Reduced-scale Tests Research Articles

Mock-up conception for experimentally investigate the creep phenomenon caused by the fluid–structure interaction in a rod bundle

Pressurized water reactors (PWRs) are employed worldwide and continue to expand in capacity. They require thorough investigation, particularly concerning their safety and operational efficiency. To ensure these factors, comprehensive research into their various components and an understanding of the diverse phenomena they experience within a PWR are imperative. These phenomena can be of mechanical, thermal, hydraulic, or neutronic nature. Among these components, fuel assemblies (FAs) hold a main role in PWRs. The intricate interplay of these physical factors results in the modification of FAs geometry, specifically permanent elongation and lateral deformations referred to as irradiation creep. The earliest reported occurrence of these deformations dates back to 1994 in Ringhals reactors, where various FAs exhibited distinct deformations (Andersson et al., 2005). Given that these phenomena occur over a time span of months to years in metallic materials, conducting investigations within the confines of a typical laboratory observation period becomes impractical. Consequently, this project proposes an alternative experimental methodology to overcome this challenge, thus gaining a deeper understanding of the fluency phenomenology in FAs behavior. This methodology consists on the design of a reduced-scale test section, capable of replicating the fluid–structure interaction (FSI) responsible for creep, the creation of spacer grids through 3D printing technology, and selection of the appropriate material for the fuel rods (FRs), with an emphasis on macroscopic coupling effects, rather than focusing into the micro-structural response of the material. To experimentally observe the deformation on the FAs, cameras were used to capture images through the time during the test, to catch the displacement of the FRs. The first results showed the mock-up was able to reproduce the FSI causing the creep on the FAs, it was possible to capture the displacement evolution along time, and to observe different types of deformation, thus, it helps to understand the phenomenon. Further tests and investigations using laser doppler velocimetry (LDV) technique to analyze the flow will be held, to a better comprehension of these burden.

Altitude Correction Method for Audible Noise of ± 800 kV UHVdc Overhead Transmission Line and its Engineering Application

With the improvement of the voltage level of DC overhead transmission lines (OHTLs), the audible noise (AN) caused by the corona discharge of conductors is an increasingly serious problem. AN has become a critical parameter that determines the selection of conductors, line structures and specifications for UHVdc OHTLs in high-altitude areas. To study the altitude correction method of AN for UHVdc OHTLs, we erected 6 × 720 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 6 × 900 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> conductors on DC full-scale test lines located at altitudes of 4,300 m and 50 m, respectively. We carried out an experimental study on AN over a long period and obtained its distribution law at high and low altitudes and its altitude-related increment. At the same time, on four DC reduced-scale test lines located at 4,300 m, 3,400 m, 1,700 m and 50 m above sea level, 6 × 95 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> conductors were erected for experiments. The law that the AN of the DC OHTL shows a nonlinear change with increasing altitude is obtained. Based on the combination of full-scale and reduced-scale tests, an altitude correction method of AN for UHVdc OHTLs considering the influences of both altitude and electric field strength on the conductor surface is proposed. From 0 to 4,300 m above sea level, when the maximum electric field strength on the conductor surface is 19 kV/cm, the increase in AN calculated with the formula suggested by this article is only 55% of the value calculated with the method recommended by the EPRI. The altitude correction formula of AN proposed herein is applicable to the design of UHVdc OHTLs in high-altitude areas, which can greatly save line investment while meeting the requirements of environmental protection.

Scale modeling of thermo-structural fire tests of wood members

Standard fire resistance testing is essential to qualifying wood-based materials to be approved for use in building assemblies. In a previous study, we developed a theoretically based, experimentally validated scaling methodology for reducing the size of the test article while maintaining the same thermal and structural response exhibited in the large-scale test. This paper is focused on demonstrating these scaling laws for wood with combined thermo-structural loading. Due to load capacity limits, dimensional lumber boards at ½-scale and ¼-scale were subjected to combined bending and thermal loading. Samples were placed in static three-point bending with the loading scaled to have structural similitude, while simultaneously, the bottom surface was exposed to a scaled fire exposure. Analytical modeling of wood pyrolysis demonstrated that, due to char kinetics as the heating rate is increased in the tests, equivalently less char is formed in the reduced-scale tests. Therefore, we developed a char timescale correction factor, calculated from both model predictions and measured charring rates, which modified the previous Fourier number time scaling laws. Scaling exposure time by our updated thermo-structural test scaling laws, the smaller ¼-scale test deflection results predict the behavior of the equivalent larger ½-scale tests by between 11.0% to 16.1%.

New method of integrating experiment for maintaining low indoor temperature into numerical modelling: A feasibility demonstration in reduced-scale building model

Reduced-scale building models have been widely used in experiments because of their convenience and flexibility. However, it is difficult to reduce its indoor temperature and maintain the low temperature at low cost. There is also a lack of accurate numerical modelling and verification of the indoor temperature control process in this model. For this purpose, a reduced-scale test chamber was constructed that can be used to conduct experiments in real outdoor environmental conditions. Lower the indoor air temperature by placing ice in the test chamber and maintain it within the range of 10–15 °C, with a temperature difference of approximately 20 °C from the outdoor air temperature. In addition, the temperature control process in experiment was modelled in detail. The experimental values were compared with the simulated values, and the coefficient of variation of the root mean square error between the two is in the range of 3.64–7.71%. This work integrates experiments into numerical modelling, which not only cross-validates the reliability of each other, but also the verified model can be used for subsequent simulation analysis, including in-depth exploration of key factors affecting experimental results, and calculation of important results that are difficult to measure directly in experiments.

Innovative PCM-incorporated foamed concrete panels for walls’ exterior cladding: An experimental assessment in real-weather conditions

This study aims to develop innovative exterior cladding panels capable of improving the walls’ thermal performance for new and existing buildings. A phase change material (PCM) was incorporated into foamed concrete (FC) to develop innovative PCM-incorporated FC (PCM-FC) cladding panels, which were assessed as an exterior finishing of cement brick wall and compared to the conventional cement rendering. The test was conducted using reduced-scale testing cells in real-weather conditions and for four cardinal orientations. The developed PCM-FC cladding panels yielded remarkable reductions in the wall’s internal surface temperature and the cell’s internal air temperature, reaching 6.75 ℃ and 5.50 ℃, respectively. Moreover, the developed cladding panels performed effectively for the four cardinal orientations, yet their effectiveness varied according to the intensity and the time of receiving direct solar radiation. Furthermore, a low decrement factor of 0.49 and a 32.1% reduction in the intensity of overheating were obtained when using PCM-FC cladding panels compared to Ref-CR. The developed PCM-FC cladding panels substantiated superior thermal performance in reducing external heat gain, which results from the combined effects of PCMs’ high thermal energy storage and FC’s low thermal conductivity. Therefore, these PCM-FC cladding panels can potentially contribute to reducing buildings’ high energy consumption.

Numerical Prediction of Cables Fire Behaviour Using Non-Metallic Components in Cone Calorimeter

ABSTRACT Electrical cables must fulfil the Construction Product Regulation (CPR) by testing them according to EN 50,399. Nevertheless, an unfordable trial and error procedure could stem from the definition of new cables. To achieve a better understanding of fire behavior of cables, researchers have been using techniques such as bench and reduced scale tests and computational fire models result in a way to minimize trial and error process. The present work proposes the combination of bench scale tests, using cone calorimeters and fire simulation modeling. In a first step, the thermal characterization of the cable parts is carried out, and then, in a second step, use these data to model complete cable samples in cone calorimeter tests. The simulations are compared with experimental data of two already rated cables. This process is intended to discard erroneous configurations, which display in bench scale signs of misbehavior compared with rated cables. This would avoid the manufacture of the complete cable if the results do not fulfill the requirements, and eventually, proceed to its production and test in full-scale when they do. This work has been carried out with two multi-core cables and the materials they were made of, and the results showed: a) the inverse modeling process to characterize materials parts obtained a fairly accurate approach, with small inaccuracies in the peaks of the curves; b) two simulation models (simple and detailed) were able to reproduce in general terms the heat release rate curve; however, they released more energy than experimental tests and some discrepancies in the peaks were observed. Despite its simplicity, simple model obtained results fairly close to the experimental curves and took less time to simulate.

Can heavy rainfall affect the burning and smoke spreading characteristics of fire in tunnels?

Extreme rainfall events are increasingly common under the current trend of global warming. This work investigates how a heavy rainfall on one exit affects the fire burning and the smoke spread in tunnels. Several reduced-scale tests are designed with various rainfall intensities (up to 60 mm/h, equivalent to 232 mm/h in nature), raindrop sizes (1.0-1.5 mm, equivalent to 4-6 mm in nature), and tunnel fire heat release rates (2.1-6.7 kW, equivalent to 2-6 MW in real scale). Experiments show that heavy rainfall on one exit can induce a longitudinal airflow inside the tunnel, and the induced airflow is caused by the increased pressure at the rainfall exit. The airflow pushes the flame tilting towards the no-rainfall portal, and the correlation models of the flame length and flame inclination are characterized by considering the induced airflow and rainfall. The rainfall-induced airflow has a limited effect on the burning rate of pool fires, but it can change the ceiling temperature and limit the smoke back-layering toward the rainfall portal. In contrast, the ceiling temperature distribution towards the no-rainfall portal is found not sensitive to rainfall, which can be well described by an empirical model.

Kv-scaling in thermal hydraulics: Background, applications and forthcoming uses

Addressing the scaling issue refers to a rather complex process of demonstrating the applicability of activities devoted to predict the behaviour of actual nuclear power plants using the knowledge acquired in scaled-down test facilities. Such activities involve, among others, the evaluation of the capability of Best Estimate codes to scale-up processes from reduced scale test facilities to full scale Nuclear Power Plants (NPP) and the quantification of the effects of scale distortions. In this context, a Kv scaled calculation is a system-code simulation in which, defined test conditions of an Integral Test Facility (ITF) are scaled-up to a NPP nodalization to reproduce the same scenario. The practical use of such kind of calculation is to permit a comparison of the behaviour of the plant and the ITF nodalizations under the same conditions. The comparison between the NPP Kv-scaled results and those of the experiment post-test calculation will show unavoidable differences or distortions. Explaining such distortions is the key process in methods devoted to qualify plant nodalizations. The aim of this paper is to show the effectiveness of Kv-scaled calculations and to outline the forthcoming use of hybrid nodalizations and scale-up nodalizations. The paper includes a thorough literature review of these type of approaches as well as the perspectives of future use of the Kv scaling analysis. Such future uses include the feedback to experimentation. Despite the fact that the hybrid calculations presented here are related to existing ITFs and NPPs, feedback to experimentation intents to show the essentials of a future practice to be mainly implemented in modular ITFs.

Causative process related method for the design of a reduced scale test facility for boron dispersion analysis in the pressurizer of SMRs

Pressurizers are important components placed in Pressurized Water Reactors (PWRs) and are responsible for pressure control. Although traditional PWRs have a continuous flow maintained by spray devices in order to promote mixing between primary coolant system and pressurizer water, one alternative for Small Modular Reactors (SMRs) is to replace surge lines and sprays by surge orifices aiming at homogenizing boron concentration in the whole primary system. Such process of homogenization is necessary in order not to promote power transients. This paper intends to compare thermal-hydraulic parameters obtained by a scaling methodology – Causative Process Related Method – with those derived by another scaling technique. The conservation equations representing boron concentration are derived for the two liquid regions inside the pressurizer. The scaling methodology is applied to these equations, providing dimensionless parameters necessary for boron dispersion similarity. By considering one-fourth symmetry and reduced scale for time (1/5) and space (1/200), a test facility based on these parameters (e.g., circulation flow and condensation rate respectively equal 0.00000335 m3/s and 0.0001 kg/s) is under construction and shall be used to evaluate boron dispersion in SMRs, providing reliable results with a reduction of costs. The evidence of trustful results is verified when normalized concentrations at the respective dimensionless times are compared for both model and prototype.

Experimental and simulation study on braking noise characteristics and noise reduction strategies of the friction pair between the SiCp/A356 brake disc and the synthetic pad

During the braking process, abnormal noise often occurs between the friction pair of SiCp/Al composite disc and synthetic brake pad. Through 1:1 bench noise test and simulation method based on complex eigenvalue analysis, the induction mechanism, influencing factors, variation rule and noise reduction strategy of braking noise were studied. The results of MM-1000 friction reduced-scale test and simulation show that the sound pressure levels of two groups of friction pairs using SiCp/A356 composite material are lower than those of FE-928W friction pair under the same working conditions. The friction surfaces of different friction pairs show different degrees of surface scratches, material transfer and peeling, which will cause the friction pairs to have different tribological properties and contact relationships, resulting in differences in braking noise. 1:1 bench test and simulation results show that the main type of brake noise of service brake parts is brake squeal, which is induced by the braking temperature rise. Its main frequency is concentrated around 2.2 kHz, and the maximum sound pressure level can reach 110 dB(A). Braking squeal is more likely to occur when the energy input of a single brake is too large, resulting in high temperature rise of the brake parts, or when the brake temperature is kept at a high level in continuous braking for several times. The orthogonal test and the control variable method were used to study the influence law of 10 variables on the tendency of braking noise. It is found that the brake pad is the main component of the braking noise, and the friction coefficient of the friction pair and the Young's modulus have a significant effect on the tendency of braking noise. Considering the test results and simulation laws, the brake noise control strategies were proposed, such as increasing the chamfer depth of the pad friction surface, reducing the friction coefficient of the friction pair, increasing the young's modulus of the pad and controlling the brake temperature rise. In addition, compared with the original model, the instability tendency coefficient (TOI) of the new disc model established through variable selection is reduced by 81.21 %, and the brake noise tendency is obviously reduced, which verifies the effectiveness of the brake noise control strategy at the simulation level.

Recent Advances in Laterally-Loaded Piles within Mechanically-Stabilized Earth Walls

Pile foundations have been increasingly installed within mechanically-stabilized earth walls (MSE) on rocks or compressible soils to support structural loads. Integral abutment bridges, sound walls, and traffic signs are common examples of the structures supported by pile foundations installed within or behind MSE walls. These structures are often subjected to lateral loads resulting from earthquakes, traffic loads, wind loads, and/or thermal expansion and contraction of bridge girders. Typical approaches available to design MSE walls are limited to MSE walls without pile foundations present within reinforced fill. To minimize the interaction between piles and the MSE wall, designers often suggest to place the piles at a distance of six to eight times the pile diameter and/or isolate the piles from the MSE wall by using corrugated pipes. These suggested designs lead to increasing the cost of projects by increasing the length of bridge spans or the diameter of piles and requiring pile embedment. Recently, several studies have been conducted to understand the interaction between piles and MSE walls when the piles are constructed within and close to wall facing. This paper provides a literature review on full-scale tests, reduced-scale tests, and numerical studies of piles constructed within or behind MSE walls. The review will focus on the effects of three key influence factors on lateral capacities of laterally-loaded piles and facing deflections of MSE walls including the plie location behind the wall facing, the ratio of the reinforcement length to the wall height, and the stiffness of the reinforcement layer. This paper will also discuss the available approaches to estimate the forces in the reinforcement layers and the lateral earth pressures behind the MSE wall facing due to the laterally-loaded piles.

Field test and numerical simulation of a full-scale RC pier under multiple lateral impacts

In recent years, the frequent occurrence of vehicle-pier collision accidents have highlighted the necessity of the research on the impact resistance of bridge piers; but until now, most of the studies employed numerical simulations or indoor reduced-scale tests, while the collision tests regarding full-scale reinforced concrete (RC) piers with actual foundations are still scarce. In order to obtain the most realistic impact responses and damage characteristics of RC pier, six successive lateral impact tests on a full-scale RC single-column pier with a monopile foundation were conducted in this study based on a self-designed large-size slide device and a rigid model vehicle. The mass of the model vehicle was 2205 kg and the impact velocity ranged from 3.17 m/s to 8.22 m/s. The tests obtained valuable test data such as vehicular impact forces, and lateral displacements, accelerations and damage pattern of the RC pier under all the six collision trials. Furthermore, finite element (FE) simulations were also performed and validated against the test results, where several problems of the commonly-used FE simulation techniques are revealed. In addition, the influences of multiple (successive) impacts on the impact forces and dynamic behavior of the pier are also discussed in this paper. This study provides valuable experimental data for the current research on RC piers subjected to vehicle collisions, and also references for the numerical simulations and theoretical analysis of RC columns under multiple lateral impacts.

An experimental and simulated investigation into the validity of unrestricted blast wave scaling models when applied to transonic flow in complex tunnel environments

Since the inception of high explosives as an industrial tool, significant efforts have been made to understand the flow of energy from an explosive into its surroundings to maximize work produced while minimizing damaging effects. Many tools have been developed over the past century, such as the Hopkinson–Cranz (H-C) Scaling Formula, to define blast wave behavior in open air. Despite these efforts, the complexity of wave dynamics has rendered blast wave prediction difficult under confinement, where the wave interacts with reflective surfaces producing complex time-pressure waveforms. This paper implements two methods to better understand blast overpressure propagation in a confined tunnel environment and establish whether scaled tests can be performed comparatively to costly full-scale experiments. Time–pressure waveforms were predicted using both a 1:10 scaled model and three-dimensional air blast simulations conducted in Ansys Autodyn. A comparison of the reduced scale model simulation with a full-scale blast simulation resulted in self-similar overpressure waveforms when employing the H-C scaling model. Experimental overpressure waveforms showed a high level of correlation between the reduced scale model and simulations. Additionally, peak overpressure, duration, and impulse values were found to match within tolerances that are highly promising for applying this methodology in future applications. Using this validated relationship, the simulated model and reduced scale tests were used to predict an overpressure waveform in a full-scale underground mine opening to within 2.12%, 2.91%, and 7.84% for peak overpressure, time of arrival, and impulse, respectively. This paper demonstrates the effectiveness of scaled, blast models when predicting blast wave parameters in a confined environment.

Failure criterion of double-plate vertically loaded anchor in saturated marine fine sand under monotonic loading

The critical penetration depth and failure displacement of vertically loaded anchor (VLA) have already been investigated. However, only few investigations focused on the double-plate VLA. Therefore, based on the finite element method, the critical penetration depth for the double-plate VLA was obtained, which is approximately 6.0 times the width of the upper fluke of the double-plate VLA. According to the reduced-scale model tests, the failure displacement of the double-plate VLA with different included angles and dimensions of the bottom fluke under shallow-embedded and deep-embedded conditions was obtained. Furthermore, the failure displacement of double-plate VLA with 30° included angle and the dimension of bottom fluke equal to that of upper fluke under shallow-embedded and deep-embedded condition is 0.29 and 0.67 times the width of upper fluke, respectively. Based on the empirical bearing capacity formula for VLA model, an improved bearing capacity formula for double-plate VLA model has been put forward; by means of the improved bearing capacity formula, the coefficient of bearing capacity for double-plate VLA under shallow-embedded and deep-embedded condition is obtained to be 5.013 and 4.106, respectively.

Eksperimentalna ocjena učinkovitosti prijenosa opterećenja na betonskim kolnicima bez moždanika

Generally, joint performance in concrete pavements is evaluated in laboratory by applying dynamic loads that require large scale experimental setups. In order to propose a simplified laboratory test, a comprehensive literary review of the fundamentals of load transfer at joints is made, and the load transfer efficiency obtained via a reduced scale test is compared under static and dynamic conditions. The results confirm feasibility of static analysis via a reduced scale test for evaluating load transfer efficiency of non-dowelled concrete pavements.

Factors influencing the fire dynamics in open-plan compartments with an exposed timber ceiling

Fires in open plan compartments have been the subject of much research over the past decade. This article presents results from an experimental study conducted to explore factors that influence fire dynamics in open-plan compartments with an exposed timber ceiling.A reduced scale testing methodology is proposed and supported by contrasting observed fire behaviour at small scale with large-scale experiments reported in the literature. The reduced-scale experiments highlight the complexity of the fire dynamics. Factors which govern the behaviour include the ignition and self-extinction of the timber; the role that the timber plays in accelerating the transition from Mode 3 (travelling) to Mode 1 (fully developed) behaviour; the ignition and self-extinction of timber which is in a downward facing orientation; the thermal inertia of the ceiling material.Results demonstrate that: different fire modes observed in large scale compartments occur in large scale compartments with combustible timber ceilings; ceiling intrusions influence the fire; and factors that influence the response of timber in open plan compartment fires can, to a large extent, be explained by existing knowledge extracted from bench scale testing and compartment fires with non-combustible linings.

Design of an Electromagnetism-Based Transmission Line Galloping Test System

Existing transmission line full-scale tests rely on natural winds and have low test efficiency. In this paper, taking a reduced-scale test line with a 35.4 m span as an example, an electromagnetism-based transmission line galloping test system is designed. The plunger electromagnet periodically provides mechanical energy which vibrates the wire system in place of complex pneumatic loads. The finite element model of the electromagnet device is established and the influence of related parameters is analyzed. The power supply and control circuit of the excitation device are designed. The vibration of the transmission line is monitored by accelerometers and the displacement calculation method based on discrete wavelet transform (DWT) is proposed. Considering the geometric nonlinearity of the wire system, an adaptive excitation method based on wavelet decomposition and reconstruction of the acceleration signal is proposed. The vibration response of the wire under different coil currents and excitation modes is monitored and analyzed. The results show that the actual line galloping can be simulated by the designed electromagnetic system, the vibration frequency is close to the second natural frequency and the vibration amplitude can be controlled by changing the coil current.

Laterally-loaded pile-MSE wall system performance under different design configurations

The need for constructing a shallow or deep foundation (e.g. piles) in a mechanically stabilized earth (MSE) wall for superstructure support has increased. However, the performance of laterally loaded piles within the MSE wall and their interaction with soil and reinforcement are not fully understood. Limited full-scale tests and numerical studies have been conducted to evaluate the behavior of laterally-loaded piles within MSE walls. In this study, thirteen reduced-scale model tests were performed to investigate the effects of changing the wall configuration (wall height, and reinforcement spacing and length) and the pile location on the performance of the pile-MSE wall system under static lateral loads. This experimental study found that the piles in high walls could develop larger maximum compressive and tensile strains. Low walls resulted in larger wall facing deflections and maximum tensile strains in the geogrid reinforcement. Small reinforcement spacing and long reinforcement length resulted in higher pile lateral load capacities, smaller wall facing deflections, and smaller reinforcement tensile strains. The pile offset from the back of the wall facing is a critical factor that affected the pile capacity, the wall facing deflection, the reinforcement tensile strain, and the lateral earth pressure distribution behind the wall facing.

Experimental Investigation of Piezoelectric Energy Harvesters Applied in Concrete Pavement

This paper proposes the application and manufacturing of piezoelectric devices based on pile and arc-bridge transducers to harvest mechanical energy from concrete pavement. Multi-scale experiments are conducted to clarify the influence of electrical connection, load resistance, traffic speed, and loading times on the electrical properties of the harvesters. The reduced-scale test shows that the transducers should be connected to rectifiers before being connected as an array. Moreover, the output power of the arc-bridge transducer with resistance variations is unstable compared with that of the pile transducer. Accelerated pavement testing illustrates that the output power of the half pile array device increases to 1.7 mW with an optimal resistance of 10.0 MΩ; reducing the internal equivalent resistance is a potential way to increase the energy output. The results also show that the load speeds significantly influence the profile of the voltage and have a minor effect on the generated electric energy in the tested conditions. Furthermore, the electrical properties of the piezoelectric device exhibit no statistical degradation after the electrical fatigue test of 100,000 tire loads, indicating a novel electrical fatigue performance. The findings in this paper can further guide the application of such piezoelectric devices in concrete pavement.

Causative Process Related Method for the Design of a Reduced Scale Test Facility for Boron Dispersion Analysis in the Pressurizer of Smrs

Causative Process Related Method for the Design of a Reduced Scale Test Facility for Boron Dispersion Analysis in the Pressurizer of Smrs