Validating insertion loss predictions for HVAC silencers

Ventilation systems normally contain large dissipative splitter silencers that are used to attenuate fan noise. Recently, numerical models have been developed that seek to predict the insertion loss of these silencers; however, there is very little experimental data available in the literature that is suitable for validating these insertion loss predictions and so questions marks still remain regarding the accuracy of the models. This issue is investigated here by comparing theory with experiment for a range of splitter silencers. Here, the insertion loss predictions are compared against experimental measurements obtained on a test rig that conforms to ISO 7235. Measurements are presented for silencers of differing geometry, although each silencer is restricted to one central splitter with two baffles lining the opposite walls of the duct. Furthermore, validation of the numerical models is based on measurements taken both with and without flow. Comparison between prediction and experiment is reported in one-third octave frequency bands up to a frequency of 8 kHz. Results indicate that the theoretical model is capable of providing accurate predictions for silencers of high percentage open area, but when the percentage open area is low significant discrepancies appear between prediction and experiment at higher frequencies

On the collapse behaviour of oil reservoir chalk

Oil exploitation in North Sea Ekofisk oilfield started in 1971, the reservoir is located in a 150 m thick layer of porous chalk (n = 40-50%) at a 3000 m depth. Enhanced oil recovery procedure by sea water injection (waterflooding) was initiated in 1987. Starting from this date, seabed subsidence due to chalk compaction evolves at a fairly constant rate (i.e. 40 cm/year). Nowadays, the decrease of the seafloor level is of about 10 m. Reservoir management and production strategies are at the origin of the growing interest of petroleum industry in disposing of a comprehensive description of the chalk mechanical behaviour. In this note the subsidence due to waterflooding is interpreted within a framework taken from the mechanics of unsaturated soils. By considering oil as the non-wetting fluid and water as the wetting fluid, chalk compaction is depicted as a collapse phenomenon due to oil-water suction decrease. A series of suction controlled tests in the osmotic oedometer cell are presented. Water weakening effects and chalk compaction (collapse) seem likely to occur through the lost of strength of the inter-granular links existing in the oil saturated sample. The nature of these links includes both capillary and physico-chemical fluids-chalk interactions, and is well characterised by the oil-water suction