Shop Test Research Articles

Development of a Zero-Dimensional Model for a Low-Speed Two-Stroke Marine Diesel Engine with Exhaust Gas Bypass and Performance Evaluation

Most large commercial vessels are propelled by low-speed two-stroke diesel engines due to their fuel economy and reliability. With increasing international concern about emissions and the rise in oil prices, improvements in engine efficiency are urgently needed. In the present work, a zero-dimensional model for a low-speed two-stroke diesel engine is developed that considers the exhaust gas bypass and geometry structures for the gas exchange model. The model was applied to a low-speed two-stroke 7G80 ME-C9 marine diesel engine and validated with engine shop test data, which consisted of the main engine performance parameters and cylinder pressure diagrams at different loads. The simulation results were in good agreement with the experimental data. Thus, the model has the ability to predict engine performance with good accuracy. After model validation, the variations in compression ratio, fuel injection timing, exhaust gas bypass valve opening portion, exhaust valve opening timing, and exhaust valve closing timing effects on engine performance were tested. Finally, the influence level of different parameters on engine performance was summarized, which can be used as a reference to determine the reasons for high fuel consumption in some cases. The developed engine performance model is considerable in digital twins for performance simulation, health management, and optimization.

Investigation and ranking the causes of delay in EPC projects of nonindustrial buildings of 9, 10, 19, 20 and 21 phases of South Pars of Iran

Delay is one of the most common causes of construction projects failure in Iran. The larger sizes of the projects, the more risks and costs of delays. In this paper, the causes of delays in EPC contracts of nonindustrial buildings were excavated from the related previous research and several interviews with experts of this subject, and adjusted by the brainstorming technique, Delphi and reconciling the nature of these projects. Then, a questionnaire was distributed among 52 experts working in the South Pars project, and the data were analyzed by descriptive and factor analysis methods. Descriptive analysis revealed that “Inflation and escalation of material prices and human resources salaries”, “Unrealistic contract duration and requirements imposed” and “Political situation” were the most significant delay factors. Meanwhile, factor analysis indicates that “Improper construction methods”, “Shortage of experienced and skilled labor” and “Long acceptance process (shop drawings, permits, tests and samples)” were the most important causes of delay.

Impact factors on the rotor dynamic stability evaluation by the sine-sweep excitation with active magnetic bearing: Numerical and experimental investigation

It is of importance to obtain the stability margin of the industrial rotating machinery to avoid the instability risk by carrying out rotordynamic stability tests. To obtain accurate stability parameters results, it is essential to measure excitation forces accurately when using the frequency response functions (FRFs) to identify stability parameters. The commonly used actuator is the active magnetic bearing (AMB) for its easy controllability and convenience of non-contact. However, because of the difficulty of measuring force accurately, estimation errors inevitably exist. Hence, the factors affecting the identification accuracy are investigated, which include the bias currents in actuator coils, the locations of excitation and measurement, the force models of AMB, the magnitudes of excitation and the offset of shaft center at the actuator node. Groups of excitation experiments are also carried out. The results show that the tedious calibration of AMB force can be made omissible by choosing a small bias current, such that the negative stiffness can be neglected, and modal parameters analysis then performed easily for the rotor system. This guidance can be used for researchers to evaluate rotordynamic stability in the laboratory, shop test or fields.

A Numerical Study on Fuel Injection Optimization for a ME-GI Dual-Fuel Marine Engine Based on CFD Analysis

A numerical study was carried out to investigate the effects of injector spray angle (SA) and injection position (IP) on the combustion and emission characteristics of a two-stroke ME-GI marine engine at full load. Three-dimensional (3D) simulations of the combustion process and emission formations inside the cylinder of the engine operating in the diesel and DF modes were performed using the ANSYS Fluent simulation software to analyze the in-cylinder pressure, temperature, and emission characteristics. The simulation results were compared and showed good agreement with the experimental results reported in the engine’s shop test technical data. The simulation results showed that the IP of 0.02 m with an SA of 40 degrees helps to enhance the engine performance; however, if the main target is reducing engine exhaust gas emissions, an IP of 0.01 m is highly recommended to be used. At this IP, the specific SA of 40, 45, or 50 degrees that should be used will depend on which emissions (NO, soot, CO2, etc.) need to be reduced. This study successfully investigated the effects of injector SA and IP on the combustion and emission characteristics of the researched engine and would be a good reference for engine design and operating engineers.

Modeling and performance analysis of diesel engine considering the heating effect of blow-by on cylinder intake gas

Recently, the stringent international regulations on ship energy efficiency and NOx emissions from ocean-going ships make energy conservation and emission reduction be the theme of the shipping industry. Due to its fuel economy and reliability, most large commercial vessels are propelled by a low-speed two-stroke marine diesel engine, which consumes most of the fuel in the ship. In the present work, a zero-dimensional model is developed, which considers the blow-by, exhaust gas bypass, gas exchange, turbocharger, and heat transfer. Meanwhile, the model is improved by considering the heating effect of the blow-by gas on the intake gas. The proposed model is applied to a MAN B&W low-speed two-stroke marine diesel engine and validated with the engine shop test data. The simulation results are in good agreement with the experimental results. The accuracy of the model is greatly improved after considering the heating effect of blow-by gas. The model accuracy of most parameters has been improved from within 5% to within 2%, by considering the heating effect of blow-by gas. Finally, the influence of blow-by area change on engine performance is analyzed with considering and without considering the heating effect of blow-by.

Визначення причин, попередження і усунення нестійких режимів газотурбокомпресорів суднових дизелів

Annotation – With commissioning of the “Socofl Star” ship’s series, negative occurrences relative to surging of the Main Engine (ME) «Hanshin Diesel» 6LF46 turbochargers (TC) VTR 401-2. To elimination of a surging, it was necessary reduce loading of ME to the safe level. This action caused the ship’s speed to fall from 11 – 10 to 4 knots which resulted in worsening of the ship’s maneuverability characteristics and lead to the failure to provide the ship’s service speed stipulated in the contractual arrangements. Existence of this problem instigated the shipowner to charge us as experts with the mission of carrying out appropriate investigations and working out recommendations as to how to prevent and eliminate surging of TC. This task was solved on the m/v “Socofl Star”. Based on results the ME shop test and trial test of the vessel and also the saved-up data of work of ME in various conditions of swimming, the analysis of the causes of a surge of the TC was made. It is established that small values of safety factor of stability of the compressor of TC on a surging – KCT which are not allowing to ensure effective functioning of TC on the main modes of loading of ME are its reason. For increase in area of steady work of TC it is necessary to reduce the hydraulic resistance of components of the Air-Gas Path (AGP) of the ME which can be realized by changes in a design of units of air supply and gas exchange or reduction of productivity and extent of increase in pressure of air in the compressor of TC. Under operating conditions vessels an optimal solution an objective is removal of a part of blowing-off air after compressor of the TC. The air can be discharged into the flue gas header after the waste heat recovery boiler or directly into the atmosphere. This allowed the shipowner not to make constructive changes to the components of the AGP of ME and TC. The description of the operated unloading device controlled remotely on removal of air which ensures effective functioning of TC and ME that is confirmed by results of natural tests and the subsequent operating experience of vessels of the “Socofl Star” series is provided.

Effects of Various Fuels on Combustion and Emission Characteristics of a Four-Stroke Dual-Fuel Marine Engine

A numerical study was carried out to investigate the effects of methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), and dimethyl ether (DME) on the combustion and emission characteristics of a four-stroke gas-diesel dual-fuel (DF) marine engine at full load. Three-dimensional simulations of the combustion process and emission formation inside the engine cylinder in the diesel and DF modes were performed using the AVL FIRE R2018a simulation software to analyze the in-cylinder pressure, temperature, and emission characteristics. The simulation results agreed well with the measured values reported in the engine shop test technical data. The simulation results showed reductions in the in-cylinder peak pressure and temperatures, as well as the emission formations, in the DF modes in comparison to the diesel mode. The DF mode could significantly reduce nitric oxide (NO) emissions (up to 96.225%) of DME compared to the diesel mode. Meanwhile, C3H8 and CH4 fuels effectively reduced the soot (up to 82.78%) and carbon dioxide (CO2) emissions (by 21.33%), respectively, compared to the diesel mode. However, the results also showed longer ignition delay times of the combustion processes when the engine operated in the DF mode, particularly in the DME-diesel mode. The combustion and emission characteristics of the engine were also analyzed when varying the injection timing; the results showed that applying the injection timing adjustment method could further address NO emission problems but led to a decrease in the engine power. Therefore, it is necessary to consider the benefits and disadvantages of adopting the injection timing adjustment strategy to address certain engine emission problems. This study successfully analyzed the benefits of using various gas fuels as alternative fuels and the injection timing adjustment method in DF marine engines to meet the International Maritime Organization (IMO) emission regulations without the use of any emission after-treatment devices.

Numerical investigation of interaction between propulsion system behaviour and manoeuvrability of a large containership

In actual operation process of a ship, the engine-propeller-hull is an integrated system with internal coupling effects, and thus there is a close interaction between the diesel engine propulsion system operation conditions and the ship manoeuvring motions. The propulsion system can experience large power fluctuation during manoeuvring, with considerable torque increase with regard to the stabilized value in straight course. However, the diesel engine propulsion system behaviour and ship manoeuvrability are usually studied separately as they are considered to belong to different disciplines. Thus, it is difficult to reflect the actual operating characteristics of the propulsion system and ship manoeuvring motion under coupled conditions in actual operation. To investigate the interaction between the propulsion system behaviour and the manoeuvrability of a large containership, this paper proposed a multi-disciplinary ship mobility model capable of coupling the marine diesel engine model and the ship manoeuvring model. In the engine model, the mean value modelling approach was adopted to simulate the two-stroke marine diesel engine considering the fact that it can capture the performance of the engine sub-systems including scavenging receiver, exhaust gas receiver, turbocharger, etc. In the manoeuvring model, the MMG-based method was used to simulate the ship manoeuvring motion with three degrees-of-freedom. The engine model and manoeuvring model were coupled through the propeller model that transferring propeller speed and torque between the two models. The coupled model was validated against the engine shop test data and the sea trial results. By applying this coupled model, a series of simulations of turning circle manoeuvres under various scenarios were performed. The simulation results presented the dynamic response of engine internal sub-systems during turning circle manoeuvring, explained the effect of the torque limiter on engine performance and ship manoeuvring motion, and analyse the influence of different propulsion system control strategies on the ship turning circle manoeuvrability. Although the presented case study has been validated on a specific ship, most of the discussed models have a general application.

A Numerical Study on the Combustion Process and Emission Characteristics of a Natural Gas-Diesel Dual-Fuel Marine Engine at Full Load

This paper presents research on the combustion and emission characteristics of a four-stroke Natural gas–Diesel dual-fuel marine engine at full load. The AVL FIRE R2018a (AVL List GmbH, Graz, Austria) simulation software was used to conduct three-dimensional simulations of the combustion process and emission formations inside the engine cylinder in both diesel and dual-fuel mode to analyze the in-cylinder pressure, temperature, and emission characteristics. The simulation results were then compared and showed a good agreement with the measured values reported in the engine’s shop test technical data. The simulation results showed reductions in the in-cylinder pressure and temperature peaks by 1.7% and 6.75%, while NO, soot, CO, and CO2 emissions were reduced up to 96%, 96%, 86%, and 15.9%, respectively, in the dual-fuel mode in comparison with the diesel mode. The results also show better and more uniform combustion at the late stage of the combustions inside the cylinder when operating the engine in the dual-fuel mode. Analyzing the emission characteristics and the engine performance when the injection timing varies shows that, operating the engine in the dual-fuel mode with an injection timing of 12 crank angle degrees before the top dead center is the best solution to reduce emissions while keeping the optimal engine power.

Organization of safe execution of works with the use of trapping nets

The organization of ensuring safe execution of building and assembly works when erecting and reconstructing buildings (structures) of various purposes based on the application of trapping nets to prevent industrial injuries in case of human or items falling from height is presented. Structural layout of a safety (catching) device with pivotally mounted brackets and a freely hanging net was considered. Appearing dynamic loads in case of items falling on trapping nets depending on impact acceleration were theoretically identified. It was found out that a trapping net with pivotally positioned brackets additionally reduces deceleration loads in relation to devices with rigidly fixed brackets and their use is more effective for cases of men falling with insignificant forward velocity. Bench and shop tests of trapping devices were carried out with the purpose of checking compliance of selected theoretical models, selection of developed options of designs and schematic diagrams, differentiation of reaction of capron and lavsan net materials from action of impulse loads. Test key results confirming matching of experimental data with presented theoretical models were showed. It was established that dynamic overloads depend both on a bracket position angle as well as on a place of an item falling into net, the value of pitch of deflection of net cloth made of lavsan and capron materials is almost similar and characteristics of values of their displacement under dynamic loads from a falling item are identical.

Identification of the Factors for the Selection of Cement Brands by Construction Companies and Selection of Optimal Cement Brand using TOPSIS for Kathmandu Valley along with the Physical Strength Comparison of Various Cement Brands

Cement comprises major proportion in any construction materials and the right selection of cement is equally important for construction companies. The objective of this research is to find the criteria used by the construction companies in cement selection and using the required criteria adopt TOPSIS (Technique of Order Preference by Similarity to Ideal Solution) as Multi Criteria Decision Making method for the selection of optimal cement brand among various cement brands for the construction projects in Kathmandu. Another objective is to find the physical characteristics of the selected cement brands in laboratory. For the methodology, non-random sampling was adopted. Data were collected by questionnaire, semi-structured interviews, KII and Lab test. For physical characteristics comparison of cement brands, samples were collected from hardware shop and lab test were conducted in private lab. For the factors in cement selection quality, ex-factory rate, credit-terms, delivery-time, relationship, self-clinker production, production-capacity, technology and financial-conditions were identified and ranked in relevant order. Six factors were chosen for TOPSIS for the six cement brands for Kathmandu valley. From TOPSIS, it was foundSarbottam cement is best suited for projects in Kathmandu valley in terms of physical strength Hongshi had the highest 3 and 7 days of compressive strength where as Sarbottam had highest 28 days strength. Maruti cement had longest setting time whereas United cement had shortest setting time. 28 days strength of all the cement were as per the NS 49whereas except for Maruti and Shivam, all the brands had strength as per IS 8112 criteria.

Organization of safe execution of works with the use of trapping nets

The organization of ensuring safe execution of building and assembly works when erecting and reconstructing buildings (structures) of various purposes based on the application of trapping nets to prevent industrial injuries in case of human or items falling from height is presented. Structural layout of a safety (catching) device with pivotally mounted brackets and a freely hanging net was considered. Appearing dynamic loads in case of items falling on trapping nets depending on impact acceleration were theoretically identified. It was found out that a trapping net with pivotally positioned brackets additionally reduces deceleration loads in relation to devices with rigidly fixed brackets and their use is more effective for cases of men falling with insignificant forward velocity. Bench and shop tests of trapping devices were carried out with the purpose of checking compliance of selected theoretical models, selection of developed options of designs and schematic diagrams, differentiation of reaction of capron and lavsan net materials from action of impulse loads. Test key results confirming matching of experimental data with presented theoretical models were showed. It was established that dynamic overloads depend both on a bracket position angle as well as on a place of an item falling into net, the value of pitch of deflection of net cloth made of lavsan and capron materials is almost similar and characteristics of values of their displacement under dynamic loads from a falling item are identical.

A fast damping ratio identification method for rotating machinery based on the singular value of a directional power spectra density function matrix

It is of great importance to accurately evaluate the stability margin of a turbomachine both in shop tests and in operation. The damping ratio of the first forward whirl mode is the key indicator of rotordynamic stability. In this paper, a fast operational modal analysis (OMA) technique based on the singular value of the directional power spectra density function (dPSDF) matrix was developed to estimate the damping ratios of the first forward and backward whirl modes. Numerical simulations and experiments were carried out to verify the accuracy of this method on a high-speed test rig. Moreover, the dPSDF-based method was compared to two conventional OMA methods - data-driven and covariance-driven stochastic subspace identification (SSI) methods - resulting in more stable and accurate estimates for the damping ratio along with a much faster identification time (less than 0.5 s). This study provides an accurate and fast method for performing stability shop tests for turbo machines and stability online monitoring.

New technique for producing items from TiC-(Ni-alloy) cermet for severe application conditions

A new technique for producing complex-shaped items from wear-resistant TiC-(Ni-alloy) cermets is described. Cermets are produced by infiltration of TiC-preforms with Ni-alloy, which combines the advantages of powder metallurgy and casting. A special vacuum induction furnace is designed to effectively implement the new technique, which enhances the production capacity and quality of a cermet item against other known technologies. The structure of new cermets is characterized by a uniform distribution of TiC grains in the Ni matrix. During infiltration, a considerable part of tungsten and some part of molybdenum migrate in TiC grains forming solid solution shells on them. The shell ensures the connection between TiC and Ni-alloy and high physical and mechanical properties of the cermet. The physical and mechanical properties of the TiC-(Ni-alloy) cermet at temperatures up to 1100 °С and the results of practical use of items from cermets in production are presented. The shop tests showed the increase of the durability of a cermet ball valve by more than 6 times as compared with conventional wedge valves.

Development of a Model to Determine the Baseline Mass Transfer Coefficient in Bioreactors (Aeration Tanks).

Over 60 percent of all wastewater treatment plants in the developed countries use the activated sludge process as their secondary treatment system. About 50 to 85 percent of the total energy consumed in a biological wastewater treatment plant is in aeration. The activated sludge process, the most common such process, is performed in large aeration basins to provide air for microorganisms to remove nutrients and pollutants through biodegradation. Designs for the air supply often fail to meet sustained peak organic loading, which may lead to unsatisfactory treatment performance and even plant failure. On the other hand, excessive safety factors used in design for the air supply may similarly lead to unsatisfactory treatment performance and energy wastage. Improper sizing of the aeration system is primarily due to inability to estimate the mass transfer coefficient (KL a) correctly for different tank depths, leading to improper blower design and to inappropriate operation, among other things. In general, the efficiency of porous fine-bubble diffuser systems varies from 10 to 30 percent or more, depending on tank depth. The term KL a is used in ASCE/EWRI Standard 2-06 to define the apparent volumetric mass transfer coefficient in a non-steady-state clean water test in an aeration tank. This parameter is a function of tank depth, due to the variation of oxygen gas depletion with depth. The objective of this paper is to introduce a baseline oxygen mass transfer coefficient (KL a0 ), a hypothetical parameter defined as the oxygen transfer rate coefficient at zero depth, and to develop new models relating KL a to the baseline KL a0 as a function of temperature, system characteristics (e.g., the gas flow rate, the diffuser depth Zd ), and oxygen solubility (Cs ). Results of this study on data extracted from the literature indicate that a uniform value of KL a0 that is independent of tank depth can be obtained experimentally. Using the baseline, a family of rating curves for KL a20 (the standardized KL a at 20 °C) can thus be constructed for various gas flow rates applied to various tank depths. The new model relating KL a to the baseline KL a0 is an exponential function, and (KL a0 )T is found to be inversely proportional to oxygen solubility in water (Cs )T to a high degree of correlation. Using a predetermined baseline KL a0 , the new model predicts oxygen transfer coefficients KL a20 for any tank depth to within 1-3% error compared to observed measurements, and similarly for the standard oxygen transfer efficiency. The discovery of a standard baseline (KL a0 )20 determined from shop tests is important for predicting the KL a20 value for any other aeration tank depth and gas flowrate, and this finding can be used in the development of energy optimization strategies for wastewater treatment plants. This work may also improve the accuracy of aeration models used for aeration system evaluations.

Performance of Alpine Touring Boots When Used in Alpine Ski Bindings.

Alpine touring (AT) equipment is designed for ascending mountains and snow skiing down backcountry terrain. Skiers have been observed using AT boots in alpine (not made for Alpine Touring) ski bindings. We tested the effect on the retention-release characteristics of AT boots used in alpine bindings. Ten AT ski boots and 5 alpine ski boots were tested in 8 models of alpine ski bindings using an ASTM F504-05 (2012) apparatus. Thirty-one percent of the AT boots released appropriately when used in alpine ski bindings. One alpine binding released appropriately for all alpine and AT boots tested; 2 alpine ski bindings did not release appropriately for any AT boots. Altering the visual indicator settings on the bindings (that control the release torque of an alpine system) had little or no effect on the release torque when using AT boots in alpine ski bindings. Many combinations released appropriately in ski shop tests, but did not release appropriately in the more complex loading cases that simulated forward and backward falls; the simple tests performed by ski shops could produce a "false-negative" test result. These results indicate that using AT boots with alpine ski bindings could increase the likelihood of lower leg injuries.

Development of a real-time two-stroke marine diesel engine model with in-cylinder pressure prediction capability

The in-cylinder pressure is an important parameter for the diesel engine but it fails to be used in the common scenes, like the control, hardware in loop, and virtual reality, for its lack of real-time capability. In order to have this capability, the conventional diesel engine models are ameliorated (named as MG model, the merged diesel engine model). These parameters that exclude the in-cylinder pressure and indicator torque are calculated by mean value model, the widely used model for real-time applications, to keep on its speed. The other parameters are calculated by the 0D model. To improve the in-cylinder pressure calculation speed, the simplification and asychronization are used. The compression, combustion, and expansion processes are calculated the same as 0D assumption but the exhausting and scavenging processes are simplified by two linear functions. Its calculation time saves about 33.3% comparing to the conventional 0D approach. The boundaries of cylinder model are asynchronous with the scavenging and exhausting manifolds by abandoning cylinder cycles at reasonable intervals so that the time can be reduced further. In practical coding, the in-cylinder pressure needs to be calculated by a parallel thread to realize asychronization. In the case that abandons 4 cycles every 5 cycles the calculation time saves nearly 80% further. Only during the dynamic process, is the reduced time positively correlated with the number of abandoned cycles. The proposed model is calibrated against shop test data, whose predicting accuracy is comparable to the 0D model. The maximum relative errors of steady MG model and steady 0D model are 3.96% and −3.23%, and the mean relative errors are 1.38% and 2.18%. In the case that abandons 4 engine cycles, the maximum relative error of explosion pressure is 0.363% during the dynamic process. This model can be used in real-time HIL, controller design, engine analysis, and simulator.

Potential for efficiency improvement of four-stroke marine diesel gensets by utilisation of exhaust gas energy

In the present paper, it is examined the potential application of a Rankine cycle exhaust gas heat recovery system which recovers and utilises energy from the exhaust gas of four-stroke marine diesel auxiliary unit before it is released to the atmosphere, increasing thus its total efficiency. For this purpose, a thermodynamic simulation model of the Rankine bottoming cycle is used. Heat utilisation is initially considered only from the main exhaust gas stream after the T/C turbine. As reference for the investigation are used the values from the official shop tests at various loads ranging from 25% up to 100%. From these using the Rankine cycle simulation model, it is investigated the potential for increase of generated cycle power output and optimisation of its efficiency. In addition, it is examined the effect of working media by considering steam and an organic. The results derived reveal that there exists a significant potential for fuel saving by utilisation of exhaust gas energy of auxiliary engines installed on commercial vessels.

Latest practical notes and recent lessons learned on compressor design, specifying and operation

Latest achievements, new guidelines and modern methods on specifying, selection, design, installation, operation and maintenance of centrifugal compressor trains are discussed. The goal is an optimum compressor train arrangement considering performance, reliability and commercial conditions. The focus is to explain latest technologies and recent methods to obtain the lowest ‘Total Cost of Ownership’. Critical areas related to mechanical design, reliability and performance of centrifugal compressors including operating map, torsional studies, process considerations, shop test and others are discussed. A case study is also presented for the torsional study of a complex multi-casing centrifugal compressor train.

On the Dynamic Properties of Pump Liquid Seals

Rotordynamic instability due to fluid flow in seals is a well known phenomenon that can occur in pumps as well as in steam turbines and air compressors. While analysis methods using bulk-flow equations are computationally efficient and can predict dynamic properties fairly well for short seals, they often lack accuracy in cases of seals with complex geometry or with large aspect ratios (L/D above 1.0). This paper presents the linearized rotordynamic coefficients for a liquid seal with large aspect ratio subjected to incompressible turbulent flow. The fluid-induced forces acting on the rotor are calculated by means of a three-dimensional computational fluid dynamics (3D-CFD) analysis, and are then expressed in terms of equivalent linearized stiffness, damping, and fluid inertia coefficients. For comparison, the seal dynamic coefficients were calculated using two other codes: one developed with the bulk flow method and one based on the finite difference method. The three sets of dynamic coefficients calculated in this study were used then to predict the rotor dynamic behavior of an industrial pump. These estimations were then compared to the vibration characteristic measured during the pump shop test, results indicating that the closest agreement was achieved utilizing the CFD generated coefficients. The results of rotor dynamic analysis using the coefficients derived from CFD approach, improved the prediction of both damped natural frequency and damping factor for the first mode, showing substantially smaller damping factor which is consistent with the experimentally observed instability of the rotor-bearing system. As result of continuously increasing computational power, it is believed that the CFD approach for calculating fluid excitation forces will become the standard in industry.