High Mechanical Efficiency Research Articles

Automated synthesis of mechanisms with consideration of mechanical efficiency

Conceptual design of mechanisms is an early stage in the product design process, which has an essential effect on product innovation. However, existing approaches for automated synthesis of mechanisms are either inextensible to achieve the conceptual design of complex mechanisms or prone to a loss of optimal solutions with consideration of mechanical efficiency. This paper is devoted to a systematic weighted directed graph-based methodology for automated synthesis algorithm of mechanisms under mechanical efficiency consideration. After the motion element pair is proposed, a general functional representation model is then put forward to generate a motion functional graph. An exhaustive functional synthesis of motion element pair with K-highest mechanical efficiency algorithm is then proposed to produce solutions with K-highest mechanical efficiency. To curb the combinatorial explosion and evaluate optimal combinatorial solutions effectively, design constraint verification approach and design evaluation approach are also proposed. The conceptual design of new devices of jacking up system for offshore platform is given as an example, which demonstrates that the methodology is helpful to produce valuable mechanism solutions with high mechanical efficiency.

Computing the power flow and mechanical efficiency of in-hub bicycle transmissions

Purpose – The analysis of power flow and mechanical efficiency constitutes an important phase in the design and analysis of gear mechanisms. The aim of this paper is to present a systematic procedure for the determination of power flow and mechanical efficiency of epicyclic-type transmission mechanisms. Design/methodology/approach – A novel epicyclic-type in-hub bicycle transmission, which is a split-power type transmission composed of two transmission units and one differential unit, and its clutching sequence table are introduced first. By using the concept of fundamental circuits, the procedure for calculating the angular speed of each link, the ideal torque and power flow of each link, the actual torque and power flow of each link determined by considering gear-mesh losses, and the mechanical efficiency of the transmission mechanism is proposed in a simple, straightforward manner. The mechanical efficiency analysis of epicyclic-type gear mechanisms is largely simplified to overcome tedious and complicated processes of traditionally methods. Findings – An analysis of the mechanical efficiency of a four-speed automotive automatic transmission completed by Hsu and Huang is used as an example to illustrate the utility and validity of the proposed procedure. The power flow and mechanical efficiency of the presented 16-speed in-hub bicycle transmission are computed, and the power recirculation inside the transmission mechanism at each speed is detected based on the power flow diagram. When power recirculation occurs, the mechanical efficiency of the gear mechanism at the related speed reduces. The mechanical efficiency of this in-hub bicycle transmission is more than 96 percent for each speed. Such an in-hub bicycle transmission possesses reasonable kinematics and high mechanical efficiency and is therefore suitable for further embodiment design and detail design. Originality/value – The proposed approach is suitable for the mechanical efficiency analysis of all kinds of complicated epicyclic-type transmissions with any number of degrees of freedom and facilitates a less-tedious process of determining mechanical efficiency. It is a useful tool for mechanical engineering designers to evaluate the efficiency performance of the gear mechanism before actually fabricating a prototype as well as measuring the numerical data. It also helps engineering designers to cautiously select feasible gear mechanisms to avoid those configurations with power recirculation in the preliminary design stage which may significantly reduce the time for developing novel in-hub bicycle transmissions.

Inter-Individual Differences in the Initial 80 Minutes of Motor Learning of Handrim Wheelchair Propulsion

Handrim wheelchair propulsion is a cyclic skill that needs to be learned during rehabilitation. Yet it is unclear how inter-individual differences in motor learning impact wheelchair propulsion practice. Therefore we studied how early-identified motor learning styles in novice able-bodied participants impact the outcome of a low-intensity wheelchair-practice intervention. Over a 12-minute pre-test, 39 participants were split in two groups based on a relative 10% increase in mechanical efficiency. Following the pretest the participants continued one of four different low-intensity wheelchair practice interventions, yet all performed in the same trial-setup with a total 80-minute dose at 1.11 m/s at 0.20 W/kg. Instead of focusing on the effect of the different interventions, we focused on differences in motor learning between participants over the intervention. Twenty-six participants started the pretest with a lower mechanical efficiency and a less optimal propulsion technique, but showed a fast improvement during the first 12 minutes and this effect continued over the 80 minutes of practice. Eventually these initially fast improvers benefitted more from the given practice indicated by a better propulsion technique (like reduced frequency and increased stroke angle) and a higher mechanical efficiency. The initially fast improvers also had a higher intra-individual variability in the pre and posttest, which possibly relates to the increased motor learning of the initially fast improvers. Further exploration of the common characteristics of different types of learners will help to better tailor rehabilitation to the needs of wheelchair-dependent persons and improve our understanding of cyclic motor learning processes.

Imperfections in a two-dimensional hierarchical structure.

Hierarchical and fractal designs have been shown to yield high mechanical efficiency under a variety of loading conditions. Here a fractal frame is optimized for compressive loading in a two-dimensional space. We obtain the dependence of volume required for stability against loading for which the structure is optimized and a set of scaling relationships is found. We evaluate the dependence of the Hausdorff dimension of the optimal structure on the applied loading and establish the limit to which it tends under gentle loading. We then investigate the effect of a single imperfection in the structure through both analytical and simulational techniques. We find that a single asymmetric perturbation of beam thickness, increasing or decreasing the failure load of the individual beam, causes the same decrease in overall stability of the structure. A scaling relationship between imperfection magnitude and decrease in failure loading is obtained. We calculate theoretically the limit to which the single perturbation can effect the overall stability of higher generation frames.

A Numerical Analysis of the Interaction between the Piston Oil-Film and the Elastic Structure in an Internal Combustion Engine

The piston secondary motion significantly influences the tribologicalcharacteristics in an internal combustion engine, such as the piston slapphenomenon and the frictional power loss.An analytical treatment was conducted to investigate piston motion and a computer program was written to predict optimum designs for high mechanical efficiency. This paper focuses on an analysis of the piston dynamic response. By coupling FDM for thehydrodynamic pressure field with the FEM for the piston deformation, wenumerically approximate the lubricantstructure interaction in an internalcombustion engine.

Optimization of fractal space frames under gentle compressive load

The principle of hierarchical design is a prominent theme in many natural systems where mechanical efficiency is of importance. Here we establish the properties of a particular hierarchical structure, showing that high mechanical efficiency is found in certain loading regimes. We show that in the limit of gentle loading, the optimal hierarchical order increases without bound. We show that the scaling of material required for stability against loading to be withstood can be altered in a systematic, beneficial manner through manipulation of the number of structural length scales optimized upon. We establish the relationship between the Hausdorff dimension of the optimal structure and loading for which the structure is optimized. Practicalities of fabrication are discussed and examples of hierarchical frames of the same geometry constructed from solid beams are shown.

Nanostructured Nb reinforced NiTi shape memory alloy composite with high strength and narrow hysteresis

An in-situ nanostructured Nb reinforced NiTi shape-memory alloy composite was fabricated by mechanical reduction of an as-cast Nb-NiTi eutectic alloy. The composite exhibits large elastic strain, high strength, narrow hysteresis, and high mechanical energy storage density and efficiency during tensile cycling. In situ synchrotron high-energy X-ray diffraction revealed that these superior properties were attributed to the strong coupling between nanostructured Nb and NiTi matrix during deformation. Furthermore, this study offers a good understanding of the deformation behavior of the nanoscale reinforcement embedded in the metal matrix deformed by stress-induced phase transformation.

Mechanical Hybrid KERS Based on Toroidal Traction Drives: An Example of Smart Tribological Design to Improve Terrestrial Vehicle Performance

We analyse in terms of efficiency and traction capabilities a recently patented traction drive, referred to as the double roller full-toroidal variator (DFTV). We compare its performance with the single roller full-toroidal variator (SFTV) and the single roller half-toroidal variator (SHTV). Modeling of these variators involves challenging tribological issues; the traction and efficiency performances depend on tribological phenomena occurring at the interface between rollers and disks, where the lubricant undergoes very severe elastohydrodynamic lubrication regimes. Interestingly, the DFTV shows an improvement of the mechanical efficiency over a wide range of transmission ratios and in particular at the unit speed ratio as in such conditions in which the DFTV allows for zero-spin, thus strongly enhancing its traction capabilities. The very high mechanical efficiency and traction performances of the DFTV are exploited to investigate the performance of a flywheel-based Kinetic Energy Recovery System (KERS), where the efficiency of the variator plays an important role in determining the overall energy recovery performance. The energy boost capabilities and the round-trip efficiency are calculated for the three different variators considered in this study. The results suggest that the energy recovery potential of the mechanical KERS can be improved with a proper choice of the variator.

Simulation and experiment of the effect of clearance of impeller wear-rings on the performance of centrifugal pump

The effect of clearance of impeller wear-rings on the performance of a centrifugal pump was investigated numerically and experimentally. The whole flow field model including front and back shrouds of pump was designed so as to accurately calculate the head and efficiency of the centrifugal pump. Based on RNG k-ε turbulence model, three wear-rings schemes were established, and the effects of clearance of impeller wear-rings on the hydraulic efficiency and mechanical efficiency of the centrifugal pump was analyzed, chiefly from the turbulent kinetic energy, vorticity and radial force angles. According to the results, it can be drawn that the head and total efficiency of the centrifugal pump increase as the clearance value of wear-rings narrows. The following reasons may account for it: firstly, as the clearance value of wear-rings declines, the turbulent kinetic energy and energy dissipation decrease within the impeller, and the impact of secondary flow at the inlet of impeller on the mainstream weakens slowly, which leads to a lower hydraulic loss, thus a higher hydraulic efficiency; secondly, radial force decreases with the clearance value of wear-rings, so the eccentric whirl of centrifugal pump is dampened, which results in a lower mechanical loss and a higher mechanical efficiency; thirdly, the front shroud leakage diminishes with the clearance value of wear-rings, therefore, the volume loss is reduced and volume efficiency improved. Finally, the first wear-ring scheme of impeller is adopted after comprehensive comparison of these three wear-ring schemes, because its efficiency is highest and it satisfies the requirements of the engineering application.

Hierarchical space frames for high mechanical efficiency: Fabrication and mechanical testing

It has been demonstrated theoretically that under certain loading conditions hierarchical structures hold a distinct advantage in efficiency over more conventional designs. Here a particular hierarchical design is studied, and we show that the power-law scaling relations between loading parameters and volume of material required to make a stable structure can be varied systematically. Through computer simulation, we construct mechanism diagrams depicting likely failure modes for a given geometry, which give insight into the optimisation. Using rapid prototyping technologies, the same structure is fabricated and mechanical testing undertaken; the results are compared to theoretical and finite element models.

Theoretical and experimental performance analysis of a synchronal rotary multiphase pump with the inlet gas volume fractions of 0–0.9

A synchronal rotary multiphase pump is a novel positive-displacement pump which is structurally simple and has a higher mechanical efficiency. A mathematic model was developed to predict the working performance of the synchronal rotary multiphase pump when the inlet gas volume fraction of the gas–liquid working fluids varies in the range of 0–0.9. The pump working process was theoretically analyzed based on the calculated results of pressure, temperature and fluid mass in the working chamber. The experiment was conducted to test the steady state performance of the synchronal rotary multiphase pump prototype at different pressure differences and inlet gas volume fractions by using air–oil mixture as the working fluids. The measured results of temperature difference between the pump inlet and outlet, volume flow rate and shaft power consumption were shown to be in good agreement with the calculations. The calculated and experimental results showed that both the volume flow rate and the pump efficiency decreased with the increase of the pressure difference. When the inlet gas volume fraction increased from 0 up to 0.9, the volume flow rate and the pump efficiency were decreasing rapidly. It meant that the inlet gas volume fraction had a significant influence on the pump performance.

Non-chromatographic mercury speciation and determination in wine by new core–shell ion-imprinted sorbents

In this study new Hg(II) core–shell imprinted sorbents (Hg(II)-IIPs) were prepared and tested for speciation and determination of Hg in wine. The silica gel, chemically modified with 3-(trimethoxysilyl)propyl methacrylate (TSPM) was used as supporting material. The Hg(II)-imprinted polymer layer was grafted by copolymerization of methacrylic acid and trimethylolpropane trimethacrylate in the presence of Hg(II) complexes with two different chelating agents: 1-pyrrolidinedithiocarboxylic acid (P(PDC-Hg)/SiG) and 1-(2-thiazolylazo)-2-naphthol (P(TAN-Hg)/SiG). High selectivity and fast kinetics of processes of sorption and desorption for Hg(II) were found by using P(PDC-Hg)/SiG. Recovery experiments performed for selective determination of inorganic mercury in wines showed that the interfering organic matrix did not influence the extraction efficiency. Column solid phase extraction scheme was developed for the determination and speciation of Hg in wines. The limit of detection (LOD) achieved for inorganic mercury determination in wine samples is 0.02μgL1 (3σ), measured by CV AAS. The relative standard deviation varied in the range 6–11% at 0.05–2μgL1 Hg levels. The sorbents showed high mechanical and chemical stability and extraction efficiency has not changed after more than 50 sorption/desorption cycles.

Column solid phase extraction and determination of ultra-trace Au, Pd and Pt in environmental and geological samples

A new sorbent based on cysteine modified silica gel (SiG-cys) was prepared and studied for preconcentration and separation of noble metals Au(III), Pd(II), Pt(II), Pt(IV). Its extraction efficiency was examined by batch and column solid phase extraction procedures. Laboratory experiments performed showed that sorbent is characterized with high selectivity, permiting quantitative sorption (93–97%) of noble metals Au, Pd and Pt from acidic media 0.1–2molL−1 HCl and unsignificant sorption (less than 2%) for common base metals like Cu, Fe, Mn and Zn. The analytes retained on the sorbent are effectively eluted with 0.1molL−1 thiourea in 0.1molL−1 HCl and measured by ETAAS or ICP OES under optimal instrumental parameters. The sorbent showed high mechanical and chemical stability and extraction efficiency was not changed after 500 cycles of sorption/desorption. The sorbent was successfully applied in analyticals procedures for preconcentration and determination of Au, Pd and Pt in geological and soil samples. Detection limits (3σ criteria) achieved, depending on the instrumental methods used are: ETAAS (0.005μgL−1 for Au in river and sea water, 0.002μgg−1 for Au in copper ore and copper concentrate); ICP OES (0.03μgL−1 for Pd and 0.06μgL−1 for Pt in river and sea water, 0.006μgg−1 for Pd in copper ore and copper concentrate and 0.002μgg−1 for soluble Pt in soil). The accuracy of the procedures developed was confirmed by added/found method for sea and river water; by the analysis of national certified materials (copper ore and copper concentrate for Au and Pd) and by determination of the sum of soluble Pt(II)+Pt(IV) in spiked soil samples.

Theoretical and experimental study of a piezoelectric flapping wing rotor for micro aerial vehicle

In this paper, investigation was made into the design, theoretical study, numerical modelling and experiment of a novel flapping wing rotor for micro aerial vehicles (MAV). Attention was firstly focused on the design of a simple, reliable and lightweight configuration of the flapping wing structure and the rotor. The design is to meet the challenging demand for high mechanical and power efficiency and vertical take-off and landing (VTOL) capability. To demonstrate the feasibility and effectiveness of the innovative design, a piezoelectric actuated flapping wing rotor model was manufactured and tested. Effort was also made to evaluate the design and analyze the dynamic behavior of the model by using finite element (FE) method. The unsteady aerodynamic force was modeled by theoretical method and CFD numerical simulation. To validate the theoretical and numerical analysis, experiment of the test model was carried out. In the experiment, the total force produced by the flapping wing rotor including the aerodynamic and inertia forces has been measured through a data process approach. The comparison shows a very good agreement between the experimental and analysis results. Improvement of the design can be made by using the methods.

Mechanical stability assessment of novel orthodontic mini-implant designs: Part 2

To assess the mechanical stability of a newly revised orthodontic mini-implant design (N2) compared with a design introduced in Part 1 of the study (N1) and the most widely-used commercially-available design (CA). To evaluate the mean buccal bone thickness of maxillary and mandibular posterior teeth using cone-beam computed tomography (CBCT). From the CBCT scans of 20 patients, six tomographic cross-sections were generated for each tooth. Buccal bone thickness was measured from the most convex point on the bone to the root surface. CA (1.5 mm in diameter and 6 mm in length), N1, and N2 (shorter and narrower than N1) were inserted in simulated bone with cortical and trabecular bone layers. Mechanical stability was compared in vitro through torque and lateral displacement tests. The bone thickness ranged from 2.26 to 3.88 mm. Maximum insertion torque was decreased significantly in N2 compared to N1. However, force levels for all displacement distances and torque ratio were the highest in N2, followed by N1 and CA (α = .05). Both torque and lateral displacement tests highlighted the enhanced stability of N2 compared with CA. Design revisions to N1 effectively mitigated N1's high insertion torque and thus potentially reduced microdamage to the surrounding bone. The N2 design is promising as evidenced by enhanced stability and high mechanical efficiency. Moreover, N2 is not limited to placement in interradicular spaces and has the capacity to be placed in the buccal bone superficial to the root surface with diminished risk of endangering nearby anatomic structures during placement and treatment.

A novel revolving vane compressor with a fixed-vane

This paper presents design improvements of a Revolving Vane (RV) compressor which significantly reduce the frictional losses. The original RV compressor has a vane that swivels during the operation. Though in general, the frictional losses of the RV compressor are significantly lower than most currently available rotary compressors, this swivel vane design has a disadvantage of relatively high vane side friction loss. The latter is caused by a high vane-side and slot contact force due to a high gas pressure differential force across the vane. In this paper, a new design concept has been introduced to totally eliminate the vane side friction loss caused by the gas pressure differential force across the vane. This is achieved by rigidly fixes the vane onto the rotor or the cylinder. This new design yielded two possible variants, each reduces the frictional losses by 18% and 41% and improves the mechanical efficiency from 93% to 94% and 96% respectively. In this paper, details analysis on the new design that leads to the improvement in performance are presented and shown. The analysis also reveals that the design with the highest mechanical efficiency comes with a small price of a higher instantaneous peak torque requirement.

Frictional Loss Studies and Experimental Performance of a New Synchronal Rotary Multiphase Pump

A new synchronal rotary multiphase pump (SRMP) is presented, which is geometrically simple and easy to manufacture. With the rotary cylinder, the frictional losses between the major components of the SRMP are minimized. Its structural design and working principles are introduced. The mathematic models of the frictional losses at various friction-couplings are formulated. Calculations on the frictional losses and mechanical efficiency are performed for a SRMP prototype, too. Experimental works on the prototype in which crude oil is used as working fluids are conducted to validate the functionality of the SRMP and the established models. The calculated results show that the frictional losses in the SRMP are mainly produced by the friction from bearings and seals. The frictional losses caused by the other part of components occupy less than 13% of the total frictional losses. In addition, the theoretical analyses of the various shaft speeds and basic geometrical parameters reveal that the cylinder rotary inertia exercises a negative effect on the friction at the sliding vane sides. Lower shaft speed and smaller eccentricity-cylinder radius ratio are helpful to reduce this effect. In the experiment, the SRMP is operated at shaft speeds of 400, 600 and 800 rpm respectively. The pressure differences are arranged within 0–2.4MPa. The measured values of the shaft consumption powers are shown to be in good agreement with the calculations. These results confirm that the SRMP is suitable for multiphase transportation and has a higher mechanical efficiency.

Application of Large Gurney Flaps on Low Reynolds Number Fan Blades

On the basis of a semi-empirical model, large Gurney flaps of 10%, 20%, and 30% of the fan blade chord length were tested in a specially designed ventilation fan facility. At the highest volumetric flowrates tested, the flapped blades all produced higher pressures than the baseline nonflapped case. When proper accounting was made of fan rotational speed, all flapped blades produced consistently higher dimensionless pressures, with the 30% flap producing the highest pressures at large volumetric flowrates. Based on the assumption that sound power varies with the sixth power of fan rotation speed, it was shown that the sound pressure level could be reduced by nearly 4 dB. All flapped configurations produced higher mechanical efficiency than the baseline case but the mass of the flap relative to that of the blade emerged as an important parameter. A 10% flap, whose mass was negligible relative to the blade, produced the largest increase of 18% in static efficiency. Further research will focus on testing the flaps over the entire operational range, as well as on redesigning stiffer and lighter Gurney flaps. The introduction of three-dimensionality such as spanwise spaced holes, slits, or serrations that have previously been used to reduce airfoil drag will also be considered.

S113014 円すいローラねじ機構の概要とローラ支持構造 : 円すいローラねじ機構の研究([S11301]機械システムの要素技術と設計(1))

In this paper, we first introduce the outline of the conic roller screw mechanism, a new device for converting rotary motion to linear motion, and explain on its roller supporting structure. The new mechanism achieves high durability by reducing Hertzian contact stress on rolling contact by bringing roller into line contact with screw shaft, and also maintains high mechanical efficiency by minimizing partial slip on the contact line. Each of three rollers that contact with screw shaft is supported by holder through tapered roller bearings, and they are permitted to tilt. The load center of tapered roller bearing is located to the proper position. This roller supporting structure is considered for long life of the tapered roller bearing. The method of mechanical efficiency estimation for the roller supporting structure is also explained, and results of the estimation varying coefficients of rolling friction are showed. It's confirmed that the roller supporting structure can hold good mechanical efficiency.

Skill acquisition of manual wheelchair propulsion: initial motor learning

Changes in propulsion technique due to motor learning might account for a higher mechanical efficiency (ME, the ratio of internal power over external power). The changes in ME and propulsion technique were studied in a learning experiment, three times a week for eight minutes, with nine able-bodied subjects, simulating early rehabilitation. Instrumented wheels measured three-dimensional forces and torques on the handrim. During practice peak torques were reduced, work per cycle increased, while push frequency decreased, at a stable power output and speed of the treadmill. Over the three weeks of practice propulsion technique kept changing in combination with an increase of ME. Results suggest skill acquisition because of motor learning. The rise in ME seems logically related to propulsion technique, but is not yet fully understood. More insight in motor learning and skill acquisition will contribute to understanding and optimizing rehabilitation strategies in the light of wheelchair provision in early rehabilitation.