The static steady-state straight line equilibrium solution computes a static equilibrium with all tire forces applied and a zero lateral force balance on the body. With this force balance, a dynamic simulation following the static solution will result in the vehicle traveling directly down the X-axis without tire transient effects at TIME=0. However, it should be noted that the vehicle may be moving with some yaw angle (i.e. dog tracking).
The balance of forces is accomplished using an auxiliary steering column joint that is rotated by the CONSUB until the lateral force and yaw moment on body are zero. The method of rotating the steering system is essential since no vehicle has a perfectly symmetric alignment and weight distribution. These slight geometry and load differences cause unbalanced lateral forces which start the vehicle model with an initial lateral acceleration. The CONSUB technique emulates the action of real drivers of real vehicles who have to compensate for vehicle asymmetries with a small steering correction. It is important to note that the aerodynamic force routines will be acting on the vehicle during the equilibrium.
The CONSUB can be invoked in the static steady-state straight line equilibrium mode by typing the following at the Adams prompt:
CONTROL/FUN=USER (1020,jpr_ary,vel,brk_flg,glev,ijm,jjm,halt,origo,sav_acc)
where:
jpr_ary | = | Id of array containing the necessary jprims, motions, sforce ids to perform the static equilibrium |
vel | = | Logitudinal velocity of the vehicle. All part velocities will be set to this values after statics in preparation of transient analysis |
brk_flg | = | flag to specify whether deceleration should be applied as braking or throttle off deceleration. For throttle off deceleration the applied deceleration is balanced by forces/moments generated at the driven wheels. For braking deceleration the deceleration is balanced by braking forces/moments at all wheels based on braking ratios (Car models only)
1 - braking deceleration
0 - throttle off deceleration (default) |
glev | = | longitudinal acceleration in g's (default is zero)
positive value = acceleration
negative value = deceleration |
ijm | = | (Optional). I MARKER on steering wheel part of new steering system JOINT. If = 0, CONSUB assumes default value of 1080 |
jjm | = | (Optional). J MARKER on auxiliary steering column of new steering system JOINT. If = 0, CONSUB assumes default value of 8010 |
halt | = | (Optional) parameter to terminate or continue a simulation after a static failure.
1 - stop the simulation if static fails (default).
0 - continue the simulation if static fails. |
origo | = | (Optional). Marker defining the coordinate system is which model was created. (Standard Adams Car models have vehicle forward as -X).Default marker id is 3 |
sav_acc | = | (Optional). Flag to specify whether the applied acceleration/deceleration is to be saved after statics in preparation of another analysis.
1 - Save the acceleration/deceleration
0 - Donot save the acceleration/deceleration (dafault) |
For modelers using the standards established in Adams Car, this routine can be invoked by typing:
CONTROL/FUN=USER (1020,555,vel)
When the user enters this command and runs a straight line equilibrium, the user code takes the following steps:
1. The velocity specified is accessed and used in the tire forces calculation. A longitudinal tire force/moment is applied to the tires in order to maintain the longitudinal reaction force at the vehicle C.G. JPRIM is zero.
2. A force is applied to the auxiliary steering column joint until the lateral forces at the C.G JPRIM are zero. For standard Adams Car models these joint, motion and force are numbered 740.
Once a static solution has been found, a dynamic analysis can be requested in Adams without the problems associated with initial tire transients and yaw angles.
Static Steady-State Straight Line Acceleration/Braking Equilibrium
The steady-state straight line acceleration/braking equilibrium solution computes a static equilibrium solution with the assumption that the vehicle can accelerate or decelerate at a certain G level. The call to this equilibrium solution is same as that of Static Steady-State Straight Line Equilibrium. User has to specify a positive glev for acceleration and a negative glev for braking
When the user enters this command to run a straight line acceleration/braking solution, the user code takes the following steps:
1. The velocity of the vehicle body is accessed and used in the tire forces calculation. A longitudinal component of gravity is added to the gravity statement. Longitudinal tire forces are applied to the tires (force split between front, rear, left, and right is based on ARRAY 92 for both acceleration and deceleration and ARRAY 61 if vehicle is braking) of magnitudes such that the longitudinal reaction force at the vehicle C.G. JPRIM is zero. Longitudinal inertia forces are calculated and placed at the C.G. of all parts in the dataset.
2. A force is applied to the auxiliary steering column joint until the lateral forces at the C.G JPRIM are zero. For standard Adams Car models these joint, motion and force are numbered 740.
Once a static solution has been found, it is not recommended to follow the static equilibrium with a dynamic analysis in Adams. This option is not yet coded.