Minimum Clearance Research Articles

Investigation into the Development and Testing of a Simplex Capacitance Sensor for Rotor Tip Clearance Measurement in Turbo Machinery

The rotor tip clearance is a vital parameter to characterize turbomachinery performance. It is an essential measurement during engine development and testing. The efficiency of the major modules like fan, compressor and turbine depends on the optimum running clearances. The capacitive sensor is preferred for tip clearance measurements because of various inherent advantages. They are fabricated through complex processes for turbomachinery application and are expensive. These sensors are exposed to harsh engine environments and are likely to exhibit degraded performance. Insulation failure at sensing head, connector contamination and micro-cracks in the MI (Mineral Insulated) cable leads to noise in the signal output. Frequent mechanical failures are also seen due to work hardening of MI cables, lead connector detachments and failure of micro fins at interconnects. Fault fixing of these is tedious and very expensive. This paper presents the concerted effort in developing a simple capacitance sensor addressing potential sensor failure issues. The design features include simple construction, ease of sensor assembly, component realization and troubleshooting. The design also addresses all safety requirements. The sensor has a large sensing area (7.6 mm diameter) producing very stable, high-level signal. The developed sensor produces output that varies from 1 VP-P to 11 VP-P for blade-tip gaps between 3 mm to 0.4 mm respectively. Blade pass simulation studies across the sensor, display almost flat response at minimum clearance. This feature results in very minimal data acquisition errors. The sensor along with RC (Resistance-Capacitance) conditioning electronics was successfully used for clearance measurement on fan stage of gas turbine engine. Test results are in line with the predictions. Extensive tip clearance measurements on the engine validate the design. The current work provides an insight into the development of a simplex capacitance sensor for tip clearance measurement.

Analysis of journal bearings in a scroll compressor considering deflections and dynamics of the crankshaft

Engineers are trying to design a scroll compressor which covers wide range of speed to realize an efficient and compact air-conditioning system. Recently, a motor with inverter technology has been driven from 15 to 150 Hz in an advanced scroll compressor. The importance of design for a crankshaft and journal bearings has been emphasized in this trend because the lubrication characteristics are greatly affected by the operating speed. In this study, the lubrication characteristics of journal bearings in a scroll compressor are analyzed considering deflections and dynamics of a crankshaft. The Reynolds equation is solved using the finite difference method to determine the pressure distribution of journal bearings, and then deflections of the crankshaft and its four-degrees-of-freedom motions are calculated by the finite element method and the fourth-order Runge–Kutta method, respectively. It is confirmed from the results that the crankshaft deflections significantly affect the minimum clearance of journal bearings.

Long-term Tai Chi practitioners have superior body stability under dual task condition during stair ascent

BackgroundStair walking contributed to 26% of self-reported falls and become the leading cause of accidental death for the elderly. The risk of fall increases while performing a cognitive task, like talking and/or reasoning. Research questionOur work aimed to found out whether body stability under physical-cognitive dual task(DT) condition during stair ascent is superior among long-term Tai Chi (TC) practitioners. MethodsFifteen healthy, elderly long-term TC practitioners and fifteen no exercise(NE) practitioners were asked to walking ascent the stairs under single task(ST) and DT conditions in this cross-sectional study. Vicon motion analysis system and Kistler force plates were used synchronously to collect data. Ninety-five% confidence intervals, effect size and statistical power were calculated for each dependent variable to confirm significant difference. ResultsCompared with NE practitioners, TC practitioners had a lower head inclination angle, trunk inclination angle, hip angle, laterial impulse and center of mass-center of pressure(COM-COP)ap/ml separation, a higher ankle angle and loading rate under DT condition; TC practitioners had a lower head inclination angle, trunk inclination angle, higher ankle angle, loading rate and COM-COPml separation under ST condition. Compared with under ST condition, TC practitioners increased in minimum foot clearance, NE practitioners increased in laterial impulse and COM-COPml separation under DT condition. Under DT condition, body stability decreased among NE practitioners, while TC practitioners remained unchanged. SignificanceAt present, there is no drug therapy proven to delay preclinical cognitive deterioration, it would be great helpful for the elderly if TC was been proved to improve their performance under cognitive related conditions.

Measured Static and Rotordynamic Characteristics of a Smooth-Stator/Grooved-Rotor Liquid Annular Seal

Electric submersible pumps (ESPs) utilize grooved-rotor/smooth-stator (SS/GR) seals to reduce leakage and break up contaminants within the pumped fluid. Additionally, due to their decreased surface area (when compared to a smooth seal), grooved seals decrease the chance of seizure in the case of rotor-stator rubs. Despite their use in industry, the literature does not contain rotordynamic measurements for smooth-stator/circumferentially grooved-rotor liquid annular seals. This paper presents test results consisting of leakage measurements and rotordynamic coefficients for a SS/GR liquid annular sdeal. Both static and dynamic variables are investigated for various imposed preswirl ratios (PSRs), static eccentricity ratios (0–0.8), axial pressure drops (2–8 bars), and running speeds (2–8 krpm). The seals' static and dynamic features are compared to those of a smooth seal with the same length, diameter, and minimum radial clearance. Results show that the grooves reduce leakage at lower speeds (less than 5 krpm) and higher axial pressure drops, but does little at higher speeds. The grooved seal's direct stiffness is generally negative, which would be detrimental to pump rotordynamics. As expected, increasing preswirl increases the magnitude of cross-coupled stiffness and increases the whirl frequency ratio (WFR). When compared to the smooth seal, the grooved seal has smaller effective damping coefficients, indicative of poorer stability characteristics.

Finite Element Approach for Failure Analysis of a Gas Turbine Blade

In the present work, a case study on the gas turbine blade is undertaken for failure analysis through finite element approach. The analysis is carried out through simulation and validated analytically and experimentally. The challenging point in the failure analysis of turbine blade is to obtain the exact morphology of the turbine blade for computation. It is accomplished by extracting the real operational turbine blade of an engine with its solid model through finite element analysis for thermo-mechanical loads. Extensive service exploitation of the engine and adverse operational conditions have made the annular gap between the blade tips and turbine casing distorted and nonuniform tip clearance. The maximum elongation of the turbine blade was found to exceed the minimum tip clearance in the rotor causing rubbing of the blade in the casing. Rubbing of the blade has been finally found to be responsible for the failure of the cantilever blade.

Behaviors of existing twin subway tunnels due to new subway station excavation below in close vicinity

This paper presents a case of Chongwenmen subway station of Beijing Subway Line 5 excavated below the existing Line 2, which was the first project of new subway construction below existing subway in Beijing. The minimum clearance between the new and the existing tunnels was 1.98 m. The layout, the geological and hydrogeological conditions, the construction process, and the monitoring measures are introduced. During construction, the maximum settlement of the existing tunnels reached 31.3 mm and the speed of trains run inside the existing tunnels was slowed down. In order to compensate the settlement of the existing tunnels and ensure the operational safety of the trains running inside the existing tunnels, compensation grouting was adopted. The pillar between the existing and the new tunnels was strengthened by grouting first. Then the pillar and the existing tunnels were uplifted together by specific controlled grouting pressure. The compensation grouting successfully uplift the existing tunnels. Moreover the subsequent settlements of the existing tunnels were small as the pillar had been sufficiently reinforced.

High voltage applications of low temperature co-fired ceramics

PurposeThe purpose of this study was to design, fabricate and test devices based on transformers integrated with low-temperature co-fired ceramic (LTCC) modules with isolation between primary and secondary windings at the level between 6 and 12 kV.Design/methodology/approachInsulating properties of the LTCC were examined. Dielectric strength and volume resistivity were determined for common LTCC tapes: 951 (DuPont), 41020, 41060 (ESL), A6M (Ferro) and SK47 (KEKO). According to the determined properties, three different devices were designed, fabricated and tested: a compact DC/DC converter, a galvanic separator for serial digital bus and a transformer for high-voltage generator.FindingsBreakdown field intensity higher than 40 kV/mm was obtained for the test samples set, whereas the best breakdown field intensity of about 90 kV/mm was obtained for 951 tape. The materials 41020 and 951 exhibited the highest volume resistivity. Fabricated devices exhibited safe operation up to a potential difference of 10 kV, limited by minimum clearance. Long-term stability was assured by over 20 kV strength of inner dielectric.Practical implicationsThis paper contains description of three devices made in the LTCC technology for application in systems with high-voltage isolation requirement, for example, for power or railway power networks.Originality/valueThe results show that LTCC is a suitable material for fabrication of high-voltage devices with integrated passives. Technology and properties of three examples of such devices are described, demonstrating the ability of the LTCC technology for application in reliable high-voltage devices and systems.

Prediction of Minimum Toe Clearance with a Radial Basis Function Network at the Start of the Swing Phase.

Prediction of minimum toe clearance (MTC) during walking can decrease the risk of tripping. In this paper, we proposed a novel MTC prediction method using a radial basis function network. Input data were the angles, angular velocities, and angular accelerations of the hip, knee, and ankle joints in the sagittal plane at the start of the swing phase. In experiments, five subjects walked on a treadmill for 360 s. The radial basis function network was trained with 60 s of gait data and tested with the remaining 300 s of gait data. The root mean square error between the true and predicted MTC values was lower than 2.79 mm in all subjects.

Research on the Fluid Excitation Force of Seal and Its Influencing Factors Based on CFD

The flow field of seal has been modeled by CFD method in this paper, and the effects of rotor rotational speed and eccentricity on the fluid excitation force are analyzed. In order to study the mechanism of induced vibration force in seal, the velocity field and pressure field of fluid in seal are analyzed in detail in this paper, the calculation result shows that the rotor rotation will form a spiral flow when the fluid flows into the seal, it causes the uneven pressure distribution in the seal cavity and the high pressure point is not match to the minimum clearance, thus producing a tangential exciting force perpendicular to the eccentric direction of the rotor. It’s the ultimate reason of rotor instability.

地域在住高齢者の膝関節固有感覚とminimum toe clearanceの関連性

地域在住高齢者の膝関節固有感覚とminimum toe clearanceの関連性

Evaluation of the minimum face clearance of a high-speed gas-lubricated bearing with Navier slip boundary conditions under random excitations

Motivated by ongoing developments in aero-engine technology, a model for a coupled gas-lubricated bearing is developed in terms of an extended dynamical system. A slip boundary condition, characterised by a slip length, is incorporated on the bearing faces which can be relevant for operation in non-ideal extreme conditions, notably where external vibrations or disturbances could destabilise the bearing. A modified Reynolds equation is formulated to model the gas flow, retaining the effects of centrifugal inertia which is increasingly important for high-speed operation, and is coupled to the structural equations; spring-mass-damper systems model the axial stator and rotor displacements. A novel model is developed corresponding to a bearing experiencing an external random force to evaluate the resulting induced displacements of the bearing components. The minimum face clearance is obtained from a mapping solver for the modified Reynolds equation and structural equations simultaneously. In the case of random excitations, the solver is combined with a Monte Carlo technique. Evaluation of the average value of the minimum gap and the probability of the gap reaching a prescribed tolerance are provided. Extensive insight is given on the effect of key bearing parameters on the corresponding bearing dynamics.

The correlational design method of the dimension tolerance and geometric tolerance for applying material conditions

This paper proposes a correlational design method for the dimension tolerance and geometric tolerance of the feature of size when applying a material condition. Based on the equivalent transformation method, the calculation equation of virtual size and extreme virtual size for a single feature during free assembly is expanded to the calculation of those of related features at the datum positioning and directional assembly, and then the application rules of the material conditions are established. Two kinds of design requirements are considered: guaranteeing the distance requirement between the surface of a single feature of size and its datum, and guaranteeing the minimum clearance and minimum interference between two features of size. For these design requirements, the correlational equations for the design of the dimension tolerance and geometric tolerance are developed. Two design cases are conducted to demonstrate the design method.

Influence of the Radial Clearance on Outlet Velocity Losses in the Unshrouded Turbine Cascade

Small-size turbines of the aviation gas-turbine plants differ by their high output losses and a high sensitivity to the value of radial clearance over the rotor blades. An increase in this clearance, for example, in-operation results in the reduced power efficiency factor due to a change in the losses in the nozzle, in the turbine wheel and output losses. Test data of the cascade of an average reliability with the rotor blade height of 20.73 mm were given for the three clearances, in particular 0.22; 0.6 and 1.0 m. An increase in the losses in the upper zone was recorded for rotor and nozzle blades with an increase in clearance. It was shown that due to a change in the distribution behavior along the radius of absolute velocity С 2 output losses can either be increased or decreased or remain unchanged at a change in the clearance depending on the averaged angle of flow output from the cascade in the absolute motion α 2. To improve the methods of one-dimensional computation of the cascade using the integral characteristics of its lattices the method of definition of output losses was suggested taking into consideration radial nonuniformity of the velocity С 2 at a high clearance value. It is assumed that the flow velocity С 2 is constant along the radius at a minimum clearance value of 0.22 mm. A degree of the radial nonuniformity of velocity С 2 was taken into consideration using the cascade test data in different modes and at different clearances. The obtained test data on the influence of clearance on absolute losses with the output velocity are naturally not multi-purpose, because even for the cascade investigation, the kinetic energy of flow behind it depends not only on the clearance value and the averaged output angle but also on some other auxiliary factors.

Tooth contact analysis of crown gear coupling with misalignment

In this paper, manufacturing methods are presented for crown gear coupling composed of a hub with longitude crowning and tip sphere teeth, and a sleeve with straight internal teeth. Complete geometrical mathematical models of tools are proposed, including the flank and tip fillet regions. The flank and root fillets of the hub and sleeve generated by the cutters are obtained based on the theories of differential geometry and gear mesh. An accurate method based on a tooth contact analysis technique is presented to determine the contact points (locations of the maximum interference or minimum clearance) and to analyze the crown gear coupling meshing with angular misalignment. In addition, the effects of misalignment angle and crowning depending on the displacement circle radius on the maximum interference, interference distribution and locations of the maximum interference in every angular position of the hub are discussed with an example. It is observed that the side edge contact of the hub tooth can be avoided by modifying the misalignment angle or displacement circle radius and that the location of the maximum value of the maximum interference during one rotation cycle of the hub tooth is around the pure tilted area.

Airborne Acquisition of Blade Tip Displacements and Vortices on a Coaxial Helicopter

A series of comprehensive flight tests investigated the flight dynamics and explored the flight envelope of a newly developed ultralight, coaxial, counter-rotating helicopter from the company edm aerotec. The present paper focuses on optical measurement techniques that were applied to study the minimum blade tip clearance and convection of blade tip vortices around the dual-rotor system. A calibrated single-camera system was used to quantify the movement and distances of the blade tips at a critical rotor azimuth for multiple steady and unsteady flight maneuvers. The measurements allowed critical flight conditions to be identified and provided flight data for the validation of comprehensive rotor codes. In an additional flight test, an airborne background-oriented schlieren system was operated aboard a second helicopter to visualize the blade tip vortices of the ultralight helicopter in forward flight. The background-oriented schlieren measurements resulted in the first visualization of blade–vortex and vortex–structure interaction effects on a full-scale coaxial helicopter. The application of optical measurement systems in the present flight tests gives valuable insight into the aerodynamics and blade dynamics of a free-flying counter-rotating helicopter and demonstrates how these methods can effectively support the development process of new rotorcraft.

Impacts of using a head-worn display on gait performance during level walking and obstacle crossing

Use of a head-worn display (HWD) may affect gait performance and increase slip and trip risks, though there is a lack of information on such effects. This study investigated how different display technologies (monocular and binocular HWDs, and a paper list) and visual information presentation modes affect gait performance. Twelve gender-balanced participants completed walking and obstacle crossing trials on a linear walking track under all experimental conditions and a baseline control (without using a technology). During these trials, information relevant to a simulated light assembly task was provided, as representative of a potential occupational application. Gait performance was assessed based on minimum foot clearance (MFC), required coefficient of friction, foot placement locations around the obstacle, and/or walking/obstacle crossing speed. Use of a HWD had no substantial effects on level walking performance. A more conservative/cautious obstacle crossing strategy was, however, observed with HWD use, including a decrease (∼3%) in obstacle crossing speed (compared to the baseline). Gender-specific foot control strategies (lead foot MFC) were also observed that depended on the specific display technology and information modes. Foot placements around the obstacle were not influenced by use of the binocular HWD, yet a conservative strategy was observed with the monocular HWD.

Empirically Determined Passenger Ferry Navigable Routes within Lagos Lagoon

Hydrographic surveys define shorelines and depths of lakes, streams, oceans, reservoirs, and other bodies of water. Sea surveying is associated with port and offshore industries and the marine environment, including measurements and marine investigations made by ship-borne personnel. In addition, accurate measurement and modelling of hydrographic information is important to control waterways boat services with existing roadway transportation services. This paper attempts an empirical analysis of hydrographic data to simulate waterway navigable route within Lagos Lagoon with a minimum under-keel clearance that must be maintained by vessel transiting a port as well as berthing. The field investigation was conducted between September 2015 and March 2016 to determine river bed topography with the deployment of DGPS receivers, Single beam SDE 28S echo sounder, speed boat, tidal observation and reduction. Hypack 2008 and Arc GIS software was used for data sorting, extraction and processing. It was observed that depth within the project area ranges between 0.0m to 14.82m when referred to the Lagos datum. Furthermore, waterway navigable chart was developed based on prevailing river bed topography along the study corridors as well as passenger ferry draught constraint. From this study, derived depths were analysed in form of graphs and charts that provides a suitable framework to support ferry transportation services within Lagos Lagoon as a complimentary mode to the dominantly depended road transportation services. Therefore, periodic hydrographic survey of the navigable routes is recommended specifically to identify possible channel accretion. Keywords : Navigable routes, hydrographic information, empirical analysis, under-keel clearance, river bed, topography

Step-by-step variability of swing phase trajectory area during steady state walking at a range of speeds.

BackgroundStep kinematic variability has been characterized during gait using spatial and temporal kinematic characteristics. However, people can adopt different trajectory paths both between individuals and even within individuals at different speeds. Single point measures such as minimum toe clearance (MTC) and step length (SL) do not necessarily account for the multiple paths that the foot may take during the swing phase to reach the same foot fall endpoint. The purpose of this study was to test a step-by-step foot trajectory area (SBS-FTA) variability measure that is able to characterize sagittal plane foot trajectories of varying areas, and compare this measure against MTC and SL variability at different speeds. We hypothesize that the SBS-FTA variability would demonstrate increased variability with speed. Second, we hypothesize that SBS-FTA would have a stronger curvilinear fit compared with the CV and SD of SL and MTC. Third, we hypothesize SBS-FTA would be more responsive to change in the foot trajectory at a given speed compared to SL and MTC. Fourth, SBS-FTA variability would not strongly co-vary with SL and MTC variability measures since it represents a different construct related to foot trajectory area variability.MethodsWe studied 15 nonimpaired individuals during walking at progressively faster speeds. We calculated SL, MTC, and SBS-FTA area.ResultsSBS-FTA variability increased with speed, had a stronger curvilinear fit compared with the CV and SD of SL and MTC, was more responsive at a given speed, and did not strongly co-vary with SL and MTC variability measures.ConclusionSBS foot trajectory area variability was sensitive to change with faster speeds, captured a relationship that the majority of the other measures did not demonstrate, and did not co-vary strongly with other measures that are also components of the trajectory.

A real‐time alarm and early warning model for windage yaw of cat‐head type tower

In recent years, accidents involving windage yaw flashover have been occurring on transmission lines frequently, affecting the operational security and the power supply reliability seriously. Moreover, it is expensive and difficult to reduce the windage yaw flashover by modifying the towers and transmission lines. Therefore, a real‐time alarm and dynamic early warning model for windage yaw of a cat‐head type tower is proposed in this paper from the perspective of operation. Starting with the side‐phase and the medium‐phase conductors of the cat‐head type tower, which are common and prone to accidents due to windage flashover, the windage yaw angle of the suspension insulator string in the real‐time alarm is provided by the inclination angle measuring instrument, while in the early warning scenario that is calculated based on meteorological forecasting information. Then the minimum gap between the line and tower is calculated. Finally, the model issues windage yaw alarms or warnings by comparing the calculated minimum gap with the minimum permissible clearance corrected by rain density and gives the operations corresponding to each alarm and warning. The correct predictions in three time intervals and the feasibility of the model can meet the requirement of engineering application. Because of the limitation of the numerical weather prediction (NWP) model and accuracy, the prediction result is not very good when the time interval is long; it could improve the prediction result when more accurate NWP data is employed. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Body-foot geometries as revealed by perturbed obstacle position with different time constraints.

This study examined the geometrical relationships between the feet, pelvis and an environmental obstruction when crossing an obstacle with unexpected changes to its position. Nine healthy young adults stepped over an obstacle 19cm high with their right leg leading. The obstacle could be static or advanced at either lead (early detection) or trail (late detection) foot contact prior to clearance to force an adaptive reorganization of body-foot geometry and foot proximity to the obstacle. Stride length, minimum foot clearance over the obstacle, and foot-obstacle horizontal proximity before and after clearance were measured along with the relative position of the pelvis to each foot at eight points (four for each foot) during approach and clearance: heel contacts before and after crossing the obstacle, maximum foot heights and foot clearances. With early obstacle movement, trail limb stride length before crossing was lengthened, but foot proximity was still far from the final obstacle position. Clearance was less affected for the trail foot as compared to the lead foot. Proximity of the lead limb following clearance was the same for both early and late perturbations and closer than for the static obstacle condition. For relative body-foot positioning, significant differences were found only in the anterior-posterior direction. Following obstacle displacement, body-foot geometry was initially adapted, but then re-established to static obstacle values with an apparent focus on a balance geometry with the forward placed foot establishing new contact. These findings support an overall balance geometry that can be temporarily adjusted and coordinated with foot proximity to the obstruction to maintain continual gait and safe clearance.