//connect to server, substitute the server/instance name with yours as necessary
Server s=new Server();
s.Connect(".\\TABULAR");

//navigate to the Demographic Facts measure group, we must add the partition to the measure group
Database db = s.Databases.FindByName("hans_rosling_project");
DataSourceView dsv = db.DataSourceViews.FindByName("Sandbox");
Cube c = db.Cubes.FindByName("Model");
MeasureGroup mg = c.MeasureGroups.FindByName("Demographic Facts");

//define the new partition
Partition p = mg.Partitions.Add("Partition 1800");
p.Source = new QueryBinding(dsv.DataSourceID, "SELECT [dbo].[DemographicFacts].* FROM [dbo].[DemographicFacts] WHERE ([Year] = 1800)");
p.StorageMode = StorageMode.InMemory;
 
//update the server with the new partition, process it, and disconnect
p.Update(UpdateOptions.ExpandFull);
p.Process(ProcessType.ProcessFull);
s.Disconnect();