text: # Copyright 2020 NREL
  
  # Licensed under the Apache License, Version 2.0 (the "License"); you may not
  # use this file except in compliance with the License. You may obtain a copy of
  # the License at http://www.apache.org/licenses/LICENSE-2.0
  
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  # WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  # License for the specific language governing permissions and limitations under
  # the License.
  
  from .base_wake_combination import WakeCombination
  from ...utilities import setup_logger
  
  
  class FLS(WakeCombination):
      """
      FLS uses freestream linear superposition to apply the wake velocity
      deficits to the freestream flow field.
      """
      def __init__(self):
          super().__init__()
          self.logger = setup_logger(name=__name__)
          self.model_string = "fls"
  
      def function(self, u_field, u_wake):
          """
          Combines the base flow field with the velocity deficits
          using freestream linear superpostion. In other words, the wake
          field and base fields are simply added together.
  
          Args:
              u_field (np.array): The base flow field.
              u_wake (np.array): The wake to apply to the base flow field.
  
          Returns:
              np.array: The resulting flow field after applying the wake to the
                  base.
          """
          return u_field + u_wake