 D was positively associated with run time and negatively associated with strength and muscle power ( β = 5.6, -1.06, and -38.4), and 24,25(OH) 2 D was negatively associated with run time ( β = -8.9; P < 0.01), after controlling for age, sex, smoking, alcohol, physical activity, time outdoors, season, and body mass index. Vitamin D metabolites (25(OH)D, 1,25(OH) 2 D, and 24,25(OH) 2 D) together explained variances of 5.0% in run time, 0.7% in strength, and 0.9% in muscle power (Δ F P < 0.001). All performance measures were superior with low 1,25(OH) 2 D:24,25(OH) 2 D ratio ( P < 0.05). VDR SNPs were not associated with physical performance (Δ FP ≥ 0.306). Vitamin D metabolites accounted for a small portion of variance in physical performance. Associations between vitamin D metabolites and run time were the most consistent. VDR SNPs explained no variance in performance. Greater conversion of 25(OH)D to 24,25(OH) 2 D, relative to 1,25(OH) 2 D (i.e., low 1,25(OH) 2 D:24,25(OH) 2 D ratio), was favorable for performance, indicating 24,25(OH) 2 D may have a role in optimizing physical performance.

Computational Investigation into Prediction of Lift Force and Resistance of a Hydrofoil Ship

The characteristics of the fore and aft foils at the various angles of attack incorporated with forward velocities have been vulnerable to induce strong nonlinearities to dynamic lift force and ship resistance. Then, a computational simulation is necessarily required to predict their performances in the calm water condition. This paper presents a computational investigation of the hydrofoil ship on predicting lift and ship’s resistance using fluid dynamic (CFD) simulation approach. Several parameters such as Froude numbers and the angle of attacks both of fore and aft foils have been accordingly taken into account. The results revealed that the subsequent increase on angle of attack of fore and aft foils was directly proportional to the lift force and the ship’s resistance. In addition, the lift force of the aft and fore foils with the angle of attacks of 10 degrees and 5 degrees, respectively, resulted in the significant increase of the lift force and the ship’s resistance. However, the subsequent increase of Froude number from 1.382 up to 1.626 has insignificant effect to the lift and the ship’s resistance of the hydrofoil. It can be concluded that CFD simulation is very beneficial to ensure an operational effectiveness of hydrofoil design towards prediction on the lift force and the hydrofoil’s resistance at the preliminary design stage.

Model-free control of the dynamic lift of a wind turbine blade section: experimental results

This work addresses the problem of developing control algorithms for the control of the aerodynamic lift of wind turbine blades using air injection, taking into account disturbances caused by turbulent perturbations. For this, a test bench is used where the lift of a 2D blade section in a wind tunnel can be controlled by a set of micro-jets close to the trailing edge. Through a continuous, local identification of the lift variations a model-free control that does not need any prior knowledge of the system is proposed. It allows the control of the flow of the micro-jets and stabilizes the lift around a tracking reference. The ability of the proposed control algorithm to track the lift reference when subjected to external perturbations, i.e., gusts, is discussed. In particular, this work demonstrates that the lift can be set to particular values using the proposed control strategy, and can be re-stabilized to pre-gust lift conditions. Experimental results illustrate globally the feasibility of such a control.

Coandă-Type Flow Actuation for Load Alleviation

Circulation control has the potential to improve current gust and maneuver load alleviation schemes, with the ultimate goal of reducing wing structure weight and saving fuel. A Coandă-type flow actuator is integrated on the pressure side of a two-dimensional airfoil model, and its load alleviation performance and dynamic behavior are determined experimentally. Quasi-steady force and wake measurements are conducted in a wind tunnel to quantify the effect of the actuator on lift and drag. Lift decrements of are reached for steady blowing, exceeding typical gust-induced wing loads in magnitude. For pulsed blowing, only moderate mass flow reductions of up to 25% are achieved, caused by discontinuous flow turning around the Coandă surface. Unsteady force and pressure measurements characterize the dynamic lift response to the actuation. The total onset time of the lift response, normalized by the ratio of chord length to freestream velocity, is for actuator activation and for actuator deactivation. These values are below typical onset times for gust loads (). The present results show a high-lift reduction potential and fast dynamic behavior of the Coandă-type flow actuator, making it a viable candidate for fast and effective load alleviation.

Dynamic responses of pitching hydrofoil in laminar–turbulent transition regime

Recently, the problem of a transitional boundary layer around a pitching foil has been attracting increasing attention. To determine the underlying physical mechanisms, in this study, a pitching hydrofoil is numerically investigated using the shear stress transport (SST) k–ω turbulence model coupled with the γ–Re˜θt transition model. First, the prediction of the static performance is compared with the experimental measurements and XFOIL data to validate and verify the numerical accuracy of the proposed method. Subsequently, the flow morphologies induced by sinusoidal and non-sinusoidal pitching laws are analyzed and compared in different reduced frequencies. The results indicate that reducing the empirical coefficient, A1, in the SST k–ω turbulence model can generate the flow separation in advance, thus improving the prediction of the hydraulic performance at a high angle of attack. The dynamic behavior of the laminar separation bubble is strongly associated with the pitching method and velocity. The collapse of the laminar separation bubble can destabilize the local boundary layer, generating multi-laminar separation bubbles. When new separation bubbles form and shed, a turbulent boundary layer moves downstream and is adsorbed on the surface simultaneously. The turbulence flow passes through the trailing edge, destroying the local vortex, contributing to a transiently elevated hydrodynamic lift. During a rapid pitching down, a counterclockwise trailing edge vortex becomes increasingly unstable, repeating the processes of inception, development, and shedding. The Theodorsen model fails to produce a reasonable hysteresis loop owing to the assumption of a fully attached flow. The results of a hybrid of the Theodorsen and Øye models show noticeable improvement in the dynamic lift prediction. The empirical coefficient, ks, of the Snel model is optimized, improving the predictions of low-frequency pitching significantly. All dynamic stall models present the same trend: low-frequency motions show better agreement than high-frequency ones. In the former, modeling of a non-sinusoidal pitching is closer to the transient numerical results than that of a sinusoidal motion.

Gust mitigation through closed-loop control. I. Trailing-edge flap response

In this work, we quantify and model the unsteady lift response to dynamic flap actuation from wind tunnel experiments at Re = $1.8\ifmmode\times\else\texttimes\fi{}{10}^{6}$. The quantification relies on two newly proposed metrics that characterize the dynamic lift hysteresis and allow describing its evolution under different pitching conditions. The modeling strategy yields one nonlinear model and a set of linear models relating the unsteady airfoil lift coefficient distribution to the flap deflection angle $\ensuremath{\delta}$.

Effects of an Unsteady Morphing Wing with Seamless Side-Edge Transition on Aerodynamic Performance

This paper presents an unsteady flow analysis of a 3D wing with a morphing trailing edge flap (TEF) and a seamless side-edge transition between the morphed and static parts of a wing by introducing an unsteady parametrization method. First, a 3D steady Reynolds-averaged Navier–Stokes (RANS) analysis of a statically morphed TEF with seamless transition is performed and the results are compared with both a baseline clean wing and a wing with a traditional hinged flap configuration at a Reynolds number of 0.7 × 106 for a range of angles of attack (AoA), from 4° to 15°. This study extends some previous published work by examining the inherent unsteady 3D effects due to the presence of the seamless transition. It is found that in the pre-stall regime, the statically morphed wing produces a maximum of a 22% higher lift and a near constant drag reduction of 25% compared with the hinged flap wing, resulting in up to 40% enhancement in the aerodynamic efficiency (i.e., lift/drag ratio). Second, unsteady flow analysis of the dynamically morphing TEF with seamless flap side-edge transition is performed to provide further insights into the dynamic lift and drag forces during the flap motions at three pre-defined morphing frequencies of 4 Hz, 6 Hz, and 8 Hz, respectively. Results have shown that an initially large overshoot in the drag coefficient is observed due to unsteady flow effects induced by the dynamically morphing wing; the overshoot is proportional to the morphing frequency which indicates the need to account for dynamic morphing effects in the design phase of a morphing wing.

EFFECT OF METAL FIBERS ON THE PROPERTY OF WELL CEMENT

Nowadays more oil and gas fields are developed in unconsolidated sandstone. When the formation consists of poorly cemented rocks, the connections between the rock particles are broken under the influence of forces acting in the bottomhole during oil production (wells), and the rock skeleton is intensively disintegrated and brought to the well by fluid flow. The sand production is considered undesirable product and the control of sand production is considered as one of the main concerns of production engineers. It can damage downhole, and surface production facilities, also increasing the risk of catastrophic failure. Choosing a method for preventing formation sand production depends on different reservoir parameters. The analysis of the production wells, where measures are taken to prevent the sand production, showed that the most effective method is to cover the bottom hole with various mortar materials. However, the current methods of bottomhole strengthening with cement mortars have a number of technological shortcomings which can include limited ductility and little resistance to cracking. According to the results, the efficiency of bottomhole reinforcement in the Absheron field is 40-50%. The reason for the low efficiency of this method is mainly the presence of lithostatic pressure and dynamic (perforation, sliding and lifting) loads applied to the cement barrier in the wellbore area. It is known that the weakest part of cement stone, prone to collapse and wear, is the perforation holes. During the oil production, the volume of sand increases that brought to the well, and around the perforation holes that on the cement stones are formed the collapses and fractures. Due to its low deformation and crack resistance, it cannot withstand these impact loads. Hence there is a need to reinforce the property of cement. The article presents the results of experimental studies of fiber-reinforced cement recommended for improving the quality of bottomhole coverage in increasing dynamic impact intervals. One of the promising directions to increase the resistance of the cement barrier under dynamic loads is its strengthening against compression and bending, using the principle of composition, which provides the compression resistance of the cement matrix. The most important properties of cement stone can be effectively regulated by using metal fibers, which allow implementation of the principle of composition in cement barrier. The main physical and mechanical properties of the cement burrier formed as a result of increasing the fiber concentration in the tampon solution change. Reinforcing metal fibers, uniformly distributed in the matrix and having different directions, received forces in any direction, preventing the formation and development of cracks in the cement stone. The metal fibers are randomly oriented and uniformly distributed throughout the volume, work together with the matrix due to the adhesion forces, and form a compact shape. When fiber adhesion is disrupted, the fibers prevent the growth and development of cracks by maintaining the integrity of the cement stone. Based on this principle, a new dispersion-enhanced buffering material consisting of a mixture of quartz sand and metal fibers was developed. Experiments were carried out to improve the physical and mechanical properties of the cement system (strength, fluidity, setting time, etc.) in the laboratory. Studies have taken a certain proportion of the water-cement mixture. Metal fibers of different quantities and lengths were added during the experiments to determine the mechanical properties of the cement stone. The test period, day and the curing temperature performed at different intervals according to the mixtures. The article shows the positive effect of fiber on the main properties of buffering solutions and the resulting stone, both theoretically and experimentally. The choice of the optimal method of cement stone reinforcement is the result of laboratory experiments. Following the results obtained, recommendations were given for the optimization of cement compositions. Keywords: cement stone, cement barrier, well area, dynamic loads, fiber, reinforcement, destruction, deformation, expansion.

Impacts of Changbai Mountain Topography on the Extreme Precipitation From Super Typhoon Maysak

Based on hourly gridded precipitation data (0.1°) calculated by the China Meteorological Administration (CMA), the European Centre Medium-Range Weather Forecasts (ECMWF) reanalysis data, and microwave measurements, this paper investigated the extreme precipitation induced by the Typhoon Maysak in Northeast China (September 2020), using the Advanced Research dynamic core of the Weather Research and Forecasting Model (WRF-ARW). The study focused on Changbai Mountain topography and the extreme precipitation in Jilin Province. The results show that two extreme precipitation centers corresponded well to the local terrain height in Jilin Province. The Changbai Mountain range, which mainly lies in southeastern Jilin Province, affected the typhoon in three aspects: blocking drag, forcing uplift, and promoting moisture convergence. Because of the blocking drag of the mountain topography, the duration of severe precipitation was prolonged. The overlap of the area affected by the peripheral cloud band of the typhoon and the direction of the typhoon was largely responsible for the extreme rainfall. The dynamic lifting by the mountainous terrain and the reinforced moisture convergence also considerably increased precipitation. Microwave measurements show that water vapor density profile increased rapidly at the peak (14 g/m3), and the high moisture density was retained for at least 15 h in the lower layer. The prolonged, continuous, and abundant moisture transport offered a sufficient water vapor supply for this severe precipitation event. According to the estimation of precipitation rate, the increment of torrential rainfall on Changbai Mountain during the severe precipitation period reached 6.8 mm/h, about 41% of the total rainfall in this period. Finally, the topographic sensitivity test indicated that when the terrain of Changbai Mountain was lower, the convergent ascending motion, precipitable water, and storm-relative helicity were weaker, and the rainfall distribution markedly changed. This finding further verifies the importance of the Changbai orography in the extreme precipitation event induced by Typhoon Maysak.

Virtual four sensor fast response aerodynamic probe (FRAP®)

This paper introduces the new fast response aerodynamic probe (FRAP®), which was recently developed at the ETH Zurich. The probe provides time-resolved, three-dimensional flow measurements using the virtual four sensor technique. Two probes work in tandem, being comparable to a pair of pneumatic needle probes. The first probe, being yaw angle sensitive, is positioned in three circumferential positions. The second probe being pitch angle sensitive is brought into exactly the same position as the first probe. The resulting set of four measurements is phaselock-averaged to one specific rotor trigger position. Then the reduced data sets are combined to four calibration coefficients, which are then further processed to determine the unsteady flow vector. The results consist of yaw and pitch flow angles as well as the total and static pressure. The outer diameter of the cylindrical probe head was miniaturized to 0.84mm, hence probe blockage effects as well as dynamic lift effects are reduced. The shape of the probe head was optimized in view of the manufacturing process as well as aerodynamic considerations. The optimum geometry for pitch sensitivity was found to be a cylindrical surface with the axis perpendicular to the probe shaft. The internal design of the probes led to a sensor cavity eigen frequency of 44 kHz for the yaw sensitive and 34kHz for the pitch sensitive probe. The steady aerodynamic characteristics of the probe were measured using the free jet probe calibration facility of the laboratory. The full set of calibration surfaces is given. Data acquisition is done with a fully automated traversing system, which moves the probe within the test rig and samples the signal with a PC-based A/D-board. An error analysis implemented into the data reduction routines revealed acceptable accuracy for flow angles as well as pressures for many turbomachinery flows. Depending on the dynamic head of the application the yaw angle is accurate within ±0.35° and pitch angle within ±0.7°. Finally, a comparison of time averaged results to five hole probe measurements is discussed.

A Lower-Back Exoskeleton With a Four-Bar Linkage Structure for Providing Extensor Moment and Lumbar Traction Force

Lower back pain and related injuries are prevalent and serious problems in various industries, and high compression force to the lumbosacral (L5/S1) region has been known as one of the key factors. Previous research on passive lower back exoskeletons focused on reducing lumbar muscle activation by providing an extensor moment. Additionally, lumbar traction forces can reduce the compression force, and is a common treatment method for lower back pain in clinics. In this paper, we propose a novel passive lower back exoskeleton that provides both extensor moment and lumbar traction force. The working principle of the exoskeleton, extending the coil springs during lumbar flexion, and its design criteria regarding the amount of each force element were provided. The kinematic model explained its operation, and the dynamic simulation estimated its performance and validated its satisfaction with the design criteria. The biomechanical model provided a brief insight into the expected exoskeleton's effect on the reduced lower back compression force. Ten subjects performed static holding and dynamic lifting tasks, and the generated force elements in two directions, parallel and perpendicular to the trunk, were evaluated using a force sensor and electromyography sensors, respectively. The experiment demonstrated a pulling force opposite to the direction of intradiscal pressure and reduced erector spinae activation. This implies the effect of wearing the exoskeleton to decrease the intervertebral pressure during static back bending or heavy lifting tasks.

Vortex Ring Formed by a Butterfly Wing and Dynamic Forces

Butterfly generates unsteady dynamic fluid force with a pair of vortex rings. In order to elucidate the flight mechanism of butterflies, it is necessary not only to clarify the vortex rings formed around the wings but also elucidate the characteristics of the unsteady fluid force generated by the flapping motion. By applying the momentum theory to the vortex rings formed during flapping motion, it is possible to estimate the force generated by flapping motion. In this study, we reconstruct a pair of vortex rings formed by flapping motion based on a small number of visualization results and elucidate dynamic fluid force characteristics. A part of estimation result of Lift estimated by the rough shape vortex rings generated by downstroke and upstroke do not match with the direct measurement result. But not only the peak value of estimation result of Lift is near with the direct measurement result quantitatively but also the value of estimation result between upstroke is a small negative as well as the direct measurement result. Although there is a phase difference between the estimation result and direct measurement result, there is a qualitative and quantitative agreement between estimation results and direct measurement result. From those results, butterfly generate the unsteady dynamic Lift between downstroke, especially at butterfly spread wing maximum (t/T = 0.40). After that, the unsteady dynamic Lift decrease and become 0 at upstroke.

LOW REYNOLDS NUMBER PERFORMANCE OF A MODEL SCALE T-FOIL

Submerged T-foils are an essential forward component of the ride control systems of high speed ferries. A model scale T-Foil for a 2.5m towing tank model of a 112m INCAT Tasmania high-speed wave-piercer catamaran has been tested for both static and dynamic lift performance. The tests were carried out using a closed-circuit water tunnel to investigate the lift and drag characteristics as well as frequency response of the T-Foil. The model T-Foil operates at a Reynolds number of approximately 105, has an aspect ratio of 3.6 and a planform which is strongly tapered from the inboard to outboard end. All of these factors, as well as strut and pivot interference, influence the steady lift curve slope ( of the model T-foil which was found to be 61% of the value for an ideal aerofoil with elliptic loading. The T-foil dynamic performance was limited primarily by the stepper motor drive system and connection linkage. At the frequency of maximum motion of the 2.5 m catamaran model (about 1.5Hz) the model T-foil has approximately 5% reduction of amplitude and 15 degrees of phase shift relative to the low frequency response. Only very small limitations arose due to the unsteady lift as predicted by the analysis of Theodorsen. It was concluded that the model scale T-foil performed adequately for application to simulation of a ride control system at model scale.

Observer Design for Nonlinear Systems with Equivariance

Equivariance is a common and natural property of many nonlinear control systems, especially those associated with models of mechatronic and navigation systems. Such systems admit a symmetry, associated with the equivariance, that provides structure enabling the design of robust and high-performance observers. A key insight is to pose the observer state to lie in the symmetry group rather than on the system state space. This allows one to define a global intrinsic equivariant error but poses a challenge in defining internal dynamics for the observer. By choosing an equivariant lift of the system dynamics for the observer internal model, we show that the error dynamics have a particularly nice form. Applying the methodology of extended Kalman filtering to the equivariant error state yields a filter we term the equivariant filter. The geometry of the state-space manifold appears naturally as a curvature modification to the classical Riccati equation for extended Kalman filtering. The equivariant filter exploits the symmetry and respects the geometry of an equivariant system model, and thus yields high-performance, robust filters for a wide range of mechatronic and navigation systems.

Experimental study on dynamic stall control based on AC-DBD actuation

To explore AC-DBD’s ability in controlling dynamic stall, a practical SC-1095 airfoil of a helicopter was selected, and systematic wind tunnel experiments were carried out through direct aerodynamic measurements. The effectiveness of dynamic stall control under steady and unsteady actuation is verified. The influence of parameters such as constant actuation voltage, pulsed actuation voltage, pulsed actuation frequency and duty ratio on dynamic stall control effect is studied under the flow condition of k = 0.15 above the airfoil, and the corresponding control mechanism is discussed. Steady actuation can effectively reduce the hysteresis loop area of dynamic lift, and control the peak drag and moment coefficient. For unsteady actuation, there is an optimal duty ratio DC = 50%, which has the best effect in improving the lift and drag characteristics, and there is a threshold of pulsed actuation voltage in dynamic stall control. The optimal dimensionless frequency will not be found; different F + have different control advantages in different aerodynamic coefficients of different pitching stages. Unsteady actuation has obvious control advantages in improving the lift-drag characteristics and hysteresis, while steady actuation can better control the large nose-down moment.

A Simple Lagrangian Parcel Model for the Initiation of Summer-time Mesoscale Convective Systems over the Central United States

AbstractMesoscale convective systems (MCSs) account for more than 50% of summer-time precipitation over the central United States (US) and have a significant impact on local weather and hydrologic cycle. It is hypothesized that the inadequate treatment of MCSs is responsible for the longstanding warm and dry bias over the central US in coarse-resolution general circulation model (GCM) simulations. In particular, a better understanding of MCS initiation is still lacking. Here a single-column Lagrangian parcel model is first developed to simulate the basic features of a rising parcel. This simple model demonstrates the collective effects of boundary layer moistening and dynamical lifting in triggering convective initiation and reproduces successfully its early afternoon peak with surface equivalent potential temperature as a controlling factor. It also predicts that convection is harder to trigger in the future climate under global warming, consistent with the results from convection-permitting regional climate simulations. Then a multi-column model that includes an array of single-column models aligned in the east-west direction and incorporates idealized cold pool interaction mechanisms is developed. The multi-column model captures readily the cold pool induced upscale growth feature in MCS genesis from initially scattered convection that is organized into a mesoscale cluster in a few hours. It also highlights the crucial role of lifting effects due to cold pool collision and spreading, subsidence effect, and gust front propagation speed in controlling the final size of mesoscale clusters and cold pool regions. This simple model should be useful for understanding fundamental mechanisms of MCS initiation and providing guidance for improving MCS simulations in GCMs.