Stefano Rossin

A Tool for the Simulation of Turbo-Machine Auxiliary Lubrication Plants

The reliability and safety of large turbo-machinery systems used in the oil and gas industries are heavily affected by the efficiency of the lubrication plant. In particular, hazard and operability (HAZOP) analyses are often performed using piping and instrumentation diagrams (P&ID; according to regulations in force, ISO 14617). Usually, these analyses are time-consuming and affected by potentially dangerous errors. In this work, a tool for the mono-dimensional simulation of thermal hydraulic plants is presented and applied to the analysis of safety-relevant components of compressor and pumping units, such as the lubrication circuits. Compared to known commercial products, the proposed tool is optimised for fixed step solvers in order to make real-time (RT) integration easier. The proposed tool defines a general approach, and can be used as a SimScape-Simulink library of thermal-hydraulic components (designed according to the P&ID definitions). Another interesting feature of the tool is the automatic scheme generation, where the Simulink model can be automatically generated by P&ID schemes.

A preliminary study of thermal hydraulic models for virtual hazard and operability analysis and model-based design of rotating machine packages

Hazard and operability analysis is a decisive factor to evaluate safety and reliability of plants considering the propagated effects due to consecutive failures of known critical components. A good design and analysis practice increases the robustness of the considered system in different operating conditions; however, in the plant design process, the use of a model-based design approach is fundamental to increase speed, efficiency and reliability. In this work, a tool for the 1-D simulation of thermal hydraulic plants is presented and applied to the analysis of critical system for compressor and gas turbine units, e.g. the lubrication circuits. Different from known commercial products, the proposed tool is implemented to work in cooperation with PidXP™ (the GE Nuovo Pignone P&ID definition tool), and it is optimized for fixed step solvers in order to easily include the rotating machine control logics within the simulation environment (essential prerequisite for hazard and operability evaluations). All the above makes it suitable for the fast prototyping of real time code. Moreover, the proposed tool represents a general tool in the model-based approach, and it can be used as a Simulink™ library of components that have been optimized and specifically designed in order to make easier the automatic generation of simulation models from P&Id schemes and technical documentation, reducing errors associated to data transcription and operator misbehaviour. In this work, proposed approach and test bench on experimental data for validation purposes are shown.

TTH library: A new tool for diagnostic assessment of Oil&Gas applications

The main task of this study is the development of diagnostics techniques in order to achieve both corrective and predictive maintenance methods. The use of simulation tools can drastically increase speed, efficiency and reliability in the design process of safety critical systems. For these reasons, a dedicated tool named TTH Lib was developed and customized for lube oil plants simulation. The proposed case study is a mineral lube oil console and the authors main purpose is to verify the tool capability to simulate a typical flow-pressure transient with fast dynamic evolution and show the great support that this tool can offer to achieve diagnostic parameters in the early stages of product development.

Effect of Structural Dynamics on the Shaft Line Rotor Response in Turbomachines

The accurate model of the complicated dynamic phenomena characterizing rotors and support structure represents a critical issue in the rotor dynamic field. A correct prediction of the whole system behavior is fundamental to identify safe operating conditions and to avoid instability operating range that may lead to erroneous project solutions or possible unwanted consequences for the plant. Although a generic rotating machinery is mainly composed by four components (rotors, bearings, stator and supporting structure), many research activities are often more focused on the single components rather than on the whole system. The importance of a combined analysis of rotors and elastic supporting structures arises with the continuous development of turbomachinery applications, in particular in the Oil and Gas field where a wide variety of solutions, such as off-shore installations or modularized turbo-compression and turbo-generator trains, requires a more complete analysis not only limited to the rotor-bearing system. Complex elastic systems such as rotating machinery supporting structures and steel foundations might, in some situations, strongly dominate the entire shaft line rotor dynamic response (mode shapes, resonance frequencies and unbalance response). They give birth to transfer functions which will introduce coupling phenomena between machines bearings, becoming enablers of a new shaft line dynamic. Since FEM theory offers a number of different solutions to represent the rotor and the rotating machine support system (beam models, solid models, transfer function, etc.), in this paper a great emphasis is given to the results of an experimental campaign done on a centrifugal compressor as validation of the new rotor dynamic approach.

Control design, simulation and validation of a turbo-machinery auxiliary plant

In the oil and gas industry, the testing of auxiliary lubrication plants represents an important preliminary activity before the whole turbo machinery train (including the auxiliary lubrication plant) can be put in operation. Therefore, the employment of both efficient and accurate plant models becomes mandatory to synthesize satisfactory control strategies both for testing and normal operation purposes. For this reason, this paper focuses on the development of innovative real-time models and control architectures to describe and regulate auxiliary lubrication plants. In particular, according to the Bond-Graph modelling strategy, a novel lumped parameter model of the lube oil unit has been developed to properly optimize the behaviour of this unit if it is controlled. The code has been compiled and uploaded on a commercial real-time platform, employed to control the pressure control valve of the physical plant, for which a new controller has been developed. The comparison between the data obtained from the simulated system and acquired from the physical plant shows good agreement and the good performance and reliability of the proposed model and control strategy. The modelling approach and the control strategy have been developed in collaboration with GE Nuovo Pignone S.p.a. while the experimental data were acquired in a plant located in Ptuj (Slovenia).

Tilting Pad Journal Bearing TEHD Analysis: An Innovative Model

Tilting Pad Journal Bearings (TPJBs) are widely used in the turbomachinery field due to their superior dynamical performances, but their operation involves several different physical phenomena. In this research work the authors propose an innovative 3D ThermoElastoHydroDynamic (TEHD) model for the analysis of TPJBs behaviour developed and experimentally validated in cooperation with General Electric Nuovo Pignone: the model is able to perform a nonlinear transient coupled analysis taking into account fluid dynamical, thermal and elastic effects and reaches a good compromise between the accuracy of the results and the computational efficiency.

Development and Validation of a Model to Describe the Bearings Interaction in Rotating Machines Due to Elastic Supporting Structures

This work focuses on the effects of the flexible supporting structures and on the bearing interaction caused by their elastic deflection on the whole rotor-substructures system [1]. More particularly, a careful theoretical and experimental analysis is performed to understand how the supporting structures influence the rotors behaviour [2, 3] through the actions of the machine bearings. To this end, this study considers a model of the whole rotating machine [4], taking into account the coupling of the dynamic behaviour of the different system components. The whole FEM model has been implemented in the ANSYS [5] simulation environment. The main goal of this research, is to offer an optimal balance between efficiency and accuracy allowing the modelling of the real physical complex system and simultaneously the reduction of calculation times. The whole analysis has been developed and validated in cooperation with General Electric S.p.A. which provided the technical and experimental data related to some tests recently performed in Massa-Carrara (Italy) on a benchmark turbocompressor machine.

Development and Preliminary Validation of Efficient 3D Models of Tilting Pad Journal Bearings

This paper mainly focuses on the development of efficient three-dimensional (3D) models of TPJBs, able to contemporaneously simulate both the rotor dynamics of the system and the lubricant supply plant. The proposed modelling approach tries to obtain a good compromise between the typical accuracy of standard 3D models and the high numerical efficiency of simpler and less accurate models. In this work, the whole model has been developed and validated in collaboration with Nuovo Pignone General Electric S.p.a. which provided the required technical and physical data. In particular, the experimental data are referred to a suitable lube oil console system, built at the GE testing center in Massa-Carrara (MS, Italy) for the verification of plant components.

Development and Preliminary Validation of a New Strategy to Model the Interaction Between Rotating Machines and Elastic Supporting Structure

The accurate modelling of the complicated dynamic phenomena characterizing rotors and support structures represents a critical issue in rotor dynamics field. A correct prediction of the whole system behavior is fundamental to identify safe operating conditions and to avoid instabilities that may lead to erroneous project solutions or possible unwanted consequences for the plant. Although a generic rotating machine is mainly composed by four components (rotors, bearings, stators and supporting structures), many research activities are often more focused on single components rather than on the whole system. The importance of a combined analysis of rotors and elastic supporting structures arises with the continuous development of turbo machinery applications, in particular in the Oil and Gas field where a wide variety of structurally optimized solutions with reduced weight on off-shore installations or modularized turbo-compression and turbo-generator trains, requires a more complete analysis not only limited to the rotor-bearing system. Complex elastic systems, in some cases, strongly affect the entire shaft line rotor dynamic response such as mode shapes, resonance frequencies, unbalance response and critical speeds. The aim of the study is a development of a new efficient methodology based on FEM approach to model the complete rotating machinery systems (rotors, bearings, stators and supporting structures), by means of appropriate transfer functions matrix. Taking advantage from the matrix of transfer functions H(ω) obtained through PSD analysis, the baseplate dynamic behavior can be timely and CPU efficiently computed, avoiding computationally expensive harmonic sweeps. The appropriate usage of undocumented ANSYS command ‘TFUN’ has been pursued in order to extract the required components of the transfer functions matrix at the bearing location. With such a solution the full dynamic interaction between the system components was accurately accounted. The outcome of the new methodology was successfully tested in a real field issue where evidences of structure to rotor interaction emerged at the proximity probe measurement during machine start-up.

A Tilting Pad Journal Bearing Model for Coupled Fluid Dynamical-Rotor Dynamical Analyses

Turbomachines are continuously developing in order to reach higher levels of speed, power and efficiency and the classical Fixed Geometry Journal Bearings have been replaced by Tilting Pad Journal Bearings to avoid instability phenomena. In this paper, the authors propose an innovative quasi-3D TPJB modelling approach that allows the simultaneous and coupled analysis of the typical phenomena involved in TPJB operations. The authors focused on the accurate analysis of the interactions between the rotor and the lubricant supply plant and on the fluid dynamical effects due to the bearing that cause those couplings, aiming at reaching a good compromise between the accuracy and the numerical efficiency of the model (mandatory to analyze systems with many bearings).The TPJB model has been developed and experimentally validated in collaboration with Nuovo Pignone General Electric S.p.a. which provided the technical data of the system and the results of experimental tests.Copyright