Nonlinear Behaviour of Concrete Buttress Dams under High-Frequency Excitations Taking into Account Topographical Amplifications

Concrete buttress dams could potentially be susceptible to high-frequency vibrations, especially in the cross-stream direction, due to their slender design. Previous studies have mainly focused on low-frequency vibrations in stream direction using a simplified foundation model with the massless method, which does not consider topographic amplifications. This paper therefore investigates the nonlinear behaviour of concrete buttress dams subjected to high-frequency excitations, considering cross-stream vibrations. For comparison, the effect of low-frequency excitations is also investigated. The influence of the irregular topography of the foundation surface on the amplification of seismic waves at the foundation surface and thus in the dam is considered by a rigorous method based on the domain-reduction method using the direct finite element method. The sensitivity of the calculated response of the dam to the free-field modelling approach is investigated by comparing the result with analyses using an analytical method based on one-dimensional wave propagation theory and a massless approach. Available deconvolution software is based on the one-dimensional shear wave propagation to transform the earthquake motion from the foundation surface to the corresponding input motion at depth. Here, a new deconvolution method for both shear and pressure wave propagation is developed based on an iterative time-domain procedure using a one-dimensional finite element column. The examples presented showed that topographic amplifications of high-frequency excitations have a significant impact on the response of this type of dam. Cross-stream vibrations reduced the safety of the dam due to the opening of the joints and the increasing stresses. The foundation modelling approach had a significant impact on the calculated response of the dam. The massless method produced unreliable results, especially for high-frequency excitations. The free-field modelling with the analytical method led to unreliable joint openings. It is therefore recommended to use an accurate approach for foundation modelling, especially in cases where nonlinearity is considered.

Surface Basins Evaluation of the Southern Desert, West Iraq

The results of the present study show that the highest elevation point is (912) meters (a.s.l.) inside Wadi Al-Khur basin while the lowest elevation point is (6) meters (a.s.l.) inside Wadi Abu-Talha basin. The biggest catchment area is represented by Wadi Al-Khur (48840 km²) whereas the smallest catchment area is Wadi Taqtaq (1748 km²). The stream direction of all streams trends from South-West towards North-East. The soil available water capacity (AWC) (Moisture Deficit) in the studied area was15 mm. The average annual rainfall was133.11 mm, the average annual temperature was 25.65 Co, the total depth amount of E Apanwas 3691.85 mm/year, the relative humidity was 40 %, the average annual sunshine is 7.9 hrs., and the average annual wind speed is 2.7 m/s. The water surplus of the total studied area 46800 km) was about 488.592 m³⁄year, while the runoff amount was about 442.190 m³ ⁄year.

The Flow Noise Calculation for an Axisymmetric Body in a Complex Underwater Environment

The flow noise of a sonar platform is one of the main background interferences for sonar applications. This paper focuses on the flow noise of an axisymmetric body in a complex oceanic environment. Under the condition of a constant stream velocity which comes from the axial direction, an analytical method for computing the flow noise power spectrum in the transition region of the axisymmetric body is given in detail. The flow noise power spectrum computed by the analytical method is in agreement with the numerical simulation result. Then the flow noise physical features of the axisymmetric body in different incoming stream directions and velocity states caused by the complex oceanic environment are computed and analyzed by the numerical method. The results show that as the incoming stream direction changes, the transition region will migrate and the flow noise radiation direction of the axisymmetric body will also rotate at an angle which equals the stream direction variation. The flow noise energy generated by other directional incoming streams is slightly larger than that generated by the stream coming from an axial direction. When the incoming stream velocity is time-varying, the vorticity change on the axisymmetric body surface is obviously stronger than that under a constant stream, and the generated flow noise energy is also significantly larger. In addition, it indicates that there is a significant correlation between the intensity of flow noise energy and the magnitude of flow velocity.

Swimming freely near the ground leads to flow-mediated equilibrium altitudes

Experiments and computations are presented for a foil pitching about its leading edge near a planar, solid boundary. The foil is examined when it is constrained in space and when it is unconstrained or freely swimming in the cross-stream direction. It was found that the foil has stable equilibrium altitudes: the time-averaged lift is zero at certain altitudes and acts to return the foil to these equilibria. These stable equilibrium altitudes exist for both constrained and freely swimming foils and are independent of the initial conditions of the foil. In all cases, the equilibrium altitudes move farther from the ground when the Strouhal number is increased or the reduced frequency is decreased. Potential flow simulations predict the equilibrium altitudes to within 3 %–11 %, indicating that the equilibrium altitudes are primarily due to inviscid mechanisms. In fact, it is determined that stable equilibrium altitudes arise from an interplay among three time-averaged forces: a negative jet deflection circulatory force, a positive quasistatic circulatory force and a negative added mass force. At equilibrium, the foil exhibits a deflected wake and experiences a thrust enhancement of 4 %–17 % with no penalty in efficiency as compared to a pitching foil far from the ground. These newfound lateral stability characteristics suggest that unsteady ground effect may play a role in the control strategies of near-boundary fish and fish-inspired robots.

Critical Resistance Affecting Sub- to Super-Critical Transition Flow by Vegetation

In order to design a vegetation structure to mitigate floods resulting from extreme events like tsunamis, vegetation density and thickness (width) are important parameters. Flow passing through vegetation faces great resistance, which results in a backwater rise on upstream (U/S) vegetation, increases the water slope inside the vegetation, and for some cases, forms a hydraulic jump downstream (D/S) of the vegetation, thus transforming a subcritical flow to supercritical [Pasha, G. A. and Tanaka, N. [2017] “Undular hydraulic jump formation and energy loss in a flow through emergent vegetation of varying thickness and density,” Ocean Eng. 141, 308–325.]. Like the concepts of critical velocity and critical slope, this paper introduces the concept of “critical resistance of vegetation,” which is defined as “resistance offered by vegetation that transforms a subcritical flow to supercritical.” An analytical approach to find the water depths U/S, inside, and D/S of vegetation is introduced and validated well by laboratory experiments. Critical resistance was determined against vegetation of variable densities ([Formula: see text], where [Formula: see text] of each cylinder in the cross-stream direction, [Formula: see text] of the cylinder), thicknesses (dn, where [Formula: see text] of a cylinder and [Formula: see text] of cylinders in a stream-wise direction per unit of cross-stream width), and the initial Froude number (Fro). A subcritical flow ([Formula: see text], without vegetation) was transformed to a supercritical flow (D/S vegetation) with a range of Froude numbers of 1.6–1.9, 1.1–1.2, and 0.85–0.98 against [Formula: see text] ratios of 0.25, 1.09, and 2.13, respectively, thus defining [Formula: see text] as the critical resistance. However, altering vegetation thickness did not change the results.

Research in the Impact of Dynamic Loads for the Development of Pentice Designs when Sinking Skip Shafts

In order to protect workers engaged in shaft sinking works artificial protective equipment (buntons) with the support element from powerful I-beams or truss structures are used. They have to withstand enormous push loading, be strong, simple in design, have less labor input during construction and dismantling. Under shaft sinking in case of skip operational winding performance, a protective bunton can be exposed to the rock mass flow in the event of an emergency full skip run. To substantiate the variables and develop the design of pentices when sinking an active hoisting shaft, the skip falls time dependence on the changes in its fall height, taking into account the velocity and the air stream direction in the shaft, was established using mathematical modeling. LLC “SibGorComplexEngineering” together with the Department of Construction of Underground Structures and Mines of T.F. Gorbachev Kuzbass State Technical University have developed several new designs variants of protective buntons for vertical shafts sinking in case of operational winding performance. It is a Z-shaped structure of the offset in height, parallel to each other of upper and lower protective buntons, bushed with sloped reflective metal sheets and it is interconnected by a vertical division wall.

Influence of yaw on propeller aerodynamic characteristics

Between the propeller axis and free stream direction, it can still be a non-zero yaw angle. This paper introduces some propeller experiments, in which the propeller aerodynamic characteristics have been determined in various yaw angle and different rotational speeds. The experimental aerodynamic characteristics are acquired dynamic values, from which the influence of yaw conditions on the frequency and the amplitude of propeller thrust and torque can be obtained.

Benefits and Problems of Monitoring the Waterway Transport on Danube and Danube Cruise Statistics Based on Monitoring the Pusher Tugboats

This article deals with benefits and problems of using GPS monitoring and Inland AIS, which is the part of river information services operating on Danube. It is based mainly on results and experience from monitoring of two pusher tugboats on Danube and Danube – Main – Rhine canal within the project Chemlog T&T. It also contains statistics of their navigation on particular Danube sections in up stream and down stream direction, such as transit durations between particular ports, proportion of speed in percentage in particular Danube sections and delays in lock chambers or in front of them.