Name: stormwater detention basin mass balance
Uploaded: 2025-02-13T15:43:21.000Z
Duration: 1 min 14 s
Channel: JoVE

La conservazione della massa è fondamentale per comprendere il flusso d'acqua in un sistema di irrigazione rotante utilizzato per l'irrigazione agricola.
L'irrigatore riceve l'acqua da una fonte fissa e la espelle attraverso ugelli rotanti per irrigare il campo.
Il volume di controllo comprende l'acqua all'interno della testa dell'irrigatore e degli ugelli, con i confini definiti dalle aperture degli ugelli e dall'ingresso della sorgente d'acqua.
L'acqua scorre costantemente attraverso il sistema mentre l'irrigatore ruota, mantenendo un modello di irrigazione continuo.
La velocità relativa dell'acqua è determinata dalla sua velocità all'uscita dall'ugello rispetto al movimento della testa rotante dell'irrigatore.
La differenza tra la velocità assoluta dell'acqua e la velocità dell'irrigatore rotante determina la velocità con cui l'acqua viene espulsa rispetto all'ugello in movimento.
Per un flusso costante, l'afflusso di acqua dalla sorgente e il deflusso attraverso gli ugelli devono essere bilanciati.
Le dimensioni dell'ugello e la velocità di rotazione sono progettate per garantire una distribuzione uniforme dell'acqua sul campo e massimizzare l'efficienza dell'irrigazione.

conservazione della massa in un volume di controllo mobile e non deformabile

Conservation of Mass in Moving, Nondeforming Control Volume

I bacini di contenimento delle acque piovane, sono essenziali per gestire il deflusso durante forti piogge, in particolare nelle aree urbane, dove le superfici impermeabili aumentano il rischio di inondazioni. Comprendere la conservazione della massa in questi sistemi, consente agli ingegneri di ottimizzare le prestazioni del bacino, bilanciando afflusso, deflusso e accumulo di acqua.

Nel contesto di un bacino di contenimento, la conservazione della massa, afferma che la massa totale di acqua che entra nel bacino deve essere uguale alla massa che esce dal bacino più qualsiasi accumulo di acqua al suo interno. Il volume di controllo, è costituito dall'acqua all'interno del bacino, con i suoi confini definiti dalle pareti del bacino, dai tubi di afflusso e dalle strutture di deflusso. Durante un evento di pioggia, l'afflusso avviene attraverso i tubi e il deflusso attraverso gli scarichi progettati. L'equazione del bilancio di massa è espressa come:

<img alt="Equation 1" src="/files/ftp_upload/18050/18050_Equation_1.svg" style="text-align: center; height: 33px;">

Dove

ṁin è il tasso di afflusso di massa,

ṁout  è il tasso di deflusso di massa e

<img alt="Equation 1" src="/files/ftp_upload/18050/18050_Equation_2.png" style="text-align: center; height: 33px;"> rappresenta la variazione di massa all'interno del volume di controllo.

Durante forti piogge, la portata di afflusso spesso supera la portata di deflusso, causando l'accumulo di acqua nel bacino. Gli ingegneri devono progettare le strutture di deflusso per controllare il rilascio di acqua a una velocità gestibile, assicurandosi che i sistemi a valle non vengano sopraffatti. Quando la tempesta si placa e l'afflusso diminuisce, l'acqua accumulata viene gradualmente rilasciata. La velocità di deflusso è in genere progettata per aumentare, con l'aumento del livello dell'acqua, seguendo curve di scarico predeterminate per mantenere il controllo sul rilascio.

La capacità del bacino di immagazzinare temporaneamente l'acqua, è fondamentale per la prevenzione delle inondazioni. I bacini di detenzione progettati correttamente, assicurano che l'acqua venga rilasciata in modo controllato anche durante gli eventi di tempesta più intensi, prevenendo traboccamenti o cedimenti strutturali.

Conservazione della Massa in un Volume di Controllo Mobile e Non Deformabile

La conservazione della massa è fondamentale per comprendere il flusso d'acqua in un sistema di irrigazione rotante utilizzato per l'irrigazione agricola.
L'irrigatore ...

conservation-of-mass-in-moving-nondeforming-control-volume

Education

Didattica

JoVE Core

Civil Engineering

Ingegneria Civile

Unit 1

Unità 1

Finite Control Volume Analysis

Analisi a volume di controllo finito

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

stormwater detention basin mass balance

Stormwater detention basins use mass balance to manage runoff during heavy rainfall. These basins are especially important in urban areas, where impervious surfaces can increase flooding risk. Engineers use the conservation of mass to track how water enters, is stored in, and leaves the basin.

In a detention basin, the control volume is the water inside the basin. Its boundaries are the basin walls, the inflow pipes, and the outflow structures. During a rain event, water comes in through the pipes and exits through the outlet system.

The mass balance equation states that the mass flowing into the basin must equal the mass flowing out plus any water that builds up inside. Here, m-dot in is the mass inflow rate, m-dot out is the mass outflow rate, and the change in mass shows how much water is accumulating in the control volume. When heavy rain causes inflow to exceed outflow, water storage in the basin increases.

Engineers design the outlet structures to release water at a manageable rate so downstream systems are not overwhelmed. As the storm weakens and inflow drops, the stored water is released more slowly. The outflow rate is often designed to rise as the water level rises, following preset discharge curves. This controlled storage is what helps detention basins prevent overflow and structural failure during intense storms.

Stormwater Detention Basin Mass Balance

conservation of mass in finite cotrol volume

conservation-of-mass-in-finite-cotrol-volume

Continuity Equation for a Fixed Control Volume

The continuity equation describes conservation of mass for a fixed control volume. In fluid mechanics, a system is a collection of the same contents over time, and its mass stays constant. That idea is the starting point for deriving the equation. To analyze flow, a fixed, non-deforming control volume is chosen so it matches the system at one instant. The Reynolds transport theorem then links the system to the control volume. It shows that the rate of change of system mass has two parts: mass...

conservation of mass in fixed, nondeforming control volume

conservation-of-mass-in-fixed-nondeforming-control-volume

Continuity and Velocity in Pipe Flow

Conservation of mass explains how fluid moves through a fixed control volume such as a pipe or duct. In a fixed, nondeforming control volume, the total mass stays constant unless mass enters or leaves through the control surfaces. For steady, incompressible flow, the mass entering the system equals the mass leaving it. A sewer pipe is a useful example of this idea. It can be treated as a fixed control volume with inlet and outlet control surfaces around the flow region. Because the fluid is...

conservation of mass in moving, nondeforming control volume

Stormwater detention basins use mass balance to manage runoff during heavy rainfall. These basins are especially important in urban areas, where impervious surfaces can increase flooding risk. Engineers use the conservation of mass to track how water enters, is stored in, and leaves the basin. In a detention basin, the control volume is the water inside the basin. Its boundaries are the basin walls, the inflow pipes, and the outflow structures. During a rain event, water comes in through the...

linear momentum in control volume

Momentum Balance for Fluid Control Volumes

Linear momentum balance for a fluid control volume links Newton’s second law to moving fluid. The law says that the rate of change of linear momentum equals the sum of the external forces acting on the system. In a fluid system, this idea helps explain how motion and force are related. A control volume can match the fluid system at a specific moment. When that happens, the forces on the control volume and the system are the same. Reynolds transport theorem explains this connection by splitting...

application of the linear momentum equation

application-of-the-linear-momentum-equation

Forces in a 180° Pipe Bend

Forces in a 180-degree pipe bend can be found by applying the linear momentum equation to flowing water. The pipe has a constant cross-sectional area of 0.01 square meters, and the water moves at 15 meters per second. The pressure at the inlet is 0.2 megapascals, and the pressure at the outlet is 0.16 megapascals. The goal is to find the force components in the x and y directions that hold the bend in place. In this case, the flow is only in the y direction at both the entrance and the exit.

moment-of-momentum equation

Wind Turbine Torque and Angular Momentum

The moment-of-momentum equation helps explain how wind turbine blades create torque. Torque is the turning effect of a force around an axis. In rotating systems, this equation links the motion of the wind with the force acting on it. The equation begins with Newton's second law for a fluid particle. That law says the rate of change of linear momentum equals the external force on the particle. To find torque, the position of the particle relative to the rotation axis is combined with that force.

conservation of energy in control volume

Turbine Work from Energy Changes

A turbine can turn fluid energy into shaft work when flow passes through a control volume. The fluid enters the turbine at one point and leaves at another. Under steady-flow conditions, there is no energy buildup inside the control volume, so the stored energy does not change with time. This steady-flow setup makes the energy equation simpler. The turbine is treated as doing mechanical work, and heat transfer is taken as negligible, so Q̇ is approximately zero. The flow at the inlet and outlet...

application of the energy equation

Centrifugal Pump Flow Rate Calculation

Centrifugal pump flow rate can be calculated with the energy equation. In this problem, water moves between two reservoirs at different elevations, and the pump provides the energy needed for the transfer. The pump input is 7500 joules per second, the elevation difference is 10 meters, and the head loss from friction and other resistances is 5 meters. Both reservoirs are open to the atmosphere, so the pressure at the inlet and outlet is the same. That means the pressure terms in the energy...

design example: forces in sluice gate

Sluice Gate Water Pressure and Reaction Force

Sluice gates control water flow in channels, reservoirs, and irrigation systems. They work as vertical barriers with an opening that can be raised or lowered. Changing the opening height changes the water velocity and pressure below the gate. The forces on a sluice gate depend on the water depths upstream and downstream, written as z1 and z2. When the gate is closed, the upstream water depth is greater. That creates a strong pressure difference across the gate and a net force toward the...

key terms and concepts

See how stormwater detention basins use conservation of mass to balance inflow, outflow, and storage during heavy rain to reduce flooding.

Stormwater Detention Basin Mass Balance | JoVE K12

JoVE Core Civil Engineering provides a foundational exploration of essential construction materials in civil engineering, focusing on bricks, stones, steel, wood, and concrete through easy-to-understand animated videos. This collection covers the properties, manufacturing processes, and practical applications of these materials. Additionally, the accompanied science-in-action videos demonstrate the research experiments performed in laboratories.

civil engineering

Stormwater Detention Basin Mass Balance

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