stan pietrzko

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Mahmoud Farag

American University in Cairo

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UNL - New University of Lisbon

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Universitas Gadjah Mada (Yogyakarta)

Athanasios Ι. Margaris

University of Thessaly

naveen noronha

Visvesvaraya Technological University

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Independent University, Bangladesh

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University of Johannesburg, South Africa

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University of Indonesia

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University of Lorraine

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The University of Texas at Austin

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Papers by stan pietrzko

Modeling the functional performance of plasma polymerized thin films

Thin Solid Films, 1999

ABSTRACT Plasma polymerized thin films are of increasing importance in the field of transparent p... more ABSTRACT Plasma polymerized thin films are of increasing importance in the field of transparent packaging. In particular, hydrocarbon coatings prepared by the reactive magnetron sputtering method combined with plasma-stimulated gas-phase polymerization have proved to have excellent diffusion barrier properties for gases and water vapor. However, the non-linear relationship between stretch failure and permeation properties poses a challenge when it comes to modeling the functional coatings to meet the required product specifications. An improvement in the functionality of these films has been achieved using the general regression neural network GRNN. The method employs the input parameters of the coating such as gas flow, pressure and process time. To improve the prediction performance the training input and output vectors were linearily transformed into the space defined by the principal components of the given training data. The degree of the polymer-like phase in the carbon network and its effect on the functional performance has been studied using a combination of spectroscopic methodology and functional testing. In conclusion, it can be stated that modeling of plasma processes according to the film characteristics makes possible a more controlled and systematic production of thin films.

Modal Investigation of an Office Building Floor

Procedures and results of an experimental and analytical Modal investigation performed on an 8.6 ... more Procedures and results of an experimental and analytical Modal investigation performed on an 8.6 x 25.8 m office building floor are presented. This floor is part of a lightweight steel construction added inside of an existing 8 m high large steel frame building at an intermediate level of roughly 4 m. Complaints of people working in the new office of unacceptable floor vibrations induced by other people walking from their desk to the copying or fax machine were the reason for this investigation. To identify the problem a preliminary test was performed. The floor vibrations were measured with a minimum instrumentation, i.e. two accelerometers, and data processing was performed on site with a two-channel frequency analyzer. One main result was that the maximum acceleration amplitude was a ≈ 0.25...0.30 m/s 2 and hence roughly ten times higher than acceptable as e.g. indicated in [1]. Furthermore, the lowest two natural frequencies of the floor were identified to f 1 ≈ 4.15 Hz and f 2 ≈ 5.90 Hz. This meant that the floor was excited by the second and third harmonics of a walking person's step frequency, f ≈ 2 Hz [2].

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Modal Analysis of a Concrete Gravity Dam: Experiment, Finite Element Analysis and Link

Proceedings of SPIE - The International Society for Optical Engineering

Within the framework of EMPA research activities on experimental modal analysis applied to civil ... more Within the framework of EMPA research activities on experimental modal analysis applied to civil engineering structures the “Vleux Emosson” concrete gravity dam In the Canton Valais has been lnvestlgated in summer 1992. The aim of this projeti was firstly to gain experience wfth modal testing techniques applied to large dams. A randomly driven servohydraullc vlbratlon generator was used as an exciter and the dam response was measured as acceleration at 53 points In three dlrectlons. Subsequently, the modal parameters such as natural frequencies, damping and mode shapes were determined. Secondly. an attempt was undertaken to update a FInhe Element model of the structure taking the experimental results Into account by using the Link-Procedures. The study shows that experlmentally supported FE model optlmlratlon is possible with reasonable effort and good accuracy. The latter can be further Improved by taking the well known structure/solVreservolr-InteractIon effects Into accoullt.

Transformation of a Damped Mechanical System into Lumped-mass Chain-like Tridiagonal System

Proceedings of SPIE - The International Society for Optical Engineering

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Eine auf Simulationsverfahren basierende Fluglärmprognose

Im folgenden Artikel wird ein Verfahren vorgestellt, welches die Simulation der Fluglarmbelastung... more Im folgenden Artikel wird ein Verfahren vorgestellt, welches die Simulation der Fluglarmbelastung durch Dusenflugzeuge in der Umgebung eines Flugplatzes ermoglicht. Das Verfahren basiert auf einer analytischen Beschreibung der Richtungscharakteristiken der Flugzeuge. Die Richtungscharakteristiken wurden durch gleichzeitiges Messen der Flugbahngeometrie und des zeitlichen Verlaufs des Larmpegels ermittelt. Basierend auf diesen Messdaten wurde ein mathematisches Modell der Richtungscharakteristiken aufgebaut. Dieses Modell in Form von trigonometrischen Polynomen berucksichtigt auch die geometrische und atmospharische Dampfung. Aufgrund der Richtungscharakteristik eines Flugzeugs kann der zeitliche Verlauf des Schallpegels an einem beliebigen Immissionsort wieder erzeugt werden. Dies erlaubt die Berechnungen von zeitintegrierten Larmbelastungsindizes wie Leq oder SEL. Durch energetische Addition der entsprechenden Indizes erhalt man eine globale Fluglarmbelastung fur samtliche betrachteten Flugbewegungen.

Modal Testing of a Gravity Dam-Influence of the Exciter Placement on the Quality of the Identified Modal Parameters

Proceedings of SPIE - The International Society for Optical Engineering

It is possible to test a mechanical system consisting of dam-foundation-sediment-water in situ as... more It is possible to test a mechanical system consisting of dam-foundation-sediment-water in situ as a black-box system by employing the measurement data of the acceleration response of the dam to some force excitation signal, with no assumption being made as to the form of the possible differential equations. When the goal of testing is the construction of a mathematical model (modal model) of the dynamics of the dam, then the residuals of the driving point (point of collocating excitation and response) frequency response function are necessary in scaling the entire modal model. The accuracy' in establishing these residues determines the accuracy of the modal parameters. The quality of the driving point frequency response functions depends strongly on the estimate of frequency response function employed, excitation signal and above all on the suitable location of excitation. In this paper we concentrate on the choice of excitation point for the modal testing of a gravity dam. A comparison of two models of the Vieux Emosson Dam in Switzerland obtained by excitation at two different points is presented and discussed. Included is a discussion of how to select a suitable excitation point for the modal testing of a gravity dam.

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Traffic Response of a Bridge as Predicted from Modal-test Data

Proceedings of SPIE - The International Society for Optical Engineering

Neural Network Modeling of Plasma Processes

Note: Editors W. Muster and K. Schlapfer. Reference LCAV-CHAPTER-2005-013 Record created on 2005-... more

A Sensitivity Based Method for the Identification the Viscous Damping Matrix of a Lumped-mass Mechanical System

Proceedings of SPIE - The International Society for Optical Engineering

In the present work, a new method to identify a viscous damping matrix D for linear time-invarian... more In the present work, a new method to identify a viscous damping matrix D for linear time-invariant mechanical systems is presented and developed as an identification procedure. This procedure is based on the equation of the test model in the form Mz(t) + Di(t) + Kz(t) = f(t) with symmetrical system parameter matrices (M,D,K). It is assumed that the mass matrix M and the stiffness matrix K are determined. Characteristic for this procedure for damping identification is the use of a frequency response function without anti-resonance frequency (transmissibility frequency response function). This is measured on the mechanical system which is to be identified. If the transmissibility frequency response function exists, then it is possible to model the dynamic properties of the system with a substitution model in the form of a chain-like lumped-mass, damped, multi-degree of freedom vibration system. The proposed procedure is based on a series of relationships between the imaginary part of the inverse of the transmissibility frequency response function and the damper of the substitution model (the elements of the damping matrix of the model). Based on these relationships, a matrix equation is developed as a measure of the sensitivity of the inverse transmissibility frequency response function to a change of the damping coefficient of the substitution model at different frequencies. The solution of this sensitivity equation explicitly yields the coefficients of the damping matrix of a substitution model. A numerical example is provided to verify this concept.

Vibroacoustical modeling and modal analysis of a double wall panel

The Journal of the Acoustical Society of America, 1998

ABSTRACT

Modeling the functional performance of plasma polymerized thin films

Thin Solid Films, 1999