Hare Research Articles

Laser Doppler velocimetry and particle image velocimetry measurements in a wind tunnel model of the jack rabbit II special sonic anemometer study

A 1:50 scale model of the Jack Rabbit II (JR-II) Mock Urban Environment (MUE) was constructed in the wind tunnel of the University of Arkansas. Laser Doppler Velocimetry (LDV) measurements show agreement between the approach wind characteristics in the tunnel model and field test. LDV velocity measurements within the MUE wind tunnel model also agree with the anemometry results obtained in JRII Special Sonic Anemometer Study (JRII-S) conducted in 2016.After demonstrating that the wind tunnel models the JRII-S field test with LDV measurements, Particle Image Velocimetry (PIV) experiments were conducted to provide velocity measurements that could not be obtained in the field tests. Velocity measurements in a horizontal plane parallel to the ground were made to compare to computational fluid dynamics (CFD) simulations of the JRII-S field tests found in the literature. PIV measurements taken in the wind tunnel model pointed out concerns with those simulations.

The Integral Dense-gas Dispersion Model (IDDM) and comparison with Jack Rabbit II data

The Integral Dense-gas Dispersion Model (IDDM) is presented and used to predict the maximum concentrations and spread of a dense-gas cloud from a short-term release. IDDM is based on integrated conservation equations and includes spreading due to source momentum and density effects, cloud-top air entrainment, height changes with time, and wind transport. The equations are solved numerically but some useful analytical results are found showing the dependence of cloud radius and height on source conditions, entrainment, and time. IDDM comparisons with the Jack Rabbit (JR) II experiments are made for two smooth-terrain Trials (6, 7) and one with a Mock Urban Array (MUA) of Conex containers (Trial 1). For the smooth-terrain cases, predicted concentrations (C) follow the observed JR II data trends with distance x, and for x>1 km are consistent with a -5/3 empirical correlation. In the near field, analytical results for C show excellent agreement with the IDDM numerical solution. For Trial 1, an internal boundary layer (IBL) model is added to obtain the modified winds, friction velocity, and IBL depth due to the MUA. With the IBL and a mean depth (10 m) included, IDDM concentrations agree with the data. Over all Trials (1,6,7), IDDM exhibits good statistical performance with 83% of the predictions within a factor of 2 of the observations. An elliptical horizontal cloud geometry is added to estimate the lateral cloud width given an anisotropy ratio (ani) of along-wind (x) to lateral (y) cloud width. With constant ani (=3), the agreement between predicted and observed width is good with a geometric mean (GM) of predicted-to-observed width of 1.02 and a geometric standard deviation (GSD) of 1.35. However, with a trial-specific ani (=0.5−3) and longitudinal wind shear included, the mean model agreement (GM) is about the same, but the model-data scatter is reduced to a GSD of ≃1.1.

The Mining Legacy of William S. Godbe

The Mining Legacy of William S. Godbe

Overview of the Jack Rabbit II (JR II) field experiments and summary of the methods used in the dispersion model comparisons

This paper serves as an introduction to the special Atmospheric Environment issue on comparisons of 17 widely-used dense-gas dispersion models using observations from the Jack Rabbit II (JR II) chlorine release experiments, which were led by the U.S. Department of Homeland Security Science & Technology (DHS S&T) Chemical Security Analysis Center (CSAC) and a collaborative team of interagency partners, and conducted at the U.S. Army Dugway Proving Ground in 2015 and 2016. Nine of the 17 models that were compared were from outside the U.S. Other papers in the Special Issue describe specific aspects (e.g., observations of emissions, meteorology, and concentrations) of the JR II field experiments, results of individual dispersion model simulations for the models and comparisons of model predictions with JR II observations and other models. This paper provides a general overview of the field experiments and a brief summary of the model comparison goals and methods.

Gaps in toxic industrial chemical model systems: Improvements and changes over past 10 years

AbstractTo assess the hazards of the releases of toxic industrial chemicals (TICs) to the atmosphere, comprehensive model systems are often used, which begin with the scenario definition and end with an estimate of health risk. In 2008 and 2010, the US Department of Homeland Security and Defense Threat Reduction Agency sponsored reports that identified knowledge gaps in TIC modeling. The current paper discusses which of the knowledge gaps were satisfactorily resolved in the past 10 years by new theoretical and experimental research, such as the 2010 and 2015–2016 Jack Rabbit field experiments. For example, the linked source emissions and transport and dispersion (T&D) models have been shown, in comparisons with Jack Rabbit II observations, to not have large mean biases. Consequently, the T&D models are less likely to be the cause of model system overpredictions of casualties observed after large TIC accidental releases, such as the Festus, Macdona, and Graniteville chlorine railcar incidents. It may be that the deposition models and/or the health effects models still need improvement. In addition to comments on the knowledge gaps identified 10 years ago, a few new knowledge gaps are addressed, such as indoor T&D and deposition, and estimating the magnitude of the saturation deposition value for various substrates and chemicals.

Dense gas plume rise and touchdown for Jack Rabbit II trial 8 chlorine field experiment

The series of nine Jack Rabbit II (JR II) chlorine release field experiments in 2015 and 2016 involved releases of pressurized liquefied chlorine from tanks containing 5–20 tons of liquid. This paper concerns JR II Trial 8, where the release hole (15.2 cm diameter) was oriented upwards at the top of the tank. To our knowledge, this is the only full-scale vertically-directed release of pressurized liquefied chlorine that is available for detailed analysis. Our aim is to improve understanding of the characteristics of the dense jet trajectory (e.g., maximum plume rise, downwind distance where the dense plume first touches the ground, and maximum concentration at touchdown). The chlorine emission rate was measured by instruments in the tank, and the plume rise geometry was estimated from photographs, videos, and lidar scans taken from several angles. During the first 10 s of the release, the videos show that the dense jet rises up to about 40 m, then sinks towards the ground, touching down at a distance of about 60 m. The portion of the plume that sinks to the ground then spreads out about 30–40 m in all directions due to gravity slumping. Due to the decrease with time of the momentum jet mass release rate, the jet gradually becomes less dense and less powerful and the plume remains aloft after about 30–60 s. However, the dense cloud that touched down in the early phases moves downwind as a typical dense cloud. The observed dense jet plume rise and touchdown distance are shown to approximately agree within about a factor of two with integral model predictions by 1) the analytical dense gas plume formulas suggested for vertical jets in 1973 by Hoot, Meroney, and Peterka (HMP), 2) the analytical formula for buoyant (positive or negative) plume trajectory suggested by Briggs in 1969, and 3) the DRIFT dispersion software, which is an integral model. Also, HMP and DRIFT model predictions of concentration at touchdown agree with Trial 8 observations within a factor of about two. It is concluded that the dense jet plume models are able to simulate the Trial 8 plume trajectory and ground level maximum concentration within acceptable ranges (i.e., most of time, within a factor of two).

Brian Hare and Vanessa Woods, Review of Survival of the Friendliest

Brian Hare and Vanessa Woods, Review of Survival of the Friendliest

Something’s Wrong!: A Bear, a Hare, and Some Underwear by Jory John

Something’s Wrong!: A Bear, a Hare, and Some Underwear by Jory John

Helmintos gastrointestinales en liebres (Lepus granatensis) del sureste de la Península Ibérica

La liebre ibérica (Lepus granatensis) es un mamífero ubicuo en la península ibérica con importantes implicaciones ecológicas y económicas. Para conocer el estatus sanitario de esta especie, se han estudiado la cavidad abdominal y órganos del aparato digestivo de 85 liebres ibéricas procedentes del Altiplano de la Región de Murcia (sureste de España). La prevalencia total de helmintos hallada fue del 87,7%, siendo la prevalencia de nematodos del 82,2%, la de metacestodos del 44,7% y, en el caso de las formas adultas de cestodos, del 5,9%. Las especies de nematodos encontradas fueron Nematodiroides zembrae (78.8%), Passalurus ambiguus (9,4%) y Trichostrongylus retortaeformis (2,4%), en tanto que las especies de cestodos detectadas fueron Cittotaenia denticulata (5,9%) y Cysticercus pisiformis (44,7%). Los resultados obtenidos demuestran la existencia de una relación positiva entre la intensidad de parasitación de N. zembrae y la presencia de C. pisiformis. The abdominal cavity and digestive organs of 85 Iberian hares (Lepus granatensis) from the Altiplano of the Region of Murcia (southeastern Spain) were studied. The overall prevalence of helminths was 87.7%, including nematodes (82.2% of prevalence), metacestodes (44.7%) and adult cestodes (5.9%). Three nematode species were found: Nematodiroides zembrae (78.8%), Passalurus ambiguus (9.4%) and Trichostrongylus retortaeformis (2.4%), while two cestode species were detected: Cittotaenia denticulata (5.9%) and Cysticercus pisiformis (44.7%). Our results show a positive relationship between N. zembrae intensity and the presence of C. pisiformis.

Development of a quality-controlled chlorine gas concentration data base for the Jack Rabbit II field experiments

The Jack Rabbit II (JR II) field experiments involved a series of trials in 2015 and 2016, each with 5–20 tons of pressurized liquefied chlorine released. All five trials in 2015 had vertically downward releases. The four trials in 2016 involved different release orientations. Roughly 200 chlorine sensors of four types (Jaz, Canary, MiniRAE, and ToxiRAE) were on the test grid at fixed locations during each trial, placed along 90 deg concentric arcs from 0.2 to 11 km from the source. These sensors use different technologies and have different detection ranges. All sensors were carefully calibrated, but pre- and post-trial challenge test results show that the MiniRAE sensors tended to drift. We applied special corrections to the MiniRAE data to correct for the drift. The roughly 19 million concentration records were further quality-assured and condensed to summary tables that include the maximum concentrations. This condensed data set was used in the model evaluation study described in the current special issue. Preliminary analyses suggest that, despite the necessary corrections to the MiniRAE data and the saturation of some sensors, the JR II concentration data in general are of good quality. For example, collocated sensors show good agreement, the arc-maximum normalized concentrations with downwind distance follow the −5/3 power law, and the limited sensor vertical profile data show that cloud heights increase with downwind distance. Future field campaigns of similar scale should carefully examine experimental setup and the latest detection technologies to avoid instrument saturation.

A dense gas dispersion model based on revised meteorological parameters and its performance evaluation

Heavy gas dispersion is significantly impacted by meteorological conditions. In this study, the widely-used heavy gas dispersion model SLAB is revised by using alternative parametrizations for the meteorological parameters, mixing layer height, and wind speed profile. The Nozaki method and the stability modified logarithmic wind profile evolved from the Monin-Obukhov similarity theory are adopted to calculate the mixing layer height and wind speed profile in the improved SLAB-M model, respectively. Dense gas dispersion model evaluation protocols are used to evaluate SLAB-M, and the datasets from the Jack Rabbit II (JR II) 2015 Trials are used to compare the accuracy of the simulations to observed data. The statistical performance measures (SPMs) of SLAB-M are overall a little better than that of SLAB, and SLAB-M effectively simulates heavy gas dispersion under the different meteorological conditions of the JR II 2015 Trials. Thus, it can better satisfy the requirements of consequence assessment and emergency response for the leakage and dispersion of hazardous gasses.

Simplified source description for atmospheric dispersion model comparison of the Jack Rabbit II chlorine field experiments

This paper provides a summary of the methods used to quantify the mass release rate and thermodynamic state of the chlorine released during the Jack Rabbit II chlorine field experiments. In the two-year campaign, eight successful field trials were conducted in which chlorine was released in quantities of 5–10 tons (4540–9070 kg) through a 6-inch (0.152 m) circular breach in the test vessel (disseminator) along with an additional 20 ton (18100 kg) release (Trial 9). Previous analysis of load cell data has been conducted to quantify the mass release rate from primary containment as well as video evidence from Trial 6 which was used to quantify the rainout (and subsequent re-evaporation) during that trial. A method was developed to extend this analysis approach to other trials (except Trial 8 which was vertically upward and Trial 9 which was not instrumented with load cells). The objective of this work was to provide a simplified description of the source suitable for comparison of calculations made using different atmospheric transport and dispersion (ATD) models in Trials 1–7. This work also provides an estimate of the momentum flux (and mean velocity) of the release for use by ATD models which would use such information as input. The recommended release rate parameters are presented along with a summary of the relevant assumptions used in the analysis.

Results of comparisons of the predictions of 17 dense gas dispersion models with observations from the Jack Rabbit II chlorine field experiment

The Jack Rabbit II (JR II) chlorine field trials in 2015 and 2016 involved nine 5–20 ton releases of pressurized liquefied chlorine from a tank mounted 1 m above a broad flat desert sand surface. A model comparison study was initiated, where 17 widely-used dense-gas dispersion models were run by scientists in seven countries. Predictions were submitted following specified formats, using specified emissions and meteorology inputs. To compare with the model predictions, sets of observations were defined for the arc-maximum 1–3 s averaged concentrations (arc max C) and for cloud widths and heights (to 20 ppm and 200 ppm contours) at distances from 0.2 to 11.0 km from the release. The initial focus is on the three field trials (1, 6, and 7) that have the highest observed concentrations and that have detailed emissions information. It is found that these models are able to satisfactorily simulate (generally within a factor of two) the observed arc max C's and their variation with downwind distance at this flat desert site. At each downwind distance, the scatter in the arc max C predictions covers about 1 ½ orders of magnitude, but the observed arc max C is within the range of the predictions. The median of the cloud width predictions is about 50% larger than the observed value for the three trials. The median of the cloud height predictions is within about 10% of the observed value. For both cloud width and/or height, there are a few models with large (factor of 3 or higher) overpredictions. Of the 17 models, when compared to observations, there is a core group of 5 or 6 with consistently (across all three trials and all distances) less mean error and scatter in their predictions of arc max C and cloud width and height. However, as a group, the 17 models are performing adequately (using the “factor of two” rule of thumb). An important caveat is that, at the JR II desert site, chlorine deposition is minimal. At a site with vegetation and/or organic-rich soil, the effects of removal of chlorine by deposition are expected to be significant.

JRII special sonic anemometer study: A first comparison of building wakes measurements with different levels of numerical modelling approaches

After the summer 2015 chlorine releases during the Jack Rabbit II field experiment at Dugway Proving Ground, a special sonic anemometer study was carried out in October 2015 and March 2016. The goal was to provide documented wind fields in similar conditions to the actual releases and to study building wakes without risk for the instruments. This study included 30 sonic anemometers that were placed around these “buildings” to best capture the recirculating regions. Building wakes are important for the dispersion of pollutants in cities and around industrial plants and therefore we have selected two time periods during March 2016, in order to present model to model and model to data comparisons. There are four models involved in the comparison ranging from a diagnostic wind model with wake parameterization and Lagrangian particle dispersion and a CFD model with a k-ε turbulence closure and solving the Eulerian dispersion equation. Detailed comparisons are carried out for the wind speed and for the turbulence level. Six virtual releases are added in the simulations to investigate how the wake resolving method can affect the dispersion. For the wind speed comparison, the models give fair to good comparison with the sonic measurements. However, for the turbulence comparison the results clearly show a need for improvement, even for the k-ε closure, which still provides the best results. For the concentrations, for which there is no corresponding measurements, we find that the simulations are much closer than for the turbulence comparison.

Urban wind field analysis from the Jack Rabbit II Special Sonic Anemometer Study

The Jack Rabbit II Special Sonic Anemometer Study (JRII-S), a field project designed to examine the flow and turbulence within a systematically arranged mock-urban environment constructed from CONEX shipping containers, is described in detail. The study involved the deployment of 35 sonic anemometers at multiple heights and locations, including a 32 m tall, unobstructed tower located about 115 m outside the building array to document the approach wind flow characteristics. The purpose of this work was to describe the experimental design, analyze the sonic data, and report observed wind flow patterns within the urban canopy in comparison to the approaching boundary layer flow. We show that the flow within the building array follows a tendency towards one of three generalized flow regimes displaying channeling over a wide range of wind speeds, directions, and stabilities. Two or more sonic anemometers positioned only a few meters apart can have vastly different flow patterns that are dictated by the building structures. Within the building array, turbulence values represented by normalized vertical velocity variance (σw2) are at least two to three times greater than that in the approach flow. There is also little evidence that σw2 measured at various heights or locations within the JRII array is a strong function of stability type in contrast to the approach flow. The results reinforce how urban areas create complicated wind patterns, channeling effects, and localized turbulence that can impact the dispersion of an effluent release. These findings can be used to inform the development of improved wind flow algorithms to better characterize pollutant dispersion in fast-response models.

Simulation of a dense gas chlorine release with a Lagrangian particle dispersion model (LPDM)

In 2015, 2016, nine chlorine releases experiments took place at Dugway Proving Ground (Utah, USA). Five trials conducted in 2015 featured a grid of CONEX shipping containers around the release tank to simulate an idealized urban area. The trials were a great occasion to collect data describing the dynamics of “high molecular weight” species in an idealized urban environment.This paper proposes a comparison of the PMSS (Parallel Micro-Swift Micro-Spray) suite against the experimental data from four of the trials, following the choice made by an international model inter-comparison team. PMSS combines two MPI parallelized urban modelling subsystems: (1) PSWIFT phenomenologically accounts for 3D wind flow and turbulence around buildings, and (2) PSPRAY simulates air-based contaminant dispersion in urban areas using a stochastic Lagrangian Particle Dispersion Model.For this comparison, PMSS is deployed first on a hypothetic configuration and compared to the Code_Saturne CFD model, and then using the data of the trials 1, 5, 6 and 7 performed during JRII (Jack Rabbit II) 2015 and 2016. The initial momentum due to the tank discharge and the dense gas and droplet effects of the pressurized chlorine release are modelled using a dedicated radial source term jet and the Glendening equations. In trials 1 and 5, the influence of the CONEX shipping containers on the wind flow and the dispersion is explicitly considered. While spread through a large interval, the chlorine concentrations are computed both in the near field and in the far field (up to 11 km) using PMSS nesting capabilities. The results of the model are compared with the experimental data and sensitivity tests are also presented.

HPAC model studies of selected Jack Rabbit II (JRII) releases and comparisons to test data

Chlorine transport and dispersion (T&D) modeling using the Hazard Prediction and Assessment Capability (HPAC) software suite was performed by the Defense Threat Reduction Agency (DTRA) Technical Reachback Division to generate concentration plumes as a function of time using the Jack Rabbit II (JRII) test series releases for Trials 1, 6, and 7. The results of the concentration time-histories and spatial location with respect to the JRII sensor arcs and pre-defined common modeling parameters are presented here in order to facilitate a model inter-comparison with other T&D modeling groups. Also, results of sensitivity studies and quantification of performance using different weather sets are presented here with the goal of identifying significant stressors in the context of an operationally relevant (real-world) framework.

DRIFT dispersion model predictions for the Jack Rabbit II model inter-comparison exercise

In 2015 and 2016, the US Army conducted nine large-scale chlorine releases at the Dugway Proving Ground in Utah, known as the Jack Rabbit II trials. The purpose of these experiments was to improve our understanding of pressure-liquefied chlorine releases and atmospheric dispersion, and to provide useful practical knowledge for emergency responders. Data from three of the Jack Rabbit II trials (Trials 1, 6 and 7) were subsequently selected for an international model inter-comparison exercise, which included modelling contributions from the US, UK, Canada, France, Germany, Sweden, Finland and the European Commission. This paper provides details of one of the UK contributions to that exercise, using the DRIFT integral dispersion model. Participants in the exercise were given a set of prescribed model input conditions. The methodology used in DRIFT to model these conditions is described here, which consisted of three runs: a baseline case and two sensitivity tests that examined the effect of variations in the modelled wind-speed profile and the dry deposition rate. A brief review is also provided of the experimental data used for the model inter-comparison exercise. Gas concentrations were measured in the Jack Rabbit II trials using an extensive array of gas sensors arranged on arcs downwind from the release point. Four types of sensors were used, which each had calibration and/or saturation limits. In some of the trials, sensors that recorded the highest concentrations on an arc were saturated with gas and under-recorded the actual concentrations. In other cases, especially near the source, there were only a few sensors on an arc and therefore it is uncertain whether the plume maximum concentrations were recorded. Results from DRIFT are compared to the Jack Rabbit II data in two ways. Firstly, against the full dataset of maximum arc-wise concentrations, and secondly against the subset of measurements that were unaffected by saturation issues or there being a sparse sensor array. In the first case, DRIFT gives higher concentrations than were measured on average, noting that some measurements probably under-recorded the concentration owing to the previously mentioned sensor saturation issues. In the second case, using the more reliable dataset, the statistical performance of DRIFT falls within commonly-used dense-gas model acceptance criteria. Sensitivity tests on the wind speed profile and dry deposition rate had an effect on the DRIFT predictions in Trial 1, but little impact in Trials 6 and 7. This behaviour is likely to be due to the changing meteorology during Trial 1, and the lower wind speed and smaller chlorine mass released in that trial. Remaining knowledge gaps and possible future directions for research are discussed. These include further work on dry deposition, modelling of the other Jack Rabbit II trials (potentially using source models as well as prescribed common source conditions), and comparisons of predicted and measured toxic load, calculated from the time-varying concentrations.

Global sensitivity analysis of the ADAM dispersion module: Jack Rabbit II test case

Abstract This paper provides the result of a parametric sensitivity study conducted on the atmospheric dispersion module of the Accident Damage Analysis Module for consequence assessment, developed by the European Commission to support the EU competent authorities for the implementation of the Seveso Directive in their countries or other legislation associated with chemical safety and security. A variance-based Global Sensitivity Analysis was conducted on a series of reference scenarios build by using the trials of the Jack Rabbit II coordinated model inter-comparison exercise, in order to establish the impact of input parameters on the model output uncertainty.

Cloud dimensions from Jack Rabbit II field trial data

Abstract Jack Rabbit II field trials recorded a large amount of point sensor data regarding meteorology and chlorine concentrations and included many video and specialized standoff measurements. Cloud dimensions must be inferred or analyzed from such data. The test data were used to identify cloud dimensions (widths and heights to the 20 and 200 ppm contours) for use in the model inter-comparison exercise. Cloud widths and heights at fixed measurement distance of 0.2, 0.5, 1 and 2 km were assessed by use of point-sensor data as well as by standoff sensor data. Some point sensor data exists at 5 and 11 km for possible future analysis. Standoff LIDAR measurements can be used for cloud heights at the 0.5, 1 and 2 km. This paper presents the analysis methods applied to concentration point sensors and concentration estimates from standoff UV LIDARs. The resulting cloud height and width observations are presented for Trials 1, 6 and 7 and initial comparisons are provided between point and standoff sensors as well as with limited model results.