Paolo Neri

Robot Assisted Modal Analysis on a Stationary Bladed Wheel

This paper shows an automated procedure to experimentally find the eigenmodes of a bladed wheel with highly three-dimensional geometry. The stationary wheel is supported in free-free conditions, neglecting stress-stiffening effects. The single input / multiple output approach was followed. The vibration speed was measured by means of a laser-Doppler vibrometer, and an anthropomorphic robot was used for accurate orientation and positioning of the measuring laser beam, allowing multiple measurements during a limited testing time. The vibration at corresponding points on each blade was measured and the data elaborated in order to find the initial (lower frequency) modes. These modal shapes were then compared to finite element simulations and accurate frequency matching and exact number of nodal diameters obtained. Being the modes cyclically harmonic, the complex formulation could be attractive, being not affected by the angular phase of the mode representation. Nevertheless, stationary modes were experimentally detected, rather than rotating, and then the real representation was necessary. The discrete Fourier transform of the blade displacements easily allowed to find both the angular phase and the correct number of nodal diameters. Successful MAC experimental to analytical comparison was finally obtained with the real representation after introducing the proper angular phase for each mode.© 2014 ASME

Excitation device for high frequency vibration analysis: Design and test results

In the present paper, the design and optimization of a high frequency excitation source is presented. The device was developed for a harmonic response analysis test bench, aimed at dynamic characterization and resonance prediction of mechanical structures. A wide frequency range must be covered, depending on the analyzed structure: the range 1–10 kHz was considered in the present work. The device was designed for a test bench aimed at investigating the vibrational response of centrifugal compressor bladed wheels. A really compact solution was needed since the final test bench provides one exciter for each blade (up to 20 devices on the circumference hoop). Both contact and contactless solutions were considered, but only the contact solution was found to fulfill all the specifications. Finally, different stinger solutions were proposed and compared in the paper. The investigated solutions were: a beam stinger (diameter 1 mm); a wire stinger (diameter 0.2 mm); and a ball stinger (diameter 3 mm) with two different support solutions. Experimental tests performed on a device prototype allowed to verify the specifications fulfillment and to choose the best stinger solution for the application.

A Ship Motion Short Term Time Domain Simulator And Its Application To Costa Concordia Emergency Manoeuvres Just Before The January 2012 Accident.

In this paper we will present a simple but reliable methodology for short term prediction of a cruise ship behaviour during manoeuvres. The methodology is quite general and could be applied to any kind of ship, because it does not require the prior knowledge of any structural or mechanical parameter of the ship. It is based only on the results of manoeuvrability data contained in the Manoeuvring Booklet, which in turn is filled out after sea trials of the ship performed before his delivery to the owner. We developed this method to support the investigations around the Costa Concordia shipwreck, which happened near the shores of Italy in January 2012. It was then validated against the data recorded in the “black box” of the ship, from which we have been able to extract an entire week of voyage data before the shipwreck. The aim was investigating the possibility of avoiding the impact by performing an evasive manoeuvre (as ordered by the Captain some seconds before the impact, but allegedly misunderstood by the helmsman). The preliminary validation step showed a good matching between simulated and real values (course and heading of the ship) for a time interval of a few minutes. The fact that the method requires only the results registered in the VDR (Voyage Data Recorder) during sea trial tests, makes it very useful for several applications. Among them, we can cite forensic investigation, the development of components for autopilots, the prediction of the effects of a given manoeuvre in shallow water, the “a posteriori” verification of the correctness of a given manoeuvre and the use in training simulators for ship pilots and masters.

An Omnidirectional Vision Sensor Based on a Spherical Mirror Catadioptric System

The combination of mirrors and lenses, which defines a catadioptric sensor, is widely used in the computer vision field. The definition of a catadioptric sensors is based on three main features: hardware setup, projection modelling and calibration process. In this paper, a complete description of these aspects is given for an omnidirectional sensor based on a spherical mirror. The projection model of a catadioptric system can be described by the forward projection task (FP, from 3D scene point to 2D pixel coordinates) and backward projection task (BP, from 2D coordinates to 3D direction of the incident light). The forward projection of non-central catadioptric vision systems, typically obtained by using curved mirrors, is usually modelled by using a central approximation and/or by adopting iterative approaches. In this paper, an analytical closed-form solution to compute both forward and backward projection for a non-central catadioptric system with a spherical mirror is presented. In particular, the forward projection is reduced to a 4th order polynomial by determining the reflection point on the mirror surface through the intersection between a sphere and an ellipse. A matrix format of the implemented models, suitable for fast point clouds handling, is also described. A robust calibration procedure is also proposed and applied to calibrate a catadioptric sensor by determining the mirror radius and center with respect to the camera.

Design and manufacturing of patient-specific orthodontic appliances by computer-aided engineering techniques

Orthodontic treatments are usually performed using fixed brackets or removable oral appliances, which are traditionally made from alginate impressions and wax registrations. Among removable devices, eruption guidance appliances are used for early orthodontic treatments in order to intercept and prevent malocclusion problems. Commercially available eruption guidance appliances, however, are symmetric devices produced using a few standard sizes. For this reason, they are not able to meet all the specific patient’s needs since the actual dental anatomies present various geometries and asymmetric conditions. In this article, a computer-aided design-based methodology for the design and manufacturing of a patient-specific eruption guidance appliances is presented. The proposed approach is based on the digitalization of several steps of the overall process: from the digital reconstruction of patients’ anatomies to the manufacturing of customized appliances. A finite element model has been developed to evaluate the temporomandibular joint disks stress level caused by using symmetric eruption guidance appliances with different teeth misalignment conditions. The developed model can then be used to guide the design of a patient-specific appliance with the aim at reducing the patient discomfort. At this purpose, two different customization levels are proposed in order to face both arches and single tooth misalignment issues. A low-cost manufacturing process, based on an additive manufacturing technique, is finally presented and discussed.

Mechanical and Geometrical Properties Assessment of Thermoplastic Materials for Biomedical Application

Clear thermoplastic aligners are nowadays widely used in orthodontics for the correction of malocclusion or teeth misalignment defects. The treatment is virtually designed with a planning software that allows for a definition of a sequence of little movement steps from the initial tooth position to the final desired one. Every single step is transformed into a physical device, the aligner, by the use of a 3D printed model on which a thin foil of plastic material is thermoformed. Manufactured aligners could have inherent limitations such as dimensional instability, low strength, and poor wear resistance. These issues could be associated with material characteristics and/or with the manufacturing processes. The present work aims at the characterization of the manufactured orthodontic devices. Firstly, mechanical properties of different materials have been assessed through a set of tensile tests under different experimental conditions. The tests have the purpose of analyzing the effect that the forming process and the normal use of the aligner may have on mechanical properties of the material. The manufacturing process could also introduce unexpected limitations in the resulting aligners. This would be a critical element to control in order to establish resulting forces on teeth. Several studies show that resulting forces could be greatly influenced by the aligner thickness. A method to easily measure the actual thickness of the manufactured aligner is proposed. The analysis of a number of real cases shows as the thickness is far to be uniform and could vary strongly along the surface of the tooth.

Finite Element Analysis of TMJ Disks Stress Level due to Orthodontic Eruption Guidance Appliances

In the present work, the effect of Eruption Guidance Appliances (EGAs) on TemporoMandibular Joint (TMJ) disks stress level is studied. EGAs are orthodontic appliances used for early orthodontic treatments in order to prevent malocclusion problems. Commercially available EGAs are usually produced by using standard sizes. For this reason, they are not able to meet all the specific needs of each patient. In particular, EGAs are symmetric devices, while patient arches generally present asymmetric conditions. Thus, uneven stress levels may occur in TMJ disks, causing comfort reduction and potential damage to the most solicited disk. On the other hand, a customized EGA could overcome these issues, improving the treatment effectiveness. In this preliminary study, a Finite Element (FE) model was developed to investigate the effects of a symmetric EGA when applied to an asymmetric mouth. Different misalignment conditions were studied to compare the TMJ disks stress levels and to analyze the limitations of a symmetric EGA. The developed FE model can be used to design patient-specific EGAs, which could be manufactured by exploiting non-conventional techniques such as 3D printing.

A Short Term Simulator for Vessel Manoeuvres Prediction

This paper presents a methodology for vessels manoeuvring prediction during navigation. The proposed algorithm allows to estimate future position and heading of the vessel on the basis of present position, velocity, propeller speed and rudder angle. The prediction algorithm, which can be very useful in emergency manoeuvres, uses a short term simulator which has been tuned up and validated in the framework of the Costa Concordia cruise ship trial. However, the methodology could be applied to any kind of ship, since it just requires a set of data recorded during a set of mandatory sea trials performed before the delivery of the ship. The prediction algorithm shows, on the electronic navigation chart, the foreseen position of the ship in the next 30–40 s, provided that helm and power settings remain unchanged, allowing the helmsman to check in advance the effect of the commands and to eventually modify the trajectory.

Interaction force between magnetic field and ferromagnetic target: analytical, numerical and experimental study

In this study, an analytical model and a finite element (FE) model were developed in order to study the force produced by a permanent magnet on a ferromagnetic target. The study was aimed at estimating the magnetic action in order to design an excitation device for vibration tests. The dynamic analysis of rotating structures as compressors’ bladed wheels requires a solicitation that reflects the operational conditions. If the component is made of ferromagnetic material, it is possible to use magnetic fields for the excitation. The present paper reports the interaction between planar parallel surfaces, first studied analytically and numerically, and the results were compared with experimental results. Then the interaction between sloping surfaces was analyzed, allowing an analytical boundary loss model to be developed. Finally, the FE model was improved to study the interaction between double curvature surfaces. A comparison with experimental results measured on an actual bladed wheel was performed.

A Ship Motion Short-Term Time Domain Simulator and Its Application to Costa Concordia Emergency Manoeuvres Just Before the January 2012 Accident

In this chapter, we will present a simple but reliable methodology for short-term prediction of a cruise ship behaviour during manoeuvres. The methodology is quite general and could be applied to any kind of ship, because it does not require the prior knowledge of any structural or mechanical parameter of the ship. It is based only on the results of manoeuvrability data contained in the Manoeuvring Booklet, which in turn is filled out after sea trials of the ship performed before his delivery to the owner. We developed this method to support the investigations around the Costa Concordia shipwreck, which happened near the shores of Italy in January 2012. It was then validated against the data recorded in the “black box” of the ship, from which we have been able to extract an entire week of voyage data before the shipwreck. The aim was investigating the possibility of avoiding the impact by performing an evasive manoeuvre (as ordered by the Captain some seconds before the impact, but allegedly misunderstood by the helmsman). The preliminary validation step showed a good matching between simulated and real values (course and heading of the ship) for a time interval of a few minutes. The fact that the method requires only the results registered in the VDR (Voyage Data Recorder) during sea trial tests, makes it very useful for several applications. Among them, we can cite forensic investigation, the development of components for autopilots, the prediction of the effects of a given manoeuvre in shallow water, the “a posteriori” verification of the correctness of a given manoeuvre and the use in training simulators for ship pilots and masters.