Zeno-Iosif PRAISACH


32-57 DESPRE MODIFICAREA FRECVENŢELOR NATURALE ALE GRINZILOR DATORITĂ COROZIUNII

ON THE NATURAL FREQUENCY CHANGES OF

BEAMS DUE TO CORROSION

 

This paper presents a relation to be used for deriving the effect of mass loss on the natural frequencies of beams. Herein the stiffness decrease is not considered, since its effect on the natural frequencies is well-known. Consequently, the beam was considered with a constant cross-section but with reduced volumetric mass density in the corroded region. By this approach, we have first analytically studied the beam dynamics from an energetic point of view and contrived the mathematical relation. Afterwards, this relation was successfully tested against FEM simulations.

 

Keywords: beam, corrosion, vibration, natural frequencies, mode shape

Cuvinte cheie: grindă, coroziune, vibraţii, frecvenţe naturale, formă modală

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29-73 SUPRAFEŢE NEUTRE PENTRU DISCULUI BIPLAN AL VANEI FLUTURE

NEUTRAL SURFACES FOR BUTTERFLY VALVE BIPLAN DISK
Due to the eccentricities of the biplane disc of the butterfly valve, the
analysis of the directional stresses can be done by using the numerical
methods. The paper presents the neutral surfaces of butterfly valve biplane disc
obtained by numerical methods. The neutral surfaces are defined as surfaces
with directional stress of zero value or, those surfaces which delimit the passing
of the directional stresses from negative values to positive values.
Keywords: neutral surfaces, butterfly valve disc, tensions
Cuvinte cheie: suprafeţe neutre, disc vană fluture, tensiuni

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27-50 OPTIMIZAREA FORMEI DISCULUI VANEI FLUTURE CU COEFICIENT DE REZISTENȚĂ HIDRAULICĂ DE 0,07

BUTTERFLY VALVE DISC SHAPE OPTIMISATION FOR HYDRAULIC RESISTANCE COEFFICIENT 0.07
The paper presents the optimization of butterfly valve disc shape to obtain hydraulic resistance coefficient 0.07 by numerical methods and by experimental measurements realized in Hydro-Engineering Co. Reşiţa. It is presented the test stand, the optimized butterfly valve disc model which measurements were made and the results of model tests. The results of model tests conducted by similarity criterion for butterfly valve with nominal diameter 4900 mm and nominal pressure of 170 mwc consists of determining the hydraulic resistance coefficient and consequently the flow coefficient and the determination of forces and moment coefficients, the coefficient of cavitation and vibration level.
Keywords: disc butterfly valve, hydraulic resistance coefficient, numerical analysis
Cuvinte cheie: disc vană fluture, coeficient de rezistență hidraulică, analiză numerică

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25-64 STUDIUL COMPORTĂRII DINAMICE A STÂLPILOR CU DIFERITE NIVELE DE ÎNCĂRCARE

A STUDY REGARDING THE DYNAMIC BEHAVIOR OF
COLUMNS SUBJECTED TO DIFFERENT TIP MASSES
The present study aims to highlight the effect of a tip mass upon the
behavior of columns. We have first analytically determined, for a specific
column, the critical buckling force to find the range in which it works in the
elastic domain. Afterwards, by means of numerical simulations, we performed
analysis regarding the influence of loads due to different additional masses and
have identified the effect upon the natural frequencies and modal shapes,
concluding that the higher the mode number, the higher the influence.
Keywords: column, buckling, natural frequency, simulation
Cuvinte cheie: stâlp, flambaj, frecvenţe proprii, simulare
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25-63 EFECTUL DEFECTELOR STRUCTURALE ASUPRA COMPORTAMENTULUI DINAMIC AL GRINZILOR COMPOZITE STRATIFICATE

EFFECT OF STRUCTURAL DAMAGES ON THE DYNAMIC
BEHAVIOUR OF LAMINATED BEAMS
This paper presents results obtained by modal analysis on composite
beam-like structures in healthy and damaged state. The aim is to obtain
damage “signatures” for all possible damage scenarios and to use these data
to assess transversal cracks based on vibration techniques, by involving natural
frequency shifts. The analysis was performed in SolidWorks software for a fivelayer
composite, 30 vibration modes being obtained by numerical simulations.
An example how to interpret the results is shown in the last section of the
paper.
Keywords: damage, finite elements, frequency, simulation, structure
Cuvinte cheie: defect, elemente finite, frecvenţă, simulare, structură
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19-90 DETERMINAREA GRAFO-ANALITICĂ PE BAZA FRECVENŢEI PROPRII A ADÂNCIMII DEFECTULUI LA BARE ÎNCASTRATE

GRAPHIC-ANALYTICAL METHOD FOR DAMAGE DEPTH
DETERMINATION BASED ON NATURAL FREQUENCIES
AT CANTILEVER BEAM
The paper presents research results of authors in determining of the
damage depth for a cantilever beams by using natural frequencies. A graphicanalytical
method is proposed which permit to evaluate the damage depth and
localize the position of the damage on the beam length. The method is based
on results obtained from the numerical modal analysis for the first ten modes of
vibration. Experimental tests have confirmed the method and the results have
application in non-destructive examination based on vibration analysis.
Keywords: natural frequencies, defect, depth, bar mixer
Cuvinte cheie: frecvenţe proprii, defect, adâncime, bară încastrată

90 DETERMINAREA GRAFO-ANALITICĂ PE BAZA


19-97 LOCALIZAREA DEFECTULUI ÎN BARE ÎNCASTRATE UTILIZÂND INDICELE ABATERII RELATIVE A FRECVENŢELOR PROPRII

LOCALIZATION OF DAMAGE IN CANTILEVER BEAMS USING
THE RELATIVE SHIFT IN NATURAL FREQUENCIES
This paper presents a method to locate the damages in cantilever
beams based on relative shift in natural frequencies. This method takes in to
account the particular manner in which the natural frequencies of the first then
modes change due to the occurrence of damage. The measured frequencies
changes are a compared with values contained in a databases, determined on
models using the finite element method. For these databases we consider a
large number of damages locations. By comparing the changes in frequencies
obtained trough measurements with those determined on models, for the first
ten vibration modes, it was possible to locate damages with high accuracy.
Keywords: vibration, bar mixer, frequencies, detecting defects
Cuvinte cheie: vibraţii, bară încastrată, frecvenţe proprii, detectarea
defectelor

97 LOCALIZAREA DEFECTULUI ÎN BARE ÎNCASTRATE


23-62 DETERMINAREA FRECVENŢELOR PROPRII ALE BARELOR COTITE

DETERMINING THE NATURAL FREQUENCIES
OF BENDED BEAMS
This paper presents the natural frequencies obtained from modal
analysis, performed with ANSYS software, for the first 60 vibration modes of a
bended bar (L shape) without defect and with defects situated on three different
locations along the column. The research was made in order to highlight the
changes of the structure’s dynamic behaviour in terms of natural frequencies.
Cuvinte cheie: frecvenţe proprii, bara cotită, detectarea defectelor, simulare
Keywords: natural frequencies, bended beam, damage detection, simulation

23-62 DETERMINAREA FRECVENŢELOR PROPRII

 


23-76 CONSIDERAŢII PRIVIND EFECTELE COROZIUNII ASUPRA COMPORTAMENTULUI DINAMIC AL GRINZILOR

CONSIDERATIONS REGARDING CORROSION EFFECTS
ON BEAMS DYNAMIC BEHAVIOR
Negative effects caused by corrosion are significant, both economically
and in terms of public safety, so incipient detection of corroded areas is
necessary to take in real-time measures to prevent the occurrence of
dangerous situations. This paper presents types of corrosion and various actual
methods used to detect corroded areas together with a new approach in
damage detection based on vibration measurements. While the proposed
method base on frequency changes, to understand the dynamic behaviour of
beams subjected to corrosion is a first step. It permits establishing appropriate
mathematical models and development of damage detection methods implying
the monitoring and analyzes of beams natural frequencies.
Cuvinte cheie: coroziune, detectarea defectelor, frecvenţe proprii
Keywords: corrosion, damage detection, natural frequency

23-76 CONSIDERAŢII PRIVIND EFECTELE COROZIUNII