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We present two spanwise-localized travelling-wave solutions in the asymptotic suction boundary layer, obtained by continuation of solutions of plane Couette flow. One of the solutions has the vortical structures located close to the wall, similar to spanwise-localized edge states previously found for this system. The vortical structures of the second solution are located in the free stream far above the laminar boundary layer and are supported by a secondary shear gradient that is created by a large-scale low-speed streak. The dynamically relevant eigenmodes of this solution are concentrated in the free stream, and the departure into turbulence from this solution evolves in the free stream towards the walls. For invariant solutions in free-stream turbulence, this solution thus shows that the source of energy of the vortical structures can be a dynamical structure of the solution itself, instead of the laminar boundary layer.
This paper reports on a theoretical analysis of the rich variety of spatio-temporal patterns observed recently in inclined layer convection at medium Prandtl number when varying the inclination angle
and the Rayleigh number
. The present numerical investigation of the inclined layer convection system is based on the standard Oberbeck–Boussinesq equations. The patterns are shown to originate from a complicated competition of buoyancy driven and shear-flow driven pattern forming mechanisms. The former are expressed as longitudinal convection rolls with their axes oriented parallel to the incline, the latter as perpendicular transverse rolls. Along with conventional methods to study roll patterns and their stability, we employ direct numerical simulations in large spatial domains, comparable with the experimental ones. As a result, we determine the phase diagram of the characteristic complex 3-D convection patterns above onset of convection in the
plane, and find that it compares very well with the experiments. In particular we demonstrate that interactions of specific Fourier modes, characterized by a resonant interaction of their wavevectors in the layer plane, are key to understanding the pattern morphologies.
Recent experimental studies have shown rich transition behaviour in rotating plane Couette flow (RPCF). In this paper we study the transition in supercritical RPCF theoretically by determination of equilibrium and periodic orbit tertiary states via Floquet analysis on secondary Taylor vortex solutions. Two new tertiary states are discovered which we name oscillatory wavy vortex flow (oWVF) and skewed vortex flow (SVF). We present the bifurcation routes and stability properties of these new tertiary states and, in addition, we describe a bifurcation procedure whereby a set of defected wavy twist vortices is approached. Further to this, transition scenarios at flow parameters relevant to experimental works are investigated by computation of the set of stable attractors which exist on a large domain. The physically observed flow states are shown to share features with states in our set of attractors.
In linearly stable shear flows at moderate Reynolds number, turbulence spontaneously decays despite the existence of a codimension-one manifold, termed the edge, which separates decaying perturbations from those triggering turbulence. We statistically analyse the decay in plane Couette flow, quantify the breaking of self-sustaining feedback loops and demonstrate the existence of a whole continuum of possible decay paths. Drawing parallels with low-dimensional models and monitoring the location of the edge relative to decaying trajectories, we provide evidence that the edge of chaos does not separate state space globally. It is instead wrapped around the turbulence generating structures and not an independent dynamical structure but part of the chaotic saddle. Thereby, decaying trajectories need not cross the edge, but circumnavigate it while unwrapping from the turbulent saddle.
We demonstrate the existence of an exact invariant solution to the Navier–Stokes equations for the asymptotic suction boundary layer. The identified periodic orbit with a very long period of several thousand advective time units is found as a local dynamical attractor embedded in the stability boundary between laminar and turbulent dynamics. Its dynamics captures both the interplay of downstream-oriented vortex pairs and streaks observed in numerous shear flows as well as the energetic bursting that is characteristic for boundary layers. By embedding the flow into a family of flows that interpolates between plane Couette flow and the boundary layer, we demonstrate that the periodic orbit emerges in a saddle–node infinite-period (SNIPER) bifurcation of two symmetry-related travelling-wave solutions of plane Couette flow. Physically, the long period is due to a slow streak instability, which leads to a violent breakup of a streak associated with the bursting and the reformation of the streak at a different spanwise location. We show that the orbit is structurally stable when varying both the Reynolds number and the domain size.
We study the turbulence transition of plane Couette flow in large domains where localized perturbations are observed to generate growing turbulent spots. Extending previous studies on the boundary between laminar and turbulent dynamics we determine invariant structures intermediate between laminar and turbulent flow. In wide but short domains we find states that are localized in spanwise direction, and in wide and long domains the states are also localized in downstream direction. These localized states act as critical nuclei for the transition to turbulence in spatially extended domains.
The creation of a medical incident response plan for the treatment of injured victims contaminated during a chemical incident challenges more man one of me rescue services involved in civil emergency response. Our main objective the was to create an incident management plan compatible with existing rescue service logistics and resources.
Under the supervision of the Schutzkommission des Inneren and with delegates from emergency medical services, fire, technical rescue services, and the German Army, a consensus conference to investigate the general conditions necessary and the existing structure available for managing victims of chemical incidents, was created. Typical injury patterns and their treatment in respect to decontamination procedures were considered, the necessary structure for casualty treatment and decontamination areas were derived, and commercially available products were tested for their usefulness in this situation. Standard operating procedures and algorithms were developed to aid realization of the concept. The suitability of the personal protective equipment and the question, if under these conditions the procedures of advanced life support can be performed, was evaluated in a standardized simulator model. The necessary training for rescue personnel involved was defined. To validate the concept, an exercise was performed.
All persons present at a chemical incident are to be classified as being contaminated. Injured persons must be separated into triage categories, and life threatening conditions treated before being decontaminated. Decontamination at the incident scene is necessary to prevent the transportation of the contaminant away from the incident scene. The principles of the decontamination of injured persons are based on the following pillars: triage, early removal of clothing, management of personal belongings and valuables, basic life support, spot decontamination, management and sealing of open wounds, application of antidotes, and primary decontamination of ambulant and non-ambulant victims.
The cooperation and the definition of roles between fire services (decontamination) and emergency medical services (triage and treatment) are necessary.
The concept uses existing decontamination vehicles used for the decontamination of fire fighters, by expanding its inventory with medical equipment, and extra technical apparatus. Using a modular approach, the system can be easily augmented by further units to treat multiple numbers of victims. However, demands on all rescue services involved are high, and must be complemented with an equally high standard of training, especially where rescue services have to learn skills not akin to their standard duties. An implementation of the system covering all geographical areas with specialized units is not possible, therefore a risk analysis to optimally position limited resources has to be conducted. Legislative bodies must strive to allow for an uncomplicated integration and disposition of disaster management resources.
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