Goal Seek

[Martin Griffith]

New in Ventsim 5 is the Goal Seek. 

The Goal Seek calculates a setting for you (such as a Fan Speed, a Resistance, a Regulator Opening or heating or cooling input) on one or more airways, so that you achieve a particular variable output (airflow quantity, pressure, temperature) on another target airway. This allows you to, for example, determine a fan speed on an intake fan which would give a particular flow rate in a different part of the mine. Rather than using trial and error back and forth to find the correct fan speed, the Goal Seek! will do it quick smart. It does so by running multiple Air and/or Heat Simulations to calculate the correct setting, using a fast numerical algorithm to minimize the time needed to calculate. 

The Goal Seek can be found under Tools -> Goal Seek

Once you've opened the Goal Seek!, you need to select the airways to adjust, or the Source airways. You can choose to adjust:

• Resistance
• Fan Speed
• Sensible Heat
• Latent Heat
• Refrigeration
• Regulator Opening
• Orifice 

For the fan and regulator options you are limited to airways which already have a fan or regulator. If you select more than one airway, then the parameters will be adjusted equally on all airways by a common factor. 

For the goal, you are limited to one airway and you can target:

• Quantity
• Total Relative Pressure
• Dry Bulb Temperature
• Wet Bulb Temperature

To select a target airway, press the select button in the Goal panel and then select a target airway. The Goal data will update with the current value for that airway; you can adjust the target up or down. 

When you're ready, press Goal Seek! and the solution algorithm will begin. The progress of the Goal Seek will update in the graph. The target is shown by the blue line. The red line shows the progress of the target airway value towards the target and the green line shows the change in the source airway parameter. 

The Goal Seek will continue until the target airway is within a small tolerance of the target. Goal Seeking tasks which involve temperatures or heating or cooling will tend to take longer, because the Heat Simulation will be running as well.

If the Goal Seek! was successful and you're happy with the result and want to keep it, close the Goal Seek and you will prompted whether you want to copy the result to your model (you can Undo any changes after closing).

Often your Goal Seek! will fail and you'll get a message telling you that the goal seeker is not converging. There are a number of reasons this can happen:

•  your target value is not functionally-related to the adjusters. This means that changes to the adjustment parameters do not have a significant effect on the target value. This can happen if you are adjusting a fan speed, but your target airway is in a part of the mine that is not affected by that fan, so when you change the fan setting, nothing changes in the target airway.
• the target value is unachievable. This means that the limitations on the adjustment parameters and the nature of the mine system is such that you can not reach the target. This can happen if you are seeking to reduce a resistance to achieve an increased airflow in the target airway. You can not reduce an airway resistance to or beyond zero, so there is a natural limit to the maximum airflow achievable, for a given supplied pressure.
• if you have Natural Ventilation Pressure switched on, then in some mine models, there can be a natural variation in temperature and airflow, indicative of a mine with no steady-state solution of air and heat. In such cases, for Goal Seek! attempts where you have chosen temperature related adjusters or target, and have Natural Ventilation Pressures on, then the Goal Seek can sometimes struggle to converge.

Where the Goal Seek! fails, it will revert to the original state and you can adjust your input parameters and try again.

If you have any questions about the Goal Seek!, any suggestions, or any feedback from your own experiences with it, please let us know in this thread. 

[Shane Ambrosio]

Very nice feature Martin.

I tested a little and think it would be value adding if you could include the following:

• At the Source include Fixed Flows (restrictive or otherwise). This will be handy when adjusting multiple points throughout a mine until such point as it is time to convert to regulators or resistances.
• At the Goal, I would like the target list to be expanded to other useful parameters we may target. I have particular need for airway velocity (a common goal in SA Coal being 1.5m/s in design). Other handy items would include getting flammable or noxious gas levels down to below a legal requirement.

Shane

[Martin Griffith]

Hi Shane.

Fixed Flows as Source settings and Velocity as a Goal, we can add those in an update soon. 

To add things like gas levels as Goals, we would need to bring the Gas Simulation into the Goal Seek!, which is possible, but would need a a fair bit more work. I'll add it to the list of potential future enhancements and keep you posted.

Thanks for the feedback and suggestions!

[Martin Griffith]

In Ventsim 5.2, we've included some more Goal Seek! targets and adjusters.

Added to the list of adjusters are Fixed Flows and Pressures, as well as Rock Wetness Fraction. Rock Wetness Fraction is often a tricky parameter to obtain, or calibrate. If you have a temperature target you are aiming for you can now use the Goal Seek! to find the needed Rock Wetness Fraction. You can do this for a single airway, or select multiple airways and adjust them together. If you prefer you can select the whole mine and adjust the Wetness Fraction globally. If you do this, the Goal Seek! will scale the existing wetness fraction, rather than set the same wetness fraction throughout, meaning any existing differences of wetness fraction in your mine will also be scaled.

In the target list, as well as including Air Velocity, we've added a list of common gases that might be simulated in a mine. This means that you could, for example, adjust a fan speed or a fixed flow in order to achieve the required dilution of a given gas to an acceptable level. 

If there's anything else you feel would be useful to include in the Goal Seek!, such as another gas, please let us know.