Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The removal of grape berries from the stems is an important step in the wine
making process. Various problems are experienced using the destemming
machines currently available, where the berries are mechanically removed and
separated from the stems by a rotating beater shaft and drum. Not all berries are
removed from the stems and broken stems can end up with the removed berries
which can result in unwanted characters and flavours in the wine. The
development of these machines is currently limited to experimental tests.
In this study, the destemming process was investigated experimentally. The
ability of the Discrete Element Method (DEM) to simulate this process was also
investigated. A range of experiments was designed to obtain the material
properties of the grapes. These experiments included the measurement of the
stem stiffness and break strength, the berry stiffness, and the force needed to
remove a berry from the stem.
Experiments were conducted to gain further insight into the destemming process.
Firstly, a simplified destemming machine with only a beater shaft and a single
grape bunch was built. The influence of the bunch size and the speed of the
beater shaft on the number of berries removed from the stems were investigated.
Secondly, field tests on a commercial destemming machine were conducted and
the performance of the machine was measured.
A DEM model of both the simplified and the commercial destemming machine
were built. Commercial DEM software was used with linear contact and bond
models. The stems were built from spherical particles bonded together and a
single spherical particle was used to represent each berry. The measured
stiffnesses and break strengths were used to set the particle and bond
properties. Modelling the simplified destemming machine, it was found that the
DEM model could accurately predict the effect of the bunch size and the speed of
the beater shaft on the number of berries removed from the stems. The model of
the commercial destemming machine could accurately predict the machine’s
performance in terms of the number of berries removed as well as the number of
broken stems. / AFRIKAANSE OPSOMMING: Die verwydering van druiwekorrels vanaf die stingels is ʼn belangrike stap tydens
die wynmaak proses. Verskeie probleme word ondervind met huidige beskikbare
ontstingelaars, waar die korrels meganies verwyder en skei word vanaf die
stingels deur middel van ʼn roterende klop-as en drom. Nie alle korrels word vanaf
die stingels verwyder nie en gebreekte stingels kan saam met die verwyderde
korrels beland, wat ongewensde karakters en geure in die wyn kan veroorsaak.
Die ontwikkeling van ontstingelaars is tans beperk tot eksperimentele toetse.
In hierdie studie is die ontstingel proses eksperimenteel ondersoek Die vermoë
van die Diskrete Element Metode (DEM) om hierdie proses te simuleer is ook
ondersoek. ʼn Reeks eksperimente is ontwikkel om die materiaal eienskappe van
die druiwe te bepaal. Hierdie eksperimente sluit in die meet van die styfheid en
breeksterkte van die stingel, die korrel styfheid, en die krag benodig om ʼn korrel
vanaf die stingel te verwyder.
Eksperimente is gedoen om verdere insig oor die ontstingel proses te bekom.
Eerstens is ʼn vereenvoudigde ontstingelaar gebou, met slegs ʼn klop-as en een
tros. Die invloed van die trosgrootte en die klop-as spoed op die aantal korrels
wat verwyder is, is ondersoek. Tweedens is ʼn toets in die veld gedoen met ʼn
kommersiële ontstingelaar om die werkverrigting van die masjien te bepaal.
ʼn DEM model van beide die vereenvoudigde en kommersiële ontstingelaar is
gebou. Kommersiële DEM sagteware is gebruik met lineêre kontak- en
bindingsmodelle. Die stingels is gebou deur sferiese partikels aan mekaar te bind
en ʼn enkele sferiese partikel is gebruik om ʼn druiwe korrel voor te stel. Die
gemete styfhede en breeksterktes is gebruik om die partikel- en
bindingseienskappe te spesifiseer. Die modellering van die vereenvoudigde
ontstingelaar het getoon dat die DEM model akkuraat kan voorspel wat die
invloed is van die trosgrootte en die klop-as spoed op die aantal korrels wat
verwyder is. Die model van die kommersiële ontstingelaar kon die werkverrigting
van die masjien akkuraat voorspel in terme van die aantal korrels wat verwyder is
asook die aantal gebreekte stingels.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/6676 |
| Date | 03 1900 |
| Creators | Lombard, Stephanus Gerhardus |
| Contributors | Coetzee, C. J., University of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering., University of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 113 p. : ill. |
| Rights | University of Stellenbosch |
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