MIKE 11 Default Values¶
In MIKE 11, a number of parameters can be supplied in the “Default Values” tab of the HD Parameters file. The subset of the parameters that are supported by MIKE 1D are described here. ALPHA Coefficient. This is the velocity distribution coefficient used in the momentum equation, see SectionA.2 Solving the Saint-Venant Equations (p. 285). The default value is 1.0. DELH Coefficient. DELH controls the depth and top elevation of the slot in low flow conditions. The slot is inserted at height DELH above the river bottom and extends to a depth 5 x DELH below this level. See Section A.4.6.2 Area preserving bottom slot (p. 312). The default value is 0.1 m. DELHS Coefficient. DELHS is used to prevent instabilities arising when the water surface gradient across a structure changes sign, see Chapter 6 on structures. It specifies the water level difference across a weir below which the flow description is linearised to obtain a stable solution. The default value is 0.01 m. DELTA Coefficient. A forward centring of the ∂h/∂x-term in the numerical scheme has a dissipating influence which can be demonstrated using the Taylor-series, see Section A.2.5 DELTA Coefficient (p. 303). The forward centring is automatically introduced into MIKE 11 where the flow has become supercritical.
The dissipative influence of the forward centring can be controlled by the user for sub-critical flows through the coefficient DELTA (0.5 <= d <= 1). A value of 0.5 (the default) has no dissipative effect, while a value of 1.0 has maximum influence.
Changing the value of DELTA from its default value should only be carried out when “short term” fluctuations are unimportant, as in the case of a wave with a period of several days or longer. FroudeExp. MIKE 1D offers two alternatives to the suppression of the convective terms in the Momentum equation for supercritical flow. If a negative value is entered for FroudeExp or FroudeMax (see below) then the default suppression is applied. FroudeExp is the exponential coefficient in the alternative suppression term. FroudeMax. FroudeMax is the value at which the suppression sets in. As above if this is set to a negative value the default suppression is applied. Inter1Max. This coefficient gives the maximum number of iterations permitted per time step to obtain a solution at a structure, see Section 6 Structures (p. 95). The default value is 10. NoITER. NoITER specifies the number of iterations used in each time step to obtain a solution. The default value is 1. See Section A.2 Solving the Saint-Venant Equations (p. 285). THETA. THETA is used in the discretisation of the momentum equation in the Fully Dynamic Wave Approximation (it is not used in the Fully Dynamic Higher Order Approximation). It can be used to dampen the instabilities from rapidly varying discharges and discharge reversals. The default value is 1.0 See Section Fully dynamic, MIKE 11 (p. 290). Zeta Min. The headloss over structures is calculated according to Section 6 Structures (p. 95). The user has the option of specifying a minimum headloss, Zeta Min which is the lowest acceptable value of the sum of the headloss factors.