Numerical Advisory Solutions
GOTHIC Modeling

Conservation equations are solved for continuous liquid, vapor and any number of interacting droplet fields.
  • The balance equations are coupled by mechanistic models for interface mass, energy and momentum transfer that cover the entire flow regime from bubbly flow to film/drop flow, as well as single phase flows.
  • Inter-phase phenomena including:
    1. Condensation on drops, films and pools including non-condensing gas effects
    2. Evaporation
    3. Boiling and flashing
    4. Drop entrainment from films
    5. Drop deposition on walls and floors
    6. Ice formation and melting
  • The multiple field approach gives separate temperatures and velocities for each of the fields, allowing for thermal non-equilibrium, phase slip and countercurrent flow.
The models for the droplet field(s) are based on aerosol mechanics.
  • GOTHIC allows one or more droplet fields each with its own mass, momentum, and energy equations.
  • Each droplet field is assumed to have a log-normal size distribution with a variable geometric standard deviation.
  • GOTHIC models the interfield and intrafield drop agglomeration and the drop deposition rate from each field thereby allowing the distribution to change with time.
  • The inclusion of one or more separate drop fields allows GOTHIC to simulate problems that involve drops with widely varying drop size and helps address several important phenomena mechanistically, which would be otherwise treated empirically by a traditional system code.
The vapor field consists of both steam and any number of non-condensing gases.
  • A library of properties for nearly 50 different gases is available or the user may define any gas for which the appropriate properties are known.
  • The multi component gas field allows for tracking concentration of hazardous gases and chemicals.
Optional fields are available to represent:
  • Mist as part of the vapor field, which is needed to track very small water droplets that form when the atmosphere becomes super saturated with steam. This mist field has the same temperature and velocity as the vapor. As the mist field density increases the mist is converted into a droplet field.
  • Ice formation/melt including the effects of condensation and sublimation at the ice surface. This feature has been used to simulate ice condenser containments and to investigate the performance of some thermal hydraulic systems exposed to cold weather.
  • Liquid components (both solid particles and dissolved gases) in the liquid and droplet fields.
    1. Solid particles can be used to model insoluble fluids or solids, including the effects of settling, resuspension and transport of the suspended and settled material. Example applications include boron dilution, debris transport for GSI-191 or atmospheric dispersion of dust or ash including washout.
      Additional Information
    2. The dissolved gas includes the effect of absorption and dissolution, which can be important for water hammer applications.
  • Tracer elements (including radioactive decay and daughtering of nuclides) in the liquid, vapor and droplet fields as well as surfaces and filters. The capability allows GOTHIC to model fission product transport and release.
Fluid regions are represented by lumped parameter volumes (0-D) or subdivided volumes, where the volume can be subdivided in 1, 2 or 3 dimensions. A finite volume technique is used with cell volume and surface porosities used to model complex geometries.
  • 3D Rectangular Coordinates.
  • Based on Flow3D FAVOR (Fractional Area Volume Obstacle Representation) methodology.
  • Surfaces can be defined with slip or no slip conditions.
  • Porosity Factors and Hydraulic Diameters from defined obstacles (Blockages) and surface conditions.
For multi-dimensional geometries, GOTHIC includes:
  • Full treatment of the momentum transport terms.
  • Optional models for molecular and turbulent diffusion models in the liquid and vapor phases. A κ-ε turbulence model is used with options for non linear source terms.
  • 2nd order accurate advection schemes.
  • Turbulence and molecular diffusion allow GOTHIC to predict the transport of mass, momentum and energy due to turbulent shear and concentration gradients and the 2nd order accurate advection schemes minimize numerical diffusion.
GOTHIC includes an extensive set of models for operating equipment, including:
  • Pumps and fans,
  • Valves and doors,
  • Heat exchangers and fan coolers,
  • Vacuum breakers,
  • Spray nozzles,
  • Coolers and heaters,
  • Volumetric fans (annular fans, deck fans, etc.),
  • Hydrogen recombiners (forced and natural convection),
  • Ignitors (spark device used to ignite hydrogen burns),
  • Pressure relief valves (PRVs),
  • Filter and sump strainer,
  • Dryer/Demisters and
  • Charcoal filters
Thermal conductors are available for modeling the transient temperature distribution in structures (e.g., walls, pipes, equipment, etc.) and heat transfer from the surface to the fluid.
  • Includes models for fluid to solid heat transfer as well as thermal radiation exchange with other structures and with steam in the vapor phase.
  • One-dimensional objects (e.g., slab/wall, cylindrical tube and solid rod) with heat transfer to or from the fluid at the conductor surfaces and conduction through the thickness of the conductor.
  • One-dimensional thermal conductors can be combined into a conductor assembly to model two-dimensional conduction.
  • Flexible nodalization allows for multiple materials and heat generation to be considered.
  • GOTHIC offers user a selectable nodalization option that automatically determines the number and spacing of nodes through the thickness of the conductor that is required to achieve an accurate and converged solution.
  • Thermal conductor surface models using the Diffusion Layer Model (DLM) to predict the condensation rate of steam in the presence of a non-condensing gas.
GOTHIC also includes modeling capabilities for the following:
  • Hydrogen burn, including the ignition and propagation of a flame in a hydrogen/oxygen mixture.
  • Laminar and turbulent leakage models to predict flow through cracks.
  • Network nodes and links for modeling building ventilation or piping systems, where the flow is essentially single phase.
  • Point neutron kinetics models to predict time dependent neutron population as well as heat generation from decay of actinides and fission products.
Hydrogen Burn
Extensive control system, table function and trip capability
  • This feature can be used to modify nominal parameter values or dynamically control modeling elements based on predicted conditions.
  • This allows GOTHIC to emulate plant response and provides a great deal of flexibility for modeling.
Additional example animations: