Wind and turbulence profiles in a simulated wind tunnel boundary layer

A system of Honeycomb Flat Plate (HFP) grid and cylindrical rods has been developed to accelerate the growth of a thick (32 cm) turbulent boundary layer, artificially, over rough floor of a low speed short test-section (0.61 m x 0.61 m) wind tunnel. Simulated profiles of wind velocity, longitudinal turbulence intensity and Reynolds stress are shown to have similarity to those of a neutral atmospheric boundary layer over a typical rural terrain. Longitudinal spectrum of turbulence measured at 10,30 and 100 mm above tunnel floor is shown to compare well with atmospheric spectrum and agree closely with the Kolmogoroff's -2/3 law in the inertial sub-range of the spectrum. Based on the length scale of longitudinal turbulence estimated from the spectrum, a scale of 1 :900 has been proposed for laboratory modeling of environmental problems wherein the transport of mass in a neutral atmospheric surface layer IS solely due to eddies of mechanical origin.

Wind and route choice affect performance of bees flying above versus within a cluttered obstacle field

Bees flying through natural landscapes encounter physical challenges, such as wind and cluttered vegetation. The influence of these factors on the flight performance of bees remains unknown. We analyzed 548 videos of wild-caught honeybees (Apis mellifera) flying through an enclosure containing a field of vertical obstacles that bees could fly within (through open corridors, without maneuvering) or above. We examined how obstacle field height, wind presence and direction (headwinds or tailwinds) affected altitude, ground speed, and side-to-side casting (lateral excursions) of bees. When obstacle fields were short, bees flew at altitudes near the midpoint between the tunnel floor and ceiling. When obstacle fields approached or exceeded this midpoint, bees typically, but not always, increased their altitudes to fly over the obstacles. Bees that flew above the obstacle fields exhibited 40% faster ground speeds and 36% larger lateral excursions than bees that flew within the obstacle fields, likely due to the visual feedback from obstacles and narrow space available within the obstacle field. Wind had a strong effect on ground speed and lateral excursions, but not altitude. Bees flew 12-19% faster in tailwinds than in the other wind conditions, but their lateral excursions were 19% larger in any wind, regardless of its direction, than in still air. Our results show that bees flying through complex environments display flexible flight behaviors (e.g., flying above versus within obstacles), which affect flight performance. Similar choices in natural landscapes could have broad implications for foraging efficiency, pollination, and mortality in wild bees.

Modelling the deformation and movement of an ice tunnel in Langjökull ice cap, Iceland

<p>In winter 2014-2015 a long tunnel was dug into the ice cap Langjökull at about 1260 m a.s.l., close to the ELA. The tunnel was opened for tourists in spring 2015 (https://intotheglacier.is/) and has since then become a popular tourist attraction.  Before the tunnel was opened in winter 2015 and in the subsequent two years measurements of the tunnel deformation, temperature and density along the tunnel has been measured.  The tunnel is both closing because of ice deformation and it deforms with the glacier flow, which causes the entrance into the ice tunnel to become gradually steeper.  We use a full-Stokes ice flow model to compute the evolution of the tunnel floor and the closure of the tunnel. The deformation measurements are used to constrain the ice viscosity and the floor measurements to validate the modeled glacier flow. The model simulations are then used to predict the movement of the tunnel in the coming few years, which is useful for the planning of the tunnel entrance renovations.</p>

Thorough Verification and Validation of CFD Prediction of FPSO Wind Load for Confident Applications

This paper presents our verification work on CFD modeling practice for the prediction of FPSO wind loads. The modeling practice was developed from the TESK CFD JDP [1]. In the verification, the measured data from a benchmark model test were used to check CFD simulation results. The exact physical model of the model test was used in the numerical modeling (model-of-the-model). To establish high confidence in the CFD modeling and simulations, the modeling practice was thoroughly verified, which covered the following critical elements: mesh resolution, domain size, outlet boundary condition, turbulence model, Reynolds effect, wind profile, prism layer effect on total wind forces, effects of the gap between wind tunnel floor and model bottom, blockage effect due to tunnel side walls and ceiling, and effects of geometry details (small size pipes). The verification results show that CFD can be used as an alternative tool for predicting wind loads and moments on a FPSO for engineering purposes following the modeling practice, and careful QA and QC.

Numerical simulation of the natural, forced and mixed convection in a tunnel with a flat track of sinusoidal shape and a roof opening

In this work, we studied the mixed convection of the airflow in a tunnel open at both ends. The tunnel has a sinusoidal trace and the horizontal ceiling is provided with an opening in the center. The tunnel floor is uniformly heated. Although of interest for many industrial applications, the configuration of this study has been studied very little from an academic point of view. Coupled equations of Naiver-Stokes and energy are solved numerically by the finite volume method with the Boussinesq hypothesis. We analyzed the effect of the parameters that characterize heat transfer, and the flow structure. Several situations have been considered by varying the Richardson number (1.3610-3≤Ri≤2.17.104) for a Prandtl number Pr = 0.71.

Blast mitigation by water in a bag on a tunnel floor

Mitigation of blast wave, caused by explosion of explosives, from a straight tube using water in a bag (water bag) was evaluated. The length of the tube was 330 mm and the cross-section area was 30 x 30 mm2. One end of the tube was closed. The water bag was placed on the floor or closed end wall of the tube near the explosive. The thickness of water was 3 mm. A specially designed small detonator, which contains lead azide of 100 mg, was ignited near the closed end wall of the tube. The blast pressure outside the tube was measured and examined. The blast wave was remarkably mitigated by the water bag. Equivalent ratio analysis revealed that the glass beads absorbed 33%-45% of explosion energy.