Surface Water Channel Research Articles

Satellite observations of surface water dynamics and channel migration in the Yellow River since the 1980s

Study regionthe Yellow River (YR) in China. Study focusDue to climate change and human activities, YR channel morphology has undergone significant spatiotemporal variations. Yet, a comprehensive understanding of channel migration in YR and its driving factors remains unclear. Here, we developed a multi-index water extraction method to track the changes in surface water and river channel migration of YR based on Landsat imagery since the 1980s. New hydrological insights for the regionWe find that the average surface water area of YR over the past four decades is 4013 km2, with 73.5 % of permanent surface water. Notably, the surface water extent has experienced a 9 % increase since the 1980s, while the river channel has undergone a 12.2 % decrease. The YR channel’s centerline exhibits diverse change patterns across the entire basin, which can be broadly categorized into six types ranging from unchanged to reverse migration. We identify that climate, particularly temperature and precipitation, contributed 71 % of channel changes in the upper reaches, while 65 % of changes in the lower reaches are from human activities, including reservoir operations and water management policies. Our results unveil the variations in water extent and channel migration of the YR, offering new insights into the interactions between channel migration and climate change and human activities in the YR over the past four decades.

A practical approach for numerical modeling of a complex and data-limited hydrological system

Abstract By their nature, wetlands represent an ecosystem base for many concurrent heterogeneous interactions, where the mission of numerical modeling requires a wide range of consistent and reliable datasets from various sources, spatially and temporally. Such a mission usually collides with the existence of tremendous missing in time-series dataset(s). In this context, MIKE SHE was used to construct an integrated surface–subsurface flow model for the Paya Indah wetland in Malaysia where huge gaps exist in the historical datasets of water level and flow rate. To calibrate and validate the model to a satisfactory level, a tri-criteria simulation approach was applied to overcome the occasional missing values in these datasets. This goal was accomplished by calibrating the surface water level and channel flow while simultaneously matching the steady-state subsurface portion of the system wherever water table depth data allowed. Quantitatively, the integrated model scored the highest values of R (0.765 − 0.927) and CE (0.748 − 0.828) during the validation. However, large RMSE values were calculated for the flow rate during calibration at SWL2 (outlet; 0.766) and during validation at Langat River (0.780). This bias was attributed to the low or occasional absence of variation in the historical time-series datasets necessary for the simulation process.

Hydrokinetic energy harvesting from slow currents using flow-induced oscillations

To harness marine hydrokinetic energy from slow flows, which constitute the majority of currents, tides, and rivers, new Passive Turbulence Control (PTC), consisting of large turbulence stimulators, is tested experimentally on circular cylinders on springs. This study experimentally investigates the effect of PTC on the onset of Flow-Induced Oscillations (FIO) and particularly the relative onset of Vortex-Induced Vibrations (VIV) and galloping. Experiments are conducted in the Low Turbulence Free Surface Water Channel, University of Michigan. Fixed are: mass ratio m* = 1.48, aspect ratio l/D = 10.29, and total damping ratio ζ = 0.04. Parameters are: cylinder diameter D, spring stiffness K, PTC location and height, and flow speed U∈[0.36 m/s-1.45 m/s]. Placing the leading edge of PTC at 40–60° induces high amplitude FIO while placement at 10–20° suppresses FIO. As PTC height increases, VIV and galloping initiate earlier and exhibit higher amplitude with a steeper slope. Lower spring stiffness initiates VIV earlier by reducing the oscillator natural frequency in water. Even though large PTC maintained its effectiveness in initiating galloping early, it has no effect on the earlier initiation of VIV, which starts at a nearly fixed reduced velocity. Lower spring stiffness and large PTC enable power generation at low current speed (0.2 m/s).

Influence of cross-section shape on energy harvesting from transverse flow-induced vibrations of bluff bodies

Hydroelastic experiments have been carried out in a free surface water channel to study the influence of the cross-section shape on the mechanical energy transfer from a uniform flow to a self-excited crossflow oscillating prism. Seventeen cross-section shapes were tested with the same mechanical properties (say, mass ratio and mechanical damping) and aspect ratio. Then, the study was focused on the role of the cross-section shape and reduced velocity on the prism dynamics and energy transfer from the fluid flow. It has been found that the geometric centroid of the semi-cross-section and the afterbody length of the cross-section represent a simple and effective metric to characterise the energy transfer. Two related dimensionless geometric parameters are introduced. The dependence of the energy transfer with these two parameters is studied and used to design successfully ‘in advance’ cross-section shapes with high energy transfer efficiencies. It has been observed from particle image velocimetry measurements that large energy transfer shapes are those in which, under strong oscillations, the flow follows the cross-section contour of one side and is fully detached on the other side.

AUnet: A Deep Learning Framework for Surface Water Channel Mapping Using Large-Coverage Remote Sensing Images and Sparse Scribble Annotations from OSM Data

Water is a vital component of life that exists in a variety of forms, including oceans, rivers, ponds, streams, and canals. The automated methods for detecting, segmenting, and mapping surface water have improved significantly with the advancements in satellite imagery and remote sensing. Many strategies and techniques to segment water resources have been presented in the past. However, due to the variant width and complex appearance, the segmentation of the water channel remains challenging. Moreover, traditional supervised deep learning frameworks have been restricted by the scarcity of water channel datasets that include precise water annotations. With this in mind, this research presents the following three main contributions. Firstly, we curated a new dataset for water channel mapping in the Pakistani region. Instead of employing pixel-level water channel annotations, we used a weakly trained method to extract water channels from VHR pictures, relying only on OpenStreetMap (OSM) waterways to create sparse scribbling annotations. Secondly, we benchmarked the dataset on state-of-the-art semantic segmentation frameworks. We also proposed AUnet, an atrous convolution inspired deep learning network for precise water channel segmentation. The experimental results demonstrate the superior performance of the proposed AUnet model for segmenting using weakly supervised labels, where it achieved a mean intersection over union score of 0.8791 and outperformed state-of-the-art approaches by 5.90% for the extraction of water channels.

Experimental research on a hydrokinetic turbine model

The renewable energy policy strongly encourages the use of all renewable sources of energy. ICPE-CA starts to develop a new hydrokinetic turbine to be implemented in small rivers or water channels with a low investment cost. In a first step, the characterization of a laboratory reduced scale turbine model is performed. The hydrokinetic turbine model is implemented in a free surface water channel. The produced power for many flow rates and rotation speed of the turbine, as well as the detailed flow characterization (PIV measurements) are presented.

Application of Grain Size Analysis for Saturated Hydraulic Conductivity Assessment of Bed Silts along Komárňanský Channel – Žitný Ostrov

The objective of this study is the evaluation of permeability of the bed silts located along the Komárňanský channel of the Žitný ostrov, Slovakia. Komárňanský channel is the largest one from three main channels at the Žitný ostrov area – the flat lowland with channel network. The bed silt permeability is expressed by value of saturated hydraulic conductivity. This parameter is one of the key inputs for estimating solute and water movement between surface water channel and surrounding groundwater in the scope of their interaction at this area. The bed silts were obtained by two ways, as disturbed samples and as undisturbed samples. In this study we deal with disturbed samples extracted from the Komárňanský channel and for that reason only the empirical formulas based on the grain size analysis could be used for saturated hydraulic conductivity assessment. The disturbed samples were extracted in three levels of silt - top, middle and bottom part of silt layer and subsequently as mixed samples in each selected profile of the Komárňanský channel. The selection of sampling place was made by thickness of bed silt in the measured profiles. The values of saturated hydraulic conductivity obtained from disturbed samples of bed silt - Kd were calculated according to three empirical formulas: 1. Bayer – Schweiger formula; 2. Špacek I formula and 3. Špacek II formula, firstly for samples from the top, middle and bottom part of the silt layer and then for mixed samples. The valid values Kd from single parts of the silt layers reached from 1.44 x 10−07 to 1.74 x 10−05 m s−1, the valid values Kd from mixed samples reached from 2.96 x 10−07 to 2.05 x 10−05 m s−1. According to results of comparison of Kd from single parts of silt layers and Kd from mixed samples it is not possible to assess explicitly the reliability of saturated hydraulic conductivity value set by that way. Therefore, in the next step, it will be necessary to compare these results with the values of saturated hydraulic conductivity from undisturbed samples of bed silt determined by the laboratory falling head method.

Flow-induced oscillation patterns for two tandem cylinders with turbulence stimulation and variable stiffness and damping

The oscillation patterns of two 1-DOF cylinder oscillators, undergoing VIV and galloping, are investigated in a free surface water channel for 3.2 × 104 ≤ Re ≤ 1.2 × 105. The cylinders are arranged in tandem and supported by springs for a range of different spring stiffness and damping parameters. The efficiency of a current energy converter (CEC), based on flow-induced oscillation (FIO) of multiple cylinders in tandem, is critically related to the cylinder oscillation patterns. Due to the limited number of studies on the FIO for multiple cylindrical or prismatic bodies, their oscillation patterns have neither been identified nor classified. The surfaces of the cylinders are modified by turbulence stimulation to enhance FIO. Three different center-to-center spacing, five stiffness, and six damping ratios, for a total of 90 sets of experiments were conducted. The current velocity range is from 0.34 m/s to 1.32 m/s. From more than 2000 tests, five major patterns, nine sub-patterns are identified and classified. The patterns are defined based on the amplitudes, frequencies and the phase angle differences between the two cylinders. The characteristics and mechanics of each oscillation pattern are explored and explained from the perspective of fluid-structure interaction (FSI). By systematically varying the parameters, the underlying hydrodynamic mechanisms, including the coupling level between vortices and cylinders, the shielding effect, the wake effect, and the stability states are revealed. Few preliminary observations on the connection between oscillation pattern and harnessed power by the tandem cylinders are reported.

Hydrokinetic Power Conversion Using Vortex-Induced Oscillation with Cubic Restoring Force

A cubic-spring restoring function with high-deformation stiffening is introduced to passively improve the harnessed marine hydrokinetic power by using flow-induced oscillations/vibrations (FIO/V) of a cylinder. In these FIO/V experiments, a smooth, rigid, single-cylinder on elastic end-supports is tested at Reynolds numbers ranging from 24,000 < Re < 120,000. The parameters of the tested current energy converter (CEC) are cubic stiffness and linear damping. Using the second generation of digital virtual spring-damping (Vck) controller developed by the Marine Renewable Energy Laboratory (MRELab), the cubic modeling of the oscillator stiffness is tested. Experimental results show the influence of the parameter variation on the amplitude, frequency, energy conversion, energy efficiency, and power of the converter. All experiments are conducted in the low turbulence-free surface water (LTFSW) channel of the MRELab of the University of Michigan. The main conclusions are: (1) The nonlinearity in the cubic oscillator is an effective way to extend the vortex-induced vibration (VIV) upper branch, which results in higher harnessing power and efficiency compared to the linear stiffness cylinder converter. (2) Compared to the linear converter, the overall power increase is substantial. The nonlinear power optimum, occurring at the end of the VIV upper branch, is 63% higher than its linear counterpart. (3) The cubic stiffness converter with low harnessing damping achieves consistently good performance in all the VIV regions because of the hardening restoring force, especially at higher flow velocity.

Ecological Connectivity in Two Ancient Lakes: Impact Upon Planktonic Cyanobacteria and Water Quality

The ancient lakes Mikri Prespa and Megali Prespa are located in SE Europe at the transnational triangle and are globally recognized for their ecological significance. They host hundreds of flora and fauna species, and numerous types of habitat of conservational interest. They also provide a variety of ecosystem services. Over the last few decades, the two lakes have been interconnected through a surface water channel. In an attempt to explore whether such a management practice might alter the ecological properties of the two lakes, we investigated a series of community metrics for phytoplankton by emphasizing cyanobacteria. Our results demonstrate that the cyanobacterial metacommunity structure was affected by directional hydrological connectivity and high dispersal rates, and to a lesser extent, by cyanobacterial species sorting. Cyanobacterial alpha diversity was twofold in the shallow upstream Lake Mikri Prespa (Simpson index average value: 0.70) in comparison to downstream Lake Megali Prespa (Simpson index average value: 0.37). The cyanobacterial assemblage of the latter was only a strict subset of that in Mikri Prespa. Similarly, beta diversity components clearly showed a homogenization of cyanobacteria, supporting the hypothesis that water flow enhances fluvial translocation of potentially toxic and bloom-forming cyanobacteria. Degrading of the water quality in the Lake Megali Prespa in anticipation of improving that of the Lake Mikri Prespa is an issue of great concern for the Prespa lakes’ protection and conservation.

Assessment of chemical and microbiological parameters on the Leite River Lithuania.

The most common source of pollution is wastewater that comes from the industrial, agricultural, and household sectors. The aim of this work is to evaluate the impact of a new innovative wastewater treatment technology on the water quality of the Leite River, Lithuania. The Leite River basin receives wastewater from the Leitgiriai agglomeration; it is then released into a channel, which is 73m away from the river. During the implementation of the BSR Interreg project "Water emissions and their reduction in village communities in the Baltic Sea Region as pilots (VillageWater)," the ineffective Leitgiriai wastewater treatment plant (WWTP) was reconstructed in September and October of 2017. Water samples from Leite River were collected in 2010-2018 in three locations: near the Kulynai, Leitgiriai, and Sausgalviai villages in Lithuania. The results show that the wastewater treatment efficiency is statistically higher than that before the reconstruction of the WWTP. The treated wastewater (before and after reconstruction) is released from the Leitgiriai WWTP into the surface water (channel), which flows into the Leite River. The highest concentrations (according to all examined indicators) have been observed in the channel and in the Leite River 500m after the release point before the reconstruction. All differences are statistically significant (p < 0.05). According to the 2018 values, the water quality of the Leite River did comply with the good ecological status/potential class indicators near the Leitgiriai village. After the Leitgiriai WWTP reconstruction, the wastewater treatment efficiency increased two times on average. Therefore, the Leite River water quality near Leitgiriai improved.

Flow-induced vibration of two elastically mounted tandem cylinders in cross-flow at subcritical Reynolds numbers

A series of experimental studies on flow-induced vibration (FIV) of two identical elastically mounted circular cylinders in tandem arrangement were carried out in a low turbulence surface water channel. The Reynolds number was between 2.86 × 104–1.14 × 105. Both upstream and downstream cylinders with diameter of 8.89 cm and mass ratio of 1.343 were allowed to oscillate in the transverse direction. Four spacing ratios T/D = 1.57, 2.57, 3.57 and 4.57 (where T is the center-to-center spacing and D is the cylinder diameter) were selected. Two virtual spring-damping oscillators were used to conduct the tests and measure the position signals of two tandem circular cylinders undergoing FIV. The vibrations and fluid forces of the cylinders were analyzed and discussed to illustrate the mechanisms of interaction between the two cylinders. The experimental results indicate that the FIV characteristics of the upstream cylinder are similar to those of a single cylinder for T/D = 2.57, 3.57 and 4.57 when the reduced velocity does not exceed 12.0. Moreover, the FIV response of the upstream cylinder in the two tandem cylinder system with T/D = 1.57 is significantly different from that of the isolated cylinder. The vibration of and the fluid force on the downstream cylinder are obviously influenced by the upstream cylinder for the spacing range tested. Vortex-induced vibration (VIV)-like response features are observed for the downstream cylinder.

Suppression of fluctuating lift on a cylinder via evolutionary algorithms: Control with interfering small cylinder

A generalized model-free method to optimize parameters for open-loop and closed-loop control in fluid mechanics applications is presented. A multi-objective evolutionary algorithm (MOEA) is employed to minimize the oscillating lift caused by vortex shedding from a cylinder of diameter D via the insertion of a secondary control cylinder of diameter D/8. The first objective of the algorithm is to minimize the fluctuating force coefficient CLRMS, while the second objective is to minimize the actuation power required to drive the control cylinder. Experiments are carried out in a free surface water channel at ReD = 12 500 and verified for robustness to changes in Reynolds number at ReD = 17 000. The control cylinder is prescribed a position as well as a periodic sinusoidal motion in two dimensions. The MOEA efficiently handles the larger optimization parameter space, with the final solution suppressing CLRMS by over 90% using near-zero actuation power. Further, the MOEA inherently provides a sensitivity study as to the influence of the different parameters and also in which spatial area the greatest influence is expressed. The dynamics of the optimal suppression case are compared to those of the baseline case (no control cylinder) using phase averaged and mean particle image velocimetry and direct force measurements.

Flow-induced vibration of tandem circular cylinders with selective roughness: Effect of spacing, damping and stiffness

Abstract Flow Induced Vibrations (FIV), and particularly Vortex Induced Vibrations (VIV) and galloping, of two locally rough, rigid, circular cylinders in tandem are studied by varying the stiffness of the supporting springs, the linear viscous damping, and the cylinder spacing. The test parameters are: mass ratio set to 1.34, center-to-center spacing of 1.57, 2.0 and 2.57 diameters; spring-stiffness 400 N/m ∼ 1200 N/m, damping-ratio 0 . 02 ζ 0 . 26 , and Reynolds number 30,000 ⩽ Re ⩽ 120,000, which falls in the TrSL3 flow regime. The virtual spring-damping system Vck developed in the Marine Renewable Energy Laboratory (MRELab) enables embedded computer controlled change of viscous-damping and spring-stiffness for fast and mathematically correct oscillator realization, without including the hydrodynamic force in the closed control loop. Experimental measurements for the oscillatory response of both cylinders, are studied to reveal the interaction of upstream and downstream cylinders. All the experiments were conducted in the Low Turbulence Free Surface Water (LTFSW) Channel of the MRELab of the University of Michigan. The main findings are: (1) In the range of spacing tested, for all the values of K and ζ , the upstream cylinder’s amplitude response is enhanced due to the presence of the downstream cylinder. This effect is very strong in galloping. (2) With the exception of the initial branch of VIV, the downstream cylinder’s amplitude response is also enhanced but with higher standard deviation in two tandem oscillating cylinders. (3) Three oscillation patterns are identified in galloping: In-phase, out-of-phase, and alternating between the two in a given experiment. (4) Four interactive zones are identified.

The spatial and temporal distribution of metals in an urban stream: A case study of the Don River in Toronto, Canada

Abstract Widespread growth of cities, the association of trace metals with urban runoff, and the potentially deleterious effect of metals on aquatic ecology have made it important to understand the distribution and transport of metals through surface water channel networks. The Don River in Toronto, Canada has been identified as an Area of Concern for pollution to Lake Ontario, with historically high levels of metal contamination. Sampling programs are sparse, therefore a model is needed to understand the spatial and temporal variability of metals in the river network. The objectives of the current study are to: i) describe the sampled spatial and temporal variability of metals in the Don River and ii) develop a modelling strategy to describe within flood metal transport dynamics. A model setup tool is developed that links Storm Water Management Model (SWMM) with the Environmental Fluid Dynamics Code (EFDC) to allow a seamless transition from catchment hydrology to in-stream hydraulic and chemical processes. Results show that lead pollution in the Don River is decreasing, likely as a result of policy changes and sediment dredging in the mouth of the river. However, zinc and copper pollution are increasingly problematic, with copper exceeding recommended lower guidelines, particularly during floods. Model results confirm that most of the sediment and metals are transported in relatively short bursts within longer flood durations and are stored in depositional hotspots within the Lower Don River. A better monitoring strategy is needed to understand and more accurately parametrize these processes in an urban river system.

Hydrokinetic power conversion using Flow Induced Vibrations with cubic restoring force

A nonlinear oscillator, using a cubic-spring restoring function with high-deformation stiffening, is introduced and studied experimentally to improve passively the harnessed marine hydrokinetic power using Flow Induced Vibrations (FIVs) of a cylinder. In this research, the FIV of a single, rigid, circular cylinder on elastic end-supports is tested for Reynolds number 30,000 ≤ Re ≤ 120,000. Damping, cubic stiffness, and flow-velocity are used as parameters. Selective roughness is applied to enhance FIV and increase the hydrokinetic energy converted by the oscillator. The second generation of the digital, virtual spring-damping system Vck, developed in the Marine Renewable Energy Laboratory (MRELab), enables embedded computer-controlled change of the functions and values of viscous damping and spring stiffness. Cubic modeling of the oscillator stiffness in parametric form is thus realized and tested. Experimental results for amplitude response, frequency response, energy harvesting, efficiency and instantaneous energy of the converter are presented and discussed. All experiments are conducted in the Low Turbulence Free Surface Water (LTFSW) Channel of the MRELab of the University of Michigan. The main conclusions are: (1) The cubic stiffness function is an effective way to raise the harnessed efficiency over a wider range of flow velocities. (2) At lower flow speed (upper and lower VIV branches), the harnessed power increases as the nonlinearity increases. A strongly nonlinear system exhibits a 100% increase in harnessed energy in this region. (3) At a higher flow speed (galloping), the cubic nonlinearity benefits the harnessed power in two ways because the natural frequency of the oscillator in water (fn,water) depends on the amplitude of oscillation. At low harness damping, the amplitude increases resulting in higher fn,water thus enhancing the harnessed power. At high harness damping, the harnessed power increases regardless of fn,water.

Interactive Flow-Induced Vibrations of Two Staggered, Low Mass-Ratio Cylinders in the TrSL3 Flow Regime (2.5 × 104 &lt; Re &lt; 1.2 × 105): Smooth Cylinders

Flow-induced vibrations (FIVs) of two elastically mounted circular cylinders in staggered arrangement were experimentally investigated. The Reynolds number range for all experiments (2.5 × 104 &lt; Re &lt; 1.2 × 105) was in the transition in shear layer 3 (TrSL3) flow regime. The oscillator parameters selected were: mass ratio m* = 1.343 (ratio of oscillating mass to displaced fluid mass), spring stiffness K = 250 N/m, and damping ratio ζ = 0.02. The experiments were conducted in the low turbulence free surface water (LTFSW) channel in the MRELab of the University of Michigan. A closed-loop, virtual spring–damper system (Vck) was used to facilitate quick and accurate parameter setting. Based on the characteristics of the displacement response, five vibration patterns were identified and their corresponding regions in the parametric plane of the in-flow spacing (1.57 &lt; L/D &lt; 4.57) and transverse cylinder spacing (0 &lt; T/D &lt; 2) were defined. The hydrodynamic forces and frequency characteristics of the vibration response are also discussed.

Hydrokinetic power conversion using Flow Induced Vibrations with nonlinear (adaptive piecewise-linear) springs

A design, adaptive to the flow velocity, is developed for a hydrokinetic energy converter based on an oscillator undergoing Flow Induced Vibrations (FIVs); primarily Vortex Induced Vibrations (VIV) and galloping. This Alternating-Lift Technology implements a nonlinear spring to passively optimize the oscillator. The FIV of a single, rigid, circular cylinder, with distributed surface roughness, suspended on end-springs with piecewise linear continuous restoring force, are studied for Reynolds number 24,000 ≤ Re ≤ 120,000. Linear viscous damping for energy harnessing and different piecewise linear spring functions are used as parameters. The harnessed power envelope is established based on the results of linear spring stiffness and two nonlinear piecewise stiffness functions. Selective roughness is applied to enhance FIV and increase the hydrokinetic energy captured by the converter at higher Reynolds numbers. The second generation of a virtual spring-damping system (Vck), developed in the Marine Renewable Energy Laboratory (MRELab), enables embedded, real-time, computer-controlled change of viscous damping and spring stiffness for fast implementation of oscillator particulars. Experimental results for amplitude response, frequency response, energy harvesting, and efficiency are presented and discussed. All experiments are conducted in the Low Turbulence Free Surface Water (LTFSW) Channel of the MRELab of the University of Michigan. The main conclusions are: (1) Each nonlinear, piecewise-linear, stiffness function has its own merits in power harnessing; the differences lie in the FIV characteristics of the different regions of the flow. (2) The nonlinear spring converter can harness energy from flows as low as 0.275 m/s with no upper limit. (3) The new adaptive function exhibits higher harnessed power in the upper VIV branch, transition from VIV to galloping, and fully developed galloping regions. (4) The FIV response is predominantly periodic for all nonlinear spring functions used. (5) Optimal power harnessing is achieved by changing the nonlinear piecewise spring function and the linear viscous damping. (6) The optimally harnessed power envelope is established according to the experimental results of the linear and nonlinear stiffness springs; four performance zones are established based on FIV.

Sensitivity to Zone Covering of the Map of Passive Turbulence Control to Flow-Induced Motions for a Circular Cylinder at 30,000 ≤ Re ≤ 120,000

Passive turbulence control (PTC) in the form of two straight roughness strips with variable width, and thickness about equal to the boundary layer thickness, is used to modify the flow-induced motions (FIM) of a rigid circular cylinder. The cylinder is supported by two end springs and the flow is in the TrSL3, high-lift, regime. The PTC-to-FIM Map, developed in the previous work, revealed zones of weak suppression (WS), strong suppression (SS), hard galloping (HG), and soft galloping (SG). In this paper, the sensitivity of the PTC-to-FIM map to: (a) the width of PTC covering, (b) PTC covering a single or multiple zones, and (c) PTC being straight or staggered is studied experimentally. Experiments are conducted in the low turbulence free surface water channel of the University of Michigan, Ann Arbor, MI. Fixed parameters are: cylinder diameter D = 8.89 cm, m* = 1.725, spring stiffness K = 763 N/m, aspect ratio l/D = 10.29, and damping ratio ζ = 0.019. Variable parameters are circumferential PTC location αPTC∈ (0–180 deg), Reynolds number Re ∈ (30,000–120,000), flow velocity U∈ (0.36–1.45 m/s). Measured quantities are amplitude ratio A/D, frequency ratio fosc/fn,w, and synchronization range. As long as the roughness distribution is limited to remain within a zone, the width of the strips does not affect the FIM response. When multiple zones are covered, the strong suppression zone dominates the FIM.

Hydrokinetic energy conversion by two rough tandem-cylinders in flow induced motions: Effect of spacing and stiffness

Flow Induced Motions (FIMs) of rigid circular cylinders, and particularly VIV (Vortex Induced Vibrations) and galloping, are induced by alternating lift. The VIVACE (VIV for Aquatic Clean Energy) Converter uses single or multiple cylinders, in tandem, on elastic end-supports, in synergistic FIM, to convert MHK energy to electricity. Selectively distributed surface roughness is applied to enhance FIM and increase efficiency. In this paper, two cylinders are used in tandem with center-to-center spacing of 1.57, 2.0 and 2.57 diameters, harnessing damping ratio 0.00<ζ < 0.24, for Reynolds number 30,000 ≤ Re ≤ 120,000. The virtual spring-damping system Vck in the Marine Renewable Energy Laboratory (MRELab) enables embedded computer-controlled change of viscous-damping and spring-stiffness for fast and mathematically correct oscillator realization, without including the hydrodynamic force in the closed control loop. Experimental results for oscillatory response, energy harvesting, and efficiency are presented and the envelope of optimal power is derived. All the experiments were conducted in the Low Turbulence Free Surface Water (LTFSW) Channel of the MRELab of the University of Michigan. The main conclusions are: (1) For the tested cylinder spacing, two cylinders harness power is between 2.56 and 13.49 times the power of a single cylinder, the efficiency of two cylinders is between 2.0 and 6.68 of a single cylinder. (2) The MHK power harnessed by the upstream cylinder is increased by up to 100%, affected by the downstream cylinder. (3) The MHK power harnessed by the downstream cylinder and its FIM are affected to a lesser extent by the interaction. (4) VIVACE can harness energy from flows as slow as 0.4 m/s with no upper limit in flow velocity. (5) Close spacing and high spring stiffness yield highest harnessed power. (6) The optimal harnessed power shifts to softer springs as spacing increases.