| 12391. |
|
|
| 12392. |
- Kulachenko, Artem, et al.
(författare)
-
Basic mechanisms of fluting formation and retention in paper
- 2007
-
Ingår i: Mechanics of materials. - : Elsevier BV. - 0167-6636 .- 1872-7743. ; 39:7, s. 643-663
-
Tidskriftsartikel (refereegranskat)abstract
- Out-of-plane deformations of paper, such as fluting, significantly deteriorate the quality of a printed product. There are several explanations of fluting presented in the literature but there is no unanimously accepted theory regarding fluting formation and retention which is consistent with all field observations. This paper first reviews the existing theories and proposes a mechanism that might give an answer to most of the questions regarding fluting. The fluting formation has been considered as a post-buckling phenomenon which has been analysed with the help of the finite element method. Fluting retention has been modelled by introducing an ink layer over the paper surface with the ink stiffness estimated from experimental results. The impact of fast drying on fluting has been assessed numerically and experimentally. The result of the study suggests that fluting occurs due to small-scale hygro-strain variations, which in turn are caused by the moisture variations created during fast convection (through-air) drying. The result also showed that ink stiffening alone cannot explain the fluting amplitudes observed in practice, but that high drying temperatures promote inelastic (irreversible) deformations in paper and this may itself preserve fluting.
|
|
| 12393. |
- Kulachenko, Artem, et al.
(författare)
-
Modelling the dynamical behaviour of a paper web : Part I
- 2007
-
Ingår i: Computers and Structures. - : Elsevier BV. - 0045-7949 .- 1879-2243. ; 85:3-4, s. 131-147
-
Tidskriftsartikel (refereegranskat)abstract
- A new shell element has been proposed for geometrically non-linear, finite element analyses of axially moving paper web. Web instability problems of paper travelling in a printing system, such as wrinkling and fluttering, pose special challenges in the numerical analyses. For examples, these are finite bending stiffness (as opposed to membrane), orthotropy, and non-uniform distributions of mechanical and hygro-properties (in different length scales). The new formulation has accounted for paper transport velocity and paper bending stiffness based on a mixed Lagrangian-Eulerian description of the motion. A natural coordinate system has been employed in the analytical and finite element formulations. Benchmarking with different finite elements in various tests showed that the proposed element is indeed more stable and reliable for the chosen application than existing elements. The usability of the shell element has been successfully demonstrated by two example problems: wrinkling of stretched isotropic and orthotropic membranes, and the vibration of a web showing a speed-tensioning effect above a critical web transport velocity.
|
|
| 12394. |
- Kulachenko, Artem, et al.
(författare)
-
Modelling the dynamical behaviour of a paper web. Part II
- 2007
-
Ingår i: Computers & structures. - : Elsevier BV. - 0045-7949 .- 1879-2243. ; 85:3-4, s. 148-157
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a finite element procedure is used to study the dynamic behaviour of a paper web in a free span between two rollers, including effects of transport velocity and surrounding air. The paper web is modelled as a three-dimensional orthotropic structure. The influence of air is accounted for by utilizing fluid-solid interaction analyses based on acoustic theory. The contribution of transport velocity is included through gyroscopic matrices and forces. The structural response on harmonic excitations has been studied using linear and non-linear models. Results show that air significantly reduces eigenfrequencies of the web. So called "edge-flutter" is nothing but the result of skew tension profile. Excessive web vibration can be eliminated by adjusting the web tension.
|
|
| 12395. |
- Kulachenko, Artem, et al.
(författare)
-
Tension wrinkling and fluting in heatset web offset printing process : post buckling analysis
- 2005
-
Ingår i: Advances in Paper Science and Technology. - : The Pulp and Paper Fundamental Research Society. - 9780954527235 ; , s. 1075-1099
-
Konferensbidrag (refereegranskat)abstract
- Geometrically non-linear, large scale post-buckling analyses were carried out to investigate the influence of different parameters on residual waviness (fluting) after printing in a heat set web offset printing press. Mixed implicit-explicit finite element techniques were used in the analyses. The numerical procedure was verified by experimentally acquired data. Results show that when the paper web is perfectly flat before printing, fluting patterns after drying and moisture recovery generally have higher wavelength than those typically observed in fluted samples. Initial cockles of imprinted sheets were found to have impacts on the fluting patterns and amplitudes. Among the factors investigated, ink thickness and hygroexpansivity had significant influences on fluting: increasing these factors increased fluting amplitudes.
|
|
| 12396. |
- Kulachenko, Artem, et al.
(författare)
-
The effect of local moisture variations on fluting in heatset web offset printing
- 2005
-
Ingår i: Proc. of 5th Biennial Johan Gullichsen Colloquium.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The effect of micro scale variations on fluting formation has been studied by using quasi-static post-buckling analyses. The analyses are based on implicit time integration techniques and incorporated the ink stiffening effect during drying in the heatset oven. A series of parametric studies have been conducted to investigate effects of bending stiffness, ink thickness, tension, and scale of moisture variations. Experiments were also performed to estimate the ink layer stiffness after drying and to investigate the retention of flutes after printing. The results showed that, in order to explain the occurrence of flutes in the wavelength of 1-2 cm, micro-scale strain variations are necessary. Such variations are most likely caused by the local moisture variations and the subsequent plastic deformation of paper due to heating. Ink stiffening alone was found to be insufficient to retain the fluting shapes after drying.
|
|
| 12397. |
|
|
| 12398. |
- Kulka, U., et al.
(författare)
-
Realising the European network of biodosimetry : RENEB-status quo
- 2015
-
Ingår i: Radiation Protection Dosimetry. - : Oxford University Press (OUP). - 0144-8420 .- 1742-3406. ; 164:1-2, s. 42-45
-
Tidskriftsartikel (refereegranskat)abstract
- Creating a sustainable network in biological and retrospective dosimetry that involves a large number of experienced laboratories throughout the European Union (EU) will significantly improve the accident and emergency response capabilities in case of a large-scale radiological emergency. A well-organised cooperative action involving EU laboratories will offer the best chance for fast and trustworthy dose assessments that are urgently needed in an emergency situation. To this end, the EC supports the establishment of a European network in biological dosimetry (RENEB). The RENEB project started in January 2012 involving cooperation of 23 organisations from 16 European countries. The purpose of RENEB is to increase the biodosimetry capacities in case of large-scale radiological emergency scenarios. The progress of the project since its inception is presented, comprising the consolidation process of the network with its operational platform, intercomparison exercises, training activities, proceedings in quality assurance and horizon scanning for new methods and partners. Additionally, the benefit of the network for the radiation research community as a whole is addressed.
|
|
| 12399. |
- Kulka, Ulrike, et al.
(författare)
-
RENEB - Running the European Network of biological dosimetry and physical retrospective dosimetry
- 2017
-
Ingår i: International Journal of Radiation Biology. - : Informa UK Limited. - 0955-3002 .- 1362-3095. ; 93:1, s. 2-14
-
Tidskriftsartikel (refereegranskat)abstract
- Purpose: A European network was initiated in 2012 by 23 partners from 16 European countries with the aim to significantly increase individualized dose reconstruction in case of large-scale radiological emergency scenarios. Results: The network was built on three complementary pillars: (1) an operational basis with seven biological and physical dosimetric assays in ready-to-use mode, (2) a basis for education, training and quality assurance, and (3) a basis for further network development regarding new techniques and members. Techniques for individual dose estimation based on biological samples and/or inert personalized devices as mobile phones or smart phones were optimized to support rapid categorization of many potential victims according to the received dose to the blood or personal devices. Communication and cross-border collaboration were also standardized. To assure long-term sustainability of the network, cooperation with national and international emergency preparedness organizations was initiated and links to radiation protection and research platforms have been developed. A legal framework, based on a Memorandum of Understanding, was established and signed by 27 organizations by the end of 2015. Conclusions: RENEB is a European Network of biological and physical-retrospective dosimetry, with the capacity and capability to perform large-scale rapid individualized dose estimation. Specialized to handle large numbers of samples, RENEB is able to contribute to radiological emergency preparedness and wider large-scale research projects.
|
|
| 12400. |
- Kulkarni, Deepak, et al.
(författare)
-
A Newton-Schur alternative to the consistent tangent approach in computational plasticity
- 2007
-
Ingår i: Computer Methods in Applied Mechanics and Engineering. - : Elsevier BV. - 0045-7825. ; 1996:7, s. 1169-1177
-
Tidskriftsartikel (refereegranskat)abstract
- We introduce a Newton-Schur alternative to the consistent tangent approach in plasticity computations and show that the structure of the consistent tangent approach is preserved in the new Newton-Schur approach. However, the local constitutive iterations used in the conventional computational plasticity analyses are eliminated when using the Newton-Schur approach. Two numerical examples are presented which illustrate the efficiencies gained by the new approach.
|
|
