Sensorless Detection of Cavitation in Centrifugal Pumps

Analysis of electrical signatures has been in use for some time for estimating the condition of induction motors, by extracting spectral indicators from motor current waveforms. In most applications, motors are used to drive dynamic loads, such as pumps, fans, and blowers, by means of power transmission devices, such as belts, couplers, gear-boxes. Failure of either the electric motors or the driven loads is associated with operational disruption. The large costs associated with the resulting idle equipment and personnel can often be avoided if the degradation is detected in its early stages prior to reaching failure conditions. Hence the need arises for cost-effective detection schemes not only for assessing the condition of the motor but also of the driven load. This prompts one to consider approaches that use no add-on sensors, in order to avoid any reduction in overall system reliability and increased costs. This paper presents an experimentally demonstrated sensorless approach to detecting varying levels of cavitation in centrifugal pumps. The proposed approach is sensorless in the sense that no mechanical sensors are required on either the pump or the motor driving the pump. Rather, onset of pump cavitation is detected using only the line voltages and phase currents of the electric motor driving the pump. Moreover, most industrial motor switchgear are equipped with potential transformers and current transformers which can be used to measure the motor voltages and currents. The developed fault detection scheme is insensitive to electric power supply and mechanical load variations. Furthermore, it does not require a priori knowledge of a motor or pump model or any detailed motor or pump design parameters; a model of the system is adaptively estimated on-line. The developed detection algorithm has been tested on data collected from a centrifugal pump connected to a 3 φ, 3 hp induction motor. Several cavitation levels are staged with increased severity. In addition to these staged pump faults, extensive experiments are also conducted to test the false alarm performance of the algorithm. Results from these experiments allow us to offer the conclusion that for the cases under consideration, the proposed model-based detection scheme reveals cavitation detection times that are comparable to those obtained from vibration analysis with a detection threshold that is significantly lower than used in industrial practice.

From Traditional to Virtual Design of Machine-Tools: A Long Way to Go ... Part 2 — The Talk Between Two Worlds

To allow easy and fast interaction between the simulation modules developed by the authors in a Virtual Design environment and the data bases set up in the past by an Italian manufacturer for the traditional design of Machining Centers for High Speed Milling, a graphic interface was created. The work was done utilising advanced features of Matlab suitable, through Microsoft Windows assisted procedures, to extract from Microsoft Excel sheets all sensitive data regarding the machine-tool components, feeding the input module of the simulation package. In this way it is now possible to perform intensive simulation campaigns quickly and easily avoiding the very burdensome procedures demanded for the input to the simulation language. This graphic module also makes it possible to quickly present and compare the results of experimental tests with the outputs of simulation runs.

Evaluation for Static and Dynamic Characteristics of a Miniaturized Machine Tool According to Its Configuration

Miniaturization for manufacturing system has been studied widely since the development of the smallest lathe in the world. Several prototypes are implemented, which are used to produce small parts with high precision. Accuracy and stiffness are the most important factors for design in the development of miniaturized systems. This study presents a method to evaluate static and dynamic characteristics of a miniaturized machine tool (mMT) according to its configuration before building the actual system. The proposed error estimation technique shows that volumetric error can be estimated indirectly at the design stage using error components of one axis and HTM (Homogeneous Transform Matrix), unlike the error modeling technique through direct measurement. Thus, accuracy of the system based on its configuration is analyzed at the design stage itself. The proposed analysis procedure is shown for the case of a 3 axis machine tool. In addition, dynamic characteristics of spindle unit affecting the spindle error are studied.

On-Line Monitoring Software and Diagnostic Tool for Centrifugal Compressor Performance Evaluation

In-house developed centrifugal compressor performance software was customized for PETROKEMYA (an affiliate of SABIC) Olefins III cracked gas compressor (CGC), the heart of ethylene plant. The software provides live performance analysis of the machine by calculating, per section, polytropic efficiency, polytropic head, and gas power using Lee-Kesler equation of state. Gas analysis is read online to reflect the minute changes in the composition on the calculated parameters. Actual operating parameters are plotted continuously and compared to the performance curves in order to predict possible performance deterioration before it becomes too late. Such information is useful in determining future maintenance requirements based on the actual performance of the machine rather than the traditional time-based maintenance. Moreover, it ensures proper timely action through optimization of wash oil or other chemical injection to help minimize fouling accumulation rate and maximize production and machine availability. Features are introduced to enable performance analysis of the compressor since commissioning to be carried out by click of a button, providing useful information for upgrading and troubleshooting. Unlike its commercially available counterpart with write-protected restrictions, the software is easily modified for additional features that are of interest to Engineers. Features planned for the future include adding intelligent system capability for predicting performance deterioration severity, auto-notifying agents etc. Performance evaluation of a 45 MW, five section process gas compressor before and after turnaround (T/A), clearly revealed the fouling prediction capability of the software.

A New Direct Deformation Measurement System to Enhance Positioning Accuracy of Machine Tools

The positioning accuracy of computer numerical control machines tools and manufacturing systems is affected by structural deformations, especially for large sized systems. Heat induced deformations, long-period deformation of foundations, and the manufacturing process itself, cause time-dependent structural deformations of the machine body, which are difficult to model and predict. In fact, the feasibility of a model-based error prediction is often limited by the complexity of the problem from both the geometrical and the physical point of view. As a consequence, only limited success has been achieved in active error compensation based on the modeling of the relationship between the generalized dynamic loads and the structural deformation field. This paper illustrates a different approach in active error compensation, which exploits a new measurement system, currently in the patenting process, able to measure, in real time, the machine structural displacement field, without any model for the dynamic structural behavior. The first part of the paper illustrates the working principle of the measurement system, which can be described as coupled hardware and software subsystems. The hardware subsystem is basically a triangular mesh of struts, whose nodes are rigidly connected to the underlying structure under measurement. The struts are instrumented with Fibre-optic Bragg Gratings providing their longitudinal strain values. The software part is an algorithm, which evaluates the discrete displacement field by computing the node positions on the basis of the strut longitudinal deformations. The second part of the work focuses on the performance, in terms of accuracy, resolution, and time stability, of a prototype of the above described measurement system. Finally, the third part illustrates two major enhancements on the system design: the design of a monolithic variant of the reticular structure (with higher performances and reduced cost), and a different computation algorithm providing increased accuracy and limited error propagation.

Constructing a Design Knowledge Base Using Natural Language Processing

Mechanical engineering, like other engineering disciplines, has witnessed maturation of various aspects of its domain, obsolescence of some areas and a resurgence of others. With a history of over 200 years of continuous research and development, both in academia and industry, the community has generated enormous amounts of design knowledge in the form of texts, articles and design drawings. With the advent of electronics and computer science, several of the classical mechanisms faced obsolescence, but with the emergence of MEMS and nanotechnology, the same designs are facing a resurrection. Research and development in mechanical engineering would derive enormous benefit from a structured knowledge-base of designs and mechanisms. This paper describes a prototype system that synthesizes a knowledge-base of mechanical designs by the processing of the text in engineering descriptions. The goal is to construct a system that stores and catalogs engineering designs, their sub-assemblies and their super-assemblies for the purposes of archiving, retrieval for launching new designs and for education of engineering design. Engineering texts have a relatively clear discourse structure with fewer ambiguities, less stylistic variations and less use of complex figures of speech. The text is first passed through a part-of-speech tagger. The concept of thematic roles is used to link different parts of the sentence. The discourse structure is then taken into account by anaphora resolution. The knowledge is gradually built up through progressive scanning and analysis of text. References, interconnections and attributes are added or deleted based upon the nature, reliability and strength of the new information. Examples of analysis and resulting knowledge structures are presented.

Optimum Conditions for Variable Pitch Milling

From the perspective of regenerative chatter, variable-pitch milling process offers a mathematically very challenging task. It can be reduced to the problem of stability assessment on a linear time-invariant dynamics (LTI) which has more than one independent delays. This mathematically notorious problem is uniquely solved by a recent paradigm. It is called Cluster Treatment of Characteristic Roots (CTCR). This paper presents a process optimization procedure using CTCR over a special milling operation with variable pitch cutters. The optimization is based on maximizing the metal removal rate while avoiding the onset of chatter, which, in turn, enables production of the parts with a desirable surface quality. The end result is a powerful tool to determine some important geometrical and operational features of the process: (i) the pitch angle selection on the tool (i.e., variable pitch cutter vs. uniform pitch cutter), (ii) the optimum cutting conditions (i.e., depth of cut and the spindle speeds).

IN2TEC: A Multidisciplinary Research Project Involving Researchers, Students and Industry

Bearing in mind that undergraduate students must get involved in research and that local industry must be a university partner, the School of Engineering, from University of Minho, has taken the initiative in funding some technical research projects in specifically defined areas (http://www.eng.uminho.pt). In this context, one of the projects founded concerns the development and testing of functional knitting which can be used with success in the lining of a shoe. The study of shoe comfort is of great importance to sport and leisure footwear manufactures, because in these particular situations, moisture disposal over a number of hours is a main problem. Three structures which combine different raw materials (soybean fiber, bamboo fiber, corn fiber, cotton, polypropylene and polyester) have been manufactured by a local textile factory. A group of students mainly from Mechanical and Textile Engineering classes are currently testing these knitting in terms of their water vapor and air permeability and other physical parameters at the laboratory. Tests with a thermal manikin have been used to measure its thermal insulation. A transient model for heat and mass transfer in a fabric has been implemented. From the solution, temperature and vapor density profiles in the fabric thickness can be obtained as well as, the amount of water dissolved in the fabric. This model has been integrated with an existing human thermal comfort model. Thermal comfort surveys are now being made at the Ergonomics Laboratory of the University of Minho with undergraduate Mechanical and Industrial Engineering students, wearing sport shoes manufactured by a local footwear factory, and these results can be compared using statistical analysis, with the experimental and numerical results already obtained.

Cracking During the Installation of Interference Fit Fasteners and Bucked Rivets in 7050-T7XXX Machined Aluminum Parts

This test program evaluated the effect of the installation of solid rivets and interference fit Hi-Tigue bolts on machined 7050 longerons (HiTigue is a registered trademark of the Hi-Shear Corporation of Torrance, (CA). Two simulated longeron specimens were machined from both 7050-T7451 and 7050-T7651 plate. Titanium Hi-Tigues and solid aluminum and Monel rivets were then installed with a pneumatic riveting hammer in sections of various thicknesses in the four machined longeron specimens. After all fasteners were installed, each fastener was subjected to a simulated mishap by applying the pneumatic riveting hammer to the installed fastener without support from an underlying bucking bar. Dye penetrant inspections to detect cracks were performed after the fastener installations and simulated mishaps. All fasteners were then removed and the open holes subjected to eddy current inspection. Visual observations concerning deformation of the machined longeron specimens during fastener installations and simulated mishaps were recorded. Cracking was noted in 0.063 inch thick longeron sections, compelling additional testing involving Hi-Tigues. Recommendations concerning the use of Hi-Tigues and solid rivets in 7050-T7XXX machined parts were made based on the results of the testing.

Mechanical Design Using Quantum-Behaved Particle Swarm Optimizer With Exponential Mutation Operator

Particle swarm optimization (PSO) is a population-based swarm intelligence algorithm that shares many similarities with evolutionary computation techniques. However, the PSO is driven by the simulation of a social psychological metaphor motivated by collective behaviours of bird and other social organisms instead of the survival of the fittest individual. Inspired by the classical PSO method and quantum mechanics theories, this work presents new Quantum-behaved PSO (QPSO) approaches using mutation operator with exponential probability distribution. The simulation results demonstrate good performance of the QPSO in solving a well-studied continuous optimization problem of mechanical engineering design.