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a)Explain the following terms as used in network analysis: i)Backward pass; ii)Crashing; ...

      

a)Explain the following terms as used in network analysis:
i)Backward pass;
ii)crashing;
iii)Slack;
iv)Earliest start times;
v)Critical-path activities;

b)XYZ Construction Company is building a 250-unit apartment complex in Embakasi, Kenya. The project consists of hundreds of activities involving excavating, framing, wiring, plastering, painting, landscaping and more. Some of the activities must be done sequentially and others can be done simultaneously. Also, some of the activities can be completed faster than normal by acquiring additional resources.

Required:
i)How would Quantitative Techniques be used to solve this problem?
ii)What would be the uncontrollable inputs?
iii)What would be the decision variables of the model? The objective function?
The constraints?
iv)Is the model deterministic or stochastic?
v)Suggest assumptions that could be made so simplify the model.

  

Answers


Moraa

(a) (i) Backward Pass
This is a network procedure for finding the latest start and finish times in a network. It entails moving backward through the network starting at the last event and writing below each event the latest date the event can occur and still enable the project to be completed on time.

(ii) Crashing
This is a network procedure used to reduce an activity time by adding resources. Thus it means there would be a cost increase of the crash the project.

(iii) Slack
This refers to the length of time an activity can be delayed without affecting the project completion time.

(iv) Earliest start time
This is the earliest time that an activity can begin.

(v) Critical path activities
These are the activities which cannot be delayed without delaying the whole project thus they are “critical” to its completion. They have a zero float and together are the activities on the longest path in a network.

(b) (i) Quantitative Techniques are useful in solving networking projects since they provide a structured quantitative approach for determining the minimum project completion time based on the activities normal and reduced or expedited times.

ii)The uncontrollable variables in such a model are: ? Normal and crashed activity completion time.
Activity crashing costs
Funds available for crashing.
Precedence relationships of project activities.

iii)Decision variables of the model include:
Activities to crash
By how much to crash them
The time to start each activity.

The objective function is:
To minimize project completion time.

The constraints are:
Activity precedence relationship.
Future funds for crashing.

iv)The model is stochastic since the normal and crash activity times are subject to variation i.e. are uncertain. Also the number of activities and their precedence relationships may change before the project is completed. Similarly, the activity crash costs are also uncertain.

To simplify the model, we can assume that:-
Normal and crash activity time are known and constraint.
Activity crash costs are known and constant.
Funds available for crashing are known.
Precedence relationships are known and constant.
v)This is to simplify the model, we may assume certainty about the uncontrollable inputs.



Moraa orina answered the question on March 31, 2018 at 10:16


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