Simulating the effect of forces pit ventilation on ammonia emission from naturally ventilated cow houses with CFD

Atmospheric NH3, mainly originates from agricultural sources, can cause serious environmental problems related to eutrophication and soil acidification. Emissions from dairy houses are 15% of total agricultural NH3 emissions. Due to open buildings, existing abatement options are limited. Pit air separation was identified as a potentially efficacious option. In this study a model simulation of a commercial dairy cow building with slatted floor is presented. The model was solved for 12 cases, differing wind speed, direction and both air and manure temperature. For each case three solutions were obtained, which correspond a) to a building where a forced pit ventilation system is applied at capacity of 250 and 500 m-3 h-1 cow-1 and b) to a building without forced pit ventilation system. The results show that due to forced pit ventilation system, at 250 and 500 m-3 h-1 cow-1, the ventilation rate was increased 3.1% and 6.2% respectively. The contribution of the pit ventilation system to the total ammonia released from the pit during winter, ranged from 31-35%, 16-19% and 11-8%, for wind speed of 1.0, 4.0 and 8.0 m s-1 respectively. Correspondingly, during summer, the contribution of the system ranged from 44-48%, 20-21% and 12-9%. Although obvious benefits arise from a forced pit ventilation system, the main mass flow of ammonia from the pit still emitted through the building ventilation openings, especially at high wind speeds

Transities naar duurzame bedekte tuinbouw in ontwikkelingslanden: Beschrijvingen van de sierteeltclusters in Zuid-Afrika, Kenia, Ethiopië en Oeganda

Bedekte tuinbouw ontwikkelde zich de afgelopen jaren razendsnel in landen in ontwikkeling. Opvallend is vooral de snelle ontwikkeling van sierteelt in de Hoorn van Afrika sinds de jaren 90. Bij veel initiatieven is Wageningen UR Glastuinbouw betrokken via onderzoek of advisering bij de te ontwikkelen kassen, teeltsystemen, duurzamere teeltwijzen en kwaliteitsbeheersing en certificering. Er zijn ook initiatieven van het Nederlandse tuinbouwbedrijfsleven. Hoe duurzaam zijn deze initiatieven nu, in termen van zelfstandigheid en levensvatbaarheid? De rol van de overheid is hier van belang, maar ook het ondernemerschap van de productiebedrijven en de bedrijven in het omringende cluster (toelevering, afzet, diensten, kennis). Er zijn in het rapport landenbeschrijvingen gegeven voor de ontwikkeling van de sierteeltsector en het tuinbouwcluster van een aantal ontwikkelingslanden in Afrika waar Nederland een rol speelt bij de ontwikkeling van de beschermde sierteelt: Zuid-Afrika als land met een redelijk succesvolle eigen sierteeltsector, Kenia met een redelijk succesvolle sierteeltsector met veel Nederlandse inbreng (vooral van het tuinbouwbedrijfsleven), en Ethiopië en Oeganda als landen waar sierteelt in een jongere fase van ontwikkeling is. Er is een overzicht van geconstateerde knelpunten, van interventies die hebben plaatsgehad en hun effecten, en van factoren die hebben bijgedragen aan de ontwikkeling van de sector

Experimental determination of rolling element bearing stiffness

In 1990, Lim and Singh presented a complete 6-dof roller-bearing stiffness model. The experimental verification (using an instrumental variables identification procedure) of all the stiffness coefficients of such a bearing appeared to be difficult, because the experimental setup showed some unexpected properties. In this paper the (modified) experimental setup will be presented to get reproducible measurements. Estimating all the stiffness matrix coefficients simultaneously from measured transfer functions still appeared to be unfeasible. Therefore, a 1-dof amplitude fit procedure has been applied. The results appear to be very promising and applicable in practice, but future research certainly is necessary to understand the remaining differences between the mathematical model and measurements. In addition to stiffnesses, the procedure also gives damping values. Finally, matters such as hysteresis, reproducibility and reciprocity have been investigated

Identification of nonlinear phenomena in a stochastically excited beam system with impact

The response of strongly nonlinear dynamic systems to stochastic excitation exhibits many interesting characteristics. In this paper, an impacting beam system under broad and small banded, Gaussian noise excitation is investigated numerically as well as experimentally. The emphasis lies on frequency domain characteristics. Phenomena like multiple resonance frequencies and stochastic equivalents of harmonic and subharmonic solutions are found. A better understanding of such stochastic response characteristics is obtained by a comparison with nonlinear periodic response features. It is shown that these stochastic response phenomena can provide valuable information on periodic response characteristics of the system