Comparing numerical methods to calculate fluid pressure

O presente trabalho teve por objetivo comparar o método de elementos finitos com o método de diferenças finitas no cálculo numérico da pressão interna do mancal com excentricidade e geometria cilíndrica, com uso da geometria para simplificação da equação de Navier-Stokes. Fez-se o uso do software de código aberto ROSS para prover os resultados com o método de diferenças finitas, enquanto que o método de elementos finitos foi programado pelo autor. Como base para checagem de erro, fez-se o uso de soluções não numéricas para o problema do mancal nos casos curto e longo, onde a equação de Navier-Stokes torna-se ainda mais simples. Avaliou-se o número de iterações até conversão da malha bem como o tempo de processamento de cada iteração. Os resultados indicaram um desempenho levemente superior do método de diferenças finitas para o cenário e os critérios avaliado e considerando diferentes configurações da malha

Impact of damper seal coefficients in rotor dynamics : uncertainties and optimization

Damper seals can have a significant impact on rotor dynamics, but the calculation of the stiffness and damping coefficients for this component can be challenging and has a high uncertainty. In the present work, a probabilistic model is proposed to model the seal coefficients, which are frequency-dependent. We develop a stochastic process (frequency indexed) so that the uncertainty in the model is taken into account. The impact of these uncertainties on the rotordynamic behavior of a compressor is analyzed. The deterministic coefficients of the seal are determined considering a bulk-flow model and values calculated by a compressor vendor based on the extrapolation of experimental data. The obtained results show that the uncertainty of these coefficients have a considerable impact on the compressor rotordynamic behavior, affecting the stability margin and the unbalance response. Based on this analysis, a procedure for the robust optimization of the compressor rotordynamic behavior is proposed. This procedure considers the seal geometric parameters as design variables. The results for the robust optimization show that the seal length and the cell hole depth can be modified to improve the unbalance response.Os selos amortecedores podem ter grande impacto na dinâmica de rotores, mas o cálculo dos valores dos coeficientes de rigidez e amortecimento para este componente é difícil e possui grande incerteza. No presente trabalho, um modelo probabilístico é proposto para modelar os coeficientes do selo, que são dependentes da frequência. Um processo estocástico (indexado na frequência) é construído de forma que o erro do modelo seja levado em consideração. O impacto dessas incertezas no comportamento rotodinâmico de um compressor é analisado. Os coeficientes determinísticos do selo são determinados considerando o modelo ‘bulk-flow’ e valores calculados por um fabricante de compressores baseado em uma extrapolação de dados experimentais. Os resultados obtidos mostram que a incerteza desses coeficientes tem um impacto considerável no comportamento rotodinâmico do compressor, afetando a margem de estabilidade e a resposta ao desbalanceamento. Baseado nesta análise, um procedimento para a otimização robusta do comportamento rotodinâmico do compressor é proposto. Este procedimento considera parâmetros geométricos do selo como variáveis de projeto. Os resultados da otimização robusta mostram que o comprimento do selo e a profundidade das células podem ser alterados com o objetivo de se obter uma melhor resposta ao desbalanceamento

Full Load Testing Of A 12.5 MW Vertical High Speed Subsea Motorcompressor

Lecturepg. 79-92In late 2006 Authors’ company was awarded a contract for the motorcompressor for the Ormen Lange Subsea Compression Pilot. This Pilot represents the first subsea motorcompressor unit ever built in a fully marinized version and tested in a water pit, which was developed specifically for the project at the customer’s site (Nhyamna, Norway). The prototype unit is a 12.5MW (16763HP) integrated motorcompressor, which runs up to 10.5krpm in a vertical configuration with the following features: Single casing; High-speed motor rigidly coupled to a multistage centrifugal compressor (3 journal bearings shaft line); Canned Active Magnetic Bearings (AMBs); Process gas used as cooling fluid for the Electric Motor; Internal separation system (to protect the bearings and the electric motor from the intrusion of solid and liquid materials); Fully marinized AMBs control system; The design and validation plan for this complex equipment were developed through a four years program where many challenging milestones were achieved. The Ormen Lange Subsea Compression Pilot motorcompressor has successfully completed an intensive full load testing campaign in the Authors’ Company plant including the following: Static-dynamic tuning of the AMBs; Mechanical Running Test; Compressor Performance Test (ASME PTC-10 Type 2 + Full Load test); Electric Motor Performance Test; Overall cooling system check; Landing test (partial landing and full speed delevitation test). The test campaign has fully demonstrated the functionality of this prototype unit capable of operation in the service conditions. The Next step will be the shipment to the costumer site where the submerged testing will be conducted. This paper will provide a detailed description of the main test results of the subsea motorcompressor covering all aspects of the test program including rotordynamic behaviour, compressor thermodynamic performance, axial load variation versus operating conditions (monitored thanks to the thrust AMB), electric motor cooling system behaviour, electric motor performance, AMBs and control system operability. Of special interest is the rotor delevitation test from full speed consisting in the two ton rotor running at 10.5krpm dropping onto the mechanical emergency bearings until the machine reached a complete stop condition. This test, which was repeated 5 times, provided a full-scale verification of the landing numerical simulation developed by the authors (Ransom et al., 2009)

Aeronautical Engineering: a Continuing Bibliography with Indexes (Supplement 243)

This bibliography lists 423 reports, articles, and other documents introduced into the NASA scientific and technical information system in August 1989. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Advances and Trends in Mathematical Modelling, Control and Identification of Vibrating Systems

This book introduces novel results on mathematical modelling, parameter identification, and automatic control for a wide range of applications of mechanical, electric, and mechatronic systems, where undesirable oscillations or vibrations are manifested. The six chapters of the book written by experts from international scientific community cover a wide range of interesting research topics related to: algebraic identification of rotordynamic parameters in rotor-bearing system using finite element models; model predictive control for active automotive suspension systems by means of hydraulic actuators; model-free data-driven-based control for a Voltage Source Converter-based Static Synchronous Compensator to improve the dynamic power grid performance under transient scenarios; an exact elasto-dynamics theory for bending vibrations for a class of flexible structures; motion profile tracking control and vibrating disturbance suppression for quadrotor aerial vehicles using artificial neural networks and particle swarm optimization; and multiple adaptive controllers based on B-Spline artificial neural networks for regulation and attenuation of low frequency oscillations for large-scale power systems. The book is addressed for both academic and industrial researchers and practitioners, as well as for postgraduate and undergraduate engineering students and other experts in a wide variety of disciplines seeking to know more about the advances and trends in mathematical modelling, control and identification of engineering systems in which undesirable oscillations or vibrations could be presented during their operation

Aeronautical engineering, a continuing bibliography with indexes

This bibliography lists 419 reports, articles and other documents introduced into the NASA scientific and technical information system in March 1985

Rotordynamic Instability Problems in High-Performance Turbomachinery, 1990

The present workshop continues to report field experience and experimental results, and it expands the use of computational and control techniques with the integration of damper, bearing, and eccentric seal operation results. The intent of the workshop was to provide a continuing impetus for an understanding and resolution of these problems

Instability in Rotating Machinery

The proceedings contain 45 papers on a wide range of subjects including flow generated instabilities in fluid flow machines, cracked shaft detection, case histories of instability phenomena in compressors, turbines, and pumps, vibration control in turbomachinery (including antiswirl techniques), and the simulation and estimation of destabilizing forces in rotating machines. The symposium was held to serve as an update on the understanding and control of rotating machinery instability problems