Catch Ratio Research Articles

Finite panel method for the simulation of wind-driven rain

In present numerical methods for the wind-driven rain (WDR) simulation, a large computational work for raindrop trajectories is required to obtain the distribution of the catch ratio because of the randomness of the initial conditions of the raindrops. A new method named Finite Panel Method (FPM) that is employed to acquire the catch ratio distribution is proposed to reduce the calculation amount and diminishes the randomness. In the FPM, raindrops ending in the corners of the panels which are divided on the surface are simulated, and then the distribution of catch ratio is acquired by a reconstruction method. As a demonstration, catch ratio results by FPM in typical flow fields are presented, including the case of the three-dimensional flow field of power-law velocity profile, and cases of the flow around two- and three-dimensional low-rise buildings. The FPM results are compared with these calculated by the classical method and literature. The results indicate that FPM can reduce the calculation amount of raindrop trajectories with equivalent accuracy compared to the classical method.

The effect of sweep bottom contact on the catch efficiency of haddock (Melanogrammus aeglefinus)

This paper illustrates the importance of length, angle and bottom contact of the sweep that connects the trawl and the otterboard for haddock (Melanogrammus aeglefinus) in Barents Sea. We compared the fishing efficiency of two different trawl setups over two cruises. During cruise 1, the sweep angle was 22.3° and the difference in sweep length with actual bottom contact was 30m. During cruise 2, the average sweep angle was 12.0°, and the difference in length with actual bottom contact was 45m. Setup 1 had less sweep bottom contact for both cruises. We estimated the relative change in length dependent catch efficiency of haddock between the two setups for each of the two cruises using catch comparison and catch ratio analyses. The results showed the importance of the length of sweep that actually contacted with the seabed for catching haddock. The differences between the two setups were significant for a limited range of length classes in both cruises, indicating that effect of the sweep bottom contact for this species is length dependent. The results also demonstrate that lack of control over the position of the doors in the water column when fishing semi-pelagic may cause loss of contact of the sweep with the seabed, reducing fishing efficiency for haddock.

Changes in Patterns of Seasonality Shown by Migratory Fish under Global Warming: Evidence from Catch Data of Taiwan’s Coastal Fisheries

In this study, we analyzed the fish species composition data of coastal capture fisheries in Taiwan between 1963 and 2010. The purpose of the analysis was to understand the long-term changes in marine ecosystems. A ratio-to-moving average method was used in conjunction with adjusted seasonal indices to determine the seasonality of individual catch items and to examine the trends shown by the species with the same seasonality. Over the 48-year timespan of the data, 31 species, i.e., 64% of the total number of species, were identified as seasonal migrants. The catch ratio for species showing a single peak in the spring increased steadily over time; however, those species with a single peak in the winter decreased. The catch ratio for those species with dual peaks in both summer and fall varied greatly before 1978. Increasing trends began in the 1980s and accelerated until 1998. As a result of this increase, the previous concentration of the fishing season in the winter months became highly diffuse. Additionally, the winter and/or spring species continued to decrease year after year as the summer and/or autumn species gradually came to dominate the catch. This change in fishing seasonality is likely not an anthropogenic effect. However, the change coincides with trends in sea surface temperature fluctuations. Such variation may not only cause structural change in marine ecosystems but can also significantly impact the economy and the livelihoods of those associated with the fishing trade.

Computational fluid dynamics simulations of wind-driven rain on a mid-rise residential building with various types of facade details

Numerical studies of wind-driven rain (WDR), reporting detailed analysis of rain exposure on building facades, focus mainly on simplified building facades. However, small-scale facade details have a large impact on the rain exposure of a building, redistributing WDR locally. The present study reports results of computational fluid dynamics simulations with Eulerian multiphase (EM) model for WDR on a stand-alone mid-rise residential building. The influence of facade details, namely roof overhangs, balconies and window sills, is analysed. It is shown that even a very small surface detail, such as a window sill with a size of 0.10 m, can decrease catch ratio by up to 37% and droplet impact speed by up to 40%. Numerical simulations also show the practicality of the EM model for detailed analysis of WDR intensity on a complex building and its ability to be used as a design tool.

Internal insulation applied in heritage multi-storey buildings with wooden beams embedded in solid masonry brick façades

The use of internal insulation is investigated in a heritage building block with wooden beam construction and masonry brick walls as part of an energy renovation. Measurements were carried out and compared to results from a hygrothermal simulation model. The risk of mould growth in the wooden beams and in the interface between the insulation and the brick wall was evaluated. Three different insulation strategies for applying internal insulation were investigated: 1) insulation applied on the entire interior façade; 2) 200 mm gap in the insulation above the floor; and 3) 200 mm gap in the insulation both above the floor and below the ceiling. The solution with a 200 mm gap in the insulation above and below the floor/ceiling showed that at low rain exposure coefficients (Catch Ratio, CR ≤ 0.1) and with wall orientations towards west, this solution can be moisture-safe. However, it not recommended to apply internal insulation on north-orientated walls, since the drying potential is reduced. Additionally, caution should be exercised also with west-orientated walls.

Estimation of Wind-Induced Losses from a Precipitation Gauge Network in the Australian Snowy Mountains

Abstract Wind-induced losses, or undercatch, can have a substantial impact on precipitation gauge observations, especially in alpine environments that receive a substantial amount of frozen precipitation and may be exposed to high winds. A network of NOAH II all-weather gauges installed in the Snowy Mountains since 2006 provides an opportunity to evaluate the magnitude of undercatch in an Australian alpine environment. Data from two intercomparison sites were used with NOAH II gauges with different configurations of wind fences installed: unfenced, WMO standard double fence intercomparison reference (full DFIR) fences, and an experimental half-sized double fence (half DFIR). It was found that average ambient temperature over 6-h periods was sufficient to classify the precipitation phase as snow, mixed precipitation, or rain in a statistically robust way. Empirical catch ratio relationships (i.e., the quotient of observations from two gauges), based on wind speed, ambient temperature, and measured precipitation amount, were established for snow and mixed precipitation. An adjustment scheme to correct the unfenced NOAH II gauge data using the catch ratio relationships was cross validated with independent data from two additional sites, as well as from the intercomparison sites themselves. The adjustment scheme was applied to the observed precipitation amounts at the other sites with unfenced NOAH II gauges. In the worst-case scenario, it was found that the observed precipitation amount would need to be increased by 52% to match what would have been recorded had adequate shielding been installed. However, gauges that were naturally well protected, and those below about 1400 m, required very little adjustment. Spatial analysis showed that the average seasonal undercatch was between 6% and 15% for gauges above 1000 m MSL.

The Spell Definition in ISO-15927 and its Impact on the Rain Deposition on the Building Facade

Wind-driven rain (WDR) is one of the most important causes for water damage in buildings. Therefore, the first crucial step to assess the hygrothermal performance of the building envelope, is the appropriate estimation of the amount of rainwater striking the building's façade. ISO 15927 offers the annual average index –mainly to assess the moisture content of absorbent surfaces, and the spell index – more related to the likelihood of water penetration through joints. To calculate these indices, assumptions are made concerning the length of the period of ‘no rain’, called ‘spell definition’. Obviously, the choice of this spell definition will characterise the WDR-amount. In this paper, WDR measurements of a 3-storey building in Vancouver, Canada are used to investigate how this spell definition affects the rain load. Different filter criteria are used to exclude errors due to measurement equipment. By means of the catch ratio as a dimensionless parameter, the results of the analysis for different spell definitions are compared to hourly and 5-min data. It is concluded that longer spell definitions result in lower catch ratios and an underestimation of the WDR load. Hourly data turns out to be a more conservative approach for WDR-assessment of this case study, but is able to represent the spread on the catch ratio most closely to the original 5min-dataset.

Overhang Effect on Reducing Wind-driven Rain for a Mid-rise Building

Roof overhangs are a common feature that can be used to protect the building façade from wind-driven rain (WDR) as field measurements and CFD modelling have shown. However, the quantitative evaluation of the effectiveness of overhangs in protecting the building façade requires further investigation. A six-storey mid-rise building with a flat roof located in Vancouver, British Columbia, Canada has been selected for the experimental study. The study involves the analysis of the spatial distribution of WDR on the building façade before and after the installation of a temporary retractable roof overhang. This paper presents the experimental setup, preliminary result analysis including the spatial variation of catch ratios on the building façade, and the performance assessment of a 1.2 m overhang under two rain events.

Precipitation measurement intercomparison in the Qilian Mountains, north-eastern Tibetan Plateau

Abstract. An experimental field study of wind-induced bias in precipitation measurements was conducted from September 2010 to April 2015 at a grassland site (99°52.9´ E, 38°16.1´ N; 2980 m) in the Hulu watershed in the Qilian Mountains, on the north-eastern Tibetan Plateau, in China. The experiment included (1) an unshielded Chinese standard precipitation gauge (CSPGUN; orifice diameter = 20 cm, height = 70 cm), (2) a single Alter shield around a CSPG (CSPGSA), (3) a CSPG in a pit (CSPGPIT) and (4) a Double-Fence International Reference (DFIR) with a Tretyakov-shielded CSPG (CSPGDFIR). The catch ratio (CR) used the CSPGDFIR as a reference (CR = CSPGX/CSPGDFIR, %; X denotes UN, SA or PIT). The results show that the CSPGSA, CSPGPIT and CSPGDIFR caught 0.9, 4.5 and 3.4 % more rainfall; 7.7, 15.6 and 14.2 % more mixed precipitation (snow with rain, rain with snow); 11.1, 16.0 and 20.6 % more snowfall and 2.0, 6.0 and 5.3 % more precipitation (of all types), respectively, than the CSPGUN from September 2012 to April 2015. The CSPGPIT and CSPGDFIR caught 3.6 and 2.5 % more rainfall; 7.3 and 6.0 % more mixed precipitation; 4.4 and 8.5 % more snowfall; and 3.9 and 3.2 % more total precipitation, respectively, than the CSPGSA. However, the CSPGDFIR caught 1.0 % less rainfall; 1.2 % less mixed precipitation; 3.9 % more snowfall and 0.6 % less total precipitation than the CSPGPIT. From most to least precipitation measured, the instruments ranked as follows: for rain and mixed precipitation, CSPGPIT > CSPGDFIR > CSPGSA > CSPGUN; for snowfall, CSPGDFIR > CSPGPIT > CSPGSA > CSPGUN. The CR vs. 10 m wind speed for the period of precipitation indicated that with increasing wind speed from 0 to 8.0 m s−1, the CRUN/DFIR and CRSA/DFIR for rainfall decreased slightly. For mixed precipitation, the wind speed showed no significant effect on CRUN/DFIR and CRSA/DFIR below 3.5 m s−1. For snowfall, the CRUN/DFIR and CRSA/DFIR vs. wind speed showed that CR decreased with increasing wind speed. The precipitation measured by the shielded gauges increased linearly relative to that of the unshielded gauges. However, the increase in the ratio of the linear correlation should depend on specific environmental conditions. A comparison of the wind-induced bias indicates that the CSPGPIT could be used as a reference gauge for rain, mixed and snow precipitation events at the experimental site. As both the PIT and DFIR effectively prevented wind from influencing the catch of the precipitation gauge, the CRPIT/DFIR had no relationship with wind speed. Cubic polynomials and exponential functions were used to quantify the relationship between catch ratio and wind speed. For snow, for both event and daily scales, the CRUN/DFIR and CRSA/DFIR were significantly related to wind speed; while for rain and mixed precipitation, only the event scale showed a significant relationship.

Wind-driven rain on two parallel wide buildings: Field measurements and CFD simulations

Most studies of wind-driven rain (WDR) reported in the literature focus either on isolated buildings or on a particular building in geometrically complex environments. There is a need for experimental and numerical studies for more generic multi-building geometries. The present study reports detailed field measurements and numerical simulations of WDR that are conducted for an idealized geometry with two parallel wide buildings with different heights, located in Dübendorf, Switzerland. The datasets of rain events and WDR measurements with high spatial and temporal resolution are made available online to download and are intended for model development and validation. Numerical simulations are performed with computational fluid dynamics (CFD) based on the 3D steady Reynolds-averaged Navier–Stokes (RANS) equations and an Eulerian multiphase (EM) model for WDR, including the turbulent dispersion of raindrops. The numerical results are validated by comparing the calculated catch ratio values and cumulative WDR amounts with data from the field measurements. The CFD simulations accurately estimate the WDR intensities at the positions of 18 WDR gauges. The average discrepancies between the numerical and experimental results are found to be 6.9% for the rain event on February 20–21, 2014 and 4.9% for the rain event on August 2–3, 2014. In different building configurations, the influences of recirculation regions, sheltering, wind-blocking effect and acceleration of wind determine the WDR distribution on the downstream building. WDR can increase due to recirculation regions and acceleration of wind, while wind-blocking effect and sheltering decrease WDR.

Influence of time resolution and averaging techniques of meteorological data on the estimation of wind-driven rain load on building facades for Canadian climates

This paper investigates the influence of time resolution of meteorological data and the averaging techniques on the quantification of wind-driven rain amount on building facades for Canadian climates using three WDR models, i.e. the ISO and ASHRAE 160P semi-empirical models, and the CFD-based catch ratio method. A cubic low-rise building is used as a case study. Meteorological data i.e. wind speed, wind direction and rainfall intensity are collected at 5-min intervals at three building sites in Vancouver, Montreal and Fredericton. The 5-min data is used as the reference. The analyses show that when semi-empirical WDR models are used, the arithmetic averaging gives a better estimation while the weighted averaging tends to overestimate the WDR amount. When the detailed CFD-based catch ratio method is used, the weighted averaging technique provides a better estimation, however, the difference between the arithmetic and weighted averaging is within 3–7% for the three Canadian cities investigated. Therefore, the choice of averaging techniques depends on the WDR models to be employed and the climates.

Research on motion of wind-driven rain and rain load acting on transmission tower

This study derives the formula of rain load based on the motion state of droplets and the law of conservation of momentum to study the rain load acting on a transmission tower. By simulating the motion of a single raindrop, the phenomenon of that the horizontal velocity of raindrop is larger than the corresponding wind speed is certified and explained, and the fitting formula of the velocity ratio is obtained from simulation results. The specific catch ratio under uniform flow is derived and then extended to the atmospheric boundary layer wind field. The vertical raindrop spectrum is calculated with the specific catch ratios obtained from two different concepts. The formula for calculating rain load is derived based on the law of conservation of momentum, and a methodology for simulating a transmission tower’s response induced by wind and rain loads is presented. When the basic wind speed is 40m/s, the maximum displacement percentages induced by rain loads relative to wind loads can only reach 1.78%. The results indicate that the influence of raindrop impinging force on a tower’s response during extreme weather conditions is not very significant and that more attention should be paid to the influence of rainfall on the aerodynamic property due to the existence of water film on the surface of tower and line.

The Dynamics of Philippine Aquaculture

Despite the endless arguments of which is more indespensible or crucial for stakeholders and key players, the national and local government primarily leads in the development of a sustainable aquaculture industry in the country. One of the initiatives led by the Bureau of Fisheries and Aquatic Resources under the umbrella of the department of Agriculture, focuses on the replenishment of wild population mostly in rivers and swamps that directly opens towards the sea. Some local species of fish such as milkfish, tilapia and scad are freed into the wild. Releasing these common species of fish will be a good source of larvae and future broodstock. Other projects include the deployment of artificial reefs and jackstone barricade to protect the endangered species and allow them to propagate or reproduce. Also, the mangrove reforestation in various locations including the national marine parks and mariculture zones is conducted every year participated by students of different levels and government officials. Interestingly, private sectors get involved in many of these government projects but focuses on the rehabilitation of marine environment using a different approach that is through a macro and micro-biotechnology. Promising as it may, these technology runs through a series of comprehensive tests or alternative methods that can be adapted on a conservative or traditional aquaculture system to a modern and sophisticated facility of either offshore or inland. In 2012-2014, the country's fish catch ratio increased irregardless of the super typhoons and other natural calamities that hit the country. Fish, shells and other aquatic plants and animals became stable in their habitat doubling its ratio. This indication gave a higher fish yield. Likewise, ponds and other inland aquaculture techniques increased its production and market value due its good quality. The height of fish production was a good instrument to measure the rhythmic structure of Philippines aquaculture in many different aspect, in respect to its growing industry and dynamics. Conforming to these changes of upright production, local fish farmers demonstrate a close indistinguishable response to adapt and likewise invest in new equipement switching some of the earliest version of floating cages made from bamboo's and drums into a multi-float made of highdensity polyethylene cages. Bustled for more alternative ways, recirculating aquaculture system made it a point as one of the best land-based system though some farmers consider it a flamboyant. Different designs were fabricated from short to medium, confined and semi-confined setting, but the basic components and principles are all the same. It may be not a high-class model, but the impression is sensational for local farmers.

Adjustment to rainfall measurement undercatch with a tipping-bucket rain gauge using ground-level manual gauges

Wind-caused undercatch is an important factor among types of systematic errors in point measurements of rainfall. The daily amount of rainfall measured by a MR3H tipping-bucket rain gauge (TBR-MR3H), which is elevated above the ground surface, was considerably underestimated on average by 46 % when compared with the corresponding measurements done by a pair of ground-level manual gauges (M-Rs). The undercatch was also confirmed by the measurements using a set of microlysimeters (MLs). The daily rainfall totals measured by the manual rain gauge were used as a reference in adjusting the rainfall undercatch with the tipping-bucket rain gauge. A simplified equation, developed based on the relationship between logarithmic wind profile and its effect on the catch ratio (CR) of the two gauges, was used to calculate the correction factor on a daily basis. The effect of wind speed depends on the intensity of rainfall. Parameters were optimized, and the proposed equation was validated. The calculated and measured daily rainfall amounts were in good agreement with a correlation coefficient of 0.99, and overall deviation of 0.04.

Impact, runoff and drying of wind-driven rain on a window glass surface: Numerical modelling based on experimental validation

This paper presents a combination of two models to study both the impingement and the contact and surface phenomena of rainwater on a glass window surface: a Computational Fluid Dynamics (CFD) model for the calculation of the distribution of the wind-driven rain (WDR) across the building facade and a semi-empirical droplet-behaviour model. The CFD model comprises the calculation of the wind-flow pattern, the raindrop trajectories and the specific catch ratio as a measure of the WDR falling onto different parts of the facade. The droplet-behaviour model uses the output of the CFD model to simulate the behaviour of individual raindrops on the window glass surface, including runoff, coalescence and drying. The models are applied for a small window glass surface of a two-storey building. It is shown that by far not all WDR that impinges on a glass surface runs off, due to evaporation of drops adhered to the surface. The reduction of runoff by evaporation is 26% for a typical cumuliform rain event and 4% for a typical stratiform rain event. These models can be used to provide the knowledge about WDR impact, runoff and evaporation that is needed for the performance assessment of self-cleaning glass or the study of the leaching of nanoparticles from building facades.

Monitoring fish distributions along electrofishing segments.

Electrofishing is widely used to monitor fish species composition and relative abundance in streams and lakes. According to standard protocols, multiple segments are selected in a body of water to monitor population relative abundance as the ratio of total catch to total samplingeffort. The standard protocol provides an assessment of fish distribution at a macrohabitat scale among segments, but not within segments. An ancillary protocol was developed for assessing fish distribution at a finer scale within electrofishing segments. The ancillary protocol was used to estimate spacing, dispersion, and association of two species along shore segments in two local reservoirs. The added information provided by the ancillary protocol may be useful for assessing fish distribution relative to fish of the same species, to fish of different species, and to environmental or habitat characteristics.

새우조망 어구의 막대 (빔)와 날개그물 길이에 따른 어획성능과 양망 작업에의 영향

Shrimp beam trawl fishery is one of the important coastal fisheries in Korea . It has a regulation to the length of beam (8 m) andwing net (7 m) of shrimp beam trawl that has been used in the district of Junlanam -do and Gyungsangnam -do . This regulationwas made in relation to the size of shrimp beam trawler of 3- ton class at that time . Now the shrimp beam fishing vessel has alimit not greater than 5 tons in gross ton . Recently , with improvement of fishing industry and fishing vessel fishermen asked theexpansion of the length of beam and wing net , therefore it is necessary to investigate the effect of lengthening the beam andwing net length . Three different beams (8 m, 10 mand 12 min length ) and three different wing net (7 m, 10 mand 13 min length )were made and the experiment was conducted near Narodo of Goheng by two fishing vessels of 4.98 and 4.88 tons in gross tonbetween June 2011 and October 2012. When the length of wing net was increased from 7m to 10 m and 13 m, the relative catchratio in total biomass was increased 25% and 79% for shrimp , (17% and 22% in total ), respectively . And when the beam lengthwas increased from 8mto 10 mand 12 m, the relative catch ratio was increased 35% and 84% for shrimp , (21% and 37% in total ),respectively . The force exerted to the iron guide of inhauler ’swith the beam length of 8mwas about 30% greater than that withthe beam length of 10 m when hauling the shrimp beam trawl net .Keywords : Beam length , Wing net length , Catch efficiency , Operation safety , Shrimp beam trawl

Improvement alternatives for determining the watertightness performance of building facades

The accurate determination of a facade's watertightness performance is important for optimizing design. Different micro-climatic conditions can affect water penetration. The recently developed Bayesian method allows this performance to be estimated for any operating condition and location, based on the results of standardized watertightness tests. This performance-based method uses semi-empirical calculations for wind-driven rain, estimates of wind velocity based on the wind profile power law and analyses of the annual maximum climatic data. This method determines the return period of climatic conditions that each facade system can withstand. Alternative approximations are studied that may be implemented using the Bayesian method to obtain more precise or functional estimations: improved friction coefficients, peaks-over-threshold analyses or catch ratios from computational fluid dynamics (CFD), among others. The effects of these alternatives on the results of the Bayesian method were evaluated by analysing different case studies in two cities in Spain. This analysis suggests that the original formulation of the method underestimates watertightness performance and highlights the fundamental importance of wind velocity to estimate the performance of any facade accurately. This will provide greater precision for estimating facade performance and provides potential for introducing performance-based codes for watertightness.

Numerical simulations of wind-driven rain on an array of low-rise cubic buildings and validation by field measurements

The relation between wind-driven rain (WDR) and its potential negative effects on the hygrothermal performance and durability of building facades can be better understood by the correct estimation of the spatial and temporal distribution of the WDR intensity. Computational Fluid Dynamics (CFD) simulations with Eulerian Multiphase (EM) modeling are used to obtain accurate spatial and temporal information on WDR. The EM model has the advantage of predicting the WDR intensity on all surfaces of a complex geometry within the domain at once. There is a lack of numerical studies on the WDR intensity in generic and idealized multi-building configurations. In this paper, WDR intensities on an array of 9 low-rise cubic building models for wind from three different wind directions are estimated numerically using the EM model including the turbulent dispersion of raindrops. The numerical results are validated by comparing the calculated catch ratio values with data from field measurements in Dübendorf, Switzerland after two rain events with different characteristics. The CFD simulations successfully estimate the WDR intensities at the positions of 18 WDR gauges for both rain events. The influence of turbulent dispersion is found to be lower than 3% for both rain events. It is found that, for oblique wind directions, even though the maximum WDR intensity on the facades is lower, the whole building is exposed to up to 57% more WDR.

Numerical modeling of turbulent dispersion for wind-driven rain on building facades

Wind-driven rain (WDR) is one of the most important moisture sources with potential negative effects on the hygrothermal performance and durability of building facades. The impact of WDR on building facades can be understood in a better way by predicting the surface wetting distribution accurately. Computational fluid dynamics (CFD) simulations can be used to obtain accurate spatial and temporal information on WDR. In many previous numerical WDR studies, the turbulent dispersion of the raindrops has been neglected. However, it is not clear to what extent this assumption is justified, and to what extent the deviations between the experimental and the numerical results in previous studies can be attributed to the absence of turbulent dispersion in the model. In this paper, an implementation of turbulent dispersion into an Eulerian multiphase model for WDR assessment is proposed. First, CFD WDR simulations are performed for a simplified isolated high-rise building, with and without turbulent dispersion. It is shown that the turbulence intensity field in the vicinity of the building, and correspondingly the turbulence kinetic energy field, has a strong influence on the estimated catch ratio values when turbulent dispersion is taken into account. Next, CFD WDR simulations are made for a monumental tower building, for which experimental data are available. It is shown that taking turbulent dispersion into account reduces the average deviation between simulations and measurements from 24 to 15 %.