Explaining Ground Effect Aerodynamics via a Real-Life Reference Frame

2014 ◽  
Vol 553 ◽  
pp. 229-234
Author(s):  
Philip Close ◽  
Tracie J. Barber
Keyword(s):  
Reference Frame ◽  
Reference Frames ◽  
Computational Simulation ◽  
Real Life ◽  
Computational Modelling ◽  
Ground Effect ◽  
The Body ◽  
Moving Body ◽  
Set Up ◽  
Insight Into

The principle of relative motion as the cause of forces on a body submersedin a uid is foundational in the study of uid mechanics. In aerodynamics the wind tunnelis used as a convenient and safe method by which to test the aerodynamic performance ofbodies. This body-stationary convention has carried over into the computational world withthe development of CFD, though there is no practical reason why the moving body/stationaryuid set-up that corresponds to reality cannot be used for computational modelling. This pointbecomes particularly important as the concept of ground e ect is introduced. With an extraboundary nearby it becomes harder to appropriatel y match the experimental set-up with reality,and the extra boundary condition also adds complexity to computational simulation. A studywas undertaken to compare the body-stationary and body-moving reference frames in grounde ect. The moving reference frame velocity elds allowed new insight into the aerodynamics ofground e ect.

A Technical Note on the appropriate CFD boundary conditions for the prediction of ground effect aerodynamics

1999 ◽  
Vol 103 (1029) ◽  
pp. 545-547 ◽  
Author(s):  
T. J. Barber ◽  
E. Leonardi ◽  
R. D. Archer
Keyword(s):  
Reference Frame ◽  
Real Life ◽  
Ground Effect ◽  
Technical Note ◽  
Wind Tunnel Testing ◽  
Life Situation ◽  
Moving Vehicle ◽  
Real Life Situation ◽  
Fixed Reference ◽  
Computational Fluid Dynamics Cfd

The accurate prediction of ground effect aerodynamics is an important aspect of wing-in-ground effect vehicle (WIG) design. Computational fluid dynamics (CFD) solutions are useful alternatives to expensive (especially in the case of ground effect) wind-tunnel testing. However, the incorporation of the rigid surface effects often leads to confusion due to such a model being in a vehicle fixed reference frame (air moving, vehicle fixed) rather than the real-life situation of a ground fixed reference frame (air fixed, vehicle moving).

Experimental Studies of Hydrodynamic Properties and Screening of Riser Fairing Concepts for Deep Water Applications

2015 ◽  
Author(s):  
Rolf Baarholm ◽  
Kjetil Skaugset ◽  
Halvor Lie ◽  
Henning Braaten
Keyword(s):  
Experimental Studies ◽  
Real Life ◽  
Cross Flow ◽  
Free Vibrations ◽  
The Body ◽  
Scale Model ◽  
Small Scale ◽  
Structural Fatigue ◽  
And Performance ◽  
Set Up

The VIV oscillations of marine risers are known to increase drag, and lead to structural fatigue. One proven method of suppressing this vibration is the use of fairings and strakes. These coverings essentially modify the flow along the cylinder, tripping the production of Karman vortices so that they act less coherently or far enough downstream so they interact less with the body. The Norwegian Deepwater Programme (NDP) has conducted a project with the objective to develop and qualify effective low drag fairing concepts with respect to VIV mitigation and galloping. Furthermore, emphasis is put on easy handling and installation. This paper describes the work and findings in an early phase of the development. This includes small scale model test campaigns. In addition to the bare riser for reference, the behaviour and performance of a total of 10 different fairing concepts are evaluated. Free oscillation tests are performed in a towing tank, where 2D fairings were tested in a pendulum set-up. The set-up enables free vibrations in up to 3 DOF (in-line and cross-flow vibrations and yaw). Fix tests with the purpose of establishing hydrodynamic coefficients for the various fairings have been performed in a large cavitation tunnel. Clear differences in performance have been noticed; particular for drag and galloping responses. Based on the results from the 2D tests, a screening of the fairing designs has been performed and the findings have set the course for further development of the most promising candidates for real life applications.

Generalized Vector Derivatives for Systems With Multiple Relative Motion

1968 ◽  
Vol 35 (1) ◽  
pp. 20-24 ◽  
Author(s):  
T. A. Sherby ◽  
J. F. Chmielewski
Keyword(s):  
Reference Frame ◽  
Relative Motion ◽  
Reference Frames ◽  
Equations Of Motion ◽  
Rigid Bodies ◽  
Main Body ◽  
Angular Velocity Vector ◽  
Relative Coordinates ◽  
Moving Body ◽  
Classical Vector

For the analysis of relative motion, classical vector mathematics is limited to the use of one moving reference frame when taking vector derivatives. However, many dynamical systems consist of a number of rigid bodies in motion relative to one another. The classical procedure requires the specification of the position of each body relative to a single “main body.” The use of relative coordinates allows a natural specification of the position of one moving body relative to another moving body in network fashion. To use relative coordinates in dynamic and kinematic analyses, it is necessary to use relative vector derivatives involving more than one moving reference frame. This paper presents general expressions for the kth-order derivative of a relative position and angular velocity vector measured in any moving reference frame in a system of m reference frames with multiple relative motion. These expressions are used to develop a procedure which generates the differential equations of motion for the system by routine substitution of the relative coordinates and their scalar derivatives. This procedure offers promise as an algorithm for machine generation of the system equations and eliminates the possibility of neglecting subtle accelerations due to relative motion. The use of the procedure is demonstrated by generating the equations of motion of an offset unsymmetrical gyroscope.

scholarly journals Attitude Determination Algorithms through Accelerometers, GNSS Sensors, and Gravity Vector Estimator

2018 ◽  
Vol 2018 ◽  
pp. 1-14 ◽  
Author(s):  
Raúl de Celis ◽  
Luis Cadarso
Keyword(s):  
Reference Frame ◽  
Velocity Vector ◽  
Reference Frames ◽  
Attitude Determination ◽  
The Body ◽  
Gravity Vector ◽  
New Approach ◽  
Spacecraft Navigation ◽  
Body Reference ◽  
Ballistic Projectiles

Aircraft and spacecraft navigation precision is dependent on the measurement system for position and attitude determination. Rotation of an aircraft can be determined measuring two vectors in two different reference systems. Velocity vector can be determined in the inertial reference frame from a GNSS-based sensor and by integrating the acceleration measurements in the body reference frame. Estimating gravity vector in both reference frames, and combining with velocity vector, determines rotation of the body. A new approach for gravity vector estimations is presented and employed in an attitude determination algorithm. Nonlinear simulations demonstrate that using directly the positioning and velocity outputs of GNSS sensors and strap-down accelerometers, aircraft attitude determination is precise, especially in ballistic projectiles, to substitute precise attitude determination devices, usually expensive and forced to bear high solicitations as for instance G forces.

scholarly journals Flexible egocentric and allocentric representations of heading signals in parietal cortex

2018 ◽  
Vol 115 (14) ◽  
pp. E3305-E3312 ◽  
Author(s):  
Xiaodong Chen ◽  
Gregory C. DeAngelis ◽  
Dora E. Angelaki
Keyword(s):  
Reference Frame ◽  
Parietal Cortex ◽  
Posterior Parietal Cortex ◽  
Reference Frames ◽  
The Body ◽  
Neural Representation ◽  
Body Orientation ◽  
Tuning Curves ◽  
The World ◽  
Posterior Parietal

By systematically manipulating head position relative to the body and eye position relative to the head, previous studies have shown that vestibular tuning curves of neurons in the ventral intraparietal (VIP) area remain invariant when expressed in body-/world-centered coordinates. However, body orientation relative to the world was not manipulated; thus, an egocentric, body-centered representation could not be distinguished from an allocentric, world-centered reference frame. We manipulated the orientation of the body relative to the world such that we could distinguish whether vestibular heading signals in VIP are organized in body- or world-centered reference frames. We found a hybrid representation, depending on gaze direction. When gaze remained fixed relative to the body, the vestibular heading tuning of VIP neurons shifted systematically with body orientation, indicating an egocentric, body-centered reference frame. In contrast, when gaze remained fixed relative to the world, this representation changed to be intermediate between body- and world-centered. We conclude that the neural representation of heading in posterior parietal cortex is flexible, depending on gaze and possibly attentional demands.

scholarly journals Basic Gestures as Spatiotemporal Reference Frames for Repetitive Dance/Music Patterns in Samba and Charleston

2010 ◽  
Vol 28 (1) ◽  
pp. 71-91 ◽  
Author(s):  
Marc Leman ◽  
Luiz Naveda
Keyword(s):  
Reference Frame ◽  
Reference Frames ◽  
Three Dimensional ◽  
Action Perception ◽  
Dance Music ◽  
Geometric Patterns ◽  
Dance Movements ◽  
Musical Cues ◽  
Music Patterns ◽  
Insight Into

The goal of the present study is to gain better insight into how dancers establish, through dancing, a spatiotemporal reference frame in synchrony with musical cues. With the aim of achieving this, repetitive dance patterns of samba and Charleston were recorded using a three-dimensional motion capture system. Geometric patterns then were extracted from each joint of the dancer's body. The method uses a body-centered reference frame and decomposes the movement into nonorthogonal periodicities that match periods of the musical meter. Musical cues (such as meter and loudness) as well as action-based cues (such as velocity) can be projected onto the patterns, thus providing spatiotemporal reference frames, or 'basic gestures,' for action-perception couplings. Conceptually speaking, the spatiotemporal reference frames control minimum effort points in action-perception couplings. They reside as memory patterns in the mental and/or motor domains, ready to be dynamically transformed in dance movements. The present study raises a number of hypotheses related to spatial cognition that may serve as guiding principles for future dance/music studies.

Real-life Bifurcation – Challenges and Potential Complications

2011 ◽  
Vol 7 (4) ◽  
pp. 283
Author(s):  
Inga Narbute ◽  
Sanda Jegere ◽  
Indulis Kumsars ◽  
Dace Juhnevica ◽  
Agnese Knipse ◽  
...  
Keyword(s):  
Stent Thrombosis ◽  
Real Life ◽  
Coronary Intervention ◽  
Side Branch ◽  
The Body ◽  
Chronic Total Occlusions ◽  
Vein Grafts ◽  
Procedural Complications ◽  
Drug Eluting ◽  
Bifurcation Lesions

Together with calcified lesions, saphenous vein grafts, chronic total occlusions and unprotected left main lesions, bifurcation lesions are complex lesions that remain among the outstanding challenges of treatment with percutaneous coronary intervention. Bifurcation lesions are associated with increased rates of procedural complications, restenosis and adverse events than lesions in the body of the vessel. The introduction of drug-eluting stents for the treatment of bifurcation lesions has dramatically decreased restenosis rates, especially in patients suffering from diabetes. However, abrupt side branch closure, side branch ostial restenosis and stent thrombosis remain areas where further improvement is needed. Although a provisional T-stent strategy is most often used when side branch stenting is required, there are true bifurcation lesions where the selected use of more complex bifurcation approaches (such as the crush technique, T-stenting or the culotte technique) seem appropriate, particularly when the main branch and side branch are larger vessels with more diffuse side branch disease. The major challenge with any technique is to ensure that the side branch is protected and there is a satisfactory final result. Many technical questions rise in trying to ensure this outcome and lower the risk of intra- and post-procedural complications such as side branch closure and restenosis, stent thrombosis, dissection and fracture of a jailed wire: how can difficult side branch access be solved? How can unfavourable side branch anatomy be re-wired after main vessel stent placement? How can fracture of a jailed wire be avoided? Is side-strut dilation beneficial?

Teacher digital competence: bringing education to the next level

2020 ◽  
Vol 11 (1) ◽  
pp. 22-26
Author(s):  
S.V. Tsymbal ◽  
Keyword(s):  
Deep Learning ◽  
Learning Experiences ◽  
Digital Competence ◽  
Digital Revolution ◽  
Access Information ◽  
Set Up ◽  
Insight Into ◽  
The Way

The digital revolution has transformed the way people access information, communicate and learn. It is teachers' responsibility to set up environments and opportunities for deep learning experiences that can uncover and boost learners’ capacities. Twentyfirst century competences can be seen as necessary to navigate contemporary and future life, shaped by technology that changes workplaces and lifestyles. This study explores the concept of digital competence and provide insight into the European Framework for the Digital Competence of Educators.

Basic Concepts and Definitions of Allergology

2019 ◽  
Author(s):  
Zoran Vrucinic
Keyword(s):  
Immune Reaction ◽  
The Body ◽  
The Other ◽  
Specific Response ◽  
Other Hand ◽  
Medical Vocabulary ◽  
The Future ◽  
Basic Concepts ◽  
Basic Insight ◽  
Insight Into

The future of medicine belongs to immunology and alergology. I tried to not be too wide in description, but on the other hand to mention the most important concepts of alergology to make access to these diseases more understandable, logical and more useful for our patients, that without complex pathophysiology and mechanism of immune reaction,we gain some basic insight into immunological principles. The name allergy to medicine was introduced by Pirquet in 1906, and is of Greek origin (allos-other + ergon-act; different reaction), essentially representing the reaction of an organism to a substance that has already been in contact with it, and manifested as a specific response thatmanifests as either a heightened reaction, a hypersensitivity, or as a reduced reaction immunity. Synonyms for hypersensitivity are: altered reactivity, reaction, hypersensitivity. The word sensitization comes from the Latin (sensibilitas, atis, f.), which means sensibility,sensitivity, and has retained that meaning in medical vocabulary, while in immunology and allergology this term implies the creation of hypersensitivity to an antigen. Antigen comes from the Greek words, anti-anti + genos-genus, the opposite, anti-substance substance that causes the body to produce antibodies.

Allocentric to Egocentric Spatial Switching: Impairment in aMCI and Alzheimer's Disease Patients?

2018 ◽  
Vol 15 (3) ◽  
pp. 229-236 ◽  
Author(s):  
Gennaro Ruggiero ◽  
Alessandro Iavarone ◽  
Tina Iachini
Keyword(s):  
Alzheimer’S Disease ◽  
Alzheimer's Disease ◽  
Reference Frame ◽  
Reference Frames ◽  
Memory Task ◽  
Spatial Representations ◽  
The Novel ◽  
Spatial Memory Task ◽  
Switching Condition ◽  
Normal Controls

Objective: Deficits in egocentric (subject-to-object) and allocentric (object-to-object) spatial representations, with a mainly allocentric impairment, characterize the first stages of the Alzheimer's disease (AD). Methods: To identify early cognitive signs of AD conversion, some studies focused on amnestic-Mild Cognitive Impairment (aMCI) by reporting alterations in both reference frames, especially the allocentric ones. However, spatial environments in which we move need the cooperation of both reference frames. Such cooperating processes imply that we constantly switch from allocentric to egocentric frames and vice versa. This raises the question of whether alterations of switching abilities might also characterize an early cognitive marker of AD, potentially suitable to detect the conversion from aMCI to dementia. Here, we compared AD and aMCI patients with Normal Controls (NC) on the Ego-Allo- Switching spatial memory task. The task assessed the capacity to use switching (Ego-Allo, Allo-Ego) and non-switching (Ego-Ego, Allo-Allo) verbal judgments about relative distances between memorized stimuli. Results: The novel finding of this study is the neat impairment shown by aMCI and AD in switching from allocentric to egocentric reference frames. Interestingly, in aMCI when the first reference frame was egocentric, the allocentric deficit appeared attenuated. Conclusion: This led us to conclude that allocentric deficits are not always clinically detectable in aMCI since the impairments could be masked when the first reference frame was body-centred. Alongside, AD and aMCI also revealed allocentric deficits in the non-switching condition. These findings suggest that switching alterations would emerge from impairments in hippocampal and posteromedial areas and from concurrent dysregulations in the locus coeruleus-noradrenaline system or pre-frontal cortex.

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