Emiliano Mucchi

EXPERIMENTAL VALIDATION OF A MODEL FOR THE DYNAMIC ANALYSIS OF GEAR PUMPS

This paper mainly concerns the experimental validation of an elastodynamic model of an external gear pump for steering systems. The model takes into account the most important phenomena involved in the operation of this kind of machines. Two main sources of noise and vibration can be considered: pressure and gear meshing. An experimental apparatus has been set up for the measurements of the case accelerations and force components in operation conditions. The model was validated by comparison between simulations and experimental results concerning forces and moments: it deals with the external and inertia components acting on the gears, estimated by the model, and the reactions and inertia components on the pump case and the test plate, obtained by measurements. The validation is carried out comparing the level of the time synchronous average in the time domain and the waterfall maps in the frequency domain, with particular attention to identify system resonances. The validation results are globally satisfactory.

Advanced Signal Processing Tools for the Vibratory Surveillance of Assembly Faults in Diesel Engine Cold Tests

This paper addresses the use of several signal processing tools for monitoring and diagnosis of assembly faults in diesel engines through the cold test technology. One specific fault is considered here as an example: connecting rod with incorrectly tightened screws. First, the experimental apparatus concerning the vibration tests is introduced. Subsequently, the dynamic analysis of the engine has been carried out in order to calculate the connecting rod forces against the crankpin for predicting the position where mechanical impacts are expected. Then, a vibration signal model for this type of faults is introduced. It deals with the cyclostationary model in which the signal is subdivided into two main parts: deterministic and nondeterministic. Finally, the acceleration signals acquired from the engine block during a cold test cycle at the end of the assembly line are analyzed. For quality control purposes in order to obtain reliable thresholds for the pass/fail decision, a method based on the image correlation of symmetrized dot patterns is proposed. This method visualizes vibration signals in a diagrammatic representation in order to quickly detect the faulty engines in cold tests. Moreover, the fault identification is discussed on the basis of the cyclostationary model of the signals. The first-order cyclostationarity is exploited by the analysis of the time synchronous average (TSA). In addition, the residual signal is evaluated by subtracting the TSA from the raw synchronized signal, and thus, the second-order cyclostationarity analysis is developed by means of the Wigner–Ville distribution (WVD), Wigner–Ville spectrum (WVS), and mean instantaneous power. Moreover, continuous wavelet transform is presented and compared with the WVD and WVS.

Combining blind separation and cyclostationary techniques for monitoring distributed wear in gearbox rolling bearings

This work seeks to study the potential effectiveness of the Blind Signal Extraction (BSE) as a pre-processing tool for the detection of distributed faults in rolling bearings. In the literature, most of the authors focus their attention on the detection of incipient localized defects. In that case, classical techniques (i.e. envelope analysis) are robust in recognizing the presence of the fault and its characteristic frequency. However, when the fault grows, the classical approach fails, due to the change of the fault signature. De facto, in this case the signal does not contain impulses at the fault characteristic frequency, but more complex components with strong non-stationary contents. Moreover, signals acquired from complex machines often contain contributions from several different components as well as noise; thus the fault signature can be hidden in the complex system vibration. Therefore, pre-processing tools are needed in order to extract the bearing signature, from the raw system vibration. In this paper the authors focalize their attention on the application of the BSE in order to extract the bearing signature from the raw vibration of mechanical systems. The effectiveness and sensitivity of BSE is here exploited on the basis of both simulated and real signals. Among different procedures for the BSE computation, the Reduced-Rank Cyclic Regression algorithm (RRCR) is used. Firstly a simulated signal including the effect of gear meshing as well as a localized fault in bearings is introduced in order to tune the parameters of the RRCR. Next, two different real cases are considered, a bearing test-rig as an example of simple machine and a gearbox test-rig as an example of complex machine. In both examples, the bearings were degreased in order to accelerate the wear process. The BSE is compared with the usual pre-processing technique for the analysis of cyclostationary signals, i.e. the extraction of the residual signal. The fault detection is carried out by the computation of the Integrated Cyclic Modulation Spectrum on the extracted signals. The results indicate that the extracted signals via BSE clearly highlight the distributed fault signature, in particular both the appearance of the faults as well as their development are detected, whilst noise still hides fault grow in the residual signals.

Indirect Measurement of the Inertia Properties of a Knee Prosthesis Through a Simple Frequency-Domain Technique

The dynamic study of humans carrying prostheses requires the rigid-body inertia properties of the prostheses. Since such properties are difficult to evaluate, in general, roughly estimated values of these quantities are used. These approximations may yield significant errors in the evaluation of some dynamic quantities (i.e., the inertia forces due to the prosthesis). This work is addressed to assess an experimental technique, based on frequency response function measurements, that indirectly measures the inertia properties of prostheses for transfemoral amputees. First, a specifically designed specimen and, then, a real prosthesis are tested for assessing the proposed technique. The results are that the measurement sensitivity is 0.002 kg m 2 for inertia-tensor entries and 3 mm for center-of-gravity coordinates. Thus, the proposed technique is effective for a precise and fast evaluation of the inertia properties of medical devices such as prostheses.

Condition Monitoring and Diagnostics in Heavy-Duty Wheels: A First Experimental Approach

This paper assesses and compares the effectiveness of different analysis techniques for fault detection and diagnostics in heavy-duty wheels by using vibro-acoustic data. Firstly, different defect types have been artificially created on the wheels, trying to replicate anomalies that could really happen within the manufacturing process. Hence, different sensors and test conditions have been tested in order to determine the set up that at the best highlights the anomalies of the wheels; moreover the Time Synchronous Average (TSA) has been computed to reduce measurement noise. Kurtosis statistical coefficient has been used to detect defect presence (condition monitoring step), whereas frequency analysis, time-frequency analysis and signal trend have been performed for identifying the type of defect (diagnosis step). Finally, the effectiveness and the limitations of the above-mentioned techniques and diagnostics procedures are compared and discussed in order to define a systematic control at the end of the production line.Copyright

A Robust Design Optimization Methodology for External Gear Pumps

This work addresses the topic of external gear pumps for automotive applications, which operate at high speed and low pressure. In previous works of the authors, a hybrid lumped-parameter/finite-element model has been developed, in order to foresee the pump dynamic behaviour in terms of gear and casing acceleration. The model includes the main important phenomena involved in the pump operation and it has been validated on the basis of experimental data. In this research, an original optimization process has been applied to such a hybrid model in order to reduce the pump vibration level, i.e. the acceleration of the external casing. The set up of the optimization process comprises a single objective (case accelerations) and some operational and geometrical input variables (oil viscosity, oil Bulk modulus, relief groove dimension and radial clearance in the journal bearings). This paper compares three optimization methodologies for the optimization of the pump vibration level. In particular common optimization processes based on simulations are compared with a combined analysis based, firstly, on Design Of Experiments (DOE) and Response Surface Modelling (RSM) and, secondly, on the application of evolutionary algorithms to reach the optimal variable combination. The different methodologies are compared in terms of time efficiency and accuracy in the solution. Finally, a robust design process has been carried out in order to consider the manufacturing tolerances of the real pump and assess their effect on the performance of the component. The results offer important information and design insights that would be very difficult to obtain without such procedures.© 2010 ASME

Modeling Run in Process in External Gear Pumps

In this work, the authors have developed a mathematical model that simulates the run in of external gear pumps, as an useful tool in the optimization of this time-consuming process. The model calculates the wear profile of the case by enveloping the tip circle of the gears concerning all the run in steps. For each step, the positions of the gear centers are obtained by the equilibrium between pressure forces and torques due to the pressure distribution, meshing forces and hydrodynamic journal bearing reactions. The pressure distribution depends on the clearance between case and gears, so for each run in step, since the positions of the gear centers change, the pressure distribution is recalculated considering the wear profile obtained in the previous step. Besides, the model also estimates the quantity of material taken away in each step and it shows the effects of modifications in the run in parameters (time, pressure and speed). In particular, the simulation results indicate that a meaningful reduction of run in global time, can be obtained by increasing the duration of the steps that remove the greater part of material and by decreasing the duration of the other steps. This model is used by TRW Automotive Italia S.p.A. (section Automotive Pumps, Ostellato, Italy) to improve the run in process with good reduction in manufacturing-time.Copyright

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.

Analyzing wind turbine flow interaction through vibration data

Wind turbines commonly undergo non-stationary flow and, not rarely, even rather extreme phenomena. In particular, rough terrains represent a challenging testing ground, because of the combination of terrain-driven flow and wakes. It is therefore crucial to assess the impact of dynamic loads on the turbines. In this work, tower and drive-train vibrations are analyzed, from a subcluster of four turbines of a wind farm sited in a very complex terrain. The main outcome of the study is that it is possible to start from the analysis of wind conditions and interpret how wakes manifest in the vibrations of the turbines, both at structural level (tower vibrations) and at the drive-train level. This wind to gear approach therefore allows to build a connection between a flow phenomenon and a mechanical phenomenon (vibrations) and can be precious to assess loads in different working conditions.

A Model for the Estimation of Pressure Ripple in Tandem Gear Pumps

The present paper addresses the development of a lumped parameters model used to analyze the dynamic behavior of a so-called tandem gear pump. The pump is composed of two coaxial stages, both with external gears: a high pressure stage with spur gears and a low pressure one with helical gears. In particular, the paper deals with the modelling and the analysis of the phenomena bound to the pressure distribution around the gears, since they have the most important effect in the dynamic behavior of the pump. The pressure variation in the inlet and outlet chambers, the variable pressure in the trapped volume as well as the pressure evolution from the low to the high pressure chamber is estimated based on the Euler’s approach. The model is developed in Matlab environment. Attention is particularly focused on the description of the methodology adopted for modelling the low-pressure stage, constituted by helical gears, and its influence on the calculation of the pump geometrical parameters. The results provided by the numerical model are compared with experimental measurements in terms of outlet pressure ripple and volumetric efficiency under different working conditions. The results of the validation can be considered satisfactory. Predicted pressure ripple is shown and the effects of interconnections between stages are analyzed studying the outlet pressure ripple in the frequency domain as well.Copyright