Validity and Reliability of Hydraulic-Analogy Bioenergetic Models in Sprint Roller Skiing

Purpose: To develop a method for individual parameter estimation of four hydraulic-analogy bioenergetic models and to assess the validity and reliability of these models’ prediction of aerobic and anaerobic metabolic utilization during sprint roller-skiing.Methods: Eleven elite cross-country skiers performed two treadmill roller-skiing time trials on a course consisting of three flat sections interspersed by two uphill sections. Aerobic and anaerobic metabolic rate contributions, external power output, and gross efficiency were determined. Two versions each (fixed or free maximal aerobic metabolic rate) of a two-tank hydraulic-analogy bioenergetic model (2TM-fixed and 2TM-free) and a more complex three-tank model (3TM-fixed and 3TM-free) were programmed into MATLAB. The aerobic metabolic rate (MRae) and the accumulated anaerobic energy expenditure (Ean,acc) from the first time trial (STT1) together with a gray-box model in MATLAB, were used to estimate the bioenergetic model parameters. Validity was assessed by simulation of each bioenergetic model using the estimated parameters from STT1 and the total metabolic rate (MRtot) in the second time trial (STT2).Results: The validity and reliability of the parameter estimation method based on STT1 revealed valid and reliable overall results for all the four models vs. measurement data with the 2TM-free model being the most valid. Mean differences in model-vs.-measured MRae ranged between -0.005 and 0.016 kW with typical errors between 0.002 and 0.009 kW. Mean differences in Ean,acc at STT termination ranged between −4.3 and 0.5 kJ and typical errors were between 0.6 and 2.1 kJ. The root mean square error (RMSE) for 2TM-free on the instantaneous STT1 data was 0.05 kW for MRae and 0.61 kJ for Ean,acc, which was lower than the other three models (all P < 0.05). Compared to the results in STT1, the validity and reliability of each individually adapted bioenergetic model was worse during STT2 with models underpredicting MRae and overpredicting Ean,acc vs. measurement data (all P < 0.05). Moreover, the 2TM-free had the lowest RMSEs during STT2.Conclusion: The 2TM-free provided the highest validity and reliability in MRae and Ean,acc for both the parameter estimation in STT1 and the model validity and reliability evaluation in the succeeding STT2.

Revival of water table experiment in fluid mechanics courses, part II

In an effort to find a simple and efficient method for observing and predicting compressible flows in an instructional environment, we revisit the classical hydraulic analogy. The focus is made on using a water table apparatus to visualize the formation of oblique surface waves in a flow around a wedge. These waves are analogous to the oblique shock waves seen in a compressible flow. A mathematical derivation of this analogy is presented together with water table experiment data collected by graduate students. The comparison between the predicted values and measured values is made and shows a remarkable correlation between the two for simulated Mach numbers.

OSCILLATION DAMPER CALCULATION BASED ON THE ELECTRO HYDRAULIC ANALOGY

The method of the synthesis and the pressure fluctuations damping calculation based on the electro-hydraulic analogy is proposed. The mathematical model describing the processes of unsteady fluid flow through the device is developed. Using the composed transfer function and its approximation, the oscillation damper parameters identification to reduce the outlet pressure pulsations in the triplex plunger pump is carried out.

Aerodynamical Performance Decay Due to Fouling and Erosion in Axial Compressor for GT Aeroengines

The ingestion of solid abrasive particles and/or foulants causes erosion of the compressor blades, resulting in a considerable reduction in the performance and working life of aviation/heavy duty GT and an increase in fuel consumption. The geometry variation at the Leading Edge (L.E. blunting) and Trailing Edge (T.E. thickness reduction), together with the general increase of airfoil surface roughness, depends on the characteristics of the incident particles, the geometry and the materials of the blade cascade, the dynamic parameters of the particles and on the type of impact. In order to rectify this degradation in performance, it is therefore necessary to re-profile the blades with machining that is highly critical for the performance of the engine, the life of the compressor blades and for maintenance costs. In order to determine an optimum and cost effective process of reprofiling, a series of tests reproducing the corresponding models of flow have been carried out on the Water Table Test Bench using Lamb’s hydraulic analogy relative to profiles of the VII and VIII stage HP of the compressor of the GT CF6-50 (G.E. Co.). The tests were carried out both on the isolated airfoil profile and on the blade cascade and both in the original conditions, at varied geometry (because of erosion and/or fouling) and after re-profiling. The trajectories of the particles have been visualised in several ways (like a false color photographic procedure), confirming results reported by various authors related to the model of impact and erosion. Particularly in the case of the dust aspiration during the arrival phase on the deck of an aircraft carrier. The test results have been discussed and compared with those available in scientific literature.

Learning benefits by integrating design, manufacturing, and testing in a course for compressible flow visualizations

Although engineering is by nature an applied and interdisciplinary field, courses in engineering can lead even the best students to develop knowledge that is disconnected from other related fields and from conditions of application. This paper describes an innovative undergraduate course that integrated the theory of shock waves, computational modeling, experimental testing, and science of sustainable manufacturing. The course supported better visualization of mechanical and aerospace engineering phenomena, such as shock waves in supersonic gas flows, by utilizing the hydraulic analogy of shallow water and a simple water table. Airfoil design and manufacture were integrated through aerospace and manufacturing theory and application. For the first course offering, student learning was assessed with regard to their views of engineering, learning experience, and transfer of learning. The course proved to increase self-efficacy as engineers, as well as their self-reported confidence in working comfortably on multi-disciplinary teams. Furthermore, scenario-based assessments confirmed that the students were able to integrate aerospace and manufacturing theory and application within new scenarios.

Revival of water table experiments in fluid mechanics courses, part I

In a classroom environment, after a comprehensive theoretical discussion of compressible flows, it is beneficial to conduct a visual experiment in which students can observe these flows and some of the features associated with them. Experimental study of compressible fluid dynamics is associated with high equipment costs; therefore, conducting an experiment is not feasible for some colleges. This article describes an experiment implemented at Manhattan College upper division and graduate fluid dynamics courses at a relatively low cost. In the experiment, a water table hydraulic analogy was used. Theoretical considerations of this analogy are explained in this article. An area–velocity relation was used to study the Mach number at the exit of a Laval nozzle. The theory and measurement came within 10% of each other, which is sufficient for a teaching demonstration. This exercise can be conducted in two class sessions: (1) discussing the theoretical considerations and (2) performing the experiment and analyzing data. The overall experience is a good way to help students understand some of the compressible flow features, and further promote their interest in fluid mechanics.

Concurrent Venous Stenting of the Transverse and Occipito-Marginal Sinuses: An Analogy with Parallel Hemodynamic Circuits

ABSTRACTNonthrombotic intracranial venous occlusive disease (NIVOD) has been implicated in the pathophysiology of idiopathic intracranial hypertension (IIH) and various non-IIH headache syndromes. Endovascular stenting of stenotic, dominant transverse sinuses (TSs) may reduce trans-stenosis pressure gradients, decrease intracranial pressure, and alleviate symptoms in a subset of NIVOD patients. We present a case in which concurrent stenting of the occipito-marginal sinus obliterated the residual trans-stenosis pressure gradient across an initially stented dominant TS. We hypothesize that this observation may be explained using an electric-hydraulic analogy, and that this patient’s dominant TS and occipito-marginal sinus may be modeled as a parallel hemodynamic circuit. Neurointerventionalists should be aware of parallel hemodynamic drainage patterns and consider manometry and possibly additional stenting of stenotic, parallel venous outflow pathways if TS stenting alone fails to obliterate the trans-stenosis pressure gradient.

Air Puff System Fundamentals for Reproducible Eyeblink Conditioning Research

Air puff systems are at once trivially straightforward and dauntingly complex. On the one hand, they are little but a pressure source, valve, and tube connected together. On the other, the air passing through them is a compressible medium, expanding approximately adiabatically while travelling at high velocity through a compliant tube, and exiting as a turbulent jet with velocity peak and profile varying non-linearly in its near-field. This complexity puts precise mathematical prediction of puff properties out of reach of most labs. There are, however, a number of phenomena fundamental to air puff system design that are worth understanding to a first order of approximation, or at least qualitatively. Using a simplified, “electronic–hydraulic analogy” model, this paper discusses these phenomena in just enough depth for the reader to confidently specify parts for an air puff delivery system, to measure its key parameters, and/or to describe a given system unambiguously in publications, thus maximizing reproducibility.