Mechanical Energy Loss Research Articles

Determination of Mechanical Energy Loss in Steady Flow by Means of Dissipation Power

Abstract When systems of simple geometry like pipes or regular channels are considered, the mechanical energy loss of the fluid flow can be expressed by local and longitudinal empirical energy loss coefficients. However, in the case of large spatially distributed objects, there are no simple approaches to this task. In practice, general recommendations addressing different types of objects are used, but they usually provide very coarse estimates of energy loss. In this work, a new methodology for determination of mechanical energy loss in steady flowis proposed. This methodology is based on the observation that the magnitude of the power of energy dissipation in turbulent flow can be determined using the averaged flow velocity and turbulent viscosity coefficient. To highlight this possibility, an analysis of the magnitudes of the power of the main and fluctuating components of turbulent flow is presented. The correctness of the method is verified using an example of laminar and turbulent flows in a circular pipe. The results obtained show clearly that the proposed methodology can be used for mechanical energy loss determination in flow objects. This methodology can be used as a basis for mechanical energy loss determination in different types of flow objects.

Unconfined lock-exchange gravity currents with variable lock width: laboratory experiments and shallow-water simulations

ABSTRACTThe dynamics of unconfined gravity currents generated by a lock-exchange with different lock widths is considered. The gravity currents were generated by density differences caused by a salinity gradient and were realized both numerically and experimentally. Several runs were carried out in order to study the role played by the lock width in the current dynamics. Numerical simulations were performed with a new single-layer, 2D, shallow-water model, which accounts for the dilution of the gravity current due to the entrained ambient fluid. By the comparison between experimental and numerical results, the relevant role played by the entrainment in the propagation velocity of the front emerges, mainly for the cases with a narrow lock. The effect of the lock width on the current dynamics is also highlighted: the lock chocks the flow causing a localized loss of mechanical energy and a consequent deceleration of the flow. Results show that the smaller is the lock, the larger is the loss of energy.

Effects of bifurcation-specific and conventional stents on coronary bifurcation flow. An experimental and numerical study

Our paper builds on existing research into conventional bare metal stents in order to assess new devices specifically designed for coronary bifurcation angioplasty. The first aim is to validate the numerical model against data from in vitro experiments on stented coronary phantoms. A surface mesh was built in accordance with micro-computed tomography images obtained from coronary stents implanted in silicone models and used for numerical analysis. Computational simulations for steady and unsteady cases generally agreed with their experimental counterparts. A second objective is to compare the hemodynamic performance of one of these new devices (Stentys) to that of conventional devices and stenting techniques in a simplified coronary bifurcation model. Four different coronary bifurcation stenting techniques were analyzed. We have focused on factors contributing to restenosis, such as wall shear stress (WSS), oscillatory shear index (OSI), pressure loss, and local normalized helicity (LNH). It was found that bifurcation-specific stents implanted in the side branch led to increased malapposition. This effect has proved to be more important than stent specific design characteristics such as strut size (different for conventional and Stentys stent). This conclusion is confirmed by means of drop in pressure and mechanical energy loss rate calculation; for the latter, the increase ranged from 9% to 17%, depending on the stenting technique, when dedicated stents were implanted in the side branch. The behavior patterns presented in this study should be double-checked against those obtained in more realistic geometries.

Determining the optimal pre-tightening force of a sandwich transducer by measuring resonance resistance

The pre-tightening force applied on a sandwich transducer plays a key role on the transducer’s vibration performance. Typically, a transducer’s optimal pre-tightening force is not known during assembly. The objective of this study is to examine a method for determining the optimal pre-tightening force for a sandwich transducer. We propose that the transducer’s optimal pre-tightening force can be measured indirectly through the resonance resistance. Resonance resistance is an equivalent electric parameter which reflects the transducer’s mechanical energy loss, and can be measured easily using an impedance analyzer. The relationship between resonance resistance and the pre-tightening force is analyzed both theoretically and experimentally. Measurement of resonance resistance based on transducer’s admittance circle is studied. Experiments involving this relationship are conducted. Results indicate that the front-end surface amplitude of the sandwich transducer reaches a maximum when the pre-tightening force is optimal, the resonance resistance tends to a minimum, but with a small offset. This indicates that the minimum value of resonance resistance corresponds closely to the highest vibration amplitude of the transducer, but not exactly. Thus, by determining the minimum resonance resistance, the optimal pre-tightening force can be determined.

An exploration of the influence of diagonal dissociation and moderate changes in speed on locomotor parameters in trotting horses.

Background. Although the trot is described as a diagonal gait, contacts of the diagonal pairs of hooves are not usually perfectly synchronized. Although subtle, the timing dissociation between contacts of each diagonal pair could have consequences on gait dynamics and provide insight into the functional strategies employed. This study explores the mechanical effects of different diagonal dissociation patterns when speed was matched between individuals and how these effects link to moderate, natural changes in trotting speed. We anticipate that hind-first diagonal dissociation at contact increases with speed, diagonal dissociation at contact can reduce collision-based energy losses and predominant dissociation patterns will be evident within individuals.Methods. The study was performed in two parts: in the first 17 horses performed speed-matched trotting trials and in the second, five horses each performed 10 trotting trials that represented a range of individually preferred speeds. Standard motion capture provided kinematic data that were synchronized with ground reaction force (GRF) data from a series of force plates. The data were analyzed further to determine temporal, speed, GRF, postural, mass distribution, moment, and collision dynamics parameters.Results. Fore-first, synchronous, and hind-first dissociations were found in horses trotting at (3.3 m/s ± 10%). In these speed-matched trials, mean centre of pressure (COP) cranio-caudal location differed significantly between the three dissociation categories. The COP moved systematically and significantly (P = .001) from being more caudally located in hind-first dissociation (mean location = 0.41 ± 0.04) through synchronous (0.36 ± 0.02) to a more cranial location in fore-first dissociation (0.32 ± 0.02). Dissociation patterns were found to influence function, posture, and balance parameters. Over a moderate speed range, peak vertical forelimb GRF had a strong relationship with dissociation time (R = .594; P < .01) and speed (R = .789; P < .01), but peak vertical hindlimb GRF did not have a significant relationship with dissociation time (R = .085; P > 0.05) or speed (R = .223; P = .023).Discussion. The results indicate that at moderate speeds individual horses use dissociation patterns that allow them to maintain trunk pitch stability through management of the cranio-caudal location of the COP. During the hoof-ground collisions, reduced mechanical energy losses were found in hind-first dissociations compared to fully synchronous contacts. As speed increased, only forelimb vertical peak force increased so dissociations tended towards hind-first, which shifted the net COP caudally and balanced trunk pitching moments.

Theoretical analysis and numerical simulation of mechanical energy loss and wall resistance of steady open channel flow

The mechanical energy loss and the wall resistance are very important in practical engineering. These problems are investigated through theoretical analysis and numerical simulation in this paper. The results are as follows. (1) A new mechanical energy equation for the total flow is obtained, and a general formula for the calculation of the mechanical energy loss is proposed. (2) The general relationship between the wall resistance and the mechanical energy loss for the steady channel flow is obtained, the simplified form of which for the steady uniform channel flow is in consistent with the formula used in Hydraulics deduced by π theorem and dimensional analysis. (3) The steady channel flow over a backward facing step with a small expansion ratio is numerically simulated, and the mechanical energy loss, the wall resistance as well as the relationship between the wall resistance and the mechanical energy loss are calculated and analyzed.

Mechanical Strength and Energy Losses Optimization of Somaloy 3P 700-Based Components

The effect of processing parameters on the properties of a soft magnetic composite prepared from Somaloy 3P 700 was investigated using a Box–Behnken design. The pressing pressure, heat treatment temperature, and soaking time were considered relevant factors to predict the transverse rupture strength (TRS) and total energy losses under the measurement conditions of maximum induction of 1 T and frequencies of 60, 500, and 1000 Hz. The highest forecasted TRS (82.7 ±13.5 MPa) was achieved with the combination of low pressing pressure (700 MPa) and high temperature of heat treatment (550 °C) for a long soaking time (15 min) under a long heat treatment cycle. On the other hand, the optimal parameters regarding the total losses presented a dependence of the operating frequency, especially concerning the heat treatment temperature due to the effect of this process parameter on the electrical resistivity.

Development of a Moving Body Type Wave Power Generator using Wave Horizontal Motions and Hydraulic Experiment for Electric Power Production

파의 왕복운동을 ì§€ì†ì ì¸ 일방향 íšŒì „ìš´ë™ìœ¼ë¡œ ìœ ë„í•˜ì—¬ ë°œì „ê¸°ì˜ 가동에 있어 ê¸°ê³„ì ì¸ 손실 에너지를 감소시켜 ë°œì „íš¨ìœ¨ì„ 극대화시킬 수 있는 파의 수평왕복운동을 ì§ì ‘ 이용하는 가동물체형 íŒŒë ¥ë°œì „ìž¥ì¹˜ê°€ 개발되었다. ê·¸ë¦¬ê³ ì‹¤ì œ ì „ë ¥ìƒì‚°ì— 관한 수리실험이 ìˆ˜í–‰ë˜ì—ˆê³ ê·¸ 결과가 í† ì˜ë˜ì—ˆë‹¤. 수리실험에서 ë¶€ë ¥ 탱크의 형상에 따른 ë°œì „ìž¥ì¹˜ì˜ ë°œì „íš¨ìœ¨ì€ íŒŒë ¥íŒì˜ 무게를 충분히 지탱하는 직경 9cm의 ê³ ì •ì‹ ë¶€ë ¥ 탱크가 í‰ê· ë°œì „íš¨ìœ¨ 14.6%로 좋은 결과를 보였으며 효율이 좋을 것으로 기대되었던 ë¶€ë ¥ 탱크가 ìžìœ ë¡œì´ 승강하는 경우는 ë°œì „íš¨ìœ¨ì´ 8.5%로 좋지 못한 결과를 보였다. ê·¸ë¦¬ê³ ì—¬ëŸ¬ 파랑조건에 따른 직경 9cm의 ê³ ì •ì‹ ë¶€ë ¥ 탱크형 ë°œì „ëª¨í˜•ì˜ í‰ê· ë°œì „íš¨ìœ¨ì´ 수심 90 cm에서 기어비 2단 3.9%, 3단 4.9%, 4단 4.9%, 5단 12%, 6단 10.0%, 7단 3.1%, ê·¸ë¦¬ê³ 8단 3.0%를 나타냈으며, 수심 80 cm의 기어비 5단에서 15%의 ë°œì „íš¨ìœ¨ì´ 계측되었다. 따라서 이 íŒŒë ¥ë°œì „ìž¥ì¹˜ëŠ” 수심 80~90 cm의 기어비 5단에서 ë¹„êµì  높은 13.5%의 í‰ê· ë°œì „íš¨ìœ¨ì„ 얻을 수 있었다. 핵심용어: íŒŒë ¥ë°œì „ìž¥ì¹˜, 가동물체형, 수리실험, 파의 수평운동, 일방향 íšŒì „ìš´ë™

Impact of operational and geometrical factors on ejector performance with a bypass

The mechanical energy loss during the mixing process and the momentum waste in the diffuser are the main reasons for the relative low entrainment ratio. In the present study, the ejector with bypass is adopted to utilize the momentum in the diffuser, hoping to increase the entrainment ratio. The influence of operational and bypass geometrical factors on the entrained capacity is analyzed through CFD method. The results show that there is always an optimal location (around the place where the lowest pressure is) for the maximum entrainment ratio, and it moves downstream as the motive or induced pressure increases. Meanwhile, the increment enlarges as the motive pressure increases, and the improvement would enlarge from 10.7% to 32.8% when the motive pressure increases from 0.3 MPa to 0.4 MPa. Moreover, it is still an effective method to improve ejector performance by enlarging bypass inlet area when the bypass is installed in the optimal location. The same conclusion could be drawn when the inclination angle decreases, especially when the motive pressure is greater than the design value. Compared with the ejector without bypass, the maximum improvement could be high up to 48.7% while the inlet area is 4 mm × 8 mm and angle is 15°.

Simulation of engagement control in automotive dry-clutch and temperature field analysis through finite element model

The tribological contact under sliding condition in the clutch facing surfaces during the engagement manoeuvre is strongly affected by heat transfer occurring in the system. The frictional forces acting on the contact surfaces produce mechanical energy losses which are converted in heat with ensuing temperature increase. Reports about the temperature rise after repeated clutch engagements prove the occurrence of interface temperature peaks as high as 300 °C. Unfortunately, only few papers address their focus towards experiments and their outcomes about the influence of temperature and the other operating parameters on the frictional behaviour of the clutch facing materials.In this paper, the Authors mainly explored the frictional behaviour modification for thermal level higher than 250–300 °C, whose effect is a sharp decline of the friction coefficient related to the decomposition of the phenol resin of the facings. Moreover, this phenomenon induces not expected transition from dry friction to mixed dry-lubricated friction which explains the reasons of the friction coefficient drop. The temperature affects also the cushion spring load-deflection characteristic and the ensuing transmitted clutch torque. Thus, an original frictional map has been implemented in a control algorithm to estimate the heat flux during vehicle launch and up-shift manoeuvres. The results of the longitudinal vehicle dynamics has been used in a FEA to predict the temperature field during repeated clutch engagement on the contact surfaces. The simulation results prove that during each engagement the interface temperature increases of 30–35 °C. This means that after only few repeated clutch engagements the temperature field could reach values near the critical point of 300 °C. In such a way, this paper aims at providing useful references to control engineers in order to improve the dry-clutch transmissions performances.

Tribological Research of Properties of Heat – Treated Cast Irons with Globular Graphite

The contribution deals with the evaluation of tribological properties of materials: isothermally heat-treated cast iron ADI, heat-treated cast iron with globular graphite HTDI with sorbitic structure of the basic metal matrix and heat-treated steel C45. The aim of the research is to gain another knowledge for the application of materials in the condition where the loss of mechanical energy and the loss of material caused by parts wear are being appeared.

Numerical simulation of turbulent flow behind sluice gate under submerged discharge conditions

The turbulent flow discharging under a sluice gate is one kind of typical flows with complicated boundaries in hydraulic and hydroelectric engineering, and the characteristics of its flow field and flow evolution are important in engineering hydraulics. Although there were many studies in this regard, which mainly focus on the discharge capacity, the local scour and the mean flow field, some issues remain to be further investigated, for example, the variation of the mechanical energy during the scouring process, and the adjustment of the unsteady turbulent flow after the local scour with the downstream steady uniform flow. In this paper, the turbulent flow behind a sluice gate is divided into a rapidly varied flow region and a gradually varied flow region, and the above problems are investigated by theoretical analysis and numerical simulation. The main conclusions are as follows: (1) In the discharging process of the turbulent flow under a sluice gate, the river bed would be scoured continuously and the water–air interface is adjusted accordingly, which leads to a decrease of the mechanical energy of the total flow in the rapidly varied flow region, and the mechanical energy loss would also decrease with the increase of the time, yet the variation of the flow discharge under the sluice gate is very small. (2) In the link between the rapidly varied flow and the uniform flow downstream, the mean wall shear stress and the coefficient for the mechanical energy loss would decrease in the longitudinal direction, the decay of the turbulent kinetic energy near the free surface is much more significant than that near the bed in the longitudinal direction, and the mean turbulent kinetic energy in the section would decrease in the longitudinal direction and the decreasing rate is smaller than that of the mean wall shear stress.

Mechanical Energy Losses in Horizontal, Inclined and Vertical Intermittent Two-Phase Flows with Drag-Reducing Polymer

Mechanical energy loss is usually considered to be generated from frictional pressure drop in pipe flow. An analytical equation was derived from hydrodynamic model to estimate the mechanical energy loss in intermittent two-phase flow. This equation indicates that only part of energy loss is generated from frictional pressure drop in inclined and vertical intermittent flows. Experiments were conducted in a gas–liquid pipeline to investigate the different effects of drag-reducing polymer (DRP) on the mechanical energy losses of turbulent intermittent flows in pipes. The inside diameter of the pipeline is 0.04 m. Whether or not DRP is used, the results show that the mechanical energy loss is highest in the vertical case and is lowest in the horizontal case among horizontal, inclined, and vertical intermittent flows. The energy loss reduction induced by DRP in horizontal intermittent flow is greater than the one in either vertical or inclined intermittent flow.

Nanoscale lubrication of ionic surfaces controlled via a strong electric field.

Frictional forces arise whenever objects around us are set in motion. Controlling them in a rational manner means gaining leverage over mechanical energy losses and wear. This paper presents a way of manipulating nanoscale friction by means of in situ lubrication and interfacial electrochemistry. Water lubricant is directionally condensed from the vapor phase at a moving metal-ionic crystal interface by a strong confined electric field, thereby allowing friction to be tuned up or down via an applied bias. The electric potential polarity and ionic solid solubility are shown to strongly influence friction between the atomic force microscope (AFM) tip and salt surface. An increase in friction is associated with the AFM tip digging into the surface, whereas reducing friction does not influence its topography. No current flows during friction variation, which excludes Joule heating and associated electrical energy losses. The demonstrated novel effect can be of significant technological importance for controlling friction in nano- and micro-electromechanical systems.

Oil filter modification for biodiesel–fueled engine: A pathway to lubricant sustainability and exhaust emissions reduction

The widespread use of biodiesel in internal combustion engines promotes frequent lubricant drain intervals which in turn affects lubricant sustainability and engine performance. In this research two endurance tests were carried out to evaluate the novel approach of strong base oil filter with palm biodiesel (PME) fueled single-cylinder diesel engine. The effects of strong base filter on lubricant rheology, piston ring/cylinder wear losses, engine performance and exhaust emissions were investigated. The results of long duration engine testing showed that the strong base filter improved the lubricant’s physical and tribological characteristics. Tribo-testing, using high stroke reciprocating test rig, proved that the mechanical energy losses due to piston ring-cylinder interaction were reduced significantly. Finally, the engine performance and exhaust emissions analysis for strong base filter testing showed an improvement in engine performance, average decrease of 2.78% in carbon monoxide (CO) emissions, 7.18% reduction in hydrocarbon (HC) emissions and 3.3% reduction in smoke opacity at full load engine conditions.

On the origin of non-linear breakage kinetics in dry milling

While population balance models (PBMs) have described the impact of mechanical interparticle interactions on the specific breakage rate in dry milling processes through a phenomenological effectiveness factor, such models lack particle-scale information and thus a mechanistic basis. In this study, a mechanistic effectiveness factor of the non-linear PBM was derived and calculated by coupling a particle-scale breakage model with interparticle interactions obtained from discrete element method (DEM) simulations of a grinding ball impacting an unconfined particle bed. Mono, binary, ternary, and polydispersed particle beds were simulated to determine the effects of granular composition on breakage kinetics. The effectiveness factor obtained from the DEM simulations shows a reduction in the specific breakage rate for coarse particles in binary mixtures. The origin of this phenomenon, commonly known as cushioning or decelerated breakage in dry milling processes, was explained by the DEM simulations: fine particles in a particle bed increase mechanical energy loss, and reduce and distribute interparticle forces thereby inhibiting the breakage of the coarse component. On the other hand, the specific breakage rate of fine particles increased due to contacts associated with coarse particles. Such phenomenon, known as acceleration, was shown to be less significant, but should be considered in future attempts to accurately quantify non-linear breakage kinetics in the modeling of dry milling processes. The phenomenological effectiveness factor was also assessed and found to accurately describe the impact of mechanical interparticle interactions in binary particle beds as well as predict the non-linear breakage behavior in ternary and polydispersed particle beds. Aside from gaining particle-scale insight into non-linear breakage kinetics, the above findings provide the guidelines for the usage of non-linear PBM framework and are expected to improve the design, control, and optimization of dry milling processes that exhibit non-linear breakage kinetics.

Dimensional analysis on resistance characteristics of labyrinth seals

Experimental investigation of stepped and straight-through labyrinth seals was designed to study the sealing performance of two different typical labyrinth seals. In order to facilitate dimensional analysis on the flow resistance characteristics of labyrinth seals, the variable cross-section of the flow channels are considered as constant cross-section flow. The mechanical energy loss of flow caused by throttle turbulence intensity is considered as caused by friction along the way. The friction coefficient of stepped labyrinth seals is bigger than that of straight-through labyrinth seals by more than 40% for the same Reynolds number and the ratio of equivalent diameter and the seal length. The expression of friction coefficient f and fRe are obtained from experimental data. The verifications indicate that the expressions are highly accurate. The contribution to the total pressure drop of each tooth cavity gradually becomes less along the flow direction.

Rheological properties of a straw layer

The experiment was performed on a layer of straw whose thickness was equivalent to the load of 4 kg m−2. Every straw sample was subjected to 15 strain cycles. A preliminary analysis of the results revealed that compression and decompression curves resemble the proper rational function, where selected parameters of that function were determined by the direction of strain and the number of strain cycles. Straw was described with the use of a rheological model where it was divided into layers subjected to elastic strain and internal friction proportional to the rate of displacement and deformation. Unknown model parameters were estimated based on an analysis of the equation describing the results of the experiment and the results produced by the model simulating the rheological properties of straw. The elastic modulus was directly proportional to load, and its value decreased in successive strain cycles. Internal friction was determined based on the loss of mechanical energy. In fluid dynamics, internal friction is associated with viscosity, whereas in fibrous materials such as straw, mechanical energy is lost mainly due to sliding friction. The losses were minimized in successive strain cycles.

A novel optimization approach to convective heat transfer enhancement for solar receiver

Convective heat transfer enhancement for solar receiver is considered as a variational problem in this paper. A predictive optimization method based on the minimum heat transfer entropy generation (MHEG) principle is developed for ideal gas in turbulent flow. A set of Euler–Lagrange equations is derived by the calculus of variations. By employing a porous media model and multiphase Volume of Fluid (VOF) model in the variational problem, the optimization constrained by the mechanical energy loss is performed to achieve a physically feasible geometry configuration to improve the performance of the convective heat transfer in a solar receiver. To validate and demonstrate the method, turbulent convection heat transfer process in a two-dimensional rectangular channel with fixed heat flux boundaries is optimized. The computation results show that higher air temperature at the outlet and lower wall temperature can be obtained, which may lead to the use of cheaper materials with lower heat-resistance for the exchanger. The present work shows that combining the calculus of variations with porous media and multiphase VOF model may be helpful for the design of efficient convective solar receiver.

The mechanical energy equation for total flow in open channels

The mechanical energy equation is a fundamental equation of a 1-D mathematical model in Hydraulics and Engineering Fluid Mechanics. This equation for the total flow used to be deduced by extending the Bernoulli's equation for the ideal fluid in the streamline to a stream tube, and then revised by considering the viscous effect and integrated on the cross section. This derivation is not rigorous and the effect of turbulence is not considered. In this paper, the energy equation for the total flow is derived by using the Navier-Stokes equations in Fluid Mechanics, the results are as follows: (1) A new energy equation for steady channel flows of incompressible homogeneous liquid is obtained, which includes the variation of the turbulent kinetic energy along the channel, the formula for the mechanical energy loss of the total flow can be determined directly in the deduction process. (2) The theoretical solution of the velocity field for laminar flows in a rectangular open channel is obtained and the mechanical energy loss in the energy equation is calculated. The variations of the coefficient of the mechanical energy loss against the Reynolds number and the width-depth ratio are obtained. (3) The turbulent flow in a rectangular open channel is simulated using 3-D Reynolds averaged equations closed by the Reynolds stress model (RSM), and the variations of the coefficient of the mechanical energy loss against the Reynolds number and the width-depth ratio are discussed.