scholarly journals FROUDE NUMBER VARIANCE WITH RESPECT TO THE HYDRODYNAMIC RESPONSE OF A NON-STATIC VEHICLE AT A LOW-LYING FLOODED ROADWAY

2021 ◽  
Vol 22 (1) ◽  
pp. 35-46
Author(s):  
Syed Muzzamil Hussain Shah ◽  
Zahiraniza Mustaffa ◽  
Shabir Hussain Khahro ◽  
Khamaruzaman Wan Yusof ◽  
Aminuddin Ab Ghani ◽  
...  

In terms of stability, the response of static cars in floodwaters has been widely investigated. However, the hydrodynamics of a non-static vehicle exposed to such events are less explored. Herein the study ponders the assessment of the hydrodynamic forces experienced by a non-static vehicle attempting to cross a low-lying flooded street. With that regards, a Perodua Viva was modeled (1:10) and tested in the Hydraulics Laboratory under partial submergence and sub-critical flows, fulfilling the similarity laws. Since the Froude number could best analyze the flow conditions, the behavior of the hydrodynamic forces and the Froude number have been the focus of this investigation. From the study of outcomes, an inverse relation of the Froude number with respect to the buoyancy force, along with positive trends relating to drag, frictional, and rolling resistance, were noticed. ABSTRAK: Dari segi kestabilan, tindak balas kereta statik dalam air banjir telah banyak dikaji. Walau bagaimanapun, hidrodinamik kenderaan tidak statik yang terdedah kepada kejadian seperti itu kurang diterokai. Kajian ini menilai daya hidrodinamik kenderaan tidak statik yang cuba melintas jalan raya yang banjir. Sehubungan itu, sebuah Perodua Viva dimodelkan (1:10) dan diuji dalam Makmal Hidraulik di bawah perendaman separa dan didedahkan kepada aliran sub-kritikal, seperti ketika kejadian. Manakala nombor Froude adalah terbaik dalam menganalisa keadaan aliran air. Oleh itu, tindak balas daya hidrodinamik dan nombor Froude menjadi fokus penyelidikan ini. Dapatan kajian menunjukkan kaitan terbalik nombor Froude pada daya apungan, sedangkan tren positif yang berkaitan dengan daya tarik, geseran dan rintangan guling diperhatikan.

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
R. C. Bowden ◽  
I. G. Hassan

The critical height at the onset of gas entrainment, in a single downward oriented discharge from a stratified gas-liquid region with liquid crossflow, was modeled. The assumptions made in the development of the model reduced the problem to that of a potential flow. The discharge was modeled as a point-sink while the crossflow was said to be uniform at the main pipe inlet. The potential function was determined from a superposition of known solutions for a point-sink and uniform flow. The resulting system of three equations demonstrated that the flow field was dominated by the discharge and crossflow Froude numbers. The system was solved numerically and provided a relationship between the geometry, flow conditions, dip location, and critical height. The model predicted that the critical height increased with the discharge Froude number and decreased with the crossflow Froude number. With no imposed crossflow, the model prediction demonstrated agreement with transient and quasisteady experimental data to within ±30%. Existing experimental correlations showed inconsistent crossflow effects on the critical height and disagreed with the model predictions at high discharge Froude numbers.


2020 ◽  
Vol 20 (6) ◽  
pp. 379-387
Author(s):  
Youngseok Song ◽  
Jingul Joo ◽  
Hayong Kim ◽  
Sangman Jeong ◽  
Moojong Park

While drainage installed in mountainous and urban areas play various roles for supplying and draining water, the standards for reduction facilities and maintenance are insufficient. In the case of small drainage, if there is an inflow of deposited debris, overflow damage occurs due to lack of water supply capacity. In this study, a reduction facility was developed to block the transport of debris in a small drainage. The equation considering installation standards was proposed by analyzing capture efficiency through hydraulic experiment. By establishing various experimental conditions, a total of 900 experiments were conducted using 90 different conditions. The reduction effect of reduction facilities was analyzed by consideration of flow conditions such as discharge and Froude Number. Multiple regression analysis was conducted to develop an equation that considers the installation standard of a small drainage. The dependent variable was capture efficiency, and the independent variables were discharge, Froude Number, and an effective cross sectional area of reduction facilities. The equation considering installation standard of small drainage is E = 1.337-5.074×Q-0.156F<sub>r</sub>-132.710A and the significance is high. The results of this study are expected to be applied to reduction facilities suitable for target capture efficiency targeting small drainage.


2021 ◽  
Author(s):  
Alexander Metelkin ◽  
Bernhard Vowinckel

&lt;p&gt;&lt;span&gt;The dynamics of cohesive sediments under various flow conditions &lt;/span&gt;&lt;span&gt;are &lt;/span&gt;&lt;span&gt;of special interest in the framework of aquatic ecosystems. Being one of the main sources of transport for minerals and organic matter, the constituents of cohesive sediments are the source of food for many aquatic organisms. Due to the additional complexity of physical mechanisms, there are only a few simulation techniques for cohesive sediments, which do not cover all spatial scales. The primary cohesive clay particles are platelets smaller than 2 &amp;#956;m, which is small enough to experience Brownian motion. Composed together under the influence of van der Waals forces, they shape rounded aggregates also known as microflocs that are rather stable. These microflocs can form fragile, larger macroflocs with complex shapes exceeding 100 &amp;#956;m in size. Owing to the huge difference in the spatial scales, it is almost impossible to simulate macroflocs as the assembly of primary clay particles in the context of cohesive sediment transport modeling. In contrast to separate sediment grains, microflocs represent porous aggregates. &lt;/span&gt;&lt;span&gt;T&lt;/span&gt;&lt;span&gt;o perform direct numerical simulations of microflocs transported in a viscous fluid flow, we are developing a computational model for immersed porous particles. The model resolves the flow outside and inside porous aggregates and accurately computes the hydrodynamic forces on the microflocs. The simulation of macroflocs is also attainable by employing &lt;/span&gt;&lt;span&gt;cohesive&lt;/span&gt;&lt;span&gt; forces between microflocs, which assembles them into bigger aggregates with the propensity of breaking up under high shear rates. Our computational model solves the system of Navier - Stokes equations directly with an additional Darcy term inside the porous aggregate. Using this approach, it becomes feasible to consider the influence of the flow inside porous media, so that we can study its impact on the mean flow characteristics depending on the properties of the porous flocs. The hydrodynamic forces are calculated implicitly based on the pressure and shear stress distribution. By comparison with methods that use Stokes-based drag coefficients, our approach allows estimating the influence of local flow conditions and the presence of neighboring aggregates on the resulting fluid force.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;&amp;#160;&lt;/span&gt;&lt;/p&gt;


Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 3665-3665
Author(s):  
Marianna M. Machin ◽  
Jennifer N. Orje ◽  
Paolo Canu ◽  
Zaverio M. Ruggeri

Abstract The initial attachment of platelets to vascular lesions exposed to a high wall shear rate (γw) depends on the interaction between the membrane glycoprotein (GP) Ibα, a component of the GP Ib-IX-V receptor complex, and the A1 domain of surface-immobilized von Willebrand factor (VWFA1). We performed perfusion experiments under different flow conditions to measure transient platelet contacts onto immobilized recombinant VWFA1 and determine the probability of bond formation (capturing) and resistance to tensile stress (bond lifetime) of VWFA1-GP Ibα interactions. To define how molecular conformations influence the biomechanical properties of the bonds, we compared fragments exhibiting the native dimeric assembly of A1 domain with monomeric fragments obtained by selective purification of recombinant protein expressed in stable D. melanogaster cell lines. The minimum coating concentration of dimeric VWFA1 at which platelet adhesion events were statistically significantly different from nonspecific interactions on uncoated glass was 1 μg/ml. In the range of γw between 30 and 30,000 s−1, there was no threshold value for the initiation of adhesion, as seen for selectins. The number of adhering platelets first increased and then decreased with monotonically increasing γw, indicating the effect of transport phenomena as well as hydrodynamic forces on the VWFA1-GP Ibα interaction. Maximum event number was at 5,000 s−1 for dimeric and 1,500 s−1 for monomeric VWFA1. The platelet count had no statistically relevant influence on the efficiency of capturing and duration of adhesive contacts. As γw increased, a higher coating concentration of the VWF A1 domain was required to initiate platelet adhesion. The coating concentration determined the number of individual adhesion events that could occur over a defined period of time but did not affect the residence time, which is a measure of the strength of the bond between the receptor and the ligand. Hydrodynamic forces generated by blood flow shortened the duration of VWF-GP Ibα interactions. The percentage of platelets that had a residence time of less than 0.1 s increased almost linearly with increasing γw. Dimeric A1 domain was more efficient than the monomeric counterpart in promoting platelet adhesion as it displayed activity at lower coating concentrations. At permissible γw, a 10-fold higher monomer than dimer coating concentration (2 vs. 20 μg/ml) was required to obtain a similar capturing efficiency. Moreover, the upper limit of γw compatible with the initiation of adhesion was significantly higher for dimeric as compared to monomeric A1 domain. Doubling the dimer coating concentration resulted in a 5-fold increase in the γw limit for adhesion, but the same increase in the monomer coating concentration did not enhance the probability of bond formation at higher γw. In spite of the substantial difference in capturing efficiency, monomeric and dimeric VWFA1 supported platelet adhesion events of similar duration at any given γw, indicating that a different molecular conformation did not affect the lifetime of the interaction with GP Ibα. These results indicate that the dimeric assembly of A1 domains in VWF multimers may be crucial to support the initiation of platelet adhesion at high shear rates, but the duration of each adhesion event is limited by intrinsic properties of the individual VWFA1-GP Ibα bond.


1974 ◽  
Vol 13 (68) ◽  
pp. 307-313 ◽  
Author(s):  
George D. Ashton

The conditions under which a floating fragment of ice is either entrained under the upstream edge of a down-stream ice cover or accumulated up-stream are examined by means of dimensional analysis and a simplified analysis of the moments acting on an idealized ice fragment. The significant parameter descriptive of the critical conditions is found to be a Froude number based on block thickness. The influence of the ratio of thickness to flow depth is shown to be due to the effect of the block constricting the flow cross-section, thus amplifying the velocity in accordance with simple continuity. Under-turning instability occurs at a lower critical velocity than required for vertical submergence. Comparison of experimental data with the theoretical results show good agreement and demonstrates the vital dependence on fragment thickness as well as providing a criterion readily applicable to special flow conditions where a Froude number based on flow depth is illogical.


Author(s):  
Leiv Aspelund ◽  
Bjørnar Pettersen ◽  
Jan Visscher ◽  
Tor-Bjørn Idsøe Næss

Traditionally, it has often been assumed that the flow conditions in a moonpool are only moderately altered when an object is introduced therein. Moreover, the hydrodynamic forces acting on the object has typically been estimated by Morison’s equation for small volume structures, using the fluid kinematics of the empty moonpool as a basis and applying correction factors for the confined flow conditions, as for an object in a tube or a channel. To investigate the validity of the traditional approach, an experimental study on the forces acting on objects in a moonpool was performed at NTNU/MARINTEK in Trondheim, Norway in 2013. The experiments were done using a simplified 2-dimensional moonpool model which was given a forced heave motion. Two objects, both with square cross sections but of different sizes, were put inside the moonpool one at the time. The resulting wave elevations inside the moonpool and the forces acting on the objects were recorded and analyzed. To get a deeper understanding of the flow characteristics in the moonpool, PIV measurements were used to obtain the fluid velocity fields. The experiments revealed that even moderately sized objects (relative to the size of the moonpool) change the fluid motions in the moonpool to a large extent; the overall wave elevation amplitude is strongly reduced and the resonance period is altered. A consequence of this is that there is a large discrepancy between the hydrodynamic forces acting on the objects measured in the experiments and the forces calculated using the traditional approach. The PIV results showed the formation of vortices at the inlet of the moonpool and at the edges of the objects, which is the main source of non-linear damping of the wave elevation inside a moonpool.


2019 ◽  
Vol 67 (3) ◽  
pp. 240-251
Author(s):  
Mohammad Reza Namaee ◽  
Jueyi Sui

Abstract In the present study, experiments were conducted in a large-scale flume to investigate the issue of local scour around side-by-side bridge piers under both ice-covered and open flow conditions. Three non-uniform sediments were used in this experimental study. Analysis of armour layer in the scour holes around bridge piers was performed to inspect the grain size distribution curves and to study the impact of armour layer on scour depth. Assessments of grain size of deposition ridges at the downstream side of bridge piers have been conducted. Based on data collected in 108 experiments, the independent variables associated with maximum scour depth were assessed. Results indicate that the densi-metric Froude number was the most influential parameter on the maximum scour depth. With the increase in grain size of the armour layer, ice cover roughness and the densimetric Froude number, the maximum scour depth around bridge piers increases correspondingly. Equations have been developed to determine the maximum scour depth around bridge piers under both open flow and ice covered conditions.


2021 ◽  
Vol 927 ◽  
Author(s):  
Francesco Romanò ◽  
Pierre-Emmanuel des Boscs ◽  
Hendrik C. Kuhlmann

The slow motion of a small buoyant sphere near a right dihedral corner made by tangentially sliding walls is investigated. Under creeping-flow conditions the force and torque on the sphere can be decomposed into eleven elementary types of motion involving simple particle translations, particle rotations and wall movements. Force and torque balances are employed to find the velocity and rotation of the particle as functions of its location. Depending on the ratio of the wall velocities and the gravitational settling velocity of the sphere, different dynamical regimes are identified. In particular, a non-trivial line attractor/repeller for the particle motion exists at a location detached from both the walls. The existence, location and stability of the corresponding two-dimensional fixed point are studied depending on the wall velocities and the buoyancy force. The impact of the line attractors/repellers on the motion of small particles in cavities and its relevance for corner cleaning applications are discussed.


1976 ◽  
Vol 3 (1) ◽  
pp. 1-10
Author(s):  
B. Michel ◽  
R. Abdelnour

An experimental study has been made on a scale model of a rectangular canal in the hydraulics laboratory of Laval University in order to simulate the destruction of a solid continuous ice cover under the effect of the tangential forces created by the flow.The canal was 6 ft (1.8 m) wide and 46 ft (14 m) long. At the lower end, an ice retention structure of reticular form was built. The ice was simulated with a wax poured in a continuous and uniform layer; whose properties correspond to that of natural ice at an average scale of 1/25. Ice covers corresponding to thicknesses of 8 to 20 in. (20.3 to 50.8 cm) were simulated at that scale.Tests consisted essentially in increasing progressively the discharge feeding the canal until complete failure of the ice cover and accumulation of the pieces in front of the grid retaining structure.Three important phenomena have been observed and measured. By chronological order the first one is the submersion of the frontal edge of the cover. This happens at a relatively constant Froude number but much higher than the one characterizing the stability of unconsolidated ice jams.An increase in discharge makes the ice cover unstable as it oscillates in the flow. This state is followed closely by the failure of the cover, the movement of the pieces with the flow and their accumulation in front of the retaining structure where they form a dry jam. This phenomenon of failure of the ice cover could be interpreted in the first approximation with two dimensionless numbers one being the Froude number and the other characterizing the ratio of failure forces to gravity forces. We have found that an exponential relationship relates these two numbers and the correlation coefficient for the 25 tests is satisfactory.Finally, we have measured the thrust exerted by the dry jams on the ice retaining structure. There is a very direct hydrostatic relationship between the thrust and flow conditions with a dry jam.These laboratory results are interesting to assess the discharges and water levels required in rivers to break-up ice covers of various resistances. One can estimate these conditions for the case of weakened ice covers before spring break-up. However, more importantly, it is possible to approximate the worst conditions of flooding with an early break-up towards the end of the winter when the ice still has its maximum strength.


2020 ◽  
Vol 10 (18) ◽  
pp. 6404
Author(s):  
Haojie Ren ◽  
Shixiao Fu ◽  
Chang Liu ◽  
Mengmeng Zhang ◽  
Yuwang Xu ◽  
...  

This work experimentally investigated the performance of hydrodynamic forces on a semi-submerged cylinder under an oscillatory flow. To generate the equivalent oscillatory flow, the semi-submerged cylinder is forced to oscillate in several combinations of different periods and amplitudes. The mean downward lift force was observed to be significant and the fluctuating lift forces show dominant frequency is twice that of oscillatory flow and amplitude that is the same as the mean lift force. Based on this main hydrodynamic feature, a novel empirical prediction formula for the lift forces on semi-submerged cylinder under oscillatory flow is proposed where the lift forces expression is proportional to the square of oscillatory flow velocity. This novel empirical formula directly assigns the fluctuating lift force with frequency twice of oscillatory flow and the amplitude that is the same as the mean lift force. This assignment of empirical lift force formula reduces parameters required to determine a dynamic lift force but is demonstrated to well predict the fluctuating lift force. The lift coefficient can reach 1.5, which is larger than the typical value 1.2 of the drag coefficient for a fully submerged cylinder with infinite depth. Moreover, relationships among hydrodynamic coefficients, Keulegan-Carpenter (KC) number, Stokes number and Froude number are studied. With the increase of KC number, the Froude number has a more significant influence on the distribution of hydrodynamic coefficients. As Froude number is increasing, the drag coefficient shows a nonlinear decay (KC < 20) but a linear increase (KC > 20), while the added mass coefficients show a nonlinear (KC < 20) and a linear (KC > 20) increase trend. The present work can provide useful references for design of the relevant marine structures and serve as the useful guideline for future research.


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