# A Review of Blast Loading in the Urban Environment
## 3 Numerical Methods  
### General Computational Fluid Dynamics Studies  
CFD (computational fluid dynamics) numerical models gained particular traction for blast applications in the early 2000s [85; 86]. Obtaining reliable and precise outputs from CFD simulations typically comes at a high computational cost [87]; however, CFD is becoming an increasingly attractive and cost-effective research tool [88; 89; 90; 91].  
Numerical simulations have previously been used to study blast propagation in simple urban areas with some success [92; 93]. [PERSON] et al. [94] and [PERSON] et al. [95] determined the equivalent mass and location of the explosive device used in the 1994 Buenos Aires terror attack by correlating the observed damage with the loading distributions from a range of numerical analyses in a congested urban environment. In a similar study, [PERSON] and [PERSON] [96] used numerical analysis and simple structural response models to back-calculate the yield of the 2011 Oslo bombings. [PERSON] et al. [97] conducted a probabilistic assessment of blast loading to determine fatality risks due to the pressure and impulse from a vehicle-borne improvised explosive device detonated at a T-junction in an urban streetscape, an extension of the work to determine fatality risks due to the detonation of an improvised explosive device inside a typical ground floor lobby of a large commercial or government building [98].  
[PERSON] et al. [99] analysed the impact of the 2020 Beirut explosion using CFD. A combination of geospatial data (a type of data used for other urban blast studies [100]) and CAST3M software was used to produce a finite element model of the cityscape for use within the numerical analysis. Such a replication was described as being able to _\"incorporate with great accuracy all the important geometric details of the buildings in an urban environment\"_. It should be noted that the phrase \"great accuracy\" is relative to the model's size. Upon closer inspection, the model is coarse (compared to models employing 10 s-100 s kg high explosive), with an average mesh size of 5 m. Additionally, small or mobile structures wereomitted from the model as they were considered insignificant. Structural details are also limited as a consequence of the mesh sizing used. Understandably, these limitations were adopted to reduce the computational cost of the analysis, but their significance to the final solution remains unknown. It is explained that decreasing the size of the finite volumes _\"does not really change the solution\"_, but this change is not quantified.  
The research claims that CFD-based simulations are necessary to reflect, more truly, the behaviour of shock waves in geometrically complex settings--agreeing with earlier claims in the field [101]. Effects such as channelling, shielding and interference from multiple wavefronts can be simulated in this computationally expensive method, leading to greater accuracy in the results. This combination of tools can facilitate the calculation of long-duration blast effects with reasonable accuracy regarding the consequences of a large-scale blast event, provided the origin and yield are known.