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Numerical calculations, scale model experiments and real-life implementations have shown that the insertion of a closely spaced array of low parallel walls of finite dimension beside a road is potentially useful for road traffic noise abatement. However, previous studies did not consider atmospheric effects. In this work, numerical techniques have been used to predict the sound reduction provided by a low parallel wall structure, subject to wind and temperature related atmospheric effects. Three full-wave prediction schemes show very good agreement when looking at the insertion loss of a low 6 m wide parallel wall structure, consisting of 24 regularly spaced 0.2-m high rigid walls. Meteorological effects are predicted not to deteriorate the insertion loss (relative to rigid flat ground) of the parallel wall array in the low frequency range. However, at high sound frequencies the insertion loss is strongly reduced by downward refraction at a distance of 50 m in case of strong wind. Consequently, overall A-weighted road traffic noise insertion loss will be significantly lower during wind episodes. Although weak turbulence does not alter the energy time-averaged insertion losses, strong turbulence reduces the noise shielding in the high frequency range also. As with conventional noise walls, when considering use of low parallel wall structures for noise reduction outdoors, even at short distances, atmospheric effects should be considered.

Numerical calculations, scale model experiments and real-life implementations have shown that the insertion of a closely spaced array of low parallel walls of finite dimension beside a road is potentially useful for road traffic noise abatement. However, previous studies did not consider atmospheric effects. In this work, numerical techniques have been used to predict the sound reduction provided by a low parallel wall structure, subject to wind and temperature related atmospheric effects. Three full-wave prediction schemes show very good agreement when looking at the insertion loss of a low 6 m wide parallel wall structure, consisting of 24 regularly spaced 0.2-m high rigid walls. Meteorological effects are predicted not to deteriorate the insertion loss (relative to rigid flat ground) of the parallel wall array in the low frequency range. However, at high sound frequencies the insertion loss is strongly reduced by downward refraction at a distance of 50 m in case of strong wind. Consequently, overall A-weighted road traffic noise insertion loss will be significantly lower during wind episodes. Although weak turbulence does not alter the energy time-averaged insertion losses, strong turbulence reduces the noise shielding in the high frequency range also. As with conventional noise walls, when considering use of low parallel wall structures for noise reduction outdoors, even at short distances, atmospheric effects should be considered.

The successful intercept of a threat ballistic missile does not completely negate all hazards to friendly personnel or assets. Prediction of the effects resulting from the various debris that result from the intercept is a science that is still growing more than 37 years after the first anti-ballistic missile system was deployed, with many remaining knowledge gaps and many people unaware of the issue of post-intercept collateral effects. The hazards can be particularly significant if the threat missile contains a Weapon of Mass Destruction payload. The article discusses early strategic missile defense, which emphasized engaging Soviet strategic intercontinental ballistic missiles (ICBM) carrying large-yield nuclear warheads. The interceptor missiles themselves carried nuclear warheads to inflict catastrophic damage on the threat nuclear payloads. With the advent of the Strategic Defense Initiative Organization (SDIO) in 1983, the objective became the defense of the entire United States against a massive nuclear strike by the Soviet Union. The means of engaging these thousands of threat missiles also changed from nuclear-tipped interceptors launched near the ground target to a wide variety of interceptors relying on conventional warheads or simple direct impact kinetic energy (hit-to-kill) or on directed energy weapons. After the demise of the Soviet Union, the SDIO became the Ballistic Missile Defense Organization (BMDO), which concerned itself far more with Theater Ballistic Missile Defense than with strategic ICBM defense, and with engaging a few missiles rather than a massive strike with thousands of inbound warheads. The remainder of the article discusses potential collateral effects of six threat warheads (Nuclear, Unitary High Explosive, High Explosive Submunition, Unitary Chemical, Chemical Submunition, and Biological Submunition), and the effects of warhead type, interceptor type, speed, altitude, weather, terrain, etc. on collateral effects., Published in Army Space Journal, v10 n2 p44-45 & 48-49, Spring-Summer Edition 2011 (Profession of Arms in Army Space and Missile Defense).

This paper aims at presenting DNS and LES as applied to the simulation of vortex wakes: in laboratory conditions (moderate to medium Reynolds numbers) and up to real aircraft conditions (high to very high Reynolds numbers). Only incompressible flows are considered. DNS and LES are able to capture complex 3-D physics provided one uses high quality numerical methods: methods with negligible numerical dissipation (i.e., methods that conserve energy in absence of viscosity and/or subgrid modelling) and with low dispersion errors (to properly transport complex vortical structures). Methods that can do that are: spectral methods, high order finite difference methods, and vortex-in-cell (VIC) methods. As the problems of interest are of large spatial extent and contain vortices with small cores, it is also essential that the methods be efficiently parallelized. As to LES of wake vortex flows, this require subgrid scale (SGS) models that are essentially inactive during the gentle, well-resolved, phases of the flow and within the vortex cores, and that become active only during the complex turbulent phases of the flow. The recent multiscale models, that act solely on the high wavenumbers modes of the LES, are seen to be most appropriate. We present some illustrative examples of DNS and LES results that were obtained within our group.

This paper aims at presenting DNS and LES as applied to the simulation of vortex wakes: in laboratory conditions (moderate to medium Reynolds numbers) and up to real aircraft conditions (high to very high Reynolds numbers). Only incompressible flows are considered. DNS and LES are able to capture complex 3-D physics provided one uses high quality numerical methods: methods with negligible numerical dissipation (i.e., methods that conserve energy in absence of viscosity and/or subgrid modelling) and with low dispersion errors (to properly transport complex vortical structures). Methods that can do that are: spectral methods, high order finite difference methods, and vortex-in-cell (VIC) methods. As the problems of interest are of large spatial extent and contain vortices with small cores, it is also essential that the methods be efficiently parallelized. As to LES of wake vortex flows, this require subgrid scale (SGS) models that are essentially inactive during the gentle, well-resolved, phases of the flow and within the vortex cores, and that become active only during the complex turbulent phases of the flow. The recent multiscale models, that act solely on the high wavenumbers modes of the LES, are seen to be most appropriate. We present some illustrative examples of DNS and LES results that were obtained within our group.

The influence of edge vortices generated by a generic double-element wing on force behaviors are discussed. The wing is equipped with end plates and operates in ground effect. The downforce-vs-height curve is divided into three distinct regions according to ground proximity and flap setting. As the wing is moved from a height in freestream to the ground plane, the downforce first experiences a rapid enhancement (region A). This process is accompanied by the presence of a concentrated vortex off the edge of the side plate and diffuser effect of the wing. At a critical height, the vortex breaks down and its contribution to the downforce is lost. This creates a change in the gradient of the downforce slope. The force enhancement process continues as the height of the wing is reduced (region B); the main diffuser effect is still present. The downforce is lost below a height where the maximum downforce is reached, due to large separation on the wing (region C). The importance of the edge vortices in defining the characteristics of the downforce curve is established.

The influence of edge vortices generated by a generic double-element wing on force behaviors are discussed. The wing is equipped with end plates and operates in ground effect. The downforce-vs-height curve is divided into three distinct regions according to ground proximity and flap setting. As the wing is moved from a height in freestream to the ground plane, the downforce first experiences a rapid enhancement (region A). This process is accompanied by the presence of a concentrated vortex off the edge of the side plate and diffuser effect of the wing. At a critical height, the vortex breaks down and its contribution to the downforce is lost. This creates a change in the gradient of the downforce slope. The force enhancement process continues as the height of the wing is reduced (region B); the main diffuser effect is still present. The downforce is lost below a height where the maximum downforce is reached, due to large separation on the wing (region C). The importance of the edge vortices in defining the characteristics of the downforce curve is established.

The influence of edge vortices generated by a generic double-element wing on force behaviors are discussed. The wing is equipped with end plates and operates in ground effect. The downforce-vs-height curve is divided into three distinct regions according to ground proximity and flap setting. As the wing is moved from a height in freestream to the ground plane, the downforce first experiences a rapid enhancement (region A). This process is accompanied by the presence of a concentrated vortex off the edge of the side plate and diffuser effect of the wing. At a critical height, the vortex breaks down and its contribution to the downforce is lost. This creates a change in the gradient of the downforce slope. The force enhancement process continues as the height of the wing is reduced (region B); the main diffuser effect is still present. The downforce is lost below a height where the maximum downforce is reached, due to large separation on the wing (region C). The importance of the edge vortices in defining the characteristics of the downforce curve is established.

VX82 - EM355, Sounds associated with oversnow vehicles, such as snowmobiles and snowcoaches, are an, important management concern at Yellowstone and Grand Teton National Parks. The John A., Volpe National Transportation Systems Center’s Environmental Measurement and Modeling, Division is supporting the National Park Service with its on-going Winter Use Planning, program. As part of this support, acoustic measurements of ten snowcoaches and six, snowmobiles were made at the south entrance to Yellowstone National Park from the 26th, through the 28th of February 2008. Measurement methodologies were guided by SAE J1161, and SAE J192. There were two primary objectives: 1) to determine which snowcoaches had, the Best Available Technology (BAT) with respect to noise emissions, and 2) to determine, if there was a significant difference between snowmobile sound levels when tested using, two revisions of SAE J192. Based on analysis of the data, it appears that among the, snowcoaches, the Yellowstone Expeditions’ modified Dodge B530 snowcoach would be an, excellent candidate for BAT classification. It was also found that measurements guided, by the two revisions of SAE J192 had very similar results.

The starting point in any empirical model such as the Federal Aviation Administration’s (FAA), Integrated Noise Model (INM) is a reference data base. In Version 5.2 and in previous versions, the reference data base consisted solely of a set of noise level data expressed as a function of aircraft power and aircraft-to-receiver distance, i.e., noise-power-distance (NPD) data. To, accurately account for the inclusion of planned future physical propagation effects in INM, e.g., ground effects and terrain shielding, this noise level data in Version 6.0 was supplemented with frequency-based spectral data.