source: issm/trunk/src/c/classes/Loads/Riftfront.cpp@ 26744

/*!\file Riftfront.cpp
 * \brief: implementation of the Riftfront object
 */

/*Headers:*/
/*{{{*/
#ifdef HAVE_CONFIG_H
        #include <config.h>
#else
#error "Cannot compile with HAVE_CONFIG_H symbol! run configure first!"
#endif

#include "shared/shared.h"
#include "modules/ModelProcessorx/ModelProcessorx.h"
#include "../classes.h"
/*}}}*/

/*Element macros*/
#define NUMVERTICES 2

/*Riftfront constructors and destructor*/
Riftfront::Riftfront(){/*{{{*/
        this->parameters=NULL;
        this->hnodes=NULL;
        this->hvertices=NULL;
        this->helements=NULL;
        this->nodes=NULL;
        this->vertices=NULL;
        this->elements=NULL;
}
/*}}}*/
Riftfront::Riftfront(int riftfront_id,int i, IoModel* iomodel){/*{{{*/

        /*data: */
        const int RIFTINFOSIZE = 12;
        int    riftfront_node_ids[2];
        int    riftfront_elem_ids[2];
        IssmDouble riftfront_friction;
        IssmDouble riftfront_fractionincrement;
        int    penalty_lock;

        /*intermediary: */
        int el1    ,el2;
        int node1  ,node2;

        /*Fetch parameters: */
        iomodel->FindConstant(&penalty_lock,"md.stressbalance.rift_penalty_lock");

        /*Ok, retrieve all the data needed to add a penalty between the two nodes: */
        el1=reCast<int,IssmDouble>(*(iomodel->Data("md.rifts.riftstruct")+RIFTINFOSIZE*i+2));
        el2=reCast<int,IssmDouble>(*(iomodel->Data("md.rifts.riftstruct")+RIFTINFOSIZE*i+3)) ;

        node1=reCast<int,IssmDouble>(*(iomodel->Data("md.rifts.riftstruct")+RIFTINFOSIZE*i+0));
        node2=reCast<int,IssmDouble>(*(iomodel->Data("md.rifts.riftstruct")+RIFTINFOSIZE*i+1));

        /*id: */
        this->id=riftfront_id;

        /*hooks: */
        riftfront_node_ids[0]=node1;
        riftfront_node_ids[1]=node2;
        riftfront_elem_ids[0]=el1;
        riftfront_elem_ids[1]=el2;

        /*Hooks: */
        this->hnodes=new Hook(riftfront_node_ids,2);
        this->hvertices=new Hook(riftfront_node_ids,2);
        this->helements=new Hook(riftfront_elem_ids,2);

        /*computational parameters: */
        this->active=0;
        this->frozen=0;
        this->counter=0;
        this->prestable=0;
        this->penalty_lock=penalty_lock;
        this->material_converged=0;
        this->normal[0]=*(iomodel->Data("md.rifts.riftstruct")+RIFTINFOSIZE*i+4);
        this->normal[1]=*(iomodel->Data("md.rifts.riftstruct")+RIFTINFOSIZE*i+5);
        this->length=*(iomodel->Data("md.rifts.riftstruct")+RIFTINFOSIZE*i+6);
        this->fraction=*(iomodel->Data("md.rifts.riftstruct")+RIFTINFOSIZE*i+9);
        this->state=reCast<int,IssmDouble>(*(iomodel->Data("md.rifts.riftstruct")+RIFTINFOSIZE*i+11));

        //intialize properties
        this->type=SegmentRiftfrontEnum;
        this->fill = IoRiftfillToEnum(reCast<int,IssmDouble>(*(iomodel->Data("md.rifts.riftstruct")+RIFTINFOSIZE*i+7)));
        this->friction=*(iomodel->Data("md.rifts.riftstruct")+RIFTINFOSIZE*i+8);
        this->fractionincrement=*(iomodel->Data("md.rifts.riftstruct")+RIFTINFOSIZE*i+10);
        this->shelf=reCast<bool,IssmDouble>(iomodel->Data("md.mask.ocean_levelset")[node1-1]<0.);

        //parameters and hooked fields: we still can't point to them, they may not even exist. Configure will handle this.
        this->parameters=NULL;
        this->nodes= NULL;
        this->vertices= NULL;
        this->elements= NULL;

}
/*}}}*/
Riftfront::~Riftfront(){/*{{{*/
        this->parameters=NULL;
        delete hnodes;
        delete hvertices;
        delete helements;
}
/*}}}*/

/*Object virtual functions definitions:*/
Object* Riftfront::copy() {/*{{{*/

        Riftfront* riftfront=NULL;

        riftfront=new Riftfront();

        /*copy fields: */
        riftfront->id=this->id;
        riftfront->type=this->type;
        riftfront->fill=this->fill;
        riftfront->friction=this->friction;
        riftfront->fractionincrement=this->fractionincrement;
        riftfront->shelf=this->shelf;

        /*point parameters: */
        riftfront->parameters=this->parameters;

        /*now deal with hooks and objects: */
        riftfront->hnodes=(Hook*)this->hnodes->copy();
        riftfront->hvertices=(Hook*)this->hvertices->copy();
        riftfront->helements=(Hook*)this->helements->copy();

        /*corresponding fields*/
        riftfront->nodes   =(Node**)riftfront->hnodes->deliverp();
        riftfront->vertices=(Vertex**)riftfront->hvertices->deliverp();
        riftfront->elements=(Element**)riftfront->helements->deliverp();

        /*internal data: */
        riftfront->penalty_lock=this->penalty_lock;
        riftfront->active=this->active;
        riftfront->frozen=this->frozen;
        riftfront->state=this->state;
        riftfront->counter=this->counter;
        riftfront->prestable=this->prestable;
        riftfront->material_converged=this->material_converged;
        riftfront->normal[0]=this->normal[0];
        riftfront->normal[1]=this->normal[1];
        riftfront->length=this->length;
        riftfront->fraction=this->fraction;

        return riftfront;

}
/*}}}*/
void    Riftfront::DeepEcho(void){/*{{{*/

        _printf_("Riftfront:\n");
        _printf_("   id: " << id << "\n");
        hnodes->DeepEcho();
        hvertices->DeepEcho();
        helements->DeepEcho();
        _printf_("   parameters\n");
        if(parameters)parameters->DeepEcho();
}
/*}}}*/
void    Riftfront::Echo(void){/*{{{*/

        _printf_("Riftfront:\n");
        _printf_("   id: " << id << "\n");
        _printf_("   hnodes: " << hnodes << "\n");
        _printf_("   hvertices: " << hvertices << "\n");
        _printf_("   helements: " << helements << "\n");
        _printf_("   parameters: " << parameters << "\n");
        _printf_("   internal parameters: \n");
        _printf_("   normal: " << normal[0] << "|" << normal[1] << "\n");
        _printf_("   length: " << length << "\n");
        _printf_("   penalty_lock: " << penalty_lock << "\n");
        _printf_("   active: " <<(active ? "true":"false") << "\n");
        _printf_("   counter: " << counter << "\n");
        _printf_("   prestable: " << (prestable ? "true":"false") << "\n");
        _printf_("   material_converged: " << (material_converged ? "true":"false") << "\n");
        _printf_("   fill: " << fill << "\n");
        _printf_("   friction: " << friction << "\n");
        _printf_("   fraction: " << fraction << "\n");
        _printf_("   fractionincrement: " << fractionincrement << "\n");
        _printf_("   state: " << state << "\n");
        _printf_("   frozen: " << (frozen ? "true":"false") << "\n");

}
/*}}}*/
int     Riftfront::Id(void){ return id; }/*{{{*/
/*}}}*/
void    Riftfront::Marshall(MarshallHandle* marshallhandle){ /*{{{*/

        _assert_(this);

        /*ok, marshall operations: */
        int object_enum = RiftfrontEnum;
        marshallhandle->call(object_enum);
        marshallhandle->call(this->id);
        marshallhandle->call(this->type);
        marshallhandle->call(this->fill);
        marshallhandle->call(this->friction);
        marshallhandle->call(this->fractionincrement);
        marshallhandle->call(this->shelf);

        if(marshallhandle->OperationNumber()==MARSHALLING_LOAD){
                this->hnodes     = new Hook();
                this->hvertices  = new Hook();
                this->helements  = new Hook();
        }

        this->hnodes->Marshall(marshallhandle);
        this->hvertices->Marshall(marshallhandle);
        this->helements->Marshall(marshallhandle);

        /*corresponding fields*/
        nodes     =(Node**)this->hnodes->deliverp();
        vertices  =(Vertex**)this->hvertices->deliverp();
        elements  =(Element**)this->helements->deliverp();

        marshallhandle->call(this->penalty_lock);
        marshallhandle->call(this->active);
        marshallhandle->call(this->frozen);
        marshallhandle->call(this->state);
        marshallhandle->call(this->counter);
        marshallhandle->call(this->prestable);
        marshallhandle->call(this->material_converged);
        marshallhandle->call(this->normal[0]);
        marshallhandle->call(this->normal[1]);
        marshallhandle->call(this->length);
        marshallhandle->call(this->fraction);
}/*}}}*/
int     Riftfront::ObjectEnum(void){/*{{{*/

        return RiftfrontEnum;

}
/*}}}*/

/*Update virtual functions definitions:*/
void  Riftfront::InputUpdateFromConstant(bool constant,int name){/*{{{*/
}
/*}}}*/
void  Riftfront::InputUpdateFromConstant(IssmDouble constant,int name){/*{{{*/

}
/*}}}*/
void  Riftfront::InputUpdateFromVector(IssmDouble* vector, int name, int type){/*{{{*/

        /*Nothing to update*/

}
/*}}}*/

/*Load virtual functions definitions:*/
void  Riftfront::Configure(Elements* elementsin,Loads* loadsin,Nodes* nodesin,Vertices* verticesin,Materials* materialsin,Parameters* parametersin){/*{{{*/     

        /*Take care of hooking up all objects for this element, ie links the objects in the hooks to their respective 
         * datasets, using internal ids and offsets hidden in hooks: */
        hnodes->configure(nodesin);
        hvertices->configure(verticesin);
        helements->configure(elementsin);

        /*Initialize hooked fields*/
        this->nodes   =(Node**)hnodes->deliverp();
        this->vertices=(Vertex**)hvertices->deliverp();
        this->elements=(Element**)helements->deliverp();

        /*point parameters to real dataset: */
        this->parameters=parametersin;

}
/*}}}*/
void  Riftfront::CreateKMatrix(Matrix<IssmDouble>* Kff, Matrix<IssmDouble>* Kfs){/*{{{*/
        /*do nothing: */
        return;
}
/*}}}*/
void  Riftfront::CreatePVector(Vector<IssmDouble>* pf){/*{{{*/
        /*do nothing: */
        return;
}
/*}}}*/
void  Riftfront::GetNodesLidList(int* lidlist){/*{{{*/

        _assert_(lidlist);
        _assert_(nodes);

        for(int i=0;i<NUMVERTICES;i++) lidlist[i]=nodes[i]->Lid();
}
/*}}}*/
void  Riftfront::GetNodesSidList(int* sidlist){/*{{{*/

        _assert_(sidlist);
        _assert_(nodes);

        for(int i=0;i<NUMVERTICES;i++) sidlist[i]=nodes[i]->Sid();
}
/*}}}*/
int   Riftfront::GetNumberOfNodes(void){/*{{{*/

        return NUMVERTICES;
}
/*}}}*/
bool  Riftfront::IsPenalty(void){/*{{{*/
        return true;
}
/*}}}*/
void  Riftfront::PenaltyCreateKMatrix(Matrix<IssmDouble>* Kff, Matrix<IssmDouble>* Kfs,IssmDouble kmax){/*{{{*/

        /*Retrieve parameters: */
        ElementMatrix* Ke=NULL;
        int analysis_type;
        this->parameters->FindParam(&analysis_type,AnalysisTypeEnum);

        switch(analysis_type){
                case StressbalanceAnalysisEnum:
                        Ke=PenaltyCreateKMatrixStressbalanceHoriz(kmax);
                        break;
                case AdjointHorizAnalysisEnum:
                        Ke=PenaltyCreateKMatrixStressbalanceHoriz(kmax);
                        break;
                default:
                        _error_("analysis " << analysis_type << " (" << EnumToStringx(analysis_type) << ") not supported yet");
        }

        /*Add to global Vector*/
        if(Ke){
                Ke->AddToGlobal(Kff,Kfs);
                delete Ke;
        }
}
/*}}}*/
void  Riftfront::PenaltyCreatePVector(Vector<IssmDouble>* pf,IssmDouble kmax){/*{{{*/

        /*Retrieve parameters: */
        ElementVector* pe=NULL;
        int analysis_type;
        this->parameters->FindParam(&analysis_type,AnalysisTypeEnum);

        switch(analysis_type){
                case StressbalanceAnalysisEnum:
                        pe=PenaltyCreatePVectorStressbalanceHoriz(kmax);
                        break;
                case AdjointHorizAnalysisEnum:
                        /*No penalty applied on load vector*/
                        break;
                default:
                        _error_("analysis " << analysis_type << " (" << EnumToStringx(analysis_type) << ") not supported yet");
        }

        /*Add to global Vector*/
        if(pe){
                pe->AddToGlobal(pf);
                delete pe;
        }
}
/*}}}*/
void  Riftfront::ResetHooks(){/*{{{*/

        this->nodes=NULL;
        this->vertices=NULL;
        this->elements=NULL;
        this->parameters=NULL;

        /*Get Element type*/
        this->hnodes->reset();
        this->hvertices->reset();
        this->helements->reset();

}
/*}}}*/
void  Riftfront::SetCurrentConfiguration(Elements* elementsin,Loads* loadsin,Nodes* nodesin,Vertices* verticesin,Materials* materialsin,Parameters* parametersin){/*{{{*/

}
/*}}}*/
void  Riftfront::SetwiseNodeConnectivity(int* pd_nz,int* po_nz,Node* node,bool* flags,int* flagsindices,int* flagsindices_counter,int set1_enum,int set2_enum){/*{{{*/

        /*Output */
        int d_nz = 0;
        int o_nz = 0;

        /*Loop over all nodes*/
        for(int i=0;i<NUMVERTICES;i++){

                if(!flags[this->nodes[i]->Lid()]){

                        /*flag current node so that no other element processes it*/
                        flags[this->nodes[i]->Lid()]=true;

                        flagsindices[flagsindices_counter[0]]=this->nodes[i]->Lid();
                        flagsindices_counter[0]++;

                        /*if node is clone, we have an off-diagonal non-zero, else it is a diagonal non-zero*/
                        switch(set2_enum){
                                case FsetEnum:
                                        if(nodes[i]->FSize()){
                                                if(this->nodes[i]->IsClone())
                                                 o_nz += 1;
                                                else
                                                 d_nz += 1;
                                        }
                                        break;
                                case GsetEnum:
                                        if(nodes[i]->gsize){
                                                if(this->nodes[i]->IsClone())
                                                 o_nz += 1;
                                                else
                                                 d_nz += 1;
                                        }
                                        break;
                                case SsetEnum:
                                        if(nodes[i]->SSize()){
                                                if(this->nodes[i]->IsClone())
                                                 o_nz += 1;
                                                else
                                                 d_nz += 1;
                                        }
                                        break;
                                default: _error_("not supported");
                        }
                }
        }

        /*Assign output pointers: */
        *pd_nz=d_nz;
        *po_nz=o_nz;
}
/*}}}*/

/*Riftfront numerics*/
ElementMatrix* Riftfront::PenaltyCreateKMatrixStressbalanceHoriz(IssmDouble kmax){/*{{{*/

        const int   numdof = 2*NUMVERTICES;
        IssmDouble  thickness;
        IssmDouble  h[2];
        IssmDouble  penalty_offset;

        /*enum of element? */
        if(elements[0]->ObjectEnum()!=TriaEnum)_error_("only Tria element allowed for Riftfront load!");
        Tria* tria1=(Tria*)elements[0];
        Tria* tria2=(Tria*)elements[1];

        /*Initialize Element Matrix*/
        if(!this->active) return NULL;
        ElementMatrix* Ke=new ElementMatrix(nodes,NUMVERTICES,this->parameters);

        /*Get some parameters: */
        this->parameters->FindParam(&penalty_offset,StressbalancePenaltyFactorEnum);
        tria1->GetInputValue(&h[0],vertices[0],ThicknessEnum);
        tria2->GetInputValue(&h[1],vertices[1],ThicknessEnum);
        if (h[0]!=h[1])_error_("different thicknesses not supported for rift fronts");
        thickness=h[0];

        /*There is contact, we need to constrain the normal velocities (zero penetration), and the 
         *contact slip friction. */

        /*From Peter Wriggers book (Computational Contact Mechanics, p191): */
        Ke->values[0*numdof+0]+= +pow(normal[0],2)*kmax*pow(10,penalty_offset);
        Ke->values[0*numdof+1]+= +normal[0]*normal[1]*kmax*pow(10,penalty_offset);
        Ke->values[0*numdof+2]+= -pow(normal[0],2)*kmax*pow(10,penalty_offset);
        Ke->values[0*numdof+3]+= -normal[0]*normal[1]*kmax*pow(10,penalty_offset);

        Ke->values[1*numdof+0]+= +normal[0]*normal[1]*kmax*pow(10,penalty_offset);
        Ke->values[1*numdof+1]+= +pow(normal[1],2)*kmax*pow(10,penalty_offset);
        Ke->values[1*numdof+2]+= -normal[0]*normal[1]*kmax*pow(10,penalty_offset);
        Ke->values[1*numdof+3]+= -pow(normal[1],2)*kmax*pow(10,penalty_offset);

        Ke->values[2*numdof+0]+= -pow(normal[0],2)*kmax*pow(10,penalty_offset);
        Ke->values[2*numdof+1]+= -normal[0]*normal[1]*kmax*pow(10,penalty_offset);
        Ke->values[2*numdof+2]+= +pow(normal[0],2)*kmax*pow(10,penalty_offset);
        Ke->values[2*numdof+3]+= +normal[0]*normal[1]*kmax*pow(10,penalty_offset);

        Ke->values[3*numdof+0]+= -normal[0]*normal[1]*kmax*pow(10,penalty_offset);
        Ke->values[3*numdof+1]+= -pow(normal[1],2)*kmax*pow(10,penalty_offset);
        Ke->values[3*numdof+2]+= +normal[0]*normal[1]*kmax*pow(10,penalty_offset);
        Ke->values[3*numdof+3]+= +pow(normal[1],2)*kmax*pow(10,penalty_offset);

        /*Now take care of the friction: of type sigma=frictiontangent_velocity2-tangent_velocity1)*/

        Ke->values[0*numdof+0]+= +pow(normal[1],2)*thickness*length*friction;
        Ke->values[0*numdof+1]+= -normal[0]*normal[1]*thickness*length*friction;
        Ke->values[0*numdof+2]+= -pow(normal[1],2)*thickness*length*friction;
        Ke->values[0*numdof+3]+= +normal[0]*normal[1]*thickness*length*friction;

        Ke->values[1*numdof+0]+= -normal[0]*normal[1]*thickness*length*friction;
        Ke->values[1*numdof+1]+= +pow(normal[0],2)*thickness*length*friction;
        Ke->values[1*numdof+2]+= +normal[0]*normal[1]*thickness*length*friction;
        Ke->values[1*numdof+3]+= -pow(normal[0],2)*thickness*length*friction;

        Ke->values[2*numdof+0]+= -pow(normal[1],2)*thickness*length*friction;
        Ke->values[2*numdof+1]+= +normal[0]*normal[1]*thickness*length*friction;
        Ke->values[2*numdof+2]+= +pow(normal[1],2)*thickness*length*friction;
        Ke->values[2*numdof+3]+= -normal[0]*normal[1]*thickness*length*friction;

        Ke->values[3*numdof+0]+= +normal[0]*normal[1]*thickness*length*friction;
        Ke->values[3*numdof+1]+= -pow(normal[0],2)*thickness*length*friction;
        Ke->values[3*numdof+2]+= -normal[0]*normal[1]*thickness*length*friction;
        Ke->values[3*numdof+3]+= +pow(normal[0],2)*thickness*length*friction;

        /*Clean up and return*/
        return Ke;
}
/*}}}*/
ElementVector* Riftfront::PenaltyCreatePVectorStressbalanceHoriz(IssmDouble kmax){/*{{{*/

        int        j;
        IssmDouble rho_ice;
        IssmDouble rho_water;
        IssmDouble gravity;
        IssmDouble thickness;
        IssmDouble h[2];
        IssmDouble bed;
        IssmDouble b[2];
        IssmDouble pressure;
        IssmDouble pressure_litho;
        IssmDouble pressure_air;
        IssmDouble pressure_melange;
        IssmDouble pressure_water;

        /*enum of element? */
        if(elements[0]->ObjectEnum()!=TriaEnum)_error_("only Tria element allowed for Riftfront load!");
        Tria* tria1=(Tria*)elements[0];
        Tria* tria2=(Tria*)elements[1];

        /*Initialize Element Matrix*/
        if(this->active) return NULL; /*The penalty is active. No loads implied here.*/
        ElementVector* pe=new ElementVector(nodes,NUMVERTICES,this->parameters);

        /*Get some inputs: */
        rho_ice=tria1->FindParam(MaterialsRhoIceEnum);
        rho_water=tria1->FindParam(MaterialsRhoSeawaterEnum);
        gravity=tria1->FindParam(ConstantsGEnum);
        tria1->GetInputValue(&h[0],vertices[0],ThicknessEnum);
        tria2->GetInputValue(&h[1],vertices[1],ThicknessEnum);
        if (h[0]!=h[1])_error_("different thicknesses not supported for rift fronts");
        thickness=h[0];
        tria1->GetInputValue(&b[0],vertices[0],BaseEnum);
        tria2->GetInputValue(&b[1],vertices[1],BaseEnum);
        if (b[0]!=b[1])_error_("different beds not supported for rift fronts");
        bed=b[0];

        /*Ok, this rift is opening. We should put loads on both sides of the rift flanks. Because we are dealing with contact mechanics, 
         * and we want to avoid zigzagging of the loads, we want lump the loads onto nodes, not onto surfaces between nodes.:*/

        /*Ok, to compute the pressure, we are going to need material properties, thickness and bed for the two nodes. We assume those properties to 
         * be the same across the rift.: */

        /*Ok, now compute the pressure (in norm) that is being applied to the flanks, depending on the type of fill: */
        if(fill==WaterEnum){
                if(shelf){
                        /*We are on an ice shelf, hydrostatic equilibrium is used to determine the pressure for water fill: */
                        pressure=rho_ice*gravity*pow(thickness,2)/2.- rho_water*gravity*pow(bed,2)/2.; 
                }
                else{
                        //We are on an icesheet, we assume the water column fills the entire front: */
                        pressure=rho_ice*gravity*pow(thickness,2)/2.- rho_water*gravity*pow(thickness,2)/2.; 
                }
        }
        else if(fill==AirEnum){
                pressure=rho_ice*gravity*pow(thickness,2)/2.;   //icefront on an ice sheet, pressure imbalance ice vs air.
        }
        else if(fill==IceEnum){ //icefront finding itself against another icefront (pressure imbalance is fully compensated, ice vs ice)
                pressure=0;
        }
        else if(fill==MelangeEnum){ //icefront finding itself against another icefront (pressure imbalance is fully compensated, ice vs ice)

                if(!shelf) _error_("fill type " << fill << " not supported on ice sheets yet.");

                pressure_litho=rho_ice*gravity*pow(thickness,2)/2.;
                pressure_air=0;
                pressure_melange=rho_ice*gravity*pow(fraction*thickness,2)/2.;
                pressure_water=1.0/2.0*rho_water*gravity*  ( pow(bed,2.0)-pow(rho_ice/rho_water*fraction*thickness,2.0) );

                pressure=pressure_litho-pressure_air-pressure_melange-pressure_water;
        }
        else{
                _error_("fill type " << fill << " not supported yet.");
        }

        /*Ok, add contribution to first node, along the normal i==0: */
        for(int j=0;j<2;j++){
                pe->values[j]+=pressure*normal[j]*length;
        }

        /*Add contribution to second node, along the opposite normal: i==1 */
        for(int j=0;j<2;j++){
                pe->values[2+j]+= -pressure*normal[j]*length;
        }       

        /*Clean up and return*/
        return pe;
}
/*}}}*/
int    Riftfront::Constrain(int* punstable){/*{{{*/

        IssmDouble  penetration;
        bool        activate;
        int         unstable;
        IssmDouble  vx1;
        IssmDouble  vy1;
        IssmDouble  vx2;
        IssmDouble  vy2;

        /*Objects: */
        Tria  *tria1 = NULL;
        Tria  *tria2 = NULL;

        /*enum of element? */
        if(elements[0]->ObjectEnum()!=TriaEnum)_error_("only Tria element allowed for Riftfront load!");

        /*recover elements on both side of rift: */
        tria1=(Tria*)elements[0];
        tria2=(Tria*)elements[1];

        /*Is this constraint frozen? In which case we don't touch: */
        if (this->frozen){
                *punstable=0;
                return 1;
        }

        /*Is this rift segment state specified by user input? :*/
        if (this->state==OpenEnum || this->state==ClosedEnum){

                if(this->state==OpenEnum)this->active=0;
                if(this->state==ClosedEnum)this->active=1;

                /*this segment is like frozen, no instability here: */
                *punstable=0;
                return 1;
        }

        /*First recover velocity: */
        tria1->GetInputValue(&vx1,vertices[0],VxEnum);
        tria2->GetInputValue(&vx2,vertices[1],VxEnum);
        tria1->GetInputValue(&vy1,vertices[0],VyEnum);
        tria2->GetInputValue(&vy2,vertices[1],VyEnum);

        /*Node 1 faces node 2, compute penetration of 2 into 1 (V2-V1).N (with N normal vector, and V velocity vector: */
        penetration=(vx2-vx1)*normal[0]+(vy2-vy1)*normal[1];

        /*activation: */
        if(penetration<0)activate=true;
        else  activate=false;

        /*Here, we try to avoid zigzaging. When a penalty activates and deactivates for more than penalty_lock times, 
         * we increase the fraction of melange:*/
        if(this->counter>this->penalty_lock){
                /*reset counter: */
                this->counter=0;
                /*increase melange fraction: */
                this->fraction+=fractionincrement;
                if (this->fraction>1)this->fraction=1.;
                //_printf_("riftfront " << this->Id() << " fraction: " << this->fraction << "\n");
        }

        //Figure out stability of this penalty
        if(this->active==activate){
                unstable=0;
        }
        else{
                unstable=1;
                this->counter++;
        }

        //Set penalty flag
        this->active=activate;

        //if ((penetration>0) && (this->active==1))_printf_("Riftfront " << Id() << " wants to be released\n");

        /*assign output pointer: */
        *punstable=unstable;
        return 1;
}
/*}}}*/
void   Riftfront::FreezeConstraints(void){/*{{{*/

        /*Just set frozen flag to 1: */
        this->frozen=1;

}
/*}}}*/
bool   Riftfront::IsFrozen(void){/*{{{*/

        /*Just set frozen flag to 1: */
        if(this->frozen)return 1;
        else return 0;
}
/*}}}*/