bluuebunny/crossref_metadata_2025 huggingface dataset:
Modified-Bolus Placement as a Therapeutic Tool in the Treatment of Pediatric Feeding Disorders: Analysis From a Retrospective Chart Review
Authors: Volkert Valerie M. , Sharp William G. , Clark Michele Cole , Spinks Hailey , Rubio Emily Kate , McCracken Courtney , Bryan Leah
Published: August 2019

Purpose

Recognizing the need to advance the treatment of pediatric feeding disorders, an emerging area of inquiry focuses on therapeutic techniques that address expulsion and packing possibly associated with oral–motor dysfunction. In the current study, we documented the use of modified-bolus placement in the treatment of pediatric feeding disorders at an intensive, multidisciplinary day-treatment center over a 26-month period.

Method

The retrospective observational cohort study involved patients admitted for the assessment and treatment of chronic food refusal from August 2013 to October 2015.

Results

Patients (
n
= 23) who received modified bolus placement displayed moderate-to-severe oral–motor deficits. Use of modified-bolus placement was associated with reduced expulsion and packing of bites during meals, and treatment gains coincided with a threefold increase in grams consumed per meal.

Conclusion

Results provide additional support for the potential therapeutic benefits of enhancing bolus placement onto the tongue as a means to improve mealtime performance in children with pediatric feeding disorders when included as an adjunct to more traditional behavioral approaches.
State estimation of 500 kV sulphur hexafluoride high‐voltage CBs based on Bayesian probability and neural network
Authors: Geng Sujie , Wang Xiuli , Sun Peng
Published: August 2019

Circuit breakers (CBs) are of vital importance for the stability of power systems, and a new two‐stage hierarchical state estimation method is proposed for 500 kV sulphur hexafluoride CBs based on Bayesian probability and perceptron neural networks. On the basis of the samples collected from Yunnan Power Grid in China, a new indicator system is constructed by association rules. Bayesian probability is applied to measure the correlation between the individual indicators and comprehensive indicators at the same status level, to weigh the individual indicators. Also, an adaptive perceptron is improved to train the weights of comprehensive indicators in different operational conditions, to eliminate the influence of the imbalance problem of relative deterioration. Then, the operating state of equipment can be inferred according to the calculated comprehensive scores. Finally, taking the actual operating equipment as an example, the effectiveness of this proposed method is proved by sample tests and comparison with other existing linear methods.
Modelling and simulation of ternary pumped storage hydropower for power system studies
Authors: Dong Zerui , Tan Jin , St‐Hilaire Antoine , Muljadi Eduard , Corbus David , Nelms Robert , Jacobson Mark
Published: August 2019

As the deployment of wind and solar energy increases in the USA, energy storage (ES) will play an important role in future electric power grids to help manage the variability from high penetration levels of renewable generation, ES can provide promising power/energy demand to coordinate with renewables generation, as a virtual power plant (VPP). There is an industry need for the capability in power system studies to model ternary pumped storage hydropower (T‐PSH), a pumped storage technology that offers increased system benefits. This study presents a comprehensive vendor‐neutral dynamic model of T‐PSH in GE's commercial software positive sequence load flow. A new governor model is developed with detailed gate valve modelling and a shared‐penstock function. Specifically, this model is designed to simulate the seamless transition among three operation modes: generation mode, pumping mode, and hydraulic short‐circuit mode. The developed T‐PSH model has been tested and validated on a 10‐bus test system. A comparison study of T‐PSH to conventional pumped storage hydropower has also been conducted on the Western interconnection system.
Towards programmable on‐demand lightpath services: current state‐of‐the‐art and open research areas
Authors: Nkosi Mpho C. , Mamushiane Lusani , Lysko Albert A. , Johnson David L. , Engelbrecht Andries P.
Published: August 2019

With emerging programmable network architectures gaining momentum in the networking industry, it is necessary to look at how the services currently offered on traditional network architectures can be fully migrated to the programmable networks. In traditional networks, lightpaths are used for providing high‐bandwidth consuming services that are usually sensitive to delay. Lightpath scheduling requires admission control mechanisms, routing and wavelength assignment algorithms, and protection and restoration mechanisms that ensure reliable and efficient lightpath routing. Software defined networking (SDN) is the emerging programmable network architecture that paves the way for easier network management and configuration by using application programming interfaces. The state‐of‐the‐art in lightpath routing for wavelength division multiplexing networks focusing on lightpath scheduling, routing, protection and restoration in optical software defined networks is surveyed. Moreover, open research issues for SDN lightpath routing solution are discussed.
Comparison of high‐order and second‐order sliding mode observer based estimators for speed sensorless control of rotor‐tied DFIG systems
Authors: Mbukani Mwana Wa Kalaga , Gule Nkosinathi
Published: August 2019

In this study, a sensorless vector control for the rotor‐tied doubly fed induction generator (RDFIG) is proposed in the grid‐connected mode. The proposed sensorless vector control method includes a slip speed/angle estimator which is based on the association of the high‐order sliding mode observer (HOSMO) with a phase‐locked loop (PLL). In addition, an extensive comparison between the PLL‐based HOSMO estimator and the PLL‐based second‐order sliding mode observer (SMO) estimator is also presented. The Lyapunov stability criterion is used to determine both observer gains to allow their convergence in finite time. Both the proposed HOSMO and the SMO use the three‐phase stator current and back‐electromotive force (EMF) as state variables which enable the start of the estimation even before the machine is connected to the grid. The proposed HOSMO takes into account the dynamics of the back‐EMF space vector. The PLL is used to extract the estimated slip speed/angle from the estimated back‐EMF. The performance of the proposed sensorless vector control strategy is validated experimentally with a 5.5‐kW custom‐designed RDFIG on a test bench based on the National Instrument (NI) PXIe‐8115 real‐time controller.
Cost function‐based modulation scheme of model predictive control for VIENNA rectifier
Authors: Dang Chaoliang , Tong Xiangqian , Song Weizhang , Han Yuchao , Wheeler Pat
Published: August 2019

Finite control set model predictive control (FCS‐MPC) has been widely used in the control of grid‐connected converters with the advantages of fast dynamics, multi‐objective control, and easy implement. However, the conventional FCS‐MPC bears with variable switching frequency, high current ripple and computational burden. An improved current model predictive with the cost function‐based modulation scheme (CFM‐MPC) is proposed for a three‐phase three‐level VIENNA rectifier to improve the power quality. First, the mathematical model and voltage vector are given according to the principle of deadbeat control. Then, the voltage vector of different voltage vectors are selected according to the location of the voltage vector reference, and the switching action time of the selected are directly calculated by the inversely proportional with cost function value of the selected vectors. It remains the merits of both the conventional MPC and space vector pulse width modulation schemes to track the optimum voltage vector without increasing the computational burden. Finally, a comparative study with the proposed CFM‐MPC and conventional FCS‐MPC has been conducted to verify the superiority of the proposed scheme. The results show the proposed CFM‐MPC has the advantages of lower power ripple, fixed switching frequency, lower total harmonic distortion and neutral point potential balance.
Design of wireless robust measurement filter based on differential geometry
Authors: Deng Changjian , Zhang Jianglin
Published: August 2019

This study introduces a new method to design a robust measurement filter. The novelty of this method lies in defining the concept of robustness scale and designing a filter based on differential geometry. Then the robustness scale is quantised as a minimum change value of a certain manifold which is used to describe a test system under environmental stressor or structural disturbance. Hence, the feature parameter abstracted from a normal environment is extended to an uncertain environment, and a feature parameter Kalman filter is designed to improve the robustness of a resource‐limited wireless measurement system. The results of experiments prove the effectiveness of the proposed methods.
Source separation and localisation via tensor decomposition for distributed arrays
Authors: Cheng Yuanbing , He Yapeng
Published: August 2019

This study focuses on the problem of power spectra separation and localisation of multiple sources using distributed arrays. First, the array structure and signal model are discussed. By cross‐correlating the multi‐channel received signals in time‐domain, a third tensor is constructed. Then, utilising the multi‐dimensional characteristic, the tensor is decomposed to separate the array manifold matrix and the power spectra matrix through alternating least square (ALS) method. Finally, the sources are located using the relative x ‐y plane relationship between the distributed arrays and the direction of arrival (DOA), which can be estimated by spectrum analysis of each column of the array manifold matrix. The effectiveness and superiority of the proposed method is demonstrated by simulation results.
Classification of RCS sequences based on KL divergence
Authors: Cheng Qiang , Chen Li , Zhang Yaolin
Published: August 2019

Radar cross section (RCS) is an important characteristic of radar targets. The mean, variance, skewness, kurtosis, varying patterns of RCS sequences provide rich features for radar target classification. In this study, an RCS classification method based on Kullback–Leibler divergence (KL divergence) is proposed. KL divergence is a measurement of the distance between two probabilistic distributions p (x) and q (x). In this method, the discrete probability distributions of the training RCS sequences and their varying patterns are firstly calculated and saved. For a target with unknown label, the corresponding probability distributions of its RCS sequence are computed. Then, the KL divergence between this distribution and the pre‐trained distributions is also computed. The label of this target is determined by these KL divergences and an adaptive threshold. The method collects statistical features and dynamic features of RCS sequences, and provides a unified solution for classifying RCS sequences, which is of great importance for radar target recognition. The efficiency of this method is verified by experiments on simulated data.
Micro‐Doppler feature extraction method for vibration targets based on the segmental intrinsic chirp component decomposition
Authors: Wenwu Kang , Yunhua Zhang , Xiao Dong
Published: August 2019

Based on the three‐antenna interferometric radar system, a novel micro‐Doppler feature extraction method for vibration targets is proposed in this study. First, the theory of interferometric processing of echo signal for vibration targets is introduced and explained. Second, short‐time Fourier transform is conducted with the time–frequency diagram of echo signal obtained. Then, the signals received by three‐antenna model are decomposed based on the segmental intrinsic chirp component decomposition. Finally, the 2D trajectory of vibration target is reconstructed and its micro‐Doppler features are effectively extracted via the interferometric phase. Besides, the micro‐Doppler parameters can also be estimated with the method. Two simulation experiments are conducted to validate the proposed method.
Research on signals extrapolation in the time domain based on wavelet analysis
Authors: Liu Huan , Ren Hongmei , Xiao Zhihe , Zhao Tao
Published: August 2019

Characteristic of modulation spectrum is important for radar targets classification and recognition, while signals with high occupation ratio cause low spectral resolution. For this case, the authors present a method for splicing sub‐band based on the Mallat algorithm. This method extracts the low‐frequency parts in the different periods of the signals, and using the state‐space method to extrapolate the signal between pulse sequence. This method sacrifices spectrum width to improve the local spectral resolution in the case of less sample data. The simulation results demonstrate that the method is effective.
Simplified and approximation autofocus back‐projection algorithm for SAR
Authors: Guo Zhenyu , Zhang Hongbo , Ye Shaohua
Published: August 2019

Due to accuracy limited inertial measurement unit systems, residual synthetic aperture radar (SAR) motion errors need to be compensated by autofocus method. Back‐projection (BP) algorithm is a time‐domain imaging process suitable for arbitrary trajectory and imaging on digital elevation model. However, traditional SAR autofocus algorithm requires a Fourier transform relationship between image domain and phase history domain. This study introduces an autofocus algorithm based on phase‐error estimation. By selecting the image sharpness as target cost function, the exact phase error is directly estimated in closed form by solving the fourth‐order polynomial with simplified approach. Another straightforward approximation autofocus method is also proposed to simplify calculation with high accuracy. The vast storage requirement for filtered BP data is reduced through a trade between time and space. Computer simulation and airborne experimental results validate the efficiency and efficacy of the proposed method.
Effect of ITCs on gate stacked JL‐TFET based on work‐function engineering
Authors: Bhardwaj Eshaan , Nigam Kaushal , Choubey Shubham , Chaturvedi Savitesh
Published: August 2019

A stacked double gate junctionless tunnel field‐effect transistor (JL‐TFET) has been proposed and examined the effects of interface trap charges (ITCs) by introducing both acceptor and donor charges at the semiconductor/insulator interface. The structure uses two isolated gates (polarity gate and control gate) over an n‐type‐doped silicon substrate to function as a TFET. The effect of ITCs has been analysed in terms of DC and analogue/radio‐frequency performance using parameters such as transfer characteristics, electric field, electric potential, transconductance (gm) for both conventional and gate stacked JL‐TFET. Additionally, they have also analysed metrics used to measure the device linearity performance and intermodulation distortion such as higher‐order transconductance coefficients (gm2, gm3) and figure of merit. All the simulations have been performed with the help of an Atlas device simulator.
Pebbles versus planetesimals: the case of Trappist-1
Authors: Coleman G. A. L. , Leleu A. , Alibert Y. , Benz W.
Published: August 2019

We present a study into the formation of planetary systems around low mass stars similar to Trappist-1, through the accretion of either planetesimals or pebbles. The aim is to determine if the currently observed systems around low mass stars could favour one scenario over the other. To determine these differences, we ran numerous N-body simulations, coupled to a thermally evolving viscous 1D disc model, and including prescriptions for planet migration, photoevaporation, and pebble and planetesimal dynamics. We mainly examine the differences between the pebble and planetesimal accretion scenarios, but we also look at the influences of disc mass, size of planetesimals, and the percentage of solids locked up within pebbles. When comparing the resulting planetary systems to Trappist-1, we find that a wide range of initial conditions for both the pebble and planetesimal accretion scenarios can form planetary systems similar to Trappist-1, in terms of planet mass, periods, and resonant configurations. Typically these planets formed exterior to the water iceline and migrated in resonant convoys into the inner region close to the central star. When comparing the planetary systems formed through pebble accretion to those formed through planetesimal accretion, we find a large number of similarities, including average planet masses, eccentricities, inclinations, and period ratios. One major difference between the two scenarios was that of the water content of the planets. When including the effects of ablation and full recycling of the planets’ envelope with the disc, the planets formed through pebble accretion were extremely dry, whilst those formed through planetesimal accretion were extremely wet. If the water content is not fully recycled and instead falls to the planets’ core, or if ablation of the water is neglected, then the planets formed through pebble accretion are extremely wet, similar to those formed through planetesimal accretion. Should the water content of the Trappist-1 planets be determined accurately, this could point to a preferred formation pathway for planetary systems, or to specific physics that may be at play.
Vibration with non-linear damping. stochastic approach
Authors: Lamrhari M.
Published: August 2019

This paper describes a stochastic approach to the vibration behavior of a nonlinear damping structure. The deterministic approach is based on motion equations including the non-linearity of damping. For the stochastic calculation, the deviations were assigned to the input parameters of the mathematical model. The probabilistic distribution of these parameters must reflect real operational situations. Numerical simulations were performed with MATLAB using the Monte Carlo and perturbation method. The resulting curves for the parameters studied can find a practical application in the optimization of rotating machines (washing machine), where the parameters of mass, position of the center of gravity, etc. change during operation.
Meshfree method for large deformation in dynamic problems
Authors: Karim Serroukh H. , Mabssout M.
Published: August 2019

We present a new meshless method, Taylor-SPH, for the numerical analysis of large deformation dynamic problems. This method is based on the previous work developed by the authors to solve solid dynamics problems within the framework of small deformation theory. The governing equations are given in terms of stress and velocity using the updated Lagrangian approach. The Jaumann rate of the Cauchy stress is used to get an objective stress rate tensor. The Taylor-SPH method is based on two sets of particles resulting on avoiding the classical tensile instability. In order to assess the accuracy of the proposed method, numerical examples based on elastic material involving large deformation are solved.
Non-Linear Forced Vibration of Fully Clamped FGM Skew Plates using Homogenization Technique
Authors: Moulay Abdelali H. , Benamar R.
Published: August 2019

The present work concerns the geometrically non-linear forced vibration of fully clamped functionally graded skew plates (FGSP). The theoretical model based on Hamilton’s principle and spectral analysis previously applied to obtain the non-linear mode shapes of thin straight structures is used. A homogenization technique is developed to reduce the FGSP problem under consideration to that of an equivalent isotropic homogeneous skew plate. Results are given for the linear and non-linear fundamental frequency of fully clamped FGSP, considering different parameters, such as the skew angle, the excitation force level. The results show a non linearity of the hardening type with a shift to the right of the bent non linear frequency response function, in the neighbourhood of the fundamental mode.
Numerical simulation of investment casting process of nickel-based alloy.
Authors: Ben Lenda O. , Tara A. , Jbara O. , Saad E.
Published: August 2019

In this paper, we elaborated the nickel-based alloy type Hastelloy G30 and we analyzed it by techniques of characterization in order to interpret the results obtained through a computer simulation. The calculation of the thermo-physical properties of the alloy and the simulation of filling and solidification of the casting was performed by the software ProCAST. The validation of the numerical results was done by the following experimental techniques: optical microscopy and hardness test. In the center of the elaborate piece, the experimental results showed the appearance of porosity and leading to embrittlement of the alloy. According to the numerical simulation, this is caused by a fraction of the liquid that remains trapped in this area.
The optimization of a hydroformed tube
Authors: Mohammed Nassraoui , Bouchaib Radi
Published: August 2019

The shaping by hydroforming process involves several complex phenomena and presents several types of nonlinearities (geometric, material,...). The development of a hydroforming operation requires a lot of testing to determine with precision the optimum loads of trips and get a room without defects. Advances in digital tools have enabled manufacturers to simulate and optimize their production facilities before launching the production in order to minimize the maximum rate of defective parts.
Thermal-Electrical-Mechanical Simulation of High Pressure Spark Plasma Sintering (HP-SPS) Process
Authors: Achenani Youssef , Cheddadi Abdelkhalek , SaÂdaoui Malika , Fantozzi Gilbert
Published: August 2019

In the present work, we investigate the stresses distribution using a high pressure die during SPS (Spark Plasma Sintering) experiments. In this context, we used a finite element modeling (FEM) in the case of the sintering of an alumina sample, chosen as an electrically insulator ceramic material. A thermal sintering cycle is imposed using a control pyrometer of temperature at the SiC inner die surface.
Simultaneous estimation of hydro-dipersive parameters using a new modified levenberg-marquardt algorithm
Authors: Qanza H. , Maslouhi A. , Hachimi M. , Hmimou A.
Published: August 2019

Determination of soil hydrodynamic parameters at field scale is of great importance for modeling soil water dynamics and for agricultural water management. The direct estimation of those parameters is time-consuming and afflicted with serious uncertainties. Inverse modeling is known to get efficient technique for solving non-linear problems in hydrology. Levenberg–Marquardt (LM) algorithm is a gradient-based method, which has been widely used for solving inverse soil water flow problems. In the LM algorithm, sensitivity coefficients are mainly evaluated by numerical differentiation methods. However, sensitivity coefficients are difficult to be precisely calculated by numerical differentiation methods, if transient states and non-linearities are involved. In this paper, a new approach is proposed for sensitivity analysis using the complex variabledifferentiation method (CVDM) to estimate simultaneously the hydraulic and dispersive properties of unsaturated soil from in-situ experiments. In this approach, the sensitivity coefficients can be determined in a more accurate way than the traditional finite difference method. The results show that the new inverse analysis method in the present work has high accuracy, validity, uniqueness and higher inversion efficiency, compared with the previous least-squares method. The simulated and measured water contents and tracer concentration were generally close. Overall, it was concluded that the CVDM is a promising method to estimate hydro-dispersive parameters in the unsaturated zone.
Numerical modeling transient flow in plastic pipes
Authors: Achak N. , Bahrar B. , Gueraoui K.
Published: August 2019

We present a numerical code for calculating transient flow in plastic pipes, especially in the polyethylene pipe, to analysis effect of material viscoelasticity on water hammer phenomena. The set partial differential equations to be solved is obtained using conservation laws and behavior for the fluid and the pipe wall, associated with constitutive equations of the two media, and relationships compatibility of interfaces on velocities and stresses. A global digital processing is achieved using the method of characteristics. The results obtained are in good agreement with those found in the literature.
Semi analytical method for calculating Dean's vortex in Torus of elliptical cross section
Authors: Ajgoun S. , Khalid Naciri J. , Khatyr R.
Published: August 2019

Based on the work of Dean (1927 and 1928) [1-2] and Cuming (1952) [3], the stationary flow of an incompressible Newtonian fluid through a curved pipe of uniform curvature and with elliptic cross section is studied. The Navier-Stokes equations are expressed in toroïdal coordinates system (s,r,θ). Following Dean’s approach, the governing equations for the fluid motion through a curved elliptical channel are solved by using an original semi analytical method for the resolution of a biharmonic equation. The main interest in this study is to test and validate in the case of an elliptical cross section the proposed semi-analytical method. The latter can then be used for other geometries for which explicit solutions are not available.
Thermal convection instability of two miscible viscous fluids in a Hele-Shaw cell
Authors: Echchadli M.
Published: August 2019

The onset of convection in two superimposed miscible fluid layers is investigated in the configuration of a geometric Hele-Shaw cell using linear stability analysis. The two fluids have different densities. We neglect the surface tension and chemical diffusion at the interface which is assumed of small amplitude. We consider only the asymptotic case, where the Prandtl number’s order is of the order of unity or larger than unity. We show, in the Hele-Shaw configuration, which can simulate convection in porous media, that the onset of convection can be either stationary or oscillatory depending on the Buoyancy number, B (the ratio of the stabilizing chemical density anomaly to the destabilizing thermal density anomaly), which depends on the viscosity and layer height ratios. When the buoyancy number is lower than a critical value, Bc, oscillating convection occurs in the whole cell height, however beyond Bc, the stratified regime develops without deformation of the interface and convection occurs separately in each layer. In this paper, the transition from oscillatory regime to stratified regime is visualised by using the streamlines at the onset of convection
Impact of model resolution on numerical weather prediction
Authors: Sahlaoui Z. , Mordane S.
Published: August 2019

Several model configurations are used in Morocco for numerical weather prediction (NWP). The aim of this work is to verify the impact of resolution on the quality of models forecast, particularly the precipitation field. Three model configurations are tested with 7.5 km, 5 km and 2.5 km resolution. A rainy event over the North-East of Morocco is studied. The impact on models performances is assessed through the comparison of precipitation forecasts with the adjusted quantitative precipitation estimate from weather radar. The results show that the model with 2.5 km resolution gives the best quality precipitation forecast in term of both intensity and localisation.
Control of the Interfacial Instabilities in a circular Hele-Shaw cell oscillating with a periodic angular velocity
Authors: Bouchgl J. , Souhar M.
Published: August 2019

The stability of an interface of two viscous immiscible fluids of diﬀerent densities and confined in a Hele-Shaw cell which is oscillating with periodic angular velocityis investigated. A linear stability analysis of the viscous and time-dependent basic flows, generated by a periodic rotation, leads to a time periodic oscillator describing the evolution of the interface amplitude. In this study, we examine mainly the eﬀect of the frequency of the periodic rotation on the interfacial instability that occurs at the interface.
Transport mechanisms inside the turbulent wake of a bluff body
Authors: Varon Eliott , Mazellier Nicolas , Kourta Azeddine
Published: August 2019

Based on the recent work of Stella et al. on the bidimensional (2D) flow behind a ramp [11, 10], the present paper aims at analysing the entrainment phenomenon in a three-dimensional (3D) turbulent wake downstream of a bluﬀ-body. Numerical and experimental data of diﬀerent configurations of the Ahmed body are investigated. This study is part of a framework on the aerodynamic drag reduction for ground vehicles by defining proper and realistic control laws derived from the entrainment.
Heat transfer enhancement using two isothermal blocks in a cylindrical heat exchanger
Authors: Touzani S. , Cheddadi A. , Ouazzani M. T.
Published: August 2019

The influence of two isothermal blocks placed in a low position φm=0.18π in a cylindrical heat exchanger is numerically studied. The governing equations are discretized by the centered finite difference method using the ADI scheme. By varying Rayleigh number range between 1000 and 10000, we are interested in the local Nusselt number and the local efficiency variations as a function of the angular coordinate φ. In one hand, we found that heat transfer is important in the superior zone of the annulus for high Ra and in the central zone for low Ra. On the other hand, compared to the without blocks configuration, heat transfer in the inferior and central zones is improved for all Ra.
Thermal transfer of Nanofluids based on carbon nanotubes/glycerol and study of their rheological behavior
Authors: Lahlou S. , Sehaqui R. , Lahlou N.
Published: August 2019

In the field of heat transfer, the use of the properties of rheological behavior inherent to suspensions of nanoparticles in heat transfer fluids has been the subject of several years of work. Our study concerns the particular case of suspensions of multilayered carbon nanotubes (MNTCs) in glycerol. We highlight the effect of the mass fraction φ of (MNTCs) on the rheology of the solutions for 0.1% ≤ φ ≤1%, on the temperature [30-80°C] and the effect on a heat exchanger. The experimental results obtained are described by viscoplastic models for which the yield stress increases with φ. We then propose a law of polynomial evolution of the apparent viscosity as a function of the volume fraction for each value of the shear rate varying from 0s-1 to 100s-1.
Direct carbon fuel cell simulation using hybrid lb-fv approach: effect of carbon fuel specific surface area
Authors: El Mansouri A. , Hasnaoui M. , Filahi I. , Amahmid A. , Alouah M. , Dahani Y.
Published: August 2019

In the present study, the simulation of the direct carbon fuel cell (DCFC) using a hybrid Lattice Boltzmann and finite volume approach is performed. The numerical model was first validated against available experimental data. Parametric studies were carried out to investigate the effect of the microstructure of the carbon fuel on the DCFC performance. The increase of the specific surface area (SSA) or porosity was found to minimize the voltage drop in the cell and ameliorate its output power density. In contrary, the increase of the tortuosity was found to inversely affect these results.
Novel Cascade Solar Desalination Still: Mathematical, Numerical and Experimental Analysis
Authors: Bouzaid M. , Mouhsin N. , Taha-Janan M. , Oubrek M. , Ansari O.
Published: August 2019

Morocco is considered as a water-stressed country and is among the countries that face fresh water scarcity. However Morocco has an important solar energy and a significant amount of seawater and ocean. Therefore converting saline water to fresh water using solar energy is the perfect and the cleanest solution. Solar still is the simplest, cleanest and cheapest technology of solar desalination. In this paper a novel solar still with stepped-slope absorber plate and baffles was proposed and developed in order to enhance the thermal performance of the conventional solar stills. In order to validate the performance of the developed technology a comparative study were elaborated. A mathematical model was developed. The energy balance equations for the various elements of the solar still are formulated and numerically solved using the dynamic simulation program Matlab/SimulinkTM and the Euler explicit method programmed by C++. Also, the experimental process of the new construction was evaluated and validates the new pattern performance. The thermal performance was investigated and shows considerable improvement through the new construction.
Parameters variation effects on energy recovery for a freely floating wave energy converter
Authors: Jabrali A. , Khatyr R. , Khalid Naciri J.
Published: August 2019

This study presents the effects of parameters variations on the recovered energy for a floating wave energy converter (WEC) device. The articulated multi body floating WEC under consideration consists of two cylinders connected by a flat plate. The connections between the parts of the WEC allow the rotational movements of cylinders and the plate. The aim of this paper is to investigate the coupled effect of the length of the plate with the amplitude and period of the wave on the recovered energy by the floating WEC. The results show that the value of the optimum length for the plate is related to the sea wave condition, and more particularly to the amplitude and wavelength of the oscillations of the free surface.
Validation of a 1-D Elastohydrodynamic lubrication model
Authors: Bahi Y. , Rahmoune M. , Elgadari M.
Published: August 2019

The sealing performance of a hydraulic cylinder depends on the characteristics of three essential elements: the rod, the seal and the fluid. To predict the behaviour of a hydraulic seal, including the friction force and leakage rate, a series of theoretical and experimental studies have been carried out. In this article, a one-dimensional elasto-hydrodynamic model of the U-cup hydraulic rod seal is developed taking into account: the roughness of the shaft and lips. The numerical results are validated by experiments previously published.
Innovations in design and production of spiroid gears in the XXI century
Authors: Goldfarb Veniamin , Trubachev Evgenii , Barmina Natalya
Published: August 2019

The paper presents the review of directions of development of the theory and practice of spiroid gears for the past two decades within the scientific production complex of Kalashnikov ISTU that involves the scientific department “Institute of Mechanics” and the small innovative enterprise “Mechanic”. This en-terprise became de facto the tasksetter and main investor of scientific and practical developments that can be divided into mutually related developments of the theory of gearing and methods of gear design, develop-ment of new varieties and advancement of the known gears, development of competitive layouts of gear-boxes and development of efficient techniques of gear and gearbox production. Development of the theory of gearing focused on creation of computer-aided means of design (the main of them is the software system “SPDIAL+”) provides the profound investigation of the process of tooth interaction with account of errors, elastic and elastoplastic strains of teeth and other elements of the design, localization of multi-pair contact, application of new schemes of tooth generation, optimization gear design with due regard to gear adaptation to real operation conditions and limitations of design and manufacturing procedures. Development and ad-vancement of different types of gears, their design and manufacturing techniques were mainly motivated by their implementation in the specific and under-investigated application area – low-speed heavy-loaded drives for pipeline valves. The practical effect of the development is illustrated by examples.
Impact of backlash, manufacturing deviations and friction on the load sharing factor of planetary gear systems
Authors: Mihailidis Athanassios , Moisiadis Anastasios , Psarros Andreas
Published: August 2019

Techniques and software tools, which were recently introduced by the authors, allowed for effi-cient automatic generation of 3D gear flanks and selective meshing of the gears of a simple planetary gear system with backlash and manufacturing imperfections. Friction of the meshing gear flanks was neglected. First results were promising and showed that even in geometrically perfect planetary gear systems the torque distribution is not uniform. It was further verified that pitch errors have a strong impact on the load distri-bution and that a self-aligning sun gear significantly enhances the torque distribution among the planets. In the current study, the procedure mentioned above is enhanced in several aspects. First, the tooth friction is considered. The friction coefficient is assumed constant along the path of contact; however different values for the sun-planet and planet-ring gear mesh may be given to account for the different contact conditions. Second, deviations are generated between given limits in a stochastic way. This feature significantly reduces the time needed to setup a model. Third, the entire analysis procedure is further automated by extensively employing Python scripting, enabling the solution of successive snapshots in much shorter time. Besides the torque distribution among the planets, the mesh load factor Kγ and the deformation of the teeth, the planet bearing load is also shown.
Bidirectional modification of gears in the generalized theory of meshing
Authors: Alipiiev Ognyan
Published: August 2019

An important part of “Generalized theory”, developed by the author of this article, is the “bidirectional modification” of involute gears. The main point of the proposed modification is that together with the traditional “radial modification” of the basic rack, an additional “tangential modification” of the side profiles of the rack-cutters is introduced. As a result, the area of possible existence of involute gear drives in the generalized theory is considerably extended. Based on the bidirectional modification, a new classification of involute gears at their meshing with a rack cutter is proposed. The classification is characterized by a significant variety, which is composed of thirteen different types of gears: a zero gear; two radially modified gears; two tangentially modified gears and eight two-way modified gears. Based on the bidirectional modification in radial and tangential directions, a new classification of the involute gear drives is proposed. The classification is composed of sixteen different types of gear drives: a zero gear drive, three equally-modified gear drives; two balanced gear drives; five positive gear drives and five negative gear drives.
Task based conceptual design of a testing machine
Authors: Darbinyan Hrayr
Published: August 2019

A novel approach of task based conceptual design(TBCD) has been successfully used as direct guider and efficient developer of unique mechanical structures for many cases of mechanical design. Nearly a decade long efforts of elaboration of efficient every day usage formats for this method have been ended in convenient design pages suitable and applicable for revealing, describing, visualizing and managing the data necessary for organizing the design process from task definition to solutions satisfying original design tasks. The aim of current study is to show steps of a solution generation within frames of a single design cycle and extend this action over consecutive design cycles. Those steps are described from standpoint of general concept design method starting from key model and finished with final aggregation matrice as ultimate step of a single design cycle. Unified mathematical expressions are used for introduction and description of all worked out and developed components of conceptual design. The paper is arranged in a way to show gradual steps of conceptual design(CD) of a power transmission system – a pipe wrench life test machine.
Enhanced application limits for crossed helical gearboxes using new geometries for smaller sliding paths or smaller contact pressures
Authors: Boehme Christoph , Vill Dietmar , Tenberge Peter
Published: August 2019

Crossed-axis helical gear units are used as actuators and auxiliary drives in large quantities in automotive applications such as window regulators, windscreen wipers and seat adjusters. Commonly gear geometry of crossed helical gears is described with one pitch point. This article deals with an extended calculation method for worm gear units. The extended calculation method increases the range of solutions available for helical gears. In general, for a valid crossed helical gear pair, the rolling cylinders do not have to touch each other. In mass production of many similar gears, individual gears can be reused because they can be paired with other centre distances and ratios. This also allows the use of spur gears in combination with a worm, making manufacturing easier and more efficient. By selecting design parameters, for example the axis crossing angle or the helix angle of a gear, positive effects can be achieved on the tooth contact pressure, the overlap ratio, the sliding paths, the lubrication condition, the tooth stiffness and, to a limited extent, on the efficiency of the gearing. It can be shown that for involute helical gears, in addition to the known insensitivity of the transmission behaviour to centre distance deviations, there is also insensitivity to deviations of the axis crossing angle. This means that installation tolerances for crossed helical gearboxes can be determined more cost-effectively.
Design of a new-concept conical positive displacement slurry pump for continuous de-clogging
Authors: Vasileiou G. , Rogkas N. , Tsolakis S. , Spitas V. , Zalimidis P.
Published: August 2019

Slurry pumps are extensively used in the construction industry while positive displacement screw pumps are used in most mobile concrete pump applications. The aggregate size is known to significantly affect pump performance in terms of clogging. Large aggregates tend to be trapped against the stator-rotor interface, blocking the continuous and smooth operation of the screw pump. In order to avoid the development of excessive stress values able to damage the rotor-stator mechanism of the pump, the typical de-clogging mechanism deployed by most positive displacement screw slurry pumps includes reversing the rotation of the pump driving motor thus allowing the aggregates to be carried away with the mixture, so that the pump can soon resume its operation. This procedure causes frequent start-stops of the pump resulting in dis-continuation of the pumped mixture lasting a few seconds, that while being of little importance in most construction applications, can be of significance in applications requiring higher levels of accuracy and continuous mixture flow. In the context of this work, a novel concept of positive displacement screw slurry pump is presented, including a continuous de-clogging mechanism, without the need to reverse the rotation of the driving motor. This de-clogging operation is achieved through the modification of the geometry of both the rotor and stator introducing a conical form along the axial direction. This configuration of the rotor-stator, allows for small displacements along the axial direction, which in turn increases the size of the cavities facilitating the de-clogging of the pump. Variable pitch is also introduced to both the rotor and stator in order to ensure constant mass flow of the mixture throughout the length of the screw pump covering for the velocity increase as a result of the conical geometry. The axial movement of the rotor in relation to the fixed stator, is achieved through the elastic support of the rotor in the axial direction, that allows for small axial displacements, when stresses induced from trapped aggregates exceed the stiffness of the support. The proposed concept comprises a passive real-time de-clogging mechanism that greatly reduces pump idle time compared to the conventional mechanism described earlier, providing smoother operation and stable mass flow of the mixture.
Progress in the development of the cutting assemblies’ construction of working machines due to the reduction in power consumption
Authors: Bochat Andrzej , Zastempowski Marcin
Published: August 2019

New construction of the cutting assembly developed at the Institute of Mechatronics and Working Machines of the University of Technology and Life Sciences in Bydgoszcz. That new construction is covered by the patent protection. The conducted and presented results of the experimental tests have shown, that it is characterised by lower power consumption as compared to the classical construction, which is commonly used in working machines.
“Top-down” design methodology utilizing abstraction of mechanical interfaces
Authors: Goranov Peter , Georgieva Desislava , Todorova Elena
Published: August 2019

CAD systems are a key design tool. As technology evolves, they provide greater functionality and solve tasks that are more complex. Consequently, the question of their effective use is becoming increasingly important. The present paper discusses the "top-down" design method. During the initial stages of a design process, the geometric description of the components is missing or it is not complete which calls into question the use of CAD. The present work proposes a “top-down” methodology that includes CAD in the early stages of the design process. The discussed methodology takes advantage of the object-oriented approach. There is originated a hierarchical scheme of objects, each of which inherits the methods and attributes of its higher class. This allows design information to spread throughout the whole design process as well as its integration. With an implementation of this model, CAD models of an assembly and its parts can be created on the basis of the information available when the product concept is being developed. The geometric description recorded in the CAD model elaborates as the design project evolves. In this way, the formation of the CAD model goes hand in hand with the clarification of the product design.
Increasing the load carrying capacity of highly loaded gears by nitriding
Authors: Koenig Johannes , Hoja Stefanie , Tobie Thomas , Hoffmann Franz , Stahl Karsten
Published: August 2019

Nitriding is a common heat treatment process for highly loaded gears. A very hard compound layer with a thickness of a few microns is produced at the surface of the gear. In the underlying material areas, a diffusion layer with nitride precipitations is formed. This publication summarizes the state of knowledge of nitrided gears and gives an overview of the current state of research in the field of nitrided gears. It can be concluded that a high load carrying capacity of nitrided gears is dependent on an adequate NHD and a stable compound layer. However, due to the increased surface roughness after nitriding, the risk of micropitting increases, too. Therefore, it may be favourable to grind the gears after nitriding. Ground gears also can provide a high load carrying capacity, but it must be taken into account that the wear performance will decrease significantly, since it is mainly influenced by the compound layer. In addition, nitrided gears usually show a high sensitivity against local load peaks. Beyond creating a stable compound the layer, the realization of a sufficient nitriding hardness depth with larger gear sizes is a focus in the current field of research.