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Dimensional analysis has been very helpful in experimentation of very large or small-scale engineering systems. A good example would be experimentation on the aircrafts and ships, which was made co...

In the recent paper “Numerical approach to define a thermodynamically equivalent material for the conjugate heat transfer simulation of very thin coating layers” by P. Olmeda, X. Margot, P. Quintero, J. Escalona, Int. J. Heat Mass Transfer 162 (2020) 120377 the authors develop a procedure to identify a thicker pseudo-material to mimic the dynamic response of a thin thermal barrier coating. A thicker layer is desired to allow efficient conjugate heat transfer analysis. They employ an ad hoc procedure for defining the thermal properties of the material to approximate dynamic similarity with low grid resolution. There exists a published analytical solution for this same problem that allows the pseudo-material’s thermal properties to be directly determined without a trial-and-error approach. The approach is elucidated and the effects of numerical resolution are explored.

The present paper deals with the experimental investigation of dynamic similarity laws of technical structures based on modal analyses of a reference and a scaled servo-screw press. At first, a brief introduction into the theoretical background is given and similarity principles for mechanical systems and used modal global and local correlation criteria are explained. After the description of the measurement setup and its evaluation, a comparison of the reference and the scaled press is carried out. The comparison is based on modal parameters obtained by experimental modal analysis where different data acquisition methods are used. For the reference press, frequency response functions (FRF) are obtained by impact hammer and acceleration sensors and for the scaled press by electrodynamic shaker and a laser scanning vibrometer. The acquired FRF’s are basis for the following curve fitting process to determine the modal parameters of both systems. Subsequently, the derivation of scale factors from modal parameters is characterized using eigenvalue and eigenvector related correlation criteria. The impact of different slide positions as well as the influence of various contact conditions between slide and frame on the scaling factors are analyzed and discussed. The investigation of slide position and contact condition influences are carried out using the obtained experimental modal parameters in combination with linear-elastic finite element models.

The model test method of the FPSO and offloading system is investigated by using the development mode of “FPSO + CALM + TANKER” working in a 1700-m depth of offshore West Africa. An equivalent design based on static and dynamic similarity criteria for oil offloading line (OOL) is discussed, and a type of creative method for the equivalent design of OOL in a model test is proposed. Based on the static similarity criterion, the truncated design of the FPSO mooring system in water depth and horizontal directions is carried out. After that, a relevant static optimization is conducted. Meanwhile, to avoid interference between the FPSO mooring system and CALM mooring system, a horizontal equivalent design for the CALM mooring system is provided. On this basis, the model test scheme is conducted. Time domain coupled analyses for the whole system before and after truncation are later performed. After comparison, it is observed that the calculated results of the truncated system are basically consistent with those of the prototype system, and the design of the model test scheme is demonstrated to be robust and reliable.

This paper shows the procedure followed to design and manufacture a scaled railroad vehicle to be used in a scaled railroad track for the development and validation of computational models. The purpose of this work is to address the background experienced by the authors from the ideal concept to the assembly one, and serve as a guideline for future railroad prototype designs. This specific vehicle, in which different inertial, guiding, recording and monitoring devices are installed, is mainly designed to be used in a 5-in. gauge railroad track for the validation of computational models and, as much as possible, designed with physical similarity with respect to a real railroad vehicle. The commitment between the imperative design requirements and the desired dynamic behavior is managed from the CAD design to its final assembly.

This paper presents an analysis of 2D PIV model test experiments performed on a series of forward-facing bent-duct type of oscillating water column (OWC) models with varied underwater geometry. Experiments of this complexity involving particle imaging velocimetry (PIV) to compare performance difference between differing geometry is the first of its type. The intent of the experiments was to investigate conversion losses and device performance by modifying the underwater geometry based on previous work by the authors. Four models were tested in total; the base model and three variations that had additional segments to afford different chamber length and lower/upper lip angles (10, 20 and 30 degrees). Dynamic similarity was assumed to be maintained between models by using a constant lower lip depth and a constant ratio of chamber length to projected underwater cross-sectional area. Performance comparisons were undertaken using phase-averaged wave probe, pressure transducer and PIV data. Additional qualitative analysis of velocity fields was performed using temporal averaging. In most test cases the new geometry with a 10 degree lip angle had marginally superior performance in terms of capture width and total power production. However, due to a number of issues, including the difference in damping factor between models; the difference in chamber length; and the void behind the upper lip on some models, it was not possible to definitively conclude that the 10 degree model was the best performer, but rather, the range of all new geometries presented have the potential for significant performance gains over the base geometry with additional modifications. Recommendations for future design of geometry are provided.

Studies on the mechanisms of natural ventilation in livestock buildings are reviewed and influences on discharge and pressure coefficients are discussed. Compared to studies conducted on buildings for human occupation and industrial buildings which focus on thermal comfort, ventilation systems, indoor air quality, building physics and energy etc., our understanding of the mechanisms involved in natural ventilation of livestock buildings are still limited to the application of the orifice equation. It has been observed that the assumptions made for application of the orifice equation are not valid for wind-induced cross ventilation through large openings. This review identifies that the power balance model, the concept of stream tube and the local dynamic similarity model has helped in the fundamental understanding of wind-induced natural ventilation in buildings for human occupation and industrial buildings. These concepts have distinguished the flow through large openings from that of ‘cracks’ (i.e. small openings), which is where the orifice equation is normally used for prediction of airflow rate. More field measurements on the effect of wind turbulence on ventilation rate need to be encouraged, particularly under conditions where the mean pressure differences through building openings are much lower than the fluctuations of pressure differences. Research on bidirectional flow that occurs at openings is also limited.

Reliable scale-up of fluidized beds is essential to ensure that analysis and performance optimization at lab-scale can be applied to commercial scales. However, scaling fluidized beds for dynamic similarity continues to be challenging because flow hydrodynamics at lab-scale are largely influenced by bed geometry making extrapolation of conclusions to large-scales infeasible. Therefore, this study is focused on analyzing the effect of bed geometry on the fluidization hydrodynamics using large-scale CFD simulations. The two fluid model (TFM) is employed to describe the solids motion efficiently and simulations are conducted for fluidization of 1150 μm LLDPE and 500 μm glass beads in beds of different sizes (diameter D = 15–70 cm and initial bed height H0 = 10–75 cm). The hydrodynamics are subsequently investigated qualitatively using time-resolved visualizations, bubble centroid and solids velocity maps as well as quantitatively using detailed bubble statistics and solids circulation metrics. It is shown that as the bed diameter is increased, average bubble sizes decrease although similar-sized bubbles rise faster because of lower wall resistance, both factors contributing to faster solids circulation. On the other hand, fluidization hydrodynamics in 50 cm diameter bed are relatively insensitive to the choice of H0 and similarities in solids circulation patterns are observed in shallow beds as well as in the lower regions of deep beds. Finally, it is shown that the size and spatial-distribution of bubbles is crucial for maintaining dynamic similarity of bubbling beds. Specifically, the bed dimensions (D, H0) must ensure that (a) bubbles are typically much smaller than the bed diameter and (b) solids circulation patterns are similar across scales of interest. Overall, insights from this study can be used for describing the gas distribution and solids motion more accurately for better design of commercial beds.

This paper investigates the vibration patterns, i.e. rigid motions of shaft and elastic deformation of support structures, of fan rotor system in aero-engine, which differs from traditional flexible rotor systems, and together with its shaft transverse motions due to unbalanced mass. The fan rotor system commonly is composed of one rigid shaft and two flexible support structures (such as squirrel cages), which is effective to decrease the critical speeds avoiding serious shaft vibration due to unbalance. Scaled test rig for realistic fan rotor system is set up according to similarity principles, governing differential equations of which are deduced by means of Lagrangian approach with four degrees of freedom. In contrast to modeling a traditional flexible rotor system, the system stiffness is not determined by the shaft but the two flexible support structures. The rigid shaft only contributes to the inertial items of the governing equations. Parameter values of dynamic model are identified from measurements on the scaled test rig, the modal shapes and the modal energy distributions are calculated. These modal characteristics of the fan rotor system are quite different from those of a traditional flexible rotor system whose stiffness mainly contributed by its elastic shaft even the system values are consistent. The obtained modal characteristics are compared and confirmed by using the simulation results of a corresponding finite element model, in which shaft is built by rotating beam elements and its flexible structures are built by equivalent spring elements. Campbell diagrams of the fan rotor system are used to illustrate the gyroscopic effect with the increasing speeds. And then the unbalance responses are calculated through the deduced analytical formula rapidly and comparisons, including the response spectrum and orbits, the amplitude and phase frequency response curves, and operating deflection shapes, are carried out in the sub- and super-critical range.

This paper studies chaotic control of a tethered satellite system (TSS) driven only by a momentum-exchange device during its attitude adjustment. In dealing with such the underactuated system, an extended time-delay autosynchronization (ETDAS) is employed to stabilize the chaotic motion to a periodic motion. To obtain the control domains of the ETDAS method, a stability analysis of the controlled tethered satellite system in elliptical orbit is implemented. According to the principle of dynamic similarity, then, ground-based experiment setups are proposed and designed to emulate the in-plane motions of the TSS. Representative experiments are presented to demonstrate the effectiveness of the ETDAS scheme in controlling the chaotic motion of the underactuated TSS.

Beginning with a laboratory-scale physical model, a scale-up correlation for a pilot unit project was determined based on the analysis of dynamic similarity correlations involving the predominant phenomena of a dissolved air flotation (DAF) chamber. The implantation costs of pilot units require special strategies due to the lack of correlations of this type, as novel flotation methods have been considered strictly from an economic standpoint. With the aid of computational fluid dynamics and videos of microbubble and floc flow, inertia and gravity were identified as the predominant phenomena in a DAF chamber. The strategy described herein is simple and reduces the likelihood of future risks in scale-up investments.

The article describes mathematical model of positive-displacement hydropercussion system of single-sided back action. The principal dynamic similarity criteria found are: the reduced ratio between areas of back-stroke chamber and gas chamber; the value proportional to the ratio between potential energy of accumulator and kinetic energy of hammer; the dimensionless lengths of back stroke and gas strut. Based on numerical calculations performed within a wide range of input parameters (similarity criteria), the author has plotted nomograms of isolines of the integral input characteristics and oscillograms of dynamic characteristics, which enables revealing basic mechanisms of behavior of the discussed system in the single-blow limit cycles. In the domain of practical significance parameters, the analytically estimated dimensionless pre-blow velocity should not be higher than 810 units.

In flutter wind tunnel test, the matching degree between scaled model and prototype would directly affect the reliability of test results. It is difficult to achieve completely dynamic similarity because of some material or technological constrains, and only lower order modes including mode shape and frequency are accurately simulated to construct a compromised model. Theoretical support would be necessary to answer the question which modes must be simulated to guarantee data validity of wind tunnel flutter test. An analytical study of a sweepback winghas been undertaken to estimate the flutter influence mode needed for accurate flutter prediction by analyzing generalized aerodynamic stiffness coefficient, unsteady aerodynamic force and flutter results. The results show that the aerodynamic stiffness coefficient with expression of mode shape could be taken as a quick criterion for mode selection in flutter model design and analysis.

A new downscale test rig is developed for investigating the contact between the wheel and rail under impact-like loading conditions. This paper presents the development process of the setup, including review and synthesis of the potential experimental techniques, followed by scalability, mechanical and operational analysis of the new setup. The new test rig intends to remedy the lack of dynamic similarity between the actual railway and the existing laboratory testing capability, by taking into account the factors that contribute to high-frequency dynamics of the wheel-track system. The paper first reviews the functionalities of the existing test techniques in the literature. Based on this survey, the category of the scaled wheel on the rail track ring is chosen. Afterwards, three potential alternatives are identified under the chosen category and the optimum mechanism is achieved through finite element modelling and analysis of the structures. A downscale test rig, consisting of multiple wheel components running over a horizontal rail track ring, effectively fulfilled the requirements needed for analogical testing of the wheel-rail contact behaviour. The new test rig is a unique experimental setup due to the involvement of high-frequency dynamic vibrations in the wheel-track system and analogy of the incorporated elements and loading to those of the real-life system. This paper further presents the results of some real experiments carried out using the newly-built setup to support substantial ideas behind its development.

This chapter discusses coronary artery flow assessment for atherosclerosis investigations. The overall goal is to foster the reader’s understanding of coronary flow assessment with CFD and experimental MRI, including advantages, shortcomings, and potential for clinical applicability. In Section 1 , we begin by introducing coronary artery disease and how it links to local blood flow and hemodynamic parameters, before introducing strategies to investigating coronary flow for risk assessment—computational modeling and experimental studies. Both of these need the artery geometry and embedded stents to be retrieved first, as detailed in Section 2 . Section 3 details the concepts of computational coronary flow modeling with computational fluid dynamics (CFD) including the governing equations, mesh discretization, and boundary and initial conditions. Section 4 introduces experimental approaches using in vitro flow sensitive magnetic resonance imaging (MRI), including dynamic scaling for steady or transient state considerations, creation of phantom, consideration of vessel compliance and motion, non-Newtonian blood properties, and the design of an experimental circuit. Postprocessing, analysis, and comparison of both methods are explained in Section 5 , before discussion of the accuracy and reliability of the results in Section 6 . Finally, current developments, particularly patient-specific profiling, are discussed in Section 7 .

Junction surface characteristics is one of the many factors influencing the performance of machine tool. It is also a major source of machine tool contact stiffness and damping. Study on the junction surface characteristics of this machine is very important to improve the performance of the machine and the machine structure optimization. According to the similarity theory, this paper will small guide rails are used as scale model, research on small rail junction surface characteristics and combining the conclusion extended to heavy machine tool surface. This paper from the geometric similarity and dynamic similarity surface on the comparative analysis of the small rail and heavy machine tool guide rail with two aspects of similarity theory, after verification, proof of small guide surface and heavy machine tool guide surface similarity.

As a primary device of the S-lay technique, the stinger is used to protect the overbend section in a pipeline. It is difficult to determine the design loads acting on the rollers during the dynamic pipelaying condition using numerical methods alone. Instead, a test model is used to analyze this complex problem. This paper introduces some similarity criteria based on the dynamic similarity of a stinger, a pipeline, and a vessel. Then, the stinger of the first pipelaying crane vessel in China, “HYSY201”, is modeled with these similarity criteria. The loads for the stinger׳s structural design and movement mechanism in the off-design conditions are simulated, producing some useful conclusions and suggesting that local reinforcement of this stinger be performed. The vessel recently began its first deep-sea pipelaying project in Liwan in the South China Sea. Thus, the model method proposed in this paper is effective and could be used to design and test other articulated stinger structures rather than relying on engineering heuristics.

For the purpose of fully and systematically observe, research and optimize the U-sharp ventilation system in Vilafruns mine, a simulation model based on the principles of geometric, kinematic and dynamic similarity is established in the simulation laboratory. By simulating a U-shape ventilation network, t he air volume distribution and wind velocity in different sections of the model were measured and compared with practical data obtained in Vilafruns mine. Results show that the lowest wind velocity in the model is higher than 0.42 m/s, thus it is in a turbulent f low state, which satisfies the kinematical and dynamic similarity principles. T he characteristic of air volume distribution and wind velocity in Vilafruns mine are basically simulated by the experimental model through the obtained data and figures, which reflects the establishment of the model is correct and successful, and the experimental data is accurate and reliable. Moreover, this model provides useful references for the selection of mine ventilation types and for the optimization of the existing ventilation network.

This paper presents an analysis of flow parameters through a bottom outlet conduit with gated operation using physical and numerical models. A physical model of the regulating bottom outlet of Shahryar dam in Iran was used to investigate the hydraulic forces on the service radial gate and flow patterns within the conduit. The model was constructed from Plexiglas, and discharge and pressure data were recorded for different gate openings. The Froude law of similarity was satisfied in the hydraulic modelling, allowing for an investigation of the dynamic similarity of inertial and gravitational forces. The numerical scheme was based on using the natural-element method to study hydraulic forces and flow parameters within the conduit and the finite-element method to evaluate the natural frequencies of the radial gate. The results of the calculations for different radial gate openings showed good agreement with those from physical modelling for the pressure distributions throughout the flow domain and on the gate.

Mitigation of landslide debris hazards sometimes requires the use of structural countermeasures such as baffles to minimise the destructive impact energy of a torrent. An array of baffles is a type of structure countermeasure frequently installed along the flow path to protect downstream facilities. They are currently designed using empirical methods since their interaction mechanism with landslide debris is not well understood. In this study, a 5 m long rectangular flume model is used to conduct experiments to investigate flow interaction between baffles and uniform dry sand. Dynamic similarity between model and prototype flows is achieved by adopting Froude scaling. The discrete element method (DEM) is then adopted to conduct numerical back-analysis of flume experiments to study the effect of varying transverse blockage on flow impedance. Results reveal that higher degrees of transverse blockages are more effective at developing upstream subcritical conditions which may develop into a granular jump and promote additional energy dissipation. An increase in the degree of transverse blockage from 20% to 37% provides up to 18% additional kinetic energy dissipation.

[1] We present the results of new laboratory experiments that provide constraints on inter bubble film thinning and bubble coalescence as a consequence of liquid expulsion by gravitational and capillary forces. To ensure dynamic similarity to magmatic systems, the experiments are at small Reynolds numbers (Re≪1) and cover a wide range of Bond numbers (10−3 ≤ Bo ≤ 102). Results indicate that at Bo 0.25 gravitational forces result in film thinning. The film drainage time scale is given by t ∼ C ln (α) τ and is orders of magnitude faster than often assumed for magmatic systems. Here, C ∼ 10 is an empirical constant and α is the ratio of initial film thickness to film thickness at the time of rupture and τ is the characteristic capillary or buoyancy time scale at values of Bo 0.25, respectively.

A physical model of molten slag granulation by rotary disk was developed based on the mechanism of Newtonian liquid granulation. For geometrical similarity, the radius ratio of model disk to the prototype disk was chosen as 1 : 1. For dynamic similarity, equality of Ohnesorge number between the model and the prototype was achieved firstly by compounding rosin and paraffin wax with mass ratio of 1 : 1 as simulation liquid of molten blast furnace (BF) slag, and the simulation material can satisfy the similarity of liquid-solid transformation during falling in the medium; then equality of Reynolds number and Weber number was obtained by controlling the volumetric flow rate and the rotary speed, respectively. Model accuracy was verified by comparing the simulation data with the results reported in literature, which showed good agreement with the calculation results of empirical equation and the actual molten BF slag granulation from the view point of particle size. Furthermore, influences of disk radius, rotary speed and liquid flow rate on granulation were discussed using the developed model, and the Kitamura equation was modified according to the simulation data which can predict particle size more accurately. Using the modified equation, the operation parameters were predicted according to the flow rate of molten industrial BF slag.

In this paper cross natural ventilation due to buoyancy assisted by wind is investigated with computational and laboratory simulation. The impact of the outlet's opening position is investigated, forming cross ventilation of variable distance h – namely, the vertical distance between midpoints of leeward and windward opening –, for three initial Froude numbers: (i) Fr 0 = 1.15, (ii) Fr 0 = 2.79, (iii) Fr 0 = 4.85. For the computational simulation a fluid dynamic software is used and the problem is solved by solving the 3D unsteady Reynolds Averaged Navier Stokes (RANS) equations in conjunction with the energy equation and the turbulence model RNG k-e. The laboratory simulation took place in an open channel and the experimental model represents a building form of orthogonal shape. The interior of the experimental model is filled with solution of ethanol at conditions of normalized gravity, but also with salted water at conditions of inversed gravity. The time taken for the indoor space to empty is calculated numerically and experimentally. Based on Froude number dynamic similarity, the experimental and computational results are characterized by good agreement and the functional process of natural ventilation is being explicated. In addition, the suggestion of using ethanol solution for the density difference between interior and exterior fluid in laboratory simulation of natural ventilation is verified successfully, as the results with use of ethanol solution are in good agreement with those using salted water.

International audience; To study transient mass transfers inside buildings equipped with ventilation systems, reduced-scale experiments have been performed by applying the scaling down methodology developed for studying isothermal airflows in a steady or a transient state [1]. Transient tests have been carried out both on simplified cases considered for the validation of the methodology and on two reference industrial configurations representative of real industrial facilities. In this article, focus is made on transient results obtained on simplified and reference industrial cases subjected to wind and internal overpressure effects. The main objectives are firstly to identify the internal transient airflow behaviour, compared with Helmholtz oscillated phenomena underlined from natural ventilation studies, secondly to analyse the pollutant containment of reference industrial configurations subjected to wind and/or internal overpressure effects due to an accident, and finally to check the ability of the SYLVIA code to model these transient phenomena. © 2013 Elsevier Ltd.

To predict the vibration characteristics of the rotor-bearing system by using the scale model and the associated scaling laws may significantly reduce the time and money required by the experiments. To this end, the dynamic similarity criteria are investigated inferring from the model behavior of rotor-bearing system to the vibration response of the prototype. The similar relationship was established by combining method of dimensional analysis and equation analysis based on similarity theory, and the effectiveness was verified through the finite element method. The result provide the theoretical rational for further study of the similarity design of the rotor-bearing system.

In practical engineerings, structures are often excited by different kinds of loads at the same time. How to effectively analyze and simulate this kind of dynamic environment of structure, named combined dynamic environment, is one of the key issues. In this paper, a novel prediction method of combined dynamic environment is proposed from the perspective of data analysis. First, the existence of dynamic similarity between vibration responses of the same structure under different boundary conditions is theoretically proven. It is further proven that this similarity can be established by a multiple-input multiple-output regression model. Second, two machine learning algorithms, multiple-dimensional support vector machine and extreme learning machine, are introduced to establish this model. To test the effectiveness of this method, shock and stochastic white noise excitations are acted on a cylindrical shell with two clamps to simulate different dynamic environments. The prediction errors on various measuring points are all less than ±3 dB, which shows that the proposed method can predict the structural vibration response under one boundary condition by means of the response under another condition in terms of precision and numerical stability.

Scale-up in combustion has been a fundamental driver in the past to utilize the economy of scale effect in industrial combustion plants. Several scaling methods have been used successfully in engineering applications to transfer the properties of smaller equipment onto larger equipment. Today, fluid dynamic scaling based on scaling criteria derived from fundamental fluid dynamic equations, describing the movement of the two-phase medium in a fluidized bed reactor, can be performed with sufficient accuracy, using cold flow models. However, combustion scaling using laboratory data obtained from a small-scale boiler inherits the difference that complete fluid dynamic similarity can never be obtained. In complete boiler design the main problem is the scale-up of known features to very large sizes; scaling can then use elements already developed in similar size and employ them in multiple numbers to reach the required throughput. In bubbling fluidized bed technology the upscaling has reached a limit, while in circulating fluidized bed boilers the strong upscaling tendency shows a slower movement. The main challenges today are the substitution of an existing fuel with a more challenging counterpart, or the use of low-grade fuel. This can cause severe problems in industrial-sized plants, mainly in terms of fuel feeding, ash discharge, and the erosion and corrosion behaviors of the flue gases. Further challenges of today exists in the increase in pressure on the return of investment of R&D projects, the high requirements on plant availability, even on prototypes, and the constant reduction in R&D budgets. Keywords: combustion; fluidized bed; gasification; fluid dynamics; operational experience; Scale-up

The characteristics of the fluid flows in tool joints were studied experimentally and theoretically in a laboratory scale. The goal of this study was to evaluate the pressure drop in accessories such as tool joints, placed along the drilling columns. The experimental fluid flow loop consisted of a 25-hp positive displacement pump, a 500-liter tank, a 3-HP mixer and a series of circular and annular pipes where the tool joints were installed. Based on the Reynolds number, the fluid flow loop was set to have dynamic similarity with respect to the real hydraulics of oil well fields. CFD simulations were implemented to aid in the design of the fluid flow loop. Pressure drop and fluid flow rate data were experimentally determined in a set of tool joints using water-based muds with non-Newtonian behavior. The CFD simulations showed a good performance on the tool joint simulations. Finally, the literature’s correlations originally employed by Petrobras were used to estimate the friction factor, and new parameters for these correlations were established. The evaluation of the parameters improved the predictive capacity mostly in the laminar regime.

The natural frequencies of the reduced scale model are higher than that of the prototype, which make it quite difficult to conduct the experimental research on the dynamic characteristics of the rotor system by using normal rotor model. Aiming at this problem, this paper has deduced the similarity criterion of abnormal rotor model based on equation analysis, and the dynamic similarity conditions between abnormal rotor model and the prototype are also discussed. Next, the mass matrix and flexibility matrix are presented based on the lumped parameter model of the rotor system. Finally, the similarities among normal rotor model, abnormal rotor model and the prototype are comparatively analyzed. The results show that the natural frequencies of abnormal rotor model and that of the prototype are all the same while the radial scaling factor is the square of the axial scaling factor. And it provided the theoretical basis for experimentally studying the dynamic characteristics of the rotor system.

This paper presents a non-tubular heat exchanger for use in a Stirling solar engine micro co-generation unit that is being developed by the University of Oviedo and the technological research centre Tekniker Foundation. The engine has been designed using scaling criteria, which imply a case of relaxed dynamic similarity, that is to say, without preserving the equality among all of the prototype’s and the derivative’s dimensionless groups. The geometrical characteristics of the heater are described and the variables that can influence the pressure drop and heat transfer in the heater are identified. The correlations for the friction factor and Stanton number have been measured under steady flow conditions to analyse the feasibility of the experimental heater. The Reynolds analogy is not fulfilled, and the compressibility effects are negligible. The comparison between the correlation predictions for the non-tubular heater and slotted or tubular heaters of well-known prototypes shows possible applications for heaters that reach high Reynolds numbers and that encounter practical problems associated with the use of bundles of tubes.

This work presents the design and experimental evaluation of a cold-flow model system, built to simulate a 100 kW chemical-looping combustor for solid fuel. A theoretical background is provided, as well as some initial results using air as fluidization medium. The system has been operated for about 10 hours and shows no indication of imbalances in the bed inventories. In the fuel and air reactors, the mass fluxes were found to be linear in the riser pressure drop and the corresponding measured mass flows were approximately proportional to the mass flows calculated from the riser pressure drop. From the study of mass flows, residence times in both the fuel and air reactor were obtained. From pressure profile investigations, it was found that the system remained stable to changes in the fluidization velocity. Thus, both the internal circulation in the fuel reactor, and the circulation between air and fuel reactor, could be varied in a large range with only minor impact on the solids inventories of the air and fuel reactors.

In order to validate the theory and select effective operational parameters in practical ice-breaking by air cushion vehicle (ACV), experimental study should be carried on firstly. The relationships of corresponding parameters between ACV model and prototype and between the ice-like material and the real ice are established on the basis of the similarity theory and the differential equation of thin elastic vibrating plate under static or moving load. According to geometric and dynamic similarity between model and prototype, for the conditions of different water depth, ice thickness, mass and velocity of ACV in actual operating mode, the pressure and velocity of ACV model, the elastic modulus and density of ice-like material in model test can be determined, the method of extending the model test results to prototype is proposed.

The liquid scale model test is set up to research on the velocity characteristics of coupling airflows between subway piston wind and platform air jet. Model test and prototype meet the dynamic similarity. Piston wind variation rules on the test are validated with previous conclusions. The coupling airflows trajectory is closer to the horizontal direction with increasing piston wind. Under the constant air supply, the coupling velocities of measuring points increase with piston wind growing. The piston wind has more obvious influence on the coupling airflows than air jet.

To focus on the key scientific problem of process control of dynamic catastrophe of high dams, presented for the first time are the modelling theory of liquid-gas-solid tri-phase coupling of the air-cushion isolation control of high dams and its numerical simulation method, and theoretical description of the complicated dynamics problem of the tri-phase coupling-thermodynamics state-material-contact bi-nonlinearity, as well as the simulation analysis of the key effects of dynamic catastrophe of the air-cushion isolated high dam engineering. The analytic solution of plane-wave with rigid-dam body was created. The simulation comparison of dynamic catastrophe processes of 305 m Jinping arch dam with and without seismic control was carried out, and the results were basically in agreement with that obtained from the large shaking table tests, and verify each other. The entire air-chamber and optimized air-cushion with varying thickness were presented to develop a optimization method. The large shaking table tests of the isolated dam model, which is satisfied with the basic dynamic similarity relations, were performed for the first time. The test data seemed to be convincing and were in agreement with the dynamic simulation results of the tested model, thereby providing an experimental verification to the simulation theory and method. The combination experiments of theoretical model and physical model demonstrated that the hydrodynamic pressure of high arch dams can be reduced by more than 70% as well as the first and third principle stresses of the dam body reduced by more than 20%–30%, thereby the global anti-seismic capacity of the high dam being improved significantly. The results have shown that the air-cushion isolation is the prior developing direction of structural control technology of high concrete dams.

Dimensional analysis and dynamic similarity requirements show that Reynolds, Froude, and Strouhal scales are important parameters to be satisfied for free-running submarine model (FRM) maneuvering experiments so that they correctly represent full-scale behavior. The requirement that all three scales be satisfied simultaneously presents conflicting demands on the relationship between the velocity U and the characteristic length L of the model. The inability to meet these demands presents technical challenges to properly satisfy dynamic similarity for the FRM. Instead, we take a first-principles approach by considering the forces and moments acting on the vehicle and seek solutions that dynamically produce the same scaled forces and moments on the model as exist on the full-scale vehicle. Thus, this paper presents an extended dynamic similarity theory, introducing scaling formulas that have been derived from similarity solutions. These are applied to an unsteady turning maneuver of the FRM to suggest an improved experimental program. The improved approach will then dynamically satisfy the aforementioned three scaling parameters.

This paper reviews the application of CFD for designing and parametric studies of wind-induced natural ventilation. The approaches employed in such applications of CFD are whole-domain and domain-decoupled CFD modelling. The domain-decoupled technique separately analyses the external airflow fields outside and internal flows inside a building. In the whole-domain approach, the outdoor and indoor airflow is modelled simultaneously and within the same computational domain. The review showed that the whole-domain approach has been more popular than the domain-decoupled approach, and with efficient computing algorithms, grid generation techniques and advances in hardware technology, can overcome the computational overhead it incurs during application. CFD has also allowed the concept of stream tube and the local dynamic similarity model (LDSM) to be used in practice. These concepts have helped in the fundamental understanding of wind-driven natural ventilation and in distinguishing flow through large ...

To repair armor blocks damaged by high waves, an expensive in-water repair work using a crane barge must be done. A wire connection with among blocks can be effective to save maintenance cost. But, to conduct hydraulic experiment of among blocks connected by wire is considerably difficult because of a lack of a physical model of wire satisfying dynamic similarity. In the present study, simple wire model based on the distinct element method has been developed to investigate the effect of wire connection of armor blocks as a resistance of damage under high waves. Validation of developed wire model is conducted by comparing model predictions with field observations.

The objective of this work is to establish dynamic similarity relationships for self-adaptive composite marine rotors. Although scaling laws are well established for rigid propellers and turbines, relative little work has been shown for flexible marine rotors that are designed to interact with the surrounding flow. Considering recent interests in the development of large-scale, energy-efficient composite marine propellers and turbines, it is crucial to understand the scaling relationships to properly design and interpret model-scale studies. Explanations of the similarity requirements are presented, along with scaling factors for the various fluid and structural parameters that control the dynamic interactions between the flexible rotor and the surrounding flow. Finally, numerical results obtained using a fully coupled, three-dimensional, boundary element method–finite element method is shown to demonstrate the validity of theoretical scaling relationships and to investigate scaling effects. The results suggest that for most marine rotors where gravitational forces are negligible compared to other dominant forces and the boundary layer is fully turbulent, it is most practical to conduct model-scale experiments to satisfy Mach number similarity, even though the Mach number will be much less than one for most marine applications.

A simulation study on the reduction of cooling loads by utilizing cross-ventilation was performed for a typically shaped house as defined by the Architectural Institute of Japan. A reduction in cooling load of around 50% could be achieved when the windows were opened liberally at night compared with the cooling load when all the windows remained closed, regardless of building coverage ratio.

To accurately predict the overall ignition transient for the reusable solid rocket motors of the space shuttle booster with head-end fin slots, it is necessary to have the knowledge of the flame-spreading rates in the fin-slot region. This paper is the second of a two part study and deals with the development of a flame-spreading correlation in the fin-slot region. A subscale (1:10) pie-shaped fin-slot motor was designed to perform diagnostic measurements for studying the flame-spreading behavior on the exposed propellant surface. Dynamic similarity was considered in the igniter design so the impinging jet had a similar exit angle onto the propellant surface in the fin-slot section. Flame-spreading measurements were gathered using a high-speed digital camera and nonintrusive optical measurement methods through an array of 36 near-infrared fast-response photodetectors installed perpendicular to representative regions of the propellant surface. Results showed that the flame-spreading phenomena was highly nonuniform, starting in the downstream portion of the fin-slot region before traveling back toward the igniter. A correlation was developed for the dimensionless flame-spreading time interval showing that it was inversely proportional to the pressurization rate to a power of 0.62, which depends strongly upon the flow parameters of the igniter induced flow and local propellant grain geometry.

Colloque avec actes et comité de lecture. Internationale.; International audience; Direct numerical simulation (DNS) is applied to investigate properties of katabatic and anabatic flows along thermally perturbed (in terms of surface buoyancy flux) sloping surfaces in the absence of rotation. Numerical experiments are conducted for homogeneous surface forcings over infinite planar slopes. The simulated flows are the turbulent analogs of the Prandtl (1942) one-dimensional laminar slope flow. The simulated flows achieve quasi-steady periodic regimes at large times, with turbulent fluctuations being modified by persistent low-frequency oscillatory motions with frequency equal to the product of the ambient buoyancy frequency and the sine of the slope angle. These oscillatory wave-type motions result from interactions between turbulence and ambient stable stratification despite the temporal constancy of the surface buoyant forcing. The structure of the mean-flow fields and turbulence statistics in simulated slope flows is analyzed. An integral dynamic similarity constraint for steady slope/wall flows forced by surface buoyancy flux is proposed and quantitatively verified against the DNS data.

Anew procedure of cross-ventilation characteristic test of inflow opening based on local dynamic similarity model has been proposed. When cross-ventilation characteristic test of actual size opening is carried out by the traditional means, there is fear that it is made an incorrect evaluation by the blockage effect to cross-section of wind tunnel. Because an opening was set parallel to floor of wind tunnel, it could avoid the influence of blockage effect by the method in this paper. The relational equation between the dimensionless indoor pressure and discharge coefficient was derived from the characteristic tests of various openings by this method. The database of primary parameters for the equation of various openings was made out.

Drill strings are used in oil and gas production as well as geothermal wells. They experience destructive vibrations, many of which are highly dependent on drill string modes. In this paper, we show that the lowest frequency modes are not necessarily the most critical and we delineate a methodology for reducing the number of modes representing the drill string. The frequency response function and stability diagram are used as measures of dynamic similarity between the proposed model and the drill string. We also introduce a novel approach to represent a drill string in laboratory test rigs. This approach not only represents the drill string dynamics but also offers flexibility to modify, remove, or augment the modes representing the system. The underlying principle is that in a multi-degree-of-freedom in-series spring-mass system with Rayleigh damping, dynamic modes can be decoupled. Applying the force to the end node (bit), the modes can then be configured separately in a parallel arrangement where their contributions to bit displacement are added algebraically. A practical arrangement for this purpose is proposed in this paper. Construction of a test rig that accurately represents the drill string dynamics is critical to validation of any test data on bits, bottom hole assemblies, instrument subs, and so on.

Some tentative results of theoretical studies of the process of positioning by a pneumatic drive obtained with a dimensionless mathematical model and dimensionless criteria of dynamic similarity are discussed. A tentative assessment of the ultimate capabilities of a pneumatic positioning system is made, and some recommendations are formulated on how to select its structure and parameters. It is shown that these systems operate reliably only providing there is a feedback loop based on the phase variables. To design a procedure of rational synthesis of a pneumatic positioning system, it should be known beforehand what its ultimate capabilities are; this can be achieved by exhaustively investigating the parameter space.

Robots are often used to perform similar tasks on vastly different scales. When utilizing traditional design approaches, this typically requires a full redesign and optimization at each specified size, a costly and time intensive process. In this work, we propose an alternative approach based on the principle of dynamic similarity. With this method, an initial design may be conceived at any size and scaled to any other without needing to re-optimize either physical or control variables. In the following study, we derive a generalized scaling method for this application that not only preserves system performance, but also affords flexibility in the scaling process. The preservation of dynamic similarity is validated in simulation. We further explore the application for robot-to-robot scaling, flexibility afforded by an additional free parameter, and the implications of scaling on both power requirements and structural loading. With these insights, we provide an improved methodology for the efficient and cost-effective development of scaled robotic systems.

Experiments with a flexible and submerged cylinder were carried out to investigate fundamental aspects of risers dynamics subjected to harmonic excitation at the top. The flexible model was designed aiming a high level of dynamic similarity with a real riser. Vertical motion, with amplitude of 1% of the unstretched length, was imposed with a device driven by a servomotor. Four values of the ratio between the exciting frequencies and the first eigenfrequency were investigated, namely ft: fN,1 = 1 : 3; 1 : 1; 2 : 1 and 3 : 1. Cartesian coordinates of 43 monitored points positioned all along the span were experimentally acquired by using an optical tracking system. A simple Galerkin’s scheme applied for modal decomposition, combined with standard Mathieu chart analysis, led to the idenfication of parametric resonances. A curious finding of this paper is that the Mathieu instability may simultaneously occur in more than one mode, leading to interesting dynamic behaviors, also revealed through standard power spectra analysis and displacement scalograms.

This article deals with the main geometric parameters, operating variables and experimental results of engines with different size and characteristics, as well as simulation predictions at operating conditions for which the working fluid may evidence real gas effects. The concept of dimensionless quasi-static indicated work, introduced previously, is computed assuming both ideal and real gas models. Both values are compared with the Schmidt's model prediction, to evaluate separately how the mechanism simplification and the equation of state affect. The influence of physical gas properties are also analysed regarding the gas circuit performance and mechanical efficiency. Pending of experimental corroboration, some simulations show the possibility of obtaining interesting operating conditions under real gas effects. Semi-empirical equations and experimental correlations are proposed as preliminary design criteria. The ratio between the dimensionless values of the maximum indicated power (a sort of ‘indicated’ Beale number) and the quasi-static indicated work is analysed. The procedure to estimate the maximum indicated power is completed by analysing the characteristic Mach number (dimensionless rotation frequency). Analogous procedure is applied for the maximum brake power and corresponding engine speed. Use of dimensionless variables facilitates the generalization of analyses by means of dynamic similarity criteria.

The Local Dynamic Similarity Model (LDSM) is a ventilation model for predicting the discharge coefficient and the inflow angle at the opening of a cross-ventilated building. This model requires a dynamic pressure generated by the wind velocity component tangential to the opening in addition to wind pressure. Also, total pressure, wind pressure, static pressure, room pressure and inflow velocity components are needed for model validation. Under cross-ventilation, it is rather difficult to measure these parameters, especially the total pressure and the velocity components at the opening, as the inflow angle is not known a priori. Therefore, an alternative was sought. This study applied a CFD method to determine the required parameters as a way of using the local dynamic similarity model. The CFD method had been validated with experimental results before the CFD data was used for LDSM. Good agreement was obtained between CFD and LDSM. Consequently the LDSM was also verified by CFD and it was viable t...

The biased subdivision of slurry feed to a number of unit operations in parallel results in each unit operating under different density volumetric flow rate, feed concentration. Consequently some of the units may operate under sub-optimal conditions leading to reduced operating efficiencies of sizing and cleaning units. The objective of this work was to identify the reasons for biased slurry subdivision in the feed distributor of Washery-II, West Bokaro, Tata Steel, Jamshedpur, India. A lab model of the feed distributor was set up at R&D using the principles of geometric similarity and dynamic similarity. A number of experimental investigations were carried out based on Design Of Experiments and the results analysed using ANOVA. The variation of feed rate of coal and its size distribution through different outlet ports were quantified through two terms, the coal split ratio and the variation index. The design of the insert, the number of water inlets, and the feeding position of coal in the distributor were the most important factors affecting the variation index. In case of coal split ratio, apart from the first two variables, none of the others had a significant effect. Four water inlets with symmetrically arranged outlets, equal water flow rate in the inlets and the material being fed in an annular ring into the distributor was found to reduce both the coal split ratio and the variation index. Upon implementation of the recommendations the bias in distribution was reduced and the efficiency of the cyclones improved and hence the coarse clean coal yield increased.