Pressure Torque Research Articles

Theoretical modeling of sliding vane compressor with leakage

Performance of a sliding vane compressor is significantly influenced by the leakage effect occurring between adjacent cells during the compression phase of the cycle. In this paper, thermodynamic and dynamical mathematical models were formulated for a double action sliding vane compressor including leakage effect modeling. The leakage modeling is incorporated through an analytic pressure model with a single tunable parameter to be adjusted to correspond with specific compressor leakage characteristics. The effect of leakage on the cell pressure, temperature, mass, and work, and total vane torque variations were qualitatively investigated. The study illustrated the significant effect of leakage on power input requirement, discharge pressure and mass delivery, and less significant effect on mechanical efficiency and specific mass delivery. The validity of the simulation results is made by comparing the pressure work calculated from both the thermodynamic and the dynamic models.

Principle of Oil Film Test on Port Pair of Axial Piston Pump and Control Characteristics

In order to study the lubrication characteristics of several key friction pairs in axial piston pump under oil or water medium, the principle of the specialized test system that adopts electrohydraulic units for active and passive control of the lubricating oil film is proposed. The principle and constitution of the simulation test system of the said test system that uses film thickness feedback to control the sealing gap of port plate pair is discussed. The action of micro gap flow on the electrohydraulic control system is simplified to the load on the damper in spring, the physical model of the valve-controlled cylinder of port plate pair in relation to the lubricating film thickness is established, and the precision cylinder displacement control equation is derived. The main control parameters affecting the lubrication performance and their interrelations are analyzed, and the dynamic characteristic of film thickness control is simulated. The preliminary test of planar port plate pair oil film is carried out by using the test system. The results show that the simulation of oil film equilibrium is basically consistent with the test, and oil supply pressure and friction torque have relatively great effect on the formation of lubricating oil film. The feedback control principle of servo proportional valve makes the system’s film thickness dynamic feedback performance tend to keep stable, but when the slope of oil supply pressure varies, the equilibrium value of film thickness has certain variation within the preset range.

Mathematical Modeling of Water Cooled Automotive Air Compressor

Mathematical modeling is the process of designing a model of a real system and conducting experiments with it for the purpose of understanding the behaviour of the system. Mathematical simulation is widely used for investigating and designing the compressors. Investigation of the processes of reciprocating compressors using mathematical models is an effective tool by high development of computing technique, which enables complicated problems to be solved with a minimal number of simplifying assumptions. A considerable number of previous works has been done on the mathematical modeling and simulation. This paper presents a simplified and effective mathematical model for the estimation of reciprocating compressor performance using personal computers that can be easily handled. The developed model has been validated using the experimental results from the compressor with reed vale in the delivery side and ring valve in the suction side. The compressor is tested for different delivery pressures and different shaft speeds. The effect of parameters speed, discharge pressure on thermodynamic behaviour of compressor in working condition has been analyzed. The model can predict cylinder pressure, cylinder volume, cylinder temperature, valve lift and resultant torque at different crank angles and free air delivered and indicated power of the compressor. The predicted results using the developed mathematical model are very much comparable with the experimental results.

Mathematical modeling and simulation of a reed valve reciprocating air compressor

Mathematical modeling is the process of designing a model of a real system and conducting experiments with it for the purpose of understanding the behavior of the system. Mathematical simulation is widely used for investigating and designing the compressors. Investigations of the processes of reciprocating compressors using mathematical models is an effective tool by high development of computing technique, which enables complicated problems to be solved with a minimal number of simplifying assumptions. A considerable number of previous works has been done on the mathematical modeling and simulation. The aim of the present work is to construct a model which is easy to understand, easy to detect errors in the process of building a model, and easy to compute a solution. This paper presents a simplified and effective mathematical model for the estimation of reciprocating compressor performance using personal computers that can be easily handled. The effect of operating parameters, speed and discharge pressure on thermodynamic behavior of compressor in working condition has been analyzed. The model has been developed for obtaining cylinder pressure, cylinder volume, cylinder temperature, valve lift and resultant torque at different crank angles and free air delivered and indicated power of the compressor. The model has been validated using experimental results.

Compliant Hybrid Journal Bearings Using Integral Wire Mesh Dampers

The following work presents a new type of hybrid journal bearing developed for enabling oil-free operation of high performance turbomachinery. The new design integrates compliant hydrostatic-hydrodynamic partitioned bearing pads with two flexibly mounted integral wire mesh dampers. The primary aim of the new bearing configuration was to maximize the load-carrying capacity and effective damping levels while maintaining adequate compliance to misalignment and variations in rotor geometry. The concept of operation is discussed along with the description of the bearing design. Several experiments using room temperature air as the working fluid were performed that demonstrate proof of concept, which include lift-off tests, bearing load tests, and rotordynamic characterization tests. The experiments demonstrate stable operation to 40,000 rpm (2.8×106 DN) of a 2.750 in. (70 mm) diameter bearing. In addition to the experimental results, an analytical model is presented for the compliant bearing system. The aeroelastic theory couples the steady state numerical solution of the compressible Reynolds flow equation with a flexible structure possessing translational and rotational compliance. This was achieved by formulating a fluid-structure force balance for each partitioned bearing pad while maintaining a global mass flow balance through the hydrostatic restrictors and bearing lands. Example numerical results for pad pressure profile, film thickness, torque, and leakage are shown.

The effect of gravitational and pressure torques on Titan's length-of-day variations

Cassini radar observations show that Titan's spin is slightly faster than synchronous spin. Angular momentum exchange between Titan's surface and the atmosphere over seasonal time scales corresponding to Saturn's orbital period of 29.5 year is the most likely cause of the observed non-synchronous rotation. We study the effect of Saturn's gravitational torque and torques between internal layers on the length-of-day (LOD) variations driven by the atmosphere. Because static tides deform Titan into an ellipsoid with the long axis approximately in the direction to Saturn, non-zero gravitational and pressure torques exist that can change the rotation rate of Titan. For the torque calculation, we estimate the flattening of Titan and its interior layers under the assumption of hydrostatic equilibrium. The gravitational forcing by Saturn, due to misalignment of the long axis of Titan with the line joining the mass centers of Titan and Saturn, reduces the LOD variations with respect to those for a spherical Titan by an order of magnitude. Internal gravitational and pressure coupling between the ice shell and the interior beneath a putative ocean tends to reduce any differential rotation between shell and interior and reduces further the LOD variations by a few times. For the current estimate of the atmospheric torque, we obtain LOD variations of a hydrostatic Titan that are more than 100 times smaller than the observations indicate when Titan has no ocean as well as when a subsurface ocean exists. Moreover, Saturn's torque causes the rotation to be slower than synchronous in contrast to the Cassini observations. The calculated LOD variations could be increased if the atmospheric torque is larger than predicted and or if fast viscous relaxation of the ice shell could reduce the gravitational coupling, but it remains to be studied if a two order of magnitude increase is possible and if these effects can explain the phase difference of the predicted rotation variations. Alternatively, the large differences with the observations may suggest that non-hydrostatic effects in Titan are important. In particular, we show that the amplitude and phase of the calculated rotation variations are similar to the observed values if non-hydrostatic effects could strongly reduce the equatorial flattening of the ice shell above an internal ocean.

On the Strong Seasonal Currents in the Deep Ocean

Abstract Using a set of models, including one with a resolution of ¼°, several aspects of the simulated seasonal currents in the deep ocean are considered. It is shown that over vast areas of the deep interior, particularly in the Indian Ocean, annual-mean circulation represents a small residual of much stronger seasonal flows. In many places the seasonal horizontal velocities are of the order of 10−2 m s−1, reaching locally to 10−1 m s−1; the corresponding vertical velocities are of the order of 10−5 m s−1. An idealized geometry model is employed to confirm the notion that much of this seasonal variability in the deep-ocean circulation can be attributed to the annual cycle of wind stress, combined with the significant increase in the vertical trapping depth for basin-scale seasonal forcing. It is suggested that, at least on seasonal time scales, the so-called bottom pressure torque can be an important term in the depth-integrated vorticity balance. An interaction of these relatively strong flows (of nontidal origin) with bottom topography may contribute to diapycnal mixing in the deep ocean in a manner similar to that proposed recently for the Southern Ocean. In addition, it is found that under a plausible climate change scenario, the amplitude of the mean annual cycle of wind stress may change. Among the regions where such changes are most pronounced is that in the extratropical North Pacific. It is shown that the data on surface wind stress can be effectively used to identify the seasons with the largest changes in the deep-reaching overturning cells. Finally, unlike what might be expected from the earlier theories, the annual-mean circulation simulated by the model with ¼° resolution has the deep interior flows that tend to group into jetlike structures, often having a predominant equatorward rather than poleward direction.

The Angular Momentum Budget of the Transformed Eulerian Mean Equations

The axial angular momentum (AAM) budget of zonal atmospheric annuli extending from the surface to a given height and over meridional belts is discussed within the framework of conventional and transformed Eulerian mean (TEM) theory. Conventionally, it is only fluxes of AAM through the boundaries and/or torques at the surface that are able to change the AAM of an annulus. TEM theory introduces new torques in the budget related to the vertically integrated Eliassen–Palm flux divergence and also new AAM fluxes of the residual difference circulation. Some of these torques are displayed for various annuli. In particular, the application of TEM theory generates a large positive torque at tropospheric upper boundaries in the global case. This torque is much larger than the global mountain and friction torques but is cancelled exactly by the new vertical AAM fluxes through the upper boundary. It is concluded that the TEM approach complicates the analysis of AAM budgets but does not provide additional insight. Isentropic pressure torques are believed to be similar to the TEM torques at the upper boundary of an annulus. The isentropic pressure torques are evaluated from data and found to differ in several respects from the TEM torques.

Formation process of the Kuroshio large meander in 2004

Formation process of the 2004 Kuroshio large meander has been examined using a data assimilation and prediction system. The small meander southeast of Kyushu that occurred in December 2003 remains stationary until the next spring. The vorticity analysis indicates that this small meander is maintained by a balance between the advection and the bottom pressure torque on the continental slope. This balance is achieved as a result of reducing the advection by a westward propagating negative‐temperature‐anomaly originating in the wind stress field. The small meander starts moving eastward around May 2004, when an anticyclonic eddy east of the Tokara Strait is intensified by coalescing of two anticyclonic eddies. At that time, a deep‐anticyclonic eddy is generated below the Kuroshio by a cross‐frontal flow. The deep‐anticyclonic eddy grows up during its eastward propagation. Then a southward flow in the eastern part of the eddy carries the Kuroshio path offshore, bringing about the large meander. The eddy energetic analysis indicates that baroclinic instability is essentially responsible for this large meander formation. The sensitivity analysis reveals that the small meander and the intensified anticyclonic eddy significantly affect the phase speed and the amplitude of the meander, respectively. It is also revealed that a slow phase speed and a large amplitude of the meander are regarded as conditions for the stationary large meander, which is also applicable to the past large meanders. In the 2004 large meander, these conditions coexist by the stationary small meander staying until the intensified anticyclonic eddy triggers baroclinic instability.

Real-Time Measurement of Friction Coefficient in the Frictional Performance Test of Brake Disk

Development and optimizing of friction material formula, oriented to improve the service life and security of brake disk, is largely based on advanced measurement method to accurately provide the friction coefficient. In this study, virtual instrumentation technique was used to design an automation measurement system of friction coefficient. With proper sensors, data of four measured variables such as temperature, rotation speed, pressure and friction torque are acquired by the computer combined with a plug-in data acquisition board. The system work principle, selection of sensors, multi-channel sampling, signal processing and anti-jamming measures have been presented in detail. Those functions of the software such as real-time data acquisition, dynamic wave displaying, high-speed report saving and inquiry, and so on, have been realized by LabWindows/CVI 7.1. The system works safely with high accuracy and friendly user interface in practical operation.

Mechanics of tunnelling machine screw conveyors: a theoretical model

A new theoretical model describing the total pressure gradient and torque in a tunnelling machine screw conveyor is proposed. The theory develops new equations relating the pressure gradient and torque to the screw geometry, the shear stresses acting in the screw conveyor, and the material flow. The equations are expressed in dimensionless form, allowing application to screw conveyors of different scales. The theory is validated against measurements from laboratory model screw conveyor tests with clay soils with varying properties and operating conditions. The theory successfully describes key features of the observed mechanics of the model conveyor operation, and accurately predicts the test measurements. The proposed theory provides insight into the fundamental mechanics of screw conveyor operations, and can be used in the design of tunnelling machine screw conveyors. The theory can also be applied to other forms of screw conveyors and extruders operating with plastic materials.

Pressure, Flow, Force, and Torque Between the Barrel and Port Plate in an Axial Piston Pump

This paper analyzes the pressure distribution, leakage, force, and torque between the barrel and the port plate of an axial piston pump. A detailed set of new equations is developed, which takes into account important parameters such as tilt, clearance and rotational speed, and timing groove. The pressure distribution is derived for different operating conditions, together with a complementary numerical analysis of the original differential equations, specifically written for this application and used to validate the theoretical solutions. An excellent agreement between the two approaches is shown, allowing an explicit analytical insight into barrel/port plate operating characteristics, including consideration of cavitation. The overall mean force and torques over the barrel are evaluated and show that the torque over the XX axis is much smaller than the torque over the YY axis, as deduced from other nonexplicit simulation approaches. A detailed dynamic analysis is then studied, and it is shown that the torque fluctuation over the YY axis is typically 8% of the torque total magnitude. Of particular novelty is the prediction of a double peak in each torque fluctuation resulting from the more exact modeling of the piston/port plate/timing groove pressure distribution characteristic during motion. A comparison between the temporal torque fluctuation pattern and another work shows a good qualitative agreement. Experimental and analytical results for the present study demonstrate that barrel dynamics do contain a component primarily directed by the torque dynamics.

Coastal jet separation and associated flow variability in the southwest South China Sea

A three-dimensional, high-resolution regional ocean model, forced with high-frequency wind stress and heat flux as well as time- and space-dependent lateral fluxes, is utilized to investigate the coastal jet separation and associated variability of circulation in the southwest South China Sea (SSCS). It is found that the circulation and its variability in the SSCS are dominated by the flow fields and eddies associated with the southward and northeastward wind-driven coastal jet separation from the coast of central Vietnam in the winter and summer, respectively. As a result of the coastal jet separation, cyclonic and anticyclonic eddies with strong flow variability are generated in the regions to the southeast of the Vietnam in the winter and to the east off central Vietnam in the summer. The separation of the wind-driven coastal jet is largely associated with the formation of adverse pressure gradient force over the shallow shelf topography around the coastal promontory off central Vietnam, balanced mainly by wind stress in the summer and by both wind stress and nonlinear advection in the winter. In the vorticity balance, a bottom pressure torque, the force exerted on the wind-driven current by the shelf topography, tends to yield an adverse vorticity favorable for the separation of coastal jet. The results suggest that the interaction between wind-driven coastal currents and shelf topography in the nearshore waters plays a crucial role in controlling the separation of the coastal jet.

The Main Effect of Design Variables for a Safety Valve on a Fracture Pressure

The safety valve has been designed to protect high pressure vessels. A fracture plate made of a circular thin plate is located within the safety valve. The circular thin plate has an outlet for fluid release and to help decrease the pressure. As such, fracture of the circular thin plate can occur at the appointed pressure. In this study, design variables of the safety valve were used to control fracture pressure so that it was easy to apply in the development of a new model of a safety valve. Design variables were fluid diameter of the safety valve, thickness of the fracture plate, filet radius of the clamping bolt, fracture pressure, and clamped torque of the clamping bolt. Design variables were selected, since the fracture experiment indicated that these variables might play a critical role in the fracture of the circular thin plate. Fracture pressure was calculated by the finite element analysis method and analyzed to affect the design variables on the fracture pressure. Using regression analysis, main design variables such as the fluid diameter, the thickness and the fillet were selected and the relationships of the variables were expressed by a regression equation. Furthermore, finite element analysis method and the regression equation were verified comparing with the experiment result.

On the relationship between fronts of the Antarctic Circumpolar Current and surface chlorophyll concentrations in the Southern Ocean

We reexamine the relationship between circulation, bathymetry, and surface chlorophyll in the Southern Ocean, using new high‐resolution maps of the frontal structure of the Antarctic Circumpolar Current (ACC) derived from satellite altimetry. The maps reveal that the ACC consists of multiple filaments or jets. By averaging surface chlorophyll measurements along streamlines, we show that the fronts define the limits of zones with similar concentrations and seasonality of surface chlorophyll. The overall pattern of surface chlorophyll is consistent with strongest upwelling of nutrient‐rich deep water south of the Polar Front (PF). However, the distribution of chlorophyll in the Southern Ocean is concentrated in a number of persistent blooms, observed downstream of islands and bathymetric features. In contrast to previous studies, we find little evidence that the fronts of the ACC are associated with enhanced productivity, at least where the fronts are distant from topography. Rather, we find that most regions of elevated chlorophyll in the open Southern Ocean can be explained by upwelling of nutrients (both macronutrients and micronutrients) where the ACC interacts with topography, followed by downstream advection. The upwelling is shown to be the consequence of the bottom pressure torque established by the large‐scale flow, rather than being due to small‐scale instabilities of the jets. The interaction of the flow with the topography therefore establishes both the large‐scale dynamical balance of the ACC and determines the productivity of the open Southern Ocean.

Addressing Hurricane Intensity through Angular Momentum and Scale Energetics Approaches

This paper addresses two avenues for gaining insight into the hurricane intensity issue—the angular momentum approach and the scale interaction approach. In the angular momentum framework, the torques acting on a parcel's angular momentum are considered along an inflowing trajectory in order to construct the angular momentum budget. These torques are separable into three components: The pressure torque, the surface friction torque, and the cloud torque. All torques are found to diminish the angular momentum of an inflowing parcel, with the cloud torques having the most important role. In the scale interaction approach, energy exchanges among different scales within a hurricane are considered as a means of understanding hurricane intensity. It is found that the majority of kinetic energy contribution to the hurricane scales originates from potential-to-kinetic in-scale energy conversions. The contribution of mean-wave interactions in the kinetic energy varies with distance from the center and with the life stage of a storm. In the early stages, as the disorganized convection becomes organized on the hurricane scales, upscale energy transfers (i.e., from small to large scale) are found to take place in the outer radii of the storm. In a mature storm, the kinetic energy transfers are downscale, except for the inner radii.

저속박용디젤기관의 순간회전속도 변동에 관한 연구

The variation of the crankshaft speed in a multi-cylinder engine is determined by the resultant gas pressure torque and the torsional deformation of the crankshaft. Under steady state operation, the crankshaft speed has a quasi-periodic variation. For the diagnosis the engine instantaneous speed versus crankshaft angle is utilized. This paper describes a simple measurement method of the engine instantaneous speed versus crankshaft angle using the teeth on the flywheel of the crankshaft. Two non-contacting magnetic pickup combinations detect the crank angle and TDC position for the data acquisition. The results from experiments on a 6 cylinder marine diesel engine demonstrate that the crankshaft speed variation are detected with good resolution. And the crankshaft speed variation is investigated according to the operation conditions. Also, it is confirmed that the engine output measured by EMS can be evaluated larger than the actual value due to TDC position error caused by instantaneous speed variation.

Fundamentals of four-quadrant axial flow compressor maps

The current paper describes the experimental determination of a complete four-quadrant map for a three stage low-speed axial flow compressor. Non-dimensional pressure rise and torque coefficients and efficiency characteristics were determined. Six possible modes of operation were identified in the four quadrants. The characteristic for a compressor with a rotational speed of zero rpm, in terms of pressure rise coefficient and flow coefficient, is S-shaped and forms the dividing line between two alternate modes of operation which exist in the second and fourth quadrants. First quadrant operation is only possible during positive rotation, and third quadrant operation during negative rotation, as the zero-speed S-curve passes through the origin and so does not pass through these quadrants. Consequently, only one mode of operation is possible in each of these two quadrants. A system of notation for describing the various modes of operation has also been developed. Second quadrant operation for positive compressor rotation, and fourth quadrant operation with negative rotation are highly dissipative conditions of operation. First and third quadrant operation are compressor-like modes. Second quadrant negative rotation and fourth quadrant positive rotation operation are turbine-like modes.

Three-axis attitude control using combined gravity-gradient and solar pressure

An attitude satellite controller that combines passive gravity-gradient torque with solar pressure torque is proposed for three-axis stabilization of a micro-satellite. A dumbbell satellite configuration is chosen to increase the gravity-gradient torque and a three-axis stabilization is pursued with the help of small solar sails. Solar pressure task is to help the gravity-gradient torque and not to oppose it. The proposed controller is applied to different test cases: first, for satellite stabilization during the tumble motion, due to a nonperfect separation manoeuvre from the launcher last stage; second, the attitude control performances are studied for different eccentric orbits. The results are given in terms of settling time and maximum amplitude oscillations.

Optimal Control Laws for Momentum-Wheel Desaturation Using Magnetorquers

E ARTH-pointing satellites are expected to maintain the localvertical/local-horizontal attitude in the presence of environmental disturbance effects. In many applications this is achieved by using momentum-wheel systems which continuously exchange angular momentum with the spacecraft (SC) body. Because of secular external disturbances, such as the aerodynamic and solar radiation pressure torque, thewheel will accumulate (or lose) angular momentum, drifting towards its maximum (or minimum) allowed speed limits. Hence, suitable control of the wheel’s angular momentum is required to counteract the influence of a persisting external disturbance torque. An external control torque must be applied to perform the wheel’s momentum dumping and force the angular velocity back into its allowable limits. Magnetic attitude control of spinning and momentum biased SC is one of the earliest techniques employed in attitude stabilization [1–4]. A number of relevant studies on wheel’s momentum dumping using magnetorquers are available, both for low earth orbiting (LEO) SC [5–11] and higher altitude satellites [12–14]. Whereas reaction thrusters allow rapid momentum dumping with a large propellant consumption, the use of magnetorquers provides a cheaper desaturation maneuver, without the use of any propellant. In this Note we derive the control laws for a satellite equippedwith magnetic dipoles which allow an optimal momentum-wheel desaturation. To this end, we minimize a cost function taking into account both the maneuvering time and the power consumption. The problem is solved through an indirect approach, and the dependence of the optimal control law on the SC orbital parameters and its characteristics is discussed. Also, the minimum time and the minimum power problem are solved by using a semi-analytical and a closed-form solution, respectively. A number of numerical simulations based on the proposed methodology have been applied to theALMASatMicrosatellite [15], whose program was established and developed at the University of Bologna in 2003.