Browsing by Author "Martins, Ricardo"
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- Design and characterisation of customised-roughness beds for open-channel flow experimentsPublication . Isidoro, Jorge; Martins, Ricardo; Pereira, Luísa Gomes; de Lima, João L.M.P.The use of laboratory channels or flumes for open-channel flow research is widespread. However, this type of equipment is often expensive, susceptible to damage, and require regular maintenance. In open-channel flow, the roughness of the channel bed is a critical property in governing the flow characteristics. Unfortunately, changing the bed properties, particularly its roughness, proves to be a challenging and time-consuming task in most laboratory channels. To address these limitations, this stud introduces a novel and cost-effective technique to build laboratory channel beds with tailored roughness. Additionally, we describe a precise photogrammetric based method for quantifying the absolute roughness of the bed. These engineered beds can be seamlessly in tegrated into various laboratory channels without posing any risk of equipment damage. In addition, they offer the flexibility to be modified to meet specific roughness conditions, thus advancing the capabilities of experi mental setups in hydraulic studies Furthermore, these specially designed beds can find utility in other facilities where control of surface properties is necessary.
- Estimating sheet flow velocities using quinine as a fluorescent tracer: bare, mulched, vegetated and paved surfacesPublication . Zehsaz, Soheil; de Lima, João L. M. P.; de Lima, M. Isabel P.; MGP Isidoro, Jorge; Martins, RicardoWhen direct flow velocity measurements are not feasible, the use of tracers can be a valuable tool. In the present study, both laboratory and field experiments were conducted to evaluate the applicability of quinine as a fluorescent tracer for estimating mean sheet flow velocities in different ambient light and surface morphology conditions. Quinine excels in low-light conditions when exposed to UVA light. This tracer was compared with dye and thermal tracers, all in liquid form. In these tracing techniques the tracers were injected into the flow, after which surface velocity was estimated by tracking the leading edge of the tracer plumes and applying a correction factor to calculate the mean velocity (in a water column). The visibility of the tracers was evaluated by measuring the relative luminance and contrast ratio of the quinine and dye tracer plumes. Results show that the quinine tracer can be used to estimate sheet flow velocities over a wide variety of soil and urban surfaces; it has better visibility in comparison to the dye tracer but, in some conditions, lower visibility than the thermal tracer. Although quinine is invisible under bright ambient light conditions, this tracer technique requires low-cost experimental setup and is useful in low-light conditions (e.g., night; twilight; shielded environments).
- Fluorescent quinine-based tracking techniques for measurement of open-channel surface flow velocities under low luminosity conditions using a UASPublication . Zehsaz, Soheil; L. M. P. de Lima, João; Isidoro, Jorge; de Lima, M. Isabel P.; Martins, RicardoThis study presents techniques based on the use of fluorescent quinine as a visual tracer for surface flows, to assess surface flow velocities in channels and streams under low luminosity conditions. Fieldwork was conducted in three open channels, with different hydraulic characteristics. A quinine solution, in both liquid and solid (ice cube) forms, was applied on the water flow surface and an Unmanned Aerial System (UAS) was used to record the movement of the fluorescent quinine. The results were compared to the velocities estimated using the thermal tracer technique and flowmeter-based velocity maps. The findings show that the quinine solution, in both liquid and solid forms, can be used to estimate open-channel surface flow velocities under low luminosity conditions. While the solid form of the quinine tracer was applied in a smaller volume than the liquid tracer, its fluorescence effect persisted longer. By comparison, the liquid tracer had the advantage of continual availability and was devoid of the constraint of melting.
- High spatiotemporal resolution free surface detection using cost-effective video equipment and computer vision techniques in nearly stationary flow along a transparent wall in the laboratoryPublication . Martins, Ricardo; Isidoro, Jorge; Lima, João L. M. P. deThe identification of the air-water interface in free surface flows traditionally involves intrusive techniques or costly equipment. Non-intrusive alternatives, such as computer vision, are emerging as highly effective substitutes or supplements for more invasive techniques in laboratory measurements, thanks to their straightforward implementation and cost efficiency. This research specifically delves in the conjunction of various naive techniques, exploring their collective precision in detecting the air-water interface along transparent walls in laboratory. A detection technique based on the double gradient of the image is applied and thoroughly examined. The study progresses through multiple refinement stages, culminating in a method that is both cost effective and easy to implement. This methodology allows for large-scale, high resolution measurements (200 mm x 1800 frames per video at a 0.25 mm, 50 Hz resolution), offering both spatial and temporal measurements by adeptly detecting the free surface along transparent walls.
- A high-frequency low-cost technique for measuring small-scale water level fluctuations using computer visionPublication . Isidoro, Jorge; Martins, Ricardo; Carvalho, Rita F.; de Lima, João L.M.P.Measuring and monitoring the water depth/level is a key issue when studying free-surface flows. These tasks are usually expensive in terms of time and money; however, even that expenditure is sometimes not enough to assure reliable and/or accurate results. Free-surface flows are complicated to deal with, as the instability caused by e.g., turbulence, wind, or air-entrainment, can cause important spatial and temporal fluctuations at the surface level. This work presents a non-intrusive, computer vision-based image treatment and segmentation technique that assures the detection and measurement of the free-surface water fluctuations along space and time. The labo-ratory physically based tests under steady flow conditions, and different channel bed roughness and slopes, showed a very good fit with manually direct measurements carried out with a point-gauge micrometre. Under unsteady flow conditions this technique also showed to successfully deal with applications requiring high spatiotemporal resolution of water depth/level measurements.
- Integrated monitoring of mola mola behaviour in space and timePublication . Sousa, Lara L.; Lopez-Castejon, Francisco; Gilabert, Javier; Relvas, Paulo; Couto, Ana; Queiroz, Nuno; Caldas, Renato; Dias, Paulo Sousa; Dias, Hugo; Faria, Margarida; Ferreira, Filipe; Ferreira, Antonio Sergio; Fortuna, Joao; Gomes, Ricardo Joel; Loureiro, Bruno; Martins, Ricardo; Madureira, Luis; Neiva, Jorge; Oliveira, Marina; Pereira, Joao; Pinto, Jose; Py, Frederic; Queiros, Hugo; Silva, Daniel; Sujit, P. B.; Zolich, Artur; Johansen, Tor Arne; de Sousa, Joao Borges; Rajan, KannaOver the last decade, ocean sunfish movements have been monitored worldwide using various satellite tracking methods. This study reports the near-real time monitoring of finescale (< 10 m) behaviour of sunfish. The study was conducted in southern Portugal in May 2014 and involved satellite tags and underwater and surface robotic vehicles to measure both the movements and the contextual environment of the fish. A total of four individuals were tracked using custom-made GPS satellite tags providing geolocation estimates of fine-scale resolution. These accurate positions further informed sunfish areas of restricted search (ARS), which were directly correlated to steep thermal frontal zones. Simultaneously, and for two different occasions, an Autonomous Underwater Vehicle (AUV) videorecorded the path of the tracked fish and detected buoyant particles in the water column. Importantly, the densities of these particles were also directly correlated to steep thermal gradients. Thus, both sunfish foraging behaviour (ARS) and possibly prey densities, were found to be influenced by analogous environmental conditions. In addition, the dynamic structure of the water transited by the tracked individuals was described by a Lagrangian modelling approach. The model informed the distribution of zooplankton in the region, both horizontally and in the water column, and the resultant simulated densities positively correlated with sunfish ARS behaviour estimator (r(s) = 0.184, p < 0.001). The model also revealed that tracked fish opportunistically displace with respect to subsurface current flow. Thus, we show how physical forcing and current structure provide a rationale for a predator's finescale behaviour observed over a two weeks in May 2014.
- Using quinine as a fluorescent tracer to estimate overland flow velocities on bare soil: Proof of concept under controlled laboratory conditionsPublication . de Lima, João L. M. P.; Zehsaz, Soheil; de Lima, M. Isabel P.; Isidoro, Jorge M. G. P.; Jorge, Romeu Gerardo; Martins, RicardoThis study presents a tracer technique based on the fluorescent properties of quinine to help on the visualization of shallow flows and allow a quantitative measurement of overland flow velocities. Laboratory experiments were conducted to compare the traditional dye tracer and thermal tracer techniques with this novel fluorescent (quinine) tracer by injecting a quinine solution and the other tracers into shallow flowing surface water. The leading-edge tracer velocities, estimated using videos of the experiments with the quinine tracer were compared with the velocities obtained by using thermograms and real imaging videos of the dye tracers. The results show that the quinine tracer can be used to estimate both overland and rill flow velocities, since measurements are similar to those resulting from using other commonly used tracers. The main advantage of using the quinine tracer is the higher visibility of the injected tracer under ultraviolet A (UVA) light for low luminosity conditions. In addition, smaller amounts of quinine tracer are needed than for dye tracers, which lead to smaller disturbances in the flow. It requires a simple experimental setup and is non-toxic to the environment.