Mr. Matsuyama formerly worked at Kumagai Gumi before starting WindStyle in 2003. WindStyle has grown rapidly, and the company has undertaken nearly three hundred projects over this time period. Engineers at WindStyle perform CFD simulations using scSTREAM and also conduct wind tunnel experiments to validate solutions before making recommendations to their customers.

　Many of WindStyle's projects involve evaluating wind flow around high-rise buildings prior to and during construction. The evaluations focus on predicting wind hazards, i.e. assessing how strong wind gust can blow things down, potentially even people, under the most severe conditions. While building codes do not require these assessments, building owners often consult with WindStyle after concerns are expressed by people and workers at the sites.

　More and more building owners are realizing the importance of conducting wind engineering analyses prior to construction. While some major construction companies are starting to consider wind hazards for their larger projects, WindStyle is one of the few consulting companies that specialize in this area. As more people pay attention to their overall living environments, wind engineering is emerging as a critical consideration.
 

Field Research to Collect Model Data

　When studying wind hazards, whether using CFD or a wind tunnel, three-dimensional geometry data is needed to construct a model. At WindStyle, a model consists of the building of interest and the surrounding buildings and features within a 300-400m (0.2 - 0.25 mile) radius. For a new construction site, this data is often provided by the customer. Unfortunately, the customer data is frequently only two-dimensional data. Engineers at WindStyle often go to the field site to obtain the information needed to describe the three-dimensional geometry. They also use available aerial surveys and photographs. With this data, a 3D wind engineering model is constructed in SketchUp.

　For wind tunnel experiments, 3D data is shaped into a 1/300 or 1/400 scale model using plastic casting 3D printers and/or by hand. Wind direction and velocity are measured using small sensors located at the points of interest.
 

Process for CFD Simulation

　For CFD simulations using scSTREAM, the CAD geometry data is output in STL format and read into scSTREAM where the mesh is generated and boundary conditions defined. Mesh size in the center of the model, where maximum resolution is needed, is on the order of 50cm (20 in). In the surroundings the mesh size is as large as 5m (16.5 ft). A typical model will contain ten to twenty million elements. Calculations are run using at least six computer cores in parallel. A set of simulations consists of running 32 different cases for each construction site, which covers sixteen different wind directions and simulates conditions before and after construction or construction modifications. Fewer simulations can be run when evaluating modifications if issues only arise for specific wind directions.

　After obtaining the baseline simulation results, the architects, simulation and construction teams discuss countermeasures against potential wind hazards. These can consist of planting roadside trees or shifting/modifying the shape of a planned building. Another set of simulations is run to confirm the results before the recommendations are provided to the customer.

　The Murakami Criteria are used to determine whether local wind conditions are severe enough to be a problem. The criteria rank the wind conditions in a local region by the frequency and strength of the wind gusts. The ranking is a sensory index based on wind engineering research. As the index increases, wind conditions become more severe. Threshold values based on experimental research are used to classify the severity of the conditions. WindStyle uses calculations from scSTREAM to evaluate wind conditions. They are able to use animations to visualize the air flow and show why the problems exist and how they can be corrected.  ​
 

Making Full Use of the Software

　When Mr. Matsuyama founded WindStyle, he evaluated several different CFD tools. He chose Cradle scSTREAM largely for its customizability. Mr. Matsuyama notes, "Because it [scSTREAM] accepted text-based inputs for boundary conditions, it made customization very easy. After a while, it was updated to become also compatible with VBScript, which made customization even easier."

　One of the most important steps when performing CFD simulations using scSTREAM is precise control and adjustment of the geometry data. This can be a tedious and timeconsuming task, however, it must be performed in great detail because minimal differences in geometry can have very large effects on the outcome. Hence, this step is not trivial but must be critically tracked throughout the simulation process.

　Mr. Matsuyama also has interesting thoughts about the importance of continually refining the mesh to improve accuracy. He argues that the methods used to assess simulation results and to translate the knowledge into improved designs are more important. "CFD results are more or less average values, and they do have a margin of error. In fact, we could make better use of the results by taking characteristics of the errors into account". This is a different perspective compared to the more traditional view of trying to eliminate all sources of error and to spend enormous amounts of time and effort trying to make the simulation results as accurate as possible.