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  • Custom Comfort and Safety Criteria

    Users can define custom comfort criteria, allowing for a more personalized and accurate analysis of outdoor pedestrian environments. With this feature, SimScale users can tailor their pedestrian wind comfort analysis to specific project requirements, ensuring that pedestrians are comfortable and safe in any outdoor environment. This enhanced functionality is sure to be of great interest to architects, engineers, and urban planners seeking to optimize the comfort and safety of pedestrian spaces.

    Defining Custom Comfort and Safety Criteria

    Step 1: Create Custom Comfort Criteria

    Under Additional result export, click on the ‘+’ button next to Custom comfort criteria to create one:

    An image of the SimScale UI, highlighting how to create a custom criteria.
    Figure 1: Create new comfort and safety criterion


    To create multiple custom comfort criteria just keep pressing the’+’ button.

    Step 2: Define Out of Bounds Name

    Change the name and define the Out of bounds name, and if applicable, change gust settings under advanced settings:

    A screenshot of the SimScale UI, showing the final definition of a custom criteria.
    Figure 2: An example of how a custom comfort criterion looks after its fully defined


    It’s essential to understand the out of bounds category in comfort plots. There is a following section dedicated to this.

    Step 3: Define a Table for Custom Comfort

    Upload or define a table containing columns for Legend, Probability or frequency, and Speed thresholds. Click on the table icon as shown in Figure 3.

    Screenshot of SimScale UI showing how a table can be uploaded for custom comfort.
    Figure 3: Custom comfort or safety is defined by a table

    You may also change the units of speed to something more appropriate to your criterion under advanced settings.

    A screenshot the SimScale UI for table editing and setting the units of speed.
    Figure 4: A typical table definition for custom comfort is highlighting how to change speed units.

    Did you know?

    Users can define as many as 12 categories per custom comfort criteria. If, in the rare circumstance, a user needs more, consider breaking them up into sub-comfort criteria, i.e. one for detailed sitting criterion, one for detailed standing etc.

    Step 4: Visualize Results

    Once the simulation is run, open the results for ‘Statistical surface solutions’, and you will find the user-defined custom criteria listed among other criteria. As with the default criteria, a user may visualize for mean speeds, gust equivalent mean, or the maximum of both.

    Screenshot of SimScale UI with custom comfort criteria highlighted.
    Figure 5: Custom comfort criterion, Boston, is shown alongside the default criteria.

    Custom Comfort and Safety Criteria: Out of Bounds

    A comfort criterion is usually defined by one of two categories, not exceeding and exceeding. For example, sitting criteria are defined as follows:

    CategoryVelocity (m/s)Probability (% of time)Activity
    A1.8<2Sitting Long
    Table 1: Example of the first line in a custom comfort criteria table, an example of not exceeding

    It says that if a wind speed is exceeding 1.8 \(m/s\) for less than 2 \(%\) of the time, then it is comfortable for sitting for longer periods. For clarity, we could also say if a wind speed is not exceeding 1.8 \(m/s\) for more than 2 \(%\) of the time, it is the same, just written from a different perspective.

    However, the other scenario could be a category like uncomfortable:

    CategoryVelocity \([m/s]\)Probability (% of time)Activity
    Table 2: Example of the last line in a custom comfort criterion table, an example of exceeding

    That location is uncomfortable if a wind speed of 7.6 \(m/s\) is exceeded for more than 2 \(%\) of the year.

    To make this easier for the user to define, and reduce the operator error when defining custom comfort criteria, we ask the user to upload a table of all the categories of the first type. So in the example:

    Category Velocity (m/s) Probability
    (% of the time)
    A 1.8 <2 Sitting Long
    B 3.6 <2 Sitting Short
    C 5.3 <2 Walking Leisurely
    D 7.6 <2 Walking Fast
    E 7.6 >=2 Uncomfortable
    Table 3: Example of the full custom comfort criterion table, green indicating what should be uploaded in the .csv file

    All the green cells would be included in the .csv file upload. Category E would then be what we call out of bounds.

    In this scenario, all the user needs to do is specify the category’s name in the provided field. The Out of bounds category is usually named something like uncomfortable for comfort criteria, or unsafe or dangerous for safety criteria.

    Custom Comfort and Safety Criteria: Advance Settings

    GEM stands for gust equivalent mean, which is a time-averaged wind speed that represents the same level of discomfort as the peak gust wind speed. It is commonly used in pedestrian wind comfort analysis to provide an overall picture of wind comfort levels.

    We have documentation here that discusses the methods used for calculation and states the values we use in our default settings. However, these settings are not always the same and may vary for custom comfort criteria.

    Gust factor

    The gust speed U_gust is calculated by adding the mean wind speed to the standard deviation of wind speed multiplied by a constant we call the gust factor (GF).

    The gust factor, with a symbol in our documentation page as k_g, is an empirically derived parameter obtained through experiment. We use 3.5 in our default calculation of GEM, but if a comfort criterion specifies another, then the user is advised to change this constant in the advanced settings.

    Typical ranges for this are between 1 and 3.5. This is typically driven by what we know as turbulent intensity, a turbulent intensity is the ratio of fluctuations (standard deviation) over average wind speed, where a lower intensity leads to a lower gust factor. The Murakami comfort criteria guidance gives us some useful ranges for different scenarios. We have added exposure categories to help your understanding.

    DescriptionExposure CategoryGF Range
    Dense urban area (turbulence is strong, but average wind speed is not so high)EC22.5-3.0
    Ordinary urban areaEC32.0-2.5
    especially Places with high wind speed (such as high-speed areas near high-rise buildings).

    This would also apply to more exposed areas.
    Table 4: Description of areas and their corresponding exposure categories and GF ranges

    GEM Corrector

    The GEM (Gust Equivalent Mean) is obtained by dividing the gust wind speed by a factor, which is typically 1.85. The factor is based on assumptions about the distribution of wind gusts and the relationship between peak gust wind speed and standard deviation.

    Last updated: June 20th, 2023