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Deflectors offer a cost-effective solution for enhancing airflow distribution. The purpose of this paper is to investigate the effect of the deflector on the indoor airflow velocity distribution under natural ventilation conditions. The results obtained from numerical simulations are validated through experimental measurements using a reduced-scale model. Subsequently, the validated reduced-scale numerical model was extended to full-size rooms. A full-size numerical simulation method is used to analyze the effect of no deflector, deflectors with different opening width-to-height ratios and deflectors with different opening shapes on the percentage of indoor velocity partitions under natural ventilation conditions. The findings reveal that the judicious installation of deflectors can enhance indoor airflow velocity distribution and increase the percentage of the indoor comfort zone. Deflectors with different opening width-to-height ratios exert distinct influences on indoor airflow velocity distribution. When the deflector opening width-to-height ratio is set at 7/6, the indoor comfort zone percentage reaches its maximum at 75.98%. Furthermore, the shape of the deflector's opening significantly affects indoor airflow velocity distribution, and when the opening shape is a rhombus shape of 4.00 cm x 9.00 cm, the proportion of indoor velocity comfort zone is the largest, which is 75.56%. This study provides a reference for the design and practice of natural ventilation in buildings. [ABSTRACT FROM AUTHOR]

Converter transformer is the key equipment in UHVDC transmission. If a local overheating fault occurs, it will inevitably form a local hot spot on the core, winding or other structural parts. Among these faults, multipoint grounding and interlaminar short circuit faults account for 30–50% of core accidents. The continuous overheating of 150–250 °C will cause ablation on the silicon steel sheet, which will destroy the insulation material and reduce the insulation performance. In severe cases, it will cause thermal expansion, resulting in local deformation or displacement of the core. Considering the scale of size and temperature parameters, the scale model of converter transformer is established based on the principle of constant magnetic flux density. By using the homogenization theory, the scaled model under multipoint grounding and interlaminar short circuit fault is simulated by electromagnetic heat. First, the single-phase four-column model of the core is established according to the scaled principle, and the core is refined. Secondly, taking the refined model as the research object, the magnetic thermal coupling simulation and analysis are carried out under multi-point grounding and interlaminar short circuit fault, and the magnetic density, eddy current loss and temperature distribution on each lamination are obtained. Finally, the correctness of the simulation is verified by the one-dimensional eddy current loss analytical equation, which provides a reference for the local overheating problem of converter transformers. [ABSTRACT FROM AUTHOR]

Deflectors offer a cost-effective solution for enhancing airflow distribution. The purpose of this paper is to investigate the effect of the deflector on the indoor airflow velocity distribution under natural ventilation conditions. The results obtained from numerical simulations are validated through experimental measurements using a reduced-scale model. Subsequently, the validated reduced-scale numerical model was extended to full-size rooms. A full-size numerical simulation method is used to analyze the effect of no deflector, deflectors with different opening width-to-height ratios and deflectors with different opening shapes on the percentage of indoor velocity partitions under natural ventilation conditions. The findings reveal that the judicious installation of deflectors can enhance indoor airflow velocity distribution and increase the percentage of the indoor comfort zone. Deflectors with different opening width-to-height ratios exert distinct influences on indoor airflow velocity distribution. When the deflector opening width-to-height ratio is set at 7/6, the indoor comfort zone percentage reaches its maximum at 75.98%. Furthermore, the shape of the deflector’s opening significantly affects indoor airflow velocity distribution, and when the opening shape is a rhombus shape of 4.00 cm × 9.00 cm, the proportion of indoor velocity comfort zone is the largest, which is 75.56%. This study provides a reference for the design and practice of natural ventilation in buildings.

Shake table tests on two-tiered metal-strip MSE walls showed that the prevention of slip surface development in the lower half of the wall, improving seismic stability by increasing failure threshold acceleration, and mitigating acceleration amplification were the main advantages of using a two-tiered configuration in constructing MSE walls. This was also found that the use of an insufficient offset distance not only eliminated the advantage of the tiered configuration for reducing wall deformations, but also increased the wall crest displacement. Hence, 0.22 H was found to be as the minimum offset distance required when constructing MSE walls in a two-tiered configuration. [ABSTRACT FROM AUTHOR]

The aeroelastic wind tunnel testing of flexible roofs made of hyperbolic paraboloid cable nets is a challenging task for designers and researchers, with very limited documented experiences in the literature. The reduced-scale model construction and its dynamic identification are the main issues to address when approaching this problem, mainly because of (i) the very small mass of the roof, (ii) the strict aeroelastic criteria to satisfy and (iii) a large number of very closely spaced significant natural frequencies. To suggest an approach to follow to investigate the wind—structure interaction for this structural typology, this paper discusses the aeroelastic scaling, the aeroelastic model construction, the dynamic modal identification and the FEM predictive numerical modelling of hyperbolic paraboloid roofs (HPRs) with square, rectangular and circular plan shapes and two different curvatures. Modal identification is especially challenging due to the presence of several closely spaced modes and it is here tackled by different methods such as Welch’s method, random decrement technique (RDT), Empirical mode decomposition with a time-varying filter (TVF-EMD) and frequency domain decomposition method (FDD). The satisfying accuracy of the aeroelastic scaling has been verified by comparing the wind-induced vertical displacements of the prototypes against those of the experimental models. Furthermore, an extensive qualitative investigation of the natural mode shapes has been carried out revealing that test models reproduce most of the prototype modes. [ABSTRACT FROM AUTHOR]

In order to test the anti-impact performance of the refuge chamber and verify the reliability of the experiment on the scaled model of the refuge chamber, the reduced-scale model and the original model of the refuge chamber were established in this paper. By using the finite element software ANSYS Workbench, the dynamic response results of the two models under impact loading are simulated and analyzed. The results show that the response results of the reduced scale model are similar to the original scale model. The response results of the reduced scale model of the rescue capsule under impact load can be used to reasonably and effectively reflect the response results of the original scale model of the rescue capsule.

This paper aims to determine the instrumental measurement uncertainty of conductance transducers for maritime reduced-scale models developed in hydraulic experimental facilities. These transducers are used for the measurements of wave levels and their variations under a dynamic regime (being the measurement principle and method briefly described in the paper). Several metrological characterization methods are also presented, aiming to identify and quantify measurement uncertainty components, namely electrical stability, linearity, reversibility, repeatability, and thermal influence. The obtained results were applied in the evaluation of the transducer instrumental measurement uncertainty. [ABSTRACT FROM AUTHOR]

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An ultra-high voltage (UHV) transmission system offers higher bulk capacity and transmission over longer distances compared with conventional transmission systems, and the dynamic responses of such systems have attracted the interest of researchers. This paper focuses on an experimental investigation of the seismic performance of a 1000 kV UHV transmission system subjected to near-fault ground motions. To reproduce the genuine structural responses, a 1:25 reduced-scale experimental model was designed and constructed based on Buckingham's theorem. Four kinds of typical natural seismic records were selected, namely, far-field, pulseless near-fault, forward-directivity near-fault and fling-step near-fault ground motions, and shaking table tests were subsequently carried out. Furthermore, the influences of the coupling effect between towers and lines, two-component ground motions, and the near-fault effect on the seismic response were investigated. The results demonstrate that the above three factors have a significant influence on the structural response and should not be neglected in seismic analysis. This research enriches the available experimental data and provides a more comprehensive understanding of the seismic performance of UHV transmission systems. [ABSTRACT FROM AUTHOR]

Featured Application: This paper proposes a new equivalent technique, the DC bias current equivalent relationship between the UHV transformer and the reduced-scale model (RSM) is established by means of the identical saturation degree, the proposed RSM is capable to reflect the actual operation of the UHV transformer under DC bias. The DC bias of transformers as a result of geomagnetically induced currents (GIC), monopole operation of high voltage direct current (HVDC) transmission and the increasing power electronic devices in the power grid, creates a high magnitude of fundamental and harmonic components in winding currents, reactive power, and vibro-acoustic noise. For transformers with large capacity, it is very expensive and difficult to carry out an in-depth DC bias effects investigation on a practical equipment, especially for the ultra-high voltage (UHV) transformer. In this paper, a reduced-scale model (RSM) based on the principle of identical saturation degree is proposed, and the equivalent relationship of DC bias current is obtained. Furthermore, the DC bias platform with the RSM is established, experiments have been conducted to analyze the characteristics of the transformer under DC bias. It turns out from the experiments that the current of high voltage side and excitation are less tolerated to the DC bias current, the distortion occurs during the first half of the cycle and peaking at the quarter. Besides, the no-load loss and total harmonic distortion (THD) increase significantly with an increasing DC bias. The results of the characteristics of RSM with load under DC bias may provide great services in protecting and reducing the DC bias effects on the UHV transformer in actual operation. [ABSTRACT FROM AUTHOR]

Floor acceleration plays a major role in the seismic design of nonstructural components and equipment supported by structures. Large floor acceleration may cause structural damage to or even collapse of buildings. For precision instruments in high-tech factories, even small floor accelerations can cause considerable damage in this study. Six P-wave parameters, namely the peak measurement of acceleration, peak measurement of velocity, peak measurement of displacement, effective predominant period, integral of squared velocity, and cumulative absolute velocity, were estimated from the first 3 s of a vertical ground acceleration time history. Subsequently, a new predictive algorithm was developed, which utilizes the aforementioned parameters with the floor height and fundamental period of the structure as the new inputs of a support vector regression model. Representative earthquakes, which were recorded by the Structure Strong Earthquake Monitoring System of the Central Weather Bureau in Taiwan from 1992 to 2016, were used to construct the support vector regression model for predicting the peak floor acceleration (PFA) of each floor. The results indicated that the accuracy of the predicted PFA, which was defined as a PFA within a one-level difference from the measured PFA on Taiwan’s seismic intensity scale, was 96.96%. The proposed system can be integrated into the existing earthquake early warning system to provide complete protection to life and the economy. [ABSTRACT FROM AUTHOR]

This paper aims to determine the instrumental measurement uncertainty of conductance transducers for maritime reduced-scale models developed in hydraulic experimental facilities. These transducers are used for the measurements of wave levels and their variations under a dynamic regime (being the measurement principle and method briefly described in the paper). Several metrological characterization methods are also presented, aiming to identify and quantify measurement uncertainty components, namely electrical stability, linearity, reversibility, repeatability, and thermal influence. The obtained results were applied in the evaluation of the transducer instrumental measurement uncertainty.

Variable Speed Hydro-Electric Plant (VS-HEP) equipped with power electronics has been increasingly introduced into the hydraulic context. This paper is targeting a VS-HEP Power Hardware-In-the-Loop (PHIL) real-time simulation system, which is dedicated to different hydraulic operation schemes tests and control laws validation. Then, a proper hydraulic model will be the key factor for building an efficient PHIL real-time simulation system. This work introduces a practical and generalised modelling hydraulic modelling approach, which is based on ‘Hill Charts’ measurements provided by industrial manufacturers. The hydraulic static model is analytically obtained by using mathematical optimization routines. In addition, the nonlinear dynamic model of the guide vane actuator is introduced in order to evaluate the effects of the induced dynamics on the electric control performances. Moreover, the reduced-scale models adapted to different laboratory conditions can be established by applying scaling laws. The suggested modelling approach enables the features of decent accuracy, light computational complexity, high flexibility and wide applications for their implementations on PHIL real-time simulations. Finally, a grid-connected energy conversion chain of bulb hydraulic turbine associated with a permanent magnet synchronous generator is chosen as an example for PHIL design and performance assessment.

The DC bias of transformers as a result of geomagnetically induced currents (GIC), monopole operation of high voltage direct current (HVDC) transmission and the increasing power electronic devices in the power grid, creates a high magnitude of fundamental and harmonic components in winding currents, reactive power, and vibro-acoustic noise. For transformers with large capacity, it is very expensive and difficult to carry out an in-depth DC bias effects investigation on a practical equipment, especially for the ultra-high voltage (UHV) transformer. In this paper, a reduced-scale model (RSM) based on the principle of identical saturation degree is proposed, and the equivalent relationship of DC bias current is obtained. Furthermore, the DC bias platform with the RSM is established, experiments have been conducted to analyze the characteristics of the transformer under DC bias. It turns out from the experiments that the current of high voltage side and excitation are less tolerated to the DC bias current, the distortion occurs during the first half of the cycle and peaking at the quarter. Besides, the no-load loss and total harmonic distortion (THD) increase significantly with an increasing DC bias. The results of the characteristics of RSM with load under DC bias may provide great services in protecting and reducing the DC bias effects on the UHV transformer in actual operation.

In developed area, there is not only dense electric power grid, but also dense gas pipelines. In this situation, the DC current injected into the earth through the grounding electrodes of a high‐voltage DC system would aggravate the corrosion and even destroy the protection devices of the pipelines. In this study, a numerical approach is put forward to simulate the potential distribution in gas pipeline, which is regarded as long grounding system with insulating coating on the grounding conductor. The main cathodic protection methods for the pipeline are also modelled. The approach is validated by the experiment on a reduced‐scale model. With this approach, the effectiveness of the measures to reduce the electrode potential distribution along the pipelines is analysed. [ABSTRACT FROM AUTHOR]

• The effect of warping deformation on FCP in balcony opening corners is studied. • FCP model tests of balcony opening corners with warping deformation are performed. • A procedure is used to assess FCP in balcony opening corners with warping deformation. Accurately predicting the fatigue crack propagation (FCP) life of thin balcony opening corner structures with warping deformation using the FCP theory is a major challenging task. Herein, a procedure for analyzing the effect of warping deformation on the FCP in thin balcony opening corner structures is presented. According to the proposed method based on the mode superposition to simulate the warping deformation (MSSWD), the stress intensity factors (SIFs) of cracks at the midpoint of balcony opening corners with warping deformation are appropriately modified. The FCP tests with reduced-scale models are also performed to provide experimental verification data for the given procedure. The fatigue lives of the specimens under various loads are calculated based on the modified SIFs and unique curve model and then are compared with the test data. The obtained results reveal that this approach can precisely predict the FCP lives of thin balcony opening corners with warping deformation. [ABSTRACT FROM AUTHOR]

This study hypothesizes that reduced-scale models for computational fluid dynamics (CFD) simulations of wind flow and related processes can save numerical resources. To test this hypothesis, both theoretical analysis and a numerical case study are conducted. The CFD simulations are validated against a set of wind tunnel experimental data. Both theoretical and numerical results support the hypothesis. It is found that a reduced-scale model requires fewer cells than a full-scale model to achieve a target near-wall z + value and prediction accuracy and therefore has the potential to save numerical resources. Quantitative analysis shows that this potential is very large, depending on many factors, such as the scaling factor, the target z + value, and the flow problem. The findings of this study should be useful for CFD simulations of wind flow and related processes, particularly over large areas. However, special attention should be paid to the disadvantages of using reduced-scale models, such as the difficulty to fulfill the similarity requirements. [ABSTRACT FROM AUTHOR]

Reduced-scale shaking table testing is a useful tool for understanding the seismic behavior of geosynthetic-reinforced soil walls. This paper presents the results from a series of reduced-scale shaking table tests on eight different configurations. The effects of change in peak ground acceleration, reinforcement length and spacing, model scale, treatment of the top two facing block layers on the accelerations on a wall face, maximum displacements of the wall face during shaking, permanent displacements, and strains in reinforcement are investigated. Maximum accelerations measured on the wall face during shaking increased from bottom to top. Geotextile length and spacing did not affect the maximum accelerations and face displacements when the geotextile length met the minimum requirements of established design procedures. No significant permanent displacements were observed. Decreasing the geotextile length and increasing the geotextile spacing increased the geotextile strains when the geotextile was long enough to provide anchorage beyond the potential failure surface. [ABSTRACT FROM AUTHOR]

Highlights: [•] We present results from a reduced-scale physical model of revolving door. [•] Air displaced by door rotation is two orders of magnitude inferior to previous data. [•] Increasing the door rotation speed does not increase significantly the air displaced. [•] Correlation-based models to be used for on-site estimation of the air displacement. [ABSTRACT FROM AUTHOR]

The possibility for DC and AC power lines running parallel to each other, sharing the same right‐of‐way or even the same tower has been increased in China. In this work, the coupled DC and AC electric field effects are analysed with a reduced‐scale model. Improved measuring methods are proposed to obtain both the DC and AC components of the ground level electric field and ion current density. Depressing effects of the AC field on the ground level DC field and of the DC field on the ground level AC field are observed when the applied DC voltage exceeds the onset value. The mechanism of the influences of AC power lines on the nearby DC power lines is analysed with experiments and simulations. Both the influence of the AC field on the corona onset on the surfaces of DC conductors and the influence of the AC field on the motion of the space charges are proved to be important in the field effects under the hybrid lines. [ABSTRACT FROM AUTHOR]

The reduced-scale model of HVDC transmission lines in the laboratory is widely used to investigate the ionized fields. This paper is aimed at analyzing impact factors of the ion-current density measurement system based on Wilson plates in the laboratory. Both experimental and numerical simulation methods are used to obtain the characteristics of the measurement system. The results show that measurement data can be calibrated with different Wilson plates, and suitable parameters are proposed in this paper to meet the requirement of measurements. The measurement system described in this paper can be used in other similar applications. [ABSTRACT FROM PUBLISHER]

Abstract: More and more urban traffic tunnels are built due to the heavy traffic in dense urban areas. Fire safety in tunnels is a concern due to the large traffic flow. Most of the urban tunnels have slope. Knowledge on smoke spread in titled tunnel is still limited. Experimental studies on the smoke spread in a titled tunnel are carried out by the reduced-scale tunnel model tests and will be discussed in this paper. Effects of the titled gradients and longitudinal ventilation speed on the temperature distribution and smoke stratification downstream from the fire along the tunnel will be studied The results show that the smoke spread upwards much faster with the slop gradient increasing, and a thick smoke layer was formed when smoke moved to the upward part of the tunnel and filled it up. The ventilation speed had a great influence on temperature distribution along the tunnel, and the smoke stratification will be distributed when the longitudinal ventilation speed becomes large. Lower ventilation speed should be adopted at the beginning to ensure the smoke downstream of the fire keep stratified to give the tunnel users more time to escape. [Copyright &y& Elsevier]

The results of an experimental study conducted on two 1:2 reduced-scale geotextile-reinforced soil retaining walls are presented and discussed. El Centro earthquake and sinusoidal harmonic motion excitations were applied to the 1.9 m tall models. The design parameter investigated was the reinforcement length (L/H = 0.9 in the 1st model and L/H = 0.6 in the 2nd model). The results were analyzed to evaluate the acceleration amplification, strains in the reinforcement layers and facing wall deformation. The test results showed that in both experiments the walls were in fact designed to behave rigidly and almost no residual displacements were observed on the front of the wall. The most important conclusion drawn from the experimental work was that Geosynthetic Reinforced Retaining Structures designed according to the current specifications behave very successfully under earthquake loading conditions. [ABSTRACT FROM AUTHOR]

This paper deals with scale models of power distribution systems for the study of lightning induced voltages on over- head lines. The scale model technique is useful for the investigation of situations which are prohibitively complex to be treated theoretically. For instance, urban distribution networks are usually characterized not only by complex topologies but also by the presence of nearby buildings, whose influence on the lightning induced effects can be successfully evaluated by means of reduced models. The paper first describes the scale model implemented for such a purpose at the University of São Paulo, São Paulo, Brazil. It then presents a comparison between the experimental data obtained with the scale model and the computer simulations obtained by using the LIOV-EMTP code, a software tool able of calculating lightning-induced electromagnetic transients in distribution systems having complex configurations. Finally, the paper shows an application of the scale model in the evaluation of lightning induced voltages on distribution networks considering the presence of nearby buildings. [ABSTRACT FROM AUTHOR]

The role of an overhead ground wire on the generation for lightning-induced voltage on a multiconductor line associated with a vertical return-stroke channel is studied based on numerical calculation. The induced voltage is calculated by a method in which the tangential component of the electric field to the wire is looked upon as an inducing source. The analyzed multiconductor line consists of three phase wires and an overhead ground wire having one or two earthing points. The influence of the overhead ground wire on the induced voltage is dependent on the direction of a return stroke, as well as the ground conductivity. When a return stroke is on the side of a power distribution line, the induced voltage decreases with a decrease in the earthing resistance of the overhead ground wire, irrespective of the ground conductivity. When a return stroke is close to an end of a distribution line, the influence of the overhead ground wire is dependent on the ground conductivity. In this case, the voltage induced on overhead wires over lossy ground sometimes increases with the presence of an overhead ground wire having only one earthing point. This effect can be avoided by adding earthing points to the overhead ground wire. © 1998 Scripta Technica. Electr Eng Jpn, 121(4): 18–27, 1997 [ABSTRACT FROM AUTHOR]

Variable Speed Hydro-Electric Plant (VS-HEP) equipped with power electronics has been increasingly introduced into the hydraulic context. This paper is targeting a VS-HEP Power Hardware-In-the-Loop (PHIL) real-time simulation system, which is dedicated to different hydraulic operation schemes tests and control laws validation. Then, a proper hydraulic model will be the key factor for building an efficient PHIL real-time simulation system. This work introduces a practical and generalised modelling hydraulic modelling approach, which is based on 'Hill Charts' measurements provided by industrial manufacturers. The hydraulic static model is analytically obtained by using mathematical optimization routines. In addition, the nonlinear dynamic model of the guide vane actuator is introduced in order to evaluate the effects of the induced dynamics on the electric control performances. Moreover, the reduced-scale models adapted to different laboratory conditions can be established by applying scaling laws. The suggested modelling approach enables the features of decent accuracy, light computational complexity, high flexibility and wide applications for their implementations on PHIL real-time simulations. Finally, a grid-connected energy conversion chain of bulb hydraulic turbine associated with a permanent magnet synchronous generator is chosen as an example for PHIL design and performance assessment. [ABSTRACT FROM AUTHOR]