Rollercoasters were in the spotlight last month after a crash at the Alton Towers theme park in Staffordshire. Sixteen people were injured, four seriously, when a carriage on the Smiler rollercoaster collided with a stationary car.
An investigation by the Health and Safety Executive is ongoing, but several industry insiders have blamed human error for the crash.
Such incidents are rare, but rightly receive much attention. More than a billion people around the world are estimated to use rides in amusement parks every year.
Marco Begotti is owner of Italian firm Ride Tek Engineering and cofounder of Remorides, which produces a software package for the operation of amusement park rides. He has designed more than 50 rollercoasters during his career. He says: “Around 90% of accidents today are caused by electrical and electronic systems or human factors. Only 10% of the time is it mechanical. In the last 10 years all the rules to control the rides have changed. Today risk assessments have to be conducted on the electronics, electrical and pneumatic systems.”
The next update to the European regulations on the design, manufacture and operation of rollercoasters is due by 2016 and is expected to focus more on maintenance and electrical procedures, as well as guarantees for the quality of manufacturing and control systems.
Some critics have said that the rides themselves are getting inherently more dangerous. Begotti says designers are now approaching the human limits for rollercoasters – generally drops of no more than 100m and speeds of 206km/h.
Explosion of creativity
These limits are being pushed by a revolution in the design tools available to engineers. Computer modelling and simulation was first used in the design of rollercoasters at the start of the 1990s, says Begotti. Inverted coasters, linear motor electromagnetic propulsion, flying coasters, diving coasters and floorless coasters were all made possible by CAD, while “simulation was used to avoid problems,” says Begotti.
“In 300 years there was just a small step in design. But in 20 years there has been an explosion, because the designer had the tools to create something really new. We could model, simulate and comply with regulations all in front of the PC.”
The main design drivers are the age range of the users of the ride, its theme, its ‘feel’ and its location. But most of all the design is driven by the business requirements of the park, says Begotti. It may want to attract families or need to differentiate itself from competitors by installing thrilling rides.
A ride takes around three months to design from the initial drawings to the documentation sent to the manufacturer. Designers start with an idea, consider the constraints of the landscape, and design the track on paper. They create multiple layouts in CAD, produce 2D drawings and 3D models and video to show how it works. They then use 2D simulation, generate 3D models with the introduction of spatial figures such as loops and corkscrews, and assess the dynamics of the ride. The final step is optimisation using multi-body analysis, to ensure the ride is safe. The 2D and 3D structural models then undergo FEM structural analysis.
Ride Tek and Enginsoft spent three years developing a bespoke plug-in to combine simulation and design
The design process has been shortened by advances in computing power and the ever-improving features of software packages. Livio Furlan, chief technical officer at Italian firm Enginsoft, has been designing the steel structures of rollercoasters for more than 20 years. Furlan says the designer has to fully understand each functional aspect of the ride to give users confidence in its safety.
Enginsoft, partnered with Ride Tek, has developed a tool that integrates the ride design in CAD with numerical simulation via FEM, and code checks. Furlan says: “Our approach is based on kinetic and multi-body simulation on the cars of the train and the rails. We use FE models of the rollercoaster structure for strength and fatigue, and model the launching and braking systems. Dynamic loads such as the cars crossing as well as environmental loads such as wind and seismic effects are considered with the structure.
“No mechanical structural behaviour is left to free interpretation or to a reasonable confidence about the quality of the response. The numerical engineering simulation is fundamental for a reliable consideration of the structures and components because life is at stake.”
Simulated strength checks are used to verify buckling. Stress deformation is conducted with tracks and rails and at joins in the structure. Fatigue damage from rain flow is calculated by a combination of the rain flow counting method and the Palmgren-Miner rule. The cycles of rain and the runs of the train are calculated to predict the amount of damage to the structure and components. The total damage also includes a sum of the constant amplitude stress from other sources.
The hot-spot stress approach is used for detailed analysis of complex welded areas. Sub-modelling is used to assess local stress ranges at supported regions of the track, where the geometry needs to be investigated extensively. This is loaded with forces from the overall FE simulation to fully optimise the results.
Complex geometry
Outside its bespoke tool, Enginsoft also simulates the cars for components and the complex geometry like the rocker arms and frames. The rocker arm is a crucial part because it supports the car as well as carrying the supporting wheels, guiding wheels and side wheels.
Furlan says that computational fluid dynamics (CFD) is also becoming an important tool as rollercoasters become higher and faster, the rides longer and the trains larger. Designers aim to reduce the loss of kinetic energy to resistance and friction. In addition, the higher the structures the more severe the wind actions. Simulation needs to be performed to take into account the interaction between the car’s velocity and the wind. CFD can simulate the airflow around the car for specific wind speeds in different incoming directions. By using CFD the designer can reduce the drag coefficient and improve the performance of the train.
Multi-body simulation is important because a modern rollercoaster has complex geometry and cars rotate around their own axis, so this requires detailed investigation of the effects on the bodies of passengers. Designers can simulate dummies to assess transversal forces and loads.
Despite the software tools, designing a rollercoaster is still largely guided by expertise and experience. There are only around 20 engineers at a handful of firms in Germany, Switzerland and Italy who have the capability in Europe, says Begotti.
He says: “A rollercoaster is a mix of an idea and engineering. The main idea is still one of the most beautiful parts of the design.”
Simulation in the cloud
The latest update to simulation software from Ansys enhances support to run computer simulations in the cloud through a built-in solution called Ansys Enterprise Cloud.
Applications such as multi-physics simulations combine fluid dynamics, electromagnetic, structural mechanics and the testing of embedded software to virtual prototypes and require extremely high amounts of computing power. Ansys hopes its new solution will remove barriers to adoption of such applications, by allowing companies faster and easier access to cloud computing resources.
Jim Cashman, chief executive of Ansys, says: “We have supported cloud solutions for a number of years, but the Enterprise Cloud provides our full suite of engineering simulation solutions on a global platform. Customers don’t want to be saddled with specifying, procuring, deploying and managing simulation infrastructure. Outsourcing the simulation data centre allows customers to focus on developing breakthrough products while freeing up capital for other investments.”