Browsing by Subject "Wind"
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Item Climate of Minnesota Part XIV - Wind Climatology and Wind Power(Minnesota Agricultural Experiment Station, 1983) Baker, Donald G.Item Production and Wind Dispersal of Canada Thistle (Cirsium arvense L.) Achenes(Minnesota Department of Transportation, 2008-09) Becker, R.L.; Haar, M.J.; Kinkaid, B.D.; Klossner, L.D.; Forcella, F.Quantity, quality and dispersal distance of wind-blown achenes and pappi were determined during the peak time of dispersal over twelve site-years in Minnesota during 2006 and 2007. Approximately twice as many pappi than achenes were trapped. Wind blown pappi tend to travel near the ground. Most achenes fell near the parent plants and their population density declined exponentially with increasing distance. Over 80% of pappi collected did not have an achene attached. Concomitantly, seed production in Canada thistle was monitored for 8 site-years in Minnesota. Averaged across years and locations, female Canada thistle shoots that flowered produced an average of 38% empty, 17% shrunken, and 44% normal achenes. Male shoots produce about half the number of seedheads compared to female shoots. A low level of hermaphroditic expression was observed in male shoots. Though seed production by female Canada thistle is extremely variable, when sufficient pollen is available, Canada thistle clearly has the potential to generate significant contributions to seedbanks to maintain invasive stands. However, dispersal by wind is for the most part, local. Long distance dispersal of significant numbers of healthy achenes would be a rare event.Item Understanding and Mitigating the Dynamic Behavior of RICWS and DMS Under Wind Loading(Minnesota Department of Transportation, 2020-06) Linderman, Lauren; Guala, Michele; French, Catherine; Schillinger, Dominik; Finley, Nicole; Heisel, Michael; Nguyen, Lam; Stoter, Stein; Vievering, Josh; Zhu, QimingDynamic Messaging Signs (DMS) and Rural Intersection Conflict Warning Signs (RICWS) are roadside signs that feature much larger and heavier signs than are typically placed on their respective support systems. The excess weight and size of these signs, in conjunction with their breakaway support systems, introduces vibration problems not seen in the past. The AASHTO 2015 LRFD Specification for Structural Supports for Highway Signs, Luminaires, and Traffic Signals (SLTS) does not yet address vibration design for these nontraditional roadside signs. DMS and RICWS were instrumented in the field and numerically modeled to explore their wind-induced behavior. A dynamic numerical model was validated with experimental field data and used to evaluate the fatigue life of the DMS support system instrumented in the field. The resulting fatigue life differed significantly from the equivalent static pressure analysis prescribed in the AASHTO specification. The fatigue life of the DMS instrumented in the field was conservatively estimated to be 23.8 years. Based on data collected from a RICWS instrumented in the field and experiments done on a scaled model of the RICWS at the St. Anthony Falls Laboratory, vortex shedding was identified as the predominant wind phenomena acting on the RICWS structure. Three modifications were proposed to reduce the impacts of vortex shedding. The investigation of these newer sign types highlights the importance of considering the impact of dynamic behavior and vortex shedding on the structural design.Item Wind-driven external aerodynamics around buildings and buoyancy-driven fluid motion and heat transfer in internal flow passages(2017-08) Bettenhausen, DanielTwo areas of focus are considered with respect to the resilience of buildings to withstand environmental forces and to the enhancement of building energy efficiency. First, wind-driven pressure and velocity fields surrounding a model building are calculated by means of computational fluid dynamics (CFD) in two- and three- dimensions using the Shear Stress Transport (SST) turbulence model. The sensitivity of pressure coefficient distributions over each building surface to the placement of the solution domain and to the applied boundary conditions is determined. Pressure coefficient magnitudes were found to be particularly sensitive to the distance separating the upstream boundary of the solution domain, where the atmospheric boundary layer velocity profile is specified, from the location of the building. The magnitude of pressure coefficients at each building surface tended to decrease with increasing upstream distance of the applied velocity profile. At the building roof, the three-dimensional representation of the building resolved off-roof-centerline periodic transient pressure coefficient variations whereas the two-dimensional model predicted steady-state pressure coefficients over the entire rooftop. Building energy efficiency was studied via CFD to determine buoyancy-based heat transfer and velocity distributions in an asymmetrically heated vertical-wall channel representing a double-walled building with and without obstructions placed within the vertical channel. Specifically, catwalks consisting of an array of rectangular slats were deployed at two floor levels of a three-story building. The numerical model employed is validated by comparison with experimental data from a literature source. Channel Nusselt numbers and Reynolds numbers were found to increase with the openness of the catwalk elements to flow passage and also with the channel Rayleigh number. A porous-medium model employing the Darcy-Forchheimer equation is considered as a means to represent the pressure drop of each catwalk grating. This approach yielded results of only moderate accuracy for the velocity field because the porous-medium model does not faithfully reproduce turbulence. On the other hand, an approximation-free model was successfully employed to yield highly accurate fluid flow and heat transfer results for the channel flow.