fix visualizer in euler beam

Author: zhiminzhang0830

examples/euler_beam/euler_beam.py

@@ -111,8 +111,8 @@ def u_solution_func(out):
             visu_points,
             ("x",),
             {"u": lambda d: d["u"]},
-            1,
-            "result_u",
+            num_timestamps=1,
+            prefix="result_u",
         )
     }