Drone Modelling and Simulation

As they grow in popularity, the types and the usage of drones have increased in complexity. Drones are not only utilitarian, but also fun to fly. The growing number of drone enthusiasts is a testimonial to their popularity. From engineering perspective though, drone designing is extremely challenging. There are various parameters that affect the performance of a drone and engineers need to consider all of them.

Drones describe a wide range of aircraft—from small remotely piloted toys, to autonomous flying robots, to full-scale military surveillance models that may be armed. One thing to remember while designing a drone is that most drones are designed to carry out a specific task. This makes the design task even more demanding.

Today's drones are able to carry increasingly complex payloads, with increased levels of autonomy and automation. This increase in complexity requirements improvements in processes and methodology used for the designing of drones. Modelling and simulation are two tools in an engineer's arsenal that helps them optimize a system or a process. Naturally, modelling in engineering context means mathematical modelling. A mathematical model is a set of equations that describe a system. Quite often, modelling involves finding an analytical solution of intricate differential equations. Many of these equations are nonlinear and extremely difficult to solve manually. Due to advances in computer technology, it is now possible to find solutions to these engineering equations using numerical methods. Simulation is nothing but the application of specifically designed software in order to find the solution of mathematical models. Thanks to engineering software companies like Altair, it is now possible to find optimal solution for drone design with less efforts and far more accuracy.

We have already covered what types of drones there are, and what advantages drones offer. In this article, we will delve into the engineering aspect of drone design.

It’s complicated... At a basic level, a drone consists of an airframe, a propulsion system, an autopilot, a task system, a communication link system and a ground control system. Drones are controlled either autonomously by onboard computers or by remote pilots on the ground or in another vehicle.There are various factors that are involved in drone design. Some of the factors that affect a drone’s performance include:

• Type: the type of drone is largely dependent on its purpose. Agricultural surveys have different drone requirement than military surveillance. Drones for delivery need different payload capacity than drones for aerial photography. The number of rotors (single, twin or more), motion required (only hover, hover as well as thrust), range, size all depends upon the type of drone application.
• Material: Drones that are required to fly in the Arctic have different material requirement than drones that fly in the deserts. Proper choice of material is therefore necessary in order to ensure correct performance of the drone.
• Flight Forces: All airborne objects are subject to four types of forces - lift, drag, thrust and gravity. Delving into all of these in this article will be too technical; suffice it to say that these forces are what affect the flight of the drone (or any other airborne object). Let us just state here that if the forces working on an object are balanced — say a push in one direction met by an equal push in the opposite direction — the object remains stationary. Only when the forces are not balanced, the object accelerates in the direction of the stronger force. And this is what makes drones fly.
• Flight Control: Drones are handled remotely, and require something to handle its movement. The remote for a drone typically contains two main joysticks that move both forward and backward as well as left to right. Control systems that govern the drone circuitry are also part of drone design.
• Throttle: The drone's forward / backward motion is controlled by the throttle, which essentially acts just as the accelerator acts for a car.
• Aerodynamics: this is nothing but the branch of Fluid Mechanics that deals with the motion of air and other gaseous fluids surrounding the drone body. The smoothness of yaw, pitch and roll of the drone - which are movements of the drone on the X, Y and Z axis - are the result of efficient aerodynamics.
• Weight: The weight of the drone is another important consideration in its design. Lighter the weight, better the flight efficiency. However, it is important to understand the purpose of the drone; if it is to fly in turbulent conditions like gusty winds, it needs to have proper weight in order to make it stable.Based on their weights, drones are classified as nano, micro air vehicles, miniature UAV, medium, and large. In terms of weight, the nano drones can be less than 0.5 kg, and the large drones can weigh as much as 150 kg.

To design the payload structure Altair helps to design light weight drone with due consideration of performance targets by using topology optimization algorithms.

Drones with minimized weights that also meet the criteria of strength, safety and noise would help meet the primary requirements. Lightweight planes would enable operators to increase the payload. Lower weight also helps reduce the size of the e-propulsion power plant, which, in turn, leads to lower operating cost and quieter operation. It can be further leveraged to reduce the battery size, which would help reduce time to recharge. Structural optimization methods have long been used in the aerospace industry for designing light weight structures that meet structural performance requirements. Topology optimization is a key technology used in the process of structural optimization, developed to optimize structures considering design parameters like expected loads, available design space, materials, and cost. Embedded early in the design process, it enables the creation of designs with minimal mass and maximal stiffness.

Design Efficient E-propulsion Systems: This system consists of below primary subsystems such as battery, motor, inverter, gearbox and fan. Below is the design consideration and to meet the design requirement Altair provides multiphysics simulation platform to address it.

• Improve battery Life and Charge time: Enough power must be reserved to complete the scheduled flight, plus additional reserves in case of rerouting or emergency scenarios.Batteries must also be designed for fire-avoidance under impact or thermal runaway scenarios.
• Motor Design: Understanding how design decisions influence the thermal, mechanical and electromagnetic attributes of motor performance is critical to optimizing the efficiency of an e-propulsion system.
• Power electronics and controls: it is important to consider power electronics and controls when refining the design of a motor through simulation and optimization.
• Gearbox design: Needs to consider Thermal, Noise, Weight aspects during Gear box Design as it will effect on the Efficiency of the Gearbox.
• Fan Performance: Rotor blades must meet safety requirements such as bird-strike and hail impact.Rotors/Propellers are a critical components providing both Thrust and Lift.
• Safety: While designing drones, the safety angle just cannot be overlooked. Drones are machines that have moving parts, and fly at a distance from the surface of earth. In case of any malfunction, there is a possibility that the drone may cause mishaps. In fact, there have indeed been a few incidences where improperly designed drones have crashed, injuring people and damaging property. This is another reason why industry standard drone development software like Altair Optistruct™, Activate®, Radioss™, etc. plays a significant role in improving the performance of the drone.

Apart from these basic considerations, there are quite a number of other gadgets that helps a drone perform its task. For example, drones contain gadgets like gyroscope, accelerometer, barometer, magnetometer (compass), global positioning system (GPS) module, power system, and control systems to handle all these.

Drone Modelling and Simulation A mathematical model of drones relies on fundamental laws of physics and are generally derived using either Euler-Lagrange method or Newton approach. 3D designing through simulation rather than creating a prototype can reduce the cost for a company.Simulation allows parameter optimization, fine tuning of drone dynamics, run a multiple 'what-if' scenarios in the safety of the lab, and also create a virtual test environment.Drones need to be reliable, lightweight and need to have topologically optimized engine parts. Engineering simulation and modelling software is vital to the success of a drone design.With the competition in drone development getting fierce, companies cannot afford to make costly mistakes. Therefore, proper selection of modelling and simulation software is the first step towards successful drone design.