The Effect of Surface Finish on the Proper Functioning of Underplatform Dampers

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Chiara Gastaldi ◽  
Teresa M. Berruti ◽  
Muzio M. Gola
Keyword(s):  
Turbine Blades ◽  
Optimization Procedure ◽  
Dissipated Energy ◽  
Contact Interface ◽  
Cross Sectional ◽  
Cycle Shape ◽  
Specific Contact ◽  
Energy Dissipated ◽  
Industrial Standards ◽  
Flat Contact

Abstract Underplatform dampers are used to limit the resonant vibration of turbine blades. In recent years, various strategies have been implemented to maximize their damping capability. Curved-flat dampers are preferred to ensure a predictable bilateral contact, while a pre-optimization procedure was developed to exclude all those cross-sectional shapes that will bring the damper to roll and thus limit the amount of dissipated energy. The pre-optimization bases its predictions on the assumption that the effective width of the flat contact interface corresponds to the nominal one. It is shown here that this hypothesis cannot be relied upon: the energy dissipated by two nominally identical dampers, machined according to the usual industrial standards, may differ by a factor up to three due to the morphology of the flat-to-flat contact interface. Five dampers have been tested on two dedicated test rigs, available in the AERMEC laboratory, specially designed to reveal the details of the damper behavior during operation. Their contact interfaces are scanned by means of a profilometer. In each case, the mechanics, the kinematics, and the effectiveness of the dampers in terms of cycle shape and dissipated energy are correlated to the morphology of the specific contact surface. To complete the picture, a state-of-the-art numerical simulation tool is used to show how this tribo-mechanic phenomenon, in turn, influences the damper effect on the dynamic response of the turbine.

scholarly journals Fractal Nature of Advanced Ni-Based Superalloys Solidified on Board the International Space Station

2021 ◽  
Vol 13 (9) ◽  
pp. 1724
Author(s):  
Vojislav Mitić ◽  
Cristina Serpa ◽  
Ivana Ilić ◽  
Markus Mohr ◽  
Hans-Jörg Fecht
Keyword(s):  
International Space Station ◽  
Fractal Analysis ◽  
Power Plants ◽  
Materials Science ◽  
Structural Characteristics ◽  
Turbine Blades ◽  
Space Station ◽  
Casting Process ◽  
Cross Sectional ◽  
International Space

Materials science is highly significant in space program investigation, energy production and others. Therefore, designing, improving and predicting advanced material properties is a crucial necessity. The high temperature creep and corrosion resistance of Ni-based superalloys makes them important materials for turbine blades in aircraft engines and land-based power plants. The investment casting process of turbine blades is costly and time consuming, which makes process simulations a necessity. These simulations require fundamental models for the microstructure formation. In this paper, we present advanced analytical techniques in describing the microstructures obtained experimentally and analyzed on different sample’s cross-sectional images. The samples have been processed on board the International Space Station using the MSL-EML device based on electromagnetic levitation principles. We applied several aspects of fractal analysis and obtained important results regarding fractals and Hausdorff dimensions related to the surface and structural characteristics of CMSX-10 samples. Using scanning electron microscopy (SEM), Zeiss LEO 1550, we analyzed the microstructure of samples solidified in space and successfully performed the fractal reconstruction of the sample’s morphology. We extended the fractal analysis on the microscopic images based on samples solidified on earth and established new frontiers on the advanced structures prediction.

scholarly journals OPTIMALLY STAGGERED FINNED CIRCULAR AND ELLIPTIC TUBES IN FORCED CONVECTION

2003 ◽  
Vol 2 (2) ◽  
pp. 65 ◽  
Author(s):  
R. S. Matos ◽  
T. A. Laursen ◽  
J. V. C. Vargas ◽  
A. Bejan
Keyword(s):  
Heat Transfer ◽  
Three Dimensional ◽  
Optimization Procedure ◽  
Total Heat ◽  
Cross Sectional ◽  
Maximum Heat ◽  
Pressure Drops ◽  
Tube Cross Section ◽  
Fixed Volume ◽  
Maximum Heat Transfer

This work presents a three-dimensional (3-D) numerical and experimental geometric optimization study to maximize the total heat transfer rate between a bundle of finned tubes in a given volume and a given external flow both for circular and elliptic arrangements, for general staggered configurations. The optimization procedure started by recognizing the design limited space availability as a fixed volume constraint. The experimental results were obtained for circular and elliptic configurations with a fixed number of tubes (12), starting with an equilateral triangle configuration, which fitted uniformly into the fixed volume with a resulting maximum dimensionless tube-to-tube spacing S/2b = 1.5, where S is the actual spacing and b is the smaller ellipse semi-axis. Several experimental configurations were built by reducing the tube-to-tube spacings, identifying the optimal spacing for maximum heat transfer. Similarly, it was possible to investigate the existence of optima with respect to other two geometric degrees of freedom, i.e., tube eccentricity and fin-to-fin spacing. The results are reported for air as the external fluid in the laminar regime, for 125 and 100 Re 2b , where 2b is the ellipses smaller axis length. Circular and elliptic arrangements with the same flow obstruction cross-sectional area were compared on the basis of maximum total heat transfer. This criterion allows one to quantify the heat transfer gain in the most isolated way possible, by studying arrangements with equivalent total pressure drops independently of the tube cross section shape. This paper reports three-dimensional (3- D) numerical optimization results for finned circular and elliptic tubes arrangements, which are validated by direct comparison with experimental measurements with good agreement. Global optima with respect to tube-to-tube spacing, eccentricity and fin-tofin spacing ( 0.5 e 0.5, S/2b and 06 . 0 f for 125 and 100 Re 2b , respectively) were found and reported in general dimensionless variables. A relative heat transfer gain of up to 19% is observed in the optimal elliptic arrangement, as compared to the optimal circular one. The heat transfer gain, combined with the relative material mass reduction of up to 32% observed in the optimal elliptic arrangement in comparison to the circular one, show the elliptical arrangement has the potential for a considerably better overall performance and lower cost than the traditional circular geometry.

Effect of Au distribution in NiO/Au film on the ohmic contact formation to p-type GaN

2005 ◽  
Vol 20 (2) ◽  
pp. 456-463 ◽  
Author(s):  
Jiin-Long Yang ◽  
J.S. Chen ◽  
S.J. Chang
Keyword(s):  
Electron Microscopy ◽  
Ohmic Contact ◽  
Incident Angle ◽  
Specific Contact Resistance ◽  
X Ray Diffraction ◽  
Cross Sectional ◽  
Ohmic Behavior ◽  
Transmission Electron ◽  
Specific Contact ◽  
P Type

The distribution of Au and NiO in NiO/Au ohmic contact on p-type GaN was investigated in this work. Au (5 nm) films were deposited on p-GaN substrates by magnetron sputtering. Some of the Au films were preheated in N2 ambient to agglomerate into semi-connected structure (abbreviated by agg-Au); others were not preheated and remained the continuous (abbreviated by cont-Au). A NiO film (5 nm) was deposited on both types of samples, and all samples were subsequently annealed in N2 ambient at the temperatures ranging from 100 to 500 °C. The surface morphology, phases, and cross-sectional microstructure were investigated by scanning electron microscopy, glancing incident angle x-ray diffraction, and transmission electron microscopy. I-V measurement on the contacts indicates that only the 400 °C annealed NiO/cont-Au/p-GaN sample exhibits ohmic behavior and its specific contact resistance (ρc) is 8.93 × 10−3 Ω cm2. After annealing, Au and NiO contact to GaN individually in the NiO/agg-Au/p-GaN system while the Au and NiO layers become tangled in the NiO/cont-Au/p-GaN system. As a result, the highly tangled NiO-Au structure shall be the key to achieve the ohmic behavior for NiO/cont-Au/p-GaN system.

scholarly journals Dynamics of Assembled Structures: Taking Into Account the Surface Defects in Interfaces

2013 ◽  
Author(s):  
Nicolas Peyret ◽  
Gaël Chevallier ◽  
Jean-Luc Dion
Keyword(s):  
Loss Factor ◽  
Surface Defect ◽  
Test Bench ◽  
Surface Defects ◽  
Dissipated Energy ◽  
Energy Losses ◽  
Proposed Model ◽  
Nonlinear Loss ◽  
Energy Dissipated ◽  
Experimental Bench

In structural dynamics, the prediction of damping remains the biggest challenge. This paper deals with the energy losses caused by micro-slip in a nominally planar interface of a structure. This paper proposes an analytical and experimental study of flexural vibrations of a clamped-clamped beam with innovative position of the interfaces. The objective of this test bench is to characterize the global rheology of the interface. The proposed model aims to characterize this rheology based on local settings of the interface. First, the test bench is described and the choice of the position of the interface is justified. The experimental bench and the dynamic behavior of this structure are presented. We propose to illustrate the mechanism of energy losses by micro-slip by making a comparison between the behavior of a “monolithic” beam and a sectioned beam. Secondly, a modeling of the interface taking into account the surface defect is presented. The energy dissipated by friction in the interface is calculated during a loading cycle. This leads to a computation of the dissipated energy and thus to a nonlinear loss factor. Finally, we confront the loss factor calculated analytically and the measured one.

Shape Opimization of Femoral Components of an Artificial Hip Prosthesis Using the Three-Dimensional P-Version Finite Element Method

2001 ◽  
Author(s):  
Masaru Higa ◽  
Ikuya Nishimura ◽  
Hiromasa Tanino ◽  
Yoshinori Mitamura
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Hip Prosthesis ◽  
Three Dimensional ◽  
Optimization Procedure ◽  
Peak Stress ◽  
Cross Sectional ◽  
Design Variables ◽  
Dimensional Shape ◽  
Element Method

Abstract The three-dimensional shape optimization of cemented total hip arthroplasty (THA) was introduced in this paper. The P-version Finite Element Method (FEM) combined with an optimization procedure was used to minimize the peak stress in the bone cement near the tip of the implant. Six-design variables were used in this study. Each variable represents the dimension of the medial-lateral width and anterior-posterior width of the three levels (proximal, distal and middle) of cross sectional area of the prosthesis. The results of the design optimization showed considerable reduction in stress concentration compared to the initial design that is currently used clinically.

An Energy Approach for Helping the Selection of Solid Lubrication Coatings Under Fretting Conditions

2009 ◽  
Author(s):  
D. B. Luo ◽  
V. Fridrici ◽  
Ph. Kapsa ◽  
M. Taillandier ◽  
C. Prud’homme
Keyword(s):  
Master Curve ◽  
Initial Energy ◽  
Energy Approach ◽  
Friction Reduction ◽  
Solid Lubrication ◽  
Dissipated Energy ◽  
Test Parameters ◽  
Definition Of ◽  
Energy Dissipated ◽  
Fretting Damage

Employing friction reduction coatings is one of the most effective methods to palliate the fretting damage. However, facing numerous available coatings, how to compare them and select the optimum one for a specific application is still a challenging task. In this paper, based on the investigation of the fretting behaviors of several bonded solid lubricant coatings, an energy approach in terms of “initial maximal dissipated energy density” was suggested to compare the tribological response of coatings. According to test results, the lifetime of each coating under different test parameters can be fitted by one master curve. The definition of this master curve for a given coating may be used for the prediction of the coating lifetime only by knowing the initial energy dissipated in the contact. The comparison of different master curves for different coatings can be employed to help the coating selection.

Optimal Vibration Control and Energy Scavenging Using Collocated Nonlinear Energy Sinks and Piezoelectric Elements

2018 ◽  
Author(s):  
Zahra Nili Ahmadabadi ◽  
Siamak Esmaeilzadeh Khadem
Keyword(s):  
Piezoelectric Element ◽  
Dissipated Energy ◽  
Vibration Energy ◽  
Energy Scavenging ◽  
Optimization Approach ◽  
Energy Harvesters ◽  
Energy Pumping ◽  
Nonlinear Energy Pumping ◽  
Energy Dissipated ◽  
Nonlinear Energy

This paper presents an optimal design for a system comprising multiple nonlinear energy sinks (NESs) and piezoelectric-based vibration energy harvesters attached to a free–free beam under shock excitation. The energy harvesters are used for scavenging vibration energy dissipated by the NESs. Grounded and ungrounded configurations are examined, and the systems parameters are optimized globally to maximize the dissipated energy by the NESs. The performance of the system was optimized using a dynamic optimization approach. Compared to the system with only one NES, using multiple NESs resulted in a more effective realization of nonlinear energy pumping particularly in the ungrounded configuration. Having multiple piezoelectic elements also increased the harvested energy in the grounded configuration relative to the system with only one piezoelectric element.

Effects of Contact Interface Parameters on Vibration of Turbine Bladed Disks With Underplatform Dampers

2011 ◽  
Author(s):  
C. W. Schwingshackl ◽  
E. P. Petrov ◽  
D. J. Ewins
Keyword(s):  
Structural Integrity ◽  
Turbine Blades ◽  
Contact Interface ◽  
Bladed Disks ◽  
Normal Contact ◽  
Input Parameters ◽  
Software Codes ◽  
Model Setup ◽  
Interface Parameters ◽  
Underplatform Damper

The design of high cycle fatigue resistant bladed disks requires the ability to predict the expected damping of the structure in order to evaluate the dynamic behaviour and ensure structural integrity. Highly sophisticated software codes are available today for this nonlinear analysis but their correct use requires a good understanding of the correct model generation and the input parameters involved to ensure a reliable prediction of the blade behaviour. The aim of the work described in this paper is to determine the suitability of current modelling approaches and to enhance the quality of the nonlinear modelling of turbine blades with underplatform dampers. This includes an investigation of a choice of the required input parameters, an evaluation of their best use in nonlinear friction analysis, and an assessment of the sensitivity of the response to variations in these parameters. Part of the problem is that the input parameters come with varying degrees of uncertainty, since some are experimentally determined, others are derived from analysis and a final set are often based on estimates from previous experience. In this investigation the model of a commercial turbine bladed disc with an underplatform damper is studied and its first flap, first torsion and first edgewise modes are considered for 6EO and 36EO excitation. The influence of different contact interface meshes on the results is investigated, together with several distributions of the static normal contact loads to enhance the model setup and hence increase accuracy in the response predictions of the blade with an underplatform damper. A parametric analysis is carried out on the friction contact parameters and the correct setup of the nonlinear contact model to determine their influence on the dynamic response and to define the required accuracy of the input parameters.

Ohmic Contact Formation to Doped GaN

1995 ◽  
Vol 395 ◽  
Author(s):  
L. L. Smith ◽  
M. D. Bremser ◽  
E. P. Carlson ◽  
T. W. Weeks ◽  
Y. Huang ◽  
...  
Keyword(s):  
Ohmic Contact ◽  
Electron Beam Evaporation ◽  
Integrated Analysis ◽  
Cross Sectional ◽  
Contact Materials ◽  
Ohmic Behavior ◽  
Specific Contact ◽  
P Type ◽  
Ohmic Contact Formation ◽  
Contact Resistivities

ABSTRACTOhmic contact strategies for n- and p-type GaN have been investigated electrically, chemically, and microstructurally using transmission line measurements, high-resolution EELS and cross-sectional TEM, respectively. The contributions to contact performance from work function differences, carrier concentrations, annealing treatments, and interface metallurgy have been examined. The contact materials of Ti, TiN, Au, and Au/Mg were deposited via electron beam evaporation; Al was deposited via thermal evaporation. As-deposited Al and TiN contacts to highly doped n-GaN were ohmic, with room-temperature specific contact resistivities of 8.6×10−5 Ω cm2 and 2.5×10−5 Ωcm2 respectively. The Ti contacts developed low-resistivity ohmic behavior as a result of annealing; TiN contacts also improved with further heat treatment. For p-GaN, Au became ohmic with annealing, while Au/Mg contacts were ohmic in the as-deposited condition. The performance, structure, and composition of different contact schemes varied widely from system to system. An integrated analysis of the results of this study is presented below and coupled with a discussion of the most appropriate contact systems for both n- and p-type GaN.

scholarly journals VII. The extinction of sound in a viscous atmosphere by small obstacles of cylindrical and spherical form

1911 ◽  
Vol 210 (459-470) ◽  
pp. 239-270 ◽  
Keyword(s):  
Bessel Functions ◽  
London Mathematical Society ◽  
Mathematical Physics ◽  
Dissipation Function ◽  
Dissipated Energy ◽  
Spherical Vessel ◽  
Spherical Form ◽  
Spherical Surfaces ◽  
Energy Dissipated ◽  
Approximate Expressions

The theory of the incidence of waves of sound in a non-viscous air upon small obstacles of cylindrical or spherical form is well known to students of mathematical physics; it has been treated in Lord Rayleigh’s ‘Theory of Sound,’ and in Prof. Lamb’s ‘Treatise on Hydrodynamics.’ The corresponding problems for a viscous air have not, however, been worked out, and this paper is devoted to an investigation of these problems. The solutions of the equations of vibration of a viscous gas with reference to cylindrical and spherical surfaces were given by Prof. L a m b in a paper entitled “On the Motion of a Viscous Fluid Contained in a Spherical Vessel” and published in the ‘Proceedings of the London Mathematical Society’ in 1884. It is easy to obtain solutions suitable to the case of divergent waves; the functions involved are Bessel functions with a complex argument. An analytical expression for the secondary waves diverging from the obstacle is obtained without difficulty. It then remains to find an expression for the loss of energy to the primary waves. In calculating this loss of energy it is necessary to consider the dissipation of energy by friction in the immediate neighbourhood of the obstacle in addition to the energy which is carried away to a distance by the secondary waves. This was pointed out to me by Prof. Lamb, at whose suggestion this paper was written. In obtaining an expression for the energy dissipated by friction I at first made use of the dissipation function. This method led to exactly the same results as that finally adopted, but the mathematics involved were cumbrous, and the physical ideas, on which they were based, were somewhat obscure. Another disadvantage of this method was that it was necessary to calculate separately the scattered and the dissipated energy. I have to thank Prof. Lamb for his kindness in pointing out to me the method of calculating the lost energy adopted in this paper. The result has been to make the paper more clear and readable. I have succeeded in obtaining expressions for the energy lost to the primary waves in the case of spherical and cylindrical obstacles. As might he expected, the problem of the cylindrical obstacle presents greater analytical difficulty than that of the spherical obstacle, and in the former case it is necessary to obtain different approximate expressions according to the diameter of the obstacle. The results for wires of 10 -1 cm. radius and for wires of 10 -3 cm. radius can be obtained without much difficulty, but when the radius of the wire is of order 10 -2 cm. it is necessary to perform very laborious calculations in order to arrive at intelligible results. The energy lost to the primary waves is, in all cases, very great compared with what would he lost in a non-viscous air, but the ratio of the lost energy to that incident upon the obstacle is at most of order 10 -2 .

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