To measure the distance between the LEGO Mindstorms EV3 infrared sensor and an object using Simulink, you can utilize the Infrared Sensor block provided by the Simulink Support Package for LEGO MINDSTORMS EV3 Hardware. This block allows you to read distance measurements directly from the sensor.
You can find detailed instructions on how to use the Infrared Sensor block on this documentation page: https://www.mathworks.com/help/simulink/supportpkg/legomindstormsev3_ref/infraredsensor.html
Do note that using this block the Simulink Support Package for LEGO MINDSTORMS EV3 Hardware add-on, which can be obtained from here: https://www.mathworks.com/matlabcentral/fileexchange/45075-simulink-support-package-for-lego-mindstorms-ev3-hardware
I hope this helps you get started with your project.