5.1 One-Pass Sequential Baseline

Definition¶

One-pass sequential design is a non-CCD baseline. The plant is optimized first using plant-level criteria. Its result is frozen, and a controller is then designed for that fixed plant:

p_{seq} = arg min_p J_p(p), g_p(p) ≤ 0.

z_{seq} = arg min_z J_c(z;p_{seq}), R(p_{seq},z)=0, g_c(p_{seq},z) ≤ 0.

There is no return path from the control optimization to the plant design. Therefore the plant optimizer cannot trade stiffness, damping, mass, geometry, or actuator sizing against closed-loop performance.

Active-suspension interpretation¶

A conventional baseline might select $k_s$ and $c_s$ from passive ride and handling requirements, then freeze them while tuning feedback gains. This workflow is useful because it reflects common engineering practice and establishes how much value is added by a joint formulation. It must not be labeled CCD.

The baseline remains fair only if its final plant–controller pair is evaluated with the same system objective, road cases, constraints, and validation model used for CCD.

Activity 5.1: quantify a one-pass sequential baseline¶

Activity 5.1: quantify a one-pass sequential baseline

A plant team evaluates three passive suspension designs before the controller is introduced.

Plant	$k_s$ (kN/m)	$c_s$ (kN·s/m)	Passive comfort $J_p$	Travel margin
A	16	1.20	1.00	22%
B	20	1.45	0.91	14%
C	24	1.70	0.88	6%

The plant team selects the lowest $J_p$ subject to at least 10% travel margin. After the selected plant is frozen, controller tuning gives $J_c=0.62$ , peak force $F_{max}=2.72$ kN, and a 2.50 kN actuator limit. The common system score is $J_{sys}=0.4J_p+0.6J_c$ .

Select the sequential plant and compute $J_{sys}$ .
Compute the actuator-force violation in kN and percent.
Explain quantitatively why the final pair is not feasible even though the plant handoff was feasible.
If retuning raises $J_c$ to 0.74 and reduces $F_{max}$ to 2.45 kN, recompute the score and force margin.
State which quantities must be reused when comparing this baseline with CCD.