Scale model tests

Scale-model testing is used with very large pumps such as water feed pumps for thermal power stations. The problems posed by such tests in establishing the full-size machine performance are well discussed in a paper contributed by workers studying pumps for the Central Electricity Board . 

The heat transfer from tubes in the freeboard was also measured for the 20 MW model. Figure 45 shows a comparison of the measured overall heat transfer coefficient in the 20 MW pilot plant versus that predicted from the scale model test. When the bed height is lowered, uncovering some tubes, the heat transfer is reduced because there are fewer particles contacting the tube surface. Although the scale model did not include proper scaling for convective heat transfer, the rate of change of the overall heat transfer should be a function of the hydrodynamics. 

All hydrocarbon fire mechanisms and estimates will be affected by to some extent of flame stability features such as varying fuel composition as lighter constituents are consumed, available ambient oxygen supplies, ventilation patterns, and wind effects. Studies into these effects have generally not progressed to the level where precise estimations can be made without scale model tests or on site measurements. 

It is important that, to optimize the collection efficiency, the gas distribution across the frontal area of the precipitator must be as uniform as possible, although some recent work has indicated that for certain conditions a skewed velocity profile can be advantageous. It is not easy to produce a typical operational gas velocity of around 1.5m/s, which has been decelerated from approximately 15m/s in the inlet approach ductwork, and an acceptable standard of distribution is an RMS deviation of 15%. This standard can be achieved through field corrective testing, large-scale model tests, or the more recent CFD approaches.f ... 

Construction of a scale model must be accompanied with an analysis to determine test conditions that ensure the test results from the scale model are representative of the processes in the prototype. In combustion applications, although most of the processes are inherently at elevated temperatures, physical modeling is usually carried out under isothermal conditions. Isothermal physical modeling technique is based on the principle of relaxation. Under this principle, the variables that are important for the phenomena under study are stressed. The variables that are stressed are duplicated as necessary to obtain a representative result. No scale physical model can be an exact model of the reality unless an exact full-scale prototype is made. However, by using accurate correlations the modeling work can provide a good qualitative understanding of the fluid dynamics in the prototype. This chapter attempts to answer the question How does one ensure that the scale model test results are representative of the actual processes in the prototype ... 

Many scale model measurements include quantitative measurement of pressure drops throughout the system. Maximum allowable system pressure drop is frequently a major constraint from the equipment manufacturer or end user when flow correction solutions are sought. System pressure drop directly relates to the operating cost due to blower/fan power consumption and the hydraulic head available for downstream power or steam generation. For scale model testing, pressure... 

Yoo, B, Lee, J H and Koo, G H, Study of reduced-scale model test results of high dampmg laminated rubber bearmg for hquid metal reactor, KAERI/TR-539/95, (1995)... 

Damping values for the reactor core are 10 percent and 20 percent for the OBE and SSE respectively. These values are based on data obtained from scale model tests on a similar core configuration of graphite fuel and reflector elements. Typical values of 20 percent were obtained when the core is... 

James Wesley Ball graduated as civil engineer from Colorado State University. He also held an MS degree in civil engineering from the University of Colorado. Ball joined the US Bureau of Reclamation USBR, Denver CO, for over 30 years, supervising scale-model tests of hydraidic structures. His research was described in a number of technical publications. 

The enterprise shall mitigate system-level risks to include products risks that were assessed to be critical to system development during concept selection. For critical risks associated with products, the enterprise utilizes simulation, scale-model tests, or prototype tests to demonstrate mitigation of risks to an acceptable level. The enterprise should assess subsystem risks and prioritize critical risks based upon probabihty of occurrence and related consequences to cost, schedule, and/or performance. 

Care has to be exercised when planning the instrumentation and analysis of either a scale model test or a full scale test. It should be ensured that adequate and correctly calibrated instrumentation and test devices are provided so that the test results may be documented and evaluated in order to verily the test results. At the same time, it is necessary to ensure that the instrumentation, test devices and electrical connections do not interfere with the model in a way that would invalidate the test results. 

When an application for approval of a package design is based to any extent on scale model testing, the application should include a demonstration of the validity of the scaling methods used. In particular, such a demonstration should include ... 

Centrifuge model test is to carry the Hn reduced-scale model test in the space with ng inertia. This test method can make the model and the prototype have equal stress and strain, similar deformation and failure mechanism. It is very useful in simulating the characteristic of geotechnical engineering where the self-weight acts as the main load. 

Jeon S., Kim X, Seo Y. 2004. Effect of a fault and weak plane on the stability of a tunnel in rock—a scaled model test and numerical analysis. International Journal of Rock Mechanics Mining Sciences. 41(3) l-6. 

It s worth noting that all the above findings are based on laboratory-scale model testing. For field applications, there are many technical problems that need to be solved, such as, the installation of horizontally arranged sensing fiber in the slope mass. 

English engineer William Froude was the first to prove the validity of scale-model tests in the design of full-size vessels. He did this in the 1870 s, building and operating a model basin for this purpose. 

Figure 14.7 shows the lateral drifts of 39 scale-model tests at the recoverability limit in comparison with the maximum achieved drifts (point D or E of Fig. 14.1 according to colunm response). Figure 14.7(a) displays colunms with flexural and lap-splice deficiencies, and columns with shear deficiencies are depicted in Fig. 14.7(b). Below the line representing the lateral drifts of the columns at the recoverability limit, columns are within the recoverable state and beyond this line, columns residual drifts are over 1%, which means columns enter into the irrecoverable state. Although lateral deformation at the recoverability limit of any of these samples does not correspond to a specific point on the idealized lateral load-deformation relationship of the FRP-RC damage-controllable structure, it is noticeable that most columns could not stay recoverable until point D of Fig. 14.1 (the end point of the achieved post-yield stiffness). 

H. Oumeraci and M. Muttray, Large scale model tests on a high-mound composite type breakwater, Research Report No. 818, Leichtweiss-Institute for Hydraulics, TU Braunschweig (1997), pp. 115. 

Scale effects result from incorrect (or distorted) reproduction of a prototype water-structure interaction in the model. The ideal model requires that both Proude s and Reynolds laws are met simultaneously. This is not possible without changing the test fluid so, scale effects cannot be avoided when performing scaled model tests. They can, however, be minimized for the main processes, and/or corrections can be applied where the distortion is understood. 

It is not expected that instability will occur at once if the uplift pressure exceeds the gravity forces. On the other hand, the above result turns out to be in good agreement with the experimental results. The experimental verification of stability of gabions is rather limited. Small scale model tests have been performed by Ashe and Brown see Fig. 19.15. 

The empirical parameter was determined by stability tests in a large and a small wave flume to Cy, = 2.75. In Fig. 21.16 only the results of the large-scale model tests are plotted to illustrate that the threshold curve between stable and imstable containers is obtained for Cw = 2.75. 

Fig. 21.16. Stability of slope containers from large-scale model tests (modified from Ref. 28).

Fig. 21.19. Stability of crest containers form large-scale model tests.

GSC-rcvetment During large / scale model tests at GWK... 

H. Oumeraci, M. Bleck, M. Hinz and S. Kiibler, Large-scale model test for hydraulic stabihty of geotextile sand containers under wave attack, Leichtweiss-Institute for HydrauHc Engineering and Water Resources, LWI Report No. 878 (2002) 62 and Annexes. 

The equilibrium between these two effects causes mixed convection and stratified flow. The stratification interface oscillates and may induce severe damage to the neighbouring structures. Furthermore, the support structures at the bottom of the hot pool have to be protected from hot sodium. The behaviour of such a region has been studied, namely for SPXl [8.27] and EFR [8.19]. Studies were mainly conducted through scale model tests, because computations are not yet able to predict the fluctuation characteristics for such complex situations. As the main physical phenomenon of interest is the interaction between buoyancy forces (natural convection) and inertia forces (forced convection from the main pool... 

William Fairbairn (1789-1874) had been testing full-size metal girders and fabrications, calibrating practical observations with theory and simple rules of thumb. He was enlisted for a series of large-scale model tests. For analytical justification of his sizes, Stephenson went to the farmer turned mathematician Eaton Hodgkinson (1789-1861), well versed in the latest theoretical developments being made on the Continent. 

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