Steady State Stimulation

In steady state simulation, a virtual pipeline is created and hydraulically solved to calculate system wide pressures, flows, temperatures and other unknowns, where operating conditions do not change over time, so for example a steady state simulation might typically represent a daily average operation on a particular day. Steady State simulations in NextGen are time stamped so that they can be more easily integrated with time dependent external data sources. The steady state section in NextGen is also where models are created, and once created, additional sections such as Transient Predictive or Online can be activated.

Steady State simulation is typically used to:

  • Design new pipelines and pipeline expansions
  • Determine Optimum pipe sizes
  • Estimate horsepower requirements at compressor stations
  • Calculate system and zone capacities
  • Determine viability of nominations and estimate allocations
  • Gauge impact of facility and system outages

Model Building Tools

There are a variety of tools available to help build models in NextGen, with the most basic being the Pipeline Builder which lets users manually build models from scratch or edit the configuration of existing models.

Each simulation section in NextGen (Steady State, Transient Predictive, …) contains one or more independent snapshots of the model, but all of the snapshots are synchronized so that they all have the same pipeline configurations. They all have the same pipes, node, valves, and so on, but the operating set points and calculated pressures and flows and other parameters may vary.

When a user enters into Pipeline Builder Mode, all sections are frozen while configuration changes such as adding new pipe sections or deleting some facilities are being made. When the user exits Pipeline Builder Mode, the changes that were made are propagated to all other sections. Pipeline Builder Mode for a model can be password protected so that only authorized users are allowed to make changes to the configuration of the pipeline, but all users are allowed to edit operating set points, make runs, view results and so on.

To facilitate the building of models, background imagery can be brought in first and the pipeline simply built on top of the imagery. NextGen supports online connections to Google Maps so that current satellite imagery can be displayed, but users can also import image files or shape files to be displayed in the background.

While building models from scratch is sometime necessary, NextGen provides a number of integration tools and modules that can be used to automate much of this process by bringing in the data from external sources such as geodatabases or GIS, and easy to use features to create and maintain the model data are also available:

  • Elevations Module
  • Facility Library
  • Detailed Station Editor
  • Ariel Library Import Module
  • Excel Import/Export
  • Data Integrator Module
  • GDS Module
  • Load Forecaster Module
  • Load Generator Module
  • SCADA Integrator

Map Component

The NextGen interface contains easy to use components to help create and edit models. The primary interface component is the Map which displays a schematic of the pipeline system, and it is the primary means of navigating through the model, adding or removing facilities from the model, and selecting objects for editing.

There are a multitude of options and features to edit data directly from the map, display text on the map, color code objects on the map, create secondary map Views, add background imagery, and manipulate the model.

The Map component is synchronized with the other components in the interface, so clicking on an object in the map will immediately display that object’s data in the Record Editor and auto-tab and auto-scroll to it in the Reports.  Components in NextGen are synchronized so as to let the user immediately view the maximum amount of data possible for an object of interest, with no need to scroll or tab over to relevant data.

In addition to building and navigating through the models, the map is also a primary means of displaying model information. Hovering over any object in the map will display information on that object, right clicking will pop up an editor for editing its data.

The Map can also be used to trace flow through the system. For example, click on a node in Flow From mode and find all paths where the flow from that node is going, or find all paths where gas came from that is arriving at the node in Flow To mode.

Regions can also be defined either manually by lassoing, or by auto creating all pressure or flow isolated regions.

An individual region, once defined, can be turned into submodel. A submodel is a portion of the model that is basically split off from the main model and treated as its own smaller model. The flows and pressure set points at the submodel boundaries are automatically reset to maintain current flowing conditions, and when runs are made, the run engine only solves the smaller submodel.

When the submodel is deactivated, the boundary conditions are reset and it is merged back into the main system, but changes the user made while it was a submodel will be retained in the main system. Submodels are a good tool for debugging models and also let users make faster runs since they only need to run the portion of the main model they are interested in.

Submodels can also be split off permanently and a new NextGen model created from the submodel.

Record Editor

Another core interface component is a fully customizable Record Editor which displays detailed information about the currently selected object such as a node, meter, valve, section of pipe, etc.

There is a default “View” that displays the most commonly used data, organized by Configuration, Set Point, and Results tabs, but users can define their own views and add additional tabs, and select what to display in each tab.

Thus, novice users might be set up with a very limited “View” with minimal data such as flows and pressures, whereas experienced users might have much more data visible such as curve fit coefficients, components, or revenue data.

Reports

The Reports component is another NextGen core Interface feature. At a high level, the Reports are used to view user selected simulation parameters. Reports are fully customizable and users can select what data fields should appear in the Reports.

Many features of the Reports component make it easier than ever to find and use your data. For example, quick column Sorting where a simple click of any column header in Reports will sort the report by that column with values ascending. Clicking the header again will reverse the sort to sort by descending values.

Utilizing standard spreadsheet selection options, users can Multi-Highlight/Select more than one item in the Reports to view in the Map or globally edit in the Record Editor.

The Reports component is another NextGen core Interface feature. At a high level, the Reports are used to view user selected simulation parameters. Reports are fully customizable and users can select what data fields should appear in the Reports.

Many features of the Reports component make it easier than ever to find and use your data. For example, quick column Sorting where a simple click of any column header in Reports will sort the report by that column with values ascending. Clicking the header again will reverse the sort to sort by descending values.

Utilizing standard spreadsheet selection options, users can Multi-Highlight/Select more than one item in the Reports to view in the Map or globally edit in the Record Editor.

Users can also create logic and data Filters to only display records that adhere to user created logic rules. For example, only show nodes with a pressure greater than 500 psig. Reports can also be filtered by Region or Zone, so only those records that lie within the selected Region will appear in the Report. Data values that are alarmed or exceed operational limits are highlighted in the Report.

As with most components within NextGen’s interface, Reports are synchronized with the other components, so clicking on any node or leg in a report will automatically focus that object in the Map and the Record Editor, or clicking on an object in the Map will highlight it in its respective Report.

Individual Reports can also be exported to Excel or data in an Excel spreadsheet can be imported into a report table.

Custom Reports

Using the Custom Reports Designer, users can create their own custom reports that can include graphics, grids, and other custom report display fields that can be tied to the model data. When the report is generated, it is populated with the latest model data and displayed on screen, and can be sent to a printer.

Gauges

The Gauges component acts as a dashboard and includes both gauges and simplified graphs and is designed to visually monitor key points of interest within the system. They are fully customizable so the user can choose what values are being gauged and what values are being graphed.

The Gauges are typically used for monitoring region-level variables, such as total supplies, deliveries, power in compressor stations, and line pack.

The Graphs are provided for monitoring groups of variables, such as the greatest magnitude nodes of supplies, deliveries, or individual compressor stations.

Both Gauges and Graphs have the option of defining high and low user-defined color bar ranges, to alert the user when certain limits or alarm levels are reached.

Graphs

Profile Graphs

Profiles Graphs display user selected values over distance, for example a pressure gradient chart showing how pressure drops over distance, steps up through compressors, and steps down across regulators. Multiple graphs can be defined and each graph will have its own tab.

3D Graphs

NextGen 3D graphs can be displayed as either smooth terrain style graphs, or as stick figure 3D graphs, are useful to display values such as pressures or elevations.

Modules

GIS Module

In many companies, pipeline models are created, in a sense, by hand, which due to most models’ complexity can be an extremely time consuming task. The GIS Import Module can automate this task by importing a model configuration that has been exported from the GIS system in the form of shapefiles and their associated dbf files.

GEI’s NextGen GIS Module is the industry leader in model creation from GIS technology, and has features that let a user control what data is used and how it is used, as well as features that will auto create connectivity if needed. Once this import process has been defined, it can be saved and reused for future model builds or for building other models. It can also be used to maintain, expand, and/or update models.

The better the data presented into the GIS Import module, the more accurate and complete the model created is. Even if a company has minimal GIS data, maybe just a path of pipes, or even just a drawing of their system, the GIS Import Module is still a tremendous benefit. For example, it allows for the automatic creation of the majority of the model connectivity, including the correct length for each pipe segment since it uses the scale within the GIS map to calculate this parameter. Creating the connectivity for a model is the most time consuming part of the model building process, and the GIS Module permits the user to do it in a fraction of the time.

Using this feature, a company has the opportunity to gain back up to 99% of the work they would have previously done before by hand, as well as define a static and repeatable process for model building and maintenance.

The GIS module not only has Import capabilities for building or updating NextGen models from GIS, it also has Export capabilities for updating the GIS from changes that were made in NextGen. For example, a user can bring in an incomplete set of shapefiles that have missing facilities, use NextGen’s model building features to add the facilities to the model, then export out a new set of updated shapefiles which contain the pipeline facilities that can be used to update the GIS.

Elevations Module

Building a model with the GIS Import and correctly orienting it with the Google Maps Module will provide a solid foundation for an extremely accurate model. NextGen can then help complete the whole picture with the Elevations Module.

Because NextGen models are geo-aware, NextGen has the ability to query a NASA generated database that comes with the Elevations Module and assign an elevation profile to each and every node in the model with the click of a button.

Elevation profiles can be easily visualized in NextGen with either a 3D graph or a contour graph, both of which can also be exported out and included in reports.

For pipelines with two-phase flow where both gas and liquid are potentially present throughout the line, it is essential to account for elevations. For these cases, NextGen offers both the Flanagan and Beggs and Brill two-phase flow equations to accurately correlate the model to the real world system. The Elevations Module also works hand-in-hand with NextGen’s AutoTune feature which helps identify areas of low efficiency, and thus suspected areas of liquid hold up.

Facility Library

The Facility Library lets users predefine common elements that make up a pipeline, define common sizes and configuration parameters, and preset many of their set points to default values.

For example, different valve sizes and valve types can be preconfigured, different pipes sizes, and so on.

When building or expanding a system that may have multiple copies of the same facility elements, for example a 6” globe valve, the user simply needs to select one of the preconfigured elements from the Facility Library, in this case the 6” globe valve, and add it to the system where needed instead of having to renter the data over and over for each instance.

Facility data can not only contain physical parameters, it can also contain set point data, and even cost information for Revenue Tracking such as the cost of the valve.

Facility Libraries can be easily exported and imported, so one user can be responsible for creating and maintaining a master Facility Library, and all other users can simply import the master library as needed.

The Facility Library also provides an easy method of automatically updating multiple elements in a model. For example, if the roughness of a 6” steel pipe was originally defined as 0.0005” in the Facility Library but the user wanted to change it to 0.001”, it would only need to be changed in the Facility Library and from the Library itself, the user has the option of updating all pipes in the model that were 6” steel pipes, or leaving them intact at the old value.

Detailed Station Calculations Module

The Detailed Station Calculation (DSC) Module, used in both steady state and transient, is the most sophisticated and dependable station calculation module in the industry for modeling complex compressor stations.

Compressor Stations are built using the Detailed Station Editor and can be set to Block Horsepower Mode to treat the entire station as a simple block horsepower (no detailed unit need to be created, but if they exist, they are not modeled), or set to DSC Mode in which case the individual units within the station are modeled.

Several centrifugal and reciprocating unit types are supported from very simple to very complex, and they can be configured in simple parallel or series arrangements, or much more complex combinations of series and parallel.

NextGen’s Detailed Station modeling simulates the actual detailed performance and operational limits of real physical compressor units within the pipeline network.

The Station logic will perform both individual compressor unit selection and control of selected compression within a compressor station to maintain a desired “set point” value such as a discharge pressure, flow and certain other parameters.

The Station logic will choose the most fuel-efficient combination of compressors to operate for a given condition or to start compressors in a user-defined sequence, and calculates for each station the lowest cost combination of power, unloading condition and torque to maintain the desired pipeline pressure and loading configuration, while maintaining the operating limitations for each compressor unit.

Ariel Library Import Module

Companies who have Ariel reciprocating compressor units frequently make use of the Ariel Performance Program from Ariel Corporation to both store the detailed unit information and perform detailed individual unit calculations.

NextGen can perform the same detailed unit calculations as the Ariel Performance Program within its station calculations, including modeling all the way down to the individual cylinder ends, considering bore, stroke, rod diameter, clearances, volumetric efficiencies, valves losses, pocket volumes, unloader steps, and so on for each cylinder.

The data required to model reciprocating units in this much detail can be daunting if it has to be manually entered, especially if there are hundreds of individual units. GEI created the Ariel Library Import Module to import all of the detailed data for all units directly from the Ariel Performance Program into the Unit Library in NextGen for use in NextGen models.

The NextGen detailed Recip #3 unit type with its option flag set to “Ariel”, duplicates the calculations performed by the Ariel Performance Program so Ariel units running in NextGen will match up with unit performance in the Ariel Performance Program.

InFlow Types

Supplies and Deliveries can be added or removed from the pipeline in the form of InFlows at nodes or meters under nodes. There are several InFlow Types that are supported:

  • None: No InFlow allowed.
  • Supply: Only supplies are allowed.
  • Delivery: Only deliveries are allowed.
  • BiDirectional: Both supplies and deliveries are allowed.
  • Gas Well (Oil Well in Liquids Mode): A reference ID must provide the points to an entry in the Well Facilities Library that contains the ARPS decline curve coefficients and other well data. The Start Date at which the well came online must also be specified. The InFlow (well production rate) is then calculated based on the start date of the well, the current simulation time, and the decline coefficients and other parameters.
  • Degree Day Load: A reference ID must provide the points to an entry in the Degree Day Facility Library that contains 2nd order polynomial degree day load coefficients and floor and ceiling degree day values. The InFlow is then calculated using the coefficients and other parameters and the current degree day. Optionally, these coefficients can used to calculate an InFlow Prorate Factor that is then applied to the InFlow Set Point at the node/meter.
  • Pressure Load: A reference ID must provide the points to an entry in the Pressure Loads Facility Library that contains 2nd order polynomial degree day load coefficients and floor and ceiling degree day values. The InFlow is calculated using the coefficients and other parameters and the current mode calculated pressure at the node or meter. Optionally, these coefficients can used to calculate an InFlow Prorate Factor that is then applied to the InFlow Set Point at the node/meter.

Making Steady State Runs in NextGen

Once a model has been created, and the editors or data integration utilities used to properly set all set points, a user simply needs to press the Run button in the top ribbon toolbar to make a simulation run.

For models that have trouble running, there are also Debug Run buttons that can be used to step through the steady state solution process. On each steady state iteration, the interface will display the results up to that point, and users can single step through each iteration and examine the results as they are being calculated.

There is even a View Differences button that will show the differences in calculated values between the last iteration and the current iteration, and let the user sort the data from highest to lowest deviations, which can be invaluable in identifying why the model might be failing or where it is blowing up due to bad boundary conditions.

NextGen’s Simulation Engine client application contains all of the calculation algorithms for all simulation types, and any connected copy of the Simulation Engine can perform any of the steady state, Sequential, or transient simulation calculations that the Simulation Server might request. After a run has been completed, the Simulation Engine puts itself on standby for any subsequent run requests, and a Simulation Engine that has just been used by the server for one model, might then be used to solve another model.

A core focus of NextGen is power, speed, and efficiency, and NextGen achieves this in the Simulation Engine by multithreading as many of the calculation processes as possible. This means that portions of the simulation calculations can be spread out among multiple cores.

The Steady State and Sequential components of the run engine use a GEI developed Newton-Raphson solution methodology to set up equations that are then solved using sparse matrix LU decomposition. This proprietary methodology is custom built, and another piece of NextGen that allows GEI to stand out above others in the industry.

Specifically, the equations and matrix construction have been built from the ground up to stabilize the solution and come much closer to a quadratic convergence, making use of certain characteristics unique to pipeline simulation equations and their behavior, as opposed to other vendors who typically just use generic Newton-Raphson network methodology that might be usable for pipeline simulation, but apply equally to electrical network simulation, or even stock market simulations.

GEI’s solution typically converges in half the number of iterations found in other solutions, and difficult to solve models that are problematic for others easily converge with GEI’s methodology.

Advanced Features available in Steady State

  • Scenario Manager
  • Multi Scenario Runs
  • Automation Scripts

Advanced Modules available in Steady State

  • Component Tracking
  • Source Tracking
  • Revenue Tracking
  • Autotune for Pipeline Efficiency Tuning
  • Autotune for Loads Tuning
  • Portable Natural Gas (PNG) Module
  • Loads Planning Module
  • Well Decline Analysis and Forecasting Module

Learn more about our Software Solutions

Call us at 281.494.8100 or email us: office@greggengineering.com.