To estimate the maneuverability of a submarine at the early design stage, an accurate evaluation of the hydrodynamic coefficients is important. In a collaborative exercise, the authors performed calculations on the bare hull DRAPA SUBOFF submarine to investigate the capability of viscous-Flow solvers to predict the forces and moments as well as Flow field around the body. A typical simulation program was performed for both the steady drift tests and rotating arm tests. The same grid topology based on multi-block mesh strategy was used to discretize the computational domain. A procedure designated drift sweep was implemented to automatically increment the drift angle during the simulation of steady drift tests. The rotating coordinate system was adopted to perform the simulation of rotating arm tests. The Coriolis force and centrifugal force due to the computation in a rotating frame of reference were treated explicitly and added to momentum equations as source terms. Lastly, the computed forces and moment as a function of angles of drift in both conditions are compared with experimental results and literature values. They always show the correct trend.Flow field quantities including pressure coefficients and vorticity and axial velocity contours are also visualized to vividly describe the evolution of Flow motions along the hull.

Weirs are common hydraulic structures that can be used in conveyance water canals for increasing the water depth upstream of turnouts or measurement of Flow discharge. In this study, the effect of hydraulic parameters and creation conditions of undular Flow in the broad-crested weirs were investigated numerically using the finite volume method and the results were evaluated by the experimental method of other researchers. Results indicated that discharge coefficients (Cd) for experimental data are between 0.321-0.332, whereas the Cd for numerical simulation (using ANSYS FLUENT) is between 0.301-0.354. Over the crest where the minimum water depth (dmin) happens, when Fr1 is less than 1.5 (Fr1<1.5), the creation of waves was observed. This type of Flow is known as the undular Flow. In this situation, measuring water depth over the broad crested weir is not easy and can introduce error for discharge estimation. For preventing of the undular Flow, the Flow depth cannot be less than a specified value. In this study, this limitation was observed for H/L > 0.1. Thus it can result that long broad-crested weirs (H/L<0.1) are more susceptible than the broad-crested weirs (0.1≤H/L<0.4) in the creation of the undular Flows. Additionally, a regression equation for estimation of the Cd in the broad-crested weirs is proposed with reasonable accuracy.

During the past two decades, bendway weirs have been used as erosion conrol structures in river bends. These structures are constructed for erosion control at the outer bank with suitable upstream angle. This research investigates the effect of the angle and length ratio of weirs on the resistance coeficients of the Flow (f, n) in a sinusoidal channel and in different hydraulic conditions. Three angles (60o, 75o and 90o), three length ratios (0.2, 0.3 and 0.4) and three submergence ratios (2.6, 2.8 and 3) were used as variables. All experiments were performed in alive bed condition with a continuous sediment injection. The results showed that the Darcy-Weisbach’s f and Manning’s n coefficients decreased with increasing of the angle and length ratio. Flow resistance coefficients “f” and “n” increased 90% and 20%, respectively and “C” coefficient decreased 27% due to weirs construction.

Rockfill dams are usually used for affecting the flood and reducing the peak discharge. The materials used in these dams will usually make the Flow turbulent, therefore Darcy's law can not be used for this kind of dams and the equations based on the non-Darcy Flow must be applied. Non-Darcy Flow equations are showed in two general ways including:i=aVN and i=rV+sV2 .One of the main parameters for Flow simulationthrough this type of media is N, which can be specified empirically using experimental data. N is a parameter for Flow turbulence and varies from 1 (laminar Flow) to 2 (fully turbulent Flow). One of the problems with some of non-Darcy equations (e.g. Ergun) is that they can not compute α and N directly. In this research using the Ergun equation and mathematical analysis, a few equations have been derived and presented for computing N and α and finally a new equation has been presented for the equivalent hydraulic conductivity (Ke) coefficients in porous media. A standard example was used for the verification of the resulting equations. Some values were assumed for the soil properties and the value of N, a were computed using the proposed equations in this research study. N was also specified using a non-linear regression analysis and was compared with the corresponding values obtained from the proposed equations. Comparison of the both sets of results showed that the computed N values are relatively precise especially for the boundaries (N=1 and 2).

As a result of the limitations in the application of Darey Law (V=ki) to linear-laminar Flow regime, through porous media and due to tire fact that in coarse alluviums, the Reynolds number may exceed its critical value, the so-called Laplas equatioll cannot be used for precise analyses of coarse granular foundations. A more general relationship is. therefore Required for such cases. However, a common relationship between piezometric gradient "i" and the approach velocity "v" within porous media shown as i=m It" leads to major difficulties in undertaking complicated tests to determine tlte values of m and n. It is shown that by combining the above-mentioned relationship with the continuity equation, a differential equation may be obtained to give piezometric hem/ and a potential function j, which, in turn, lead to the uplift force distributions and the seepage quantities through porous media. To overcome difficulties associated with m and n estimations in the model and as a result of fulfilling, extensive research programme, afresh and reliable procedure has been developed and explained to assess m and n by means <!simple stepped pump-out test. The practicial applicability of the method for a given confined aquifer is also examined. Find in indicates that the proposed procedure a) makes the use of the differential equation for turbulent Flow in porous media possib and b) provides means to determine the nonlinear equation parameters (m&n) at an acceptable precision. The computed values the parameters are also submitted.

IntroductionAs we know, the calculation of hydraulic gradient is highly important in the analysis of steady Flow inside rockfill materials. Binomial and exponential relationships are used to calculate the hydraulic gradient based on the non-Darcy Flow velocity, and the binomial relationship is more accurate and efficient than the exponential relationship. Since it is necessary to use an exponential relationship in the two-dimensional analysis of non-Darcy Flow in coarse porous media, in the past, researchers have provided relationships to calculate the coefficients m and n of the exponential relationship based on the coefficients a and b of the binomial relationship. In some previous studies, Vmax= 1 has been considered, even though the maximum Flow velocity depends on the physical characteristics of the pebbles and the characteristics of the Flow and is not necessarily equal to one. For this reason, in this research, by designing and equipping the laboratory and recording the laboratory data, the maximum velocity based on the values of a, b and Re of the analytical model of Ahmed and Sunada(1969) is proposed.As mentioned above, various researchers tried to calculate the coefficients of the exponential relationship using the values of a and b in the binomial relationship. One of the most important relationships is presented by George and Hansen (1992) as follows.n=(5a+6bV_max)/(5a+3bV_max ) (1)m=(5a+4bV_max )(4a+3bV_max )/(4(5a+3bV_max ) (V_max )^(n-1) ) (2)Further, by stating that in the coarse-grained porous medium, the slope of the energy line (Sf) is equal to the hydraulic gradient (i), it can be stated that one of the most important parameters in the investigation of the Flow in the gravel medium in free Flow and under pressure is the calculation of it is a hydraulic gradient. In this research, using the coefficients of the binomial relationship, we presented a solution to calculate the values of m and n in the exponential relationship with better accuracy. Therefore, considering that the exponential relationship is used in the two-dimensional analysis of the non-Darcy Flow in porous gravel media, this can play a significant role in reduction of the error of hydraulic gradient calculation.MethodologyIn the current research, the laboratory data recorded in the hydraulic laboratory of the Faculty of Civil Engineering of Zanjan University were used. For this purpose, an attempt was made to design and set up a test device and perform tests on different gravel materials. Experiments were carried out in a laboratory flume with the ability to tilt, with dimensions of 1m×1m and a length of 15m, and the length of 2.2m of the mentioned flume is filled with rockfill. The walls of the flume are made of plexiglass, and to measure the piezometric height along the porous media, 23 piezometers are used on the bottom of the channel, which are arranged at certain distances from each other and along them. The water Flow in the channel is created by a pump with a maximum Flow capacity of 90 liters per second. In order to create a porous media, three types of rockfill materials with small, medium and large diameters have been used in the experiments. During the tests, to ensure a stable Flow, the pump was working for about 10 minutes with the desired Flow and after the stability of the Flow, the desired parameters were measured. These parameters include the piezometric height at the location of 23 piezometers as well as the water depth at the location of each piezometer. Piezometric values are read using a calibrated table. The water depth was also measured and recorded directly by a ruler.Results and DiscussionSince the exponential relationship is only accurate for a certain range of Reynolds numbers and the user area recommended for this relationship by its providers is only non-quiet Flow conditions, therefore, if the exponential relationship is used in the two-dimensional solution of the equations, there will be a large error will enter the calculations. To avoid this problem, various researchers have tried to convert the binomial relationship into an exponential relationship. If the minimum Flow velocity Vmin and the maximum Flow velocity Vmax in the conversion area of the binomial relationship is in the form of an exponential relationship. In order to convert the two mentioned relations, relations (1) and (2) can be used. According to the conducted tests, in most cases, Vmin is considered zero and Vmax value is assumed to be equal to one, while the maximum Flow velocity depends on the physical characteristics of the pebbles and the characteristics of the Flow and is not necessarily equal to one. Therefore, Vmax can be calculated from the following relationship according to Ahmed and Sunada's(1969) analytical model and the definition of the Reynolds number as Re=ρVd/μ.V_max=Re_max a/b (3)By using relations (1), (2) and (3), it is possible to take advantage of the accuracy of the binomial relation and the practical property of the exponential relation in the two-dimensional analysis in porous media.If relations (1) and (2) are used in the calculation of the coefficients of the exponential relationship of steady Flow in gravel materials, the average relative error between the calculated and recorded hydraulic gradients in the laboratory assuming Vmax=1 (according to previous research) in fine gravel materials, medium and coarse are calculated to be 21.95%, 22.98% and 21.97%, respectively. While if relation (3) is used (the solution presented in the current research), the average relative error values of the hydraulic gradient are equal to 11.39, 14.69 and 19.72%, respectively.ConclusionIn general terms, by using relations (1) and (2) and using the relation proposed in the present study instead of Vmax=1, the average values of the relative error of the hydraulic gradient in fine, medium and coarse rockfill materials have decreased to 10.56, 8.29 and 2.25%, respectively, which indicates the high accuracy and efficiency of the proposed solution.Keywords: Non-Darcy Flow, exponential relation, binominal relation, rockfill, hydraulic gradient.

The hydrodynamic coefficient of an underwater manipulator varies with changes in posture and Flow field, presenting significant challenges for precise control and localization. This study, conducted numerical simulations to investigate the patterns of variation in Flow field and hydrodynamic coefficients. Results showed that hydrodynamic performance remained consistent when the posture of the manipulator was either axisymmetric or origin-symmetric. Upon rotation, axial Flow extended across the entire downstream surface, and the Karman vortex street entirely eliminated. Pressure coefficients on the back pressure surface of the manipulator increased with the Reynolds number within the range of 6×103 ≤ Re ≤ 3×104, while the pressure coefficient on the upstream surface remained unchanged. Within this range, drag coefficients for the upper and lower arms decreased by 27.4% and 23.9%, respectively. The hydrodynamic performance of the lower arm was independent of the upper arm's posture, with a maximum drag coefficient of 1.48 achieved at α = −90°. As the posture angle of the manipulator varied from 30° to 60°, the pressure coefficient on the upstream surface decreased from 0.75 to 0.25.

Non uniform Flow Transverse velocity distribution in the main channel’s interface zone with floodplain in compound channels cause uncertainty to estimate in following parameters: the water surface profile, flood routing and sediment and pollution transport. The correction coefficients, (α) and (ß) were used respectively, to employ the impact of this uniformity on the kinetic energy and momentum values. In this study, via FCF data for compound channels, the influence of floodplain width (4.1, 2.25 and 0.75 m) on α and ß coefficient was investigated in symmetric and asymmetric compound channels. According to the results, the maximum value of α and ß was increased, due to increasing the width of the floodplain. Finally, the Flow discharge was determined, with α and ß calculating values via CES software. Afterward, these values were compared with FCF laboratory data. The normalized root mean square error (NRMSE) was estimated in appropriate range, it equal to %15.6. This investigation showed that the high performance of the CES in determining the hydraulic parameters of Flow such as discharge, in symmetric and asymmetric compound channels. But in general, this software overestimated the value of discharge.

Extraction of sugar from sugarcane produces a high volume of effluent carrying large amounts of organics and BOD5. Discharging the effluent into rivers and into the environment endangers the aquatic life and increases the risks of environmental pollution. This study was conducted in 2012 to determine the kinetic coefficients of the anaerobic treatment systems (UASB) at the wastewater treatment plant of Imam Khomeini Sugarcane Agro-industrial Plant in Shushtar. The parameters of BOD5, COD, and TSS were measured at the inlet and outlet of the WWTP. Subsequently, the operation and design parameters of the system were determined. Using the modified Monod Equations, the kinetic coefficients Ks, Y, Kd, mmax, and K max for employing the UASB process at the WWPT in question were calculated as 506.4mg/l, 0.11 g VSS/g COD, 0.0045 d-1, 0.0069 d-1, and 0.055 d-1, respectively. The kinetic coefficients obtained in this study can be used in the steering and operation as well as fundamental design of similar plants, especially in hot areas.