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 “Precision Press with Arcs”

Produžen anestrus post partum i reproduktivna performansa muznih krava (pregled)

Tokom  nekoliko zadnjih decenija, genetski napredak u proizvodnji mleka, povezan sa primenom novih reproduktivnih tehnologija, doveo je do značajnog smanjenja fertiliteta u zapatima krava visoke mlečnosti širom 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 mogućnost smanjenja uticaja ovog faktora na sledeću reproduktivnu performansu visoko mlečnih 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 različitim 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 mliječna mast: proteini, i parametara reproduktivne efikasnosti. Istraživanje je sprovedeno na ukupno 350 oteljenih krava holštajn rase (121 prvotelka, 115 drugotelki i 114 krava koje su se telile tri i više puta), smještenih na farmi mliječnih krava industrijskog tipa, u slobodnom sistemu držanja i hranjenih uobičajenim 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 mliječna mast : proteini (OMP 1,3). Podjela krava unutar svakog pariteta (prvotelke, drugotelke, krave sa tri i više teljenja), izvršena je na osnovu trajanja servis perioda (SP do 60 dana, SP 61-90 dana, SP 91-135 dana). Praćeni su sljedeći reproduktivni parametri: period do prvog vještačkog osjemenjavanja (dani), trajanje servis perioda (dani), trajanje perioda od prvog vještačkog osjemenjavanja do uspostavljanja steonosti (dani), indeks osjemenjavanja, trajanje graviditeta (dani) i trajanje međutelidbenog intervala (dani). Uzorci mlijeka uzimani su u okviru uzorkovanja za potrebe selekcijske službe. U uzorcima mlijeka su određene koncentracije mliječne masti i proteina, te je izračunat njihov međusobni odnos (OMP). Podaci su statistički obrađeni metodama deskriptivne statistike, a značajnost razlika između grupa testirana je t-testom. Pored numeričkih vrijednosti za ispitane parametre, za sve ispitane grupe krava u radu je dat i grafički prikaz odnosa mliječne 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 način podjele, ustanovljen je veliki procenat krava sa vrijednostima OMP izvan fizioloških okvira, bilo da se radi o povišenim ili sniženim vrijednostima. Zbirni podaci za svaku od ispitanih grupa krava, prikazani na grafikonima, ukazuju na generalno nepovoljan metabolički status krava na ispitanoj farmi i visok procenat subkliničkih poremećaja zdravlja, prije svega subkliničke forme ketoze, udružene sa različitim stepenom zamašćenja jetre, što se odražava i na vrijednosti reproduktivnih parametara. Podaci o trajanju perioda do prvog vještačkog osjemenjavanja u svim ispitanim grupama krava, bez obzira na način grupisanja, ukazuju na visok stepen varijacija, kao rezultat različite sposobnosti krava prilagode nepovoljnom bilansu energije,. Energetski status grla je, preko različitih mehanizama opisanih u radu, uticao i na trajanje perioda od prvog do uspješnog vještačkog osjemenjavanja i servis perioda, kao i na vrijednost indeksa osjemenjavanja u svim ispitanim grupama krava, pri čemu 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 značajnom ograničavajućem faktoru za postizanje optimalnih reproduktivnih rezultata na ispitanoj farmi. Prosječno trajanje graviditeta u svim ispitanim grupama krava kretalo se u okvirima za datu vrstu i rasu, te je stoga trajanje međutelidbenog intervala bilo primarno uslovljeno trajanjem servis perioda. Rezultati ovog istraživanja ukazuju da postoji pozitivna veza između energetskog statusa krava, iskazanog kroz vrijednosti odnosa mliječna mast : proteini, i reproduktivnih parametara, pri čemu prilikom tumačenja dobijenih rezultata treba imati u vidu i niz dodatnih faktora, kao što su rasa, visina dnevne proizvodnje mlijeka, sastav i konzumacija obroka, ambijentalni uslovi i slično. Odabir grla na kojima je istraživanje sprovedeno uslovio je da se reproduktivni rezultati svih ispitanih grupa krava kreću u okvirima koji se u literaturi navode kao zadovoljavajući, iako su njihove vrijednosti na nivou cijele farme značajno nepovoljnije. Rezultati ovog istraživanja ukazuju na značajan potencijal primijenjene metode za rano otkrivanje grla sa predispozicijom za nastanak poremećaja zdravlja i reprodukcije, te pravovremeno preduzimanje dijagnostičkih i terapijskih procedura sa ciljem da se posljedice negativnog bilansa energije tokom perioda rane laktacije ublaže, i time omogući 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