Comparison of Numerical Forced Response Predictions with Experimental Results Obtained in a Subsonic Test Turbine Facility

In order to achieve the ACARE targets regarding reduction of emissions it is essential to reduce fuel consumption  drastically. Reducing engine weight is supporting this target and one option to reduce weight is to reduce the overall  engine length (shorter shafts, nacelle). However, to achieve a reduction of engine length the spacing between stator  and rotor can be minimised, thus changing rotor blade excitation. Related to the axial spacing, a number of excitation  mechanisms in respect to the rotor blading have to be considered already during the design process. Based on these  facts several setups have been investigated at different engine relevant operating points and axial spacing between  stator and rotor in the subsonic test turbine facility for aerodynamic, acoustic, and aeroelastic investigations (STTF- AAAI) at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. In order to  avoid upstream effects of supporting struts, these struts are far downstream of the stage which is under investigation.  In this paper the capability to predict forced response vibrations of selected rotor blades is evaluated with  experimental results for two different axial gaps between rotor blade and stator vane row. The investigation is done for  engine relevant operating conditions. For rotor blade vibration measurements a novel telemetry system in  combination with strain gauges is applied. The stage was modelled using the software package ANSYS. Flow fields up  and downstream of the turbine stage are analysed and visualised for two axial gaps and compared to the forced  response of the blading. Detailed structural dynamic investigations show critical modes during operation which are  identified by the telemetry measurements as well. Finally, the influence of the axial spacing regarding the rotor blade  excitation and vibration can be elaborated and is prepared to get a better understanding of basic mechanism. The  paper shows that reducing axial spacing is a promising option when reducing engine weight. However, prediction of  forced response vibrations is still challenging due to the variety of unknown parameters of a real life engine such as  coupling stiffness, damping, blade mass, etc

On the Influence of a Five-Hole-Probe on the Vibration Characteristics of a Low Pressure Turbine Rotor while Performing Aerodynamic Measurements

For many reasons it is essential to know and assess the flow field and its characteristics up- and downstream of a turbine stage. For these purpose measurements are conducted in test rigs such as the STTF-AAAI (subsonic test turbine facility for aerodynamic, acoustic, and aeroelastic investigations) at the Institute for Thermal Turbomachinery and Machine Dynamics at Graz University of Technology. A low pressure turbine is operated in engine relevant operating conditions. The turbine is experienced high mechanical loads and is excited to vibrate (forced response). In the rotor design process forced response predictions and structural assessments are performed. However, it is not common to include instrumentation (e.g. total pressure and temperature rakes, five-hole-probes, fast response aerodynamic pressure probes) in these forced response predictions. But, these measurement devices are essential and therefore this paper investigates the influence of such an instrumentation onto the vibrational behaviour of a low pressure turbine rotor of the STTF-AAAI. Several vibration measurements at distinct circumferential and radial positions of the five-hole-probe in the flow channel are conducted. These measurement results are compared to measurements performed without a five-hole-probe in the flow channel. A clear influence of the five-hole-probe on the vibration level is shown

Globalisation from Above? Corporate Social Responsibility, the Workers' Party and the Origins of the World Social Forum

In its assessment of the origins and early development of the World Social Forum this article challenges traditional understandings of the Forum as representing ‘globalisation from below’. By tracing the intricate relations among elements of business, civil society, and the Workers’ Party in the first years of the Forum, this article reveals the major role played by a corporate movement stemming from the Brazilian democratisation process in the 1980s, and how this combined with the transformed agenda of the Workers’ Party as it gained higher political offices to constrain the Forum’s activities from the outset. In so doing, this article challenges not only widespread conceptions of the Forum as a counter‐hegemonic alternative but also current critiques concerning its subsequent limitations. Furthermore, it reveals how traditional understandings of the World Social Forum and of global civil society are underpinned by flawed assumptions which typecast political activities in the global ‘South’

A two dimensional electromechanical model of a cardiomyocyte to assess intra-cellular regional mechanical heterogeneities

Experimental studies on isolated cardiomyocytes from different animal species and human hearts have demonstrated that there are regional differences in the Ca2+ release, Ca2+ decay and sarcomere deformation. Local deformation heterogeneities can occur due to a combination of factors: regional/local differences in Ca2+ release and/or re-uptake, intra-cellular material properties, sarcomere proteins and distribution of the intracellular organelles. To investigate the possible causes of these heterogeneities, we developed a two-dimensional finite-element electromechanical model of a cardiomyocyte that takes into account the experimentally measured local deformation and cytosolic [Ca2+] to locally define the different variables of the constitutive equations describing the electro/mechanical behaviour of the cell. Then, the model was individualised to three different rat cardiac cells. The local [Ca2+] transients were used to define the [Ca2+]-dependent activation functions. The cell-specific local Young’s moduli were estimated by solving an inverse problem, minimizing the error between the measured and simulated local deformations along the longitudinal axis of the cell. We found that heterogeneities in the deformation during contraction were determined mainly by the local elasticity rather than the local amount of Ca2+, while in the relaxation phase deformation was mainly influenced by Ca2+ re-uptake. Our electromechanical model was able to successfully estimate the local elasticity along the longitudinal direction in three different cells. In conclusion, our proposed model seems to be a good approximation to assess the heterogeneous intracellular mechanical properties to help in the understanding of the underlying mechanisms of cardiomyocyte dysfunction.This study was partly supported by grants from Ministerio de Economia y Competitividad (ref. SAF2012-37196, TIN2014-52923-R); the Instituto de Salud Carlos III (ref. PI11/01709, PI14/00226) integrado en el Plan Nacional de I+D+I y cofinanciado por el ISCIII-Subdirección General de Evaluación y el Fondo Europeo de Desarrollo Regional (FEDER) “Otra manera de hacer Europa”; the EU FP7 for research, technological development and demonstration under grant agreement VP2HF (n° 611823); The Cerebra Foundation for the Brain Injured Child (Carmarthen, Wales, UK); Obra Social “la Caixa” (Barcelona, Spain); Fundació Mutua Madrileña; Fundació Agrupació Mutua (Spain) and AGAUR 2014 SGR grant n° 928 (Barcelona, Spain). P.G.C. was supported by the Programa de Ayudas Predoctorales de Formación en investigación en Salud (FI12/00362) from the Instituto Carlos III, Spain. P.G.C wants to acknowledge to Boehringer Ingelhiem Fonds for the travel grant to do her research stay at LaBS group in Politecnico di Milano

A two dimensional electromechanical model of a cardiomyocyte to assess intra-cellular regional mechanical heterogeneities.

Experimental studies on isolated cardiomyocytes from different animal species and human hearts have demonstrated that there are regional differences in the Ca2+ release, Ca2+ decay and sarcomere deformation. Local deformation heterogeneities can occur due to a combination of factors: regional/local differences in Ca2+ release and/or re-uptake, intra-cellular material properties, sarcomere proteins and distribution of the intracellular organelles. To investigate the possible causes of these heterogeneities, we developed a twodimensional finite-element electromechanical model of a cardiomyocyte that takes into account the experimentally measured local deformation and cytosolic [Ca2+] to locally define the different variables of the constitutive equations describing the electro/mechanical behaviour of the cell. Then, the model was individualised to three different rat cardiac cells. The local [Ca2+] transients were used to define the [Ca2+]-dependent activation functions. The cell-specific local Young's moduli were estimated by solving an inverse problem, minimizing the error between the measured and simulated local deformations along the longitudinal axis of the cell. We found that heterogeneities in the deformation during contraction were determined mainly by the local elasticity rather than the local amount of Ca2+, while in the relaxation phase deformation was mainly influenced by Ca2+ re-uptake. Our electromechanical model was able to successfully estimate the local elasticity along the longitudinal direction in three different cells. In conclusion, our proposed model seems to be a good approximation to assess the heterogeneous intracellular mechanical properties to help in the understanding of the underlying mechanisms of cardiomyocyte dysfunction

Different images recorded during the cardiomyocyte electrical stimulation experiments, with a pacing rate of 1Hz.

<p>A: Transmitted light image of the whole cell. The blue arrow corresponds to the line-scan where the images acquisition was performed. B: Line-scan transmitted light image. The red box indicates a region within the cell with zero displacement. C: Confocal FM4-64 image where the T-Tubule and sarcolemma are visible. D: Confocal Fluo-4 image corresponding to cytosolic [<i>Ca</i>²⁺]. The vertical axis corresponds to the line-scan (blue arrow) and the horizontal one to the time. The line-scan images resolution is 3.2 ⋅ 10⁻³ <i>s</i> × 0.28<i>μm</i>.</p

Experimental measured local and global [<i>Ca</i>²⁺] transients and dynamic vs. steady-state force and [<i>Ca</i>²⁺] relationship.

<p>A: Experimental measured local [<i>Ca</i>²⁺] transients normalised to basal fluorescence (<i>F</i>₀) at different positions along the longitudinal axis of the cell (Long. pos). B: Global experimental measured (solid line) and fitted (dash line) with the two exponential functions (<i>Z</i>(<i>t</i>) in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182915#pone.0182915.e008" target="_blank">Eq 4</a>) [<i>Ca</i>²⁺] transients. C: Individual time course of cytosolic [<i>Ca</i>²⁺] and active stress (<i>S</i>_<i>act</i>). D: Phase-plane plot relating force to <i>Ca</i>²⁺ for both heterogeneous and homogeneous <i>Ca</i>²⁺ activation. The dynamic behaviour for a single contraction is compared with the steady-state relation.</p

Synthetic data generated for validating the inverse problem procedure and results of the proposed framework validation in presence of gaussian noise.

<p>A: Local [<i>Ca</i>²⁺] transients. B: Active stress <i>S</i>_<i>act</i>(<i>t</i>) at different longitudinal positions (Long. pos) of the synthetic cell. C: Undeformed (grey) and deformed mesh of the synthetic cell at maximum contraction time frame. Colormap indicates the simulated longitudinal strain. D: Original (black solid line) and simulated strains along the longitudinal axis of the cell at maximum contraction time frame after the optimisation process with 0% (*), 5% (□), 10% (◇) and 15% (∘) of noise. E: Original (black solid line) and estimated local Young’s moduli along the longitudinal axis (line-scan) of the cell with 0% (*), 5% (□), 10% (◇) and 15% (∘) of noise.</p

Results of the cell-specific simulations performed for three different cardiomyocytes, for both [<i>Ca</i>²⁺]-activation (Act.) scenarios: Homogeneous (homo.) and heterogeneous (hetero.)

<p>Results of the cell-specific simulations performed for three different cardiomyocytes, for both [<i>Ca</i>²⁺]-activation (Act.) scenarios: Homogeneous (homo.) and heterogeneous (hetero.)</p

Coefficients of the multivariate linear regression analysis for the dependent variables: Maximum contraction amplitude (), time of re-lengthening (<i>τ</i>_<i>sl</i>) and maximum strain rate ().

<p>The independent variables included in the analysis were: , [<i>Ca</i>²⁺] transient amplitude; <i>τ</i>_<i>fall</i>, time constant of [<i>Ca</i>²⁺] transient decay; <i>E</i>, Young’s Modulus; <i>f</i>_<i>max</i>, the maximal tension delivered by the sarcomere; <i>ε</i>_<i>opt</i>, the optimal deformation at the maximal activation state; <i>s</i>, the sensitivity to the actin-myosin overlap.</p