Simple factor analysis of measured data

Kozar, Ivica,Kozar, Danila Lozzi,Malic, Neira Toric Techno-Press 2022 Coupled systems mechanics Vol.11 No.1

Quite often we have a lot of measurement data and would like to find some relation between them. One common task is to see whether some measured data or a curve of known shape fit into the cumulative measured data. The problem can be visualized since data could generally be presented as curves or planes in Cartesian coordinates where each curve could be represented as a vector. In most cases we have measured the cumulative 'curve', we know shapes of other 'curves' and would like to determine unknown coefficients that multiply the known shapes in order to match the measured cumulative 'curve'. This problem could be presented in more complex variants, e.g., a constant could be added, some missing (unknown) data vector could be added to the measured summary vector, and instead of constant factors we could have polynomials, etc. All of them could be solved with slightly extended version of the procedure presented in the sequel. Solution procedure could be devised by reformulating the problem as a measurement problem and applying the generalized inverse of the measurement matrix. Measurement problem often has some errors involved in the measurement data but the least squares method that is comprised in the formulation quite successfully addresses the problem. Numerical examples illustrate the solution procedure.

Analysis of body sliding along cable

Kozar, Ivica,Malic, Neira Toric Techno-Press 2014 Coupled systems mechanics Vol.3 No.3

Paper discusess a dynamic engineering problem of a mass attached to a pendulum sliding along a cable. In this problem the pendulum mass and the cable are coupled together in a model described by a system of differential algebraic equations (DAE). In the paper we have presented formulation of the system of differential equations that models the problem and determination of the initial conditions. The developed model is general in a sense of free choice of support location, elastic cable properties, pendulum length and inclusion of braking forces. Examples illustrate and validate the model.

Material model for load rate sensitivity

Kozar, Ivica,Ibrahimbegovic, Adnan,Rukavina, Tea Techno-Press 2018 Coupled systems mechanics Vol.7 No.2

This work presents a novel model for analysis of the loading rate influence onto structure response. The model is based on the principles of nonlinear system dynamics, i.e., consists of a system of nonlinear differential equations. In contrast to classical linearized models, this one comprises mass and loading as integral parts of the model. Application of the Kelvin and the Maxwell material models relates the novel formulation to the existing material formulations. All the analysis is performed on a proprietary computer program based on Wolfram Mathematica. This work can be considered as an extended proof of concept for the application of the nonlinear solid model in material response to dynamic loading.

Data driven inverse stochastic models for fiber reinforced concrete

Kozar, Ivica,Bede, Natalija,Bogdanic, Anton,Mrakovcic, Silvija Techno-Press 2021 Coupled systems mechanics Vol.10 No.6

Fiber-reinforced concrete (FRC) is a composite material where small fibers made from steel or polypropylene or similar material are embedded into concrete matrix. In a material model each constituent should be adequately described, especially the interface between the matrix and fibers that is determined with the 'bond-slip' law. 'Bond-slip' law describes relation between the force in a fiber and its displacement. Bond-slip relation is usually obtained from tension laboratory experiments where a fiber is pulled out from a matrix (concrete) block. However, theoretically bond-slip relation could be determined from bending experiments since in bending the fibers in FRC get pulled-out from the concrete matrix. We have performed specially designed laboratory experiments of three-point beam bending with an intention of using experimental data for determination of material parameters. In addition, we have formulated simple layered model for description of the behavior of beams in the three-point bending test. It is not possible to use this 'forward' beam model for extraction of material parameters so an inverse model has been devised. This model is a basis for formulation of an inverse model that could be used for parameter extraction from laboratory tests. The key assumption in the developed inverse solution procedure is that some values in the formulation are known and comprised in the experimental data. The procedure includes measured data and its derivative, the formulation is nonlinear and solution is obtained from an iterative procedure. The proposed method is numerically validated in the example at the end of the paper and it is demonstrated that material parameters could be successfully recovered from measured data.

Inverse model for pullout determination of steel fibers

Kozar, Ivica,Malic, Neira Toric,Rukavina, Tea Techno-Press 2018 Coupled systems mechanics Vol.7 No.2

Fiber-reinforced concrete (FRC) is a material with increasing application in civil engineering. Here it is assumed that the material consists of a great number of rather small fibers embedded into the concrete matrix. It would be advantageous to predict the mechanical properties of FRC using nondestructive testing; unfortunately, many testing methods for concrete are not applicable to FRC. In addition, design methods for FRC are either inaccurate or complicated. In three-point bending tests of FRC prisms, it has been observed that fiber reinforcement does not break but simply pulls out during specimen failure. Following that observation, this work is based on an assumption that the main components of a simple and rather accurate FRC model are mechanical properties of the concrete matrix and fiber pullout force. Properties of the concrete matrix could be determined from measurements on samples taken during concrete production, and fiber pullout force could be measured on samples with individual fibers embedded into concrete. However, there is no clear relationship between measurements on individual samples of concrete matrix with a single fiber and properties of the produced FRC. This work presents an inverse model for FRC that establishes a relation between parameters measured on individual material samples and properties of a structure made of the composite material. However, a deterministic relationship is clearly not possible since only a single beam specimen of 60 cm could easily contain over 100000 fibers. Our inverse model assumes that the probability density function of individual fiber properties is known, and that the global sample load-displacement curve is obtained from the experiment. Thus, each fiber is stochastically characterized and accordingly parameterized. A relationship between fiber parameters and global load-displacement response, the so-called forward model, is established. From the forward model, based on Levenberg-Marquardt procedure, the inverse model is formulated and successfully applied.

Calculation model for layered glass

Ivica Kozar,Goran Suran Techno-Press 2023 Coupled systems mechanics Vol.12 No.6

This paper presents a mathematical model suitable for the calculation of laminated glass, i.e. glass plates combined with an interlayer material. The model is based on a beam differential equation for each glass plate and a separate differential equation for the slip in the interlayer. In addition to slip, the model takes into account prestressing force in the interlayer. It is possible to combine the two contributions arbitrarily, which is important because the glass sheet fabrication process changes the stiffness of the interlayer in ways that are not easily predictable and could introduce prestressing of varying magnitude. The model is suitable for reformulation into an inverse procedure for calculation of the relevant parameters. Model consisting of a system of differential-algebraic equations, proved too stiff for cases with the thin interlayer. This novel approach covers the full range of possible stiffnesses of layered glass sheets, i.e., from zero to infinite stiffness of the interlayer. The comparison of numerical and experimental results contributes to the validation of the model.

Nonlinear viscous material model

Ivica Kozar,Ivana Ban,Ivan Zambon Techno-Press 2023 Coupled systems mechanics Vol.12 No.5

We have developed a model for estimating the parameters of viscous materials from indirect tensile tests for asphalt. This is a simple Burger nonlinear rheological two-cell model or standard model. At the same time, we begin to develop a more versatile and complex multi-cell model. The simple model is validated using experimental load-displacement results from laboratory tests: The recorded displacements are used as input values and the measured force data are simulated with the model. The optimal model parameters are estimated using the Levenberg-Marquardt method and a very good agreement between the experimental results and the model calculations is shown. However, not all parts of the model are active in the loading phase of the experiment, so we extended the validation of the model to the simulation of the relaxation behaviour. In this stage, the other model parameters are activated and the simulation results are consistent with the literature. At this stage, we have estimated the parameters only for the two-cell uniaxial model, but further work will include results for the multi-cell model.

社會規範影響力:探究其對可持續性服飾購買行爲的有效性

( Kim Y Hiller Connell ),( Joy M Kozar ) 한국마케팅과학회 2012 Journal of Global Fashion Marketing Vol.3 No.4

據調?顯示?使消費者非常了解?關心服飾産品與消費引發的環境與社會問題, 能?執行可持續性服飾購買行爲(SAPBs)的人數比率依然?低。因此, ?到削弱這種態度-行爲代溝的有效方法是?有必要的。規範性社會影響可以鼓勵可持續性環保行爲(Cialdini, Reno,& Kallgren, 1990)。此硏究之前的文獻中顯示社會規範對可持續性環保行爲是有影響力的, 包括家庭能源的節約(Nolan,Schultz, Cialdini, Goldstein, & Griskevicius, 2008)與酒店資源的節約(Goldstein, Cialdini, and Griskevicius, 2008)。也就是說, 硏究表明爲了促進可持續性環保行爲, 重點强調他人的可持續性消費者行爲是有效的。因此, 本硏究旨在分析對規範性社會影響的提倡對促進SAPBs是否有效。本硏究參加人員共分爲四組, 運用預備測試, 後續測試與擬實驗設計的方法, 同時利用三組拉門吊?裝置請消費者參與到SAPBs中來。第壹組拉門吊?裝置的信息條中含有呼?可持續性環保的信息, ?不包括社會規範影響。?外兩組拉門吊?裝置都包括規範性社會影響的信息, 其中壹個主要針對可持續性發展人權方面的信息, ?壹個則注重環境方面的影響。數據來源于美國中西部四年制大學中女子社團的學生們。調?抽樣隨機選取四個女子社團。每個社團與居民的選取都是隨機性的直到50個硏究對象名額報滿爲止。每個社團會被隨機分配到四個試驗小組中:管理組、可持續性環保信息組、人權信息組以及環境信息組。試驗開始後(Time 1), 硏究者首先請硏究對象完成預備測試以便于評?他們參與可持續性服飾購買行爲的程度。本調?包括人口統計學選項, 8項可持續性服飾購買行爲(SAPB)測算(Kozar & Hiller Connell, 2010)以及20項可持續性服飾購買(SAA)測算。SAPB測算範圍從1(非常不同意)至7(非常同意), 測算內容例如他們爲否爲血汗工廠中生産的廉價成衣花費的更多。SAA測算範圍從1(從不)至5(總是), 測算內容爲硏究對象參與到可持續性環保服飾購買行爲的頻率。預備測試數據收集完成後, 拉門吊?裝置會根據已經安排好的試驗小組分配到調?對象的房間中, 管理組不會安排拉門吊?裝置。在接下來的10周中, 對調?對象可持續性服飾購買的參與程度進行重新評?, 隨後完成調?對象的後續測試。硏究運用科隆巴赫標准化alpha系數確保測算的可?性(所有alpha?皆大于或等于.89)。接下來, 對SAPB與SAA進行加和平均爲預備測試與後續測試的數據得出兩個複合變量。本硏究采用項間與項內綜合ANOVA評?拉門吊?裝置對SAPB與SAA測算分數的影響, 四個試驗小組分別作爲相間變量, Time 1 與Time 2 作爲相內變量, SAPB總分數(與SAA分數)在不同時間段分別作爲獨立變量。Wilks`` lambda(組內平方和與總平方和之比)在本硏究中作爲檢驗統計量使用。總體來說, 196名調?對象參與了此項硏究。所有調?對象爲女性, 年齡在18至23歲之間。大多數調?對象(94.9%)爲非西班牙裔白人。SAPB的調?對象中, SAPB分數呈顯著變化, 範圍從Time 1(M=2.90, SD=1.25)至Time 2 [M=2.66, SD=1.30, F(1,192) =.967, p=.012]。但是, SAPB測算中調?對象的分數呈降趨勢-也就是說, 在呼?過社會規範影響力後, 他們參與SAPB的程度仍不高。?外, 拉門吊?信息類型(環境、人權、標准)對SAPB的影響沒有呈現統計顯著性, 四組之間?沒有明顯區別[F(3,316)=2.336, p=.074]。同樣, 分數對SAA測算的主要影響範圍從Time 1 (M=1.87, SD=.75)至Time 1 (M=1.87, SD=.75)沒有呈現統計顯著性。拉門吊?信息類型(環境、人權、標准)對SAA沒有顯著影響[F(3,316)=.728, p=.536]。本硏究闡述了雖然規範性社會影響對消費者的可持續性環保行爲有促進作用, 但服飾購買行爲是複雜的, 來自于社會同代人的壓力對有些消費者可持續性服飾消費的模式促進作用不足。在未來的硏究中, 將以此硏究爲基礎?繼續?掘規範性社會影響力的潛力, 以改變服飾消費者的行爲。同時, 進壹步探尋能?鼓勵可持續性服飾消費的機制. Even when consumers are knowledgeable and concerned about sustainability issues related to apparel production and consumption, their level of engagement in sustainable apparel purchasing behaviors is low. Through a four-group pretest posttest, quasi-experimental design, this exploratory research examined the persuasive appeal of door hangers employing social normative influence and petitioning consumers to engage in sustainable apparel-purchasing behaviors. Data were collected from students living on campus at a university in the Midwestern United States. At the start of the experiment, the participants completed a survey that assessed engagement in sustainable apparel purchasing. Door hangers were then distributed to the participants`` rooms. After 10 weeks, the students`` engagement in sustainable apparel purchasing was reassessed by having the participants complete an identical survey. Results indicate that engagement in sustainable apparel-purchasing behaviors among the participants was low. Furthermore, normative social influence was not an adequate motivator to increase consumption of sustainable apparel.

The relevance of turbulent mixing in estuarine numerical models for two-layer shallow water flow

Krvavica, Nino,Kozar, Ivica,Ozanic, Nevenka Techno-Press 2018 Coupled systems mechanics Vol.7 No.1

The relevance of turbulent mixing in estuarine numerical models for stratified two-layer shallow water flows is analysed in this paper. A one-dimensional numerical model was developed for this purpose by extending an immiscible two-layer model with an additional source term, which accounts for turbulent mixing effects, namely the entrainment of fluid from the lower to the upper layer. The entrainment rate is quantified by an empirical equation as a function of the bulk Richardson number. A finite volume method based on an approximated Roe solver was used to solve the governing coupled system of partial differential equations. A comparison of numerical results with and without entrainment is presented to illustrate the influence of entrainment on both the salt-water intrusion length and lower layer dynamics. Furthermore, one example is given to demonstrate how entrainment terms may help to stabilize the numerical scheme and prevent a possible loss of hyperbolicity. Finally, the model with entrainment is validated by comparing the numerical results to field measurements.

Three-dimensional FE analysis of headed stud anchors exposed to fire

Josko Ozbolt,Ivica Kozar,Rolf Eligehausen,Goran Periskic 한국계산역학회 2005 Computers and Concrete, An International Journal Vol.2 No.4

In the present paper a transient three-dimensional thermo-mechanical model for concrete is presented. For given boundary conditions, temperature distribution is calculated by employing a three-dimensional transient thermal finite element analysis. Thermal properties of concrete are assumed to be constant and independent of the stress-strain distribution. In the thermo-mechanical model for concrete the total strain tensor is decomposed into pure mechanical strain, free thermal strain and load induced thermal strain. The mechanical strain is calculated by using temperature dependent microplane model for concrete (Ozbolt, et al. 2001). The dependency of the macroscopic concrete properties (Young's modulus, tensile and compressive strengths and fracture energy) on temperature is based on the available experimental database. The stress independent free thermal strain is calculated according to the proposal of Nielsen, et al. (2001). The load induced thermal strain is obtained by employing the bi-parabolic model, which was recently proposed by Nielsen, et al. (2004). It is assumed that the total load induced thermal strain is irrecoverable, i.e., creep component is neglected. The model is implemented into a three-dimensional FE code. The performance of headed stud anchors exposed to fire was studied. Three-dimensional transient thermal FE analysis was carried out for three embedment depths and for four thermal loading histories. The results of the analysis show that the resistance of anchors can be significantly reduced if they are exposed to fire. The largest reduction of the load capacity was obtained for anchors with relatively small embedment depths. The numerical results agree well with the available experimental evidence.