Reduced-scale Model Experiments Research Articles

Paragliders' launch trajectory is universal

We designed and built a reduced-scale model experiment to study the paragliding inflation and launching phase at given traction force. We show that the launch trajectory of a single skin glider is universal, that is, independent of the exerted force. As a consequence, the length of the take-off run required for the glider to reach its “ready to launch” vertical position is also universal. We successfully compare our results to full-scale experiments and show that such universality can be understood through a simple theoretical model.

Study on emergency ventilation strategies for various fire scenarios in a double-island subway station

The double-island subway station with complex structure and dense crowds brings about serious fire safety issues. Aiming to control fire-induced smoke, numerical simulations were conducted to investigate the emergency ventilation strategies. The numerical model was validated by the reduced-scale model experiments and full-scale experiments. Various ventilation modes were compared under different fire scenarios and platform screen door (PSD) types. The results demonstrated that a reasonable co-work mode of ventilation system was vitally important in preventing smoke dispersion and reducing pollutant concentration. Opening the screen doors was found to be conducive to the joint ventilation in the platform and tunnel under the type of full-height PSD, whereas whether opening the half-height PSD had little influence on ventilation effect. On this basis, the optimal ventilation modes were developed respectively for platform fire, fire inside the carriage and carriage fire, among which the best control measurement for carriage fire was related with the location of the train. Additionally, a reasonable optimization of the ventilation system could further improve the safe environment. This work could provide guidance for emergency response under sudden fire accident, and provide reference for engineer design of ventilation system in the metro stations.

Improving indoor air flow and temperature prediction with local measurements based on CFD-EnKF data assimilation

Mastering detailed multiphysics distribution information is an important prerequisite for creating suitable building environments. This study considered the simulation errors caused by the uncertainty of boundary conditions in computational fluid dynamics (CFD) and aimed to correct simulations with limited observational data. Based on the Ensemble Kalman Filter (EnKF), which is a sequential data assimilation algorithm, a technical framework for accurate indoor airflow and temperature field simulations was established. We evaluated the performance of this method through reduced-scale model experiments and verifying that simulation errors were significantly reduced, and that this approach is applicable to both mechanical ventilation and natural convection conditions. On this basis, further research explored the impact of the measuring point arrangement scheme and ensemble size on assimilation performance, and the optimal setting principles of the above parameters are presented in this paper. The proposed method can effectively weaken the negative impact caused by the uncertainty of boundary conditions in the CFD simulation, thereby improving the prediction accuracy and reliability and providing a positive impetus for realizing a global monitoring of the physical field of a building space.

Experimental study on the mechanical behavior and deformation characteristics of lining structure of super-large section tunnels with a small clearance

The knowledge of the mechanical behavior and deformation characteristics of lining structure of super-large section tunnels with a small clearance can help to optimize the tunnel lining design and reduce the construction costs. Based on Xinwu twin tunnels with eight lanes in China, a reduced-scale model experiment was carried out to investigate the deformation characteristics, the crack behaviors, the ultimate bearing load and internal force of the super-large section tunnels under different clearances. The results show that the positions in order (from largest to smallest deformation) are as follows: crown, right spandrel, left spandrel, invert, springs. 12 m (about half the width of tunnel) can be considered as the smallest reasonable spacing for large section tunnels in grade IV surrounding rock. With the increase of loading level, the cracks mainly appeared at the invert and the springs of the two tunnels. After the secondary lining was damaged, the deformation of each measuring point did not decrease but gradually increased with the clearance. These findings can provide significant reference data for the design optimization and safety assessment of super-large section tunnels with a small clearance.

Improving Indoor Multiphysics Prediction with Local Measurements Based on Data Assimilation

Accurately mastering the distribution of multi-physical field is an important prerequisite for rationally formulating building environment construction scheme. In practical engineering projects, sensor monitoring can obtain more accurate environmental state parameter values. However, due to the constraints of investment cost, spatial limitations and other factors, the number of on-site measured monitoring points is limited. On the contrary, CFD simulation can obtain global distribution information of the physical field, but the uncertainty of parameters such as boundary conditions seriously affects the reliability of simulation results. In view of the above problems, based on Ensemble Kalman Filter (EnKF), which is a sequential data assimilation algorithm, a technical framework for accurate indoor multiphysics simulation is established. We evaluated the performance of this method with reduced-scale model experiments, verifying that the simulation errors can be significantly reduced. The proposed method has a positive impetus for realizing the global monitoring of the physical field of the building space.

A study on the airtightness of a high-speed train using a reduced-scale method

The pressure comfort of a high-speed train is closely related to the static and dynamic airtightness performance of the train carriage, and this performance is studied mainly with field surveys and tests on full-scale trains. Considering the high cost and difficulty of full-scale tests, the applicability of the reduced-scale model experiment method in the study of train carriage airtightness performance is worth exploring. In this study, a power–law relationship between the scale factors and static airtightness coefficients of carriage models was first established using numerical simulations, to determine the fundamental theoretical support for the reduced-scale model experiments. A series of static and moving model experiments were conducted on a newly designed 1/20th-scale special train carriage model. The static airtightness coefficients obtained from static model experiments showed a discrepancy less than 5% to their theoretical values, which revealed the experimental feasibility of the reduced-scale model for studying the static airtightness performance. The pressure spectrum characteristics of the measured pressure from the moving model experiment indicated that not only the high-intensity aerodynamic alternating pressure load with a frequency peak around St = 1.76 but also the high-frequency mechanical vibrations around St = 17.03 from the wheel-rail coupling system were experienced by the carriage body traveling through a tunnel, which might cause some potential leakages to appear on the carriage body. This provides a new understanding of the potential causes of the deterioration of the train’s dynamic airtightness performance.

Evaluation of stack ventilation in a large space using zonal simulation and a reduced-scale model experiment with particle image velocimetry

Stack-driven airflow is extensively utilized to improve thermal comfort and exploit energy saving potential during summertime. However, the thermal environment in large spaces is obviously stratified, and the stack ventilation is complex and dynamic. This paper presents a practical zonal stack ventilation method by combining the merits of the intuitive analytical model and the universal zonal model, thereby expanding their application in stack ventilation. As the boundary condition at the opening, the ventilation flow is obtained based on the building geometry, flow characteristics and nonuniform pressure gradient prompted by temperature disparity. Inside the space, an airflow network is constructed, and the airflow movement is determined by a simplified impulse equation, thereby balancing accuracy and efficiency. Moreover, an appropriate solution procedure was developed. Then, this general method was applied to an example large space. A reduced-scale building model was established to approximate the complex and stratified thermal environment in the large space, involving multiple realistic environmental conditions. A particle image velocimetry (PIV) measurement was conducted to investigate the integrated stack-induced airflow pattern in the thermal stratification and further explore the characteristics of the zonal model. After experimental verification, the ventilation flow rate at the opening was 0.001 kg/s for both the simulation and measurement. Inside the space, the maximum air temperature deviation was −0.16 °C, and the root-mean-square error was 0.21 °C.

Study on the optimal operation mode of ventilation system during metro double-island platform fire

Large metro transfer stations have been widely constructed in China, among which the double-island station faces the serious fire safety issues owing to its large passenger flow. In this paper, simulation cases were carried out to investigate the effectiveness of different ventilation modes by jointly operating tunnel ventilation fan (TVF) and platform screen doors (PSD) under two typical fire scenarios in the platform. The numerical model was established by Fire Dynamics Simulator software and verified via reduced-scale model experiments. The results indicate that the TVF mode of supplying at the end near fire and exhausting at the other end is superior to that of exhausting at both ends. Besides, activating more PSD and TVF on the both sides of platform will restrict smoke in one end to the greater extent. During a fire in the middle of the platform, opening all PSD near tunnel-2 and TVF in tunnel-2 and tunnel-3 is the most appropriate mode. While during a fire at the left end of the platform, activating all PSD and TVF on both sides is the optimal operation mode. The conclusions can provide guidance for smoke control design and on-site emergency ventilation operation in double-island platform fire.

Analysis of the DC Bias Effects on the UHV Autotransformer with Rated Load Based on a Reduced-Scale Model Experiment

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.

Reduced-scale Model Experiment for Examination of Natural Vent and Fire Curtain Effects in Fire of Theater Stage

Reduced-scale Model Experiment for Examination of Natural Vent and Fire Curtain Effects in Fire of Theater Stage

The comparison of vertical temperature distributions between the reduced-scale model experiments and the prototype on-site tests of a large space building with low-sidewall air inlets and middle air outlets

ABSTRACTThis paper aims to take an insight into to what extent the reduced-scale model can reflect the thermal environment of a full-scale large space building with a stratified air conditioning system and how to improve the accuracy.A reduced-scale model for a large space building has been designed and constructed confined to the similarity principles. The indoor air inlets and outlets dimensions of the scale model are strictly designed according to the prototype with a geometry ratio of 1:4. The experiment results show that the Ar number and the Re number are both important in the stratified air-conditioned room. With the Re number increasing, the vertical temperature deviation from the scale model to the prototype decreases, which indicates that the self-similar zone for Re should be reconsidered. The non-air-conditioned zone in the large space building with stratified air conditioning system cannot be depicted well by a reduced-scale model.

Simulation of pump-turbine prototype fast mode transition for grid stability support

The paper explores the additional services that Full Size Frequency Converter, FSFC, solution can provide for the case of an existing pumped storage power plant of 2x210 MW, for which conversion from fixed speed to variable speed is investigated with a focus on fast mode transition. First, reduced scale model tests experiments of fast transition of Francis pump-turbine which have been performed at the ANDRITZ HYDRO Hydraulic Laboratory in Linz Austria are presented. The tests consist of linear speed transition from pump to turbine and vice versa performed with constant guide vane opening. Then existing pumped storage power plant with pump-turbine quasi homologous to the reduced scale model is modelled using the simulation software SIMSEN considering the reservoirs, penstocks, the two Francis pump-turbines, the two downstream surge tanks, and the tailrace tunnel. For the electrical part, an FSFC configuration is considered with a detailed electrical model. The transitions from turbine to pump and vice versa are simulated, and similarities between prototype simulation results and reduced scale model experiments are highlighted.

Scaled Experimental Study on Maximum Smoke Temperature along Corridors Subject to Room Fires

In room–corridor building geometry, the corridor smoke temperature is of great importance to fire protection engineering as indoor fires occur. Theoretical analysis and a set of reduced-scale model experiments were performed, and a virtual fire model was proposed, to investigate the correlations between the maximum smoke temperature in corridors and the smoke temperature in rooms. The results show that the dimensionless virtual fire heat release rate (HRR) is characterized by quadratic-polynomial of the dimensionless smoke temperature in fire rooms. The dimensionless distance from a virtual fire source to the corridor ceiling varies linearly with the dimensionless smoke temperature in a room. Results of multiple regression indicate that, at the impingement area of virtual fire, the dimensionless maximum smoke temperature in corridors is only related to the dimensionless virtual fire HRR; in the non-impingement area of a virtual fire, the dimensionless maximum smoke temperature in corridors is a function of the dimensionless virtual fire HRR and dimensionless longitude distance. The viscosity and conduction exhibit an insignificant impact on the maximum temperature in the corridor. Through replacing the parameters of virtual fire with the dimensionless smoke temperature in fire rooms, the correlations between dimensionless maximum temperature in corridors and the dimensionless smoke temperature in fire rooms were proposed.

Hot Radial Upset-Extruding Process for Tube Structure with a Nozzle of 316LN Stainless Steel

AP1000 nuclear power main pipe, a type of complicated thick-walled tube structure with both high and thick-walled nozzles, is one of the key parts in nuclear island. It is required to be manufactured by integral plastic forming technique. Up to now, no economical and efficient plastic forming process for AP1000 main pipe has been reported. To aim for forming the tube structure with a nozzle such as AP1000 main pipe, a radial upset-extruding (RUE) process was developed, in which the initial billet is an extruded tube with a hole. RUE process is an extrusion method which realizes radial outflow of the metal around the hole of tube billet through an axial upsetting force and restriction of dies. Thick-walled tube structure with a nozzle derived from AP1000 main pipe was simplified to be a thick-walled three-way pipe, on which RUE process was analyzed based. Combined with reduced scale model experiments, thermomechanical coupled finite element analysis integrated with recrystallization models of 316LN was performed to investigate RUE process. Metal flow, deformation distribution, recrystallization distribution, and extrusion load and clamping load in RUE process was analyzed. The experimental workpiece of pure lead based on reduced scale model validate metal flow behavior predicted by using numerical simulation. The results indicate that the essence of RUE process is to deflect the flow of the material around the orifice of the tube billet. The loads of dies are significantly sensitive to the initial forming temperature and the friction coefficient, while the impact of the extrusion velocity is negligible. RUE process could be used to form thick-walled tube structure with a nozzle, and it has a potential for solving the manufacture of AP1000 main pipe.

Application of Reduced-scale Model Experiments to the Fire Safety Research of Buildings

Application of Reduced-scale Model Experiments to the Fire Safety Research of Buildings

Lightning surge characteristics on inclined incoming line to substation based on reduced-scale model experiment

The lightning protection design of a substation is generally based on the surge overvoltage incoming to the substation, which is generated by the back-flashover across an insulator string of the transmission tower that is closest to the substation and struck by a lightning return stroke. In this case, surges propagate along non-horizontal or non-uniform lines such as the tower and the inclined lines incoming to the substation. Although the surge characteristics of a tower have been intensively studied as of today, those of inclined incoming lines to a substation have not yet been investigated. In this paper, experiments have been conducted using a reduced-scale model to clarify the surge characteristics of the conductor system that is composed of horizontal transmission line, two towers, inclined incoming line and a substation gantry. It turns out from the experiments that the potential (voltage) generated at the tower arm rises gradually, compared with the current injected in the tower top. Furthermore, it is found that the power line potential at the gantry is smaller than that that at the tower where the back-flashover occurs, while the opposite trend is obtained from a circuittheory- based simulation in which the inclined incoming line is represented by a horizontal line. The latter approximation has been usually employed in representing inclined incoming lines in lightning surge simulations using the Electromagnetic Transients Program (EMTP) or its alternatives. The fact that the power line potential at the gantry, evaluated by the present experiment, is smaller than the EMTPcomputed value would contribute to a more economical and rational design of a substation.

Examination of Vehicle Motion Characteristics of a Maglev Train Set Using a Reduced-scale Model Experiment Apparatus

This paper focuses on the vehicle dynamics of superconducting magnetically levitated (Maglev) vehicles as a train set, and reports results of computer simulation as well as results of experiments using a reduced-scale Maglev model vehicle dynamics experiment apparatus (MAGMOX). The previously constructed MAGMOX consisting of a single car was expanded to form a train set comprising several cars. The computer simulations and MAGMOX experiments produced results that demonstrated their effectiveness in reproducing testing conditions of the full-scale Maglev system that are difficult to achieve on an actual full-scale vehicle due to vehicle structure constraints and rigging space.

Smoke Control Using A Double-skin Facade

Double-skin facades have been increasingly used as they open up new possibilities for clients and planners seeking creative new designs that are intelligently adapted to environmental conditions. Among them natural ventilation is commonly carried out in a building with double-skin facades. However double-skin facade construction is still not covered by statutory building regulations. Virtually no information exists on the behavior of this kind of facade in case of a fire. Usually for a building with a multistory double-skin facade, smoke of a fire room escaping through the inner facade into the intermediate space between the two skins may accumulate and spread horizontally and/or vertically to other rooms that have openings connected to the intermediate space for the purpose of natural ventilation. However if smoke pressure in the intermediate space can be kept lower than that of the room, smoke spread through the openings will be prevented. Considering similarity of smoke movement and stack natural ventilation, in this paper a double-skin facade used for natural ventilation is also considered for smoke control. As the results, it is proved that smoke spread can be prevented with suitable opening arrangements. Therefore natural ventilation and smoke control can be realized through one system. Reduced scale model experiments and computational fluid dynamics (CFD) analysis are carried out in this research.

Natural ventilation performance of a double-skin façade with a solar chimney

Double-skin façade is getting more and more attention as it provides many possibilities for energy conservation and at the same time creates good indoor environment. In this paper, natural ventilation performance of a double-skin façade is highlighted. A prototype building is proposed, which is thought to be an eight-storey office building with an atrium space in the north side. The south façade of the building is a double-skin façade and a thermal storage space called solar chimney is considered above the double-skin space. Actually, the double-skin space is connected with the chimney channel. Reduced scale model experiments and computational fluid dynamics (CFD) analysis are carried out in this research to evaluate the natural ventilation performance of the prototype building.

Smoke control based on a solar-assisted natural ventilation system

The possibility of using the same system for natural ventilation and smoke control is examined. As an example, a prototype building is proposed. The proposed prototype is an eight-storey building with a solar chimney on top of the atrium. Reduced scale model experiments and Computational fluid dynamics analysis are conducted. As a result, when the area ratio of outlet to inlet is greater than 2, air change rate of the utility space reaches over 2 times per hour and in an event of a fire breaking out in the atrium, the neutral pressure plane of the smoke layer stays inside the chimney. Smoke infiltration into adjacent spaces used for evacuation is prevented.