Combined Rotation and Translation Subsequent to Collision
A technique for generating initial estimates of the collision separation conditions:
INPUTS
Rest position and
orientation
(feet and degrees)
Position and
orientation at separation
(feet and degrees)
a + b = Wheelbase, inches
k2 = Radius of gyration squared for complete vehicle
in yaw, in2
=
Nominal tire-ground friction coefficient
=
Decimal portion of full deceleration
g = Acceleration of gravity
= 386.4 inches/sec2
1.0
inches
2.0
radians
3.0
4.0
GO TO
10.0
5.0
6.0
7.0
8.0
deg/sec
9.0
inches/sec
GO TO 12.0
10.0
deg/sec
11.0
inches/sec
12.0
inches/sec
13.0
inches/sec
14.0 Return with starting values: uS, vS inches/sec
degrees/sec
Note that the above calculations can be simplified by means of the following steps:
Let
(7)
Then
deg/sec
(8)
inches/sec
(9)
Several possible shortcomings in the cited technique for the generalized case have been investigated (see Reference Error! Bookmark not defined.). This technique should be considered a first approximation technique for the estimation of separation conditions which will produce better approximations than conventional constant deceleration techniques
(i.e., V2 =2as).
Launch
As a part of the continuing research at McHenry Consultants, Inc. in conjunction with McHenry Software, a simple Launch program has been created to determine the minimum possible speed required for a projectile launch. The program was created to permit investigation of the possible variations in assumption about throw distances and the ratio of the distance traveled in air, distance traveled on the ground, the assumed coefficient of the ground surface, and any possible elevation difference between the launch point and the landing area.
The normal equations and assumptions for a Simple ballistic trajectory of an occupant travel of a distance R is that the occupant is assumed to stop at the landing point. A problem with that assumption is that for most launch angles the occupant will have a horizontal component of velocity at the landing point. Therefore the occupant will continue to travel after landing.
Figure 90 is the assumptions and equations used in the Launch program. The figure depicts a more likely scenario for a pedestrian impact with a vehicle or a occupant ejected from a vehicle, The occupant is normally at a elevation different than the landing area. For example an occupant may be struck by a car in a standing position and land in a prone or laying position. This would require a 2 to 3 foot elevation change between the impact and landing position.
Figure 89 Equations used in McHenry Software Launch Program
Also considered in Figure 90 is the distance traveled from the landing point to the point of rest. The occupant does not follow a simple ballistic trajectory. At the landing the horizontal component of the launch continues. Many assumptions are required for this scenario. At what approximate elevation does the launch occur? What is the friction coefficient for the landing area? What range of values for the friction coefficient is associated with the landing area? What is the probable launch angle for the particular accident? What effect would a variation in the assumed launch angle and/or the assumed friction coefficient of the landing zone have on the approximate launch velocity?
The Launch routine was created to compute all these variations to determine a minimum speed for an ejected occupant to travel a given distance.
Lsqfit – A, B Coeff Calculator
Least Square Fit routine for creation of fits. For b0,b1 fits, enter Crash test results in form: Residual Crush (in), Speed change (mph)
For CRASH A,B coefficients calculated: Residual Crush (in), Speed change (mph), Test weight(lbs), Damage Width(in)
An optional no damage intercept (mph) is then input. Program assumptions include (1) Speed change is to point of common velocity and (2) Single point Crush is average crush. The program will calculate the natural and forced intercept b0,b1 fits. If weight & width given, program will then calculate A,B CRASH coefficients A graphical display of results can then be printed
CAUTION: Use of a single crash test is discouraged due to variations in crash test results. Damage analysis accident reconstruction techniques should be viewed as a Tool. Damage analysis should be used in combination with other accident reconstruction Tools
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The next section of the Tools menu is reseved for individual user menu items. The items can be added from the Options dialog box. The two examples, DOS and Notepad are demonstrations of adding either a DOS or a windows program to the customizable menu. medit permits the addition of user Tools to the interface.
Tools are any programs, batch files, or other commands you commonly execute and you would like to have easy access from the medit environment. Tools added may also have predefined arguments passed to them ($FILE sends the current file name) or you may indicate for a given Tool that you want to be prompted for arguments to pass to the program. Then when you select the Tool menu item the program will automatically ask you for a parameter and then execute the Tool from the medit environment.
DOS
Sample addition of a user customizable Tool menu item.
Notepad
Sample addition of a user customizable Tool menu item.
The Options menu pops up dailog boxes related to various choices for the user of the medit environment.
The medit environment has been set up with the beginner user in mind. As you use and become more familiar with the medit environment, you may wish to change the Option defaults to modify the way the program behaves. The options are separated into 5 main categories:
1. medit
2. Defaults
3. m-smac
4. Config
5. Misc Pgms
6. m-hvosm
Choice of the Options menu item produces a popup tab-delimited Option specification form. You first select the Options section you wish to check and modify by clicking on the tab at the top of the form. For Example, to select the Config Options Choices, simply click with the mouse on the tab entitled Config. A description of the options available follows.
Options: medit tab