Analytical Tools for Determination of Damped Unbalanced Rotor Response

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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).

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Steam for Power

Turbine technology being central to energy-producing industry, research and development efforts is directed towards cost-savings (increased efficiency, reliability, and component lifespan), sustainability (alternative fuels, lower emissions), and cost-competitiveness (particularly for the emerging technologies) [1]. This blog post is the first in a series of three that will focus on steam, gas and hydraulic turbines for power generation.

Going back to the Archimides era we will find the idea of using the steam as a way to produce work. However, it was not until the industrial revolution when the first reciprocating engines and turbines developed to take advantage of steam power. Since the first impulse turbine development by Carl Gustaf de Laval in 1883 and the first reaction type turbine by Charles Parsons one year later, the development of turbines have sky-rocketed, leading to a power output increase of more 6 orders of magnitude[2].

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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

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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.

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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.

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Outlook for the Future HVAC Market

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According to the new market research report, the industry of heating, ventilation and air conditioning (HVAC) is predicted to rise at a solid, stable compounding annual growth rate of 5.9% up to the year 2022. With the growing trend of smart homes and changing weather conditions, cooling equipment is expected to remain the largest major share of the entire HVAC market taking around 70% of the entire market totaling to a prediction of 24.28 Billion USD  – including coolers and room air conditioners.

With global warming and increased temperatures taking effect, demand for cooling systems continues to rise in geographical areas where weather is a significant factor, such as Asia Pacific. Countries such as China, Japan and India are significantly driving the growth of this market, as the automotive air conditioning sector plays an important role in these geographical areas as they are still the leaders of the automotive manufacturers by volume.  Rise in middle income (and improvement of environmental standard) in developing countries also push the construction boom and replacement of older technology in air conditioning.

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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.

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Revamping a Turbomachine Train

The demands of the plant construction and energy sector after a shorter response time for questions upon newly defined operating points of a turbomachine train are one of the biggest challenges in the service business. This becomes particularly obvious if the future points can only be realized by redesigning the flow-relevant components. Often, it is necessary to have more time to check the dynamic behavior of the train, than in the development of the appropriate revamp measures for the core machine itself.

In addition to the different utilization rates of the affected departments, the causes of the delays often lie in the lack of interface quality between the design/ calculation and train integration team. On top of that, a certain amount of time will be required by manufacturers of the critical components such as gearboxes or drives to perform a lateral check. This lateral check is not only mandatory, in case of a component modification such as changing the transmission ratio or upgrading the drive, but it is also necessary if the coupling between the train components must be changed to ensure torsional stability.

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Axial Compressor Challenges in Hyperloop Designs

Back when the California high-speed rail project was announced, Elon Musk (CEO of SpaceX and Tesla Inc. and perhaps the most admired tech leader of present day) was not only disappointed with this project, but also introduced an alternative to this system called the Hyperloop in 2012.  Since the abstract of this project was introduced, many engineers around the world have started to evaluate the feasibility of this “5th Mode of Transportation”.

Hyperloop Alpha Conceptual Design Sketch
Hyperloop Alpha Conceptual Design Sketch

The general idea for the Hyperloop consists of a passenger pod operating within a low-pressure environment suspended by air bearings.  At the realistic speeds estimated by NASA of 620 mph, the pod will be operating in the transonic region.  While Japan’s mag-lev bullet train has succeeded at achieving speeds of up to 374 mph, the scale and complexity of a ground transportation system rising above 600 mph bring to surface an unusual number of engineering challenges. As well, brand new designs such as the one proposed by Musk have a certain amount of risk involved due to this technology inherently having no previous run history on a large scale.

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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.

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