5 - practical uses of podds discolouration modelling capability in · 2017. 2. 10. · 30 september...

DNV GL © 2014

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30 September 2015 SAFER, SMARTER, GREENERDNV GL © 2014

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30 September 2015Mark Grainger

OIL & GAS

Practical Uses of PODDS Discolouration Modelling Capability in Synergi 4.9

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Presentation Objectives

To raise awareness of the new PODDS modelling capability available in Synergi4.9

To show some potential practical examples of how this can be applied to real world problems

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Outline

Turbidity/PODDS overview

Running a turbidity analysis

Practical examples

– Site Re-Design Study

– Effectus 2015

– Trunk Main Conditioning

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PODDS Theory

Discolouration material is held in stable cohesive layers attached to the pipe walls of the systems and that these layers are conditioned by the daily hydraulic regime within the system

The cohesive layers have a defined profile of discolouration potential versus layer strength, with an increase in potential corresponding to a decrease in strength

The strength of the layers is dictated by the shear stress imposed within each pipe at the time of peak daily flow and hence peak daily flow controls the discolouration potential.

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PODDS Theory

The occurrence of disequilibria hydraulic conditions (burst, re-zoning, increased daily flow etc.) is considered to expose the layers to forces in excess of their conditioned cohesive strength and this leads to a mobilisation of the cohesive layers and results in a discolouration event.

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Turbidity Modelling in Synergi

Incorporated into the latest versions of Synergi Water

Two types of turbidity modelling

– Standard method

– Based on PODDS (Prediction Of Discolouration in Distribution Systems)

– Enhanced method

– Based on VCDM (Variable Condition Discolouration Model)

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Standard Model (based on PODDS)

The Standard method is based on the Prediction of Discoloration in Distribution Systems (PODDS) model developed at the University of Sheffield, and helps you model changes in turbidity due to erosion of material attached to pipe walls.

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Enhanced Method (based on VCDM)

The Enhanced method is based on VCDM (Variable Condition Discoloration Model), also developed at the University of Sheffield, and helps you model both erosion and regeneration of material attached to pipe walls, and can give you a better representation of observed turbidity behaviour.

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Process for Running a Turbidity Analysis

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Overview

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Calibrated Hydraulic Model

Layer Condition Calibration

Event modelling

Prior-to-event Pressure and

Flow data

Event Pressure and Flow data

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Calibrated Hydraulic Model

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Will work with any Synergi model

Ideally however, requires a more accurate calibration then a purely hydraulic model

– Calibration usually done using pressures and DMA inlet flow data

Accurate turbidity modelling requires accurate calculations of shear stresses

– Recommended that more flows be included in model calibration to get a more accurate representation of shear stresses and travel times (Boxall, Saul and Skipworth, 2004)

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Now the model has been calibrated, the initial layer condition needs to be estimated

– For the standard method, this means estimating/calculating the initial shear strength

– For the enhanced method, this means estimating/calculating the initial shear band condition versus shear strength profiles

For this presentation, I will mostly focus on the standard method

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Ensure model is running as in normal operating conditions

– i.e. no special events, bursts etc

– Nothing that will disturb cohesive layers attached to pipe walls

We can now use the peak daily flow from the model to represent initial conditions

– Involves running the model for an extended period, and retaining the shear strengths as new initial conditions for the model

This can now be saved as your PODDS conditioned model, ready for further analysis

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1414

In the Conditioned Model;

Equals Peak Daily Shear

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Event Turbidity Modelling

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Using the conditioned model, we can now see any increased turbidity responses for an events we model

– E.g Bursts, re-zones, new-connections, flow reversals etc.

Turbidity (measured in NTUs) becomes an attribute that can be viewed on any pipe in the model, at any time during the analysis period

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Practical Usage – Site Re-design Study

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Site Re-design Study

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Site-specific study from early 2015

Due to increased demand over the last few years, low pressures were observed in a tower block

DNVGL were asked to investigate the area, and suggest potential improvements to the network

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Recommendations

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Required pressures could be achieved by changing the metering and valvingconfiguration of the network as shown below

Valves opened

Valves closed

Meter relocated

Cross-connection installed and meter

relocated

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PODDS Analysis

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The proposed changes were made and the model re-run to highlight the areas of the network likely to experience an increase in Shear Stress and therefore be potentially subject to discolouration.

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PODDS Analysis

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The model shear stresses before any changes have been made

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PODDS Analysis

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After the proposed changes have been modelled

Increased shear

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PODDS Analysis

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Predicted turbidity response

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PODDS Analysis

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It was recommended that robust flushing or mains conditioning of these sections was incorporated as part of the reconfiguration works.

Undertake over a period of several days to ensure the network is conditioned to the increasing flows gradually, in order to keep the turbidity response low

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Practical Usage - Effectus

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Effectus 2014

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Systemised outage analysis of every modelled asset including; pipes, pumps, tanks, and sources

• Identifies areas affected by;

– Low pressure (DG2)

– Supply interruption (DG3)

– Discolouration potential (based on shear stress increases and flow/velocity changes

• Outputs Include;

– Pipes affected by DG2/3 and discolouration

– Number of customers affected in each case

– List of valves and pipes forming isolated section

– Valves proximity data & Drain-down time analysis

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Effectus 2014

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Effectus 2015

Now expanded to include

– DMA rezoning

– Open DMA boundary valves

– Hydrant flushing

– Simulate hydrant operation

– Burst main analysis

– Simulate a burst at each main

Every applicable analysis for Effectus 2015 will also include a PODDS turbidity simulation

The above analyses have been carried out on a test DMA model

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Effectus 2015 - Rezoning

Simulate DMA inlet failure

Trace all DMA boundary valves

Sequentially open valve meeting a certain criteria in turn on report on the consequences

Report on consequences (pressures, flows, turbidity etc.)

Identifies DMAs where the network flexibility exists to allow feasible rezones options

Identifies DMAs where no viable rezone exists. Risk of supply interruptions are unmitigated

Identifies discolouration risks associated with each viable rezone. Highlights excess shear pipes and the parts of the network likely to experience a turbidity response

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SummaryEffectus 2015 – Rezoning ExampleEffectus Analysis Process

DMA shear stress values at peak demand time

Inlet

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Predicted turbidity response from conditioned model

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Shear stresses with inlet closed, and valve opened to re-zone DMA

Inlet closed

Boundary valve opened

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Predicted turbidity response from re-zone (maximum over 24 hours)

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Effectus 2015 – Hydrant Operation

Create a stand pipe element

Simulate each hydrant operation running through the stand pipe


Identifies hydrants which do not achieve a predetermined set of flushing criteria

Identifies pipes associated with each hydrant operation that experience an increase in shear stress above an agreed threshold

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SummaryEffectus 2015 – Hydrant Operation ExampleEffectus Analysis Process

Max Shear = 0.00413

Max Shear = 0.2174Max Shear = 0.02526

Max Shear = 0.05821

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Max Shear = 0.06212

Max Shear = 0.68372

Max Shear = 0.36874

Max Shear = 0.18939Hydrant Flushed

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Effectus 2015 – Burst

Analyse all mains in the network

Simulate a burst main


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SummaryEffectus 2015 – Burst Main ExampleEffectus Analysis Process

DMA shear stress values at peak demand time

Inlet

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Trunk Main ConditioningEffectus Analysis Process

TM Contingency Planning

Sweetening Flow around 1-2 Ml/d

Emergency Demand Flows around 50 Ml/d

Required to maintain regional supplies during critical asset outage

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Trunk Main ConditioningProcess

TM Model Conditioned to turnover flow

Emergency demand applied and Turbidity response predicted

Turbidity at 12 NTU

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Incremental Increases of 1 Ml/d enabled STW to achieve the Emergency flow rate whilst keeping the turbidity response below 2 NTU

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Trunk main conditioned to 50Ml/d

Confidence that trunk main is in a state of readiness for any emergency flows

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Summary

Turbidity/PODDS now available in Synergi software

– Version 4.9 onwards

Easy to implement

– Only requires a calibrated model

– Minimal set up time

We plan to use this functionality more going forward in our work

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5 - practical uses of podds discolouration modelling capability in · 2017. 2. 10. · 30 september...

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