Dynamic simulation of ship-system thermal load management

Anticipating highly dynamic and reconfigurable future ships, the US Navy has sought to develop modeling and simulation capabilities for transient, electrical-mechanical-thermal, shipboard interactions at the system level. In support of this work, an object-oriented Dynamic Thermal Modeling and Simulation (DTMS) framework written in C++ has been in use for several years. As reported in this paper, DTMS has recently been augmented to model two-phase flow and heat transfer for simulation of a shipboard vapor-compression chiller and its attendant loads. A controls methodology has been implemented in the heat exchanger models to monitor their relevant states, chilled water enthalpy, and refrigerant liquid level. These heat exchangers have been integrated with a heavily-customizable, centrifugal compressor model focused on required power input rather than the detailed dynamics of fluid compression. The heat exchangers and centrifugal compressor, along with a model of a thermostatic expansion valve, have been used to assemble a simulation of a 200-ton marine chiller predicated on baseline parameters for the Navy´s current destroyer. This chiller has been connected with thermal loads of varying magnitude to demonstrate controller response during full-load and part-load operation. The final simulation reported here consists of 22 thermal loads ranging from 8 to 256 kW with chilled water supplied by two chillers. Results are compared with both steady-state-predicted values and previous dynamic simulations using commercial software.