Systems and devices configured to reduce thermal design clearances (e.g., between stationary nozzles connected to the inner casing and rotor buckets connected to the rotor) in turbines by actively controlling casing movements and/or locations during turbine operation are disclosed. In one embodiment, a clearance management system includes: a first inner casing support arm shaped to connect to an inner casing of a turbine and extend through an outer casing of the turbine; a seal system disposed about the first inner casing support arm and configured to connect to the outer casing; and a set of actuators disposed on a turbine foundation of the turbine and connected to the first inner casing support arm, the set of actuators located external to the outer casing and configured to adjust a position of the inner casing relative to the outer casing via manipulation of the first inner casing support arm.