Performance Simulation and Optimization of CCPP with Turbine Inlet Air Cooling

It is well established that the performance of combustion air turbines (gas turbines) is sensitive to ambient air temperature. As the ambient air temperature increases beyond standard design point  (ISASLS), the power output and exhaust gas flow rate reduces while the heat rate and exhaust gas temperature increases. While the trends are similar for heavy duty and aeroderivative gas turbines, due to the inherent nature of design the results are steeper for aeroderivatives.  Various types of turbine inlet cooling technologies such as evaporative cooling, refrigerated inlet cooling and thermal energy storage systems have been practiced with varying degree of success, each having its potential advantages and limitations.  Simplicity and cost advantage gained in evaporative cooling is offset by limitation of cooling along web bulb depression line (and is a function of site relative humidity). Refrigerated inlet cooling (direct and indirect) offer advantage of higher cooling and lesser sensitivity to site conditions, and result in greater power output with an impact on relative cost and complexity. Selection of optimum technology of turbine air inlet cooling is hence a tradeoff between competing factors.

Combined Cycle
              Combined Cycle Power Plant

The complexity of combined cycles, without any turbine inlet air cooling, poses significant challenge in design of steam system and HRSG due to competing factors such as pinch point, heat and mass flows optimization etc. Knowledge of fluid viz properties of standard air (psychrometrics), standard gas for Joule Brayton cycle, steam for bottoming Rankine cycle and refrigerant for cooling system( for refrigerated inlet air cooling) as applied to complete cycle makes the process complete as well as complex. AxCYCLE™ is one such unique tool to simulate such combined cycle processes with multi fluid-multi phase flows including refrigeration. The standard HVAC features can easily be used for inlet air cooling refrigeration and integrated into the CCPP. Once a digital representation of the complex process is replicated and successfully ‘converged’ at design point, the challenge of optimization emerges. To facilitate optimization various tools namely AxCYCLE™ Map, Quest, Plan and Case are embedded integrally. As a first cut, users based on their experience apply AxCYCLE™ Map and vary one or two parameters to see the effect of operational parameters on cycle performance. AxCYCLE™ Quest opens the gates by allowing users to vary unlimited parameters, according to quasi-random Sobol sequences. mutli-Parameter optimization tasks are possible using AxCYCLE™ Plan – it uses design of experiments concepts. Once optimized the AxCYCLE™ Case tools allows off design simulation tasks. Exhibit below represents complexity of a combined cycle plant represented conveniently:

To learn more please check out the following demos:

Cost Estimation & Economic Analysis http://learn.softinway.com/Webinar/Watch/51

Vapor Compression Refrigeration System http://learn.softinway.com/Webinar/Watch/86

Gas for Power

Gas turbines are one of the most widely-used power generating technologies, getting their name by the production of hot gas during fuel combustion, rather than the fuel itself. Today, the industry is clearly driven by the need of fast and demand-oriented power generation, thus additional effort is put in extremely short installation times, low investment costs and an enormously growing volatility in the electrical distribution in order to achieve higher levels of reliability in the power grid [2].

The majority of land based gas turbines can be assigned in two groups [3]: (1) heavy frame engines and (2) aeroderivative engines. The first ones are characterized by lower pressure ratios that do not exceed 20 and tend to be physically large. By pressure ratio, we define the ratio of the compressor discharge pressure and the inlet air pressure. On the other hand, aeroderivative engines are derived from jet engines, as the name implies, and operate at very high compression ratios that usually exceed 30. In comparison to heavy frame engines, aeroderivative engines tend to be very compact and are useful where smaller power outputs are needed. Gas turbine image

Nowadays, The increase of energy demand along with the growth of transportation market led to requirements for machines of highest efficiency (i.e. minimal fuel consumption), ability to operate in some certain range of conditions, and weight restrictions. In addition, to maintain competitiveness, it is essential to decrease the amount of time needed to complete the design cycle [4]. Most of machine’s geometrical properties are selected during preliminary design phase and remain almost unchangeable throughout next design phases, predefining its layout significantly. Therefore, the preliminary design task is the basis and the effort must be put in developing complete engineering tools to cover this task taking into account all possible aspects of a successful gas turbine design. In particular, a key advancement to the future of turbine technology is the turbine cooling of components in gas turbine engines to achieve higher turbine inlet temperatures, as increased inlet temperatures lead to better performance and higher lifespan of the turbine [5].

SoftInWay has extensive experience with gas turbine design and optimization. From our flagship software platform AxSTREAM® to AxCYCLE™ , designed for the thermodynamic simulation and heat balance calculations of heat production and electric energy cycles, to our extensive engineering consultant services, you can rest assured that all your project needs will be met by our engineering experts. The use of gas turbines for generating electricity dates back to 1939, where a simple-cycle gas turbine was designed and constructed by A. B. Brown Boveri in Baden, Switzerland, and installed in the municipal power station in Neuchâtel, Switzerland [6]. Today, SoftInWay Switzerland GmbH is located not far from Baden and allows the support of our European clients by offering consulting services, software and training for all engineers tastes. Visit our website and find out how you can take advantage of SoftInWay turbomachinery expertise.

References

[1]http://www.wartsila.com/energy/learning-center/technical-comparisons/gas-turbine-for-power-generation-introduction

[2]https://library.e.abb.com/public/ccb152e5e798b1cdc1257c5f004d64c1/DEABB%201733%2012%20en_Gas%20Turbine%20Power%20Plants.pdf

[3]https://energy.gov/fe/how-gas-turbine-power-plants-work

[4]http://softinway.com/wp-content/uploads/2013/10/Integrated-Environment-for-Gas-Turbine-Preliminary-Design.pdf

[5]Joel Bretheim and Erik Bardy, “A Review of Power-Generating Turbomachines”, Grove City College, Grove City, Pennsylvania 16127

[6]https://www.asme.org/about-asme/who-we-are/engineering-history/landmarks/135-neuchatel-gas-turbine

Analytical Tools for Determination of Damped Unbalanced Rotor Response

Blog 4 image 2
Representative Rotor Response Plot (API Standards) & Analytical Simulation

Lateral rotor-dynamic behavior is the most critical aspect in determining the reliability and operability of rotating equipment in the oil and gas industry – be it a centrifugal pump , compressor, steam or gas turbine, motor or generator. One way to evaluate operating reliability is identifying lateral rotor response to unbalance, i.e. by analytically determining damped unbalanced rotor response. Torsional response is sought only for train units comprising three or more coupled machines (excluding any gears). Experience suggests that the effect of other equipment in the train is normally not included in the lateral damped unbalanced response. Hence brief summary of various characteristics and a technique for analytical predictions of lateral behavior deserves attention by all.

The purpose of damped unbalanced rotor response is to identify critical speeds, associated amplification factors-AF (as per API standards AF greater than or equal to 2.5 is considered critical) and ability of rotor dynamics system to meet the separation requirements (margin of operating speed away from critical speed/s). The first step is ‘undamped’ unbalance response analysis for identifying mode shapes and critical speed-support stiffness map.  ‘Damped’ unbalanced response analysis then follows for each critical speed within the speed range of 0 % to 125 % of trip speed. Unbalance or side load is placed at the locations that have been determined by the undamped analysis to affect a particular mode most adversely. The magnitude of the unbalances is four times the value of U as calculated by U = 6350 W/N. The aim then is to identify the frequency of each critical speed, frequency-phase and response amplitude data, deflected rotor shape due to unbalance and bode plots to compare absolute shaft motion with shaft motion relative to the bearing housing (support stiffness <  3.5 times the oil-film stiffness).

Blog 4 image

To verify the analytical model, subject to various practical requirements, an unbalanced rotor response test could be performed as part of the mechanical running test. The actual response of the rotor on the test stand to the same arrangement of unbalance as used in the analysis is the criterion for determining the validity of the damped unbalanced response analysis. Sample summary results generated using SoftInWay’s integrated tool for rotor dynamics AxSTREAM®, as shown below indicate a very good agreement between test results and analytical predictions, for both amplitude and frequency.

For further understanding the analytical procedure, testing to validate damped unbalanced rotor response and implications please view http://learn.softinway.com/Webinar/Watch/90 or contact us to learn more.

Simultaneous Design for Turbocharger Compressors and Turbine Wheels

AxSTREAM Blade Profiling
Figure 1- AxSTREAM 3D Blade Profiler for Radial Designs

Increasing regulation for reducing emissions has forced the automotive industry to accept different technologies over the years in order to stay ahead of the market. In an industry that is so accustomed to internal combustion engines, new solutions such as electric motors and turbocharger systems have allowed experts in other industries to cultivate an influence in the automotive market. Specifically in the realm of turbomachinery, increased development has gone into designing turbochargers in order to minimize the effect and size of internal combustion engines. Design challenges are inherent in the fact that an engine is a positive displacement device whereas the turbocharger falls under aerodynamic turbomachinery. The two separate machine types have distinctly different flow characteristics, and the proper sizing of a turbocharger for its parent engine requires proper modeling of the engineering system as a whole.

In general, initial turbocharger sizing becomes a matter of obtaining the necessary boundary conditions required for a preliminary design. A thermodynamic cycle analysis of an ICE-Turbocharger system will allow the designer to obtain an initial idea of the bounds

Axmap for turbocharger
Figure 2 – Simultaneous Turbine (color) and Compressor (dotted) Maps – Power vs. MFR (left) & Pressure Ratio vs. MFR (right)

necessary for the compressor and turbine design. Given the engine information, necessary inlet conditions of the compressor such as temperature and pressure, efficiencies required, and heat transfer of the system, the user can then obtain the boundary conditions for the turbocharger compressor and turbine wheels.

From this point, the process becomes an exercise in turbomachinery design and analysis. With SoftInWay’s turbomachinery design and analysis platform, a boundary condition realization of the system eventually manifests into a full 3D design of the turbine/compressor wheel. Once the engineer designs both the turbine and compressor wheels, they will be left with two discrete physical systems. However, these two designs must eventually coincide into a harmonious system that accurately represents the “turbocharger”. In order to facilitate this representation, the user can overlay the different compressor and turbine maps based on a number of varying parameters. Given the Power and Pressure Ratio curves for a number of varying shaft speeds and temperatures, an off-design performance of the turbocharger system can be analyzed via AxSTREAM’s matching module (Figure 2). Another simultaneous analysis of the turbine and compressor wheels must be made on the component that connects them, the rotor. Rotor design, rotor dynamics, and bearings analysis are crucial to a legitimate turbocharger design and will be a topic of a next week’s blog post. If you would like to learn more about turbocharger design and analysis methods, please follow this link

References:
http://www.automotive-iq.com/engine/articles/high-boost-and-two-stage-turbo-power-systems

Steam Heat & Mass Balance Considerations in Refineries

Optimizing the heat and mass flow i.e. steam balance in a plant that has several levels of steam pressures is not a simple task due to the vast array of equipment such as turbines, heat exchanges, steam auxiliaries and accessories used. The steam balance of a refinery plant is further complicated because of use of steam for chemical processes and compression. Depending on processor licensor, technologies and many other traditional factors, it is not uncommon to see steam pressure levels defined in refineries as simply HP & LP or HP,MP & LP or as complex as VHP, HHP, HP, MP and LP.

The traditional approach to designing a steam system is to install steam generators able to generate steam at the maximum pressure and temperature with enough redundancy in capacity as required by the process. Modern steam generators tend to be inclined towards higher pressure steam rather than lower pressure steam – saturated high pressure steam has higher temperature meaning  less exchange surface in heat exchangers and reboilers, high density of high pressure steam requires less bore in the steam mains. Consequently, the usage of high pressure steam represents less capital expenditure. The resultant philosophy is to generate steam at the highest possible temperature and pressure, expand steam from a higher pressure to a lower pressure level through the most efficient means possible and use process at the lowest economically attractive pressure and temperature.

Concepts drawn from CHP namely topping and bottoming cycle have been implemented in refineries. In the topping cycle, fuel is used in a prime mover such as a gas turbine or reciprocating engine that generates electricity or mechanical power. The hot exhaust is then used to provide process heat, hot water, or space heating/cooling for the site. In a bottoming cycle, which is also referred to as Waste Heat to Power (WHP), fuel is first used to provide thermal input to a furnace or other high temperature industrial processes. A portion of the rejected heat is then recovered and used for power production, typically in a waste heat boiler/steam turbine system. To be effective, a bottoming cycle must have a source of waste heat that is of sufficiently high temperature (around 300 Deg C) for the system to be both thermodynamically and economically feasible.

A refinery with such steam pressure requirements at the design phase, in its life cycle however may operate under two distinct scenarios- excess or deficit steam. In the excess situation, equipment is shut or steam is vented off, and in deficit situation steam balance is made up by letting down from an immediate higher level.Blog 3

An optimal way to design and operate the steam balance system involves “what if” analysis and requires inputs from multiple sources such as process engineers, OEMs, equipment vendors, piping designers etc.  With the current trend in crude prices and need to maintain gross refining margins, an all possible mean need to be adopted for ensuring reduced costs. Though estimates vary, some figures indicate up to 130 Gigawatts (GW) of untapped potential at existing industrial and commercial facilities. To identify area of improvement in steam balance and optimize, a simplistic approach is an analysis using pressure and temperatures. A more detailed analysis requires estimation of enthalpy, entropy, exergy and anergy. Such an approach would consist of:

  1. Reconcile heat and mass balance for the steam system and achievement of LHS=RHS account (missing steam).
  2. Estimation of the performance of the existing cycle equipment from an efficiency and economic perspective.
  3. Ascertain inefficiencies in the steam system and opportunities for improvement and optimization by accurate simulation, modelling and scenario comparison.
  4. Assessment of the technical and economic feasibility of installing a rerate/upgrade/replacement


AxCYCLE™ is one such unique tool for design, analysis and optimization of thermodynamic systems (simulation, heat and mass balance calculation of heat producing and electric energy cycles) typically used for any heat and electric energy cycles including aircraft propulsion. Using AxCYCLE™ Economics – an extension to AxCYCLE™ it is possible to estimate capital/running investment calculation (CAPEX and OPEX) , fuel type selection, comparing different scenarios and return on investment.

Aircraft Engines: A Need for Increased Performance and Safety

Turbine engine of airplaneThe necessity for a robust aircraft engine design is strongly associated with not only flight performance, but also to passengers’ safety. The fatigue on the blade of CFM56 engine did not prove to be fatal in last August’s incident. None of the 99 passengers was hurt, but parts of the engine broke apart damaging the fuselage, wing and tail, and forcing the Boeing Co. 737-700 to an emergency landing. However, that was not the case in July 6, 1996, when the left power plant on a Boeing MD-88 broke apart while accelerating for take-off and the shrapnel was propelled into the fuselage killing a mother and a child seated in the Delta Air Lines Inc. aircraft [1]. A few years earlier, in January 8, 1989, a CFM56-3 blade failure proved to be fatal for 47 out of 118 passengers of the British Midlands Airways (BMA) Ltd Flight 92 departed from London Heathrow Airport en route to Belfast International Airport. Based on Federal Aviation Administration’s accident overview [2] post-accident investigation determined that the fan blade failed due to an aero-elastic vibratory instability caused by a coupled torsional-flexural transient non-synchronous oscillation which occurs under particular operating conditions. An animation describing this process is available at the following link: (Fan Blade Failure).

The last example [3] of this not so cheerful post took place on July 29, 2006, when a plane chartered for skydiving experienced jet engine failure and crashed. Tragically, there were no survivors. The failure was attributed to aftermarket replacement parts. The aircraft was originally equipped with Pratt & Whitney jet engines, specifically made with pack-aluminide coated turbine blades to prevent oxidation of the base metal. However, during the plane’s lifetime, the turbine blades were replaced with different blades that had a different coating and base metal. As a result of the replaced turbine blade not meeting specification, it corroded, cracked and caused engine failure.

As it can be observed, there are several reason why an engine can fail varying from inspection mistakes, manufacturing processes and design strategies. Nowadays, engine failures are far below the leading causes of accidents and death. Nevertheless, they are ranked fourth in the decade from 2006 through 2015 with 165 fatalities, according to Boeing statistics [4]. When it comes to blade fatigue regular inspections and maintenance play the most important role. However, the design process is equally important to ensure an efficient and powerful design. The design of the machine under specific flight conditions, taking into account aero-structure interaction, as well as vibration and Rotor dynamics analysis is essential to get a streamlined solution. AxSTREAM allows the user to investigate a variety of design points and further analyse the best solution that meets the constraints and operating conditions requirements. Moreover, AxSTREAM NET can now be used to estimate leakages and cooling or bleed air flow parameters for different fluid path sections while taking into account heat exchange of cooling flow with metal surfaces.

References:

[1] https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR9801.pdf

[2] http://lessonslearned.faa.gov/ll_main.cfm?TabID=2&LLID=62&LLTypeID=2#null

[3] http://www.robsonforensic.com/articles/aircraft-engine-materials-expert

[4] http://www.dallasnews.com/business/airlines/2016/09/12/investigators-cracked-engine-blade-broke-southwest-airlines-flight-last-month

Rotating Equipment Specialist in the Oil and Gas Industry – A Turbomachinery Professional

Turbomachinery is a core subject in many engineering curriculums. However, many graduates joining the oil and gas industry are designated as rotating equipment engineers. Though turbomachinery and rotating equipment are used synonymously, all turbomachinery are rotating equipment but not vice versa. Turbinis in Latin implies spin or whirl, and a natural question that arises is – what are the factors that differentiate turbomachinery?  In a general sense the term, “rotating” covers  the majority equipment used in the industry be it in the upstream, mid-stream or the downstream segment. Yet top rotating equipment specialist in the industry are seen spending their prime time or often being associated with certain unique and specific types of critical rotating machines – the turbomachines.Oil and Gas

In a classical sense, turbomachines are devices in which energy is added into or taken out from a continuously flowing fluid by the dynamic action of one or more moving blade rows. By this definition propellers, wind turbines and unshrouded fans are also turbomachines but they require a separate treatment. The subject of fluid mechanics, aerodynamics, thermodynamics and material mechanics of turbomachinery when limited to machines enclosed by a closely fitting casing or shroud through which a measurable quantity of fluid passing in unit time makes the practical linkage to rotating equipment – those which absorb power to increase the fluid pressure or head (fans, compressors and pumps) and those that produce power by expanding fluid to a lower pressure or head (hydraulic, steam and gas turbines). Further classification into axial, radial and mixed type (based on flow contour), and impulse & reaction (based on principle of energy transfer) is common. It is the large range of service requirement that leads to different type of pump (or compressor) and turbine in service.

From the oil and gas industry perspective, standards namely API governs the specifications of design, material and systems requirements of rotating equipment. In line with such standards, equipment under the purview of APIs SOME (Sub Committee on Mechanical Equipment) are considered to quantify rotating machine. Falling under the turbomachinery group are centrifugal pumps (API 610), general and special purpose steam turbines (API 611 & 612), gas turbines (API 616) , axial and centrifugal compressors and expander- compressors (API 617), special purpose fans (API 673) and integrally geared compressors (API 672).

It is understandable that universities and academic institutions will continue their focus on turbomachinery as a fundamental subject of the curriculum, with increased emphasis on training and use of CAE tools. Basics remaining the same, the special nature of application of turbomachinery in the industry makes job of a rotating equipment engineer a challenge. At a conceptual level four important facets of rotating equipment (turbomachines) that an engineer in the oil and gas industry need to comprehend are as follows: Kinematic, energetics and thermodynamics of performance– fluid-aero thermal design and analysis; integrity of rotor, bearings, seals, casing and structure – mechanical design and analysis; the complete hardware – metallurgy, material mechanics and manufacturing and finally the associated systems. As the oil and gas industry entrusts its specialist rotating equipment engineers with a demanding level of reliability and availability of turbomachines, new ways are required to enhance competence. The practical experience of rotating equipment engineers coupled with exposure to design principles and use of CAE and simulation tools is one such way to help them add more value to their business.  AxSTREAM® is an advanced  software suite that covers many aspects of various critical rotating equipment for the oil and gas industry on a single platform.

For an overview of AxSTREAM for design, analysis, retrofitting, and so on, visit our past webinars recording http://learn.softinway.com/Webinar .

Liquid Rocket Propulsion with SoftInWay

Preliminary Design of Fuel Turbine

Operation of most liquid-propellant rocket engines, first introduced by Robert Goddard in 1926- is simple. Initially, a fuel and an oxidizer are pumped into a combustion chamber, where they burn to create hot gases of high pressure and high speed. Next, the gases are further accelerated through a nozzle before leaving the engine. Nowadays, liquid propellant propulsion systems still form the back-bone of the majority of space rockets allowing humanity to expand its presence into space. However, one of the big problems in a liquid-propellant rocket engine is cooling the combustion chamber and nozzle, so the cryogenic liquids are first circulated around the super-heated parts to bring the temperature down.

Rotordynamics analysis
Rotordynamics Analysis

Because of the high pressure in the combustion chamber needed to accelerate the hot gas mixture, a feed system is essential to pressurise and to transport the propellant from the propellant tank(s) to the thrust chamber. In today’s rocket engines, propellant pressurization is accomplished by either (turbo)-pumps or by a high pressure gas that is released into the propellant tank(s), thereby forcing the propellants out of the tank(s). In space engineering, especially for high total impulse, short duration launcher missions, the choice is almost exclusively for pump-fed systems.

To design such systems, a highly sophisticated and complete tool is required. SoftInWay has developed AxSTREAM, the most integrated engineering platform in the market, for turbomachinery design, analysis and optimization. The long experience in the field along with the use of AxSTREAM allow SoftInWay to support its customers in the space industry. Below, you can catch a glimpse at AxSTREAM’s capabilities through a demonstration project of the RL10-A3-3 fed system. The RL10-A3-3 rocket engine is a regeneratively cooled, turbopump fed engine with a single chamber and a rated thrust of 15,000 lb at an altitude of 200,000 ft., and a nominal specific impulse of 444 sec. Propellants are liquid oxygen and liquid hydrogen injected at a nominal oxidizer-to-fuel ratio of 5:1 [1]. The design focused creating new rotating parts of the RL10-A3-3 feed system as presented in Figures 1 and 2, including full scope of rotordynamics analysis.

New Rotating Parts for RL10-A3-3 Feed System

Contact us for an AxSTREAM demonstration and attend one of our training courses to get a trial with AxSTREAM and become SoftInWay’s next success story.

References

[1]https://pslhistory.grc.nasa.gov/PSL_Assets/History/C%20Rockets/Design%20Report%20for%20RL-10-A-3-3.pdf

The Future of Nuclear Power Plants

With the blast of the French nuclear power plant a few weeks ago, safety of nuclear power plant designs has fallen under more scrutiny. Although according to sources the blast took place in the turbine hall and no nuclear leak was found, this event has brought more attention to improved design and operation standards.

Following the incident earlier this month Toshiba, a Japanese multinational company, announced the resignation of its chairman following a $6.3 billion loss in their nuclear sector –also withdrawing from the nuclear business. The two back to back events have highlighted the main two problems of nuclear power: high cost and environmental/safety concerns. Said to be a green technology, nuclear power raises concerns with potential nuclear meltdown and risk of safety from toxic waste, accompanying the fact that building a new plant cost around $5,000.00 per kilowatt of capacity with around 6 years of lead time. Each dollar invested on a nuclear power plant has about 2-10 less carbon savings and is 20-40 times slower compared to other alternatives. Yes, evidently nuclear power is found to be very reliable, enabling consistent baseload energy production at any time of day and night. Though, it has been questioned whether this reliability is worth the high cost of nuclear production, in fact all nuclear plants are still operating with 100% subsidized.

Transatomic power, a company started by two MIT PhD candidates, came up with a new approach to safer and cheaper nuclear reactors. Utilizing molten salt reactors, which has not really been used commercially and so far is only existed in paper, the technology is promised to cut initial cost and increase safety. Today’s conventional nuclear reactor is cooled by water, due to the high operating temperature, failure to do so will open the risk of radiation leak as well as hydrogen explosion. The high boiling point of salt helps solve some of the problems associated with the technology. The new design also incorporates ways of producing faster neutrons, enabling the reactor to burn most waste materials, thus keep waste to minimum. The ability of this smaller unit to be made in a factory (and not onsite) as well as cost reduction on the safety side makes this attractive economically as well. That being said, this generation 4 nuclear reactor is still in design and development will take years and high capital cost.

References:

https://www.nytimes.com/2017/02/14/business/toshiba-chairman-nuclear-loss.html?_r=0

http://fortune.com/2017/02/16/toshiba-nuclear-power-plants/

Turbomachinery Rotor Dynamics – Latest Modelling & Simulation CAE for Design and Analysis, using SoftInWay’s Integrated Tool

The Rotor-Dynamic System of a typical turbomachine consists of rotors, bearings and support structures. The aim of the designer undertaking analysis is to understand the dynamics of the rotating component and its implication. Today the industry practices and specifications rely heavily on the accuracy of rotor-dynamic simulated predictions to progressively reduce empirical iterations and save valuable time (as repeated direct measurements are always not feasible). Be it a centrifugal pump or compressor, steam or gas turbine, motor or generator, the lateral rotor-dynamic behavior is the most critical aspect in determining the reliability and operability. Such analytical predictions are often tackled using computer models and accuracy in representing the physical system is of paramount importance.  Prior to analysis it is necessary to create a detailed model, and hence element such as cylindrical, conical , inner bore fillet/chamfer, groove/jut, disk / blade root and shroud, copy/mirror option, bearing element and position definition are built. Stations (rather than nodes) having six DOF (degrees of freedom) are used to model rotor-dynamic systems. Typically for lateral critical analysis each station has four DOF, two each translational and rotational (angular). Decoupled analysis followed by coupled lateral, torsional and axial vibration makes prediction realistic and comprehensive. The mathematical model has four essential components, i.e. rotating shafts with distributed mass and elasticity, disks, bearing and inevitable synchronous imbalance excitation. Components such as impellers, wheels, collars, balance rings, couplings – short axial length and large diameter either keyed or integral on shaft are best modelled as lumped mass. Bearings, dampers, seals, supports, and fluid-induced forces can be simulated with their respective characteristics. Bearing forces are linearized using dynamic stiffness and damping coefficients and together with foundation complete the bearing model. The governing equation of motion for MDOF system require  determination of roots (Eigenvalue) and Eigen Vectors. Lateral analyses – such as static deflection and bearing loads, critical speed analysis, critical speed map, unbalance response analysis, whirl speed and stability analysis, torsional modal and time transient analyses are then performed.Aashish blog 1 image

Indeed rotor-dynamic modelling with practical experience and engineering judgement improves accuracy.  Its ability to model complexities such as flexible supports, foundation, rotor seal interaction, and instabilities while making the CAE model comprehensive, user friendly, and fully integrated with other well proven and mature suites for flow path and  blade design makes SofInWay’s software platform unique.

Integrated Approach within AxSTREAM® Platform

Suited to meet the diverse needs of designers, analysts and users of turbomachinery, SoftInWay’s webinar in collaboration with Test Devices Inc scheduled on Mar 2, 2017, 10 AM EST helps you to understand HOW rather than why. It will  cover rotor and bearing types, principles of an integrated approach to rotor-dynamics system design and simulation, purpose and procedures for rotor-dynamic and structural analysis. The software demonstration will include modelling features, import/export options, lateral and torsional capabilities, bearing analyses and modelling capabilities, and case studies. It will also briefly highlight fundamentals such as characteristic influence of shaft rotational on natural frequencies in comparison to classical natural frequencies and modes in structures, gyroscopic effects, rigid vs flexible rotors, free and forced vibration as applicable to turbomachine rotors, impact of bearing characteristics and concept of cross coupling, modes, Campbell diagram, stead and transient response, instabilities, condition monitoring, testing, evaluation and acceptance criteria (log dec and margins) and much more. Testing methods covered by Tech Devices Inc. highlight testing procedures and methods for design validation and building confidence that the design exceeds expectations.