bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Energy Release Rate During Global Thermo-Mechanically-Induced Phase Transformation in Shape Memory Alloys
Authors: Parrinello Antonino , Baxevanis Theocharis , Lagoudas Dimitris
Published: February 2014

In this work, the effect of thermo-mechanically-induced global phase transformation (actuation) on the crack driving force in Shape Memory Alloys (SMAs) is investigated by means of the finite element method. The prototype problem of an infinite center-cracked SMA plate is analyzed during a thermal cycle in isobaric, plane strain loading conditions. The temperature variation is sufficient to induce global phase transformation. The Virtual Crack Closure Technique (VCCT) is employed to measure the crack tip energy release rate during the entire actuation cycle. Results show that the energy release rate can increase drastically during actuation, an order of magnitude for specific material systems. This in turn implies that crack growth may be triggered as a result of thermo-mechanically-induced phase transformation. The sensitivity of the crack tip energy release rate during actuation on key thermo-mechanical parameters is studied.
Carbon Fiber Reinforced Shape Memory Nanocomposites Incorporated With Highly Conductive Carbon Nanopaper for Electro Actuation
Authors: Liang Fei , Gou Jihua , Shen He , Xu Yunjun , Mabbott Bob
Published: February 2014

Shape memory polymers (SMPs) are one of the most popular smart materials due to light weight and high elastic deformation capability. In this study, highly conductive carbon nanofibers paper (CNFP) was coated on the surface of SMP as a conductive layer for electro actuation of SMP. To overcome the drawback of low modulus and low strength of shape memory polymer (SMP), continuous carbon fiber reinforcement was also incorporated with SMP by autoclave processing. The dynamic mechanical analysis (DMA) result showed over 600% increase of storage modulus of SMP by introducing carbon fiber reinforcement. Also, the shape recovery time of SMP has been reduced over 150%, while the recovery ratio of SMP has been improved to 99% by incorporating with carbon fiber reinforcement. Additionally, the mechanical property degradation of SMP composites has been investigated after different electro actuation cycles. After 50 actuation cycles, the decrease of flexural modulus of SMP composites is negligible (< 2%), and the ultimate flexural strength of SMP composites only decreased 25%. The SMP composite shows high strength and modulus, and good durability.
Design of a Passive/Active Autoparametric Cantilever Beam Absorber With PZT Actuator for a Building-Like Structure
Authors: Abundis-Fong H. F. , Silva-Navarro G. , Vazquez-Gonzalez B.
Published: February 2014

An experimental and theoretical investigation is carried out on a system consisting of a primary structure coupled with a passive/active autoparametric vibration absorber. The primary structure consists of a building-like mechanical structure with two rigid floors connected by flexible columns made from aluminium strips, while the vibration absorber consists of a cantilever beam with a PZT patch actuator cemented and actively controlled through an acquisition card installed on a PC running on a Matlab/Simulink platform. The overall system is then a coupled nonlinear oscillator subjected to sinusoidal excitation, obtained from an electromechanical shaker, in the neighborhood of its external and internal resonance. The addition of the PZT patch actuator to the cantilever beam absorber, cemented to the base of the beam, makes active the autoparametric vibration absorber, thus enabling the possibility to control the effective stiffness and damping associated to the passive absorber and, as a consequence, the implementation of an active vibration control scheme able to preserve, as possible, the autoparametric interaction as well as to compensate varying excitation frequencies and parametric uncertainty.
Design of Flexible Hybrid Tactile Display Using Electro-Vibration and Electroactive Polymer Modules
Authors: Yang Tae-Heon , Choi In-Mook , Woo Sam Yong , Park Won-Hyeong , Kim Sang-Youn , Kim Min Seok , Song Han Wook , Park Yon-Kyu
Published: February 2014

When a user explores over an object, mechanoreceptors in human’s fingertip dominantly detect small-scale shapes and textures on the surface of the object. For generating and conveying virtual tactile sensations to users, we developed a new flexible hybrid tactile display consisting of an electroactive polymer (EAP) module and an electro-vibration module. The EAP module was used to construct an ultra-thin 3×3 pin-array module for mimicking small-scale shapes on the object. Since each cell of the proposed 3×3 EAP module is independently actuated with high vertical stroke, it is enough to create various micro-shapes. The electro-vibration module was attached on the EAP module. The electro-vibration module consists of two plates coated with compliant electrodes. The electro-vibration module creates micro-vibration to imitate virtual texture on the objects. To design the proposed hybrid tactile display, the equations for the mechanical models of the proposed tactile display were derived. The working principle of the modules was verified based on the mechanical model. To control the developed combined tactile display, a high-volt multichannel controller was developed by using a high-volt DC-DC converter and opto-couplers. The proposed hybrid tactile display with its control system generates sufficient performances to create realistic and vivid virtual tactile sensations.
Correlation of Rheological and Electrical Percolation in PVDF-MWNT Nanocomposites
Authors: Rizvi Reza , Naguib Hani
Published: February 2014

This study investigates the evolution of filler particle networks using electrical and rheological property measurements. Polyvinylediene Flouride (PVDF) was used as the matrix thermoplastic polymer which was reinforced with multiwall carbon nanotubes (MWNT) as the filler phase using high shear twin screw extrusion mixing. Electrical conductivity and dielectric constant measurements were done using impedance spectroscopy. Viscosity and storage modulus measurements were performed using a dynamic rheometer. Morphologies of the composites were observed using scanning electron microscopy. The percolation behavior in electrical conductivity was determined to be 1.3 wt% MWNT content in PVDF. This is in contrast to the nanocomposite viscosity percolation threshold which occurred at 1.9 wt%.
Optimization and Comparison of Electromagnetic Vibration Energy Harvesters Under Constant Volume Conditions
Authors: Lee Hanmin , Kim Young-Cheol , Lim Jaewon , Park Seong-Whan
Published: February 2014

Previous studies on optimization of electromagnetic vibration energy harvesters assumed the radius and the height of a cylindrical construction volume to be fixed. We present optimization and comparison of three different types of electromagnetic vibration energy harvesters under constant volume conditions where the radius or the height can also be a design variable. The voltage and the power output are calculated for each architecture using finite element analysis. We found that different types of electromagnetic coupling architectures can be optimized with different shapes of the construction volumes.
Modeling and Control of Lozenge-Shaped Dielectric Elastomer Generators
Authors: Moretti Giacomo , Fontana Marco , Vertechy Rocco
Published: February 2014

Dielectric Elastomers (DEs) are a very promising technology for the development of energy harvesting devices based on the variable-capacitance electrostatic generator principle. As compared to other technologies, DE Generators (DEGs) are solid-state energy conversion systems which potentially feature: 1) large energy densities, 2) good energy conversion efficiency that is rather independent of cycle frequency, 3) easiness of manufacturing and assembling, 4) high shock resistance, 5) silent operation, 6) low cost. Envisioned applications for DEGs are in devices that convert ocean wave energy into usable electricity.

This paper introduces the Lozenge-Shaped DEG (LS-DEG) that is a specific type of planar DE transducer with one degree of freedom. A LS-DEG consists of a planar DE membrane that is connected along its perimeter to the links of a parallelogram four-bar mechanism. As the mechanism is put into reciprocal motion, the DE membrane varies its capacitance that is then employed as a charge pump to convert external mechanical work into usable electricity.

Specifically, this paper describes the functioning principle of LS-DEGs, and provides a comparison between different hyper-elastic models that can be used to predict the energy harvesting performances of realistic prototypes. Case studies are presented which address the constrained optimization of LS-DEGs subjected to failure criteria and practical design constraints.
Applications of Nano-Composite Piezoelectric Foam Sensors
Authors: Merrell A. Jake , Fullwood David T. , Bowden Anton E. , Remington Taylor D. , Stolworthy Dean K. , Bilodeau Adam
Published: February 2014

This study develops highly flexible, adaptable, portable gauges that give real-time measurements in many applications where compression is of interest. They can be embedded into elastomeric foams, and preserve the desirable physical properties of the foams in dispersing impact energy. We anticipate that these novel and inexpensive sensors will enable real-time measurement of human impacts and athletic performance based on data collected in the field, rather than the current standard of trying to replicate these experiences in the lab. In previous work, we have validated the performance of tensile strain sensors based on a similar technology embedded in thin sheets of silicone. These sensors are capable of measuring up to 50% strains in real time with minimal interference in tissue motion. With the addition of the sensors described in the present work, it is possible to measure both tensile and compressive strains.
Combined Evaluation Composite Pressure Vessel With Thin-Wall Metal Liner by Acoustic Emission and Strain Gauges
Authors: Zhao Junqing , He Xiaodong
Published: February 2014

Filament wound composite pressure vessel with thin-wall alloy liner might exist local buckling during manufacture and in service, this phenomenon have great influence on the security and service lifetime of pressure vessel. AE (acoustic emission) technique is employed to monitor the damage progression of the vessel during hydraulic pressure experiment. Two sensors of acoustic emission (AE) were attached to front dome and cylinder to monitoring the behavior of the vessel bearing maximum 4.5MPa water pressure during loading, keeping load and unloading. Meanwhile ten strain gauges were bonded to front dome, equator and cylinder of the outer surface by meridian and hoop direction respectively in order to monitor the vessel deformation characters. Analysis show that strain gauges is suitable for evaluate deformation character of the outer surface of the vessel. Analysis indicated AE is more suitable to monitoring the damage propagation of the vessel. AE analysis explained the local buckling of inner thin-wall liner.
Structural Health Monitoring via Connectivity Constrained Reference Basis Model Updating
Authors: Halevi Yoram
Published: February 2014

The paper presents a structural health monitoring method that is based on the model updating method connectivity constrained reference basis. The method combines two separate approaches, reference basis and parametric methods, and it is computationally efficient because it does not require calculation of sensitivity functions. The paper discusses why connectivity constrained reference basis is generally suitable for structural health monitoring and what are the modifications required in the new application. The derivation includes noise propagation analysis of the algorithm and its effect on the new structural health monitoring application.
Flexible Multiwall Carbon Nano-Tubes/Polyaniline Composite for Supercapacitor Application
Authors: Lee Ka Yeung Terence , Naguib Hani , Lian Keryn
Published: February 2014

In this study, the electrochemical performance of Multi-walled Carbon nanotubes (MWCNT) and polyaniline (PANI) composite (PANI/MWCNT) as supercapacitor electrode material was investigated. An improvement in capacitive performance due to the combination of pseudo capacitance and double layer capacitance was observed. A nano-composite was fabricated by polymerizing pseudo-capacitive polyaniline onto the MWCNT surface through the in-situ chemical polymerization approach. Ammonium persulphate (APS) was used as oxidant to polymerize PANI and HCl was used as dopant. Stainless steel thin foil was used as a current collector as well as a flexible back bone. Graphite conductive ink as binder was used to form a conductive paste. Different composition is varied by varying the PANI concentration from 0.1M, 0.3M, and 0.5M to 1M molar concentration. For material characterization, Scanning Electron Microscopy (SEM) was used to characterize surface morphology of the composite. Cyclic Voltammetry and Electrochemical Impedance Spectrometry in three electrodes set up found that 0.1M PANI/MWCNT yields the best electrochemical performance. Two electrodes setup evaluation on 0.1M PANI/MWCNT reviews promising characteristic suitable for device application. The improved electroactivity of the PANI/MWCNT composite is discussed in detail.
An Origami-Inspired Self-Deployable Array
Authors: Zirbel Shannon A. , Wilson Mary E. , Magleby Spencer P. , Howell Larry L.
Published: February 2014

The objective of this paper is to show the development of a compact, self-deploying array based on the tapered map fold. The tapered map fold was modified by applying an elastic membrane to one side of the array and adequately spacing the panels adjacent to valley folds. Through this approach, the array can be folded into a fully dense volume when stowed. The panels are dimensioned to account for the panel thickness when folded, which otherwise would prevent the model from reaching a fully dense form.

The folding motion is achieved by creating a rigid-foldable model of the origami-inspired crease pattern. The paper discusses a variety of approaches for creating rigid origami from the map fold, including pleat hinges and spacer panels. The tapered map fold is rigid-foldable through the incorporation of tapered spacer panels. By choosing appropriate values for the angles and tapered spacer panel dimensions, the tapered map fold is fully dense when stowed. The tapered spacer panels also enable the model to have a single degree of freedom of actuation. Stored strain energy in the elastic membrane enables self-actuation of the model. Applying a membrane also simplifies fabrication of the array.

Potential applications for the array include a collapsible solar array, or other military or backpacking applications.
Ferrofluids for Concurrent Vibration Absorption and Energy Harvesting
Authors: Alazemi Saad F. , Daqaq Mohammed F.
Published: February 2014

This paper proposes a novel Tuned Magnetic Fluid Damper (TMFD) with energy harvesting capabilities to concurrently mitigate structural vibrations and harvest vibratory energy. The energy harvesting TMFD consists of a rectangular container carrying a magnetized ferrofluid and mounted on a vibrating structure. The ferrofluids geometric and material properties (height, surface area, magnetization) are tuned such the first modal frequency of the fluid column matches the first modal frequency of the structure. The one-to-one resonant interactions between the structure and the fluid column results in a direct energy transfer mechanism which mitigates the vibration of the structure by channeling energy to the ferrofluid. Consequently, the fluid undergoes a sloshing motion with large-amplitude surface waves that change the orientational order of the magnetic dipoles in the fluid. This creates a time-varying magnetic flux, which induces an electromotive force in a coil wound around the container. The electromotive force transforms a small part of the fluids kinetic energy into electricity by generating a current in the coil. Experimental studies performed on an actual TMFD prototype clearly demonstrate its vibration suppression potential and energy generation capabilities.
Oriceps: Origami-Inspired Forceps
Authors: Edmondson Bryce J. , Bowen Landen A. , Grames Clayton L. , Magleby Spencer P. , Howell Larry L. , Bateman Terri C.
Published: February 2014

This paper presents the conceptualization and modeling of a compliant forceps design, which we have called Oriceps, as an example of origami-inspired design that has application in a variety of settings including robotic surgeries. Current robotic forceps often use traditional mechanisms with parts that are difficult to clean, wear quickly, and are challenging to fabricate due to their complexity and small size. The Oriceps design is based on the spherical kinematic configurations of several action origami models, and can be fabricated by cutting and folding flat material. This design concept has potential implementation as surgical forceps because it would require fewer parts, be easier to sterilize, and be potentially suitable for both macro and micro scales. The folded and planar characteristics of this design could be amenable to application of smart materials resulting in smaller scale, greater tool flexibility, integrated actuation, and an adaptability to a variety of tool functions. The suitability of shape-memory materials for use in Oriceps is discussed.
Electromechanical Characterization of Piezoelectric Shear Actuators
Authors: Malakooti Mohammad H. , Sodano Henry A.
Published: February 2014

Piezoelectric materials exhibit electromechanical coupling which has led to their widespread application for sensors, actuators, and energy harvesters. These materials possess anisotropic behavior with the shear coefficient have the largest electromechanical coupling coefficient. However the shear mode is difficult to measure with existing techniques and thus has not been fully capitalized upon in recent devices. Better understanding of the full shear response with respect to the driving electric field would significantly help the design of optimized piezoelectric shear devices. Here a simple and low cost direct measurement method based on digital image correlation is developed to characterize the shear response of piezoelectric materials and its nonlinear behavior as a function of external field. The piezoelectric shear coefficient (d15) of a commercial shear plate actuator is investigated in both bipolar and unipolar electric fields. Two different nonlinearities and hysteresis behaviors of the actuators were observed, and the relation between the driving field amplitude and the corresponding d15 coefficient is determined. Moreover, the measured transverse displacement of the plate actuator in simple shear condition is validated through a laser interferometry technique.
Response of an Axially-Loaded Terfenol-D Rod to a Harmonic Base Excitation
Authors: Panyam Meghashyam , Daqaq Mohammed F.
Published: February 2014

Performance characteristics of the giant magnetostrictive alloy, Terfenol-D, have been studied by many researchers for actuation, sensing and energy harvesting applications. Mathematical models characterizing the magneto-elastic behavior and describing the effects of bias conditions — compressive prestress and magnetic bias — on the material performance, have been developed. For the most part, the models used to describe the material are linear models that can hide essential features of the dynamic performance. While nonlinear constitutive models of Terfenol-D exist, such models have not been utilized to study the dynamic frequency response characteristics that are essential towards a comprehensive understanding of its performance in actuation, sensing or energy harvesting. To address this problem, this effort investigates the role of empirically determined material nonlinearities in the dynamic performance of Terfenol-D. Towards that objective, a polynomial type stress-strain relation is used to construct a nonlinear distributed-parameters model for a Terfenol-D rod fixed at one end and mass loaded at the other while being subjected to a sinusoidal base excitation. Additionally, the model accounts for the rod being subjected to an axial prestress prior to excitation. Using the method of multiple scales, the nonlinear frequency response of the rod is investigated by obtaining analytical expressions for the steady-state response amplitude. It is demonstrated that the axial prestress results in a shift in the fundamental vibration frequencies of the rod and a change in the effective nonlinearity of the system. A qualitative analysis of the solution reveals that, the magnitude of axial load can be used to maximize the response amplitude over a larger bandwidth of frequencies.
A Thermo-Mechanical Model for SMA-Based Crank Heat Engines
Authors: Furgiuele Franco , Maletta Carmine , Niccoli Fabrizio , Sgambitterra Emanuele
Published: February 2014

Shape memory alloys (SMA) provide unique functional features and several SMA-based heat engines have been proposed in recent years, exploiting the thermally induced recovery capabilities of such class of materials. These engines represent simple and environmentally-friendly solutions to obtain mechanical energy from low-grade energy sources, such as warm wastewater, geothermal and solar sources. However, despite the scientific interest in last years, no commercial devices have been developed. One of the reasons of these unsuccessful commercial development is the lack of robust design tools. In the proposed work a thermo-mechanical model has been developed, which describes the mechanical response of a SMA-based crank heat engine, as a function of several geometrical configurations, such as the dimension and total number of cranks, as well as for different thermo-physical properties of the heating and cooling thermal sources. In particular, the engine is made of two parallel crankshafts and uses nickel-titanium helical springs operating between warm water and cold air. The model has been developed within the MatLab® Simulink software platform, and several simulations have been carried out to analyze the mechanical response of the engine, in terms of output characteristics (torque, specific power, thermodynamic efficiency) as a function of the aforementioned geometrical and physical parameters.
Evaluation of Millimeter-Size Fluidic Flexible Matrix Composite Tubes
Authors: Vashisth Aniruddh , Zhu Bin , Wimmer Benjamin M. , Bakis Charles E. , Rahn Christopher D.
Published: February 2014

Fluidic flexible matrix composite (F2MC) tubes are fiber-reinforced tubes that have been designed to change structural characteristics (e.g., shape, stiffness, damping, actuation force, etc.) based on the control of fluid flow and pressure inside the tubes. In the current investigation, miniature F2MC tubes (2 mm diameter) are designed and evaluated. The tubes are made with fine steel wire and a flexible polyurethane matrix. Tubes with reinforcement angles of ±40 and ±24 degrees relative to the longitudinal axis were evaluated in terms of blocked force and free strain versus internal pressure and axial modulus of elasticity. Sheets of multiple, unidirectionally aligned tubes positioned side by side and potted into a surrounding compliant matrix material were evaluated as well. Encouraging agreement with elasticity solutions based on infinitely long multi-layer tubes with internal pressurization was observed. Over the long term, this line of research is aimed at the development of thin skins for structures that can change shape and stiffness differently as a function of direction.
Shrouding the First Blade of High Temperature Turbines
Authors: Mamaev B. I. , Petukhovsky M. M. , Pozdnyakov A. V.
Published: February 2014

Blade shrouding gives an opportunity to increase the HPT (high pressure turbine) first stage efficiency by 2–3 %. However, if high gas temperature and high circumferential velocity are at the stage, shrouding can be problematic due to load increasing at blade/disk attachment and high temperature of the shroud itself.

To make blade/disk attachment more reliable the shroud axial width has to be decreased by increasing a relative pitch of airfoil cascades t (t = t / b, where t – pitch, b – chord) at the blade tip span. According to experience for a flow with β1 = 50 – 85°, M2 = 0.8 – 1, and Re = (0.8 – 1)•106 high efficient cascades with t = 0.93 – 1.05 can be designed. Application of such a profiling for GTE (gas turbine engine) turbine is demonstrated here. In the turbine meridian flow path the blade was drastically tapered to the tip (tip width was 53 % of the mean width and 46 % of the hub width).

To lighten the blade a partial shrouding can be also applied. Model turbine tests showed that local cuts at the front shroud area and the aft shroud area at the airfoil pressure side influenced the efficiency weakly.

Required shroud temperature is provided with a cooling. The aircraft turbine with a governed cooling system and a radial clearance control is an example here.

In this case the shroud had 3 labyrinth ribs. The shrouding decreased radial clearance by 0.8 mm at main design modes that increased efficiency by ∼ 1.5 %.

To cool down the shroud the air downstream the compressor was fed into the cavity behind the front labyrinth rib. At maximal mode with full cooling the relative coolant mass flow (to the compressor mass flow) was mc = 1.3 % and gas leakages through the labyrinth were 0.2 %. It gave acceptable mixed temperature of 530°C in the cavity over the shroud. At cruise high altitude mode and a lower gas temperature and partial cooling with mc = 0.4 % and gas leakages of 0.1 % the mixed temperature also did not exceed 530°C over the shroud.

The assessment with taking into account changes of the clearance, the coolant mass flow, and gas leakages showed that the shrouding provided the engine economy improvement by 0.7 – 0.9 % for both modes.

For GTPU (gas turbine power unit) the first blade shrouding can be more complicated. However, even the slight turbine efficiency increase provides considerable profits due to GTPU huge power output and long term running.

So, when GTE and GTPU designing starts, it is reasonable to consider the turbine first blade shrouding. Here the integral evaluation criterion, which includes the assessment of a possible income from the unit full life cycle running, has to be applied.
Turbine Split Rings Thermal Design Using Conjugate Numerical Simulation
Authors: Tikhonov Aleksei S. , Shvyrev Andrey A. , Samokhvalov Nikolay Yu.
Published: February 2014

One of the key factors ensuring gas turbine engines (GTE) competitiveness is improvement of life, reliability and fuel efficiency. However fuel efficiency improvement and the required increase of turbine inlet gas temperature (T*g) can result in gas turbine engine life reduction because of hot path components structural properties deterioration.

Considering circumferential nonuniformity, local gas temperature T*g can reach 2500 K. Under these conditions the largest attention at designing is paid to reliable cooling of turbine vanes and blades. At present in design practice and scientific publications comparatively little attention is paid to detailed study of turbine split rings thermal condition. At the same time the experience of modern GTE operation shows high possibility of defects occurrence in turbine 1st stage split ring.

This work objective is to perform conjugate numerical simulation (gas dynamics + heat transfer) of thermal condition for the turbine 1st stage split ring in a modern GTE.

This research main task is to determine the split ring thermal condition by defining the conjugate gas dynamics and heat transfer result in ANSYS CFX 13.0 package. The research subject is the turbine 1st stage split ring. The split ring was simulated together with the cavity of cooling air supply from vanes through the case. Besides turbine 1st stage vanes and blades have been simulated. Patterns of total temperature (T*Max = 2000 °C) and pressure and turbulence level at vanes inlet (19.2 %) have been defined based on results of calculating the 1st stage vanes together with the combustor.

The obtained results of numerical simulation are well coherent with various experimental studies (measurements of static pressure and temperature in supply cavity, metallography).

Based on the obtained performance of the split ring cooling system and its thermal condition, the split ring design has been considerably modified (one supply cavity has been split into separate cavities, the number and arrangement of perforation holes have been changed etc.). All these made it possible to reduce considerably (by 40…50 °C) the split ring temperature comparing with the initial design.

The design practice has been added with the methods which make it possible to define thermal condition of GTE turbine components by conjugating gas dynamics and heat transfer problems and this fact will allow to improve the designing level substantially and to consider the influence of different factors on aerodynamics and thermal state of turbine components in an integrated programming and computing suite.
Building Up Suitable Contact Forces in Integrally Shrouded Blade Rows for Reducing Vibration Amplitudes
Authors: Bachschmid Nicolò , Pesatori Emanuel , Bistolfi Simone , Sanvito Massimiliano
Published: February 2014

The beneficial effects of the contact between shrouds are described extensively in recent literature: natural blade frequencies are increased and additional damping is available. Different models are proposed for analyzing its linear and nonlinear behavior, selection of optimum contact forces are proposed for reducing vibration amplitudes to a minimum. Results from different non linear analyses that use different models all based generally on a reduced modal model of the blade row and on the harmonic balance approach for modeling the non linear contact forces, are sometimes contradictory: some claim e.g. that increasing excitation amplitude leads to a reduction of the dynamic magnification factor (due to friction damping increase) some other claim the opposite. The contribution to this topic of the present paper is the analysis of the effect of a “contact shim” which can be inserted in a cavity between adjacent shrouds. The shim generates suitable contact forces between the shrouds of the blades of a row, which without shim would vibrate as free standing blades.
Aerothermal Performance of Shroudless Turbine Blade Tips With Effects of Relative Casing Motion
Authors: Virdi A. S. , Zhang Q. , He L. , Li H. D. , Hunsley R.
Published: February 2014

Recent work has indicated qualitatively different heat transfer characteristics between a transonic blade tip and a subsonic one. High resolution experimental data can be acquired for blade tip heat transfer research using a high speed linear cascade. While recognising an important role played by the cascade tests in validating computational models at the same conditions, some questions arise in relation to the effects of relative casing motion:

1) Does the relative casing movement change the main flow physics influencing the blade tip aerothermal performance?

2) Can a cascade set up with stationary casing wall rank different designs?

3) How do the effects of the casing motion depend on tip design configurations?

A combined experimental and CFD study on several high pressure blade tip configurations is conducted to address these issues.

Firstly, extensive experimental tests with aerodynamic loss and heat transfer measurement in a high speed linear cascade have been carried out for a squealer tip configuration at engine representative aerodynamic conditions. A systematic validation of the CFD solver (Rolls-Royce HYDRA) is presented, which serves as a basis for the computational analyses of the effects of the relative casing motion.

Two tip configurations (squealer and flat tip) at three tip gaps (0.5%, 1.0%, 1.5% span) are analysed. The main aerodynamic impact of the casing motion is seen to promote the passage vortex, which consequently supresses the pitchwise reach of the tip leakage vortex. Inside the tip gap, the behaviour is dominated by the extra wall friction in relation of the inertia of the bulk fluid through the gap. As such, the moving casing effect is particularly strong for the flat tip at a small tip gap. For the large and medium tip gaps, both stationary and moving casing results are shown to consistently capture the trends in overall aerothermal performances.

The present results confirm that even with relative casing motion, there is still a significant portion of transonic flow over a blade tip. For both the stationary and moving casing cases, the gap dependence of the over-tip heat transfer shows opposite trends for the transonic and subsonic regions respectively. The gap dependence of the blade tip heat transfer is shown to be clearly dependent on tip geometry configurations, as the bulk flow in a squealer cavity is subsonic regardless of the tip gap size, whilst the local flow state over a flat tip is much more responsive to the change of gap size.
Direct Numerical Simulations of a Transonic Tip Flow With Free-Stream Disturbances
Authors: Wheeler Andrew P. S. , Sandberg Richard D.
Published: February 2014

In this paper we use direct numerical simulation to investigate the unsteady flow over a model turbine blade-tip at engine scale Reynolds and Mach numbers. The DNS is performed with a new in-house multi-block structured compressible Navier-Stokes solver purposely developed for exploiting high-performance computing systems. The particular case of a transonic tip flow is studied since previous work has suggested compressibility has an important influence on the turbulent nature of the separation bubble at the inlet to the gap and subsequent flow reattachment. The effects of free-stream turbulence, cross-flow and pressure-side boundary-layer on the tip flow aerodynamics and heat transfer are investigated. For ‘clean’ in-flow cases we find that even at engine scale Reynolds numbers the tip flow is intermittent in nature (neither laminar nor fully turbulent). The breakdown to turbulence occurs through the development of spanwise modes with wavelengths around 25% of the gap height. Cross-flows of 25% of the streamwise gap exit velocity are found to increase the stability of the tip flow, and to significantly reduce the turbulence production in the separation bubble. This is predicted through in-house linear stability analysis, and confirmed by the DNS. For the case when the inlet flow has free-stream turbulence, viscous dissipation and the rapid acceleration of the flow at the inlet to the tip-gap causes significant distortion of the vorticity field and reductions of turbulence intensity as the flow enters the tip gap. This means that only very high turbulence levels at the inlet to the computational domain significantly affect the tip heat transfer. The DNS results are compared with RANS predictions using the Spalart-Allmaras and k–ω SST turbulence models. The RANS and DNS predictions give similar qualitative features for the tip flow, but the size and shape of the inlet separation bubble and shock positions differ noticeably. The RANS predictions are particularly insensitive to free-stream turbulence.
Impact of Passive Tip-Injection on the Performance of Partially Shrouded Turbines: Basic Concept and Preliminary Results
Authors: Ghaffari Pouya , Willinger Reinhard
Published: February 2014

In terms of efficiency improvement many methods for reducing the blade tip-leakage mass flow rate have been proposed. Some of these methods are based on increasing the flow resistance with aid of geometrical modifications of the blade tip (squealers, winglets, shrouded blades, etc.) whereas other methods take advantage of aerodynamical resistance with passive tip-injection as an example. The objective of this paper is a combination of both methods in order to achieve higher reduction in tip-leakage mass flow rate. In the first part of this work necessary characteristic parameters of modern low pressure turbine blades in aircraft gas turbines are estimated. These parameters are taken into consideration to calculate the range of physical quantities influencing tip-leakage flow. Subsequently a two dimensional flow model is obtained with the so called discharge coefficient as the ratio of the actual tip gap mass flow rate to its highest possible value. The investigations are based on dimensionless calculations. In the end the results obtained from dimensionless 2D CFD-simulations are presented and compared with the analytical results. This leads to conclusions regarding the impact of various parameters on the effectiveness of the passive tip-injection.
Leakage Flow Impact on High Aspect Ratio Steam Turbine Reaction Blades
Authors: Nettis Leonardo , Lombardi Luca
Published: February 2014

The steam turbine stage efficiency is significantly affected by clearance losses due to leakage flow re-entering the main flowpath. The impact, in terms of delta of efficiency Δη, is usually assessed by assuming the proportionality Δη = K × (mLeak/mMain), being mLeak/mMain the fraction of the leakage flow relative to the main mass flow rate and K the constant evaluated by experimental and numerical evidence. Several studies are present in the literature concerning low aspect ratio blades, where this constant K is found to be equal to 1, or even higher for very low percentage leakage massflow.

The main purpose of the current work consists of assessing this factor in the case of steam turbine reaction blades of the HP sector, characterized by a high aspect ratio. A numerical analysis has been set up where the detailed 3D geometry of two HP stages has been modeled and simulated by a 3D-CFD approach. Then a sensitivity analysis has been carried out by varying the leakage flows coming from stator and rotor labyrinth seals, realized by changing the radial gap of the clearance. This analysis has been repeated for several working points in order to obtain the leakage impact in the whole operating range of the reaction stages. The K factor comes out to be close to 0.8 at design point, whilst it increases up to 1 for highly loaded off-design condition.
Numerical Study of Heat Transfer and Cooling Effectiveness on a Flat-Tip Turbine Blade
Authors: Huang Qihe , Wang Jiao , He Lei , Xu Qiang
Published: February 2014

A numerical study is performed to simulate the tip leakage flow and heat transfer on the first stage rotor blade tip of GE-E3 turbine, which represents a modern gas turbine blade geometry. Calculations consist of the flat blade tip without and with film cooling. For the flat tip without film cooling case, in order to investigate the effect of tip gap clearance on the leakage flow and heat transfer on the blade tip, three different tip gap clearances of 1.0%, 1.5% and 2.5% of the blade span are considered. And to assess the performance of the turbulence models in correctly predicting the blade tip heat transfer, the simulations have been performed by using four different models (the standard k-ε, the RNG k-ε, the standard k-ω and the SST models), and the comparison shows that the standard k-ω model provides the best results. All the calculations of the flat tip without film cooling have been compared and validated with the experimental data of Azad[1] and the predictions of Yang[2]. For the flat tip with film cooling case, three different blowing ratio (M = 0.5, 1.0, and 1.5) have been studied to the influence on the leakage flow in tip gap and the cooling effectiveness on the blade tip. Tip film cooling can largely reduce the overall heat transfer on the tip. And the blowing ratio M = 1.0, the cooling effect for the blade tip is the best.
Development of New Abradable/Abrasive Sealing Systems for Clearance Control in Gas Turbines
Authors: Scrinzi Erica , Giovannetti Iacopo , Sheng Nuo , Leblanc Luc
Published: February 2014

Abradable/abrasive sealing systems are currently used in gas turbines to reduce the blade tip gas leakage and consequently improve the turbine efficiency. The coatings selection is directly related to the section in which they are used. Seal systems for hot gas paths are primarily required to withstand high temperature. The abradable coating should be easily removed by the tip blade without causing significant blade wear, whereas the blades should have sufficient cutting capabilities. Durability properties, such as erosion resistance, are also required.

Owing to their temperature capabilities, porous ceramic coatings are successfully used as abradable coatings. Although they are characterized by good abradability properties, their resistance to environmental attacks, such as solid particle erosion, is limited by the porous microstructure which negatively affects their service life.

It is apparent that durability and abradability are the main targets to be simultaneously achieved for ensuring longer service life and improved efficiency. The present work is aimed at developing new abradable/abrasive coatings pairs able to ensure both the durability performances of the coatings and good abradability properties.

Three ceramic abradable coatings with DVC and porous microstructure have been studied. The down-selection process has been carried out by considering the microstructure, the hardness, the tensile adhesion strength, the erosion resistance, and the furnace cycle test resistance.

A composite coating made by NiCoCrAlY matrix containing abrasive grits applied by electrolytic process was selected as abrasive material system. The abrasive grits (patent application in process by GE Oil&Gas) consists of a mixture of ceramic particles. These grits ensure both short-term cutting capability and thermal stability, assuring the clearance maintenance over time.

The abradability of the seal system was assessed by a properly designed test, namely Rub Rig test, which simulates the blade incursion in the abradable coating. Surface patterns on abradable coating were also considered to further enhance the abradability. Engine tests are foreseen for assessing the service behavior of this seal system.
Equivalence of adaptive time reversal and least squares for cross talk mitigation
Authors: Song H. C.
Published: February 2014

A recent paper [H. C. Song et al., J. Acoust. Soc. Am. 127, EL19–EL22 (2010)] demonstrated adaptive time reversal (ATR) using at-sea experimental data which significantly suppressed the cross talk among users (or transmitters) over conventional time reversal. In this letter, the ATR approach is shown essentially equivalent to the least squares solution to an over-determined system.
Structural Insights into Ubiquinone Biosynthesis in Membranes
Authors: Cheng Wei , Li Weikai
Published: February 2014

Catalysis in the Membrane

Enzymes in the UbiA superfamily of integral membrane proteins synthesize lipid-soluble aromatics such as ubiquinones and chlorophylls that function in energy storage and energy transfer in mitochondrial and chloroplast membranes.
Cheng and Li
(p.
878
) report structures of an archaeal UbiA protein in both apo and substrate-bound states. The structures show a large active site with a lateral portal that is likely to give access to the long-chain isoprenoid substrates. The findings suggest a mechanism for substrate recognition and catalysis and can explain disease-related mutants in eukaryotic homologs.
Dendritic Inhibition in the Hippocampus Supports Fear Learning
Authors: Lovett-Barron Matthew , Kaifosh Patrick , Kheirbek Mazen A. , Danielson Nathan , Zaremba Jeffrey D. , Reardon Thomas R. , Turi Gergely F. , Hen René , Zemelman Boris V. , Losonczy Attila
Published: February 2014

Fear, Memory, and Place

Contextual fear conditioning (CFC) is widely used as a hippocampal-dependent classical conditioning task to model human episodic memory.

Lovett-Barron
et al.

(p.
857
) combined in vivo imaging with pharmacology, pharmacogenetics, and optogenetics and they found that somatostatin-expressing, dendrite-targeting γ-aminobutyric acid–releasing interneurons in hippocampal area CA1 are required for CFC. During CFC, sensory features of the aversive event reach hippocampal output neurons through excitatory cortical afferents and require active inhibitory filtering to ensure that the hippocampus exclusively encodes the conditioned stimulus.
Growth Factors Engineered for Super-Affinity to the Extracellular Matrix Enhance Tissue Healing
Authors: Martino Mikaël M. , Briquez Priscilla S. , Güç Esra , Tortelli Federico , Kilarski Witold W. , Metzger Stephanie , Rice Jeffrey J. , Kuhn Gisela A. , Müller Ralph , Swartz Melody A. , Hubbell Jeffrey A.
Published: February 2014

Toward Successful Tissue Repair

The therapeutic use of growth factors in tissue regeneration has suffered from safety and efficacy issues. Reasoning that the unmet potential may be because of nonphysiological delivery,

Martino
et al.

(p.
885
) engineered growth factors to bind strongly to extracellular matrix proteins. These variants were able to induce superior tissue repair, compared to the wild-type proteins. Furthermore, unwanted side effects were decreased: For example, the engineered angiogenic growth factor VEGF showed reduced vascular permeability, a concern that has limited the therapeutic efficacy of wild-type VEGF.
Fibers Do the Twist
Authors: Yuan Jinkai , Poulin Philippe
Published: February 2014

Twisted fibers provide a simple, low-cost route to high-energy artificial muscles.

[Also see Report by

Haines
et al.

]
DNA Sequencers Still Waiting for the Nanopore Revolution
Authors: Pennisi Elizabeth
Published: February 2014

While one sequencing company breaks the $1000 genome barrier with high-end machines, another takes the first steps toward cheap, hand-held sequencers.
Rival Detectors Prepare to Take Snapshots of Distant Worlds
Authors: Clery Daniel
Published: February 2014

In the coming months on two mountaintops in Chile, two new state-of-the-art instruments—the North American Gemini Planet Imager and the European SPHERE—will start scanning the skies for planets around other stars.
Hepatitis A Virus Adaptation to Cellular Shutoff Is Driven by Dynamic Adjustments of Codon Usage and Results in the Selection of Populations with Altered Capsids
Authors: Costafreda M. Isabel , Pérez-Rodriguez Francisco J. , D'Andrea Lucía , Guix Susana , Ribes Enric , Bosch Albert , Pintó Rosa M.
Published: February 2014

Hepatitis A virus (HAV) has a highly biased and deoptimized codon usage compared to the host cell and fails to inhibit host protein synthesis. It has been proposed that an optimal combination of abundant and rare codons controls the translation speed required for the correct capsid folding. The artificial shutoff host protein synthesis results in the selection of variants containing mutations in the HAV capsid coding region critical for folding, stability, and function. Here, we show that these capsid mutations resulted in changes in their antigenicity; in a reduced stability to high temperature, low pH, and biliary salts; and in an increased efficacy of cell entry. In conclusion, the adaptation to cellular shutoff resulted in the selection of large-plaque-producing virus populations.

IMPORTANCE
HAV has a naturally deoptimized codon usage with respect to that of its cell host and is unable to shut down the cellular translation. This fact contributes to the low replication rate of the virus, in addition to other factors such as the highly inefficient internal ribosome entry site (IRES), and explains the outstanding physical stability of this pathogen in the environment mediated by a folding-dependent highly cohesive capsid. Adaptation to artificially induced cellular transcription shutoff resulted in a redeoptimization of its capsid codon usage, instead of an optimization. These genomic changes are related to an overall change of capsid folding, which in turn induces changes in the cell entry process. Remarkably, the adaptation to cellular shutoff allowed the virus to significantly increase its RNA uncoating efficiency, resulting in the selection of large-plaque-producing populations. However, these populations produced much-debilitated virions.