Nicolae Constantin

Extraction of dispersion curves for waves propagating in free complex waveguides by standard finite element codes.

This paper presents a fast and reliable method, for obtaining all the range of dispersion curves for wave propagation usually used in practice, by numerical simulation only, via common commercial finite element codes. Essentially, the method is based on a simple and robust approach, consisting in a few series of modal analyses for a representative part of the inspected structure. In this way, for different wave lengths, one can find the mode shapes and corresponding natural frequencies by solving some real, symmetric and well numerically conditioned eigenvalue problems. The method allows the extraction of propagating modes only and, in spite of not producing continuous dispersion curves, it is not susceptible to aliasing effects, as some similar methods are. Additionally, complete graphical representations of guided waves are possible with some minor calculus effort.

Advanced adaptive techniques for multivariable nonlinear processes

Abstract Neural-network techniques are investigated in an application to the identification and subsequent on-line control of a process exhibiting nonlinearities and typical disturbances. The method proposed consists from a novel identification technique based on extended memory adaptation (EMA) and an efficient implementation of the predictive control based on a nonlinear programming method. An forced circulation evaporator was chosen as a realistic nonlinear case study for the techniques discussed in the paper.

Some Challenges for the Cyber Physical Energy System

Abstract This paper presents some challenges for securing the electric power system and the major vulnerabilities introduced by the increasing complexity of these systems. By integrating computers, communications and control at all levels of production, transmission, distribution, consumption and storage of electrical energy, the vulnerabilities are increased and also the security aspects become more complex. It is also presented a synthesis of the most important security and protection aspects, as well as some directions of action to improve the availability and security of the smart grid. The paper tries to formulate some future directions to develop the next generation of Intelligent Distributed Autonomous power systems considering the connection between PROSUMERS.

Links between Low Velocity Impact Results and the Residual Mechanical Performance of Sandwich Composite Materials

The paper presents results obtained during low velocity impact tests, performed on sandwich materials of different types. The common force history curves are discussed along with the visual inspections, in order to asses, in a first stage, the structural integrity of the materials subjected to this aggressive and hazardous event.

Some Aspects Concerning the Mechanical Characterization versus Manufacturing Technology of Sandwich Composite Materials

The paper presents aspects observed during classic three-point test bending of various sandwich materials. These aspects outline the need to spare special attention to such test, in connection with the particular material and service life conditions it will endorse. Such special care is needed in conditions of scarcity of dedicated standards and some evasive formulations in the existing ones.

Results of Nondestructive Inspection of Layered Composites Using IR Thermography and Ultrasonics

Polymeric layered composites exhibit a variety of damages following in service loading conditions, like delamination, matrix cracking or even fibre breaking. Detection of such damages and assessing their extension and severity is vital during maintenance cycle, in view of keeping the normal operational reliability. For local inspections, IR thermography and ultrasonic scanning are among the best valued NDT methods. The paper describes the inspections performed by IR active thermography, in different variants, and pulse-echo ultrasonic scanning on GFRP. A variety of layered composites and defects/damages were inspected and the results are evaluated independently, in some cases being compared each other, with valuable conclusions for the users of the mentioned NDI techniques.

Linking the Impact Force History with Residual Mechanical Characteristics and NDI - A Smart Way to Perform SHM in Composites

Structural integrity monitoring (SHM) and evaluation of residual mechanical performance are highly needed in assessing the post-impact behaviour of composite materials and structures. The link between impact force history and the damage level was not followed enough in research studies upon the SHM of composites. The authors put in evidence a clear link in this matter in a variety of layered composite materials. The link was assessed by evaluating the residual mechanical performance and by nondestructive inspection (NDI) – ultrasonics and infrared thermography (IRT) - on the impacted samples. Such a link may prove a very useful and reliable shortcut for backing the online SHM and condition based maintenance.

Adaptive Predictive Control Based on Neural Networks

Abstract Predictive techniques based on neural networks are investigated in an adaptive structure for on-line control of a process exhibiting nonlinearities and typical disturbances. The method proposed consists of a novel identification technique based on extended memory adaptation (BMA) and an efficient implementation of the predictive control based on a nonlinear programming method. A forced circulation evaporator was chosen as a realistic nonlinear case study for the techniques discussed in the paper.

SHM of a Small Wind Turbine Unit by Assessment of Vibration Behavior

Small wind turbines are generally supplying green energy for individual consumers, in more or less isolated locations. This fact creates the need to combine simplicity and efficiency of design with reliable running and easy exploitation. The paper presents effective and affordable ways meant to avoid or detect dangerous vibrations of the quite complex structure of a wind turbine unit, incorporating the runner, the turning platform and the supporting tower, the last structural element also housing solar panels and water tanks.

Study upon the Damage Tolerance of Thick Sandwich Materials

Sandwich composite materials are widely used in various applications, due to their advanced flexibility in responding to special design requirements. This paper presents the evaluation of thick sandwiches, aimed to be imbedded in platforms of a green energy unit, accommodating storage water tanks. The evaluation of the damage tolerance was made having in view previous studies on similar materials and covered assessment of results obtained during low velocity impact tests and post-impact tests, aimed to establish the residual mechanical performance. Ways to increase the damage tolerance, by diminishing the invasive effect of low velocity impact, were also explored.