Physical Model Study Research Articles

Hydrodynamic analysis of rectangular reactors With suspended bafles

Historically, contact tanks have been designed by empirical correlation, physical model studies or tracer studies conducted after the construction of the contact tank. Recently, the Lattice Boltzmann D2Q9 method, using a numerical code (LBM - FORTRAN) was applied to study the transport of fluxes and solutes in disinfection tanks. The objective of this article is to present the results of a numerical study undertaken to investigate the effect of the number of deflectors on the performance of a contact tank. Several two-dimensional, time-variable, steady state numerical simulations were performed with the LBM method for the standard k-e model in a contact tank geometry where a different number of deflectors was considered. Residence time distribution (RTD) curves were calculated for any number of deflectors to evaluate and compare their performance. Finally, we calculated the concentrations at the outlet of the tank as a function of time and of the size of the baffles for all cases.

A Methodology to Quantify the Effective Vertical Thickness of Prephonatory Vocal Fold Medial Surface

ObjectiveThe shape of the vocal fold medial surface, particularly its vertical thickness, has been shown in computational and physical modeling studies to be highly influential in regulating glottal closure during phonation. However, because of the difficulty to quantify the vertical thickness in real vocal folds, this influence has often been overlooked in clinical contexts. Therefore, the goal of this study is to present a method to calculate an effective vertical thickness of the medial surface that is predictive of the glottal closure pattern during phonation. MethodsAn effective vertical thickness of the medial surface is calculated as a weighted integral of the medial surface contour along the vertical dimension. The weight is one for the part of the medial surface within a fixed threshold distance from the most medial point, and decays exponentially otherwise. The influence of the threshold distance value on the effective thickness value is investigated. Additionally, the sensitivity of the calculated effective thickness to slight misidentification of the vertical glottal midline is also studied. The methodology is validated on the vocal fold medial surface data from a canine hemilarynx at different levels of thyroarytenoid muscle activation. ResultsFor most threshold distances, the thickness follows an expected sigmoid-like trend with respect to the thyroarytenoid muscle activation level. A threshold distance of 0.05 mm appears optimal as it produced thickness changes in a range comparable to previous computational and experimental studies. The methodology is relatively robust to slight misidentification of the vertical glottal midline. ConclusionsA methodology to estimate the effective vocal fold vertical thickness from medial surface contours is proposed. The methodology can be applied in future studies to correlate medial surface shape to relevant parameters characterizing vocal fold vibration as well as clinical evaluation of treatment effectiveness.

The physical and numerical modeling to design the breast wall spillway – AS case study

ABSTRACT The river systems in the Himalayan region exhibit year-round flow due to precipitation during the rainy season and snow/glacier melt in summer. These rivers carry massive sediment loads, especially during monsoons. Hydraulic engineers face the challenge of designing infrastructure capable of managing this sediment. Breast wall spillways are recommended for their ability to handle floodwaters and sediment disposal. The hydraulics of breast wall/orifice spillways changes with the varying reservoir level. The flow is free flow for reservoir water levels below the top of the sluice, whereas for higher water levels the flow is orifice flow. Orifice spillways are designed to pass water through openings or gates, where the flow is primarily governed by the hydraulic head and the orifice size. The flatter bottom profile helps in smoothly directing the flow through the opening without causing significant turbulence or separation, especially when the gate is partially open. Hence, the crest profile is flatter as compared to the overflow crest profile to avoid flow separation and negative pressures on the crest for small gate openings. Kwar Hydro Electric Project is one such Himalayan region project planned across the Chenab River in which a breast wall spillway has been provided to serve the dual-purpose of flood and sediment disposal. The present paper describes the physical and numerical hydraulic model studies conducted for Kwar H .E. Project, Jammu and Kashmir, to evolve a breast wall spillway profile, ski jump type energy dissipator at the toe of the spillway.

Stepped chute energy dissipation structure downstream of a low-level river crossing for embankment protection

A low-level river crossing is an economic means of providing access for lower-order roads during high-frequency flood events. Conventionally, culverts are employed to enable the flow to traverse the road, albeit with allowance for overtopping. This overtopping flow from the approach roads, however, possesses the potential to cause erosion of the downstream embankment, thereby jeopardising the foundational integrity of the structure. A physical modelling study was undertaken to investigate the hydraulic performance of stepped chutes in terms of flow patterns, air-water flow properties, and energy dissipation. Various types of stepped chutes were investigated, namely horizontal steps with a chute wall, horizontal steps without a chute wall but with riprap placed directly downstream of each chute, step-inclined steps (backward sloping), steps with pooled cascades, and steps with baffle blocks. Notably, chutes with horizontal steps were the most efficient configuration in terms of relative energy dissipation. Furthermore, this research culminated in the formulation of a new regression formula to establish a quantifiable relationship between the required step length and the overflow depth and discharge, thereby offering a valuable tool for design purposes.

Physical modelling study on wave damping induced by an idealized floating kelp farm

A physical modelling study was carried out to investigate random wave damping promoted by an idealized floating kelp farm. The experimental conditions spanned intermediate water depths and both linear and nonlinear water waves. Unlike previous studies of wave damping promoted by vegetation, the floating kelp farm was placed close to the water surface with a ratio between vegetation height and water depth close to 0.25. The wave transmission coefficient induced by the floating kelp farm ranged between 0.56 and 0.96. This coefficient decreased for longer floating kelp farms and it was a function of the ratio between kelp farm length and incident wavelength and of the relative wave depth. Spectral analysis showed that wave damping was not frequency-dependent for wave frequencies close to the peak frequency. The wave transmission coefficients of a floating kelp farm with about 100 culture lines and with an extension of approximately 200 m were similar to those of submerged detached breakwaters with a relative crest freeboard smaller than -0.4. Furthermore, the bulk drag coefficient of near-surface idealized floating kelp farms can be modelled as a function of the Keulegan-Carpenter number. This study highlights the potential viability of nature-based solutions such as floating kelp farms for coastal protection.

Sound Insulation of an Acoustic Barrier with Layered Structures of Sonic Crystals – Comparative Studies of Physical and Theoretical Models

Sound Insulation of an Acoustic Barrier with Layered Structures of Sonic Crystals – Comparative Studies of Physical and Theoretical Models

Modeling mobile shales under contraction: Critical analyses of new analog simulations of shale tectonics and comparison with salt-bearing systems

Weak substrates, such as salt and mobile shales, exert a strong control on deformation styles in all structural settings, especially those undergoing contraction. Despite both materials being very weak, they are mechanically very different. Salt is weak and will flow in a ductile fashion under most geologic conditions, whereas shales only become mobile after reaching a critical state. Many sandbox-style physical or analog modeling studies have typically used a salt analog, viscous silicone polymer, as a proxy for mobile shales. However, to more accurately model mobile shale behavior, the model material needs to exhibit yield strength. One such material is Carbopol, which is made up of microgel grains that are elasto-plastic, separated by a viscous interstitial fluid. The abundance of the grains depends on the concentration of the mixture. Our results show that Carbopol does behave much differently than the traditional salt analog during contraction. Polydimethylsiloxanes typically undergoes bulk deformation and inflation under contraction, whereas Carbopol forms discrete, intense shear zones and contains zones of little to no strain where its yield strength has not been exceeded. Below the shale analog, brittle layers typically form imbricate thrust stacks, jacking up the overburden, with shear zones propagating out from thrust tips along and through the shale proxy. Strain analyses reveal complex switching of activity within the Carbopol and overlying sediments. Models reveal that even a very thin layer of Carbopol can act as a highly efficient detachment, and form more geologically realistic shortening structures, especially where these detachments are vertically stacked and horizontally offset. We believe that Carbopol is a powerful mobile-shale analog and opens new modeling directions because, as far as we are aware, this material has never been incorporated into a traditional sandbox model. Future work will seek to incorporate this material into more complex and 3D sandbox-style models.

Attenuation of sound signals in foams for the basic oxygen furnace using physical modelling techniques

The control of slag foaming is important for optimising basic oxygen furnace (BOF) performance. Acoustics systems monitoring wide frequency bandwidths have been applied to BOF monitoring for the purpose of understanding slag foam height and density but there is limited information about their accuracy and repeatability. Improved understanding of the fundamental behaviour of sound in slag foam could help resolve these issues. In this cold physical model study using, aqueous foams generated in a cylindrical vessel were used to study the attenuation of sound in large samples of foam. Sound pulses over the range of 201 to 1801 Hz were transmitted through varying aqueous foam heights of 100 to 250 mm and acoustic signals detected via a measurement microphone were analysed. The results indicated aqueous foams consisting of smaller bubbles in the range of 0.4 to 0.75 mm with visibly thicker outer films displayed a stronger correlation between the attenuated sound and the stationary foam heights. It was also observed that frequencies above 1009 Hz were more sensitive in terms of their attenuation in varying foam heights and the time-dependant drainage of bubbles compared to lower frequencies. These frequencies were generally higher than those used for industrial slag foam monitoring systems.

Hydraulic investigation of flows at high-head overflow spillway with multiple aerators: a physical and numerical study of Mohmand Dam, Pakistan

ABSTRACT A spillway is the essential part of the dam body, which releases surplus flows. At higher floods, the spillway operates at high heads, which results in high flow velocities along the chute and may cause negative pressures and cavitation. Therefore, to minimize such issues, aerators are provided along the spillway's chutes. This study aims to analyze the performance of the high-head overflow spillway of Mohmand Dam, Pakistan, having a steep chute of 32° with multiple aerators. Based on Froude's law of similitude, the physical model study was carried out at Irrigation Research Institute, Nandipur, on a scale of 1:60, while FLOW-3D numerical models were used to compare different hydraulic parameters, i.e., flow depth, velocity and pressure. The numerical models were validated with the results of a physical model, which were found in an acceptable range (i.e., 4.93%), and the hydraulic performance of two aerators was evaluated at different discharges. The models indicated negative pressures inside the aerator cavity, which allowed the suction of air to the lower nappe. The maximum air entrainment at the first aerator was about 8.5%. The results also showed that air entrainment to the lower nappe decreased when discharge was increased, whereas the maximum air detrainment reached 11.3% downstream of the second aerator.

Design of Underwater Compressed Air Flexible Airbag Energy Storage Device and Experimental Study of Physical Model in Pool

Renewable energy is a prominent area of research within the energy sector, and the storage of renewable energy represents an efficient method for its utilization. There are various energy storage methods available, among which compressed air energy storage stands out due to its large capacity and cost-effective working medium. While land-based compressed air energy storage power stations have been constructed worldwide, their efficiency remains low. Underwater compressed air energy storage has the potential to significantly enhance efficiency, although no such device currently exists. This paper presents the design of an UWCA-FABESD utilizing five flexible air bags for underwater gas storage and discharge. Additionally, it introduces the working principle of the adiabatic underwater compressed air energy storage system and device. Furthermore, a small-scale physical model with similar functionality was designed and manufactured to simulate the charging process of the air bag in onshore charging and discharging tests as well as posture adjustment and lifting arrangement tests, along with underwater charging and discharging tests. These experiments validated the related functions of the designed underwater compressed air flexible bag energy storage device while proposing methods for its improvement. This research provides a new approach to underwater compressed air energy storage.

Probing the microstructure and deformation mechanism of an FeCoCrNiAl0.5 high entropy alloy during nanoscratching: a combined atomistic and physical model study.

High entropy alloys (HEAs) exhibit superior mechanical properties. However, the nanoscratching properties and deformation behaviour of FeCoCrNiAl0.5 HEAs remain unknown at the nanoscale. Here, we investigate the effect of scratching depth on the microstructural and tribological characteristics of an FeCoCrNiAl0.5 HEA using molecular dynamics simulations combined with a physical model. The scratching force increases significantly as the scratching depth increases. In the lower part of the scratching region, there is a clear atomic movement process, with the load generated in the normal direction causing the atoms to shift downwards. Noticeable shear bands are formed in the subsurface area, and they are both small and narrow compared with the pure Ni. The plastic deformation mechanism of the compressed surface is mainly governed by the formation and expansion of stacking faults during the subsurface evolution process. The evolution process of screw dislocations is similar to that of edge dislocations. In addition, the high strength and deformation resistance of FeCoCrNiAl0.5 HEAs are further evaluated by establishing a microstructure-based physical model. The combined effect of the lattice distortion strengthening and dislocation strengthening promotes the high strength of the FeCoCrNiAl0.5 HEA, which is significantly better than the single strengthening mechanism of pure metals. These results accelerate the understanding of the mechanical properties and deformation mechanisms of HEAs.

Physical model study on failure mechanism of strip footing on reinforced granular deposit

This study proposes guidelines for predicting the failure mechanism of a shallow strip footing resting on geosynthetic-reinforced granular deposit at different stages of footing settlement. Physical model tests are performed on footings resting on unreinforced and geosynthetic-reinforced soil. The reinforcement parameters varied include the depth between consecutive reinforcements, number of layers and the depth of the reinforced zone. Additionally, contours of deformation and maximum shear strain of soil and mobilised tensile strain in reinforcement with increasing footing settlement are studied. The improvement of bearing capacity ratio and the peak tensile strain in the reinforcement was monitored for three normalised settlement ratios of 5% (low), 10% (medium) and 25% (high). The reinforced soil models were found to depict primarily a punching shear failure limited solely within the reinforced zone at s/B of 5%. This was supplemented with a well-formed triangular wedge in the underlying unreinforced soil at s/B of 10%. In addition to above mechanisms, the radial shear zones were prominent at s/B of 25%. Failure mechanisms have been proposed eventually for each s/B value investigated, including guidelines on the upper and lower bounds of the load dispersion angle in the reinforced soil and wedge angle of the underlying unreinforced soil.

A physical model study on the hydraulic performances of vertical breakwaters with retreated wave walls

This paper describes a 2D physical model study on the hydraulic performances of composite vertical breakwaters with retreated wave walls. The research is an expansion of a previous experimental study by the same Authors: a very large number of experiments, in the order of 2,000, have been carried out by exploring and varying a wide range of wave and geometrical parameters of the structure, to investigate their effect and importance. In order to make feasible the execution of this large number of tests, a small-scale wave flume was used and regular wave conditions were reproduced. The influence of the wave wall retreat has been investigated in terms of wave-induced forces, reflection coefficients and wave overtopping discharges, comparing the hydraulic performances of structures with retreated walls with those of a flushed wall configuration under the same wave conditions. The large number of experiments allowed to formulate a detailed description of the complex phenomena at hand, providing statistical indicators that can be used as guidelines for preliminary design purposes of such structures, quantifying the relevant sources of uncertainty. The analysis confirmed and extended the previous findings and indicates that, on average, the hydraulic performances of structures with retreated crown wall vary significantly from those of flushed wall configurations. Specifically: (I) the forces acting on the wave wall increase of a factor up to 1.5, due to the occurrence of impulsive loads; (II) the forces acting on the caisson trunk decrease of a factor up to 0.91; (III) the global forces can decrease reaching a minimum reduction factor of 0.87, although some dangerous exceptions, in which equal or larger loads, than those occurring for standard flushed wall configuration, have been registered; (IV) the reflection coefficients decrease of a factor up to 0.83; (V) the wave overtopping discharges increase up to 2.55 times those with flushed walls.

Physical Model Study Of Standing Wave Impact Loads On Gates And Decks Of The Existing Discharge Sluices In The Afsluitdijk The Netherlands

To anticipate the rising sea level and to meet the increased flood safety standards the Afsluitdijk in the northwest of The Netherlands is currently being reconstructed. The Afsluitdijk is the dam, with a length of 30 km, that closes the IJsselmeer basin, the former Zuiderzee. Outside the dam lie the Waddenzee and the North Sea. The reconstruction of the dam includes the reinforcement of the dam and the raising of the crest level, the renovation of the existing discharge sluices and the building of new pumping stations, discharge sluices and flood gates. Higher design waves and water levels, including the effects of sea level rise, present determining loads for drawing up the strength and stability of these hydraulic structures. One of these loads is the wave impact load on the gates, supporting beams and bridge decks of the discharge sluices. At first, these loads have been calculated using a design approach which has been based on analytical models, only partially validated (Almeida and Hofland, 2020). It showed that these loads due to vertical wave impacts can be higher than the strength of the gates and the existing bridge decks. Therefore, load reduction measures are required. To better predict the wave impact loads, which strongly depend on the configuration of the gates and decks, a physical model study in a wave flume has been carried out at Deltares (Capel and van der Werf, 2023). This abstract is about the results of this model study, focusing on the wave impacts on the existing discharge sluices near Kornwerderzand, because at this location these loads are the highest.

Large Scale Physical Model Study On Clay Erosion With Gras Cover On Primary Coastal Defence Structures

Sea dikes in the Netherlands consist of sandy or clay core with a clay layer with grass. The lower outer slope is often covered with a hard revetment, such as asphalt or a placed block revetment, to protect the dike material against wave impact. Since the strength of the clay layer with a grass subject to severe wave impact is unknown, the hard revetment needs to be constructed on a large part of the outer slope to ensure that the flood defence meets the safety requirements. Therefore, a research programme was started to determine the strength of the clay layer with grass on the upper slope of a dike. As a first step, large scale physical model tests have been performed. In the second step the CFD model OpenFOAM has been used to extend the physical model results by computing the peak pressure of the hydraulic load on the clay for the tested geometries and additional geometries with varying parameters that may influence the erosion rate. With all results, it was possible to derive formulas for failure probability calculations in the final step. The knowledge development on the erosion of a clay layer with grass on the outer slope by wave attack resulted into formulas that are currently used in the safety assessment of dikes contributing towards safer deltas and resilient designs of dikes.

Experimental Study Of Parsian Port Breakwater Toe Stability

The stability performance of toe layer in structures with single-layer concrete armoures such as accropods and Xblocks is more crucial regarding their fast instability propagation and failure mechanism. This paper presents the case study concerning toe stability of Pasrsian port breakwater by experimental tests on physical model in Tarbiat modares university wave flume. Parsian industrial port is located in the south of Iran at Persian Gulf coastline. Its nineteen berths in final phase will be protected by approximately 1500 meter breakwater which at the most critical section, W5, reaches the sea bed level of -25 m.C.D. Figure 1. In concrete armored breakwaters, heterogeneous packing could increase the porosity in top rows and eventually result in instability. Therefore the number of rows in which the concrete units can be placed would be limited. According to the SUGRA guidance for Accropode units, this the maximum number of rows shall be 20, which leads designers to consider toe berm for breakwaters in deep water. Hence, it was vital to conduct a comprehensive physical model study.

Study of the effect of spur dikes on beach protection based on physical model experiment

The Qiantang River is a typical strong tide estuary, the world-famous tidal bore have huge turbulent energy and causes damage to the sea wall. Spur dike is an important engineering to prevent the seawall foundation from tidal bore. But the tidal bore occurs at the low tide level, strong turbulence, high flow velocity, water level rises sharply. The spur dike height, length, inclination angle need to be determined by physical model according to the specific bore dynamic conditions. In the tests, the fixed-bed model was used to study the tidal current velocity reduction rate and region, the falling current circulation characteristics in dike field. The movable-bed model test is used to study the effect of each test on protecting the beach. This physical model study reveals the rule of spur dike influence on tidal bore dynamics so the effect of spur dike on protecting the beach is clear.

Analysis of Seismic Response Characteristics of Fractured Carbonate Reservoirs Based on Physical Model (Tarim Basin)

Anomalous bright spots, called the string of bead-like response, are typical seismic migration profile features in carbonate fractured reservoirs in the Tarim Basin, and they are indicators of high-quality oil and gas reservoirs. Correctly recognizing the correspondence between fractures and the SBLR can contribute to the efficient drilling of target carbonate fractured reservoirs. Physical models can describe fractured reservoirs more directly and efficiently than real situations and have obvious advantages in accurately and quantitatively designing parameters such as dipping angles and the number of layers of fractured reservoirs. Under such a background, according to the real tectonic characteristics of the Tarim Basin, among the main hydrocarbon reservoirs, fractured reservoirs with various parameters were designed and a physical model was constructed according to the real stratigraphic parameters. After seismic data acquisition and processing, the response characteristics of the string of bead-like response were extracted and summarized from seismic migration profiles for all fractured reservoirs, which provided targeted analyses and discussions on the fracture dipping angle, number of fracture layers, overlying stratigraphic influences, and planar attributes of the fractured reservoirs. In general, the larger the fracture dip, the more difficult it is to identify, while the slope of reflection strength and maximum absolute amplitude attributes can be important markers for fractured reservoir identification. The physical modeling study of fractured reservoirs in this paper can provide a basis for the analysis and prediction of carbonate fractured reservoirs in the Tarim Basin.

Role of Gas Aspiration through Ladle Shroud and Influence on Tundish Hydrodynamic Performances: A Physical and Mathematical Modeling Study

Gas aspiration through ladle shroud, during the teeming of a ladle into a tundish, has been investigated via physical and mathematical modeling. To this end, a volume of fluid‐based two‐phase turbulent flow model (in conjunction with the standard k–ε turbulence model) and a full‐scale two‐strand bloom casting tundish have been applied. Both flow and residence time distribution measurements are carried out in the full‐scale tundish system, adopting well‐established measurement techniques. Computational results, supported appropriately with experimentally measured data, indicate that gas aspiration alters flow and turbulence profoundly in the vicinity of the shroud entry zone. Early reversal of jetting flow toward the free surface, due to the buoyancy of the entrained gas, increases the overall intensity of motion in the tundish, creating more mixing flow volumes at the expense of plug flow volume. Most importantly, however, gas aspiration through shroud tends to drastically cut down interactions between the down coming liquid jet metal and the pouring box, making the specific design and shape of a pouring box redundant toward desirable flow modification. Finally, it is shown that strong surface flows and turbulence, generated due to gas aspiration, can be suitably damped by deploying a set of weirs, increasing plug flow volume in tundish.

A compressible degree of freedom as a means for improving the performance of heaving wave energy converters

A compressible degree of freedom (CDOF) can provide a means of improving wave power capture by adjusting the system stiffness and providing short-term energy storage, reducing or even eliminating the requirement for two-way electrical power flow as is typical in wave energy control systems. With the overarching goal of investigating and facilitating the application of a CDOF within wave energy converter (WEC) design, this paper focuses primarily on the case of heaving buoys, and on using air volumes to provide the compressible spring effect. Analytical formulae for the natural frequencies are used to gain fundamental insights into the main design considerations. Numerical methods are used to augment this understanding, helping to elucidate the effect of geometric parameters and scale on the required compressible volumes and the efficacy of the CDOF. Beginning with the WaveBot WEC, case studies are then used to demonstrate the design drivers in a more applied context, as well as highlighting the benefit of a self-reacting power take-off (PTO) system. The assimilation of these results with the findings of a detailed literature review culminates in a set of recommendations (or guiding principles) for designing a compressible degree of freedom to improve the performance of a heaving wave energy converter. These recommendations apply both to full-scale WECs, and to the design of scale physical modelling studies for validating the analytical and numerical models.