Here is a picture of a sonar sensor, the HC-SR04, an extremely inexpensive sensor that works well in these sorts of situations:
These sonar sensors are available at most online electronics stores, including amazon.com. There are ways to connect this sensor directly to the BeagleBone Blue; however, there are two disadvantages to this approach. First, you'd need to learn the Programmable Real-Time Unit (PRU) process for BeagleBone Blue development. These sensors need specifically timed pulses, and the PRU system would allow you to create them. Also, since you're going to use multiple sensors to look around your mobile platform, you would need a significant number of General Purpose Input/Output (GPIO) connectors.
For these reasons, you're going to a use a simple and inexpensive processor, an Arduino, to connect to the sensors...