Verbesserte Tribokorrosionsbeständigkeit des martensitischen Stahls X54CrMoVN17-1 durch die Erzeugung von expanded martensite

Seal-free, media-lubricated rolling bearings have a high-energy efficiency as the absence of the seal minimizes frictional loss and increases the efficiency of the driven machine. In addition, the environment is protected by the absence of hazardous lubricants. However, media-lubrication increases tribocorrosive attack on the bearing surface. Therefore, the tribocorrosion resistance of the bearing surface can be increased by a thermal surface treatment called low-temperature plasma nitriding. The produced “expanded martensite” in martensitic steels features a high hardness with comparatively good corrosion resistance. Tribocorrosion tests in 0.9 % NaCl-solution show that the material loss could be reduced by 70 % due to expanded martensite compared to the initial state of the steel.

A New Analytical Approach To Calculate a Slippage inside a Progressing Cavity Pump with a Metallic Stator Using a Middle Streamline and a Structural Periodicity

Summary Simplified and 3D models have been studied to predict the performance of progressing cavity pumps (PCPs). Simplified models were mainly made for metallic stator PCP performance. Their purpose was to represent the relationship between pump flow rate and differential pressure. Previous studies proposed to solve the system of mass conservation equations. In these studies, the geometry of the gap area was not clearly represented by neglecting the curvatures of stator and rotor. In addition, only frictional loss was considered, but local loss by gradual contraction or expansion of the gap area was not considered. In this study, we present a new analytical approach considering curvature and local loss. The depth of the gap area and local loss could be calculated analytically by a middle streamline and a curvature. On the basis of periodicity of distribution of cavities, simplified calculation for a slippage was possible without a system of mass conservation equations. Therefore, this model represents clearer geometry and a more simplified approach. The results show that this model shortens the calculating time and facilitates programing; in addition, the model validation is good in matching with experimental data.

Dynamic Modeling and Design of a Radial Hydrostatic Piston Pump for Integrated Pump-Motor

There is a current trend towards the electrification of high force/torque density machines that have traditionally been dominated by diesel engine driven hydraulics. Power dense electric machines tend to favor high operating speeds whereas a hydraulic pump is more efficient at low speed and high torque conditions. The power density of a pump can be increased by decreasing the displacement and increasing the operating speed to provide the flow demand. This miniaturization of the pump allows it to be directly integrated into an electric motor inside a single casing. This integrated pump-motor is free of shaft seals and eliminates a set of bearings otherwise required when coupling an electric motor and pump with a shaft. Additionally, the leakage from the hydraulic pump can be used as coolant for the electrical machine, thereby improving the power density. In this paper, a hydrostatic radial piston pump has been evaluated for integration with an axial flux PM machine. The proposed hydrostatic piston pump uses a spherical head piston that can tilt while reciprocating inside the cylinder, eliminating the need for a joint at the slipper. To reduce the frictional loss between the slipper pad and the cam at high operating speeds, the cam freely rotates. A detailed model of the pump, with focus on the hydrostatic piston slipper, has been developed and a grid search approach has been utilized to select the critical parameters of the pump. Finally, an efficiency map has been presented for this pump at different operating conditions which shows around 86% efficiency at the 12500 rpm speed for 7 MPa pressure differentials.

A Novel Positive Displacement Axial Piston Machine With Bent Cylinder Sleeves

In this paper, an investigation of a novel positive displacement axial piston machine using a bent cylinder sleeve configuration is presented. The proposed design eliminates the side moments on the piston/cylinder interface, therefore, reduces the frictional loss and improves the total energy efficiency. A multi-physics elastohydrodynamic lubrication model was used to aid the design of the piston/cylinder and the cylinder block/port block interface. Then, a lumped parameter model was used to optimize the port block geometry. Groove geometry was chosen primarily to reduce flow ripple, tilting moment, and cavitation risk. To improve the housing stiffness, the lumped parameter model was combined with a finite element analysis. This ensured safety for the testing. In the end, steady-state experiments were performed on the prototype based on the ISO4409 normative. The unit’s speed was set to 500 rpm, then increased by 500 rpm until it reached 3000 rpm. The supply pressure was set to 20 bar. The outlet pressure was set to 70 bar at first, then increased by 50 bar until it reached 220 bar. The results show a remarkable volumetric efficiency with a peak of 99.5%. It is however noted that due to some of the issues with the initial iteration of the current design, there is a reduction in mechanical efficiency. The causes and possible future solutions to these issues are discussed in the manuscript.

Research on the influence of key structural parameters on piston secondary motion

Piston secondary motion not only influences the side knocking of piston and frictional loss, but also influence the in-cylinder oil consumption and gas blow-by. An inline four-cylinder common rail diesel engine was chosen as the research object. Dynamic simulation model of piston assembly was built based on the piston and cylinder liner temperature field test. The impacts of pinhole offset, liner clearance and piston skirt ovality on piston secondary motion were researched. Based on the surface response method, the influence of multiple factors on friction power loss and slapping energy is estimated. The results indicate that: in-cylinder stress condition of piston will change with its structural parameters, then the secondary motion of piston will be affected as a result. Pinhole offset, liner clearance, piston skirt ovality and the interaction of the latter two all have significant effects on the friction power loss, while the slapping energy is significantly affected by liner clearance. Therefore, the parameters can be designed based on the significance level to optimize the secondary motion characteristics of the piston.

Scheduling Period Selection Based on Stability Analysis for Engagement Control Task of Automatic Clutches

The clutch engagement process involves three phases known as open, slipping, and locked and takes a few seconds. The engagement control program runs in an embedded control unit, in which discretization may induce oscillation and even instability in the powertrain due to an improper scheduling period for the engagement control task. To properly select the scheduling period, a methodology for control–scheduling co-design during clutch engagement is proposed. Considering the transition of the friction state from slipping to being locked, the co-design framework consists of two steps. In the first step, a stability analysis is conducted for the slipping phase based on a linearized system model enveloping the driving and driven part of the clutch, feed-forward and feedback control loop together with a zero-order signal hold element. The critical period is determined according to pole locations, and factors influencing the critical period are investigated. In the second step, real-time hardware-in-the-loop experiments are carried out to inspect the dynamic response concerning the friction state transition. A sub-boundary within the stable region is found to guarantee the control performance to satisfy the engineering requirements. In general, the vehicle jerk and clutch frictional loss increase with the increase in the scheduling period. When the scheduling period is shorter than the critical period, the rate of increase is mild. However, once the scheduling period exceeds the critical period, the rate of increase becomes very high.

Determination of the permeability coefficient and airflow resistivity of nonwoven materials

Air penetration behavior plays a vital role in the performance of fibrous material in various industrial applications. Two parameters, the permeability coefficient and airflow resistivity, can describe the air penetration behavior of fibrous material. FX 3300 Textech Tester III and AFD300 AcoustiFlow devices were used to respectively characterize the permeability coefficient and airflow resistivity of nonwoven materials. Nonwoven samples were compressed due to the load from the test head of the FX 3300. Finite element analysis along with the mathematical method were implemented to recover the airflow permeability of samples at the uncompressed state. The effects of pressure drop on the airflow velocity and permeability coefficient were analyzed by the Ergun-type model. The determination of airflow resistivity based on the permeability coefficient is carried out via two approaches, that is, the direct method and the extrapolation method. The results show that the airflow velocity is not linearly related to the pressure drop, which differs from Darcy's law. This non-linear relation is mainly attributed to the influence of frictional loss. By comparing the relative error between assessed and measured airflow resistivity, most of the assessed values of the compressed samples are overestimated. The results also suggest that the direct and extrapolation methods are applicable to assess airflow resistivity on an airflow velocity (or air permeability) test device. Moreover, the Ergun-type model is also applicable to determine the permeability coefficient and airflow resistivity of nonwoven materials.

Invented Forces in Supercell Models

This paper examines methods used in supercell models to maintain a steady, sheared, horizontally uniform environment with a three-force balance in the planetary boundary layer (PBL) and a two-force balance above it. Steady environments are maintained while ignoring the thermal-wind balance that permits large shear above the PBL. The Taylor-Proudman theorem indicates that wind profiles above the PBL must be unidirectional for balanced environments. In principle, supercell models that do not accommodate thermal advection should not support balanced steady environments with veering horizontally uniform winds.Recent methods add a permanent, pervasive, horizontal external force that varies only with height. By adding two more degrees of freedom, this force circumvents the Taylor-Proudman theorem and enables a static, horizontally uniform environment for any wind profile. It succeeds by adding spurious energy in lieu of flow towards low pressure to offset frictional loss of kinetic energy. However, the artificial force has downsides. It decouples the environmental horizontal equation of motion from the hydrostatic equation and the thermodynamics from the dynamics. It cancels environmental friction and the part of the Coriolis force that acts on the environmental wind. Within the storm, its curl can speciously generate significant horizontal vorticity near the ground. Inaccuracies arise in circulations around material circuits because of modifications by the artificial force and resulting miscalculations of parcel trajectories. Doubt is cast on conclusions about tornadogenesis drawn from recent simulations that contain an invented force.

Diamond-Shaped Extended Fins for Heat Transfer Enhancement in a Double-Pipe Heat Exchanger: An Innovative Design

Heat transfer enhancement in heat exchangers results in thermal efficiency and energy saving. In double-pipe heat exchangers (DPHEs), extended or augmented fins in the annulus of the two concentric pipes, i.e., at the outer surface of the inner pipe, are used to extend the surface of contact for enhancing heat transfer. In this article, an innovative diamond-shaped design of extended fins is proposed for DPHEs. This type of fin is considered for the first time in the design of DPHEs. The triangular-shaped and rectangular-shaped fin designs of DPHE, available in the literature, can be recovered as special cases of the proposed design. An h-adaptive finite element method is employed for the solution of the governing equations. The results are computed for various performance measures against the emerging parameters. The results dictate that the optimal configurations of the diamond-shaped fins in the DPHE for an enhanced heat transfer are recommended as follows: If around 4–6, 8–12, or 16–32 fins are to be placed in the DPHE, then the height of the fins should be 20%, 80%, or 100%, respectively, of the annulus width. If frictional loss of heat is also to be considered, then for fin-heights of 20–80% and 100% of the annulus width, the placement of 4 and 8 diamond-shaped fins, respectively, is recommended for an enhanced heat transfer. These recommendations are for the radii ratio (i.e., the ratio of the inner pipe radius to that of the outer pipe) of 0.25. The recommendations are be modified if the radii ratio is altered.

Estimation of Cuttings Concentration and Frictional Pressure Losses During Drilling Using Data-Driven Models

Drilling practice has been evolving parallel to the developments in the oil and gas industry. Current supply and demand for oil and gas dictate search for hydrocarbons either at much deeper and hard-to-reach fields, or at unconventional fields, both requiring extended reach wells, long horizontal sections, and 3D complex trajectories. Cuttings transport is one of the most challenging problems while drilling such wells, especially at mid-range inclinations. For many years, numerous studies have been conducted to address modeling of cuttings transport, estimation of the concentration of cuttings as well as pressure losses inside the wellbores, considering various drilling variables having influence on the process. However, such attempts, either mechanistic or empirical, have many limitations due to various simplifications and assumptions made during the development stage. Fluid thixotropy, temperature variations in the wellbore, uncertainty in pipe eccentricity as well as chaotic motion of cuttings due to pipe rotation, imperfections in the wellbore walls, variations in the size and shape of the cuttings, presence of tool joints on the drillstring, etc. causes the modeling of the problem extremely difficult. Due to the complexity of the process, the estimations are usually not very accurate, or not reliable. In this study, data-driven models are used to address the estimation of cuttings concentration and frictional loss estimation in a well during drilling operations, instead of using mechanistic or empirical methods. The selected models include Artificial Neural Networks, Random Forest, and AdaBoost. The training of the models is determined using the experimental data regarding cuttings transport tests collected in the last 40 years at The University of Tulsa – Drilling Research Projects, which includes a wide range of wellbore and pipe sizes, inclinations, ROPs, pipe rotation speeds, flow rates, fluid and cuttings properties. The evaluation of the models is conducted using Root Mean Square Error, R-Squared Values, and P-Value. As the inputs of the data-driven models, independent drilling variables are directly used. Also, as a second approach, dimensionless groups are developed based on these independent drilling variables, and these dimensionless groups are used as the inputs of the models. Moreover, performance of the data-driven model results are compared with the results of a conventional mechanistic model. It is observed that in many cases, data-driven models perform significantly better than the mechanistic model, which provides a very promising direction to consider for real time drilling optimization and automation. It is also concluded that using the independent drilling variables directly as the model inputs provided more accurate results when compared with dimensional groups are used as the model inputs.