Wyniki wyszukiwania - Biblioteka Nauki

1

Numerical modeling of unsteady state operation of tube and plate fin heat exchangers

100%

Taler D. , Korzeń A.

Journal of Energy Science

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2012

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tom Vol. 1, nr 2

103--117

EN

Cross-flow tubular heat exchangers are applied as condensers and evaporators in air conditioners and heat pumps or as air heaters in heating systems. They are also applied as water coolers in so called 'dry' water cooling systems of power plants, as well as car radiators. There are analytical and numerical mathematical models of heat exchangers of that type to determine the steady state temperature distribution of fluids and the rate of heat transferred between fluids. In view of the wide range of applications in practice, these heat exchangers were experimentally examined in steady-state conditions, mostly to determine the overall heat transfer coefficient or the correlation for the heat transfer coefficients on the air side and on the internal surface of the tubes. There exist many references on the transient response of heat exchangers. Most of them, however, focus on the non-steady-state heat transfer processes in parallel and counter flow heat exchangers. In this paper, the new equation set describing transient heat transfer process in tube and fin cross-flow tube exchanger will be given and subsequently solved using the finite volume method.

2

Experimental Validation of Riveting Process Fe Simulation

100%

Wronicz W.

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tom Iss. 10

63--72

EN

Rivets are critical areas in metal airframes from the fatigue point of view. Fatigue behaviour of riveted joints depends strongly on the residual stress system around the rivet holes. The both most convenient and most common method of determining these stresses is the Finite Element (FE) analyses. The validation of models used is necessary to ensure the reliability of results. This paper presents the validation process of the riveting FE simulations for the universal and the countersunk rivets. At first, the material model of the rivets was validated with the use of the force-displacement curves of the press stamp obtained experimentally. Because of the displacement measurement method, it was necessary to take into account the flexibility of the stand. After that, good correlation between the numerical simulations and the experiment was obtained for both rivet types. At the second stage, strains around driven heads measured with the use of strip gauge patterns were compared with the results of the FE simulations. Quite good correlation was obtained for the countersunk rivet. In the case of the universal rivet, the numerical results are significantly higher values than the measured ones. Differences in correlation of the experiments and FE simulations for the analysed rivet types probably result from material differences of the rivets.

3

Experimental validation of a CFD model of a ground heat exchanger with slinky coils

100%

Grzywacz R. , Teper M.

Polish Journal of Chemical Technology

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2024

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tom Vol. 26, nr 2

86--91

EN

Rising energy prices have increased the popularity of many renewable energy sources including heat pumps. In the case of ground heat pumps research related to the analysis of the operation and selection of ground heat exchangers as a heat source are insufficient. With this in mind, on the operation of the horizontal slinky coil heat exchanger research work has been undertaken. As a research tool, the Computational Fluid Dynamics has been used. To check the adequacy of the CFD model, a validation of the model was carried out using the results of research on a real heat exchanger. Comparison was made: values of ground temperatures, outlet temperatures from the exchanger, and heat flux exchanged by the heat exchanger. In the opinion of the authors, the validation of the CFD model was successful.

4

Analytical and experimental investigation of asymmetric floating phenomena of uniform bodies

100%

Gu J. , Fernandes A. C. , Chai W. , Bu S. X. , Han X.

Polish Maritime Research

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2024

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tom nr 1

16--23

EN

Uniform symmetric bodies can be observed floating asymmetrically under certain circumstances. Previous explanations of this are mostly abstract and lack experimental verification, making their understanding and application difficult. This article presents in detail alternative insights into the floating equilibria of uniform prisms and parabolic cylinders. The intrinsic characteristics of the equilibrium curves are investigated, and several equilibria different from those in the literature are found. The inflection points in the equilibrium curves are analyzed quantitatively due to their significance for floating states. Furthermore, experiments have been conducted for the square prism which validate the derived equilibrium curve, and provide a practical impression of the asymmetric floating phenomenon of symmetric bodies. These results have the potential to be applied in naval and ocean engineering, such as in the design of vessels and floating offshore structures.

5

Validation of Services Supporting Healthcare Standards Conformance

75%

Górski J. , Jarzębowicz A. , Miler J.

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nr 2

6

A friction model of microbearings with thin metallic compliant coatings

75%

Stiharu I. , Bhat R. , Hong H.

International Journal of Applied Mechanics and Engineering

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2003

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tom Vol. 8, no 2

317-329

EN

The paper presents experimental results of the investigation on the micro-tribological properties of Ti thin film layers deposited on metallic substrates of various hardness. The tests were carried out under standard dry friction conditions using a miniature pin on disk apparatus. The experimental results found for the friction coefficient developed between 52100 steel pin and Ti as a compliant layer deposited on various hardness substrates from soft to hard are consistent with other results presented in literature for the pair steel/Ti. A friction model that assumes the plowing of microasperities into the soft thin film layer supported by the elastic substrate as the main factor in the originating friction is further proposed. A simplified one-asperity model is assessed against the compliant layer assumed deposited on a rigid substrate. The analysis of the influence of the stress developed at the interface substrate-film is assumed in this model. Tests carried out qualitatively confirmed that the influence of the inter-laminar stress is significant to friction. Given the simplification assumptions, the proposed model exhibits reasonable agreement with the experimental results. It is further suggested that the lubrication of the hard surfaces with thin compliant metallic layers of Ti represents an alternative for the friction improvement in the small bearings belonging to miniature mechanical systems and the Micro-Electro-Mechanical Systems (MEMS).

7

Identification of layers distribution in the composite coupon using finite element method and three point bending test

75%

Mazurkiewicz Ł. , Małachowski J. , Damaziak K. , Baranowski P. , Gotowicki P.

Acta Mechanica et Automatica

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2013

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tom Vol. 7, no. 3

160--165

EN

The main objective of the study is to develop experimentally validated FE model and perform numerical analysis of layered composites made by hand lay-up techniques during tension and bending test. The research object is glass - polyester laminate made of four unidirectional layers. In order to validate the numerical models experimental test were performed. Due to the very different stiffness modulus in tension and bending loading the material properties obtained from standard test are not suitable to apply in numerical model. Significantly different behaviour compared to experimental test was obtained for tree point bending where the numerical model becomes too stiff. Simple coupons, relatively easy to manufacture presented in the paper have very low quality. The differences in actual and theoretical bending stiffness (obtained from tension stiffness) exceed 70%. In order to represent the actual structure the layers of the composite were divided by resin layers and also additional resin layer at the top and bottom of the model were defined. Single stage optimization process was used to adjust the material layout. After layer set-up modification very significant improvement can be seen for flexural behaviour.

8

Validation of services supporting healthcare standards conformance

75%

Górski J. , Jarzębowicz A. , Miler J.

Metrology and Measurement Systems

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2012

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tom Vol. 19, nr 2

269-282

EN

The paper presents the results of experimental validation of a set of innovative software services supporting processes of achieving, assessing and maintaining conformance with standards and regulations. The study involved several hospitals implementing the Accreditation Standard promoted by the Polish Ministry of Health. First we introduce NOR-STA services that implement the TRUST-IT methodology of argument management. Then we describe and justify a set of metrics aiming at assessment of the effectiveness and efficiency of the services. Next we present values of the metrics that were built from the data collected. The paper concludes with giving the interpretation and discussing the results of the measurements with respect to the objectives of the validation experiment.

9

Application of the KUKA KUBE test-bed for the hardware-in-the-loop validation of the space manipulator control system

75%

Wojtunik M. , Łuczak P. , Rybus T. , Granosik G.

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2023

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tom Vol. 58, Special Issue 1

231--248

EN

The on-ground validation of control systems designed for manipulators working in orbit is very difficult due to the necessity of simulating the microgravity environment on Earth. In this paper, we present the possibilities of utilising the KUKA KUBE test-bed with industrial robots to experimentally verify space systems using hardware-in-the-loop tests. The fixed-base KUKA industrial robot is operated in gravitational environment, while the space system model plant is solved in real time parallel to on-ground experiment. The test-bed measurements are the input of the model plant, and the output of the model is treated as an input for the industrial robot actuation. In the performed experiment, the control system based on the Dynamic Jacobian is validated. The desired point that is reached by the manipulator’s endeffector is constant in the simulated environment and moving with respect to the test-bed frame. The position of the space manipulator’s end-effector is calculated by evaluating dynamics of the satellite in real-time model. The results show that the control system applied to the KUKA robot works correctly. The measurements from the torque sensors mounted in KUKA robot’s joints are in accordance with the simulation results. This fact enhances the possibilities of gravity compensation, thus simulating microgravity environment on the test-bed.

10

Zmiana temperatury podczas odkształcenia plastycznego stali austenitycznych

75%

Paćko M. , Nowak J. , Grzesiak J.

Hutnik, Wiadomości Hutnicze

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2003

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tom Vol. 70, nr 2

66--71

PL

W artykule przedstawiono wyniki badań zmian temperatury oraz dokonano pomiaru parametrów siłowych dla półprzemysłowego, posobnego procesu odkształcenia stali austenitycznej 304L. Uzyskane wyniki stanowią podstawę do określenia wpływu wielkości odkształcenia i temperatury na kinetykę rekrystalizacji w tych stalach. Przeprowadzono również wstępne obliczenia za pomocą programu Elroll, symulując zmiany temperatury i struktury dla stali austenitycznej podczas odkształcenia.

EN

Results of testing temperature variations have been presented and measurements of force parameters for semi-industrial and multi-pass deformation of austenitic 304L steel have been carried out. The obtained results are the first step to determine the influence of the size of deformation and temperature on the recristallization kinetics in austenitic stainless steels. The article also presents the preliminary results of simulation of temperature variations obtained by using the Elroll program.

11

Numerical modelling of post-ground subsystem in road safety barrier crash tests

75%

Klasztorny M. , Nycz D. B. , Dziewulski P. , Gieleta R. , Stankiewicz M. , Zielonka K.

Engineering Transactions

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2019

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tom Vol. 67, iss. 4

513--534

EN

A new analytical algorithm for determining the elastoplastic parameters for soft, medium and hard plastic cohesive soils, corresponding to *MAT_005_SOIL_AND_FOAM material model available LS-Dyna FE code, was formulated. The numerical modelling of the post-soil subsystem, applicable in the modelling of road safety barrier crash tests using this material model of the roadside dehydrated ground, was developed. The methodology was presented on the example of a Sigma-100 steel post partly driven into the soil and subjected to a static flexural-torsional test using a horizontal tensioned rope. The experimental validation of the numerical modelling and simulation was carried out on the testing site at the Automotive Industry Institute, Warsaw, Poland. The simulations were carried out for numerical models with soil solid elements with reduced integration (ELFORM_1) and full integration (ELFORM_2). The simulation results are in the form of graphs of the rope tension vs. displacement of the upper measurement point of the post and in the form of deformation of the post-soil system. It was shown that the validation experiment was carried out on the post embedded in hydrated soft plastic cohesive soil.

12

Experimental validation of novel microRNA candidates in the liverwort Pelliia endiviifolia

63%

Piszczalka P. , Alaba S. , Pietrykowska H. , Plewka P. , Karlowski W. , Szweykowska-Kulinska Z.

BioTechnologia. Journal of Biotechnology Computational Biology and Bionanotechnology

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2013

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tom 94

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nr 3

13

Numerical model of the human cervical spinal cord - the development and validation

63%

Czyż M. , Ścigała K. , Jarmundowicz W. , Będziński R.

Acta of Bioengineering and Biomechanics

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2011

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tom Vol. 13, no. 4

51-58

EN

The influence of mechanical load on the extent of nervous tissue damage in the spinal cord at the time of trauma is presently incontestable. Although numerical modelling cannot fully replace physical testing, it seems to be the perfect complement to experiments in terms of the analysis of such a complex phenomenon as traumatic spinal cord injury. Previous numerical models of the human cervical spinal cord have been limited by several factors: two-dimensional modelling, spinal cord geometry simplification and incomplete reflection of specific anatomical and biomechanical relations of the objects being modelled. The objective of this study was to develop and validate an accurate and universal numerical Finite Element Method (FEM) model of the human cervical spinal cord. Our survey focuses mainly on geometric, constraint and material aspects. Experimental validation was carried out based on a controlled compression of the porcine spinal cord specimens. Each stage of compression was simulated using the FEM model of the compressed segment. Our 3D numerical simulation results compared with experimental results show a good agreement. It is possible to use the developed numerical model of the human cervical spinal cord in the biomechanical analysis of the spinal cord injury phenomenon. However, further clinical evaluation is clearly justified.

14

The influence of the microfibril angle on wood stiffness: a continuum micromechanics approach

63%

Hofstetter K. , Hellmich C. , Eberhardsteiner J.

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tom Vol. 13, No. 4

523-536

EN

Wood exhibits an intrinsic structural hierarchy. It is composed of wood cells, which are hollow tubes oriented in the stem direction. The cell wall is built up by stiff cellulose fibrils which are embedded in a soft polymer rnatrix. This structural hierarchy is considered in a four-step homogenization scheme, predicting the macroscopic elastic behavior of different wood species from tissue-specific chemical composition and microporosity, based on the elastic properties of nanoscaled universal building blocks. Special attention is paid to the fact that the fibrils are helically wound in the cell wall, at an angle of 0°-30°, generally denoted as microfibril angle. Consideration of this microfibril angle in the continuum micromechanics model for wood is mandatory for appropriate prediction of macroscopic stiffness properties, in particular of the longitudinal elastic modulus and the longitudinal shear modulus. The presented developments can be readily extended to the prediction of poroelastic properties, such as Biot and Skempton coefficients.

15

Modelowanie i walidacja wytrzymałościowa kompozytowej skorupy nośnej fotela kolejowego

63%

Gołębiowski Ł. , Siwek M. , Ciesielski M. , Zagórski A. , Krauze S. , Majewski R.

Problemy Kolejnictwa

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2020

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tom Z. 189

7--16

PL

Przedmiotem prac modelowych i badań doświadczalnych jest kompozytowa skorupa nośna fotela kolejowego. Zaprojektowano kształt geometryczny i strukturę materiałową konstrukcji oraz dobrano materiały. Do budowy skorupy wykorzystano kompozyty włókniste o osnowie polimerowej (kompozyty FRP – Fiber Reinforce Polimer), które są lżejsze w porównaniu ze stalą i jednocześnie zapewniają odpowiednie standardy z zakresu wytrzymałości i bezpieczeństwa. Opracowano obliczeniowy model skorupy i przeprowadzono analizę wytrzymałościową zgodnie z wytycznymi branżowej normy oraz hipotezami wytrzymałościowymi dotyczącymi kompozytów FRP. Obliczenia przeprowadzono za pomocą oprogramowania ANSYS (Ansys Composite PrepPost), bazującego na metodzie elementów skończonych. W artykule przedstawiono analizę wytrzymałościową zoptymalizowanego modelu kompozytowej skorupy nośnej fotela. Na podstawie wytycznych z prac modelowych wytworzono model fizyczny (walidacyjny), w technologii laminowania próżniowego na gorąco. Walidację doświadczalną modelowania z wynikiem pozytywnym przeprowadzono na stanowisku badawczym firmy S.Z.T.K. TAPS – Maciej Kowalski.

16

Modelling and Validation of the Composite Shell of a Train Seat

63%

Gołębiowski Ł. , Siwek M. , Ciesielski M. , Zagórski A. , Krauze S. , Majewski R.

Problemy Kolejnictwa

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2020

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tom Z. 189

75--84

EN

The subject of the modelling work and the conducted experiments is the composite shell of a train seat. The activities carried out involved designing the geometry, planning the material structure, and selecting the materials to be used. The shell was built using polymer matrix fibrous composites (i.e. FRP – Fibre Reinforced Polymer – composites), which are lighter than steel and comply with the relevant standards for strength and safety at the same time. This was followed by creating a computational model for the shell and conducting a strength analysis in accordance with the guidelines of the relevant industry standard and strength hypotheses adopted for FRP composites. The calculations were conducted using ANSYS Composite PrepPost software based on the finite element method. The article offers a strength analysis of an optimised composite shell of a train seat. Based on the guidelines obtained as a result of the conducted modelling work, a physical prototype (validation model) of the seat was created. Hot vacuum lamination technology was applied in the production process. The experimental validation of the model, producing a positive result, was conducted using a test stand owned by S.Z.T.K. TAPS – Maciej Kowalski.

17

Analysis of radiative heat transfer impact in cross-flow tube and fin heat exchangers

63%

Hanuszkiewicz-Drapała M. , Bury T. , Widziewicz K.

Archives of Thermodynamics

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2016

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tom Vol. 37, no. 1

99--112

EN

A cross-flow, tube and fin heat exchanger of the water – air type is the subject of the analysis. The analysis had experimental and computational form and was aimed for evaluation of radiative heat transfer impact on the heat exchanger performance. The main element of the test facility was an enlarged recurrent segment of the heat exchanger under consideration. The main results of measurements are heat transfer rates, as well as temperature distributions on the surface of the first fin obtained by using the infrared camera. The experimental results have been next compared to computational ones coming from a numerical model of the test station. The model has been elaborated using computational fluid dynamics software. The computations have been accomplished for two cases: without radiative heat transfer and taking this phenomenon into account. Evaluation of the radiative heat transfer impact in considered system has been done by comparing all the received results.

18

Search for the most useful geometry of an acoustic journal bearing

63%

Gawarkiewicz R.

Tribologia

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2017

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tom nr 3

57--66

EN

Computer simulations of a number of journal bearing’s geometries utilising acoustic levitation were carried out. The choice of the best geometry depended on the ability of a deformed shape, created by piezo-electric elements, to facilitate squeeze film ultrasonic levitation, and also to create three evenly distributed diverging aerodynamic gaps. Deformations of analysed variants of the bearing’s shape were generated by numerical simulations utilising the finite element method. For the chosen shapes of geometry, prototype bearings were made and their usefulness verified experimentally. As a result, the bearing with the highest load carrying capacity was identified.

PL

Przeprowadzono analizę użyteczności szeregu geometrii panwi łożyska poprzecznego wykorzystującego lewitację akustyczną. Wybór najlepszego z przeanalizowanych rozwiązań zależał od zdolności do uzyskiwania kształtu jego powierzchni czynnej sprzyjającego powstaniu ponaddźwiękowej lewitacji akustycznej (wykorzystującej efekt „wyciskania” filmu smarnego), a także umożliwiającego tworzenie zbieżnych równomiernie obwodowo rozmieszczonych szczelin smarnych, które były warunkiem powstawania filmu aerodynamicznego. Kształt części czynnej łożyska zależał od jej deformacji wywoływanej elementami piezoelektrycznymi. Spodziewane deformacje poszczególnych wariantów panwi otrzymywano na drodze symulacji numerycznych wykorzystujących metodę elementów skończonych. Dla wytypowanych geometrii wykonano prototypy łożysk, których przydatność zweryfikowano podczas badań doświadczalnych. Ostatecznie udało się uzyskać postacie panwi łożyskowej o bardzo dużej stabilności pracy, nawet w warunkach impulsowego obciążenia poprzecznego.

19

Numerical model of a cross-flow heat exchanger with non-uniform flow of media

63%

Hanuszkiewicz-Drapala M. , Bury T. , Widziewicz K.

Journal of Power Technologies

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2013

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tom Vol. 93, nr 5

295--302

EN

This paper presents thermal-hydraulic analyses of finned cross flow heat exchangers working in media flow maldistribution conditions. The authors postulate a possibility of performing such analyses through the use of CFD models of recurrent segments of the heat exchangers. Media inflow to each recurrent segment may be individually defined and thus the flow maldistribution in the whole heat exchanger could be considered. The methodology of creating these models, running calculations and results of very initial experimental validation is presented in the paper.

20

The comparison of density-elastic modulus equations for the distal ulna at multiple forearm positions : a finite element study

63%

Neuert M. A. C. , Austman R. L. , Dunning C. E.

Acta of Bioengineering and Biomechanics

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2013

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tom Vol. 15, no. 3

37--43

EN

The accuracy of an empirically derived density-modulus equation for bone depends upon the loading conditions and anatomic site of bone specimens used for experimentation. A recent study used FE modeling to compare the ability of three density-modulus relationships to predict strain during bending in neutral forearm rotation in the distal ulna; however, due to the inhomogeneous nature of these FE models, the performance of each equation is not necessarily consistent throughout forearm rotation. This issue is addressed in the present study, which compares the performance of these equations in pronation and supination. Strain gauge data were collected at six discreet locations of six ulna specimens loaded in bending at 40° of pronation and supination. Three FE models of each specimen were made, one for each density-modulus relation, and the strain output compared to the experimental data. The equation previously shown to be most accurate in predicting ulnar strain in neutral forearm rotation was also most accurate in pronation and supination. These results identify this one equation as the most appropriate for future FE analysis of the ulna (including adaptive remodeling, and further show that isotropic and inhomogeneous FE bone models may provide consistent results in different planes of bending.