force modify direct general_force

The GENERAL_FORCE corresponds to the Adams GFORCE statement.

A GENERAL_FORCE creates a six component force element that applies the forces between two parts of the system. Here, force means three orthogonal translational components and three orthogonal rotational components. The element applies actions to the part to which the I marker belongs and corresponding reactions to the part to which a "floating_marker" belongs. This "floating marker" is automatically created by Adams View and is positioned to be coincident with the I marker. Subsequently, the GENERAL_FORCE internally establishes the position of the "floating_marker". As the system moves, Adams moves the "floating_marker" on its part to keep the "floating_marker" and I markers always superimposed. Thus, Adams applies the reaction force to the part containing the "floating_marker" marker at the instantaneous position of the I marker. The magnitude of the force depends on expressions or subroutines that the user supplies. The value of the force is the resultant (i.e., the square root of the sum of the squares) of (up to) three mutually orthogonal force components together with the resultant (i.e., the square root of the sum of the squares) of (up to) three mutually orthogonal torque components.

The resultant vector formed by the three user-defined component forces along the reference marker axes defines the direction of the translational force action. The reaction is equal and opposite to the action.

The resultant vector formed by the three component torques determines the direction of the rotational torque action. The user defines these torques about the reference marker axes. The reaction is equal and opposite to the action.

If the general force is not visible on the screen, you must type the name. You may also find it convenient to type the name even if the general force is displayed.

If you created the general force by reading an Adams data set or graphics file, the general force name is the letters GFO followed by the Adams data set general force ID number. The name of Adams GFORCE/101 is GFO101, for example. If you created the general force during preprocessing, you gave it a name at that time.

If a general force is available by default, you may identify it by entering its name only. If it is not, you must enter its full name. To identify a general force under another model, for instance, you may need to enter the model name as well. For example, you may specify general force 'spring' from the model 'suspension' by entering ".suspension.spring". If you type a "?", Adams View will list the general force available by default.

You must separate multiple general force names by commas.

If the general force is visible in one of your views, you may identify it by picking on any of the graphics associated with it.

You need not separate multiple general force picks by commas.

By enclosing the name in double quotes, you may use other printable characters, or start the name with a numeral. If a name contains characters, or starts with a numeral, you must always quote the name when entering it.

Note that you can specify the parentage of an entity (e.g. what part "owns" a marker or a geometry element) when you CREATE it by changing the name. If you enter just the entity name, then the default parent will be assigned by Adams View. If you type in the full name, then you may over ride the default parent. In most cases, when creating an entity, Adams View will provide a default name. The default name that Adams View provides will specify the parentage that it has assumed. You may, or course, delete this name and use your own. The form of a full name is:

The number of levels used varies from case to case and the parentage must exist before an entity can be assigned to it.

You may also enter zero as an identifier, either explicitly or by default. The next time you write an Adams file, Adams View will replace the zero with a unique, internally-generated identifier. Adams View will permanently store this identifier with the element just as if you had entered it yourself.

Normally, you would let all identifiers default to zero, and Adams View would generate the identifiers for you. You are never required to enter a non-zero identifier. You only need to specify it if, for some reason, you wish to control the Adams file output.

The "floating" marker is automatically created by Adams View on the part specified in the J_PART_NAME parameter.

If the marker is not visible on the screen, you must type the name. You may also find it convenient to type the name even if the marker is displayed.

If you created the marker by reading an Adams data set or graphics file, the marker name is the letters MAR followed by the Adams data set marker ID number. The name of Adams MARKER/101 is MAR101, for example. If you created the marker during preprocessing, you gave it a name at that time.

If a marker is available by default, you may identify it by entering its name only. If it is not, you must enter its full name. To identify a marker under a different part, for instance, you may need to enter the model and part names as well. For example, you may specify marker 'pivot' from model 'links', part 'lower_arm' by entering ".links.lower_arm.pivot". If you type a "?", Adams View will list the markers available by default.

You must separate multiple marker names by commas.

If the marker is visible in one of your views, you may identify it by picking on it.

You need not separate multiple marker picks by commas.

The easiest way to enter a function expression in Adams View is to use the text editor in combination with the function builder. To invoke the text editor for entering a function expression, highlight the function field and then either pick the "EDIT" button at the top of the panel or type a ^t (control-t). The Adams View "function builder" is discussed below.

The syntactical correctness of a function expression can be investigated by using the "VERIFY" button at the upper right of the text editor. If there is a syntax error, a message is printed and the cursor is put near the problem. Proper unit consistency is not checked during function expression verification.

The remainder of this explanation will cover the components of FUNCTION expressions as summarized in the following table.

FUNCTION expressions can include integers, real numbers, and exponents. In other words, any numbers that are legal in Adams are legal in a FUNCTION expression.

In a FUNCTION expression, Adams allows any of the operators **, *, /, +, and -. Adams executes these operators according to the following precedence rules:

From greatest to the least, the operators have the following priorities. ** then * / then + -. In other words, Adams executes exponentiation (**) before all other operators and executes multiplication (*) and division (/) before addition (+) and subtraction (-).

When a statement has operators of the same priority, Adams executes them from left to right.

You can use parentheses to alter the precedence of operators. For example, in the equation,

Adams subtracts TIME from one before it performs multiplication and division.

You can include the following system constants in a FUNCTION expression:

The following example of a FUNCTION with a system constant multiplies the system constant PI by the displacement of marker 10 with respect to marker 14:

A FUNCTION expression can contain any number of blank spaces. Five consecutive blank spaces in an expression do not terminate input of the expression (by indicating that what follows is a comment) as they do in an Adams statement. However, you should remember these two restrictions.

You can use a comma to continue FUNCTION expressions. You can break the expression anywhere except in the middle of a number, in the middle of a name, or between a function and its left bracket. Put a continuation comma in column one of the following line before the rest of the expression. If you break the expression at a comma that is part of the expression, you must use both, the expression comma and the continuation comma. You may use more than one continuation comma to extend an expression over several lines.

The FUNCTIONS button at the right side of the Adams View text editor provides a means for constructing an Adams function string. These functions are briefly described below. Upon picking the FUNCTIONS button, you will be presented with the list of available functions in the "selection window". After you select the desired function, a panel will appear with fields representing the various parameters for the function. You will have full access to on-line help with this panel just like you have with regular panels. After you have completed the panel and selected the DONE button on the panel, the function string will be constructed and inserted at the current text cursor location in the text edit window.

A FUNCTION expression may access the current value of a system variable and use the value in computations. These values are accessed through a collection of functions. The accessible system variables include the following: Time, Mode, Displacements (Translational and Rotational), Velocities (Translational and Rotational), Accelerations (Translational and Rotational), Forces (Translational and Rotational), and User-defined variables. Invoke the text edit window and pick the FUNCTIONS button to get a list of functions that can be accessed.

In general, you use a function character string (such as DM, VX, or FZ) and a list of values (e.g. i1, i2, and i3) to access a system variable in an expression. For example, the value i1 may be the name of the marker for which you want to measure a quantity (such as displacement, velocity, acceleration, or force), i2 is the name of the marker with respect to which you want to measure the quantity, and i3 is the name of the marker you want to use to resolve the components of the quantity. If you do not specify marker i3, Adams computes the result in the ground reference frame.

Arithmetic IFs allow you to conditionally define FUNCTION. The format for arithmetic IFs follows.

Adams evaluates expression 1. If expression 1 is less than zero, the arithmetic IF equals expression 2; if expression 1 equals zero, the arithmetic IF equals expression 3; and if expression 1 is greater than zero, the arithmetic IF equals expression 4.

A FUNCTION expression with an arithmetic IF and its four expressions is as given below:

If the radial velocity between markers 10 and 31 is less than or equal to zero, the value of the FUNCTION expression is zero; but if the radial velocity between markers 10 and 31 is greater than zero, the value of the FUNCTION expression is six hundred.

In some ways, you may treat IF as a variable. For example, you can place it anywhere in the expression. In addition, you can nest arithmetic IFs nine levels deep.

You can use the FORTRAN functions ABS, ATAN, ATAN2, COS, EXP, LOG, LOG10, MIN, MAX, SIN, SQRT, and TAN in your expression. For more information about these functions, see a FORTRAN reference manual. Invoke the text edit window and pick the FUNCTIONS button to get a list of functions that can be accessed.

In general, an Adams function evaluates a mathematical equation and returns a value to your FUNCTION expression. The following table lists all the Adams functions and their purposes. Invoke the text edit window and pick the FUNCTIONS button to make a list of functions that can be accessed.