An Accelerating Sweep Frequency Excitation Method for the Rotordynamic Coefficients Identification of Annular Gas Seals Based On Computational Fluid Dynamics

2021 ◽  
Author(s):  
Qianlei Gu ◽  
Jiangang Yang ◽  
Wanfu Zhang ◽  
Mingjie Zhang
Keyword(s):  
Transient Flow ◽  
Numerical Models ◽  
Identification Accuracy ◽  
Frequency Resolution ◽  
Response Force ◽  
Sweep Frequency ◽  
Rotordynamic Coefficients ◽  
Frequency Excitation ◽  
The Impact ◽  
Excitation Method

Abstract This paper proposes a rotordynamic identification method using the accelerating sweep frequency excitation method (ASFE). The CFD transient solution combined with the moving grid method is utilized to obtain the transient flow field of the seal excited by the whirling rotor with an accelerating frequency. Rotordynamic coefficients at swept frequencies are obtained by analyzing the transient response force acting on the rotor. Rotordynamic coefficients of three published experimental seals including a labyrinth seal (LABY), a fully partitioned pocket damper seal (FPDS) and a honeycomb seal (HC) are identified to validate the proposed method. The results show that the predicted rotordynamic coefficients are all well agreement with the experimental data. Compared with the existing numerical models based on transient solutions, the CPU consumption of the proposed method is substantially reduced by 98% when achieving the same frequency resolution. In addition, the impact of the exciting acceleration on the identification accuracy is also illustrated.

scholarly journals Simulation evaluation of dynamic characteristic identification accuracy of sliding bearing considering test error

2021 ◽  
Vol 13 (12) ◽  
pp. 168781402110668
Author(s):  
Runlin Chen ◽  
Chen Du ◽  
Xiaotuan Wang ◽  
Yanchao Zhang ◽  
Kai Liu
Keyword(s):  
Dynamic Characteristic ◽  
Dynamic Characteristics ◽  
Low Frequency ◽  
Identification Accuracy ◽  
Single Frequency ◽  
Sliding Bearing ◽  
Test Error ◽  
Simulation Evaluation ◽  
Frequency Excitation ◽  
Excitation Method

Aiming at the dynamic characteristics test bench of sliding bearings, the dynamic model is established. Based on the forward and inverse dynamic problems of the bearing, a simulation evaluation method for the identification accuracy of the sliding bearing dynamic characteristics is proposed and the algorithm is verified. The identification errors of dynamic characteristic coefficients under different excitation frequencies are analyzed, the sensitivities of single frequency excitation method and dual-frequency excitation method to test error are contrastively analyzed, and the influence laws of dynamic characteristic identification accuracy of sliding bearing are evaluated. Based on which the traditional single frequency excitation method has been improved. The dynamic characteristic test should be carried out respectively in the low frequency range and the high frequency range. The main stiffness and cross damping are the average of two tests, the main damping is the identification value in the high frequency, and the cross stiffness is the identification value in the low frequency. That will effectively reduce the impact of test error. The obtained data and laws could support the improvement of the dynamic characteristics test method of sliding bearings and the confirmation of test parameters, thereby the accuracy of dynamic characteristics identification is improved.

scholarly journals A Rational Numerical Method for Simulation of Drop-Impact Dynamics of Oleo-Pneumatic Landing Gear

2021 ◽  
Vol 11 (9) ◽  
pp. 4136
Author(s):  
Rosario Pecora
Keyword(s):  
Numerical Method ◽  
Initial Conditions ◽  
Impact Load ◽  
Numerical Models ◽  
Landing Gear ◽  
Design Stage ◽  
Impact Dynamics ◽  
State Variables ◽  
Adopted Model ◽  
The Impact

Oleo-pneumatic landing gear is a complex mechanical system conceived to efficiently absorb and dissipate an aircraft’s kinetic energy at touchdown, thus reducing the impact load and acceleration transmitted to the airframe. Due to its significant influence on ground loads, this system is generally designed in parallel with the main structural components of the aircraft, such as the fuselage and wings. Robust numerical models for simulating landing gear impact dynamics are essential from the preliminary design stage in order to properly assess aircraft configuration and structural arrangements. Finite element (FE) analysis is a viable solution for supporting the design. However, regarding the oleo-pneumatic struts, FE-based simulation may become unpractical, since detailed models are required to obtain reliable results. Moreover, FE models could not be very versatile for accommodating the many design updates that usually occur at the beginning of the landing gear project or during the layout optimization process. In this work, a numerical method for simulating oleo-pneumatic landing gear drop dynamics is presented. To effectively support both the preliminary and advanced design of landing gear units, the proposed simulation approach rationally balances the level of sophistication of the adopted model with the need for accurate results. Although based on a formulation assuming only four state variables for the description of landing gear dynamics, the approach successfully accounts for all the relevant forces that arise during the drop and their influence on landing gear motion. A set of intercommunicating routines was implemented in MATLAB® environment to integrate the dynamic impact equations, starting from user-defined initial conditions and general parameters related to the geometric and structural configuration of the landing gear. The tool was then used to simulate a drop test of a reference landing gear, and the obtained results were successfully validated against available experimental data.

Assessment of the impact of gaseous ship emissions in ports using physical and numerical models: The case of Naples

2021 ◽  
pp. 107812
Author(s):  
Domenico Toscano ◽  
Massimo Marro ◽  
Benedetto Mele ◽  
Fabio Murena ◽  
Pietro Salizzoni
Keyword(s):  
Numerical Models ◽  
Ship Emissions ◽  
The Impact

scholarly journals Aluminium Alloy Foam Modelling and Prediction of Elastic Properties Using X-ray Microcomputed Tomography

Metals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 925
Author(s):  
Diogo Heitor ◽  
Isabel Duarte ◽  
João Dias-de-Oliveira
Keyword(s):  
Aluminium Alloy ◽  
Finite Element Modelling ◽  
Effective Properties ◽  
Numerical Models ◽  
Microcomputed Tomography ◽  
Cellular Materials ◽  
Metallic Foams ◽  
X Ray ◽  
The Impact ◽  
Structural Imperfections

X-ray microcomputed tomography has been gaining relevance in the field of cellular materials to characterize materials and analyse their microstructure. So, here, it was used together with finite element modelling to develop numerical models to estimate the effective properties (Young’s modulus) of aluminium alloy foams and evaluate the effects of processing on the results. A manual global thresholding technique using the mass as a quality indicator was used. The models were reconstructed (Marching Cubes 33), then simplified and analysed in terms of mass and shape maintenance (Hausdorff distance algorithm) and face quality. Two simplification procedures were evaluated, with and without small structural imperfections, to evaluate the impact of the procedures on the results. Results demonstrate that the developed procedures are good at minimizing changes in mass and shape of the geometries while providing good face quality, i.e., face aspect ratio. The models are also shown to be able to predict the effective properties of metallic foams in accordance with the findings of other researchers. In addition, the process of obtaining the models and the presence of small structural imperfections were shown to have a great impact on the results.

scholarly journals NEOShield - A global approach to NEO Impact Threat Mitigation

2012 ◽  
Vol 10 (H16) ◽  
pp. 478-479
Author(s):  
Patrick Michel ◽  
Keyword(s):  
European Union ◽  
Physical Properties ◽  
Technological Development ◽  
Numerical Models ◽  
Physical Contact ◽  
International Strategy ◽  
The European Union ◽  
Design Development ◽  
Asteroid Deflection ◽  
The Impact

AbstractNEOShield is a European-Union funded project coordinated by the German Aero-space Center, DLR, to address near-Earth object (NEO) impact hazard mitigation issues. The NEOShield consortium consists of 13 research institutes, universities, and industrial partners from 6 countries and includes leading US and Russian space organizations. The project is funded for a period of 3.5 years from January 2012 with a total of 5.8 million euros. The primary aim of the project is to investigate in detail promising mitigation techniques, such as the kinetic impactor, blast deflection, and the gravity tractor, and devise feasible demonstration missions. Options for an international strategy for implementation when an actual impact threat arises will also be investigated.The NEOShield work plan consists of scientific investigations into the nature of the impact hazard and the physical properties of NEOs, and technical and engineering studies of practical means of deflecting NEOs. There exist many ideas for asteroid deflection techniques, many of which would require considerable scientific and technological development. The emphasis of NEOShield is on techniques that are feasible with current technology, requiring a minimum of research and development work. NEOShield aims to provide detailed designs of feasible mitigation demonstration missions, targeting NEOs of the kind most likely to trigger the first space-based mitigation action.Most of the asteroid deflection techniques proposed to date require physical contact with the threatening object, an example being the kinetic impactor. NEOShield includes research into the mitigation-relevant physical properties of NEOs on the basis of remotely-sensed astronomical data and the results of rendezvous missions, the observational techniques required to efficiently gather mitigation-relevant data on the dynamical state and physical properties of a threatening NEO, and laboratory investigations using gas guns to fire projectiles into asteroid regolith analog materials. The gas-gun investigations enable state-of-the-art numerical models to be verified at small scales. Computer simulations at realistic NEO scales are used to investigate how NEOs with a range of properties would respond to a pulse of energy applied in a deflection attempt. The technical work includes the development of crucial technologies, such as the autonomous guidance of a kinetic impactor to a precise point on the surface of the target, and the detailed design of realistic missions for the purpose of demonstrating the applicability and feasibility of one or more of the techniques investigated. Theoretical work on the blast deflection method of mitigation is designed to probe the circumstances in which this last line of defense may be the only viable option and the issues relating to its deployment. A global response campaign roadmap will be developed based on realistic scenarios presented, for example, by the discovery of an object such as 99942 Apophis or 2011 AG5 on a threatening orbit. The work will include considerations of the timeline of orbit knowledge and impact probability development, reconnaissance observations and fly-by or rendezvous missions, the political decision to mount a mitigation attempt, and the design, development, and launch of the mitigation mission. Collaboration with colleagues outside the NEOShield Consortium involved in complementary activities (e.g. under the auspices of the UN, NASA, or ESA) is being sought in order to establish a broad international strategy.We present a brief overview of the history and planned scope of the project, and progress made to date.The NEOShield project (http://www.neoshield.net) has received funding from the European Union Seventh Framework Program (FP7/2007-2013) under Grant Agreement no. 282703.

Simulated Foreign Object Damage on Blade Aerofoils: Real Damage Investigation

2008 ◽  
Author(s):  
Pierangelo Duo´ ◽  
Christian Pianka ◽  
Andrej Golowin ◽  
Matthias Fueller ◽  
Roger Schaefer ◽  
...  
Keyword(s):  
Fatigue Strength ◽  
Numerical Models ◽  
Research Work ◽  
Experimental Simulation ◽  
Foreign Object ◽  
Foreign Object Damage ◽  
Special Cases ◽  
Hcf Strength ◽  
Residual Fatigue ◽  
The Impact

During operating service, gas turbine aero-engines can ingest small hard particles which typically produce damage to the aerofoils. If the damage found is a tear or a perforation at the leading edge, it is known as a Foreign Object Damage or FOD and this leads to a reduction of the subsequent High-Cycle-Fatigue (HCF) strength. The objective of research work in this area is to assess the effect of FOD on the residual fatigue strength of compressor blades and to provide predictive tools for engineering judgment. The methodology followed is normally to carry out experimental simulation of FOD, followed by fatigue tests to assess subsequent performance. To date, research related to fatigue following FOD events has concentrated on HCF loading and the impact geometry is frequently that of a sphere against a flat surface or the edge of a blade-like specimen. Both of these aspects do not correspond to the worst cases of real FOD. Here it is intended to investigate the effect of a V-notch geometry, which is more representative of severe FOD found in service. Alongside this, numerical models can be used to simulate the damage and to evaluate the residual stress field. In addition analytical model are used to predict the residual fatigue strength. The current work explains the development of a new rig impact test and discusses the improvements necessary to obtain a sufficient repeatability of the impacts. From the experience gained with a gas gun, an alternative method using a pistol and a barrel, capable of achieving the necessary velocity of simulated FOD, was developed. The applied velocity was in the range of 250m/s to 300m/s and a technique to describe the impact is here discussed. Furthermore the introduction of a high speed camera has allowed to have a complete description of the impact scene and to better understand the impact. The impacted blades were measured and HCF tested. As a result, this has produced a large scatter in the residual fatigue strength. The current method to describe a notch using a 2D approach, which was applied to several geometries of notches, is here critically reviewed. The proposed method would incorporate a more sophisticated method, which reconstruct the real geometry using optical measurement. This latter measurement can fully describe the 3D geometry, showing particularly zones inside the notch where compressive residual might appears. Tears and shear of the material can also be described by applying this technique. The findings are compared with the residual HCF strength and the results are compared to special cases of HCF to justify the results out of theoretical prediction.

Numerical Study of Corrugated Metal Panels Subjected to Windborne Debris Impacts

2014 ◽  
Vol 626 ◽  
pp. 109-114
Author(s):  
Wen Su Chen ◽  
Hong Hao ◽  
Hao Du
Keyword(s):  
Extreme Event ◽  
Numerical Study ◽  
Numerical Models ◽  
Economic Loss ◽  
Wind Loading ◽  
Windborne Debris ◽  
Study Laboratory ◽  
The Impact ◽  
Metal Panels ◽  
Corrugated Metal

Hurricane, typhoon and cyclone take place more and more often around the world with changing climate. Such nature disasters cause tremendous economic loss and casualty. Various kinds of windborne debris such as compact-like, plate-like and rod-like objects driven by hurricane usually imposes localized impact loading on the structure envelopes such as cladding, wall or roof, etc. The dominant opening in the envelope might cause serious damage to the structures, even collapse. To withstand the impact of such extreme event, the requirements on panel capacity to resist windborne debris impact has been presented in the Australian Wind Loading Code (2011) [1]. Corrugated metal panels are widely used as building envelop. In a previous study, laboratory tests have been carried out to investigate the performance of corrugated metal panels subjected to a 4kg wooden projectile by considering various impact locations, impact velocities and boundary conditions. In this study, numerical models were developed to simulate the responses of the corrugated metal panels subjected to wooden debris impacts by using commercial software LS-DYNA. The predicted data from the numerical simulations were compared with the experimental results. The validated numerical model can be used to conduct intensive numerical simulation to study the failure probabilities of corrugated structural panels subjected to windborne debris impacts.

Influence of Phase Transformations on Residual Stresses in Welded Structures

2013 ◽  
Author(s):  
R. J. Dennis ◽  
R. Kulka ◽  
O. Muransky ◽  
M. C. Smith
Keyword(s):  
Phase Transformation ◽  
Residual Stresses ◽  
Phase Transformations ◽  
Numerical Models ◽  
Material Model ◽  
Transformation Model ◽  
Austenitic Steels ◽  
Beam Specimen ◽  
Welded Structures ◽  
The Impact

A key aspect of any numerical simulation to predict welding induced residual stresses is the development and application of an appropriate material model. Often significant effort is expended characterising the thermal, physical and hardening properties including complex phenomena such as high temperature annealing. Consideration of these aspects is sufficient to produce a realistic prediction for austenitic steels, however ferritic steels are susceptible to solid state phase transformations when heated to high temperatures. On cooling a reverse transformation occurs, with an associated volume change at the isothermal transformation temperature. Although numerical models exist (e.g. Leblond) to predict the evolution of the metallurgical phases, accounting for volumetric changes, it remains a matter of debate as to the magnitude of the impact of phase transformations on residual stresses. Often phase transformations are neglected entirely. In this work a simple phase transformation model is applied to a range of welded structures with the specific aim of assessing the impact, or otherwise, of phase transformations on the magnitude and distribution of predicted residual stresses. The welded structures considered account for a range of geometries from a simple ferritic beam specimen to a thick section multi-pass weld. The outcome of this work is an improved understanding of the role of phase transformation on residual stresses and an appreciation of the circumstances in which it should be considered.

Numerical simulation of submarine landslide and generated tsunamis : Application to the Mayotte seismo-volcanic crisis

2021 ◽  
Author(s):  
Pablo Poulain ◽  
Anne Le Friant ◽  
Rodrigo Pedreros ◽  
Anne Mangeney ◽  
Andrea Filippini ◽  
...  
Keyword(s):  
Ground Deformation ◽  
Numerical Models ◽  
Morphological Data ◽  
Submarine Landslides ◽  
Submarine Slide ◽  
Seismic Swarms ◽  
Submarine Slides ◽  
High Resolution Bathymetry ◽  
The Impact ◽  
The Waves

<p>Since May 2018, Mayotte island has experienced an important seismic activity linked to the on-going sismo-volcanic crisis. The epicenters of the seismic swarms are located between 5 and 15 km east of Petite Terre for the main swarm, and 25 km east of Petite Terre for the secondary swarm. Although variations in the number of earthquakes and their distribution have been observed since the start of the eruption in early July 2018 [Lemoine A.(2020), Cesca et al.(2020)], a continuous seismicity persists and could generate several earthquakes of magnitudes close to M4 widely felt by the population. This recurrent seismicity could weaken the steep submarine slopes of Mayotte, as highlighted by the high resolution bathymetry data collected during the MAYOBS cruise in May 2019 (Feuillet et al.,submitted) and trigger submarine landslides with associated tsunamis.</p><p>To address the hazards associated with such events, we analyzed morphological data to define 8 scenarios of potential submarine slides with volumes ranging from 11,25.10<sup>6</sup> to 800.10<sup>6</sup> m<sup>3</sup> and we simulate the landslide dynamics and generated waves. We use two complementary numerical models: (i) the code HYSEA to simulate the dynamic of the submarine granular flows and the water wave generation, and (ii) the Boussinesq FUNWAVE- TVD model simulate the waves propagation and the inundation on Mayotte. The effect of the time at which the models are coupled is investigated.</p><p>The most impacting submarine slide scenarios are located close to Petite Terre at a shallow depth. They can locally generate a sea surface elevation more than a meter in local areas especially at Petite Terre. The various simulations show that parts of the island are particularly sensitive to the risk of tsunamis. Indeed, some scenarios that does not cause significant coastal flooding still seems to cause significant hazards in these exposed areas. The barrier reef around Mayotte has a prominent role in controlling the wave propagation towards the island and therefore reducing the impact on land. It should be noted that the arrival of tsunamis on the coastline is not necessarily preceded by a retreat from the sea and the waves can reach the coasts of Mayotte very quicky (few minutes).</p><p> </p><p>Cesca, S., Letort, J., Razafindrakoto, H.N.T. et al. Drainage of a deep magma reservoir near Mayotte inferred from seismicity and deformation. Nat. Geosci. <strong>13, </strong>87–93 (2020). https://doi.org/10.1038/s41561-019-0505-5</p><p>Feuillet, N, Jorry, S. J., Crawford, W, Deplus, C. Thinon, I, Jacques, E. Saurel, J.M., Lemoine, A., Paquet, F., Daniel, R., Gaillot, A., Satriano, C., Peltier, A., Aiken, C., Foix, O., Kowalski, P., Laurent, A., Beauducel, F., Grandin, R., Ballu, V., Bernard, P., Donval, J.P., Geli, L., Gomez, J. Guyader, V., Pelleau, P., Rinnert, E., Bertil, D., Lemarchand, A., Van der Woerd, J.et al. (in rev). Birth of a large volcano offshore Mayotte through lithosphere-scale rifting, Nature.</p><p>Anne Lemoine, Pierre Briole, Didier Bertil, Agathe Roullé, Michael Foumelis, Isabelle Thinon, Daniel Raucoules, Marcello de Michele, Pierre Valty, Roser Hoste Colomer, The 2018–2019 seismo-volcanic crisis east of Mayotte, Comoros islands: seismicity and ground deformation markers of an exceptional submarine eruption, Geophysical Journal International, Volume 223, Issue 1, October 2020, Pages 22–44, https://doi.org/10.1093/gji/ggaa273</p>

scholarly journals Nautilus multi-grain model: Importance of cosmic-ray-induced desorption in determining the chemical abundances in the ISM

2018 ◽  
Vol 615 ◽  
pp. A20 ◽  
Author(s):  
Wasim Iqbal ◽  
Valentine Wakelam
Keyword(s):  
Grain Size ◽  
Surface Temperature ◽  
Gas Phase ◽  
Numerical Models ◽  
Cosmic Ray ◽  
Grain Sizes ◽  
Small Grains ◽  
Grain Model ◽  
Grain Surface ◽  
The Impact

Context. Species abundances in the interstellar medium (ISM) strongly depend on the chemistry occurring at the surfaces of the dust grains. To describe the complexity of the chemistry, various numerical models have been constructed. In most of these models, the grains are described by a single size of 0.1 μm. Aims. We study the impact on the abundances of many species observed in the cold cores by considering several grain sizes in the Nautilus multi-grain model. Methods. We used grain sizes with radii in the range of 0.005 μm to 0.25 μm. We sampled this range in many bins. We used the previously published, MRN and WD grain size distributions to calculate the number density of grains in each bin. Other parameters such as the grain surface temperature or the cosmic-ray-induced desorption rates also vary with grain sizes. Results. We present the abundances of various molecules in the gas phase and also on the dust surface at different time intervals during the simulation. We present a comparative study of results obtained using the single grain and the multi-grain models. We also compare our results with the observed abundances in TMC-1 and L134N clouds. Conclusions. We show that the grain size, the grain size dependent surface temperature and the peak surface temperature induced by cosmic ray collisions, play key roles in determining the ice and the gas phase abundances of various molecules. We also show that the differences between the MRN and the WD models are crucial for better fitting the observed abundances in different regions in the ISM. We show that the small grains play a very important role in the enrichment of the gas phase with the species which are mainly formed on the grain surface, as non-thermal desorption induced by collisions of cosmic ray particles is very efficient on the small grains.

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