Laboratory Test Rig Research Articles

LQG Control of an Open Circuit Axial Piston Pump

In recent years, the development of hydraulic variable displacement axial piston machines has been focused in two main directions: improvement of their construction and improvement of their displacement control methods. The goal of both directions is to increase the efficiency of the machines. Increasing their efficiency is key to improving the efficiency of the entire hydraulic system, whether they are used as pumps or hydraulic motors. This motivates the present work, which essentially contains a developed embedded control system designed for a known type of open circuit axial piston pump. The developed solution is implemented on a laboratory test rig. A detailed description of the hydraulic system in the context of pump displacement control is presented, as well as the developed system architecture for its control. The control system is based on a linear-quadratic Gaussian (LQG) controller. The controller is synthesized on the basis of a model obtained by means of identification based on experimental data. The designed controller is validated through experimental studies, enabling the analysis of its performance.

An Industrial Approach for the Optimization of a New Performing Coated Adsorber for Adsorption Heat Pumps

In the present work, the optimization of a new coating formulation was investigated, taking attention to an industrially focused research approach used for the engineering design of the adsorber. The adsorbent was a composite zeolite or silica-gel based coating applied by using new flexible polymer matrices. The FC-80 formulation represents a good compromise between mechanical stability and absorption capacity. Using the developed coating process, a new compact HEX design was developed to reach the AHP target performance with easy and fast manufacturing. The specific cooling power of the coated heat exchanger was estimated to be about 500 W/kg of adsorbent. The new coated HEX was integrated in a new adsorption chiller and has been tested by a laboratory test-rig under realistic operating conditions. Results of preliminary testing demonstrated that the prototype provides a cooling capacity of around 10 kW with a COP of 0.54.

Effects of environmental vibration on ancient stained-glass windows

• Lead cames are the most critical part of historical windows subjected to vibrations. • Pressure waves can damage historical windows because of fatigue on lead. • 3D vision in laboratory tests allows locating critical regions in lead junctions. • Long term tracking of natural frequencies can indicate the conservation state. • Concerts produce excitations two orders of magnitude greater than daily vibrations. Ancient stained-glass windows are delicate pieces of art that need to be carefully maintained in order to be preserved over time. Several studies address the problem of stained-glass windows degradation, however, the effect of ambient vibrations on the conservation state of these artworks is not thoroughly studied and understood. In the present work, a wide and general approach was adopted to better address the problem. Two monitoring campaigns have been carried out on the stained-glass windows of the Milan Cathedral, to understand the characteristics of the typical daily excitation and that of shorter duration events, like concerts taking place in the square in front of the cathedral. Starting from the gathered data, experimental tests have been performed on a facsimile window panel. The direct exposure to concert-like sound pressure waves has been reproduced with a laboratory test rig and the evolution of the window panel dynamics has been tracked through a series of measurements. Lead cames, which form the internal metallic structure of a window panel, proved to be the most critical element of a stained-glass window, rather than the glass pieces themselves. In fact, when subjected to a prolonged direct exposure to the pulsating actions produced by concerts or similar events, severe metal fatigue phenomena were observed. On the other hand, glass pieces remained intact during the tests. This suggests that their possible detachment is not due to their direct failure when subjected to a direct exposure to the pressure waves, rather to an improper or weakened fastening of the lead cames. The mechanical damaging processes of stained-glass windows appear to be more related to metal fatigue and subsequent glass chattering, rather than to an expected intrinsic fragility of the artwork. Nevertheless, since the windows of the façade of the Milan Cathedral are protected by an additional structure comprising glass windows, they are not directly exposed to the sound pressure waves, as a filter is introduced between the source and the window panes. This strongly mitigates the vibration levels reaching the window panels. Such an arrangement appears to be of importance for the conservation of the stained-glass windows from a mechanical point of view.

An experimental study on the damping characteristics and tuning of the liquid column vibration absorber

This paper deals with an experimental investigation of the damping characteristics of the liquid column dynamic vibration absorber. The laboratory test rig of a single degree of freedom system integrated with a liquid column dynamic vibration absorber was designed and manufactured to study the efficiency of this type of dynamic absorbers. The system response has been measured and recorded by using a (DXL-345) accelerometer and data acquisition system. The effects of mass ratio, length ratio, and the opening ratio of the central orifice on the vibration reduction of the main structure in free vibration mode were evaluated. The results showed that the tuned liquid column vibration absorber has a good ability to reduce or eliminate unwanted vibration by the suitable selection of the combination of its design parameters. The maximum damping of the main system was achieved at the mass, length and orifice opening ratios equal to 7.7 %, 87% and 74% respectively.

Design and Evaluation of Low-Cost Vibration-Based Machine Monitoring System for Hay Rotary Tedder.

Vibration monitoring provides a good-quality source of information about the health condition of machines, and it is often based on the use of accelerometers. This article focuses on the use of accelerometer sensors in fabricating a low-cost system for monitoring vibrations in agricultural machines, such as rotary tedders. The aim of the study is to provide useful data on equipment health for improving the durability of such machinery. The electronic prototype, based on the low-cost AVR microcontroller ATmega128 with 10-bit ADC performing a 12-bit measurement, is able to acquire data from an accelerometer weighing up to 10 g. Three sensors were exposed to low accelerations with the use of an exciter, and their static characteristics were presented. Standard experimental tests were used to evaluate the constructed machine monitoring system. The self-contained prototype system was calibrated in a laboratory test rig, and sinusoidal and multisinusoidal excitations were used. Measurements in time and frequency domains were carried out. The amplitude characteristic of the preformed system differed by no more than 15% within a frequency range of 10 Hz–10 kHz, compared to the AVM4000 commercial product. Finally, the system was experimentally tested to measure acceleration at three characteristic points in a rotational tedder, i.e., the solid grease gearbox, the drive shaft bearing and the main frame. The RMS amplitude values of the shaft vibrations on the bearing in relation to the change in the drive shaft speed of two tedders of the same type were evaluated and compared. Additionally, the parameters of kurtosis and crest factor were compared to ascertain the bearing condition.

The coupled bending-torsional dynamic behavior in the rotating machinery: modeling, simulation and experiment validation

The nonlinear coupling between bending and torsional vibrations would greatly affect the dynamic behavior of the rotor system. Different from the traditional way, in this paper the unbalance mass that causes the internal and external couplings is treated as an independent nonlinear element when establishing a finite element model of the coupled bending-torsional (CBT) rotor system with six degrees of freedom for each node. To improve the efficiency of transient numerical simulation, a general algorithm named with linear and nonlinear nodes separation method is proposed, which decreases the dimension of nonlinear iteration matrix, resulting in a great calculation efficiency of solving transient vibration responses of the high-dimension nonlinear motion equation. With the presented nonlinear CBT model, simulations for steady and transient torsional excitation processes are carried out, resulting that the torsional excitation would generate sideband frequency components in the spectra of lateral vibrations and vice versa, and the effect of gravity is considerable and non-negligible in CBT modeling. Additionally, results of experiments with two different scales of setups, a laboratory test-rig and an industrial centrifugal compressor platform, are well agreed with the numerical ones. The investigation provides a complete modeling and high efficient solution method not only for CBT rotordynamic problems, but also for other problems with nonlinear forces.

Applications of Operational Modal Analysis in Gearbox and Induction Motor, Based on Random Decrement Technique and Enhanced Ibrahim Time Method

There have been steadily growing requirements from the academia and industry, demanding non-invasive methods and reliable measurement systems of research devoted to operational mode analysis (OMA). Due to the simplicity of performing only structures surface vibration measurements, OMA is frequently applied in machine fault diagnosis (MFD) and structure health monitoring (SHM). OMA can handle big structures, such as bridges, buildings, machines, etc. However, there is still an open question: how to properly handle the harmonic effects of rotating components and the difficulty of closely estimating space modes are still a nightmare to deal with. Therefore, the main objective of this paper is to identify the structure of natural frequencies by the regeneration of frequency response functions (FRFs) for complex structures based on OMA. The novelty of our approach is to use the random decrement technique (RDT), correlation function estimation (CFE), and enhanced Ibrahim time method (EITM) to overcome OMA’s difficulties and limitations. To reduce further rotational harmonics effects, gear mesh and side band frequencies, digital signal processing techniques based on notching filters, and liftering analysis techniques were also used. All the experiments were performed at the laboratory test rig and conducted by using three accelerometers, one impedance hammer, one force sensor, and one data acquisition board. To reduce data’s variabilities, each test was measured three times for 5 min. The data sampling frequency for all the experiments was 25.6 kHz. To validate the proposed methodology, extensive OMA tests were performed for the generation of FRFs. The measured objects were a steel bar, induction motor, and gearbox. Five structural natural frequencies for the induction motor and eight structural natural frequencies for the gearbox were generated, respectively.

Flexible 3D‐Printed Test Rig for Liquid Distribution Characterization of Laboratory‐Scale Packings

AbstractIn distillation, additive manufacturing can facilitate the design and fabrication of laboratory‐scale packed columns that overcome the existing miniaturization limits while maintaining scalability. Liquid distribution is one of the appraisal criteria for new packing structures. For this purpose, a flexible 3D‐printed laboratory test rig is presented. The setup offers a wide liquid load operation range from approx. 2.5 to 20 m3m−2h−1 for column diameters of 20–50 mm. First results regarding steady‐state development, initial liquid distribution effect and liquid load variation are shown using a 3D‐printed version of the Rombopak 9M in a 20‐mm diameter column.

Experimental investigation of R744 transcritical flow and mixing in the two-phase ejector

In this work, the laboratory test rig for visualisation of the CO2 ejector is shortly presented. The internal flow structures in the premixing chamber and expansion cone are visualised using two different measurement arrangements, i.e. Particle Image Velocimetry (PIV) system and high-speed camera system. Both systems allow to determine some characteristic features of the R744 flows and propose some important quantities (i.e. expansion and mixing angles) describing expansion and mixing processes. Potentials of those preliminary results for field validation data are also pointed out.

Variable operation of a renewable energy-driven reverse osmosis system using model predictive control and variable recovery: Towards large-scale implementation

Powering Reverse Osmosis (RO) systems with Renewable Energy (RE) is essential for decarbonising water production. Integration of RE requires large-scale RO plants to operate efficiently using variable power. Nevertheless, variable operation (involving matching the RO load to available power without battery back-up) has only been implemented for small-scale systems. This paper presents a variable-speed operation technique suitable for large-scale RO systems using an optimised operational strategy and a Model Predictive Controller (MPC). The technique was validated using a laboratory test rig having comparable performance to large-scale systems. A dynamic plant model was used to design the operational strategy and control system. Several operational strategies were explored for varying the operating parameters according to power available from a RE source. An advanced control system based on MPC was designed and compared to a conventional Proportional-Integral-Differential controller. The results showed that operation at variable recovery with constant brine flowrate delivered the lowest specific energy consumption and widest operation range for a system with an isobaric pressure exchanger. The MPC controller improved the settling time for a 10% step-change in permeate flowrate by 47%. Moreover, it improved energy utilisation, giving a 2.35% increase in hourly permeate production for a defined power input time-series.

Physics-Informed LSTM hyperparameters selection for gearbox fault detection

A situation often encountered in the condition monitoring (CM) and health management of gearboxes is that a large volume of CM data (e.g., vibration signal) collected from a healthy state is available but CM data from a faulty state unavailable. Fault detection under such a situation is usually tackled by modeling the baseline CM data and then detect the fault by examining any deviation of the baseline model versus newly monitored data. Given that the CM data is mostly time series, the long-short term memory (LSTM) neural network can be employed for baseline CM data modeling. The LSTM is free from the choice of the number of lagged input time series and can also store both long-term and short-term time series dependency information. However, we found that an LSTM with its hyperparameters selected whilst minimizing validation mean squared error (VAMSE) does not differentiate the faulty and healthy states well. There is still room for detectability improvement. In this paper, we propose a physics-informed hyperparameters selection strategy for the LSTM identification and subsequently the fault detection of gearboxes. The key idea of the proposed strategy is to select hyperparameters based on maximizing the discrepancy between healthy and physics-informed faulty states, as opposed to minimizing VAMSE. Case studies have been conducted to detect the gear tooth crack and tooth wear using laboratory test rigs. Results have shown that the proposed physics-informed hyperparameters selection strategy returns an LSTM that can better detect these faults than the LSTM returned from minimizing VAMSE.

Influence of Blade Types, Cutting Velocity and Stalk Diameter of Sorghum Crop on Cutting Energy and Cutting Force

Sorghum (Sorghum bicolor L.) popularly known as “Jowar”, a cereal grain found in tropical and subtropical climate. India ranks fifth in total sorghum production with 4.7 million tonnes (USDA, 2020). Sorghum is grown in India in an area about 4.82 m ha with production of 4.78 m tonnes and productivity of 989 kg/ ha.In Karnataka, it is grown in 0.94 m ha with a production of 0.98 million tonnes and productivity of 945 kg/ha (INDIASTAT, 2020). A designed and fabricated laboratory test-rig of a pendulum impact tester was used to conduct the experiment in the Department of Farm Machinery and Power Engineering, College of Agricultural Engineering, Raichur. The experiment was conducted to determine the engineering properties of sorghum stalk. The independent variables viz., two types of blades (smooth edge and serrated blade), four levels different stalk diameters (12, 16, 20, 24 mm) and three levels of blade cutting velocity (4.40, 6.30, 7.40 m/s) were selected. Results showed that the maximum cutting energy of 35.47 J was recorded at a blade cutting velocity of 4.40 ms-1 at 24 mm stalk diameter and the least cutting energy of 5.23 J was recorded for 12 mm stalk diameter at blade cutting velocity of 7.40 m s-1 for serrated blade for smooth edge blade and the more cutting energy was recorded of 28.65 J for 24 mm stalk diameter at blade cutting velocity of 4.40 ms-1 and the least cutting energy 3.55 J were recorded for 12 m stalk diameter at 7.40 ms-1 for serrated cutting blade. The maximum cutting force of 1477.92 N was recorded at a blade cutting velocity of 4.40 ms1 at 24 mm stalk diameter. The least cutting force of 435.81 N was recorded for 12 mm stalk diameter at blade cutting velocity of 7.40 m s-1 for smooth edge blade and for serrated cutting blade, the more cutting force was recorded of 1193.75 N for 24 mm stalk diameter at blade cutting velocity of 4.40 ms-1 and the least cutting energy 295.84 N were recorded for 12 m stalk diameter at 7.40 ms-1.

Robustness Analysis of an Electrohydraulic Steering Control System Based on the Estimated Uncertainty Model

The impossibility of replacing hydraulic drives with other type drives in heavy duty machinery is the main reason for the development of a system for controlling hydraulic power steering. Moreover, the need for remote automatic control of the steering in specific types of mobile machinery leads to significant scientific interest in the design of embedded systems for controlling electro-hydraulic steering units. This article introduces an approach, which has been developed by authors, for robust stability and robust performance analysis of two embedded systems for controlling electro-hydraulic power steering in mobile machinery. It is based on the suggested new more realistic “black box” SIMO model with output multiplicative uncertainty. The uncertainty is obtained by parameters confidence interval and Gauss approximation formula. The embedded control systems used a linear-quadratic Gaussian (LQG) controller and H∞ controller. The synthesis of the controllers was performed on the basis of a nominal part of an uncertainty model. Robust stability and robust performance analyses were performed in the framework of a so-called structured singular value, μ. The obtained theoretical results were experimentally approved by real experiments with both of the developed control systems, which were physically realized as a laboratory test rig.

Linear friction tester design and validation

Due to the complexity of friction phenomena, empirical analysis is the best way to predict the friction coefficient. To accomplish this, laboratory test rigs are needed. Although a rotary dynamic friction test bed was available to the authors, it had its limitations, such as low speed, inducement of lateral force, and the limitation of testing samples with different shapes. This paper will explain the process of designing and manufacturing a novel test setup for measuring friction and wear of the tire. The newly designed test rig can apply dynamic loading during the tests, and it can automatically measure the wear rate and temperature between cycles. In addition, it can be used for measuring the wear rate of rubber samples sliding on different types of surfaces. Therefore, experiments can be run under more controlled conditions. The designed linear friction tester can slide flat and round rubber samples approximately three meters across a large flat surface. The frictional force of rubber samples can be measured for various normal loads, velocities, and surface conditions. The new setup can automatically control the applied normal load on the sample using proportional–integral–derivative controller control. The important difference between this novel design and the existing testers used by other researchers is implementing the ball screw technology and the servo motor with high accuracy encoder to achieve highly accurate test results. In this design, the new mechanism for the ball screw is designed to increase the speed limit and eliminating vibrations while keeping the precision. In addition, in this design, the sample's mass can be measured automatically after each test cycle, thus providing a measure of the rate of wear of the rubber. In this study, the data collected by the linear friction tester is validated by comparing the data to the data collected by the dynamic friction tester (a validated rotary friction tester that exists in CenTiRe Lab). The data collected by the new setup was later used to benchmark the Persson analytical friction model.

A novel tacholess order analysis method for bearings operating under time-varying speed conditions

Order tracking (OT) of vibration envelope signal based on instantaneous frequency (IF) estimated from a time-frequency representation (TFR) is generally applied to detect bearing defects under time-varying speed conditions. However, these TFR based OT approaches require a high resolution for accurate estimation of the IF. To overcome these issues, a tacholess OT technique based on the fast dynamic time warping (FDTW) algorithm is applied to detect bearing defects for the first time in this paper. FDTW based signal transformation is initially applied to align a filtered shaft signal to a reference signal of constant frequency, followed by reconstructing the bearing envelope signal. The resulting envelope signal is able to provide a richer fault indication than the original signal. The efficacy of the developed OT method is established using a simulation analysis followed by experimental validation using measurements obtained from a laboratory test-rig and a wind turbine bearing.

Rotating blade faults classification of a rotor-disk-blade system using artificial neural network

<span lang="EN-US">In this paper, the artificial neural network (ANN) has been utilized for rotating machinery faults detection and classification. First, experiments were performed to measure the lateral vibration signals of laboratory test rigs for rotor-disk-blade when the blades are defective. A rotor-disk-blade system with 6 regular blades and 5 blades with various defects was constructed. Second, the ANN was applied to classify the different </span><em><span lang="EN-US">x</span></em><span lang="EN-US">- and </span><em><span lang="EN-US">y</span></em><span lang="EN-US">-axis lateral vibrations due to different blade faults. The results based on training and testing with different data samples of the fault types indicate that the ANN is robust and can effectively identify and distinguish different blade faults caused by lateral vibrations in a rotor. As compared to the literature, the present paper presents a novel work of identifying and classifying various rotating blade faults commonly encountered in rotating machines using ANN. Experimental data of lateral vibrations of the rotor-disk-blade system in both </span><em><span lang="EN-US">x</span></em><span lang="EN-US">- and </span><em><span lang="EN-US">y</span></em><span lang="EN-US">-directions are used for the training and testing of the network.</span>

Development of a new test method for evaluating the abrasivity of granite building stones during polishing process based on weight loss of abrasive tool

Abrasivity of building stones is one of critical parameters during polishing stage in stone processing plants, which can significantly affect the abrasive tool consumption and the processing costs. Hence, the main purpose of this paper is to evaluate the building stone abrasivity based on the weight loss of abrasive tool during polishing process. For this purpose, a new laboratory test rig was developed, which can simulate the polishing process in laboratory scale as far as possible. Using this laboratory rig, a new test method was proposed, which gives an index herein called building stone abrasivity index (BSAI). This index was defined as the weight loss of abrasive tool during polishing process in order to estimate the building stone abrasivity. The proposed test method was carried out on 15 different types of Iranian granite building stones and the correlation of obtained BSAI with the physico-mechanical and petrographic properties of stone was investigated. Meaningful and reasonable relationships were observed. To evaluate the accuracy of proposed method, the correlation of BSAI with two most common abrasivity indices i.e. Schimazek abrasivity factor (F) and rock abrasivity index (RAI) was also discussed. The results indicated that there is a strong relationship between these indices, which verifies the accuracy of proposed method. Furthermore, the laboratory results were compared with data obtained from stone processing plants in order to validate the proposed test method. It was shown that the obtained BSAI has a good agreement with abrasivity of building stones in real conditions of stone processing plants. Therefore, the proposed test can be adopted as an accurate and rapid tool for evaluating the abrasivity of building stones in polishing process. Finally, relationship between BSAI and the abrasive tool lifespan (ATL) was examined and a model was suggested to predict ATL with acceptable accuracy.

Advanced Switching Sequences Based Model-Predictive Control for Single-Phase NPC Converters

This article presents a continuous control set model-predictive control (MPC) technique based on advanced switching sequences (SSs) for a grid-connected single-phase three-level neutral-point-clamped converter. The SSs are developed considering the tracking performance of the current feed to the utility grid, the dc-bus capacitor voltage balancing, and the switching loss of the semiconductor devices. In the proposed strategy, with the same sampling frequency, the number of pole state changes (SCs) per control cycle is only two, while in the optimal SS and the modulated MPC (pulse pattern similar to the conventional space vector modulation technique) schemes, the number of pole SCs is four. The reduction in the number switching SCs per control cycle considerably reduces the switching loss of semiconductor devices. Moreover, to avoid the challenges of utilizing the weighting factor, a single-objective cost function is adopted to track the reference current, and the dc-bus capacitor voltages are balanced using the redundancy nature of the voltage vectors. Furthermore, the proposed scheme can ensure a fixed-switching-frequency operation, which is advantageous for selecting filter parameters during real-life implementation. The effectiveness of the proposed strategy is validated by the results obtained from both the simulation in MATLAB/Simulink and the experiment carried out using a downscaled laboratory test rig.

Rock Stress Measurements for Unlined Pressure Tunnels: A True Triaxial Laboratory Experiment to Investigate the Ability of a Simplified Hydraulic Jacking Test to Assess Fracture Normal Stress

To avoid hydraulic failure of unlined pressure tunnels, knowledge of minimum principal stress is needed. Such knowledge is only obtainable from in situ measurements, which are often time-consuming and relatively costly, effectively limiting the number of measurements typically performed. In an effort to enable more stress measurements, the authors propose a simplified and cost-effective stress measuring method; the Rapid Step-Rate Test (RSRT), which is based on existing hydraulic testing methods. To investigate the ability of this test to measure fracture normal stresses in field-like conditions, a true triaxial laboratory test rig has been developed. Hydraulic jacking experiments performed on four granite specimens, each containing a fracture, have been performed. Interpretation of pressure-, flow- and acoustic emission (AE) data has been used to interpret fracture behaviour and to assess fracture normal stresses. Our experimental data suggest that the proposed test method, to a satisfactory degree of reliability, can measure the magnitude of fracture normal stress. In addition, a clear correlation has been found between fracture closure and sudden increase in AE rate, suggesting that AE monitoring during testing can serve as a useful addition to the test. The rapid step-rate test is also considered relevant for field-scale measurements, with only minor adaptions. Our findings suggest that the RSRT can represent a way to get closer to the ideal of performing more testing along the entire length of pressure tunnel, and not only at key locations, which requires interpolation of stress data with varying degree of validity.

An analytical model for squirrel cage induction machine with broken rotor bars derived based on the multiple coupled circuit theory and the winding function approach

SummaryIn this paper, a squirrel cage induction machine (SCIM) with broken rotor bars is modeled by using the multiple coupled circuit theory and the winding function approach. This analytical model includes all the spatial harmonic components of air gap magnetomotive force and is applicable to the study of transient machine behaviors. Equivalent circuits that are consistent with the topologies of healthy and faulty cage rotors are developed. The equivalent circuit for the healthy rotor of a SCIM having an integer number of rotor bars per pole is simplified further by exploiting the symmetry of the winding functions of the stator. In the equivalent circuit for a healthy rotor, inserting an independent current source in the bar that breaks in the damaged rotor, whose current is the negative of the current through the same bar, and replacing all the voltage sources in the rest of the bars with short circuits result in an equivalent circuit that can be employed to solve for the deviations in rotor mesh currents caused by bar breakage. A simulation is carried out in MATLAB/Simulink for a 2.2 kW, three‐phase, four‐pole SCIM with 28 rotor bars and a laboratory test rig is built. The effectiveness of the proposed model was validated by the good agreement of the simulation results with the experimental data.