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The basic tribological experiments have reported that nano-graphene lubricating oil has excellent anti-friction and anti-wear properties, which has been widely concerned. However, the real anti-friction effect of nano-graphene lubricating oil and its impact on engine power performance, economic performance and emission performance remain to be proved. This has seriously hindered the popularization and application of nano-graphene lubricating oil in the engine field. In this paper, nano-graphene powder was chemically grafted to prepare nano-graphene lubricating oil with high dispersion stability. The influence of nano-graphene on physicochemical properties of lubricating oil was studied, and the influence of nano-graphene on engine power performance, economic performance and emission performance was explored. The results show that after modification, the dispersion of nano-graphene in lubricating oil is improved. Compared with pure lubricating oil, the addition of nano-graphene makes the kinematic viscosity of lubricating oil slightly lower, and has little effect on the density, flash point, pour point and total acid value of lubricating oil. The reversed towing torque of nano-graphene lubricating oil is reduced by 1.82–5.53%, indicating that the friction loss decreases. The specific fuel consumption of the engine is reduced, which indicates that the fuel economic performance is improved. Engine HC+NOX, CH4, CO2 emissions do not change much, but particulate matter (PM) emissions increase by 8.85%. The quantity concentration of nuclear particles, accumulated particles and total particles of nano-graphene lubricating oil are significantly higher than that of pure lubricating oil. And the increase of the quantity concentration of accumulated particles is more obvious than that of nuclear particles, and the larger the load, the more obvious this phenomenon. In order to apply nano-graphene lubricating oil to the engine, it is also necessary to further study its impact on the post-processing system, adjust the control strategy of the post-processing system and then test and calibrate. [ABSTRACT FROM AUTHOR]

This work focuses on the evolution of lubrication wedge shaping in internal combustion piston engines, taking into account liquid microflows on curved surfaces and coating microgeometries. It introduces a new approach to the analysis of friction losses by simulating the microflow of lubricating oil between the surfaces of piston rings cooperating with the cylinder surface. The models used take into account three types of microgeometry and material expansion. Key results indicate that microirregularities with a stereometry of 0.1–0.2 µm significantly influence the distribution of oil film thickness in the phase of maximum working pressure, which is critical for the functioning of the seal ring. The innovation of the work consists of demonstrating that, despite small changes in the friction force and power in the piston rings, changes in the minimum values of the oil film thickness are significant. The work highlights the failure to take into account microgeometry parameters in friction models, which leads to significant errors in the simulation results, especially in terms of oil film continuity and the contribution of mixed friction. The simulations also indicate that advanced geometric models with high mesh resolution are necessary only for the assessment of changes in oil film thickness during the highest pressure increase in the combustion chamber and taking into account various mixed friction conditions. The results suggest significant progress in engine design and performance, confirming the importance of advanced fluid and mixed friction models in piston engine lubrication research. [ABSTRACT FROM AUTHOR]

An optimal shift control strategy for electric vehicles with the two-speed dual-clutch transmission is proposed to reduce the vehicle jerk and friction work during gear shift. The dynamic model of the powertrain considering the stick–slip friction of clutch is built. The developed control scheme is divided into two stages. For the upper level control, a finite-time linear quadratic regulator (LQR) is designed to optimize the target trajectories of torque and speed of motor and clutch by integrating both jerk and friction work in the cost function. Considering that the clutch torque is necessary for calculating the target trajectories but cannot be measured directly, the Kalman filter is employed to estimate the clutch torque. For the lower level control, a combination of torque feedforward and speed feedback controller is constructed to control the motor torque and clutch pressure. To validate the effectiveness of the proposed strategy, comparisons with the strategies based on the polynomial method and unsmooth LQR are carried out. Simulation results and hardware-in-loop test reveal that the jerk and friction work are both reduced, indicating better shift performance. [ABSTRACT FROM AUTHOR]

Polymers are widely used in bearing applications. In the case of water-lubricated stern tube bearings, thermoplastic polyurethane (TPU)-based composites are used due to their excellent wear resistance, corrosion resistance, and tunable mechanical properties. Their tribological performance, however, depends on operating conditions. In this work, TPU was blended with carbon fiber, graphene platelet, and ultra-high molecular weight polyethylene (UHMWPE). Friction tests of TPU based-composites against copper countersurface were carried out in water to mimic the actual operating conditions of the bearing. Most of the resulting contacts were in the boundary lubrication regime, in which friction was attributed to both contact mechanics of asperities as well as water lubrication. Our results show that the viscoelasticity of TPU has a considerable impact on its tribological performance. Water lubrication at 50 °C promotes the softening of polymer surface material during sliding, resulting in higher fluctuation in the coefficient of friction and wear loss. This is attributed to the reduced thermomechanical properties. In addition, Schallamach waviness is observed on worn surface. The tribological properties of TPU are significantly improved by the inclusion of carbon fiber, graphene platelet, and UHMWPE. The formation of graphene transfer-layers and UHMWPE transfer film reduces friction and wear loss, while the inclusion of carbon fiber enhances wear resistance due to improved mechanical properties and load bearing capacity. [ABSTRACT FROM AUTHOR]

The wear-resistant cermet coating of WC-Cr3C2-Ni was deposited via high-velocity air–fuel spraying on the beryllium bronze substrate. The wear characteristics of the coatings were investigated under different types and parameters of wear while comparing the effects of various factors on measurement accuracy and visibility. The friction coefficient of the WC-Cr3C2-Ni coating exhibited a lower value in the reciprocating wear experiment compared to that observed in the sliding wear experiment. The mass loss and friction coefficient of the coating increased with the rise in sliding speed and normal load in sliding wear. The wear of the coating is primarily attributed to adhesive wear, with a relatively lower proportion observed in reciprocating wear compared to sliding wear. The proportion of adhesive wear decreased with increasing speed, while it increased with increasing normal load. Moreover, the sensitivity of adhesive wear to normal load surpassed that of sliding speed. The experimental results showed that the tribological properties of WC-Cr3C2-Ni coating can be well demonstrated by both the reciprocating wear test and sliding wear test when the wear parameters of low load and high speed were used. This study will offer theoretical backing for the selection and assessment of polyphase hard coating materials across diverse industries. high-velocity air–fuel (HVAF). [ABSTRACT FROM AUTHOR]

The authors investigate a semi‐flooded cooling technology for modular permanent magnet machines using flux gaps (FGs) in alternate stator teeth for extra cooling channels. The investigated machine is separated into stationary and rotational components by a polyether ether ketone sleeve. Liquid is directed into the stationary component to achieve a significant temperature reduction, at the same time, avoiding the liquid leakage into the rotating component that will cause an increase in friction losses. The FGs in the modular machine increase the contact area between coolant and machine components, resulting in better cooling efficiency. Furthermore, the FGs contribute to reduced pressure loss by minimising system flow resistance. The influence of the FG width on improving machine cooling efficiency, lowering machine temperature, and reducing pressure losses is delved. Additionally, the investigation considers the impact of inlet and outlet areas to reveal the influences stemming from fluid expansions and contractions in these regions. Computational fluid dynamics (CFD) modelling is employed to simulate the cooling performances of the investigated machines. In addition, the flow network analysis has also been employed to help understand the fluid behaviour within machines. A series of tests have been carried out to validate the CFD modelling. [ABSTRACT FROM AUTHOR]

Many collective irrigation systems have been operating for decades, facing high degradation of existing infrastructures and huge water-energy efficiency problems. Predominantly composed of open canals, they have been partially or entirely converted into pressurised pipe systems, implying a considerable increase in energy consumption and operation and maintenance costs. Simple, easy-to-use, and comprehensive approaches for energy efficiency assessment in collective irrigation systems are needed for diagnosis and assisting decision-making on implementing adequate improvement measures. This research proposes and demonstrates an innovative approach based on the water and energy balances and performance indicators to assess the effect of water losses, network layout and operation, energy recovery, and equipment on energy efficiency. A novel methodology for energy balance calculation is proposed for open canal, pressurised and combined systems. The application to a real-life open canal system and network areas allowed the identification of efficiency problems mainly due to water losses in canals, followed by the dissipated energy in friction losses. Less critical are pumping and manoeuvring equipment inefficiencies. Also, a considerable excess of gravity energy is recovered in hydropower plants. In raising pipe systems, in which shaft input energy predominates and costs for pumping play a key role, surplus and dissipated energy in friction losses are the most relevant issues. Significant energy is lost in the water conveyance and distribution in both systems. Consequently, the potential to improve energy efficiency through water loss management, network layout, and operation improvement, besides pumping and manoeuvring equipment replacement, is considerable. [ABSTRACT FROM AUTHOR]

It is well known that the ratio of disk friction loss of low specific speed pumps is large. When the specific speed is 100 min−1, m3/min, m or less, the disk friction loss increases remarkably. In this study, focusing on the clearance flow from the diffuser outlet to the impeller outlet (This is called the outward flow) behind the centrifugal pump, a fin was installed on outer diameter side of the rotating wall on the back side of a centrifugal pump as a countermeasure, and the influence of changes in velocity distribution near the wall on disk friction loss was investigated by torque measurements, velocity measurement, and computational fluid dynamics (CFD) analysis. As a result, it was clarified that disk friction loss is decreasing by installing the fin in both torque measurements and CFD results, because the clearance flow is separated by fin and circumferential velocity is increased in the wake region of the fin in both measurements and CFD. In addition, it was clarified that disk friction coefficient (normalized torque) can be expressed as a function of the inlet swirl ratio and Reynolds number. Also, prediction equation is derived for each shape (with and without fin). According to the equation, it was found that disk friction loss reduction effect by installing a fin becomes larger when Reynolds number and the inlet swirl ratio are small. [ABSTRACT FROM AUTHOR]

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This paper aims to study and demonstrate the possibilities of using reinforcement learning for the synthesis of multi-objective controllers for radial actively lubricated hybrid fluid film bearings (ALHBs), which are considered to be complex multi-physical systems. In addition to the rotor displacement control problem being typically solved for active bearings, the proposed approach also includes power losses due to friction and lubricant pumping in ALHBs among the control objectives to be minimized by optimizing the lubrication modes. The multi-objective controller was synthesized using the deep Q-network (DQN) learning technique. An optimal control policy was determined by the DQN agent during its repetitive interaction with the simulation model of the rotor system with ALHBs. The calculations were sped up by replacing the numerical model of an ALHB with its surrogate ANN-based counterpart and by predicting the shaft displacements in response to operation of two independent control loops. The controller synthesized considering the formulated reward function for DQN agent is able to find a stable shaft position that reduces power losses by almost half compared to the losses observed when using a passive system. It also is able to prevent the established limit of the minimum fluid film thickness being exceeded to avoid possible system damage, for example, when the rotor is unbalanced during the operation. Analysis of the development process and the results obtained allowed us to draw conclusions about the main advantages and disadvantages of the considered approach, and also allowed us to identify some important directions for further research. [ABSTRACT FROM AUTHOR]

This paper focuses on determining the friction energy loss in the mechanism of a mechanical crank press. After defining the crank press mechanism and how it works, we describe the energy balance of a technological operation—forming. Four distinct methodologies for calculating friction loss in the mechanism are then presented, namely an empirical method, a spreadsheet calculation utilising force decomposition in a crank mechanism, an analytical calculation of the dynamic behaviour of a press, and a multibody simulation. Each additional approach expands the possibilities for approaching reality, but as the primary aim of the study is to compare the approaches, these possibilities are not exploited. Multibody simulation has proved itself to be accurate and suitable for simulating press mechanisms and investigating their dynamics. Multibody simulation is a much more powerful tool that can lead to a digital twin, which can help us to develop a less energy-demanding press. Confirmation of the multibody simulation results is the main outcome of the comparison and will be used in future work. [ABSTRACT FROM AUTHOR]

This paper develops a tsunami inundation model, filling the current void between industry applied simplified methods (bathtub and attenuation) and comprehensive numerical modeling. The proposed model utilizes two‐dimensional equations established on hydraulic principles (energy conservation and friction loss) to produce the finite‐difference, two‐dimensional model. While the sophistication of depth‐averaged numerical modeling has not been entirely replicated, the incorporation of hydraulic roughness and gravitational effects (slope) through the Bernoulli energy equation, accompanied by suitable assumptions, significantly improves performance over simplified bathtub and attenuation methods. This improvement not only retains excellent efficiency (completing case studies in under 100 s) but also yields inundation results comparable to traditional numerical modeling, which typically takes multiple hours to days. This is the first application of such equations to a two‐dimensional tsunami inundation model, leading to simulations at Gisborne and Christchurch, New Zealand, for validation against the numerical model, COMCOT. F1 scores produced from inundation extent comparisons were upwards of 84%. Inundation depth discrepancies recorded 77% within a ±$\pm$1 m range, while over 93% within a ±$\pm$2 m range. [ABSTRACT FROM AUTHOR]

This research investigates the impact of vortex generators integrated with a corrugated absorber plate of solar air heater on the enhancement of heat transfer and thermal-hydraulic performance utilizing a 3D numerical model for Reynolds numbers varying from 7,000 to 25,000. Three different types of vortex generators (rectangular, trapezoidal, and delta) are investigated separately. Vortex generators in two pairs with various angles of attack of 15º, 30º, 45º, and 60º are mounted on the entrance section's upper wall of the domain of computation. The current numerical models are validated by comparisons with experimentally published data. The velocity vectors, turbulent kinetic energy, friction factor, Nusselt number, and thermal-hydraulic performance parameters are examined for the considered current cases considered. The numerical results demonstrate a significant impact of vortex generators on friction loss and transmission of heat. The values of thermal-hydraulic performance for utilizing a corrugated absorber plate integrated with vortex generators are found to be considerably higher than those for using a corrugated absorber plate alone. The highest value of the thermal-hydraulic performance parameter is 0.91 in the case of rectangular vortex generators at Re of 7000 and an angle of attack of 30º. [ABSTRACT FROM AUTHOR]

This article presents a study of aerothermal performance of tubes with regularly-spaced multi-channel twisted tape elements (RS-MTT) installed. This research aimed to find the proper design RS-MTTs that induce swirl flow which potentially improves fluid mixing between the core fluid and the fluid near the tube wall, thereby accelerating the heat transfer rate. Additionally, the effects of Reynolds numbers and free-spacing ratios (s/y) on heat transfer, friction loss, and thermal performance behaviors were examined. The RS-MTTs having different free-spacing ratios (s/y) of 0.0, 0.25, 0.5, 0.75, and 1.0 were tested. Air was utilized as the testing fluid in experiments with Reynolds numbers (Re) spanning from 6000 to 20,000. The utilization of RS-MTTs with s/y = 0.0, 0.25, 0.5, 0.75, and 1.0 augmented heat transfer rates up to 1.74, 1.80, 1.85, 1.90, and 2.15 times given by the plain tube alone while the friction factors increased by 4.22, 4.61, 3.87, and 4.05 times, respectively. At the lowest Reynolds number of 6000, the thermal enhancement factors of the tube containing the RS-MTTs with s/y = 0.0, 0.25, 0.5, 0.75, and 1.0 reached the maximum values of 1.42, 1.35, 1.31, 1.27, and 1.23, respectively. Among the RS-MTTs tested, the RS-MTT with s/y = 0.0 showed the best thermal enhancement factor of 4.56%, corresponding to the heat transfer augmented of 11.52% with a friction penalty of 8.71%. [ABSTRACT FROM AUTHOR]

Centrifugal pumps consume majority of energy used by the electric motor driven systems among all end users of the industrial sector. Only in European region, a 1% improvement in efficiency (η) of the centrifugal pump is capable enough to reduce CO2 emissions by at least 572 tons per day. The prime motive of this research is to assess the applicability of the novel back cavity filling (BCF) in reducing the disk friction losses of centrifugal pumps without changing the pump's original design. By adding a solid ring to the bearing housing's back-cover plate, the BCF was applied to a medium specific speed pump ( N s = 54 rpm), resulting in a 1 mm back axial clearance from 13 mm. Numerical simulations and experiments were carried out to investigate the effect of BCF on pump performance under two conditions: with and without BCF at best efficient point (BEP) and various partload conditions for 1450 rpm (rated) as well as 1000 rpm. Pump performance characteristics were enhanced by BCF at both rpms for the whole flow rate range. At 1450 rpm, BCF resulted in an average 0.74% increment in total head, 2.08% reduction in input torque, and 2.70% increment in overall efficiency over the flow rate range. While an average 2.04% improvement in total head, 1.33% reduction in input torque, a 3.30% enhancement in overall efficiency were obtained at 1000 rpm. Performance parameter enhancement was higher at lowest part load compared to the BEP on rated rpm. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to propose an optimization framework using deep neural networks (DNN) coupled with nondominated sorting genetic algorithm II and technique for order preference by similarity to an ideal solution method to improve the tribological properties of camshaft bearing pairs of internal combustion engine. Design/methodology/approach: A lubrication model based on the theory of elastohydrodynamic lubrication and flexible multibody dynamics was developed for a V6 diesel engine. Setting DNN model as fitness function, the multi-objective optimization genetic algorithm and decision-making method were used to optimize the bearing pair structure with the goal of minimizing the total friction loss and the difference of the average values of minimum oil film thickness. Findings: The results show that the lubrication state corresponding to the optimized bearing pair structure is elastohydrodynamic lubrication. Compared with the original structure, the optimized structure significantly reduces the total friction loss. Originality/value: The optimized performance and corresponding structural parameters are obtained, and the optimization results were verified through multibody dynamics simulation. Peer review: The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-12-2023-0417/ [ABSTRACT FROM AUTHOR]

Machine tool (MT) thermal errors induced by external and internal heat sources (e.g. changing environment, friction and power losses in MT components) are an important element in machined workpiece inaccuracies. In the past few decades, indirect software compensation techniques have been used to address thermal errors on account of their economic and ecological aspects. Many slightly different approaches are described in the literature. If thermal error models are properly identified based on experiments with sufficiently varying input parameters, they usually work within similar calibration and verification conditions. As the sensory equipment of machines increases, models can be adapted to regions with higher thermo-mechanical system nonlinearity and inhomogeneity through the introduction of deformation feedback from direct measurements into model structures. However, adaptive functionalities require discrete interruptions of the MT's work cycle, which threaten the integrity of the machined surface and complicate the model structure and thus also implementation and industrial deployment possibilities. In this research, a novel approach of automatic post-process adaptation suitable for repetitive manufacturing, which takes advantage of transfer functions (TF), is proposed for thermal error reduction. The method respects basic heat transfer mechanisms in the MT structure by combining linear parametric models, requires a minimum of additional gauges, and feedback from direct measurements is obtained only during technological pauses in the production process. Post-process adaptation is solved retrospectively by updating model parameters using the heuristic method of genetic algorithms (GA). First, the approach was tuned on a case study of a heavy-duty milling machine with a horizontal headstock for a configuration with an exchangeable spindle head and a configuration with a change in the position of the headstock in the workspace, both of which were different from the initial model's calibration range. Subsequently, the developed approach was applied to repeated production on a medium-sized milling centre. Another goal of the paper is to emphasize the need for quality input information for modelling efforts and the industrial applicability of scientific results. • An indirect compensation model of machine tool (MT) thermal errors distinguishing between the heating and cooling phases is developed. The model includes the influence of ambient temperature change. • Granular structure of transfer-function-based model enables possibility of modifying the magnitude of the approximation value and of adapting the time constant of the simulation to the approximated phenomenon. • The thermal error compensation strategy based on post-process updating of model parameters is demonstrated on heavy-duty milling machine and applied on medium-size milling centre. • Spatial thermal errors, MT equipment modularity and process liquid presence are considered in post-process modelling effort. • The necessity of quality and correct input signals to the compensation model is emphasized. • Only the measured residual deformations in technological pauses are used to update the parameters of the model for repeated production. [ABSTRACT FROM AUTHOR]

The evolution of high-performance computing facilitates the simulation of manufacturing processes. The prediction accuracy of a numerical model of the cutting process is closely associated with the selection of constitutive and friction models. The reliability and the accuracy of these models highly depend on the value of the parameters involved in the definition of the cutting process. Direct of inverse methods are used to determine these model parameters. However, these identification procedures often neglect the link between the parameters of the material and the friction models. This article introduces a novel approach to inversely identify the best parameters value for both models at the same time and by taking into account multiple cutting conditions in the optimization routine. An artificial intelligence (AI) framework that combines the finite element modeling with an adaptive Bayesian multi-objective evolutionary algorithm (AB-MOEA) is developed, where the objective is to minimize the deviation between the experimental and the numerical results. The arbitrary Lagrangian-Eulerian (ALE) formulation and the Ti6Al4V alloy are selected to demonstrate its applicability. The investigation shows that the developed AI platform can identify the best parameters values with low computational time and resources. The identified parameters values predicted the cutting and feed forces within a deviation of less than 4% from the experiments for all the cutting conditions considered in this work. [ABSTRACT FROM AUTHOR]

Reducing fuel consumption to decrease CO2 emissions has become a key development factor in the automotive industry. An effective way to decrease fuel consumption is to reduce the influence of various sources of energy loss. One way to increase engine efficiency is to use low-viscosity engine oils to reduce friction losses in the engine's tribological systems. The aim of the article was to analyze the relationship between the type of engine oil and fuel consumption in a group of 12 passenger cars. This was a homogenous group of identical cars, equipped with the same engine, operated under very similar conditions. Three groups of engine oils (Revline, Total, Orlen) were tested in vehicles and stressed with comparable workloads. The experiment was conducted over two years (two stages of research). The collected results were presented using graphs and compared using statistical tests, split into two stages of research, with four seasonal temperature groups. The study provides a detailed description of fuel consumption differences taking into account variations in ambient temperature. The analyses were focused on finding answers to two research questions: does the type of engine oil affect the variation in combustion levels, and what is the variability of fuel consumption in different seasons due to the ambient temperature variability? Briefly, in both stages of the study, vehicles using Revline oil attained the highest average fuel consumption throughout the study period. Vehicles using Total oil showed similar results to those using Revline oil, with the difference in fuel consumption not as noticeable during warmer months. Conversely, vehicles using Orlen oil demonstrated the lowest fuel consumption values during colder months, but higher levels during warmer months. [ABSTRACT FROM AUTHOR]

This study performed a sensitivity analysis to correlate the frictional head loss calculated by the Darcy-Weisbach (D-W) and the Hazen-Williams (H-W) formulas. For a broad variety of fluid temperatures, velocities, and pipeline diameters, this study considered an extensive discussion and analysis to determine friction loss within pressurized pipelines using Microsoft Excel. Regression analysis and statistical tools were applied to improve the relationship between the two equations. A more accurate expression was developed to calculate the friction loss in terms of the H-W equation. The estimated values were compared with previous experimental and numerical studies, and a good agreement was observed. The proposed model was evaluated using WaterGEMS software in an application example of a water supply system against the D-W and H-W equations. Good agreements were recorded between predicted values and previous studies, with an error of less than 1%. These findings can be used to improve the hydraulic design of engineering applications. [ABSTRACT FROM AUTHOR]

The present work experimentally investigates the effect of novel turbulators on improving heat exchanger (HE) performance. Tests are conducted by insertion of three types of turbulators, 3PS, 4PS, and 5PS, including two pitch ratio PR (5-3.76). The results showed that the enhancement in heat transfer (HT) when using 5PS was more than the remaining two types. The greatest worth was at the lowest pitch ratio. The outcomes of experiments showed that the enhancement in the Nusselt number for each type of 5PS, 4PS and 3PS for small pitch ratio was 194%, 177% and 164% more than that of the plain tube, correspondingly. Also, the thermal performance factor, friction factor, and Nusselt number are all increased as the pitch ratio decreases. As a result, the small pitch ratio delivers a more considerable rate of HT and lower loss in friction. In addition, the results showed that the factor of thermal performance was more significant compared to unity for each type studied, and the maximum value of thermal performance factor acquired at η=1.54 is accomplished for the 5PS turbulators. The Correlations between the friction factor and Nusselt number were evolved for the range of Reynolds number (Re) of 12385 to 24766. The most relevant results of the evaluated study were presented to aid researchers in understanding the advances in HT enhancement in double pipe HE using novel turbulators inserts. [ABSTRACT FROM AUTHOR]

The influence of the ratio of TiN powder, graphite powder, and Ni60 powder on the phase composition, microstructure, microhardness, and wear properties of the TiCN Ni‐based coating on H13 steel is investigated. The findings indicate that varying proportions of TiN powder, C powder, and Ni60 powder have a minimal impact on the coating's phase composition. The diffraction peak intensity of TiC0.3N0.7 increases with the addition of (C + TiN) in the blended powder, while the crystallinity of TiC0.3N0.7 in the Ni‐based coating with a 30% (C + TiN) mass fraction decreases. The grain structure of the 20% Ni‐based coating is fine and uniform, while the microstructure of the 30% Ni‐based coating is characterized by a large polymerization phase‐containing Ti elements, with the TiCN‐reinforced phase exhibiting irregular grain morphology. The microhardness HV0.5 of the coating with a 20% (C + TiN) mass fraction ranges from 725 to 772, with an average hardness of 747.8 HV0.5, which is 3.4 times the hardness of the substrate material and 1.3 times the hardness of the Ni‐based coating. As the mass fraction of (C + TiN) in the hybrid powder increases, the friction loss mass of the coating tends to decrease and then increase. The average wear of the Ni‐based coating with a 20% (C + TiN) mass fraction is ≈22.4% of that of the substrate and 50% of that of the Ni‐based coating, demonstrating excellent wear resistance. The wear mechanism is primarily characterized by brittle spalling and abrasive wear. [ABSTRACT FROM AUTHOR]

• Single- and two-phase frictional pressure losses in stainless steel smooth tubes (5.5 and 8.5 mm) and six aluminium straight inner-grooved profiles have been experimentally studied on ammonia. • The adequacy of existing correlations and approaches has been validated. • A new correlation has been proposed for the frictional pressure losses in inner-finned tubes. The experimental study of single-phase and two-phase frictional pressure losses has been performed with ammonia flow in stainless steel smooth tubes (internal diameter of 5.5 mm and 8.5 mm) and six straight inner-grooved aluminium tubes with different nominal diameters (7.15 to 13.3 mm), length (0.45 to 2.0 mm) and thickness (0.35 to 0.8) of fins. Single-phase test boundary conditions correspond to Reynolds numbers of 1000 to 20,000. Two-phase tests have been carried out at saturation temperature of 45 to 65 °C, mass velocity of 50 to 210 kg· m −2s−1 and vapour quality of 0.1 to 0.9. Comparison of obtained test data with the existing frictional losses approaches shows that the Blasius model is appropriate to single-phase flows in smooth tubes, and Müller-Steinhagen and Heck's (1986) model is most accurate in predictions of two-phase frictional losses in smooth tubes. Existing approaches of single-phase frictional pressure loss predictions in the pipes and channels with longitudinal fins (Carnavos, 1980; Edwards and Jensen, 1994) are not adequately suited to the ammonia test points obtained in the considered straight inner-grooved tubes. A new semi-empirical model has been proposed, based on generalisation around the revealed geometric dimensionless factor, which accurately describes friction pressure losses in the considered inner-finned profiles. The simplest homogeneous model for defining two-phase friction pressure losses, using McAdams et al.'s (1942) recommendation for mixture dynamic viscosity definition and a new model of single-phase friction factor, best fit both quantitatively and qualitatively to ammonia two-phase test points in most of the considered straight inner-grooved tubes. [ABSTRACT FROM AUTHOR]

To reduce the friction loss and the piston-knocking noise from the perspective of the design of the cylinder bore profile, the piston-ring cylinder bore (PRCB) dynamic model of an L6 diesel engine was developed using AVL-Excite-Piston & Rings. Based on the full-scale test method, the effects of bore taper, starting height of tapered profile, and ellipticity on the friction power and knocking energy of the PRCB system were investigated, and the optimization of the design of the bore profile was carried out with the objectives of minimizing the system's friction power and the peak knocking kinetic energy. The results showed that the taper of the cylinder bore has the greatest influence on the system's friction power and the peak knocking kinetic energy, followed by the starting height of the conical profile. For the peak knocking kinetic energy of the piston, there was an obvious interaction between the taper and the starting height of the conical profile. When the taper was 35 μm and 45 μm, the peak knocking kinetic energy showed a decreasing and then increasing trend with the increase in the starting height of the profile, and when the taper was 55 μm the peak knocking kinetic energy monotonically was decreased with the increase in the starting height of the conical profile. The optimization results showed that the system's friction power was decreased by 15.05% and the peak knocking kinetic energy was decreased by 21.41% for a taper degree of 55 μm, a tapered profile starting height of 31 mm, and an ellipticity of 50 μm compared to the initial cylindrical cylinder bore. [ABSTRACT FROM AUTHOR]

Coatings as a protection for mechanical equipment and components is one of the major targets for the scientific research. Coatings are widely applied in various applications such as turbine blades, valve bodies, pump housings. In this context, present study aims to improve the mechanical and physical properties of mechanical equipment/component surfaces to maximize their life-time using fillers/epoxy coatings. This can be achieved by optimizing the filler concentration in epoxy coatings to maximize the surface hydrophobicity, reduce the friction losses, and to increase abrasion and impact resistance. In this work, four different ceramic fillers, namely, nano silica, nano silicon carbide (SiC), nano zinc oxide (ZnO) and micro zinc oxide have been incorporated as fillers into epoxy polymeric matrix. 0.5, 1, 2, 3 wt pct of silica and nano ZnO were added to eight epoxy matrices, while 5, 10, 15, 20 wt pct of SiC and micro ZnO were added to another eight matrices. In total 16 formulas as a surface coating were used for both steel and glass substrates. The coated samples were left to cure in the ambient conditions for 7 days. Abrasion, hardness, impact, pull-off, surface tension and corrosion tests were performed. The results revealed that silica composites have the highest hydrophobicity. Increasing hydrophobicity of composites is a very good trend which shall contribute in solving degradation and corrosion problems, accordingly increasing life time of the mechanical parts. On the other hand, silicon carbide composite has the highest abrasion resistance and tensile strength. [ABSTRACT FROM AUTHOR]

• A new design of an oil-free rotary-vane compressor with a mechanical efficiency exceeding 0.9 has been proposed. • A mathematical model for calculating power losses due to friction for the new design of an oil-free rotary-vane compressor has been developed, with a calculation error not exceeding 10 %. • The power losses due to friction in the working chamber of the new oil-free rotary-vane compressor in the range of rotor speeds from 1000 to 3700 rpm are 4 to 20 times lower than those for the traditional design. Additionally, the frictional power losses in the rotor slot are 20–30 % lower, and on the stator, they are 16–20 times lower. This paper presents the design of an oil-free rotor vane stage with a new tribological scheme. The new scheme differs from existing ones in that the sealing vane contain protrusions that rest on rolling unloading bearings located in the end covers of the cylinder. Experimental results on friction power losses in the new and traditional stages are provided, demonstrating that the implementation of the new stage design allows for an average reduction in friction power losses by a factor of 10. A mathematical model for calculating friction power losses in the rotor vane type compressor stage, implementing the new tribological scheme, has been developed. The analysis based on the mathematical model confirms the possibility of achieving mechanical efficiency values higher than 0.9 in oil-free rotor vane stages with a pressure ratio of 3 and a rotor speed of 3000 rpm, through the use of the new tribological scheme. It has been found that there is a redistribution of the importance and values of the main design parameters recommended for the design of oil-free rotor vane stages with the new tribological scheme, which determine its structural configuration, compared to its traditional design. [ABSTRACT FROM AUTHOR]

The Pumps as Turbines (PAT) is a well-established technology suitable for standalone micro-hydropower plants and energy recovery systems. But being lower performance than the dedicated turbines, there are continuous efforts to improve it keeping cost benefits intact. One of the recent modifications of the back cavity filling plays a crucial role in the performance of PAT which is not investigated in detail. In the present paper, the PAT back cavity is filled with a solid ring of various sizes and shapes (back cavity filling) to explore its impact. The developed test facility is used to validate the experimental results with the numerical results for the base case. A numerical model after validation has been employed to investigate the impact of back cavity filling on the internal flow dynamics and the PAT performance. Additionally, the study explored the influence of axial clearance on flow physics, associated losses, and the PAT performance, an aspect rarely discussed by researchers in the PAT mode. After back cavity filling, secondary flow-based disk friction losses were reduced, leading to a 3.5 % increase in PAT efficiency. An analysis of the axial clearance showed that increasing it from 0.015 to 0.076 (mean axial gap/impeller radius) led to a 2.6 % reduction in PAT efficiency. This decline can be primarily attributed to elevated losses associated with disk friction, increased volumetric losses, and the formation of a mixing zone at the impeller inlet, which impeded the flow into the impeller's flow zone. [ABSTRACT FROM AUTHOR]

Longitudinal slip tests of the 215/55 R17 tire were carried out using a six-component tire bench test instrument. By comparing with Abaqus simulation data, the longitudinal forces and slip ratios of the tire with a constant tire pressure under different speeds and vertical loads were analyzed. A tire finite element model was established, and the energy loss of the tire under the action of ground friction was examined using the model. It was predicted that the heat loss of the tire was mainly caused partially by the sliding of the tire against the ground and partially by rolling friction. The friction force of the tire is concentrated at the shoulder position. The results showed that the longitudinal force increased with the increase in the vertical load at the same slip ratio, but the velocity had little effect on the longitudinal force. In the braking slip stage, the heat loss due to friction was greater than that in the driving slip stage. The energy loss due to friction increased with the increase in the velocity and vertical load. In the whole sliding process, the energy release due to frictional work was the largest at 80 km/h and 6396 N. [ABSTRACT FROM AUTHOR]

To understand the effect of particulate contaminants on pavement skid resistance, the friction numbers of three surfaces under different pollution conditions (particle size, coverage fraction, and shape factor) were measured using a British Pendulum Tester (BPT). The results show that less than 45% coverage fraction of the particles above 0.3 mm even results in almost 50% friction loss at a low speed of 10 km/h. In this situation, the rougher surface has a stronger holding particles capacity. Moreover, the particle size determining the lowest friction level gradually increases as the surface roughness increases. The particle size of 1.18–2.36 mm is the most typical size range leading to a low friction level. In addition, the friction first drops sharply and then increases slowly with the coverage fraction increases, which also conforms to the Stribeck curve. The skid resistance of road surfaces covered with particles was tested. Effects of particle size, coverage fraction, and shape on friction were analysed. Potential hazard scenarios with particulate contaminants were discussed. [ABSTRACT FROM AUTHOR]

For future internal combustion engines, driven by regenerative fuels, efficiency is more important than ever. One approach to reduce the losses inside the piston cylinder unit (PCU) is to improve the alignment of the liner and the piston. Therefore, a cylinder liner with a free form was developed at the Institute of Technical Combustion (ITV) of the Leibniz University Hannover which compensates radial and linear deformations along the stroke. The layout is based on a FEM simulation. The liner was manufactured by the Institute of Production Engineering and Machine Tools (IFW) of Leibniz University of Hannover with a novel turn-milling process. The liner was investigated on the heavy-duty Floating-Liner engine of ITV with a displacement of 1991 ccm and a bore diameter of 130 mm. The experimental results show improvement in the friction losses over the whole engine map in the range of 9% and up to 17.3% compared to a serial liner. Sealing efficiency could be improved up to 28.8%, depending on the operational point. Overall, the investigation aims for lower fuel consumption which would in result fewer emissions. [ABSTRACT FROM AUTHOR]

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Currently, mechanical gears with cycloid engagement are increasingly used in mechanisms along with involute ones. In modern drive mechanisms, using pin gears and gears with intermediate rolling elements (IRE) is widespread, which simultaneously use cycloid gears. To a greater extent, pin gears are now being investigated, but IRE gears have their undeniable advantages. Many works are devoted to the study of cycloid toothing for certain gears, but the efficiency, especially that of IRE gears, has practically not been investigated. Therefore, the analysis of power losses in the engagement of a gear with IRE and a free cage (IREFC) is relevant. In this analysis, the authors of the work have used laws of mechanics, methods of energy flows and a secant normal. Mathematical expressions have been obtained to estimate slip speeds and power friction losses in the engagement of a gear with IREFC, and a formula has been derived to determine the efficiency of a mentioned mechanical transmission. The calculation of slip speeds and power losses at the points of contact of a rolling element with cycloid profiles of wheels for selected initial parameters of a gear with IREFC has been presented. The friction power and the overall efficiency of the entire gear engagement have also been calculated. This work shows that power friction losses at the points of contact of a rolling element with cycloid profiles of tooth wheels of a gear with IREFC are not the same. The friction power in the contact of a rolling element with a cycloid profile of a cam is an order of magnitude higher than the friction power in the contact of a rolling element with a cycloid profile of a crown. [ABSTRACT FROM AUTHOR]

The frictional properties of the coarse aggregate used in asphalt concrete are a major contributor to the friction of the surface mixes. Selecting an aggregate that is not only polish and crush resistant to withstand the mechanical degradation and grinding under traffic loading, but also has a low friction loss rate and reasonable friction life is vital. A laboratory aggregate test program was carried out to evaluate the polishing/friction and crushing performance of 25 different aggregate sources from different locations. Two widely used friction test methods, i.e., British pendulum testing (BPT) and dynamic friction testing (DFT) in conjunction with the three-wheel polishing testing (TWPD) and the aggregate crushing value test (ACV) were used to quantify the polishing and crushing resistance of aggregates, respectively. Several frictional and crushing test parameters were introduced, analyzed, and finally, a correlation analysis was performed to relate different aggregate friction, polishing, and crushing test parameters. All three tests showed low variability when replicate samples were compared. A strong correlation (R value of 0.92) was found between the friction loss rate and the ACV test parameters and a linear correlation with R2 of greater than 0.80 was observed between the final friction life of the aggregate and the BPT test parameters. The ACV and TWPD/BPT tests can be potentially considered as an alternative test for friction evaluation of the coarse aggregates in case the DFT device is not available, with some loss in the sensitivity in characterizing marginal materials. [ABSTRACT FROM AUTHOR]

Calculation of diagrams of components of residual stress tensor arising in the surface layer of a tribomaterial under sliding friction is used to formulate ideas about the role of the medium in creating a plasticizing and strengthening triboeffect. The characteristics of the structural state of the surface layers of brasses, aluminum and tin bronzes during their friction against steel in surface-active lubricants are presented. The conditions for achieving minimum power losses to friction and wear are determined. The role of local diffusion phenomena in quasi-spinodal phase transitions observed in surface micro-volumes of copper alloys during their contact deformation is revealed. It is shown that among industrial copper alloys, brass of the L90 type, aluminum bronzes BrA5, BrA7, and tin bronzes BrOF4-0.25, BrOF6,5-0,15 have the greatest wear resistance in surface-active lubricants. Examples of implementation of the phenomenon of selective transfer in friction pairs are given. Recommendations are developed for its use in friction units of machines and devices. [ABSTRACT FROM AUTHOR]

Reducing friction energy losses is crucial in mechanical systems, often achieved through lubrication strategies employing friction modifiers. These additives adsorb onto surfaces, forming boundary film to prevent solid–solid contacts. However, atomistic simulation techniques used to study these additives often ignore surface roughness due to high computational cost. This study addresses this gap by employing Coarse-Grained Molecular Dynamics (CG MD) to investigate the impact of surface roughness on the adsorption of Organic Friction Modifiers (OFMs) under shear. Traditional self-diffusion methods prove inadequate for determining the damping coefficients in CG models because of strong OFM adsorption effects. Therefore, shear-induced motion is introduced for the coefficient determination. The simulation reveals that a symmetrical model (identical opposing surfaces) shows OFM slip, desorption, and re-adsorption trends on rough surfaces, while an asymmetrical model (smooth cylinder on a flat surface) demonstrates increased adsorption on rough flat surfaces (up to 60.9%) compared to smooth flat surfaces under similar shearing conditions. However, rough flat surfaces with a smaller wavelength (6 nm) exhibit faster OFM desorption along the asperity region, up to four times more than a 24 nm wavelength surface. This research emphasizes the importance of considering surface roughness in simulating OFM behavior for lubrication applications. [ABSTRACT FROM AUTHOR]

Ultrapermeable membranes (UPMs) have the potential of improving water production efficiency. However, operating at high water fluxes will intensify concentration polarization and membrane fouling. Inspired by the V-formation of birds in nature we propose a transformative membrane module that enables a doubled mass transfer coefficient with a moderately increased friction loss coefficient. Moreover, we present a practical technological pathway for the UPM systems to achieve 338% improvement of average water flux and 18% energy savings relative to state-of-the-art seawater desalination plants. The work makes it practical to operate at a high average water flux of 84 L m−2 h−1 with a controlled concentration polarization for the UPM systems. It breaks through the module development bottlenecks for the next-generation UPM systems and has enormous potential application for alleviating water scarcity crisis in the coming decades. [ABSTRACT FROM AUTHOR]

Friction losses and scuffing failures are interesting research topics for worm gears. One of the factors leading to scuffing is the heat generated in the contact of gear teeth. The contact geometry of worm gears is complex, leading to high friction between contact surfaces. High friction between contact surfaces during operation generates heat friction that causes the occurrence of scuffing, which in turn determines the scuffing load capacity. To analyse the thermal characteristics of a worm-gear pair and the thermal behaviour of contact teeth, a direct-coupled thermal–structural 3D finite element model was applied. The heat flux due to friction-generated heat was determined on the gear tooth to investigate thermal characteristics and predict transient temperature fields. This study permits an in-depth understanding of the temperature fields and the friction heat generation process. Also, better control of the contact pattern between worm-gear teeth would decrease friction heat and increase scuffing load capacity. This paper investigates the transient thermal behaviour among different pinion machine setting parameters that can result in an optimal tooth-contact pattern that produces a lower temperature field, thus achieving higher transmission efficiency. [ABSTRACT FROM AUTHOR]

This work aims at determining the heat transfer enhancement as well as friction losses of CeO2 nanofluids (NFs) in a double pipe heat exchanger. Cerium Oxide nanopowder was characterised by Energy-Dispersive X-ray Spectroscopy (EDX), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Thermo-physical properties were measured at different temperatures and concentrations of the NF. Friction factor and Nusselt numbers were determined for various particles loading of 0.1%, 0.2% and 0.3%. Thermal conductivity enhanced by 7.92% to 12.9% than the based fluid. Experiments were performed for the range of Reynolds numbers of 2000 to 9000. Experimental results showed that for 0.3% concentration of NF, the maximum augmentation in the Nusselt number is 32.35% with a penalty of 1.18 times in terms of friction factor at a Reynolds number of 8720 in contrast to that of the carrier fluid. [ABSTRACT FROM AUTHOR]

The effects of different spargers on the hydrodynamics and mass transfer of an airlift loop reactor were investigated. The gas holdup, liquid loop velocity, and volumetric mass transfer coefficient of the reactor were tested using a ring orifice distributor and a jet nozzle. The study was conducted in a 6 m high airlift loop reactor at a superficial gas velocity of 0.01~0.04 m/s, and the superficial liquid velocity was maintained at 0.0154 m/s. The results showed that using the jet nozzle provided a higher gas holdup, liquid loop velocity, and mass transfer. When the superficial gas velocity was less than 0.0325 m/s, the liquid loop velocity generated by the jet nozzle was approximately 1.1-fold higher than that generated by the ring orifice distributor, and the disparity in gas holdup between the riser and downcomer enhanced the power of liquid circulation. When the superficial gas velocity was more than 0.0325 m/s, the jet kinetic power dominated the improvement in the liquid loop velocity, and the energy input from the nozzle to the airlift loop reactor was greater than 10.8 J/(s·m2). This indicated a threshold of energy input for overcoming the friction loss. In this situation, the liquid loop velocity in the jet form increased considerably, thus favoring the mixing performance and temperature uniformity of the reactor. It was also of significance for avoiding the formation of a flow dead zone in scale-up airlift loop reactors. [ABSTRACT FROM AUTHOR]

An AC excitation power supply will produce a series of harmonic currents in motors compared to the conventional power supply, increase the time harmonic component, and then generate a harmonic magnetic field; harmonics will cause motor vibrations and noise in the motor and will produce a corresponding additional loss, increasing the motor temperature rise; these key technical problems need to be solved in domestic pumped storage AC excitation motor engineering applications. Herein, the no-load loss characteristic test of a 3 MW alternating current excited motor was mainly carried out using a test prototype of the 3 MW alternating current excitation motor. Further, with the aid of the finite element method, the numerical study of the no-load loss characteristics of a 3 MW alternating current excited motor was performed. The relationship between the key factors such as the no-load characteristics, no-load loss characteristics, and constant loss and voltage per unit value is analyzed, and the variation law of the no-load core loss of motors under different loads is explored. The results demonstrate that, under no-load conditions, when the applied voltage was less than the rated voltage, the voltage was proportional to the current. When the applied voltage was more significant than the rated voltage, the current increased as the voltage increased, but the relationship between the two was no longer proportional. The constant loss of the motor maintained a linear relationship with the square of the unit value of the voltage scale. When the square of the unit value of the voltage scale was zero, the loss was equivalent to the wind friction loss under no load. The core loss increased with the increase in load, and the greater the load, the faster the increase rate of the motor iron loss. The comparison deviation between the test and simulation results was less than 10%. The simulation and experimental results verified the effectiveness of finite element modeling and the finite element calculation method. [ABSTRACT FROM AUTHOR]

Multistage multi-cluster hydraulic fracturing has enabled the economic exploitation of shale reservoirs, but the interpretation of hydraulic fracture parameters is challenging. The pressure signals after pump shutdown are influenced by hydraulic fractures, which can reflect the geometric features of hydraulic fracture. The shutdown pressure can be used to interpret the hydraulic fracture parameters in a real-time and cost-effective manner. In this paper, a mathematical model for shutdown pressure evolution is developed considering the effects of wellbore friction, perforation friction and fluid loss in fractures. An efficient numerical simulation method is established by using the method of characteristics. Based on this method, the impacts of fracture half-length, fracture height, opened cluster and perforation number, and filtration coefficient on the evolution of shutdown pressure are analyzed. The results indicate that a larger fracture half-length may hasten the decay of shutdown pressure, while a larger fracture height can slow down the decay of shutdown pressure. A smaller number of opened clusters and perforations can significantly increase the perforation friction and decrease the overall level of shutdown pressure. A larger filtration coefficient may accelerate the fluid filtration in the fracture and hasten the drop of the shutdown pressure. The simulation method of shutdown pressure, as well as the analysis results, has important implications for the interpretation of hydraulic fracture parameters. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to study the clearance compatibility of active magnetic bearing (AMB) and gas bearing (GB) to achieve a single-structured hybrid gas-magnetic bearing (HGMB), which uses a single bearing structure to realize both the functions of gas bearing and magnetic bearing. Design/methodology/approach: Because the radial clearance size of the AMB is typically ten times larger than that of the GB, radial clearance compatibility of GB and AMB needs to maximize the radial clearance of GB by adjusting structural parameters. Parametric analysis of structural parameters of GB is explored. Furthermore, a general structural design principle based on static analysis, rotordynamic performance and system stability is established for the single-structured HGMB. Findings: Load capacity is vastly reduced due to the enlarged radial clearance of the GB. A minimum clearance needs to be ensured by increasing the bearing diameter or width to compensate for the reduced load capacity, yet indirectly raising the bearing load. Increased bearing load is conducive to stability, yet it raises the risk of rotor abrasion. In addition, excessively large bearing diameter leads to system instability, and inappropriate bearing width affects critical speeds. A general structural design principle is established and the designed HGMB–rotor processes optimal performances. Originality/value: A single-structured HGMB is proposed to address the urgent demand for high-speed, cryogenic turboexpanders with frequent starts/stops. This design applies a single-bearing structure to realize the characteristics of both GB and AMB, greatly simplifying the implementation, reducing air friction loss and raising critical speeds. This paper provides a fresh perspective on the development of cryogenic turboexpanders for hydrogen liquefaction. It theoretically validates the feasibility and provides a design guide for a single-structured HGMB system. [ABSTRACT FROM AUTHOR]

The rotor of a high-power water-filled submersible motor rotates at high speed in liquid during operation. while working motor internal air gap fluid flow in complicated cases, fluid flow characteristics is not only directly affect the water of the rotor friction loss, also affect the submersible motor cooling effect. In this paper, the fluid field in the inner cavity of submersible motor is deeply studied. The air-gap fluid grid model was established according to computational fluid dynamics, and the influence of air-gap on fluid velocity of submersible motor was studied based on ANSYS and FLUENT software. The results show that the pressure decreases linearly after the cooling water enters the motor air gap, the maximum pressure is located at the air gap inlet and the minimum at the air gap outlet; the outlet and inlet pressure of the air gap fluid grows with the increase of the air gap inlet fluid flow rate, and the growth rate tends to decrease in different degrees. The research results provide a basis for the design of submersible motor and the determination of the reasonable flow of fluid in the motor. [ABSTRACT FROM AUTHOR]

This document provides a summary of research papers on the phenomenon of water hammer, which occurs when there are abrupt changes in flow within pressurized pipes. The papers explore various aspects of water hammer, including different flow conditions, pipe materials, and related phenomena. The authors present new advances in modeling and experimental verification of water hammer phenomena, such as analyzing the behavior of air valves and surge tanks, simulating the dynamic behavior of air cushion surge chambers, and modeling valve closure using computational fluid dynamics. The studies highlight the importance of considering factors such as viscoelastic behavior, friction losses, and valve operations in hydraulic transient simulations. [Extracted from the article]

The presence of emitters along the lateral, as well as of connectors along the manifold, causes additional local head losses other than friction losses. An accurate estimation of local losses is of crucial importance for a correct design of microirrigation systems. This paper presents a procedure to assess local head losses caused by 6 lateral start connectors of 32- and 40-mm nominal diameter each under actual hydraulic working conditions based on artificial neural networks (ANN) and gene expression programming (GEP) modelling approaches. Different input–output combinations and data partitions were assessed to analyse the hydraulic performance of the system and the optimum training strategy of the models, respectively. The range of the head losses in the manifold (hsM) is considerable lower than in the lateral (hsL). hsM increases with the protrusion ratio (s/S). hsL does not decrease for a decreasing s/S. There is a correlation between hsL and the Reynolds number in the lateral (ReL). However, this correlation might also be dependent on the flow conditions in the manifold before the derivation. The value of the head loss component due to the protrusion might be influenced by the flow derivation. DN32 connectors and hsM present more accurate estimates. Crucial input parameters are flow velocity and protrusion ratio. The inclusion of friction head loss as input also improves the estimating accuracy of the models. The range of the indicators is considerably worse for DN40 than for DN32. The models trained with all patterns lead to more accurate estimations in connectors 7 to 12 than the models trained exclusively with DN40 patterns. On the other hand, including DN40 patterns in the training process did not involve any improvement for estimating the head losses of DN32 connectors. ANN were more accurate than GEP in DN32. In DN40 ANN were less accurate than GEP for hsM, but they were more accurate than GEP for hsL, while both presented a similar performance for hscombined. Different equations were obtained using GEP to easily estimate the two components of the local loss. The equation that should be used in practice depends on the availability of inputs. [ABSTRACT FROM AUTHOR]