Search results for "Drag"
showing 10 items of 179 documents
The macrophyte, Stratiotes aloides, protects larvae of dragonfly Aeshna viridis against fish predation
2004
Predation could be one force determining which contemporary species occupy a certain habitat. Aeshna viridis is an endangered dragonfly species with a larval distribution strongly associated with lakes where the water plant, water soldier, Stratiotes aloides, occurs. In this study, the larvae were almost exclusively found in patches of S. aloides. To study larval association with S. aloides further, we conducted a series of laboratory experiments. Behavioural experiments indicated that larvae preferred S. aloides. Aeshna viridis larvae were nocturnal and rather inactive. Larvae on S. aloides were less susceptible to predation by the perch, Perca fluviatilis, than larvae on another water pla…
A Seven Mode Truncation of the Kolmogorov Flow with Drag: Analysis and Control
2009
The transition from laminar to chaotic motions in a viscous °uid °ow is in- vestigated by analyzing a seven dimensional dynamical system obtained by a truncation of the Fourier modes for the Kolmogorov °ow with drag friction. An- alytical expressions of the Hopf bifurcation curves are obtained and a sequence of period doubling bifurcations are numerically observed as the Reynolds num- ber is increased for ¯xed values of the drag parameter. An adaptive stabilization of the system trajectories to an equilibrium point or to a periodic orbit is ob- tained through a model reference approach which makes the control global. Finally, the e®ectiveness of this control strategy is numerically illustra…
Influence of temperature and photoperiod on embryonic development in the dragonflySympetrum striolatum(Odonata: Libellulidae)
2015
Temperature and photoperiod play major roles in insect ecology. Many insect species have fixed degree-days for embryogenesis, with minimum and maximum temperature thresholds for egg and larval development and hatching. Often, photoperiodic changes trigger the transfer into the next life-cycle stadium. However, it is not known whether this distinct pattern also exist in a species with a high level of phenotypic plasticity in life-history traits. In the present study, eggs of the dragonfly Sympetrum striolatum Charpentier (Odonata: Libellulidae) are reared under different constant and fluctuating temperatures and photoperiodic conditions in several laboratory and field experiments. In general…
2020
The complex surface geometries of hailstones affect their fall behavior, fall speeds, and growth. Systematic experimental investigations on the influence of the number and length of lobes on the fall velocity and the drag coefficient of hailstones were performed in the Mainz vertical wind tunnel to provide relationships for use in numerical models. For this purpose, 3D prints of four artificial lobed hailstone models as well as spheres were used. The derived drag coefficients show no dependency in the Reynolds number in the range between 25,000 and 85,000. Further, the drag coefficients were found to increase with increasing length of lobes. All lobed hailstones show higher or similar drag …
The Dynamics of Eye Formation and Maintenance in Axisymmetric Diabatic Vortices
2009
Abstract This paper investigates the occurrence, formation, and maintenance of eyes in idealized axisymmetric balanced vortices with diabatic forcing. Two key elements of the model setup are temperature relaxation toward a specified equilibrium temperature Te and Ekman pumping from a turbulent boundary layer. Furthermore, the flow is assumed to be almost inviscid in the interior. The model does not attempt any closure for moist convection. Previous work by the authors has shown that there is a continuous transition from monsoonlike vortices to hurricane-like vortices. This transition is governed by the ratio ℱ = αT /cD, where αT is the thermal relaxation rate and cD the surface drag coeffic…
A Frozen-Flow Approximation to the Evolution of Large-Scale Structures in the Universe
1992
A new approximation to the evolution of large-scale structures in the Universe is proposed which is based on neglecting the role of particle inertia compared to the damping implied by the Hubble drag. We call this approximation frozen flow because particles move by updating at each step their velocity to the local value of the peculiar velocity field, here approximated by its growing linear mode: stream-lines are then frozen to their initial shape. The situation is quite different from that of the Zel'dovich algorithm, where the velocity is kept constant along each particle trajectory
Hydrodynamical forces acting on particles in a two-dimensional flow near a solid wall
2000
The hydrodynamical forces acting on a single particle and on a random rigid array of particles suspended in a two-dimensional shear flow of Newtonian fluid near a rigid wall were studied numerically in the flow regime where the relevant Reynolds numbers are of the order of unity. The simulations were done with conventional finite volume method for single-particle cases and with lattice-Boltzmann method for many-particle cases. A set of comparison cases was solved with both methods in order to check the accuracy of the lattice-Boltzmann method. For the single-particle case analytic formulae for the longitudinal drag force and for the transverse lift force were found. A modification to Darcy'…
Statistical analysis of the influence of forces on particles in EM driven recirculated turbulent flows
2011
The present paper contains an analysis of the statistical distribution of forces affecting non-conducting particles dispersed in an EM induced recirculated flow in induction furnaces. The simulation is conducted adopting the LES-based Euler-Lagrange approach in the limit of dilute conditions (one-way coupling). It is done by means of a development of OpenFOAM software code. The used Lagrange equation for particle tracking includes drag, EM, buoyancy, lift, acceleration and added mass forces. The relevant approximations for the forces are chosen on the basis of the statistical analysis of the non-dimensional parameters (particle Reynolds number, shear stress and acceleration parameter). The …
Experimental and numerical investigations of a two-body floating-point absorber wave energy converter in regular waves
2019
Abstract This paper presents experimental and numerical studies on the hydrodynamics of a two-body floating-point absorber (FPA) wave energy converter (WEC) under both extreme and operational wave conditions. In this study, the responses of the WEC in heave, surge, and pitch were evaluated for various regular wave conditions. For extreme condition analysis, we assume the FPA system has a survival mode that locks the power-take-off (PTO) mechanism in extreme waves, and the WEC moves as a single body in this scenario. A series of Reynolds-averaged Navier–Stokes (RANS) simulations was performed for the survival condition analysis, and the results were validated with the measurements from exper…
Focusing ions by viscous drag and weak electric fields in an ion guide
1991
Abstract A new special ion guide has one or more grids at low electric potential in the space between nozzle and skimmer. Viscous drag caused by helium flow is used together with weak electric fields for focusing ions through the skimmer. A typical yield through the skimmer is 75% of that through the nozzle. The focusing device is called a “squeezer”. Most properties of the “squeezer ion guide” are similar to those of an ordinary ion guide. Because the kinetic energies are only of the order of 10 eV, however, problems caused by ion scattering are greatly reduced as compared to ordinary ion guides.