Effect of full helmet systems on human head responses under blast loading

This paper focuses on helmet design for head protection under blast threats. It is presented a numerical investigation of the head response accruing to blast loads on helmet protective systems. Various combinations of the helmet, visor and mandible guard were numerically analyzed for a given mass of TNT at a distance to the target representing an anti-vehicle buried mine threat. Limited published articles on the subject are available in the scientific literature. In this paper, a 3D head helmet numerical model for blast analyses is developed in the finite element code ABAQUS/Explicit. The results showed that individual protective systems are not effective enough to mitigate the damage caused by blast loading. The complete protective equipment reduces the pressures on the brain by up to 5 times and ensures that no fracture in the skull appears. This numerical study aims to provide helmet manufacturers and users with some insight in what possible brain injuries are to be expected in various blast scenarios so as to help in better diagnosis of unsuspected brain injury.The Ministry of Economy and Competitiveness of Spain and FEDER program under the Project RTC-2015-3887-8 for the financial support of the work

Experimental and numerical studies of acoustical and ventilation performances of glass louver window

The noise attenuation and ventilation performances of the glass louver window were investigated using experimental and numerical methods in order to improve the understanding of this common feature in noise mitigation issue. Sound pressure levels (SPLs) data were measured for frequencies ranging from 100 Hz to 6000 Hz for a room fitted with a louver window. It was found that the louver window was able to attenuate 1.4 %, 5.5 % and 12.0 % of the noise when the panels were partially and fully closed at 30°, 60° and 90°, respectively. For frequencies below 3000 Hz, the best attenuation occurred around 1700 Hz to 2000 Hz for all panel angles. The insertion loss (IL) is similar for frequencies ranging from 3000 Hz to 6000 Hz when the louver window was fully closed at 90°. The velocity magnitude of the air passed through the louver panels increased with increased panel angle. The reduction of the mass flow rate for air passed through the louver window when the panels were partially closed at 30° and 60° are 7.7 % and 46.2 %, respectively

Dynamic behavior of a vehicle with rear axle compliance steering

Rear axle compliance steering (RACS) is a technology of passive four-wheel steering, which is designed to improve the vehicle handling and stability at medium or high speed. This paper focuses on the dynamic behavior of the vehicle with RACS. Firstly, the compliance steering principle for different rear suspensions is illustrated. Then, the viscoelastic members with fractional order derivative properties are introduced into RACS, and the fractional order model of RACS is formulated. Next, the dynamic model of the vehicle with RACS is established, the adjusting rules for the compliance steering stiffness are derived, and the vehicle stability is investigated. Finally, numerical experiments are performed to illustrate the effects on the vehicle dynamic behavior caused by the compliance steering stiffness, the viscoelastic members and the vehicle longitudinal velocity. Research results show that, the vehicle with RACS has better dynamic characteristics than that without RACS at medium or high speed; and the compliance steering stiffness, the viscoelastic members and the vehicle longitudinal velocity have different impacts on the vehicle lateral dynamic behavior

Air Drag on a Stratospheric Balloon in Tropical Regions

Stratospheric balloons are popular for scientific applications as they can carry heavy payloads to perform observations for a long duration. However, for practical applications, a major challenge is the control of the trajectories of the balloons as well as station keeping for a period of time due to severe weather condition such as strong wing at the stratosphere. In order to have a better control of the movement of a stratospheric balloon, we need to have a better understanding of the air flow drag acting on a typical stratospheric balloon. In this paper, numerical simulation studies using the Star CCM+, a computational fluid dynamics software, are carried out to investigate the air drag coefficients of a balloon in the stratosphere in tropical region. By analyzing the weather data provided by the local Meteorological Service for the past three years and considering the balloon size according to the payload capacity, the characteristic Reynolds numbers and flow regime are identified. Thereafter, numerical investigations are performed to study the air drag acting on a pumpkin-shaped stratospheric balloon under typical stratospheric weather conditions in tropical regions, which is justified by referring to the drag force acting on a sphere when a flow past it under those Reynolds numbers that is obtained by using the respective empirical and semi-empirical solutions obtained from experiments

Air Drag on a Stratospheric Balloon in Tropical Regions

Stratospheric balloons are popular for scientific applications as they can carry heavy payloads to perform observations for a long duration. However, for practical applications, a major challenge is the control of the trajectories of the balloons as well as station keeping for a period of time due to severe weather condition such as strong wing at the stratosphere. In order to have a better control of the movement of a stratospheric balloon, we need to have a better understanding of the air flow drag acting on a typical stratospheric balloon. In this paper, numerical simulation studies using the Star CCM+, a computational fluid dynamics software, are carried out to investigate the air drag coefficients of a balloon in the stratosphere in tropical region. By analyzing the weather data provided by the local Meteorological Service for the past three years and considering the balloon size according to the payload capacity, the characteristic Reynolds numbers and flow regime are identified. Thereafter, numerical investigations are performed to study the air drag acting on a pumpkin-shaped stratospheric balloon under typical stratospheric weather conditions in tropical regions, which is justified by referring to the drag force acting on a sphere when a flow past it under those Reynolds numbers that is obtained by using the respective empirical and semi-empirical solutions obtained from experiments

Experimental and numerical studies on the design of a sonic crystal window

Four sets of numerical models were created to study the effects of shapes, staggering patterns, Helmholtz resonators and array configurations on the acoustical performance of sonic crystals (SCs) in order to design an efficient SC window to mitigate the traffic noise level at a room in a student hostel of NUS. Rectangular SCs consistently obtained highest transmission loss for frequencies ranging from 300 Hz to 3000 Hz compared to diamond and semi-circle SCs. Fully staggered pattern performed better than non-staggered and 50 % staggered patterns for frequencies below 1700 Hz. Helmholtz resonators were useful for enhancing low frequency noise mitigation. The prototype of the final designed SC window was fabricated and tested in order to validate the simulation result. Generally, numerical and experimental results were in similar trends. Maximum transmission loss of the SC window was found to be occurred at 900 Hz which was about 18 dB

Computational Fluid Dynamics Study of Balloon System Tethered to a Stratosail

In this paper, we present a numerical study of a stratospheric balloon system tethered to a passive device, known as the Stratosail, for station-keeping operation. For scientific applications, stratospheric balloons that operate at altitudes between 15 and 20 km will need to maintain station over a fixed point above the earth for a prescribed period of time. This is a challenging problem due to the limitation of payloads and lack of an energy source. The present study uses computational fluid dynamics (CFD) simulations to analyze the drift velocity of such a balloon-Stratosail system under typical wind conditions in the stratosphere. The Stratosail is attached below the super-pressure helium balloon via a long and thin tether about 10 to 15 km below the balloon, providing a drag force to alter the flight path of the balloon. Its operation depends on the natural differences in the wind speed and wind direction at different altitudes in the atmosphere that act on the balloon and the Stratosail (spaced far apart by 10km to 15 km). In this study, we calculated the drag forces on the balloon and Stratosail for typical wind speeds at various altitudes in the stratosphere. The tether was also modelled as a cable joining the balloon and sail. With this model, the drift velocity of the system was calculated for various altitudes and the angle of attack of the sail