Z-Coupled Full System for Attenuation of Vibrations

Executive Summary:

The aim of this project was to find and demonstrate an optimal system for minimising the transmission of vibrations generated in the Counter Rotating Open Rotor to the fuselage. The Sustainable and Green Engine (SAGE) ITD, DREAM projects and Clean Sky were FP7 R&D projects devoted to develop the innovative engines for the future aircrafts. Under an event of a blade loss, expected vibrations coming from the damaged CROR engine are particularly high and compromise the manoeuvrability of the aircraft. In addition, the environmental conditions on the surroundings of the engine area are highly demanding. Close to the excitation source, temperatures from 250 to 650ºC are expected.

All kinds of conventional –passive, dynamic, active and semiactive- solutions for reduction of vibrations were considered for optimisation. The hard constraints of space, temperature and low frequency had spoiled most of the well-known conventional approaches. However, in order to overcome these difficulties and to increase the efficiency of these “well-known” solutions the use of a new technology of Impedance coupling has been assessed during this project.

The Z-Damper technology, patented by MAGSOAR SL, provided a non-contact, reliable mechanism able to multiply the efficacy of any conventional element (passive dampers, tuned vibration absorbers, active actuators or semiactive devices) reducing the overall required mass and volume of the devices. Two main prototypes have been manufactured and tested:

• Z-Transmitter prototype of an impedance coupling device that can be coupled to external elements such as springs or inertial mass. Operation as an impedance coupling device and as a tuned vibration absorber has been demonstrated.

• Z-Damper prototype, a passive solution consisting of a integrated high-temperature pure dissipative damper able to work at temperatures up to 250ºC.

Both prototypes have been tested under realistic operational conditions demonstrating the expected behaviour. In addition, a dummy of the Z-Damper has been designed and manufactured in order to evaluate various linear bearing technologies when operating under the expected Z-Damper conditions.

Project Context and Objectives:
The general objective of VIAFUMA is the development of a new and fully validated approach to predict the dynamic response of a lean burn fuel manifold system. Exploiting basic and detailed linear and nonlinear dynamic modelling approaches will allow feasibility studies of the design during the early development and enable detailed analysis and optimisation during the later design stages. The immediate advantages lie in a general increase of life of the fuel manifold system, but the developed strategies will also help to reduce the weight of upcoming designs, leading to a lighter and more efficient jet engine.
VIAFUMA consisted of two Work Packages (WP), WP1 concerned with experimental work, and WP2 focussed on the analytic modelling approach.
2.1 WP1: Experimental
The overall objective of WP1 was to identify the linear and nonlinear dynamic behaviour of the basic, sub, and full assembly of the fuel manifold, and to provide reliable validation data for the newly developed analysis techniques from WP2.
Initially an experimental characterisation of basic pipe assembly (Task 3) was planned to:
• Develop specific test setup for each component of pipework assembly that isolates its vibration behaviour from the support structure. Straight and bend pipes will be investigated together with different types of mounts, inserts, and clips.
• Conduct low level impact hammer and shaker tests for each component, extracting operating deflection shapes with the help of a Scanning Laser Doppler Vibrometer (SLDV).
• Identify from frequency response the stiffness, damping and nonlinear behaviour of each component.
• Investigate the most basic assembly of a straight and bend pipe with the minimum amount of mounts, clips and inserts.
• Design, build and test a setup with a short length of pipe that can be pressurised with oil at different levels to characterise the mass loading and damping properties of the liquid inside the pipe.
• Introduce known misalignment in the assembly to achieve controlled pre-stressing of the pipework and evaluate the effect on the dynamic response.
This was followed by planned operational level testing of the fuel pipe assembly in Task 5:
• A sub-assembly will be tested consisting of several bend pipes, different mounting systems, inserts, and damping elements. Empty and pressurised pipework will be used
• A flat rigid and a flexible curved substructure will be used to determine the influence of impedance on the measured dynamic response
• The tests will be conducted with the High Amplitude Dynamic Excitation System (HADES) at Imperial College London. Operational level vibrations with sine sweep, random and wave form replication inputs will be used
• Non contact SLDV measurement techniques will be used in combination with strain gauges to determine the response of the system during testing
• The dynamic behaviour of the system will be measured, the main sources of nonlinearity identified, and the influence of pressurised pipework on the response investigated
• Misalignment will be introduced to the pipe assembly to generate a known pre-stress in the system, and its influence on the linear and nonlinear response investigated
• Several reassembles of the setup will be tested to understand the variability in the measurement results and provide averaged values for the model validation
The experimental work was to be completed by operational level testing of the full casing assembly in Task 8, including:
• A simplified full casing assembly will be manufactured and tested on the HADES shaker system to reach realistic excitation levels in the required frequency range.
• The linear and nonlinear dynamic response will be monitored with a SLDV to obtain full field operating deflection shapes of the cylindrical structure.

2.2 WP2: Analytical
The overall objective of this task was the development of low and high order models for the prediction of the nonlinear dynamic response of a fuel manifold, including all its components.
This included an initial state of the art review on current pipe work modelling (Task 1) and then focused on the development of detailed models for the basic pipe-mount assembly (Task 4)
• Development of detailed three dimensional solid linear finite element models for each pipework component.
• Validation of the developed linear models against available test data from Task 3
• Nonlinear response predictions of the basic pipework assembly with the in house multiharmonic balance solver FOrced Response SuitE (FORSE)
• Inclusion of fuel effect in to the finite element model by distributed mass loading
• Analysis of pre-stress due to misalignment in the assembly and predictions of its effect on the linear and nonlinear dynamic response of the assembled system.
• Validation of the developed nonlinear models against available test data from Task 3
The knowledge obtained during the basic modelling was then to be used for the development of a high order modelling approach for fuel pipes on the casing (Task 6)
• A detailed solid finite element model of the rigid and flexible subassembly with and without pressurised fuel will be created and its linear dynamic response predicted.
• Based on the linear model of the subassembly a nonlinear dynamic analysis in FORSE will be conducted to predict the forced response of the pipework.
• The sub assembly models will be validated against the obtained test data from Task 5.
• A detailed full assembly model will be generated and its linear and nonlinear dynamic response predicted. This will involve large scale linear and nonlinear modelling with several 1000 nonlinear elements, for which new modelling techniques will be required.
• A comparison between the rigid and flexible support will be used to identify the influence of impedance of the substructure on the test results and to understand how obtained test data can be used to validate the full-assembly model.
As an additional approach to model the fuel manifold response a low order modelling approach for fuel manifolds would be developed (Task 7):
• A low fidelity model of each component, based on a mixture of shell and beam elements will be created to allow a fast computation of the dynamic results. These models will be validated against test and detailed FE data.
• Based on the identified main source of nonlinearity in the assembly, it is proposed to develop a new implicit nonlinear element for FORSE that allows a quick and reliable prediction of the pipework response. The element will require typical characteristics of the components as input, such as amplitude dependent damping and stiffness.
• The pre-stress in the low fidelity models will either be included by modifying the linear modelling approach, or adding a stiffness term during the nonlinear computation of the response.
• The assembled low fidelity model will be validated against the measured data obtained from Task 5 and 8.
Given the novelty of the set task, with a very limited understanding of the fuel manifold dynamic response, the objectives as stated in the Annex A of VIAFUMA, were adjusted to include the obtained knowledge and ensure the most effective way to analyse large scale fuel pipe networks.

Project Results:

Transmission of vibrations through a structure and systems to reduce, mitigate or supress them are one of the most studied topics in Mechanical Engineering. The simplest way to reduce vibrations transmissivity of, for example, a rotating machine to the ground is to increase the elasticity of the ground-connections.

Mechanical impedance is a key concept for studying vibrations in mechanical systems as well. The concept is equivalent to that of impedance in an electric circuit (the opposition a circuit presents to the flow of a current given an input voltage) which is of great importance in the design of AC electric circuits and device. By definition, the mechanical impedance (Z) of a vibratory system is:

Z=F/v

where F is the acting force and v the response velocity.

The Z-Damper patented technology, allows impedance coupling (without backlash) between and input and an output stage that enhances the performance of any damping system. The working principle is based on the technology development of the MAGDRIVE FP7 project extended to a linear system:

A wave generator (typically input) generates a magnetic wave that interacts with an output part composed of soft magnetic materials and a linear spline. Depending on the relative number of teeth in the output and the linear spline, a reduction/amplification relationship is automatically defined with zero backlash.

For the Z-Damper, a multiplication ratio of 7 had been designed. The relationship between the input and the output stages is then defined for displacements and forces as:

F_zi=n·F_z0

X_o=n·X_i

where

F_zi is the input force,

F_zo is the output force,

X_ithe input displacement

and X_o is the output displacement,

Impedance of the input and output stages are then defined as:

Z_i=F_zi/v_i and Z_o=F_zo/v_o

And then related by the impedance coupling number as:

Z_i=n^2 Z_o

A trade-off study has been done, analysing passive, semi-active and actives technologies for vibration damping. Z-Damper technology has been selected for evaluation in this project as an outcome of this task. One of the strongest point of the technology is its temperature range of use, with the possibility to operate at temperatures up to 550ºC.

Multyphicisal Finite Element Simulations has been performed in order to design the Z-Damper: a magneto-mechanical simulation procedure has been set-up and experimentally validated in the laboratory. Prototype experimental results validated the design proccess and were used to optimize it. Structural simulations were performed in the critical design of the prototypes. Ventilation requirements were stablished using thermal simulations. An optimised fin distribution was designed to minimise the weight of the dissipator and maximize the heat transfer coefficient.

Based on this impedance coupling effect, two prototypes have been designed, manufactured and tested. A dedicated test bench has been designed, manufactured and set-up. The test-bench allows the reproduction of the CROR environmental conditions, from -50ºC to 250ºC. A ventilation system provides the ventilation requirements to the prototypes

Three main prototypes were manufactured and tested:

• Dummy of the Z-Damper: a dummy of the Z-Damper prototype was designed, manifested and tested. The objective of that prototype was to simulate the lateral loads on the linear bearing. Made of SmCo magnets and a steel yoke, the lateral force on the bearings is generated by contactless forces between those elements. The prototype has been used at temperature up to 250ºC and with input vibrations of 5 mm amplitude and frequencies up to 50 Hz. The prototype has been used to analyse various commercial linear bearing and to asses and adapt them to the most critical operational conditions of the Z-Damper. The coefficient of friction and the wear effects have been assessed.

• Z-Transmitter: A prototype of an impedance coupling device with multiplication ratio n=7. The device is made of NdFE 45H permanent magnets combined with soft steel magnetic material. The structural components have been manufactured in Titanium grade 5 to make the device as light as possible. This resulted in a device with a mass of about 9.6 kg, 500 mm in length and about 82 mm in diameter with a force capability slightly below 5 kN.

The prototype has been tested under sinusoidal input excitations of amplitudes up to 5 mm and in a frequency bandwidth from 0 to 120 Hz. It has been tested at environmental temperatures from room temperature to up to 100ºC. An average multiplication ratio of 7±0.3 Hz has been demonstrated. The device output stage has been connected to a set of external springs from 10 to 100 N/mm. A maximum input stiffness of 2200 N/mm has been measured. A video of the Z-Transmitter operating at various input excitation frequencies when coupled to an external stiffness can be watch in the following link:

In addition, the device has been tested as a tuned vibration absorber.

• Z-Damper: a prototype of a high-temperature integrated magnetic damper with a multiplication ratio n=7, 500 mm in length and about 100 mm in diameter. The prototype multiples input motion in a factor of 7. Then, power is dissipated by Eddy currents in a Electrolytic Copper tube by the motion of the fast stage magnets. The use of Sm2Co17 magnets makes possible the operation of the device from -50ºC to up to 250 ºC. The device has been tested in a frequency range from 0 to 50 Hz for various motion amplitudes and different temperatures.

A great increase on the damping was measured once the copper dissipated is assembled. Now, the Z-Damper show a supercritical damping in accordance with the simulations performed at room temperature.

When temperature is increase, the electric resistivity of copper is reduce therefore, limiting the maximum damping of the system.

A maximum equivalent viscous damping coefficient of about 40 Ns/mm for sinusoidal input excitations of 5 mm amplitude has been measured at 200ºC, a world record for any kind of damping system operating at this temperature.

Conclusions:

A new technology development on vibrations isolation was demonstrated in the FP7 Z-Damper project. The technology is based in impedance matching to optimise vibration isolation. Because no grease or lubricant is required for operation of the Z-Damper. It is able to operate from cryogenic temperatures to very hot environments (from -200ºC to up to 500ºC). The Z-Damper demonstrated an adequate performance for the CROR engine isolation requirements. Moreover, the potential applications of this technology are well beyond the scope of this project and not only in the aircraft industry, but also in the space market and many other industrial sectors.

Two prototypes and a dedicated testbench have been manufactured:

• Z-Transmitter: A prototype able to operate to up to 100ºC has been manufactured and tested coupled to external devices such as an inertial mass or a spring. The prototype has been tested in a bandwidth from 0 to 120 Hz at different temperatures. Results were very promising, especially when compared to classical tuned vibration absorbers. A reduction of about one order of magnitude in the required mass of the system has been estimated.

• Z-Damper: A prototype of an integrated high-temperature damper, able to operate in a temperature range from -55ºC to up to 250ºC. The Z-Damper is the only one of its kind with a great equivalent viscous damping coefficient up to 40 Ns/mm at 200ºC. The performance of the device has been analysed at different temperatures in a bandwidth from 0 to 60Hz and input amplitude between 0.05 and 5 mm. The prototype showed excellent damping performance at low frequencies.

The experimental results have been compared to the analytical and FEM simulation models. A user-friendly software tool has been generated which allows the user to identify the performance and characteristics of a Z-Damper depending on its vibration isolation requirements.

A European patent application has been presented.

Potential Impact:

• Potential impact and main dissemination activities and exploitation results

The Z-Damper project has allowed the development of new vibration damping technology that gives the opportunities to mechanical engineers for vibration isolation. The improvement on damping performance of the Z-Damper, based on the impedance matching, is a real breakthrough in vibration attenuation systems. It is relevant, that Z-Damper is a development that did born with another FP7 project, the MAGDRIVE project, were a rotatory magnetic gearbox was development by part of the engineering team of MAGSOAR SL and is based on a similar principle.

The Z-Damper technology will make possible vibration damping at temperatures (from -200 ºC up to 550ºC) where any other current technologies are able to operate. In addition, the impedance coupling in the Z-Damper will improve the vibration damping performance and reduce its overall weight.

Socio-economic impact will come in the following ways:

1. Impact of the technology:

a. Impact of the Technology in the Aeronautic and Aerospace Industry

The temperature range of use of the Z-Damper will allow damping of vibration closer to the source of vibrations, multiplying its effectivity. In addition, the impedance coupling effect will give further options for shock and impact isolation. Some potential fields of applications identified are: Aircraft Engines and Turbofans, Landing Gear dampers, docking dampers for Space Applications, dampers used to isolate launch loads or reduced mass tuned vibration absorbers for use in, for example, helicopters and satellites.

b. Impact of the Technology in other industrial fields

Z-damper technology will provide a useful tool for stroke and velocity amplification in servo-electrical actuators which is currently one of their main limitations. The lack of mechanical contact in this short of devices will allow them to achieve higher accelerations without damage and increase the maximum operational frequency. Z-Damper can also be used to amplify piezo-electric displacements.

The lack of backlash in the Z-Transmitter technology will give engineers a way to improve precision positioning, especially in demanding environments such as in cryogenics engineering. This will be of special interest for micro-vibration damping for example.

Vibration damping in cryogenic engineering is a frequent challenge. The cold temperatures (below -150ºC) do not allow the use of any liquid viscous damper. In addition, properties of resilient material change vary significantly and suffer from creep in this range of temperatures. For those situations were damping is required at very low temperatures, like for example in cryo-pumps in the gas liquefaction industry, Z-Damper technology is called to fulfil the needs of cryogenic engineers.

In addition, Z-Damper technology will enable a reduction of cost and weight in eddy current dampers being currently used in the railway industry for high speed trains, The TSI (Technical Specifications of Interoperability) recommends that all newly built high-speed lines should make the eddy current brake possible. The Z-Damper technology will also provide a new toll for shock dampers for military vehicles and roller coasters end of stroke brakes among others.

2. Socio Economic Impact of the Exploitation

The exploitation of the technology development in the Z-Damper project was straightforward to the industry since the Consortium Coordinator (MAGSOAR) was the sole owner of the technology patent. The socioeconomic benefit of job creation and economy activation will be produced in the European Union, especially in Spain and Germany.

Airbus potential market (2013-2032) for new aircraft was estimated in 29226 units among single-aisle, twin-aisle and very large aircrafts. This means a potential market of 4.4 trillion dollars. Z-Damper technology could be used, for example, in the future A30X airbus aircrafts, which release is planned for 2020. Commercial forecast for this plane is about 400 A/C per year. This will mean a total of 800 units per year of Z-Damper, just in this Airbus A30X. Improved efficiency in vibration isolation expected for Z-Damper technology will contribute to a direct weight, size and cost reduction of the current solutions, translating in direct cost saving. Further on, this project will have direct impact in the enhancement of the EU competitiveness against main suppliers of solutions to vibration isolation like the American company LORD Corporation. In addition, development of Z-Damper technology in the spin-off company MAG SOAR (results of other FP7 projects) may be appreciated as being compliant with the current vision on enhancing the European competitiveness.

Besides the direct economic impact, the impact on the environment was also considered in this project. Open rotor engines provide a 25-30% reduction in fuel consumption and CO emissions relative to current equivalent turbofan engines. Open-rotor powered aircraft could save around $3 million and 10,000t of carbon dioxide a year per aircraft. According to IATA (2008), aviation contributes about a 3% to the total worldwide CO2 emissions. However, IPCC alerted that, despite emissions being relatively low, ambient impact of aviation is of potential risk due to impact of different chemical compounds as NOx. For instance, the- Advisory Council for Aeronautics Research in Europe (ACARE) has set some goals for CO2 and NOx emissions as a reduction of 60% in NOx emissions for 2020.

However, in order to spread the use of CROR, an improvement in the vibration and noise isolation to the cabin is required. In this sense, Z damper provides an efficient solution in terms of weight, cost and size. Therefore, the successful development of this project will lead to a direct increase in the use of CROR engines.

3. Enabling of new technological possibilities

In the particular case of the CROR project, the success of this Z-damper project will remove its main obstacle or drawback, the level of vibrations. If the vibrations are supressed, the CROR can provide better performance than other available engines in terms of energy consumption. This is a global high-impact benefit for the whole aeronautical industry across Europe. Although it is difficult to estimate, this can represent a enabling technology for a business of many billion euro in the aeronautical sector.