Shaft Load Research Articles

Flat Plate Honeycomb Seals Friction Factor Analysis

Among the various types of seals used in gas turbine secondary air system to guarantee sufficient confinement of the main gas path, honeycomb seals perform well in terms of enhanced stability and reduced leakage flow. Due to the large amount of honeycomb cells typically employed in real seals, it is generally convenient to treat the sealing effect of the honeycomb pack as an increased distributed friction factor on the plain top surface. That is why, this analysis is focused on a simple configuration composed by a honeycomb facing a flat plate. In order to evaluate the sealing performance of such honeycomb packs, an experimental campaign was carried out on a stationary test rig where the effects of shaft rotation are neglected. The test rig was designed to analyze different honeycomb geometries so that a large experimental database could be created to correlate the influence of each investigated parameter. Honeycomb seals were varied in terms of hexagonal cell dimension and depth in a range that represents well actual honeycomb packs employed in industrial compressors. For each geometry, seven different clearances were tested. This work reports the findings of such experimental campaign whose results were analyzed in order to guide actual seals design and effective estimates of shaft loads. Static pressure measurements reveal that the effects of investigated geometrical parameters on friction factor correlate well with a corrected Mach number based on the cell depth. The presence of acoustic effects in the seals was further investigated by means of hot wire anemometry. Acoustic forcing due to flow cavity interaction was found to be characterized by a constant Strouhal number based on cell geometry. Numerical simulations helped in the identification of system eigenmodes and eigenfrequencies providing an explanation to the friction factor enhancement triggered at a certain flow speed. Finally, the generated dataset was tested comparing the predicted leakage flow with experimental data of actual seals (with high pressure and high rotational speed) showing a very good agreement.

Tribological performance of dimpled thrust bearings with phyllotactic patterns

This study explored a novel method of arranging lubricating dimples on the working surface of thrust bearings. Because these dimples influence the frictional performance of the thrust bearing, we performed experiments to measure the friction coefficient under various dimple arrangements and phyllotactic coefficients. The surface of the experimental thrust bearing was designed to hold CuZn25Al6Mn4 material, and dimples were positioned on the bearing surface in different patterns via mask electrolysis. For friction experiments, L-AN46(GB/T7631.13-1995) lubricant with kinematic viscosity of 41.4–50.6mm2/s, −10°C congealing point, and 180°C flash point was used as the media. Low friction coefficient was achieved under reasonable phyllotactic parameters – a 27% maximum reduction in friction was achieved under optimal dimple pattern and phyllotactic parameters. We also compared the measured friction coefficients of our dimpled thrust bearing setup against those conventional linear patterns, and found that the proposed phyllotactic pattern showed better lubricating effect in the dimpled thrust bearing under normal load and normal frictional shaft rotation speed. Under various normal forces, average reductions of 16.8% and 15.7% in friction are achieved for the tested parameters at phyllotactic pattern.

Design, analysis and predicting hydrokinetic performance of a horizontal marine current axial turbine by consideration of turbine installation depth

In the last decade, there has been a growth of interest in tidal power as a renewable and clean source of energy. Southern part of Iran is a well placed in this regard, as the currents in this area are primarily tidal. Horizontal Axis Marine Current Turbine (HAMCT) is widely used as an extraction devise for tidal energy. In this paper, Blade Element Momentum Theory (BEMT) and CFD have been conducted on this devise. Based on installation depth of HAMCT, turbine is subjected to gravity wave induced loads. A numerical study was conducted to design, analysis and predict hydrokinetic performance of HAMCT with and without extreme gravity waves. The fluid model has been created with appropriate dimensions. In order to model the high amplitude of wave ocean wave, linear wave theory for gravity waves is used. Numerical results of steady and transient solution have been compared to available experimental data. The simulation results demonstrate that by increasing the installation depth of HAMCT from the free surface, shaft loads and power coefficient of the turbine experience oscillate respectively. The simulation results demonstrate that compared with turbine only rotating in constant inflow, pressure and velocity contours experience oscillation respectively.The results of this study can provide data to choose appropriate installation depth for HAMCT to obtain higher power coefficient and avoid undesirable phenomena e.g. fatigue and cavitation.

Tilting 상태인 테이퍼 로울러의 탄성유체윤활 해석

Tapered roller bearings are widely used in equipment where high combined thrust and radial loads are experienced. A certain amount of tilting between the tapered rollers and the races always occurs because of bending moment load conditions and shaft deflection. It is now well understood that a coherent elastohydrodynamic lubrication (EHL) film separates the rollers and races. In spite of extensive study on EHL problems for over half a century, relatively few studies have focused on the finite line contacts problem. This study presents a complete numerical analysis of the effects of roller tilting on the EHL characteristics in a tapered roller bearing. We systematically analyze this highly nonlinear problem using finite differences with fully non-uniform grids and the Newton-Raphson method. Detailed EHL pressure distributions and film shapes are presented under moderate loads and material parameters. A very small roller tilting significantly affects the pressure distributions and film shapes near both ends of the roller. Moreover, the effect of tilting on the EHL characteristics at the small end is much greater than that at the large end. Therefore, in designing optimum profiles for tapered roller bearings, the profile radius should be larger at the small end.

An improved wake description by higher order velocity statistical moments for single screw vessel

Unfavorable wake and separated flow from the hull might cause a dramatic decay of the propeller performance in single-screw propelled vessels such as tankers, bulk carriers and containers. For these types of vessels, special attention has to be paid to the design of the stern region, the occurrence of a good flow towards the propeller and rudder being necessary to minimize fuel consumption and avoid excessive vibratory shaft loads and risk for cavitation erosion. The present work deals with the analysis of the propeller inflow in a single-screw chemical tanker vessel affected by massive flow separation in the stern region. Detailed flow measurements by Laser Doppler Velocimetry (LDV) were performed in the propeller region at model scale, in the large Circulating Water Channel of CNR-INSEAN. These tests were undertaken with and without the propeller in order to investigate its effect on the inflow characteristics and the separation mechanisms. In this context, the study also concerned a phase locked analysis of the propeller perturbation at different distances upstream of the propulsor. The study shows the effectiveness of the 3rd order statistical moment (i.e., skewness) for describing the topology of the wake and accurately identifying the portion affected by the detached flow. The skewness coefficient also suggests that a better physical representation of the propeller inflow is provided by the mode value of the velocity, which is the maximum of the probability density function, rather than the mean velocity.

Analysis and Technology of the Bricard Linkage Kinematic Parameters Comparative Experiments

The article considers kinematic parameters of the 6R Bricard linkage characteristic point obtained analytically. Computer simulation of this mechanism resulted in diagrams of changes in the special orientation of the coordinate system of the characteristic point and a projection of its velocities to the basic coordinates system. In addition, we developed a prototype model for experimental studies. The difference between data obtained using the experimental model and the data obtained by computer analysis is less than 5%. This article describes the components of the experimental model. Using a stepper motor requires solving additional tasks: resonance, peaks at the first and the last steps, step dividing, ensuring the smooth acceleration of the motor shaft, smooth increasing of the shaft load, etc.

Influences of off-sized rollers on mechanical performance of spherical roller bearings

Based on a set of formulae for calculating elliptical contact parameters and elastic deformation developed by Houpert and mechanical analysis, a numerical model is established for calculating the roller load distribution and shaft axis orbit of spherical roller bearings with considering off-sized rollers in this paper. A numerical calculation example is carried out to investigate the effects of single off-sized roller and multiple off-sized rollers on spherical roller bearing roller load distribution and axis orbit. Results show that the roller maximum load will increase as its off-sized diameter becomes larger than the nominal diameter, and the roller maximum load will decrease as its off-sized diameter is smaller than the nominal diameter. The maximum loads of the rollers in the two rows neighboring on the off-sized roller/rollers can also be affected. Meanwhile, roller diameter error will largely affect the axis orbit and inner ring radial displacement of spherical roller bearings.

IDENTIFICATION OF SHIP PROPELLER TORSIONAL VIBRATIONS

The article presents identification methods of ship propeller torsional vibrations in dimensional space and ways for their dumping. Propeller torsional vibrations are caused by static, dynamic and hydrodynamic unbalance of propeller itself and its operation in non-uniform velocity field of ship hull. The propeller working in uneven velocity field of the hull creates cyclic thrust forces, peripheral vibrations of shaft as well as flexural and torsional load of propeller shaft. Vibrations cause additional thrust load on shaft bearings and shaft bending moment. Vibrations of ship hull, particularly its stern section cause variation of pressure field created by propeller. Amplitude of particular parts of the hull comes from the action of cyclic forces created by working ship propeller. They can be very large. Therefore, the ways to reduce vibrations caused by running propeller are very important. Given in the article methods of vibration dumping calculations conduct to determination of vibration dumping coefficients. Calculation results are comparable to measuring results in spite of fact they were determined under assumption of different velocity fields of water flowing through propeller circle. Amplitudes of vibrations depend on number of propeller blades and pulsate with the basic frequency equal to product of the rotational speed and number of blades. Causes of such vibrations and additional load of vessel stern are described in the article. An attention was paid to assure the greatest possible uniformity of velocity field by adequate design of stern shape and accessories. The ways to reduce torsional vibrations of propeller by the appropriate selection of blades number and their accurately machining are also given in the article.

Robust global sliding model control for water-hull-propulsion unit interaction systems - Part 1: System boundary identification

Unexpected severe hull deformation caused by the wave loads would significantly influence the dynamical behaviours of the propulsion system in large scale ships, resulting in degradation of the ship control performance. A new global sliding model control (GSMC) for marine water-hull-propulsion unit systems is proposed to obtain more accurate control performance in this paper. The GSMC was firstly employed to establish the marine propulsion control model with nonlinear uncertainties. In the GSMC model, the saturation function method is applied to eliminate chattering on the sliding surface. Then the Lyapunov stability criterion is adopted to confirm the stability of the control system. Following, for the first time, the boundary problem of the nonlinear model uncertainties were investigated quantitatively. The bounded nonlinear model uncertainties required in the proposed GSMC model, involving engine torque loss / variations, power transfer for various load conditions and shaft rotational speeds, were derived based on the experiments carried out on a marine shaft-line test-bed of the integrated propulsion system as well as a sea trial implemented for a running bulk carrier. An upper boundary of 1,85 % for the model uncertainty has been obtained, which would be introduced into the GSMC for the integrated marine propulsion system to derive the total control law realising the robust control of the system

Оптимизация состава смесевых биотоплив для дизельных двигателей

The advantages of vegetable oil-based biofuels using in diesel engines have been demonstrated. Methods for determining
 of optimal composition for mixed fuels containing petroleum diesel fuel and methyl ester of rapeseed oil have been
 proposed. Optimization calculations of such mixed fuel composition for a type 245.12С diesel engine have been carried
 out using the proposed methods. It has been shown that a mixture containing 60 % of petroleum diesel fuel and 40 %
 of methyl ester of rapeseed oil has the best ecological characteristics among the researched mixed biofuels. Even better
 ecological characteristics are reached when such mixture’s ingredients are regulated according to changes of the engine’s
 shaft rotation speed and load.

Field Testing of Feedforward Collective Pitch Control on the CART2 Using a Nacelle-Based Lidar Scanner

This work presents the results from a field test of LIDAR assisted collective pitch control using a scanning LIDAR device installed on the nacelle of a mid-scale research turbine. A nonlinear feedforward controller is extended by an adaptive filter to remove all uncorrelated frequencies of the wind speed measurement to avoid unnecessary control action. Positive effects on the rotor speed regulation as well as on tower, blade and shaft loads have been observed in the case that the previous measured correlation and timing between the wind preview and the turbine reaction are accomplish. The feedforward controller had negative impact, when the LIDAR measurement was disturbed by obstacles in front of the turbine. This work proves, that LIDAR is valuable tool for wind turbine control not only in simulations but also under real conditions. Furthermore, the paper shows that further understanding of the relationship between the wind measurement and the turbine reaction is crucial to improve LIDAR assisted control of wind turbines.

하한지지력이 현장타설말뚝의 저항계수에 미치는 영향

한계상태설계법의 하나인 하중저항계수설계법의 이용이 북미를 중심으로 점차 확산되고 있는 가운데, 국내에서도 이에 대한 연구가 활발하게 진행되고 있다. 하지만, 국내에서는 자료가 충분히 확보되지 못하여 기초구조물의 설계에 AASHTO에서 제안한 저항계수를 설계에 이용하고 있다. AASHTO에서 제안하고 있는 저항계수는 북미에 보편적으로 존재하는 암반조건을 이용하여 결정된 저항계수로서, 국내지반에 적합한 저항계수를 독자적으로 개발할 필요가 있다. 또한, 기존의 신뢰성 분석 기법에서는 하중저항계수를 결정할 때, 저항의 최소값을 0으로 가정하는 일반적인 대수정규 분포를 이용하기 때문에, 이로부터 산정한 파괴확률은 비현실적이라고 알려져 있다. 따라서, 이를 개선하기 위하여 저항계수를 산정할 때 저항의 하한값이 0이 아닌, 현실적으로 의미가 있는 하한지지력을 이용하는 방법이 최근에 고안되었다. 따라서, 본 연구에서는 국내에서 수행된 현장타설말뚝 13본에 대한 재하시험자료를 면밀히 분석하여 저항계수를 산정한 다음, 현실성 있는 하한지지력을 산정하여 저항계수 값을 보정하였다. 그 결과, 목표신뢰도지수가 3.0일때, 기존의 신뢰성 분석 기법으로부터 산정된 주면저항계수와 선단저항계수는 각각 0.13-0.32, 0.19-0.29 이었으며, 하한지지력을 보정하여 구한 주면저항계수와 선단저항계수는 Carter & Kulhawy 공식의 경우 각각 8%와 13% 증가하였다. Load and Resistance Factor Design (LRFD) is one of the limit state design methods, and has been used worldwide, especially in North America. Also, the study for LRFD has been actively conducted in Korea. However, the data for LRFD in Korea were not sufficient, so resistance factors suggested by AASTTO have been used for the design in Korea. But the resistance factors suggested by AASHTO represent the characteristics of bedrocks defined in the US, therefore, it is necessary to determine the resistance factors for designs in Korea, which can reflect the characteristics of bedrocks in Korea. Also, the calculated probabilities of failure from conventional reliability analyses which commonly use log-normal distribution are not realistic because of the lower tail that can be extended to zero. Therefore, it is necessary to calibrate the resistance factors considering the lower-bound resistance. Thus, this study calculates the resistance factors using thirteen sets of drilled shaft load test results, and then calibrates the resistance factors considering the lower-bound resistance corresponding to a target reliability index of 3.0. As a result, resistance factors from conventional reliability analyses were determined in the range of 0.13-0.32 for the shaft resistance, and 0.19-0.29 for the base resistance, respectively. Also, the lower bounds of resistance were determined based on the Hoek-Brown failure criteria (2002) and GSI downgrading. Considering the lower-bound resistances, resistance factors increased by 0~8% for the shaft, and 0~13% for the base, respectively.

Field investigation of the axial resistance of helical piles in dense sand

This paper presents the results of compression and tension load tests performed on a single helical pile installed in dense sand. The pile was instrumented using strain gauges that allowed the shaft and base load resistance to be separated and the distribution of shaft resistance along the pile during the test to be determined. The pile was loaded first in compression, with a maintained load test, followed by a constant rate of penetration load test being performed to assess the effects of creep on the pile’s response to compression loading. The pile was then loaded in tension using a maintained load test procedure. Finite element analyses were performed using Abaqus and these helped to provide additional insights to explain the response of the instrumented pile during loading. The test showed that during compression loading, substantial bearing pressures developed beneath the pile helix, which provided the majority of axial load resistance. During tension loading, uplift pressure mobilized on the helix again provided the majority of axial resistance. The strain gauges suggested that the pile load response to compression loading was ductile. During tension loading, the pile response was brittle. Whilst load tests performed on only one instrumented pile test are presented, the use of instrumentation and finite element analyses allowed important insights into the load–displacement response of helical piles.

A fully coupled 3D thermo-elastohydrodynamics model for a bump-type compliant foil journal bearing

Coupled thermo-elastohydrodynamics model has been developed to predict three-dimensional thermal, structural and hydrodynamic performance of foil bearings. Bearing deformation and film pressure has been coupled in FEM considering thermal/centrifugal growths, and thermo-mechanical material properties. Energy equation has been solved for film temperature using FDM, which is also coupled to FEM via successive iterations. Augmented-Lagrangian method and thermal contact models have been applied to solve for mechanical and thermal contacts. The predicted values have been benchmarked against published measurements, which indicated reasonable correlation. A parametric study has been conducted for various shaft speeds and load conditions to visualize bearing performance.

The effects of surge motion of the floating platform on hydrodynamics performance of horizontal-axis tidal current turbine

Under practical operation conditions, hydrodynamic characteristics of floating horizontal-axis turbine are affected by the wave-induced motion response of the floating platform for the turbine system. In this thesis, CFX software is adopted to analyze the hydrodynamic performance of the turbine in constant inflow with the turbine being forced vibrating and to study how the hydrodynamic performance of the turbine is influenced by surge frequency, surge amplitude and speed ratio. Based on the simulation data from CFX, axial damping coefficient can be obtained by least square fitting the time-varying axial force curves of surging turbine. The simulation results demonstrate that compared with turbine only rotating in constant inflow, shaft loads and energy utilization ratio of the surging turbine experience oscillations respectively; the oscillation amplitudes of these two parameters have a positive correlation with the frequency and amplitude of the surge and speed ratio; the frequency and amplitude of the surge have little impact on axial damping coefficient but this coefficient is positively proportioned to the rotational speed of the turbine. The results of this study can provide data to study motion response of floating platform for floating tidal current turbine system and control design of the output electricity.

Principal resonance bifurcation of bending–torsion coupling of aero-engine compressor blade with assembled clearance under lateral displacement excitation of rotor shaft

The principal resonance of bending–torsion coupling of a compressor blade with an assembled clearance and a cubic structural nonlinearity, subjected to the lateral displacement excitation of rotor shaft and aerodynamic loads, is analyzed to explore the topology transformation of amplitude–frequency response along with the changes of the physical parameters. The bifurcation equation of the first-order principal resonance response is derived from using the averaging method. The transition set and the bifurcation figures of the response solution are obtained by the singularity theory. The effects of the main physical parameters of the system on the topology transformation of amplitude–frequency response are discussed.

연직진동말뚝의 동적 하중전이 특성

Abstract In this study, the dynamic load transfer function, which is necessary for analyzing a pile installed by avibro hammer, was determined by comparing the results of the analyses and instrumented tests. The static load transfer function was modeled by the Ramberg-Osgood model through an analytical method before determining the dynamic load transfer curve. The parameters of the Ramberg-Osgood model were correlated with the N value of thestandard penetration test and average values of the correlation coefficient were 0.97 for the shaft load transfer and0.98 for the base load transfer. The dynamic load transfer function was simulated using the modified Ramberg-Osgoodmodel. The results showed that there were little differences in the characteristics of dynamic load transfer betweenthe results of the measurement and prediction. Key Words : Dynamic load transfer function, Static load transfer curve, Ramberg-Osgood model, Modified Ramberg-Osgood model * Corresponding Author : Ki-Yong Yoon(Sunmoon University)Tel: +82-41-530-2326 email: kyyoon@sunmoon.ac.krReceived March 3, 2014 Revised March 21, 2014 Accepted June 12, 2014

Analysis of field-oriented controlled induction motor drives under sensor faults and an overview of sensorless schemes

To obtain high dynamic performance on induction motor drives (IMD), variable voltage and variable frequency operation has to be performed by measuring speed of rotation and stator currents through sensors and fed back them to the controllers. When the sensors are undergone a fault, the stability of control system, may be designed for an industrial process, is disturbed. This paper studies the negative effects on a 12.5 hp induction motor drives when the field oriented control system is subjected to sensor faults. To illustrate the importance of this study mine hoist load diagram is considered as shaft load of the tested machine. The methods to recover the system from sensor faults are discussed. In addition, the various speed sensorless schemes are reviewed comprehensively.

A 5MW direct-drive generator for floating spar-buoy wind turbine: Development and analysis of a fully coupled Mechanical model

This work forms the first of a two-part investigation aimed at identifying the challenges and opportunities of implementing a direct-drive generator for a spar-buoy type floating wind turbine. Preliminary specifications are presented for a fully coupled aero-hydro-servo-elastic model of a floating wind turbine with a 5 MW direct-drive generator. The drive-train model uses a low-speed, high-torque radial flux permanent magnet generator supported by two main-shaft bearings. The mechanical properties of the drive-train, including the main dimensions, mass of major nacelle equipment and details for the hub/nacelle assembly are presented. The rationale behind the adjustments to the tower and platform properties and the motivation to selection of best arrangement that is appropriate for supporting the developed system is explained. A discussion on the development of the variable speed-variable pitch control system suitable for the direct-drive system including modifications to avoid negative damping and blade-pitch instability are presented. Fully coupled simulations for the developed aero-hydro-servo elastic model were carried out in HAWC2 for the normal operating conditions of the wind turbine. The aerodynamic response of the model was verified and compared with that of a geared floating wind turbine system. Some initial results comparing the main shaft loads of the land-based and floating versions of the direct-drive wind turbine suggest satisfactory dynamic behaviour of the drive-train. The results prompt further research using a detailed drive-train model to verify the internal response, loading and durability of the components to assess their compatibility with a floating wind turbine system.

Theoretical and Experimental Studies on the Resilience of Driven Piles

This paper deals with the resilient condition that may be reached by driven piles, during its installation as well as under static cyclic and monotonic loading tests. During the 1950’s Van Weele observed its effect in the context of a method for the separation of the toe and shaft loads at failure using the results of static cyclic loading tests on driven piles. Under this condition and based on a mathematical model that uses Cambefort’s Relations and takes into account pile compressibility and residual loads, this paper shows that there is a homothetic relation between the loading and the unloading-movement curves at pile head. A graphical construction is presented along with a numerical procedure allowing to improve the understanding of pile behavior and to determine significant parameters of pile-soil interaction under static or driving loadings. Application of the homothetic relations is made to several piles and particularly a new procedure was developed to analyze dynamic loading tests with a single blow record, considering the residual load at the toe.