Dorian Nedelcu

Dorian Nedelcu
Babeş-Bolyai University | UBB · Department of Engineering Sciences

Full Professor PhD

About

92
Publications
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227
Citations

Publications

Publications (92)
Article
Thermoplastic materials have great usage through FDM 3D printing technology. Today, FDM 3D printer is available to the broad population, and some of the thermoplastic materials is widely used due to their small price and availability. Such thermoplastic materials are ABS (Acrylonitrile butadiene styrene) and PLA (Polylactic acid). In this paper the...
Article
Initially developed as a rapid prototyping tool for project visualization and validation, the recent development of additive manufacturing (AM) technologies has led to the transition from rapid prototyping to rapid manufacturing. As a consequence, increased attention has to be paid to the mechanical, chemical and physical properties of the printed...
Article
Full-text available
The characterization of flow through Pelton hydro turbines allows the optimization of their operation and maximization of energy performance. The flow in the injector of Pelton turbines and in the free jet area (the area from the injector outlet surface to the runner bucket inlet surface) is influenced by several parameters: the geometry of injecto...
Conference Paper
Full-text available
Because real beams have non-ideal boundary conditions, it is necessary to use advanced models to determine the real modal parameters. The model proposes imperfect clamping consisting of an open crack at the end of the perfectly fixed beam. We can hence consider a cracked cantilever beam with non-ideal clamping as a beam with a perfectly fastened en...
Article
Full-text available
Non-destructive testing of structures involving vibration-based damage detection methods implies knowing the beam’s boundary conditions. For perfect boundary conditions, numerous damage detection methods are developed and ensure more or less accurate estimation of the crack type, position, and severity. On the contrary, for imperfect boundary condi...
Article
Observing the occurrence of cracks in the early stage remains a challenge, as changes in the modal parameters produced by these cracks are small. This remark is also valid for deeper cracks because in most experiments it is possible to acquire short signals, which ensure a coarse frequency resolution. Therefore, the accurate estimation of frequency...
Chapter
Detecting damage in the early state is crucial in assessing structural integrity. Most current vibration-based damage detection methods use frequency shifts to assess the damage, observed as a change of the positions on which the peaks in the spectrum are located. However, accurate estimation of the natural frequencies can be challenging due to the...
Chapter
In this paper, we present a simple predictive model to estimate the natural frequencies of steel cantilever beams with branched cracks. The model considers the cracked beam as a beam with constant cross-section, on which acts an equivalent bending moment. This bending moment takes into account the modification of the rigidity on the beam segment on...
Article
Full-text available
The paper describes the PyChart module (aimed at analysis and visual view of 2D/3D Charts), which was created with the help of free and Open Source resources, using Python as a programming language and wx.Python as a graphical user interface toolkit. The chart data is imported from a Excel/ CSV file with a template structure and is drawn in the PyC...
Article
Full-text available
We propose in this paper a method to calculate the antiderivative of signals that have the integral close to null, as the signals measured on structures during earthquakes are. The method implies performing a series of numerical integration considering the initial value being zero. Afterward, the average value for the primitive function is calculat...
Article
Full-text available
Detecting damage in the incipient state is of crucial importance in monitoring the health of engineering structures. Approaching damage detection as an inverse problem is a common method when vibration-based techniques are used. It implies a precise a priori estimation of the modal parameters. We present in this paper a model to predict the frequen...
Article
Full-text available
Detecting damage by using vibration signals is popular because it permits evaluating the structural integrity without being necessary scanning of the whole structure. The effect of transverse cracks is presented in detail in the literature, but in reality, the cracks can shift the direction of propagation and even split, resulting in the so-called...
Article
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Beginning with the last century, visionaries and researches from all over the world have invested o lot of energy and time in the development of various drives for generating propulsion force. The present paper is dedicated to the kinematic and dynamic investigation of an inertial propulsion drive using the facilities of the Motion module from Soli...
Article
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We introduce in this paper an application developed in the Python programming language that can be used to generate digital signals with known frequencies and amplitudes. These digital signals, since have known parameters, can be used to create benchmarks for test and numerical simulation.
Article
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We propose a continuous model for rectangular plates that involves a mesh of slender interconnected beams. These beams are disposed orthogonally. The advantage of this model is that simple equations are involved and the behavior of the plate is accurately described. After a brief description of the model, we present an application written in the Py...
Article
Full-text available
Starting with the last century, a lot of enthusiastic researchers have invested significant time and energy in proposing various drives capable to generate linear propulsion force. Regrettably, only a few of these devices passed the patent phase and have been practically materialized. The aim of this paper was to simulate the dynamic behavior of an...
Article
Full-text available
The present paper is dedicated to the investigation of the kinematic and dynamic behavior of an inertial propulsion system, using rotating masses. The analytical results were compared with the results of a simulation using the SolidWorks Motion software. The following elements were considered: positional analysis, kinematic analysis of velocities a...
Preprint
Full-text available
The paper describes the PyChart module (aimed at analysis and visual view of 2D/3D Charts), which was created with the help of free and Open Source resources, using Python as a programming language and wx.Python as a graphical user interface toolkit. The chart data is imported from a Excel/ CSV file with a template structure and is drawn in the PyC...
Article
Full-text available
The paper describes the PyChart module (aimed at analysis and visual view of 2D/3D Charts), which was created with the help of free and Open Source resources, using Python as a programming language and wx.Python as a graphical user interface toolkit. The chart data is imported from a Excel/CSV file with a template structure and is drawn in the PyCh...
Article
Full-text available
We propose herein a mathematical relation to calculate the severity of transverse cracks which affect a prismatic beam. It is known that the damage severity depends on the depth of the crack located at the slice on which the biggest bending moment is achieved. The frequency drop due to this crack is proportional to the severity associated with it....
Article
Full-text available
We propose in this paper a mathematical relationship to calculate the natural frequency shifts of beams due to multiple cracks. The relationship is based on the application of the superposition principle. A crack alters the frequencies for the bending vibration modes in a particular manner, with respect to the crack depth and location. We have show...
Article
Full-text available
The objective of the paper is to apply the reverse engineering in the mechanical field to reconstruct the geometry of two types of model turbine blade: axial blade and Pelton bucket. To generate the point clouds, the geometry of the blades was scanned by laser and digital photogrammetry. The Creaform HandySCAN 700 laser scanner and VXelements softw...
Article
Full-text available
The objective of the paper is to calculate the kinematic and dynamic behaviour of the shaker mechanism and compare the theoretical with the following SolidWorks Motion results: the positional analysis, kinematic analysis of velocities, kinematic analysis of accelerations and kinetostatic analysis.
Article
This paper describes a hip implant model designed to assess the Fused Deposition Modeling (FDM) process for manufacturing investment casting master patterns. In addition, an indirect approach toward manufacturing master pattern via silicone rubber moulding in conjunction with 3D Printing process manufactured hip implant master pattern has been inve...
Article
Full-text available
The objective of the paper is to calculate the velocities and accelerations for some points of the punching cards mechanism and to compare the results calculated through grapho-analytical method with the SolidWorks Motion results
Conference Paper
Full-text available
Using interpolation methods to find the true harmonic component of a signal on an inter-line position in the spectrum is a usual practice in frequency estimation. The disadvantage of this method is that the points on which the interpolation is made have to be on the main lobe. Most researchers consider the maximizer and its biggest neighbor to sati...
Conference Paper
Full-text available
In this paper we present a direct method to determine the harmonic components of a signal. The method bases on the fact that the distribution of the samples in the spectrum derived with the Discrete Fourier Transform (DFT) follow the sinc function. We found a correction term that places the estimated frequency on an inter-line position. Therefore,...
Conference Paper
Full-text available
The retrieval of information from historical analogical records is essential for the study of the seismic activity and of the seismic danger in the vulnerable areas during the earthquake. This is possible due to modern techniques and methods of processing and converting analog data into digital data. This paper presents a method of the digitization...
Conference Paper
Full-text available
In the current paper we aim to evaluate the accuracy of a previously developed method to determine the frequency drop of a cantilever beam having an L-shaped damage with a well-defined position and size. The method is based on the fact that the deformation energy lost by reducing a section of the beam is proportional to the deflection of the same b...
Article
Full-text available
The retrieval and storage of information from historical earthquake records are very important for the study of seismic activity and the prevention of the danger that earthquakes represent in areas with intense seismic activity. This is possible due to modern techniques and methods of processing, converting old data into digital data and storing th...
Article
Full-text available
Photogrammetry is the technique used to convert a real geometry of a part into a 3D computer file starting from images. The paper aims to compare some free and commercial application packages used in Photogrammetry, based on the same images taken from an axial turbine blade. The blade geometry can be included in a bounding box with the following di...
Article
Full-text available
In the context of actual production, more and more adapted to the principles of Industry 4.0, the machines have to interact with other machines and with persons, and transmit in real time information that is processed and used to manage the production chains. The most important challenge is to make the machines working whit low or without human int...
Article
Full-text available
Hydraulic turbine components that define the water flow, generally have a complex geometry. In the design of these components a major role is played by model tests. The complex geometry of runner�s blades and wicked gates determines high manufacturing times and high fabrication cost if they are made by classical manufacturing technologies (casting,...
Article
Full-text available
The Reverse Engineering is a reliable technique to convert a real geometry of a part into 3D computer file. One reason for scanning a part may be the lack of the drawings to manufacture a new one that will replace the old part. The paper illustrates the Reverse Engineering of a Francis runner geometry with a diameter of 1160 mm and 19 blades, which...
Article
Full-text available
In the paper are presented two seismic isolation systems. One is classic, made out of two rubber plates, with a metallic plate vulcanized between the two. For fastening, the isolator has another two clamping plates vulcanized on it. The proposed model has same components as the classical one, having on top and under, attached to the rubber, two thi...
Article
Full-text available
The HydroHillChart software is a complex one used to calculate the hill chart for hydraulic turbines. The application was developed in the Python programming language, while the mathematical tool used for interpolation is the cubic spline type function. The paper presents the HydroHillChart - Kaplan module application, used to calculate the hill ch...
Article
Full-text available
The study presented in this paper shows the results of simulation made on a rigid structure isolated with four simple friction pendulums. We created a model in SolidWorks that was used to find out how the pendulums radii and friction coefficients respectively the frequency of the excitation influences the structural response. It has also been found...
Article
Full-text available
The paper presents the comparative analysis of two types of welded structures used in railway bridges. The differences between the two types of structures are given by the configuration of welded joints (HEM profiles are used for both structures). Constructive and technological analysis made for each structure are presented, highlighting the differ...
Article
Full-text available
The paper presents a constructive solution for the metallic structure of a city railway bridge, with pedestrian area. The structure made of HEM beams has a modular design in order to facilitate the transport and in-situ assembling. The results obtained from static, dynamic and fatigue analyses are presented. Static analysis highlights areas with ma...
Article
Full-text available
This paper presents simulations that highlight the influence of the friction pendulum radius on the behavior of isolated structures. A model was created in SolidWorks, which is employed to find out the structural response. The excitation in term of displacements, ensured by a feature of the software program, follows a sine function. The study has s...
Article
Full-text available
The paper presents a study regarding the effect of the simple friction pendulum radius on the behavior of isolated structures equipped with this kind of device. A model created in SolidWorks is employed in the research to find out the structural behavior. The excitation, ensured by a simulated shaking table, follows a harmonic displacement. The stu...
Conference Paper
Full-text available
The paper presents a mathematical relation to express the effects of a T-shaped crack on beam-like structures. The study is performed by using the finite element method (FEM) and contrived analytical formulas for proving the existing correlation between deflection, strain energy, and natural frequency changes. The damaged beam static and dynamic be...
Article
Full-text available
The paper presents a procedure to precisely estimate the natural frequencies of structures. It implies the acoustic excitation of the structure and the evaluation of the frequencies from the response signals, involving an advanced method developed by the authors. The study is performed on a cantilever beam. To demonstrate the efficiency of the cont...
Article
Full-text available
This paper presents simulations that highlight the influence of the friction pendulum radius on the behavior of isolated structures. A model was created in SolidWorks, which is employed to find out the structural response. The excitation in term of displacements, ensured by a feature of the software program, follows a sine function. The study has s...
Article
Full-text available
For a blade runner of a Kaplan turbine, with its 3D geometry obtained through the Photogrammetry technique, the paper aims to determine the following geometric parameters of the blade profile: the stagger angle, the chord length, the relative thickness (maximum thickness / chord length) and relative thickness position, the relative maximum camber a...
Article
Full-text available
The paper illustrates the reverse engineering process of a blade, from a Kaplan runner with a diameter of 5400 mm, using the following software packages: Agisoft Photoscan and Geomagic Design X (formerly Rapidform XOR); the next step was to generate the solid geometry of the blade using the SolidWorks software. The last step was to compare, using G...
Article
Full-text available
This study aims to present the general aspects of the speed increaser gearboxes. The second part of this study will focus on the identification of the possibility to replace the special materials used for gearing execution of the speed increaser gearboxes with materials having inferior mechanical characteristics. Gearing execution from 18CrNiMo7-6...
Article
Full-text available
The Pelton turbines convert hydraulic energy into mechanical energy, through the Pelton runner, by using high heads and small discharges. The runner has a complex geometry, described in drawings by transversal and longitudinal sections that form continuous surfaces. The SolidWorks software was used to design two Pelton runners: the R1 runner with 2...
Article
Engineers think twice before using plastic bearings in their designs, because they have trusted steel bearings for years or because they think plastic can't handle demanding applications or environments. Plastic bearings can endure extreme temperatures, heavy loads and high speeds and offer more freedom when it comes to maintenance. Their resistanc...
Article
The paper presents a method developed and used by the CCHAPT researchers for the graphic plotting of the index tests results for hydraulic turbines, the comparison of the efficiency curves resulted from testing to those obtained by the model transposition [1] i.e. the determination and comparison of the existing combinatory cam with that obtained f...
Article
Full-text available
The manufacturing of hydraulic turbine runners designed for experimental research on the model is carried out, usually, by precision casting or CNC machining. These processes involve technological difficulties, high manufacturing times and high production costs, which are generated by the complex geometry and the small dimensions of the runner. Rap...
Article
Full-text available
During the testing of the materials’ cavitation erosion resistance on vibratory systems by direct method (ASTM G32), the thread from the ultrasonic horn – test specimen connection, is subjected to fatigue. Operational experience has shown the occurrence of cracks and fractures in this area after a number of stress cycles that was lower than anticip...
Article
The paper presents the possibilities to apply Numerical Simulation and Additive Manufacturing (AM) technology in designing the prototypes of master patterns of knee implants for investment casting. The master pattern manufacturing by wax injection is the starting operation in the investment casting procedure. Errors caused by shrinkage, air traps a...