Vertical force generation of a vectorial thruster that employs a rigid flapping panel

2021 ◽  
Vol 33 (6) ◽  
pp. 061906
Author(s):  
Haizhou Hu ◽  
Yankui Wang
Keyword(s):  
Force Generation ◽  
Vertical Force

Numerical investigation of the aerodynamic performance of dragonfly-like flapping foil in take-off flight

2019 ◽  
Vol 233 (15) ◽  
pp. 5801-5815
Author(s):  
AR Shanmugam ◽  
CH Sohn
Keyword(s):  
Thrust Force ◽  
Aerodynamic Performance ◽  
Force Generation ◽  
Vertical Force ◽  
Tandem Configuration ◽  
Flapping Foil ◽  
Flow Interactions ◽  
Two Parameters ◽  
Thrust Forces ◽  
Weakly Dependent

In this study, the aerodynamic performance of a dragonfly-like flapping foil is investigated in take-off flight using two-dimensional numerical simulations. Two parameters, foil spacing L * ( L/c) and the phase shift between forefoil and hindfoil ψ, which characterize the flow in the tandem configuration, are varied to explore their impact on the resulting aerodynamic performance. Both the vertical and thrust forces generated in one cycle are found to be strongly dependent on ψ and relatively weakly dependent on L *. The tandem configuration is beneficial for the vertical force generation in the range of 0° ≤  ψ ≤ 30°, and further, it aids the thrust force generation for 40° ≤  ψ ≤ 110°. The flow interactions between the forefoil and hindfoil can increase the vertical force generated in a cycle by a maximum of ∼1.2 times when ψ is close to 0° relative to the no foil–foil interaction case (additive effect of two single foils). These interactions can also increase the thrust force generated in a cycle by a maximum of ∼2.8 times when ψ is close to 80°. The vortex structures reveal that the enhancement in thrust force mainly depends on the timing of interactions and how the hindfoil utilizes the vortex detached from the forefoil to benefit from it. Further, we find that dragonflies use in-phase stroking pattern ( ψ = 0 °) with a large downstroke angle of attack, α D ( α D = 86 °), in the initial phase of take-off as it aids in generating additional vertical force. Our findings can significantly contribute to the design of micro aerial vehicles.

scholarly journals Clap-and-fling mechanism in a hovering insect-like two-winged flapping-wing micro air vehicle

2016 ◽  
Vol 3 (12) ◽  
pp. 160746 ◽  
Author(s):  
Hoang Vu Phan ◽  
Thi Kim Loan Au ◽  
Hoon Cheol Park
Keyword(s):  
Drag Force ◽  
Cfd Simulation ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Flapping Wing ◽  
Micro Air Vehicle ◽  
Force Generation ◽  
Vertical Force ◽  
Cfd Model ◽  
Air Vehicle

This study used numerical and experimental approaches to investigate the role played by the clap-and-fling mechanism in enhancing force generation in hovering insect-like two-winged flapping-wing micro air vehicle (FW-MAV). The flapping mechanism was designed to symmetrically flap wings at a high flapping amplitude of approximately 192°. The clap-and-fling mechanisms were thereby implemented at both dorsal and ventral stroke reversals. A computational fluid dynamic (CFD) model was constructed based on three-dimensional wing kinematics to estimate the force generation, which was validated by the measured forces using a 6-axis load cell. The computed forces proved that the CFD model provided reasonable estimation with differences less than 8%, when compared with the measured forces. The measurement indicated that the clap and flings at both the stroke reversals augmented the average vertical force by 16.2% when compared with the force without the clap-and-fling effect. In the CFD simulation, the clap and flings enhanced the vertical force by 11.5% and horizontal drag force by 18.4%. The observations indicated that both the fling and the clap contributed to the augmented vertical force by 62.6% and 37.4%, respectively, and to the augmented horizontal drag force by 71.7% and 28.3%, respectively. The flow structures suggested that a strong downwash was expelled from the opening gap between the trailing edges during the fling as well as the clap at each stroke reversal. In addition to the fling phases, the influx of air into the low-pressure region between the wings from the leading edges also significantly contributed to augmentation of the vertical force. The study conducted for high Reynolds numbers also confirmed that the effect of the clap and fling was insignificant when the minimum distance between the two wings exceeded 1.2c (c = wing chord). Thus, the clap and flings were successfully implemented in the FW-MAV, and there was a significant improvement in the vertical force.

Arms are different from legs: mechanics and energetics of human hand-running

1995 ◽  
Vol 78 (4) ◽  
pp. 1280-1287 ◽  
Author(s):  
J. W. Glasheen ◽  
T. A. McMahon
Keyword(s):  
Human Subjects ◽  
Low Cost ◽  
Force Production ◽  
Metabolic Cost ◽  
Legged Locomotion ◽  
Force Generation ◽  
Human Hand ◽  
Vertical Force ◽  
Constant Stiffness ◽  
Limb Stiffness

To determine whether nonlocomotor limbs (arms) differ from locomotor limbs (legs), we trained human subjects to run on their hands while supporting a fraction of their body weight. We wanted to know whether the low cost of force production and the speed-independent limb stiffness of locomotor limbs were characteristics associated with locomotion or were inherent properties of all limbs. We found that the limb stiffness of the human arm increases by 135% over less than a fourfold range in peak vertical force. In contrast, human legs and a variety of other mammalian locomotor limbs maintain a constant stiffness, regardless of speed and loading, for normal running. In addition, we explored the energetics of locomotion in hand-running. The economy of force generation (in J/N) is invariant with speed, as is found in legged locomotion. However, our results show that the metabolic cost of force generation while running on human arms is four to five times greater than the cost of force generation for the locomotor limbs of running quadrupeds.

Force Plate Analysis of Dogs with Bilateral Hip Dysplasia Treated with a Unilateral Triple Pelvic Osteotomy: A Long-term Review of Cases

1998 ◽  
Vol 11 (02) ◽  
pp. 85-93 ◽  
Author(s):  
Joanne R. Cockshutt ◽  
H. Dobson ◽  
C. W. Miller ◽  
D. L. Holmberg ◽  
Connie L. Taves ◽  
...  
Keyword(s):  
Gait Analysis ◽  
Hip Dysplasia ◽  
Weight Bearing ◽  
Force Plate ◽  
Case Series ◽  
Pelvic Osteotomy ◽  
Vertical Force ◽  
Long Term Outcome ◽  
Case Series Study

SummaryA retrospective case series study was done to determine the long-term outcome of operations upon dogs treated for canine hip dysplasia by means of a triple pelvic osteotomy (TPO). Twentyfour dogs with bilateral hip dysplasia, that received a unilateral TPO between January 1988 and June 1995, were re-examined at the Ontario Veterinary College. The assessment included physical, orthopedic and lameness examinations, standard blood work, pelvic radiographs and force plate gait analysis. They were compared to bilaterally dysplastic dogs that had not been treated, and also to normal dogs. Force plate data analysis demonstrated a significant increase in peak vertical force (PVF) and mean vertical force over stance (MVF) in the limb that underwent surgical correction by means of a TPO, when compared to the unoperated hip. It was determined that performing a unilateral TPO on a young dysplastic dog resulted in greater forces and weight bearing being projected through the TPO corrected limb when compared to the unoperated limb.Dogs with bilateral hip dysplasia treated with a unilateral triple pelvic osteotomy (TPO) were assessed by force plate gait analysis, radiographs and orthopedic examination. There was a significant increase in hip Norberg angles over time, although degenerative changes did progress. Limbs that had been operated upon had significantly greater peak and mean ground reaction forces than limbs that had not received an operation.

Lack of myostatin in mice results in excessive muscle but impaired force generation, tubular aggregates and alterations in fibre type profile

2005 ◽  
Vol 36 (02) ◽  
Author(s):  
H Amthor ◽  
R Navarette ◽  
SC Brown ◽  
R Macharia ◽  
F Muntoni ◽  
...  
Keyword(s):  
Fibre Type ◽  
Force Generation ◽  
Tubular Aggregates

Some Consequences of Coulomb Friction in Modeling Longitudinal Traction

1990 ◽  
Vol 18 (1) ◽  
pp. 13-65 ◽  
Author(s):  
W. W. Klingbeil ◽  
H. W. H. Witt
Keyword(s):  
Shear Force ◽  
Coulomb Friction ◽  
Interfacial Shear ◽  
Force Generation ◽  
Behavior Patterns ◽  
Inflation Pressure ◽  
Friction Law ◽  
The Coefficient Of Friction ◽  
Coulomb Friction Law ◽  
Perfect Adhesion

Abstract A three-component model for a belted radial tire, previously developed by the authors for free rolling without slip, is generalized to include longitudinal forces and deformations associated with driving and braking. Surface tractions at the tire-road interface are governed by a Coulomb friction law in which the coefficient of friction is assumed to be constant. After a brief review of the model, the mechanism of interfacial shear force generation is delineated and explored under traction with perfect adhesion. Addition of the friction law then leads to the inception of slide zones, which propagate through the footprint with increasing severity of maneuvers. Different behavior patterns under driving and braking are emphasized, with comparisons being given of sliding displacements, sliding velocities, and frictional work at the tire-road interface. As a further application of the model, the effect of friction coefficient and of test variables such as load, deflection, and inflation pressure on braking stiffness are computed and compared to analogous predictions on the braking spring rate.

Fore-Aft Forces in Tire-Wheel Assemblies Generated by Unbalances and the Influence of Balancing

1991 ◽  
Vol 19 (3) ◽  
pp. 142-162 ◽  
Author(s):  
D. S. Stutts ◽  
W. Soedel ◽  
S. K. Jha
Keyword(s):  
Mathematical Model ◽  
Elastic Foundation ◽  
Torsional Oscillation ◽  
Vertical Direction ◽  
Torsional Stiffness ◽  
Rolling Motion ◽  
Vertical Force ◽  
Horizontal Force ◽  
Wheel Rim ◽  
Open Question

Abstract When measuring bearing forces of the tire-wheel assembly during drum tests, it was found that beyond certain speeds, the horizontal force variations or so-called fore-aft forces were larger than the force variations in the vertical direction. The explanation of this phenomenon is still somewhat an open question. One of the hypothetical models argues in favor of torsional oscillations caused by a changing rolling radius. But it appears that there is a simpler answer. In this paper, a mathematical model of a tire consisting of a rigid tread ring connected to a freely rotating wheel or hub through an elastic foundation which has radial and torsional stiffness was developed. This model shows that an unbalanced mass on the tread ring will cause an oscillatory rolling motion of the tread ring on the drum which is superimposed on the nominal rolling. This will indeed result in larger fore-aft than vertical force variations beyond certain speeds, which are a function of run-out. The rolling motion is in a certain sense a torsional oscillation, but postulation of a changing rolling radius is not necessary for its creation. The model also shows the limitation on balancing the tire-wheel assembly at the wheel rim if the unbalance occurs at the tread band.

Israel’s Ground Forces in the Occupied Territories

2020 ◽  
Vol 35 (2) ◽  
pp. 37-57
Author(s):  
Eyal Ben-Ari ◽  
Uzi Ben-Shalom
Keyword(s):  
High Intensity ◽  
Force Generation ◽  
Institutional Autonomy ◽  
Multiple Forms ◽  
The West ◽  
Occupied Territories ◽  
Media Monitoring ◽  
Israel Defense Forces ◽  
And Control ◽  
Over Time

The Israel Defense Forces (IDF) routinely rotate ground forces in and out of the Occupied Territories in the West Bank. While these troops are trained for soldiering in high-intensity wars, in the Territories they have long had to carry out a variety of policing activities. These activities often exist in tension with their soldierly training and ethos, both of which center on violent encounters. IDF ground forces have adapted to this situation by maintaining a hierarchy of ‘logics of action’, in which handling potentially hostile encounters takes precedence over other forms of policing. Over time, this hierarchy has been adapted to the changed nature of contemporary conflict, in which soldiering is increasingly exposed to multiple forms of media, monitoring, and juridification. To maintain its public legitimacy and institutional autonomy, the IDF has had to adapt to the changes imposed on it by creating multiple mechanisms of force generation and control of soldierly action.

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