Alessandro Rivola

Automatic Leak Detection in Buried Plastic Pipes of Water Supply Networks by Means of Vibration Measurements

The implementation of strategies for controlling water leaks is essential in order to reduce losses affecting distribution networks of drinking water. This paper focuses on leak detection by using vibration monitoring techniques. The long-term goal is the development of a system for automatic early detection of burst leaks in service pipes. An experimental campaign was started to measure vibrations transmitted along water pipes by real burst leaks occurring in actual water supply networks. The first experimental data were used for assessing the leak detection performance of a prototypal algorithm based on the calculation of the standard deviation of acceleration signals. The experimental campaign is here described and discussed. The proposed algorithm, enhanced by means of proper signal filtering techniques, was successfully tested on all monitored leaks, thus proving effective for leak detection purpose.

A non-linear elastodynamic model of a desmodromic valve train

Abstract A lumped-parameter model of a motorbike engine’s desmodromic valve train is developed for the simulation of the dynamic behaviour of such an uncommon train. The model takes into account several non-linear effects and is highly time-varying. The estimation of the model parameters is discussed and the effectiveness of the model is assessed by a comparison with experimental results. The model is employed to predict the magnitude of forces, impacts and bounces, and to detect unacceptable dynamic phenomena; thus, it may be used as a tool both in design optimization and diagnostics.

Vibroacoustic Measurements for Detecting Water Leaks in Buried Small-Diameter Plastic Pipes

AbstractLeak detection is an essential topic within the policies of water loss management in drinking-water supply networks. This paper reports the results of an experimental campaign performed for...

Preliminary Investigations on Automatic Detection of Leaks in Water Distribution Networks by Means of Vibration Monitoring

The efficiency of water supply networks is an important issue. In order to reduce water losses, policies of leak reduction are essential. The paper deals with a preliminary study on the use of vibration monitoring tools for the detection of leaks in water service pipelines. The long-term project is the development of a system for automatically detecting burst leaks occurring in service pipes. Preliminary experimental tests were performed on both a test rig and an actual service pipe of the water distribution system. Three main objectives were achieved: firstly, the effectiveness of vibration monitoring for leak detection purposes was assessed providing a positive response; then, a prototypal detection procedure was studied, implemented and tested on the preliminary experimental data; finally, the specifications for a prototypal acquisition equipment were also determined. This paper illustrates the experimental campaign and its main results.

Elastodynamic Effects of Mass-Balancing: Experimental Investigation of a Four-Bar Linkage

This paper deals with static balancing of closed-loop mechanisms. The long-term goal of the research is enhancing the performance of parallel robots by means of effective static balancing strategies that take into account the system dynamic behaviour. In this contribution, the influence of mass-balancing on the elastodynamic performance of a four-bar linkage, intended as the simplest example of closed-loop mechanism, is experimentally investigated. The design of the experimental apparatus is discussed and the results of tests on both an unbalanced linkage and its balanced variant are presented. Base-transmitted forces and vibrations are monitored for constant-speed operations and for velocity ramp tests in order to characterize the elastodynamic behaviour of the linkages. The analysis is supported by implementing a flexible multibody model of the experimental apparatus that enhances the interpretation of the experimental data.

Numerical and Experimental Dynamic Analysis of IC Engine Test Beds Equipped with Highly Flexible Couplings

Driveline components connected to internal combustion engines can be critically loaded by dynamic forces due to motion irregularity. In particular, flexible couplings used in engine test rig are usually subjected to high levels of torsional oscillations and time-varying torque. This could lead to premature failure of the test rig. In this work an effective methodology for the estimation of the dynamic behavior of highly flexible couplings in real operational conditions is presented in order to prevent unwanted halts. The methodology addresses a combination of numerical models and experimental measurements. In particular, two mathematical models of the engine test rig were developed: a torsional lumped-parameter model for the estimation of the torsional dynamic behavior in operative conditions and a finite element model for the estimation of the natural frequencies of the coupling. The experimental campaign addressed torsional vibration measurements in order to characterize the driveline dynamic behavior as well as validate the models. The measurements were achieved by a coder-based technique using optical sensors and zebra tapes. Eventually, the validated models were used to evaluate the effect of design modifications of the coupling elements in terms of natural frequencies (torsional and bending), torsional vibration amplitude, and power loss in the couplings.

Static Balancing of a Parallel Kinematics Machine With Linear-Delta Architecture

The study deals with the compensation of gravity loads in closed-loop mechanisms as a possible strategy for enhancing their working performance. This work focuses on the Orthoglide 5-axis, a prototypal parallel robot for milling operation, characterized by linear-delta architecture with two further serial DOFs. Starting from a general theory formerly proposed by the authors, gravity compensation of the mechanism is analytically carried out. The statically balanced Orthoglide 5-axis can be obtained by installing on one leg a proper set of extension springs and a simple additional linkage. A feasible design solution for developing the device in practice is presented. The proposed balancing device can be implemented with minor modifications of the original robot design, thus appearing a profitable solution to be possibly extended to other machinery with similar architecture.Copyright

Displacement measurement on specimens subjected to non-Gaussian random vibrations in fatigue life tests

High-cycle fatigue life tests conducted using controlled random vibrations are commonly used to evaluate failure in components and structures. In most cases, a Gaussian distribution of both the input vibration and the stress response is assumed, while real-life loads may be non-Gaussian causing the response to be non-Gaussian as well. Generating non-Gaussian drive signals with high kurtosis and a given power spectral density, however, does not always guarantee that the stress response will actually be non-Gaussian, because this depends on the adherence of the tested system to the Central Limit Theorem. On the other side, suitable measurement methods need to be developed in order to estimate the stress amplitude response at critical failure locations, and therefore to evaluate and select input loads. In this paper, a simple test rig with a notched cantilevered specimen was developed to measure the response and examine the kurtosis values in the case of stationary Gaussian, stationary non-Gaussian, and non-...

Design Optimization of a Laser Cutting Machine by Elastodynamic Modeling

This study deals with the elastodynamic modeling of a laser cutting machine and illustrates the guidelines followed for the design optimization of the machine’s basic structure from the dynamic behavior point of view. A finite element model was set up along with the conceptual design of the new machine, with the aim of performing dynamic simulations. The main purpose is to predict the vibrations arising in the structure that could significantly deteriorate the product quality in order to evaluate different design solutions. The vibrations can be excited by variable forces acting on the moving masses and by the oscillations affecting the machine basement due to external causes. The original modeling of the excitations is presented herein. Modal analysis and forced simulations were performed on the finite element model of the first conceptual design of the machine structure. The analysis of the results indicated some critical parts of the system to be stiffened in order to mitigate the vibrations, that is to improve the cutting quality. Structural modifications to the first conceptual design were therefore suggested and a new model of the machine was developed and simulated. The results of the simulations before and after the design modifications are reported and discussed.Copyright

Response measurement by laser Doppler vibrometry in vibration qualification tests with non-Gaussian random excitation

In the field of vibration qualification testing, random excitations are typically imposed on the tested system in terms of a power spectral density (PSD) profile. This is the one of the most popular ways to control the shaker or slip table for durability tests. However, these excitations (and the corresponding system responses) exhibit a Gaussian probability distribution, whereas not all real-life excitations are Gaussian, causing the response to be also non-Gaussian. In order to introduce non-Gaussian peaks, a further parameter, i.e., kurtosis, has to be controlled in addition to the PSD. However, depending on the specimen behaviour and input signal characteristics, the use of non-Gaussian excitations with high kurtosis and a given PSD does not automatically imply a non-Gaussian stress response. For an experimental investigation of these coupled features, suitable measurement methods need to be developed in order to estimate the stress amplitude response at critical failure locations and consequently evaluate the input signals most representative for real-life, non-Gaussian excitations. In this paper, a simple test rig with a notched cantilevered specimen was developed to measure the response and examine the kurtosis values in the case of stationary Gaussian, stationary non-Gaussian, and burst non-Gaussian excitation signals. The laser Doppler vibrometry technique was used in this type of test for the first time, in order to estimate the specimen stress amplitude response as proportional to the differential displacement measured at the notch section ends. A method based on the use of measurements using accelerometers to correct for the occasional signal dropouts occurring during the experiment is described. The results demonstrate the ability of the test procedure to evaluate the output signal features and therefore to select the most appropriate input signal for the fatigue test.