cantera/include/cantera/kinetics/Falloff.h

#ifndef CT_FALLOFF_H
#define CT_FALLOFF_H

#include "cantera/kinetics/reaction_defs.h"

namespace Cantera
{

/**
 *  @defgroup falloffGroup  Falloff Parameterizations This section describes the
 *  parameterizations used to describe the fall-off in reaction rate constants
 *  due to intermolecular energy transfer.
 *  @ingroup chemkinetics
 */

/**
 * Base class for falloff function calculators. Each instance of a subclass of
 * Falloff computes one falloff function. This base class implements the
 * trivial falloff function F = 1.0.
 *
 * @ingroup falloffGroup
 */
class Falloff
{
public:
    Falloff() {}
    virtual ~Falloff() {}

    /**
     * Initialize. Must be called before any other method is invoked.
     *
     * @param c Vector of coefficients of the parameterization. The number and
     *     meaning of these coefficients is subclass-dependent.
     */
    virtual void init(const vector_fp& c);

    /**
     * Update the temperature-dependent portions of the falloff function, if
     * any, and store them in the 'work' array. If not overloaded, the default
     * behavior is to do nothing.
     * @param T Temperature [K].
     * @param work storage space for intermediate results.
     */
    virtual void updateTemp(doublereal T, doublereal* work) const {}

    /**
     * The falloff function. This is defined so that the rate coefficient is
     *
     * \f[  k = F(Pr)\frac{Pr}{1 + Pr}. \f]
     *
     * Here \f$ Pr \f$ is the reduced pressure, defined by
     *
     * \f[
     * Pr = \frac{k_0 [M]}{k_\infty}.
     * \f]
     *
     * @param pr reduced pressure (dimensionless).
     * @param work array of size workSize() containing cached
     *             temperature-dependent intermediate results from a prior call
     *             to updateTemp.
     *
     * @return Returns the value of the falloff function \f$ F \f$ defined above
     */
    virtual doublereal F(doublereal pr, const doublereal* work) const {
        return 1.0;
    }

    //! The size of the work array required.
    virtual size_t workSize() {
        return 0;
    }

    //! Return an integer representing the type of the Falloff parameterization.
    virtual int getType() const {
        return SIMPLE_FALLOFF;
    }

    //! Returns the number of parameters used by this parameterization. The
    //! values of these parameters can be obtained from getParameters().
    virtual size_t nParameters() const {
        return 0;
    }

    //! Get the values of the parameters for this object. *params* must be an
    //! array of at least nParameters() elements.
    virtual void getParameters(double* params) const {}
};


//! The 3- or 4-parameter Troe falloff parameterization.
/*!
 * The falloff function defines the value of \f$ F \f$ in the following
 * rate expression
 *
 *  \f[ k = k_{\infty} \left( \frac{P_r}{1 + P_r} \right) F \f]
 *  where
 *  \f[ P_r = \frac{k_0 [M]}{k_{\infty}} \f]
 *
 * This parameterization is defined by
 *
 * \f[ F = F_{cent}^{1/(1 + f_1^2)} \f]
 *    where
 * \f[ F_{cent} = (1 - A)\exp(-T/T_3) + A \exp(-T/T_1) + \exp(-T_2/T) \f]
 *
 * \f[ f_1 = (\log_{10} P_r + C) /
 *              \left(N - 0.14 (\log_{10} P_r + C)\right) \f]
 *
 * \f[ C = -0.4 - 0.67 \log_{10} F_{cent} \f]
 *
 * \f[ N = 0.75 - 1.27 \log_{10} F_{cent} \f]
 *
 *  - If \f$ T_3 \f$ is zero, then the corresponding term is set to zero.
 *  - If \f$ T_1 \f$ is zero, then the corresponding term is set to zero.
 *  - If \f$ T_2 \f$ is zero, then the corresponding term is set to zero.
 *
 * @ingroup falloffGroup
 */
class Troe : public Falloff
{
public:
    //! Constructor
    Troe() : m_a(0.0), m_rt3(0.0), m_rt1(0.0), m_t2(0.0) {}

    //! Initialization of the object
    /*!
     * @param c Vector of three or four doubles: The doubles are the parameters,
     *          a, T_3, T_1, and (optionally) T_2 of the Troe parameterization
     */
    virtual void init(const vector_fp& c);

    //! Update the temperature parameters in the representation
    /*!
     *   @param T         Temperature (Kelvin)
     *   @param work      Vector of working space, length 1, representing the
     *                    temperature-dependent part of the parameterization.
     */
    virtual void updateTemp(doublereal T, doublereal* work) const;

    virtual doublereal F(doublereal pr, const doublereal* work) const;

    virtual size_t workSize() {
        return 1;
    }

    virtual int getType() const {
        return TROE_FALLOFF;
    }

    virtual size_t nParameters() const {
        return 4;
    }

    //! Sets params to contain, in order, \f[ (A, T_3, T_1, T_2) \f]
    virtual void getParameters(double* params) const;

protected:
    //! parameter a in the 4-parameter Troe falloff function. Dimensionless
    doublereal m_a;

    //! parameter 1/T_3 in the 4-parameter Troe falloff function. [K^-1]
    doublereal m_rt3;

    //! parameter 1/T_1 in the 4-parameter Troe falloff function. [K^-1]
    doublereal m_rt1;

    //! parameter T_2 in the 4-parameter Troe falloff function. [K]
    doublereal m_t2;
};

//! The SRI falloff function
/*!
 * The falloff function defines the value of \f$ F \f$ in the following
 * rate expression
 *
 *  \f[ k = k_{\infty} \left( \frac{P_r}{1 + P_r} \right) F \f]
 *  where
 *  \f[ P_r = \frac{k_0 [M]}{k_{\infty}} \f]
 *
 *  \f[ F = {\left( a \; exp(\frac{-b}{T}) + exp(\frac{-T}{c})\right)}^n
 *              \;  d \; exp(\frac{-e}{T}) \f]
 *      where
 *  \f[ n = \frac{1.0}{1.0 + {\log_{10} P_r}^2} \f]
 *
 *  \f$ c \f$ s required to greater than or equal to zero. If it is zero, then
 *  the corresponding term is set to zero.
 *
 *  \f$ d \f$ is required to be greater than zero.
 *
 * @ingroup falloffGroup
 */
class SRI : public Falloff
{
public:
    //! Constructor
    SRI() : m_a(-1.0), m_b(-1.0), m_c(-1.0), m_d(-1.0), m_e(-1.0) {}

    //! Initialization of the object
    /*!
     * @param c Vector of three or five doubles: The doubles are the parameters,
     *          a, b, c, d (optional; default 1.0), and e (optional; default
     *          0.0) of the SRI parameterization
     */
    virtual void init(const vector_fp& c);

    //! Update the temperature parameters in the representation
    /*!
     *   @param T         Temperature (Kelvin)
     *   @param work      Vector of working space, length 2, representing the
     *                    temperature-dependent part of the parameterization.
     */
    virtual void updateTemp(doublereal T, doublereal* work) const;

    virtual doublereal F(doublereal pr, const doublereal* work) const;

    virtual size_t workSize() {
        return 2;
    }

    virtual int getType() const {
        return SRI_FALLOFF;
    }

    virtual size_t nParameters() const {
        return 5;
    }

    //! Sets params to contain, in order, \f[ (a, b, c, d, e) \f]
    virtual void getParameters(double* params) const;

protected:
    //! parameter a in the 5-parameter SRI falloff function. Dimensionless.
    doublereal m_a;

    //! parameter b in the 5-parameter SRI falloff function. [K]
    doublereal m_b;

    //! parameter c in the 5-parameter SRI falloff function. [K]
    doublereal m_c;

    //! parameter d in the 5-parameter SRI falloff function. Dimensionless.
    doublereal m_d;

    //! parameter d in the 5-parameter SRI falloff function. Dimensionless.
    doublereal m_e;
};

}

#endif