Bond graph modeling of centrifugal compression systems

A novel approach to model unsteady fluid dynamics in a compressor network by using a bond graph is presented. The model is intended in particular for compressor control system development. First, we develop a bond graph model of a single compression system. Bond graph modeling offers a different perspective to previous work by modeling the compression system based on energy flow instead of fluid dynamics. Analyzing the bond graph model explains the energy flow during compressor surge. Two principal solutions for compressor surge problem are identified: upstream energy injection and downstream energy dissipation. Both principal solutions are verified in bond graph modelings of single compression system equipped with a surge avoidance system (SAS) and single compression system equipped with an active control system. Moreover, the bond graph model of single compressor equipped with SAS is able to show the effect of recycling flow to the compressor upstream states which improves the current available model. The bond graph model of a single compression system is then used as the base model and combined to build compressor network models. Two compressor networks are modeled: serial compressors and parallel compressors. Simulation results show the surge conditions in both compressor networks.© SAGE. This is the authors’ accepted and refereed manuscript to the article

Control requirements for future gas turbine-powered unmanned drones: JetQuads

The next generation of aerial robots will be utilized extensively in real-world applications for different purposes: Delivery, entertainment, inspection, health and safety, photography, search and rescue operations, fire detection, and use in hazardous and unreachable environments. Thus, dynamic modeling and control of drones will play a vital role in the growth phase of this cutting-edge technology. This paper presents a systematic approach for control mode identification of JetQuads (gas turbine-powered quads) that should be satisfied simultaneously to achieve a safe and optimal operation of the JetQuad. Using bond graphs as a powerful mechatronic tool, a modular model of a JetQuad including the gas turbine, electric starter, and the main body was developed and validated against publicly available data. Two practical scenarios for thrust variation as a function of time were defined to investigate the compatibility and robustness of the JetQuad. The simulation results of these scenarios confirmed the necessity of designing a compatibility control loop, a stability control loop, and physical limitation control loops for the safe and errorless operation of the system. A control structure with its associated control algorithm is also proposed to deal with future challenges in JetQuad control problems

Modeling and control of the starter motor and start-up phase for gas turbines

Improving the performance of industrial gas turbines has always been at the focus of attention of researchers and manufacturers. Nowadays, the operating environment of gas turbines has been transformed significantly respect to the very fast growth of renewable electricity generation where gas turbines should provide a safe, reliable, fast, and flexible transient operation to support their renewable partners. So, having a reliable tools to predict the transient behavior of the gas turbine is becoming more and more important. Regarding the response time and flexibility, improving the turbine performance during the start-up phase is an important issue that should be taken into account by the turbine manufacturers. To analyze the turbine performance during the start-up phase and to implement novel ideas so as to improve its performance, modeling, and simulation of an industrial gas turbine during cold start-up phase is investigated this article using an integrated modular approach. During this phase, a complex mechatronic system comprised of an asynchronous AC motor (electric starter), static frequency converter drive, and gas turbine exists. The start-up phase happens in this manner: first, the clutch transfers the torque generated by the electric starter to the gas turbine so that the turbine reaches a specific speed (cranking stage). Next, the turbine spends some time at this speed (purging stage), after which the turbine speed decreases, sparking stage begins, and the turbine enters the warm start-up phase. It is, however, possible that the start-up process fails at an intermediate stage. Such unsuccessful start-ups can be caused by turbine vibrations, the increase in the gradients of exhaust gases, or issues with fuel spray nozzles. If, for any reason, the turbine cannot reach the self-sustained speed and the speed falls below a certain threshold, the clutch engages once again with the turbine shaft and the start-up process is repeated. Consequently, when modeling the start-up phase, we face discontinuities in performance and a system with variable structure owing to the existence of clutch. Modeling the start-up phase, which happens to exist in many different fields including electric and mechanical application, brings about problems in numerical solutions (such as algebraic loop). Accordingly, this study attempts to benefit from the bond graph approach (as a powerful physical modeling approach) to model such a mechatronic system. The results confirm the effectiveness of the proposed approach in detailed performance prediction of the gas turbine in start-up phase

Development of a vibration-based non-destructive testing method for in-service utility poles

Wooden utility poles for electric networks are widely used, with approximately two million poles in North America. A reliable and cost-effective non-destructive testing (NDT) method is necessary for strength evaluation during the life span of the poles. To improve an emerging modal testing-based NDT method, this thesis develops a novel method to measure natural frequencies and damping ratios of poles even though they are connected to conductors. This thesis makes contributions to the wood pole NDT state of the art in two major areas – analytical and numerical modeling of pole-cable systems, and frequency-domain decoupling methods to identify pole properties despite their connection to cables. Improved analytical models of the “cable-beam” system were developed in order to understand the coupled vibration behavior of the system. Bending stiffness and sag of the cable were considered in the modeling and the effects of them on vibration behavior of the system was studied. Two-dimensional and three-dimensional dynamic models using bond graph method were developed for vibration of stranded cables and vibration of the cable-beam system. The models were verified by experiments in free and forced vibration. The second contribution area is the development of substructure decoupling-related methods to decouple the beam frequency response function (FRF) from the assembled cable-beam system. The FRF of the beam was obtained as an independent substructure after decoupling analysis and the FRF was compared to the directly measured FRF from modal testing of the beam substructure. A good agreement showed that the substructure decoupling method can be used to filter out the effects of cables from the assembled system in cabled structures, assuming that all points in the system are accessible for measurement. An FRF-based finite element model updating was then developed to overcome the practical limitation of accessing some measurement points in the field. The FRFs of accessible points were used as a basis for updating the FE model and then the FRFs of inaccessible points were obtained from the updated (optimized) FE model. A substructural damage detection was also developed for the systems that consist of a few substructures but only the main (target) substructure is susceptible to damage. In the developed method, FRF of the main substructure is first obtained using the substructure decoupling method and then FRF-based finite element model updating is used for damage detection, localization and quantification. The method was successfully able to identify location and magnitude of damage, which was modeled as a localized reduced stiffness due to material degradation or cracking. Finally, in support of the larger ongoing NDT research project, full-scale pole modal testing was done in the field. In-ground pole FRF’s with and without cables were generated, for future use in model validation. In-ground poles without cables were subjected to modal testing, and then brought to the lab for modal and destructive testing. The differences in the resulting FRF’s allow future simulation-based prediction of the foundation properties, and the destructive tests have added to the research group’s database for correlation of modal properties and pole strength