Research on acoustic behaviors of water pipelines with guide vanes

In this paper, the pipeline with guide vanes was taken as the research object, the flow noise was studied based on the hybrid calculation method, then the acoustic-structure coupling method was introduced to study the vibration and radiation noise, and then explored the best position of the guide vanes. Based on the pipeline experimental platform and improved experimental methods, it was found that the guide vanes had a better noise reduction effect on the elbows; based on that, a simulation study was carried out on the elbow with guide vanes, and the mechanism of the guide vanes on the velocity field and pulsating pressure of the pipeline was explored. Finally, the noise reduction effect at different positions of the guide vanes under different flow speeds was studied. The results indicated that the guide vane at the middle of the elbow had the best effect on improving the flow field and reducing noise in the working conditions studied in this article, providing a calculation basis for the design of the guide vane.

Effect of Flow Induced Parameters on the Output of A High Repetition Rate Dye Laser

The factors influencing the optical path stability in a dye laser flow cell are studied numerically and experimentally. A specially designed curved metallic dye flow cell providing a gain medium of 25 mm x 0.5 mm x 0.2 mm along with a compact resonator mechanical assembly is used in the study. The same configuration with gain medium of 15 mm x 0.5 mm x 0.2 mm is successfully used for single mode dye laser. The effects of flow induced vibrations on dye flow cell are studied with and without mechanically coupling it with the resonator structure for flow speeds varying from 1.33 m/s to 6.67 m/s at laser pump position. The effect of the mechanical instability, velocity fluctuation and temperature fluctuations in flowing dye solution on dye laser performance are studied at different flow speeds. These results are compared with the dye laser output parameters and found to be in good agreement. This study is useful in designing a high stability narrowband dye laser.

STUDY ON PROPULSIVE PERFORMANCE OF TWO GEOMETRICALLY SIMILAR PODDED PROPULSORS

This paper presents the outcome of a research to evaluate the effect of size on the propulsive performance of podded propulsors in cavitating and non-cavitating open water conditions. Two cases are examined, namely: propeller-only case and pod-unit case. In the propeller-only case, a commercial propeller dynamometer is used to measure the thrust and torque of two propellers of different size at the four quadrants of propellers with varied shaft and flow speeds. Also, both propellers are tested at different tunnel pressure to study and compare the behaviour under similar cavitation conditions. In the pod-unit case, two geometrically similar but different sized pod-units are tested using two separate custom-made pod dynamometer systems in two towing tank facilities in straight-ahead and static azimuthing conditions. The study showed that the performance characteristics stabilize at lower Reynolds Number for the smaller propeller than the larger propeller. The propulsive performance of the two propellers was comparable in the four-quadrant experiments. Also, the experiments at the cavitating conditions showed that the cavitation characteristics of the two propellers were consistent at corresponding operating conditions. The experiment results of the two pod-units were also comparable for forces and moments in the three coordinate directions in the straight-ahead and static azimuthing conditions. A brief discussion on the uncertainty assessments for each of the measurements is also presented.

Upstream rheotaxis of catalytic Janus spheres

Fluid flow is ubiquitous in many environments that form habitats for microorganisms. The tendency of organisms to navigate towards or away from flow is termed rheotaxis. Therefore, it is not surprising that both biological and artificial microswimmers show responses to flows that are determined by the interplay of chemical and physical factors. In particular, to deepen understanding of how different systems respond to flows, it is crucial to comprehend the influence played by swimming pattern. In recent studies, pusher-type Janus particles exhibited cross-stream migration in externally applied flows. Earlier, theoretical studies predicted a positive rheotactic response for puller-type spherical Janus micromotors. To compare to a different swimmer, we introduce Cu@SiO2 micromotors that swim towards their catalytic cap. Based on experimental observations, and supported by flow field calculations using a model for self-electrophoresis, we hypothesize that they behave effectively as a puller-type system. We investigate the effect of externally imposed flow on these spherically symmetrical Cu@SiO2 active Janus colloids, and we indeedobserve a steady upstream directional response. Through a simple squirmer model for a puller, we recover the major experimental observations. Additionally, the model predicts a unique “jumping” behaviour for puller-type micro- motors at high flow speeds. Performing additional experiments at high flow speeds, we capture this phenomenon, in which the particles “roll” with their swimming axes aligned to the shear plane, in addition to being dragged down- stream by the fluid flow.

Rectified tidal transport in Lofoten–Vesterålen, northern Norway

Vestfjorden in northern Norway, a major spawning ground for the northeast Arctic cod, is sheltered from the continental shelf and open ocean by the Lofoten–Vesterålen archipelago. The archipelago, however, is well known for hosting strong and vigorous tidal currents in its many straits, currents that can produce significant time-mean tracer transport from Vestfjorden to the shelf outside. We use a purely tidally driven unstructured-grid ocean model to look into non-linear tidal dynamics and the associated tracer transport through the archipelago. Of particular interest are two processes: tidal pumping through the straits and tidal rectification around islands. The most prominent tracer transport is caused by tidal pumping through the short and strongly non-linear straits Nordlandsflaget and Moskstraumen near the southern tip of the archipelago. Here, tracers from Vestfjorden are transported tens of kilometers westward out on the outer shelf. Further north, weaker yet notable tidal pumping also takes place through the longer straits Nappstraumen and Gimsøystraumen. The other main transport route out of Vestfjorden is south of the island of Røst. Here, the transport is primarily due to tracer advection by rectified anticyclonic currents around the island. There is also an anticyclonic circulation cell around the island group Mosken–Værøy, and both cells have flow speeds up to 0.2 m s−1, magnitudes similar to the observed background currents in the region. These high-resolution simulations thus emphasize the importance of non-linear tidal dynamics for transport of floating particles, like cod eggs and larvae, in the region.

Short-term forecasting of wind and solar power generation

It is important to note that the generated power of renewable sources depends on the natural conditions at a particular geographic point, the level of wind flow speeds and solar radiation. The patterns characterizing these parameters depend on the time of year, locality and are purely probabilistic in nature. Taking into account the above-mentioned conditions for the effective implementation of “green” objects in the power supply system, the purpose of this work is to build forecasting models that are more likely to be able to determine what part of the load can be covered by the power supply system based on wind power and solar installations. This purpose was achieved by constructing and training artificial neural networks with data on the speed of wind flow and solar radiation obtained from real renewable energy facilities. The most significant result is the identification of the necessary forecasting horizon, taking into account the preservation of a relatively good quality of metrics, as well as understanding what additional data is required to improve this quality. The significance of the results obtained lies in the fact that they make it possible to determine what reserve capacity is required to be included in the project.

Numerical Simulation of Tidal Current in Majishan Sea Area of Zhoushan Based on SCHISM

Based on the SCHISM ocean model, this paper constructs a numerical model of the Majishan sea area in Shengsi County, Zhoushan City, and numerically simulates the tidal and tidal current conditions in the sea area. The non-structural triangular elements are used to construct the high-precision nearshore terrain to accurately simulate the tidal and tidal conditions. Yearly measured tidal current data. Have a deeper understanding of the tidal currents in the Majishan sea area of Zhoushan. The results show that the Majishan sea area of Zhoushan belongs to regular shallow sea currents dominated by recurrent currents. In the actual measurement, the speed of the rising and falling tides varies, and the maximum and average flow speeds are both the high tide is greater than the medium tide and the small tide. The tidal changes are mainly controlled by the forward waves of the East China Sea, and the direction of the current is basically the same as the direction of the rising and falling tides.

Vortex Formation Times in the Glottal Jet, Measured in a Scaled-Up Model

In this paper, the timing of vortex formation on the glottal jet is studied using previously published velocity measurements of flow through a scaled-up model of the human vocal folds. The relative timing of the pulsatile glottal jet and the instability vortices are acoustically important since they determine the harmonic and broadband content of the voice signal. Glottis exit jet velocity time series were extracted from time-resolved planar DPIV measurements. These measurements were acquired at four glottal flow speeds (uSS = 16.1–38 cm/s) and four glottis open times (To = 5.67–23.7 s), providing a Reynolds number range Re = 4100–9700 and reduced vibration frequency f* = 0.01−0.06. Exit velocity waveforms showed temporal behavior on two time scales, one that correlates to the period of vibration and another characterized by short, sharp velocity peaks (which correlate to the passage of instability vortices through the glottis exit plane). The vortex formation time, estimated by computing the time difference between subsequent peaks, was shown to be not well-correlated from one vibration cycle to the next. The principal finding is that vortex formation time depends not only on cycle phase, but varies strongly with reduced frequency of vibration. In all cases, a strong high-frequency burst of vortex motion occurs near the end of the cycle, consistent with perceptual studies using synthesized speech.

How a ball free to orbit in a circular track mitigates the galloping of a square prism

Transverse galloping is a type of flow-induced vibration (FIV) that leads to critical design considerations for engineering structures. A purely nonlinear energy sink (NES) composed of a ball free to rotate in a circular track experimentally mitigated the galloping of a square in a previous study. The current study introduces a model for simulating the dynamics of the square prism coupled with a ball-in-track (BIT) NES and predicting the system behaviour at high flow speeds beyond the limits of the previously presented experiments. Numerical simulations employ the fitting of experimental data as inputs to define parameters. Wind tunnel static experiments provide the galloping force coefficient [[EQUATION]] relative to the prism angle of attack. Additionally, free rotation tests allow evaluating the ball damping coefficient [[EQUATION]] as a function of its mass and the NES track radius. The result of the rotation tests provides a critical angular speed beyond which the ball damping increases non-linearly. We point out the damping variation as an advantage of the BIT-NES; less damping at low angular velocities helps the ball start its rotation, while relatively large damping at higher speeds dissipates more energy from the vibrating system. Numerical results exhibit four response modes for the NES; oscillatory at low flow speeds, intermittent within a small range of higher flow speeds, rotational at higher flow speeds, and ineffective regime at flow speeds out of the NES effective range. Modelling the primary mass as a parametric excitation source for the NES provides an analytical estimation of the boundary between the oscillatory and intermittent regimes. Furthermore, we advance an analytical analysis of the power flow across the integrated prism-NES system to explain the NES behaviour and predict the limit of its effective range.

Fluidic bacterial diodes rectify magnetotactic cell motility in porous environments

Directed motility enables swimming microbes to navigate their environment for resources via chemo-, photo-, and magneto-taxis. However, directed motility competes with fluid flow in porous microbial habitats, affecting biofilm formation and disease transmission. Despite this broad importance, a microscopic understanding of how directed motility impacts the transport of microswimmers in flows through constricted pores remains unknown. Through microfluidic experiments, we show that individual magnetotactic bacteria directed upstream through pores display three distinct regimes, whereby cells swim upstream, become trapped within a pore, or are advected downstream. These transport regimes are reminiscent of the electrical conductivity of a diode and are accurately predicted by a comprehensive Langevin model. The diode-like behavior persists at the pore scale in geometries of higher dimension, where disorder impacts conductivity at the sample scale by extending the trapping regime over a broader range of flow speeds. This work has implications for our understanding of the survival strategies of magnetotactic bacteria in sediments and for developing their use in drug delivery applications in vascular networks.