Simplified calculation of airblast variability and reliability-based design load factors for spherical air burst and hemispherical surface burst explosions

There can be significant uncertainty and variability with explosive blast loading. Standards and codes of practice are underpinned by reliability-based principles, and there is little reason not to apply these to explosive blast loading. This paper develops a simplified approach where regression equations may be used to predict the probabilistic model of airblast variability and associated reliability-based design load factors (or RBDFs) for all combinations of range, explosive mass and model errors. These models are applicable to (i) hemispherical surface bursts, and (ii) spherical free-air bursts. The benefit of this simplified approach is that the equations can be easily programed into a spreadsheet, computer code or other numerical methods. There is no need for any Monte-Carlo or other probabilistic calculations. Examples then illustrate how model error, range and explosive mass uncertainty and variability affect the variability of pressure and impulse, which in turn affect the damage assessment of residential construction.

Boiling Curve and Droplet Evaporation Lifetime on Hot Hemispherical Copper Surface

The objective of this paper is to investigate the droplet evaporation lifetime and boiling curve on hot copper surface using ethanol liquid. We focus our study to find the Critical Heat Flux (CHF) and Leidenfrost temperature in the boiling curve. Copper material which has a high thermal conductivity, k was chosen as a test material. The copper material dimension was approximately 28.0 mm in height and 50.0 mm in diameter. The copper surface was modified into hemispherical surface in order to maximize the evaporation lifetime. The hemispherical surface was constructed using Electrical Discharge Machining (EDM). After completing the EDM process, the dimension of the hemispherical surface area was approximately 15.0 mm in depth and 30.0 mm in diameter. Meanwhile, ethanol liquid which has a low boiling point of 78 °C was chosen as a test fluid. The droplet diameter was approximately 3.628 mm. The impact height was set to be around 4.0 mm corresponding to drop impact velocity of 0.886 m/s. As a result, it was found that the critical heat flux (CHF) and Leidenfrost temperature range on hemispherical copper surface was approximately TCHF = 100.4-117.7 °C and TL = 170.0-175.8 °C, respectively.