11 research outputs found
Reproductive Performances of Holstein Cows with Different Milk Fat to Protein Ratio during Successive Stages of Lactation
Aim of study was to determine relationship between the energy status of cows, expressed through different milk fat to protein ratio values (FPR<1.0, 1.0-1.3 and >1.3), and their reproductive performances (interval from calving to first artificial insemination; calving to conception interval; insemination index; pregnancy duration; intercalving interval) during succesive stages of lactation (day 15th to 45th; day 46th-75th; day 76th-105th; day 106th to 135th of lactation). The study included a total of 350 fresh calved Holstein cows (121 primiparous, 115 secundiparous and 114 cows which calved three or more times), kept and fed in usual farm conditions. Milk samples were taken during morning milking, and FPR value was calculated from concentrations of milk fat and protein for all milk samples. Reproductive parameters were calculated from farm data. Values of all reproductive parameters, except pregnancy duration, had generally increasing trend in all groups during successive stages of lactation. During successive stages of lactation, cows with optimal FPR values had generally better reproductive performances, compared to cows with increased or decreased FPR values, which indicates importance of FPR monitoring during early lactation for timely detection of cows predisposed for poor reproductive results
Experimental determination and study of structural damping and dry friction
The challenge that will be posed to researchers for an even longer period is
the development of a predictable model for describing mechanical connections, their
variable stiffness and dissipative contact interaction processes. The main challenge to this
goal lies in the lack of understanding of how friction behaves on a small scale. Coulomb
friction, a large heuristic model is not predictable and has actually been proven to be
untrue in many modes. Expecting a universal law of friction for all types of materials and
therefore contact interactions is not very realistic. Instead, the goal of the international
research community is to develop a predictable model for a limited range of cases. So far,
the metal-metal contact is most often tested, respectively the contact interaction behaviour
of aluminium and steel elements of different quality. We also know that in the application
those two metals are most often found in making mechanical connections. The aim of this
paper is to make a brief overview of some of the previous tests and approaches to the study
of contact interaction in mechanical connections and the role of friction in energy
dissipation
Development of a tool for measuring the effect of surface roughness on steel structural response
Driven by the industry's needs to address energy dissipation issues in mechanical connections,
the set goals of the global scientific community, and previous research efforts to interpret how
the condition of contact surfaces between two bodies in contact can be significant, a unique
experimental setup has been devised to study the impact of the state of contact interaction
between two bodies on the system's response. The purpose of the designed experimental setup
is to correlate the roughness of contact surfaces with the deformation of a specially designed
experimental sample. The roughness of contact surfaces represents the most dominant
influencing factor in the contact interaction of two bodies. In terms of scale, the study,
measurement, and analysis of surface roughness fall under the micro and nano scales. On the
other hand, the change in deformation of the experimental sample as a result of the change in
roughness falls under the macro scale. Based on all the aforementioned, the fundamental idea of
the designed experimental setup can be seen. Considering that it is not possible to enter into
contact interaction and explicitly analyse the influence of roughness on the response of a
mechanical connection, the idea in overall research is to consider the macro behaviour of a
specially prepared experimental sample depending on the level of roughness of the contact
interaction surfaces at the micro level. The aim of this paper is to present details and challenges
in the construction of an instrument necessary for such precise examinations, named āPrecision
Press with Arcsā
Produžen anestrus post partum i reproduktivna performansa muznih krava (pregled)
Tokom Ā nekoliko zadnjih decenija, genetski napredak u proizvodnji mleka, povezan sa primenom novih reproduktivnih tehnologija, doveo je do znaÄajnog smanjenja fertiliteta u zapatima krava visoke mleÄnosti Å”irom sveta. Produžen postpartalni anestrus je jedan od glavnih uzroka smanjenog fertiliteta i ekonomskih gubitaka u intenzivnoj proizvodnji mleka. Cilj ovog rada je da se prikažu uzroci i moguÄnost smanjenja uticaja ovog faktora na sledeÄu reproduktivnu performansu visoko mleÄnih krav
Penalty method for 1d problem of two rods with basic concepts of contact mechanics of frictionless contact
Problems involving contact are of great importance in industry related to
mechanical and civil engineering, but also in biomechanics and other applications. The
contact interaction between surfaces in a bolted splice connection joint or area through
which tire interacts with the road is not known a priori, leading to a nonlinear boundary
value problem. Due to the rapid improvement of modern computer technology, today one
can apply the tools of computational mechanics to analyze contact problems with limited
accuracy, depending on design requirements. However, even now most of the standard
finite element software is not fully capable of solving contact problems, including friction,
using robust algorithms. The aim of this paper is to present some basic concepts of Contact
Mechanics. To illustrate the difficulties arising in computational contact mechanics,
Newton-Raphson scheme was used to solve simple 1D contact problem using penalty
method
Numerical and experimental analysis of structural damping for bolted splice connection joint
This paper presents the finite element modeling of bolted joints for structural
dynamic analysis to achieve a reasonable accuracy in simulation results. Non-linear
effects in splice connected joints involve normal compressive loads holding components
together combined with dynamic lateral loads inducing some amount of shear slip in
contact interaction between elements of splice connection joint. The complexities of the
slip process are responsible for the nonlinear nature of the interfaces, both in terms of
stiffness and dissipation. Exploring the physics of joints directly is not readily done
because key interactions takes place at the interface of surfaces, where instrumentation
cannot be placed without changing the problem. Consequences of the specific conditions
of joint connections are increased dynamic problems related to vibrations and dissipative
processes in structure connection joints. Structural joints are the main reason for the
significant level of energy dissipation and source of structural damping. The aim of this
paper is to present some problems regarding research of structural damping and the
importance of study Contact Mechanics to better understand the problem of structural
damping
Experimental and numerical study of structural damping in a beam with bolted splice connection
The objective of this research is to develop a numerical model of one widely used bolted beam splice connection
that dissipates energy through structural damping. The reference experimental setup is carefully designed to
obtain the highly nonlinear dynamic response due to the suddenly released load. The fact that the monolithic
beam with welded connection has a linear response is utilized for the initial calibration of the numerical and
experimental models. Then, the numerical model of bolted beam splice connection is verified and adopted
through an iterative process. The influences of time and spatial integration, bolt load application, element
type, contact formulation, bulk viscosity, and mass scaling are discussed. A special attention is given to the
load application and load release functions. After the verification, the Abaqus/Explicit numerical model is
validated through the comparison with experimental data, where an appropriate friction coefficient is adopted.
It is demonstrated that the nonlinear structural damping occurs due to the complex micro slip behavior at the
contact interface
Reproduktivne performanse krava sa razliÄitim odnosom sadržaja masti i proteina u mlijeku do uspostavljanja gravidnosti
Cilj istraživanja bio je da se ustanovi povezanost energetskog statusa krava u postpartalnom periodu, iskazanog kroz vrijednost odnosa mlijeÄna mast: proteini, i parametara reproduktivne efikasnosti. Istraživanje je sprovedeno na ukupno 350 oteljenih krava holÅ”tajn rase (121 prvotelka, 115 drugotelki i 114 krava koje su se telile tri i viÅ”e puta), smjeÅ”tenih na farmi mlijeÄnih krava industrijskog tipa, u slobodnom sistemu držanja i hranjenih uobiÄajenim obrocima za datu rasu goveda, proizvodnu kategoriju, stadijum laktacije i period godine. Sve ispitane krave, bez obzira na paritet, podijeljene su u odnosu na stadijum laktacije (15-45 dana, 46-75 dana, 76-105 dana i 106-135 dana), a u okviru svakog njih formirane su podgrupe u odnosu na vrijednost odnosa mlijeÄna mast : proteini (OMP 1,3). Podjela krava unutar svakog pariteta (prvotelke, drugotelke, krave sa tri i viÅ”e teljenja), izvrÅ”ena je na osnovu trajanja servis perioda (SP do 60 dana, SP 61-90 dana, SP 91-135 dana). PraÄeni su sljedeÄi reproduktivni parametri: period do prvog vjeÅ”taÄkog osjemenjavanja (dani), trajanje servis perioda (dani), trajanje perioda od prvog vjeÅ”taÄkog osjemenjavanja do uspostavljanja steonosti (dani), indeks osjemenjavanja, trajanje graviditeta (dani) i trajanje meÄutelidbenog intervala (dani). Uzorci mlijeka uzimani su u okviru uzorkovanja za potrebe selekcijske službe. U uzorcima mlijeka su odreÄene koncentracije mlijeÄne masti i proteina, te je izraÄunat njihov meÄusobni odnos (OMP). Podaci su statistiÄki obraÄeni metodama deskriptivne statistike, a znaÄajnost razlika izmeÄu grupa testirana je t-testom. Pored numeriÄkih vrijednosti za ispitane parametre, za sve ispitane grupe krava u radu je dat i grafiÄki prikaz odnosa mlijeÄne masti i proteina. U prilogu je dat pregled vrijednosti parametara deskriptivne statistike za ispitane parametre za sve ispitane grupe krava. U svakoj od ispitanih grupa krava, bez obzira na naÄin podjele, ustanovljen je veliki procenat krava sa vrijednostima OMP izvan fizioloÅ”kih okvira, bilo da se radi o poviÅ”enim ili sniženim vrijednostima. Zbirni podaci za svaku od ispitanih grupa krava, prikazani na grafikonima, ukazuju na generalno nepovoljan metaboliÄki status krava na ispitanoj farmi i visok procenat subkliniÄkih poremeÄaja zdravlja, prije svega subkliniÄke forme ketoze, udružene sa razliÄitim stepenom zamaÅ”Äenja jetre, Å”to se odražava i na vrijednosti reproduktivnih parametara. Podaci o trajanju perioda do prvog vjeÅ”taÄkog osjemenjavanja u svim ispitanim grupama krava, bez obzira na naÄin grupisanja, ukazuju na visok stepen varijacija, kao rezultat razliÄite sposobnosti krava prilagode nepovoljnom bilansu energije,. Energetski status grla je, preko razliÄitih mehanizama opisanih u radu, uticao i na trajanje perioda od prvog do uspjeÅ”nog vjeÅ”taÄkog osjemenjavanja i servis perioda, kao i na vrijednost indeksa osjemenjavanja u svim ispitanim grupama krava, pri Äemu su grla sa povoljnijim energetskim statusom generalno imala povoljnije vrijednosti ovih parametara. Pored energetskog statusa, podaci prikazani u radu govore i o neadekvatnoj organizaciji otkrivanja estrusa, kao znaÄajnom ograniÄavajuÄem faktoru za postizanje optimalnih reproduktivnih rezultata na ispitanoj farmi. ProsjeÄno trajanje graviditeta u svim ispitanim grupama krava kretalo se u okvirima za datu vrstu i rasu, te je stoga trajanje meÄutelidbenog intervala bilo primarno uslovljeno trajanjem servis perioda. Rezultati ovog istraživanja ukazuju da postoji pozitivna veza izmeÄu energetskog statusa krava, iskazanog kroz vrijednosti odnosa mlijeÄna mast : proteini, i reproduktivnih parametara, pri Äemu prilikom tumaÄenja dobijenih rezultata treba imati u vidu i niz dodatnih faktora, kao Å”to su rasa, visina dnevne proizvodnje mlijeka, sastav i konzumacija obroka, ambijentalni uslovi i sliÄno. Odabir grla na kojima je istraživanje sprovedeno uslovio je da se reproduktivni rezultati svih ispitanih grupa krava kreÄu u okvirima koji se u literaturi navode kao zadovoljavajuÄi, iako su njihove vrijednosti na nivou cijele farme znaÄajno nepovoljnije. Rezultati ovog istraživanja ukazuju na znaÄajan potencijal primijenjene metode za rano otkrivanje grla sa predispozicijom za nastanak poremeÄaja zdravlja i reprodukcije, te pravovremeno preduzimanje dijagnostiÄkih i terapijskih procedura sa ciljem da se posljedice negativnog bilansa energije tokom perioda rane laktacije ublaže, i time omoguÄi postizanje adekvatnih reproduktivnih rezultata
Review of basic concepts of contact mechanics of frictionless contact with emphasis on penalty method
Problems involving contact are of great importance in industry related to mechanical and civil
engineering, but also in biomechanics and other applications. The contact interaction between
surfaces and different bodies like in a bolted splice connection joint or area in which a tire interacts with the soil is not known a priori, leading to a nonlinear boundary value problem. Due to the rapid improvement of modern computer technology, one can today apply the tools of computational
mechanics to analyze contact problems with required accuracy, depending on design requirements. However, even now most of the standard finite element software is not fully capable of solving contact problems, including friction, with robust algorithms. The aim of this paper is to present some basic concepts of Contact Mechanich
A numerical verification of IPE-80 steel cantilever beam with bolted and welded splice connection joint
The aim of this paper is to discuss numerical analysis and verification of experimentally tested bolted and weld splice connections in the commercial Abaqus software. The first step in verifying a numerical model with an experimental one is to compare the modal frequencies. The problems that arise when modeling multiple bodies in a contact interaction, such as in the case of bolted splice connection joint, arise from the behavior of the contact itself [2] and [1]. In order for the numerical model to be stable and without calculations convergence issue, it is necessary to: define an adequate type and size of finite elements, determine the master and slave surfaces, and properly define the constraints and connections of the separate parts of the bolted welded connection structure. Tests with a modal hammer were performed in order to find the oscillation tones of the cantilever beam under consideration, which would be compared with the numerical model. Based on a comparison of numerical and experimental results, it is discussed whether the experimental beam is adequately designed and constructed and the effects of the support and splice connections on the frequencies are considered