International Journal of Hydromechatronics (7 papers in press)
A Mathematical Analysis of a Hydraulic Binary Counter for Hydraulic Exoskeleton Actuation
by Rudolf Scheidl, Simon Mittböck
Abstract: Low weight and compactness are the main requirements on components for exoskeletons. For drives this means also high efficiency to keep energy storage and power transducing devices small. The digital hydraulic cylinder drive is an excellent candidate to become a superior technology for exoskeleton actuation. It requires several valves to control pressure in its many chambers. Solenoid valves suffer from the high weight and space of the solenoids. In this paper the hydraulic binary counter in a configuration with only passive elements is studied mathematically, since it can control a digital cylinder with much smaller space and weight than magnetically actuated valves. From qualitative considerations of the system equations supplemented by a numerical study it is shown that such a counter works properly. But it poses requirements on the control pressure range which are difficult to fulfil for digital cylinder drives with more than five chambers.
Keywords: Binary counter; digital hydraulics; digital cylinder drive; exoskeleton.
Heat transfer in flow through branching tubes.
by Antonio F. Miguel
Abstract: Allometric scaling relations for how branching tubes deliver fluid, are often based on the assumption of isothermal conditions which are not always fulfilled. This work reports on the sizes of branching tubes for fluid flow subjected to constant wall heat flux. This paper explores how the delivery of fluid and heat influences the optimal size of a tube and the optimal configuration of branching tubes for both laminar and turbulent flow. This study suggests an analytical basis for evaluation of optimal size of tubes that minimize the power loss associated with the pumping power and the heat transfer. The findings obtained in this study may have important implications for design of systems with minimum thermodynamic losses, and may contribute to explain the structure branching structure in the natural flow systems.
Keywords: optimal design; bifurcated tubes; heat flux; fluid flow; laminar and turbulent flows; minimum expenditure of power; Hess-Murray’s law; constructal law.
Ecological Friendly Functional Fluids and Lubricant Techniques in Machining Processes: A Review
by Deepak Sharma, Krishna Pandey
Abstract: Now a days cutting fluids or metalworking fluids are selecting on various factors like it should be environmental friendly, healthiness impact on activities of industry. Because of increasing consciousness in the society to the regulation of government imposed on industry to decrease the vital use of cutting fluids that are based on minerals. Metalworking fluids are the portion of a big family of lubricants. From last 200 years metalworking fluids have been widely used for cutting the metal. In the initial phase these fluids contain a simple oil which applied directly by using brushes to diminish the temperature of metals. Latest cutting fluids for cutting the metal are difficult mixture of a number of various constituents, each of which accomplishes exact functions. Various types of metalworking fluids are available in the market & the most communal category of theses fluids are water mixing fluids. In this article the methods of lubrication using during various operations of machining is presenting and also represent the various benefits of these functional fluids in machining with respect to surface finish, cutting force, temperature at the zone of cutting. The disadvantages and performance of various methods are discussed in terms of output variables & parameters of machining. From the various literature it can be reported that fluids of cutting which are made by the oil of vegetable, could be eco-friendly in machining mode with same in performance achieved after using the metalworking fluid which are based on mineral oil. The various lubrication methods are going to be finish because of less cooling rate. Now a days nanofluids are using for rapid cooling in various machining processes.
Keywords: Vegetable oils; Lubricants; Safety; Health; Eco-friendly; Nanofluids etc.
A method to perform prognostics in electro-hydraulic machines: the case of an independent metering controlled hydraulic crane
by Yuri Ghini, Andrea Vacca
Abstract: Remaining useful life (RUL) estimation is a topic that has gained more and more attention in the field of fluid power systems thanks to the tremendous potentials shown for improving safety and reduce production losses. However, many challenges related to RUL estimation are not solved yet, mainly connected to the definition of the health status of each component. A prognostic method based on a data-driven methodology for hydraulic systems is here proposed, to estimate the percentage of life already spent by the monitored components. The potentials of the methodology are shown considering the case of a truck-mounted hydraulic crane, for which a simulation model was available. An artificial neural network is designed along with a fuzzy logic system to attain the estimation goal on supply pump and hydraulic control valve. The simulation results show how this method could be used as reference for developing prognostic methods applicable to hydraulic machines.
Keywords: Prognostic; Remaining useful life; Artificial neural network; hydraulic machine.
Numerical Investigation on Influence of Focusing Gas Type on Liquid Micro-Jet Characteristics
by Rizwan Zahoor, Saša Bajt, Božidar Šarler
Abstract: Liquid micro-jets, produced from gas dynamic virtual nozzles (GDVNs), are used as sample carriers for interaction with X-ray beam in serial femtosecond crystallography (SFX).
A numerical investigation of the effect of the focusing gas type on the liquid micro-jet properties (its length and thickness) is presented. The study complements our previous research on the influence of operating conditions and the nozzle geometry on GDVN performance. The influence of helium, argon, carbon dioxide and nitrogen gases (at a fixed mass flow rate of 1.6
Keywords: gas dynamic virtual nozzle; focusing gas; micro-jet; compressible multiphase flow; finite volume method; volume of fluid; jetting; dripping.
Applications of shear thickening fluids: a review
by Tongfei Tian, Masami Nakano, Weihua Li
Abstract: Shear thickening fluids (STFs) are a type of Non-Newtonian fluids. In the equilibrium state, the STFs are in liquid-state. However, they become to solid-state under a sudden strike or impact. And when the strike or impact is removed, the STFs can turn back to their equilibrium properties. This paper provides a detailed review on relevant literature related to the applications with shear thickening fluids. It introduced the factors affecting shear-thickening behaviour including volume fraction, particle size, particle shape, carrier fluid viscosity, temperature and some other factors. The review has concisely demonstrated the compositions and rheological properties of shear thickening fluids. Particular emphasis is laid on the applications of shear thickening fluids such as body armours, smart structures, multifunctional materials, and other potential applications.
Keywords: shear thickening; fluids; applications; modelling; hydrocluster; nano partciles; effecting factors; liquid body armour; smart structure; multifunction.
Thermohydrodynamic lubrication model of a slipper in swashplate type axial piston machines--validation through experimental data
by Toshiharu Kazama
Abstract: A thermohydrodynamic lubrication (THL) model of hybrid (hydrostatic and hydrodynamic) thrust bearings, which is applicable to slippers of swashplate type axial piston pumps and motors, was validated by experimental results. The model consisted fundamentally of the generalized Reynolds equation, three-dimensional energy equation, and the heat conduction equation. The numerical calculation was performed in fluid film lubrication under the experimental conditions and the solutions were compared with the data. Reverse flow and oil mixing were considered in solving the energy equation. The comparison of the temperature distributions and centre clearances was made at supply pressures up to 35 MPa and rotational speeds up to 26.7^-1. The simulation showed good agreement with the experiment and the theoretical model was validated.
Keywords: tribology; fluid power systems; hydraulics; piston pumps and motors; slipper; hybrid bearings; thermohydrodynamic lubrication; simulation; experiment; validation.