applications He went on to explain that Louisiana has a


fairly unusual geography due to the presence of the Mississippi river delta, and expansive wetlands and vegetation which have an impact in the event of a hurricane. Chen concluded: ‘We can improve the physics;


we can collaborate with other universities on combining certain aspects of other physics to design a model that provides a more realistic representation of the costal systems.’


Legacy software One thing that Mula-Valls stressed was that these collaborations mean that not everyone involved with the project has a wealth of HPC experience, and many projects deal with code that may be 20-30 years old. Mula-Valls said: ‘You can find routines in the


3D visualisation from the Caliope model forecasting European air quality.


➤these kinds of runs, especially an approaching hurricane,’ said Chen. He went on to explain that it is not just the


waves themselves that must be simulated but also a wave’s impact on the coast. Erosion, sediment transport, and coastal erosion caused by a hurricane must also be simulated. Chen concluded: ‘For impact studies, we


also have sediment transport and water quality models. Hurricanes can cause erosion to the coast, but they can also transport sediment and there can be some sediment deposition on the wetlands; so you must look at the overall impacts, which requires large computational resources.’ Finding these computational resources is not


always easy. Chen said that the LSU had been very lucky: it had got involved with HPC more than a decade ago, and currently has three large HPC clusters in addition to some several smaller systems. ‘We have a number of clusters here at LSU: our


latest is SuperMIKE2 and SuperMIC which is a Xeon Phi cluster; we also have QB2 which is a state wide resource.’


Collaboration across different disciplines At the BSC, Reyes is faces similar challenges. Although the BSC has one of the largest supercomputers in Europe his team still cannot get enough core hours to complete some of the largest simulations. Reyes said: ‘If we want to run them at very high resolution, we are talking – just for single simulation – resources in the region of 10-20 million hours, which is not something you get from one day to the next.’ Reyes was keen to stress that it is not just in the


quest for computational resources that he must collaborate with European partners. Tey must also collaborate just to get their models to run efficiently, because there are so many different


50 SCIENTIFIC COMPUTING WORLD


disciplines involved in this area of science, from physical scientists to computer scientists to climate experts. Reyes highlighted that it can be tough job to


get all these different experts together, but the BSC has worked hard to generate a community of researchers from different disciplines that can work effectively on a common goal. He said: ‘Getting all those experts next to the climate modellers is something unique. It is not something that you find in other weather research or climate research groups in Europe. It is not easy to bring together people with such a different range of profiles.’ Tese intricate soſtware models cannot be


developed without collaboration and this is not only between scientists of different back grounds but also between institutions whether through direct collaboration or building soſtware through open source initiatives.


Open Source aids collaboration Chen from LSU has found that open source models were the key to being able to integrate the different physical models needed to develop a better understanding of storm surge physics and its impact on the coastal communities. Chen said: ‘One example is that most models


do not consider the effect of wetlands, of vegetation, on the storm surge and waves. Most places have sandy beaches and only a small area has a lot of wetlands. Louisiana is different.’ Chen continued: ‘Te waves that are near the


coast are non-linear, they are very hard to predict the way that they interact with structures with coastal landscapes, forest and vegetation so we have to develop a model called Cafunwave which has the capability to simulate the waves near the coast. However at the same time it can simulate the storm surge conditions, combining them into one model.


code from the 1980s or the 1990s so, in some cases, it is really ancient code that one has to maintain. It can be difficult to work with these models. But bringing all these experts here can provide another point of view, and it can make the code development a lot easier.’ Reyes said: ‘What I want to convey is that this


is a community effort, and in that community we play a double role. One is to improve the science


WE IMPROVE THOSE MODELS BECAUSE THEY ARE OPEN SOURCE


that goes into the models, but also we increasingly play the role of being one of the few places that can help these scientists, the physical scientists, to improve the performance of their codes and to teach them what they are doing wrong.’ At the LSU, Chen has found a similar model


works for his research also. Chen said: ‘A typical model will have around ten students, some of whom are from engineering disciplines and then two or three from computer science. We work together as a team, but actually it is the students that are gaining that experience and collaborating to get a lot of things done quickly.’ Reyes said: ‘I think one of the problems that


has been overlooked in the past is how the users are going to interact with these very complex machines, and how they are going to run their experiments in an efficient way without wasting months trying to learn how to access that machine and how to get the data out of that machine.’ He concluded: ‘It is something where we really


want to spend a lot of effort, not just making our models 10 per cent faster on a specific architecture, but also how to make the work of the physical scientists much faster because this means money. We need solutions that are not just applicable to the BSC but applicable all across Europe.’ l


@scwmagazine l www.scientific-computing.com


Barcelona Supercomputing Centre /Google Earth


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